M A B Digest
1
4#
•• V . L I
EUTROPHICATION
M A N A G E M E N T F R A M E W O R K FOR
THE P O L I C Y - M A K E R
Walter Rast
Marjorie Holland
Sven-OlofRyding
The designations employed and the presentation of material throughout this publication do
not imply the expression of any opinion whatsoever on the part of Unesco concerning the
legal status of any country, territory, city or area of its authorities, or concerning the delimitation of its frontiers or boundaries. The opinions expressed in this digest are those of the
authors and not necessarily those of Unesco or the authors' employers.
Addresses of the authors of this report
Walter Rast
U . S . Geological Survey
8011 Cameron Road
Austin, Texas 78753
USA
Marjorie Holland
Ecological Society of America
9650 Rockville Pike
Bethesda, Maryland 120814
USA
Sven-Olof Ryding
Federation of Swedish Industries
P . O . Box 5501 .
S-114 85 Stockholm
Sweden
Overall direction: Bernd von Droste
Series editor: Malcolm Hadley
Computer assisted layout: Lucia Fabbri
Cover and graphical design: Jean-Francis Cheriez
Photograph on back cover: M . S p u m y
Suggested citation: Rast, W . ; Holland, M ; Ryding, S.-0.1989. Eutrophication management
framework for the policy-maker. M A B Digest 1. Unesco, Paris.
Published in 1989 by the United Nations
Educational, Scientific and Cultural Organization
7 Place de Fontenoy, 75700 Paris
Printed by Imprimerie des Presses Universitaires
de France, V e n d ô m e
© Unesco 1989
Printed in France
PREFACE
About this series...
The M A B Digest Series was launched by Unesco in 1989. Three main types of
publication are envisaged. First are distillations of the substantive findings of
M A B activities. Second are overviews of recent, ongoing and planned activities
within M A B in particular subject or problems areas. Third are proposals for
n e w research activities.
T h e intended audience will vary from one digest to another. S o m e will be designed with planners and policy-makers as the main audience in mind. Others
will be aimed at collaborators in the M A B Programme. Still others will have
technical personnel and research workers as the target, whether or not they are
involved in M A B .
...and M A B Digest 1
Eutrophication of lakes and reservoirs ranks as one of the most pervasive water
quality problems around the world and the purpose of this digest is to highlight
those aspects of eutrophication control which are of primary importance to the
policy-maker or 'decision-maker' (e.g. executive, legislator, senior administrator, director, etc.). M o r e especially, the aim is to provide :
• Quantitative tools for assessing the state of eutrophication of lakes and reservoirs;
• A framework for developing cost-effective eutrophication management strategies;
• A basis upon which strategies can be tailored for each specific case according to the physical, social, institutional, regulatory and economic characteristics of the local area or region; and
• Specific technical guidance and case studies regarding the effective management of eutrophication.
The approach presented in this digest is sufficiently general that it can be applied, with relatively little modification, to the assessment of other environmental problems and to the development of effective management strategies for such
problems.
The digest has been prepared by Walter Rast, Marjorie Holland and SvenOlof Ryding. It represents a distillation for planners and policy-makers of a
more substantive, technical synthesis on The Control of Eutrophication of Lakes
and Rivers (Ryding and Rast 1989). This 320-page book is the first number in
the M a n and the Biosphere Series, a co-production of Unesco and Parthenon
Publishing. The preparation of this synthesis enjoined the efforts of a multi-national team of contributing authors, with successive versions being checked and
revised by over fifty scientists, engineers and water managers. It was prepared
within the framework of M A B Programme activities on freshwater ecosystems
( M A B Project Area 5), in cooperation with one of Unesco's other intergovernemental programmes of scientific cooperation in the environmental sciences
field, the International Hydrological Programme (IHP).
The present digest is clearly not meant to be a treatise on the subjects of eutrophication. Instead, it is an attempt to bring existing knowledge and experience together in a form for use by policy-makers, as well as a technical audience. It is emphasized that this document is not an official policy statement,
either of Unesco or of the h o m e organizations of the individuals involved in its
preparation. Rather, it represents the personal and professional expertise and
experience of the authors and of the m u c h larger team of specialists w h o have
contributed to the process of preparing the two publications on eutrophication..
In terms of this digest, the authors wish to express their appreciation to several individuals for their stimulating and helpful discussions, suggestions and
insights on various facets of eutrophication and its policy-making context.
These individuals include D . J. Gregor, J.G. Moore, J.C. Stephens, G . Thornburn and J.A. Thornton.
CONTENTS
Summary
9
The role of the policy-maker
11
Identify eutrophication problems and establish management goals
17
Assess the extent of information available about the waterbody
27
Identify available options for management of eutrophication
29
Analyze all costs and expected benefits of alternative
management strategies
35
Analyze adequacy of existing legislative/regulatory framework
for implementing eutrophication control programmes
45
Select eutrophication control strategy and disseminate summary
to affected parties prior to implementation
49
Provide periodic progress reports on control programme to the
public and other interested parties
63
References
65
Glossary of terms
73
SUMMARY
Eutrophication of lakes and reservoirs ranks as one of the most pervasive water
quality problems around the world. Eutrophication refers to the excessive nutrient
enrichment of water which results in an array of undesirable symptomatic changes,
including nuisance production of algae and other aquatic plants, deterioration of
water quality, taste and odour problems, andfishkills. Each of these can significantly interfere with human use of water resources. In spite of efforts by governments at many levels to control the causes of eutrophication, water quality has continued to deteriorate in many streams, lakes, reservoirs and coastal areas.
Therefore, development of a sound eutrophication management strategy is essential for a satisfactory solution to this significant water-pollution problem.
The purpose of this digest is to highlight the aspects of eutrophication control which are of primary importance to the policy-maker or 'decision-maker'
(executive, legislator, senior administrator, director, etc.). It is difficult to present a characterization of the 'policy-maker' which is accurate in all cases. Furthermore, because of the differing (and sometimes conflicting) concerns and
perspectives within an individual country, and on a global scale, the elements
discussed in this document will have different priorities in different countries.
Thus, the circumstances in a given situation may require the policy-maker to
interject issues and concerns other than those discussed here in the formulation
of the 'solution' to a given problem.
The effects of eutrophication are considered negative in many places around
the world, and often reflect human perceptions of good versus bad water quality.
Excessive algae and aquatic plant growths are highly visible, and can interfere
with the uses and aesthetic quality of a waterbody. One consequence of such
growths can be the production of taste and odour problems in drinking water
drawn from a lake or reservoir, even though the water may be treated and filtered prior to use. The water treatment process itself can become more expens-
9
ive and time-consuming for eutrophic waters.The water transparency of a lake
or reservoir may be greatly reduced.
There are also significant ecological consequences related to cultural (or
human-induced) eutrophication. As algal populations die and sink to the bottom of a waterbody, their decay by bacteria can reduce oxygen concentrations
in bottom waters to levels which are too low to support fish life, resulting in fish
kills. Such oxygen-deficient conditions can also result in excessive levels of iron
and manganese in the water, which can interfere with drinking water treatment.
There are also negative potential health effects, especially in tropical regions,
related to such parasitic diseases as schistosomiasis, onchocerchiasis and
malaria, all of which can be aggravated by cultural eutrophication, which can
enhance the appropriate habitats for these organisms.
Because of the type of concerns identified above, this document attempts to
incorporate the need for balance in evaluating the potential impacts of human
activities and pollution control programmes on the environment. Recognizing
that the specific needs of policy-makers are usually different from those of the
strictly technical audience, the primary purpose of this document is:
• To provide quantitative tools for assessing the state of eutrophication of
lakes and reservoirs;
• To provide a framework for developing cost-effective eutrophication management strategies;
• To provide a basis upon which strategies can be tailored for each specific
case according to the physical, social, institutional, regulatory and economic
characteristics of the local area or region; and
• To provide specific technical guidance and case studies regarding the effective management of eutrophication.
An initial discussion on the role of the policy-maker isfollowed by sections outlining proposed successive steps in eutrophication control: identifying eutrophication problems and setting of management goals; assessing the extent of information available about the waterbody; identifying the available optionsfor managing
eutrophication; analyzing all the costs and expected benefits of alternative management strategies; analyzing the adequency of existing legislative and regulatory
frameworks for implementing entrophication control programmes; selecting the
eutrophication control strategy and disseminating an overview of the control programme to all interested parties prior to implementation; providing periodic progress reports on the control programme to the public and other interested parties.
A glossary of some 150 terms is also provided.
The approach presented is sufficiently general that it can be applied, with relatively little modification, to the assessment of other environmental problems and to
the development of effective management strategies for such problems.
10
THE
R O L E OF THE P O L I C Y - M A K E R
Introduction
H u m a n development is rapidly becoming limited by increasing pollution of air
and water. O n e aspect of water pollution, eutrophication of lakes and reservoirs,
ranks as one of the most pervasive water quality problems around the world.
Eutrophication often becomes apparent to the public in m a n y countries as a
function of the progressive growth of densely populated areas. Eutrophication
refers to the excessive nutrient enrichment of water which results in an array of
undesirable symptomatic changes (Organization for Economic Cooperation and
Development 1982), including nuisance production of algae and other aquatic
plants, deterioration of water quality, taste and odour problems, and fish kills;
each of these changes can significantly interfere with human use of water resources. In spite of efforts by governments at m a n y levels to control the causes
of eutrophication, water quality has continued to deteriorate in m a n y streams,
lakes, reservoirs and coastal areas. Therefore, development of a sound eutrophication management strategy is essential for a satisfactory solution to this pervasive problem.
The purpose of this document is to highlight those aspects of eutrophication
control which are of primary importance to the policy-maker or 'decisionmaker' (e.g. executive, legislator, senior administrator, director, etc.). A s a preface, it is difficult to present a characterization of the 'policy-maker' which is
accurate in all cases. Furthermore, because of the differing (and sometimes conflicting) concerns and perspectives within a country, and on a regional and global scale, the elements discussed in this document will have different priorities
in different countries. Thus, the circumstances in a given situation m a y require
the policy-maker to interject issues and concerns other than those discussed here
in the formulation of the 'solution' to a given problem.
11
Eutrophication of lakes and reservoirs
Both the public and responsible officials are becoming increasingly concerned
with changes in environmental quality resulting from human activities. These
changes are related to a number of environmental stresses, including eutrophication, toxic substances and acid rain. A n example of this concern is reflected
in the United Nations' designation of the 1980's as the 'Water Decade', more
officially k n o w n as the International Drinking Water Supply and Sanitation D e cade. However, this increased environmental consciousness is occurring coincident with significant socio-economic concerns such as depressed economies,
unemployment and other financial constraints. Recognizing these sometimes
conflicting pressures, this manual was developed to provide both a management
and technical framework for addressing one of these important issues; namely,
the eutrophication of lakes and reservoirs. This long-term problem continues to
be of environmental, economic and social concern around the world.
Eutrophication, in the original sense, represents the natural ageing process
of a lake. A lake receives inflows of water from its surrounding drainage basin,
along with materials carried in the water from the land surface (e.g., following
a rain storm or from irrigation drainage). Materials associated with rain, snow
and wind-blown substances, as well as ground water inflows (sub-surface flow),
can also directly enter a lake. The observed water quality and biological communities in a lake, therefore, reflect the cumulative impacts of all the water and
material inflows into the lake.
Over time, a lake will be slowly filled-in with soil and other materials carried by inflowing waters, and eventually become a marsh and, ultimately, a terrestrial system. This process usually takes m a n y hundreds or thousands of years
to occur and is largely irreversible. Lakes undergoing such natural eutrophication generally have good water quality and exhibit a diverse biological c o m munity throughout much of their existence.
Where humans have not settled a drainage basin, the growth of algae and
other aquatic plants in a lake in the drainage basin is usually minimal, and generally in balance with the input of plant nutrients. However, human settlement of
a drainage basin, and the associated clearing of forests, development of farms
and cities, etc., usually changes the natural eutrophication process in a dramatic
way. The runoff of most materials from the land surface to the waterbody is
greatly accelerated. A n increased input of plant nutrients (mainly phosphorus
and nitrogen) to a lake or reservoir can stimulate algal and aquatic plant growths
which, in turn, can stimulate the growth of fish and other higher trophic level
organisms in the aquatic food chain. This latter phenomenon is often termed
'cultural eutrophication' to distinguish it from the natural process (the terms
'artificial', 'anthropogenic' or ' m a n - m a d e ' are also often used to describe the
12
same phenomenon). A lake or reservoir undergoing cultural eutrophication can
be treated so that it will again exhibit an 'ageing' rate more characteristic of
natural eutrophication. However, for waterbodies undergoing extensive cultural eutrophication, the necessary control measures can be quite expensive and
difficult to administer.
During the last twenty years, the word 'eutrophication* has been used more
and more to denote this artificial and undesirable addition of plant nutrients to
waterbodies. In some situations, this view can be misleading, since what is an
undesirable addition to one waterbody m a y be harmless, or even beneficial, in
another waterbody. Nevertheless, as previously noted, eutrophication is most
commonly k n o w n as the state of a waterbody which is manifested by an intense
proliferation of algae and higher aquatic plants, and their accumulation in the
waterbody in excessive quantities. These accumulations can result in detrimental changes in the water quality of a waterbody, and interfere significantly with
human uses of the water resource.
The effects of eutrophication are considered negative in m a n y places around
the world, and often reflect human perceptions of good versus bad water quality.
Excessive algae and aquatic plant growths are highly visible, and can interfere
significantly with the uses and aesthetic quality of waterbodies. O n e consequence of such growths can be the production of taste and odour problems in
drinking water drawn from a lake or reservoir, even though the water m a y be
treated and filtered prior to use. The water treatment process itself can become
more expensive and time-consuming for eutrophic waters. T h e water transparency m a y be greatly reduced. There are also significant ecological consequences related to cultural eutrophication. A s algal populations die and sink to
the bottom of a waterbody, their decay by bacteria can reduce oxygen concentrations in bottom waters to levels which are too low to support fish life, resulting in fish kills. Such oxygen-deficient conditions can also result in excessive
levels of iron and manganese in the water, which can interfere with drinking
water treatment. There are also negative potential health effects, especially in
tropical regions, related to such parasitic diseases as schistosomiasis, onchocerchiasis and malaria, all of which can be aggravated by cultural eutrophication,
which can enhance the appropriate habitats for these organisms. The primary
exception to these negative aspects is the use of the eutrophication process to
enhance the production of fish, or for other types of aquaculture, for the purpose of producing food supplies. In these latter cases, particularly in developing
countries, the management goal is to maximize or optimize such productivity
at minimal cost and effort.
This general description of the eutrophication process applies both to natural lakes and reservoirs (man-made impoundments). Reservoirs are waterbodies which have been created artificially by the construction of a d a m
13
across a flowing river or stream. There are some fundamental differences in
lakes and reservoirs which need to be considered when assessing their degree
of eutrophication. Nevertheless, as pointed out by Ryding and Rast (1989),
the important factors to be considered in selecting eutrophication control
measures for these two types of waterbodies are usually sufficiently similar
that the terms 'lake' and 'reservoir' are generally used interchangeably in this
digest. The reader is referred to Ryding and Rast (1989) for detailed information regarding the differences that do exist between natural lake and reservoir
systems, as well as guidance on h o w these differences should be considered
when developing effective eutrophication control programmes for these
waterbodies. Additional details regarding the eutrophication process and its
effects on water quality are found in the reports of Sawyer (1966), Stewart
and Rohlich (1967), Vollenweider (1968), National Academy of Sciences
(1969), Lee (1971), Landner (1976), Rast and Lee (1978), Duncan and Rzoska (1980), Welch (1980), Steenvoorden and Rast (1981), Organization for
Economic Cooperation and Development (1982), Jolankai and Roberts (1987)
and Lauga et al. (1988).
With this background, it is noted that the role of the policy-maker often focuses on the development and implementation of management strategies
and/or control programmes for dealing effectively with environmental issues
such as the continuing eutrophication problem. Indeed, effective environmental management usually requires substantial recognition that an environmental problem exists in the first place, as well as sufficient support to formulate
and implement a corrective policy. Yet, because of both public and political
pressures, decisions regarding environmental management or control programmes sometimes have to made in a relatively short time frame, regardless
of the state of scientific knowledge on a specific item of concern. Development of strategies to combat the detrimental impacts of eutrophication is no
exception to this fact.
Furthermore, in some cases the problem m a y not even be lack of information regarding an environmental issue such as eutrophication, but rather the
resolution of 'an array of more or less persuasive fact or opinion on both sides'
of an issue. In such a setting, the policy-maker m a y be called upon to resolve
conflicting claims, sometimes with 'little real knowledge of the facts and less
knowledge about the consequences' (González 1984). Indeed, the policymaker often will be confronted simultaneously by advisors and supporters
w h o argue that immediate action is vital, as well as by those w h o contend that
corrective efforts should be delayed until more is known about the extent and
severity of the problem and the most desirable measures to treat it. Therefore,
responsible officials must attempt to balance the need and desire for immediate action against the need for further study.
14
Development of eutrophication
management framework
Because of the type of concerns identified above, this digest attempts to incorporate the need for balance in evaluating the potential impacts of h u m a n activities and pollution control programmes on the environment. Recognizing that
the specific needs of policy-makers and administrators are usually different
from those of the strictly technical audience, the primary purpose of this digest
is to provide quantitative tools for assessing the state of eutrophication of lakes
and reservoirs; to provide a framework for developing cost-effective eutrophication management strategies; to provide a basis upon which strategies can be
tailored for each specific case according to the physical, social, institutional,
regulatory and economic characteristics of the local area or region; and to provide specific technical guidance and case studies regarding the effective m a n agement of eutrophication.
The approach presented in this document (Figure 1) also is sufficiently
general that it can be applied, with relative little modification, to the assessment
of other environmental problems and to the development of effective management strategies for such problems.
A n approach for achieving the basic objectives stated above consists of the
following components, applied approximately in the order presented: identify
eutrophication problem and establish management goals; assess the extent of
information available about the lake/reservoir; identify available options for
management of eutrophication; analyze all costs and expected benefits of alternative management/control options; analyze adequacy of existing institutional
and regulatory framework for implementing alternative management strategies;
select desired control strategy and distribute summary to interested parties prior
to implementation; and provide periodic progress reports on control programme
to public and other interested parties.
Each of these steps are discussed in the following sections. A graphical representation of this basic approach is provided in Figure 1. In addition, specific
chapters in the book The Control of Eutrophication of Lakes and Reservoirs
(Ryding and Rast 1989) provide detailed discussions on these topics. This book
is Volume 1 of the M a n and the Biosphere Series of Unesco and Parthenon Publishing Group.
15
Institutional concerns
ESTABLISH OBJECTIVES
(Based on desired use ol waterbody
Regulatory concerns
•
Water d e m a n d
Assess factors affecting
achievement
of objectives
Problems/conflicts
Land usage
Water quality
•
Identify available remedial
measures to achieve objectives
Ecological concerns
Technical concerns
Assess cost-effectiveness
of alternatives in relation to
achieving objectives
Selection of most feasible
remedial measures
Economic concerns
entof
Sociological concerns
1
a.
Implementation of
remedial programmes
'
FlG.l. Sequence of decisions to be made in the development and implementation of
eutrophication control programmes.
[Source: Redrawn from Ryding and Rast (1989).]
16
IDENTIFY E U T R O P H I C A T I O N
P R O B L E M S A N D ESTABLISH
MANAGEMENT GOALS
W h y is eutrophication a problem ?
As shown in Figure 2, the eutrophication process in a lake or reservoir involves
complex interactions between a number of natural and human-induced factors.
However, from a practical perspective, scientists have accumulated considerable evidence linking accelerated lake and reservoir eutrophication to the excessive input of aquatic, plant nutrients from point and non-point sources in the
drainage basin. Consequently, nutrient loading concepts are frequently used in
the assessment of nutrient control measures.
The main objective of traditional water pollution control efforts was to clean
up raw wastewaters and gross industrial wastes, which are potential sources of
pathogens and toxic materials. However, since treatment of such effluents is
becoming more c o m m o n , especially in industrialized nations, the environmental impacts of other types of pollution in the drainage basin have assumed
greater importance in recent years. For example, pollution from non-point
sources, such as urban and rural runoff, is n o w being seriously considered in
the development of effective water pollution control programmes. Accordingly, there is a definite, continuing need to develop an integrated view of land,
atmosphere and water interactions in the drainage basin, as they relate to the
assessment and treatment of cultural eutrophication.
In industrialized countries, especially those with water surpluses, the need
for an integrated view of land, atmosphere and water interactions in the drainage basin is necessary because of increasingly serious water quality problems,
due both to point and non-point source pollutant inputs to surface and ground
waters. In arid and semi-arid regions, socio-economic development can result
in rapidly increasing water demands. In such cases, the availability of water
17
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"PRO DUCT ITT
can become an ultimate constraint to development. This often is due to the
combined effect of large populations and climatically related water demands
for increasing agricultural production. Furthermore, as population and development continue to increase, the uses to which water is being put are increasing. Yet, at the same time, the availability of suitable water for such uses is
decreasing.
Eutrophication of lakes and reservoirs ranks as one of the most widelyspread water quality problems around the world. The effects of cultural eutrophication on a waterbody can render the water unsuitable for m a n y uses, or
else require that the water be treated (often expensive and time-consuming)
prior to its use by m a n .
Eutrophication can also result in detrimental effects on the biological stability of a lake or reservoir ecosystem, affecting virtually all the biological
populations and their interactions in the waterbody. Consequently, eutrophication of lakes and reservoirs can have significant negative ecological, health,
social and economic impacts on m a n ' s use of a primary and finite resource.
Criteria c o m m o n l y used to assess eutrophication of lakes and reservoirs are
summarized in Table 1, and an example of the expected changes in these and
other criteria in response to increased eutrophication is provided in Table 2 .
T A B L E 2. Trophic criteria and their responses to increased eutrophication1.
Physical
Chemical
Biological2
Transparency ( D )
(e.g. Secchi disc)
Suspended solids (I)
Nutrient concentrations (I)
(e.g. spring m a x i m u m )
Chlorophyll a (I)
Electrical conductance (I)
Dissolved solids (I)
Hypolimnetic oxygen
Algal b l o o m frequency (I)
Algal species diversity ( D )
Phytoplankton biomass (I)
Littoral vegetation (I)3
Zooplankton (I)
deficit (I)
Epilimnetic oxygen
supersaturation (I)
Bottom fauna (I)3
B o t t o m fauna diversity ( D )
Primary production (I)
Fish (I)4
1. (I) signifies the value of the parameter generally increases with the degree of eutrophication; (D) signifies the value generally decreases with the degree of eutrophication.
2. The biological criteria have important qualitative (e.g. species) changes as well as quantitative (e.g.
biomass) changes, as the degree of eutrophication increases.
3. Aquatic plants in the shallow, nearshore area m a y decrease in the presence of a high density of phytoplankton.
4. Fish m a y be decreased in numbers and species in bottom waters (hypolimnion) beyond a certain
degree of eutrophication, as a result of hypolimnetic oxygen depletion.
5. Bottom fauna m a y be decreased in numbers and species in high concentrations of hydrogen sulphide
(H2S), methane (CH4) or carbon dioxide (CO2), or low concentrations of oxygen (O2) in hypolimnetic
waters.
[Source : Modified from Brezonik 1969, Taylor et al. 1980, O . Ravera, personal communication,
E U R A T O M 1984, M . Straskraba, personal communication, Czechoslovak Academy of Science 1985.]
19
T A B L E 1. Primary criteria for assessing the eutrophication status of a waterbody.
Units1
Parameter
Morphometric conditions
Lake surface area
Lake volume (average condition)2
M e a n and m a x i m u m depth
Location of inflows and outflows
km2
10 s m 3
m
—
Hydrodynamic conditions
V o l u m e of total inflow (including ground water) and
outflow for different months
Theoretical m e a n residence time of the water
(renewal time, retention time)
Thermal stratification (vertical profiles along longitudinal
axis, including the deepest points)
Flowthrough conditions (surface overflow or deep release,
and possibility of bypass
flow)
ln-lake nutrient conditions
Dissolved reactive phosphorus; total dissolved phosphorus;
and total phosphorus
Nitrate nitrogen; nitrite nitrogen; ammonia nitrogen;
and total nitrogen
Silicate (if diatoms constitute a large proportion of
phytoplankton population)
m3/d
y
—
—
|ig P/l
mg N/1
m g SiOJi
ln-lake eutrophication response parameters
Chlorophyll a; Pheophytin a
Transparency (Secchi depth)
Hypolimnetic oxygen depletion rate (during period of
thermal stratification)
Primary production3
Diurnal variation in dissolved oxygen 3
Dissolved and suspended solids3
Major taxonomic groups and dominant species of phytoplankton,
zooplankton and bottom fauna3
Extent of attached algal and macrophyte growth in littoral zone3
mg/1
m
gCV.d
gC/m3.d; g C/m2.d
mg/1
mg/1
—
—
1. The terminology and units proposed by the International Organization of Standardization is recommended for expressing the parameters.
2. A bathymétrie map and hypsographic curve is necessary in many cases.
3. Can provide additional information on the trophic conditions of a waterbody; recommended if resources are adequate or if special situations require more detailed information.
[Source : Ryding and Rast 1989.1
20
Establishment of eutrophication
management goals
The designation of bad (unacceptable) versus good (acceptable) water quality
in this digest is based on the specific intended use or uses of the water resource.
That is, water quality management goals for a lake or reservoir should be a function of the major purpose(s) for which the water is to be used.
Obviously, there are water quality conditions to be avoided because of their
interference with water uses. Ideally, for example, a lake or reservoir used as a
drinking water supply should have water quality as close to an oligotrophy state
as possible, since this would insure that only a m i n i m u m amount of pre-treatment would be necessary to yield a water suitable for human consumption. For
such a waterbody, the content of phytoplankton (and their metabolic products)
in the water should be as low as possible to facilitate this goal. Further, if the
water is taken from the bottom waters of a lake during the s u m m e r (usually the
period of m a x i m u m algal growth), it should be free of interferring substances
resulting from decomposition of dead algal cells. Eutrophic lakes and reservoirs
also could be used as a drinking water supply. However, extensive pre-treatment would be necessary before the water was suitable for h u m a n consumption.
S o m e water uses m a y require no treatment at all, regardless of the existing
water quality. Examples are fire-fighting purposes and the transport of c o m m e r cial goods by ship. Further, in areas with extremely limited water resources, virtually all of the water m a y be used for various purposes (with or without treatment), regardless of its quality. Therefore, although humans can use water
exhibiting a range of water quality, there is a desirable or optimal water quality
for virtually any type of water usage. Though it is not quantitative in nature, a
summary of intended water uses and the optimal versus minimally-acceptable
trophic state for such uses is provided in Table 3. In addition, an example of the
values of several commonly measured water quality parameters corresponding
to different trophic conditions, based on the international eutrophication study
of the Organization for Economic Cooperation and Development (1982), is provided in Table 4. Thus, it is possible to identify acceptable or optimal water
quality for given water uses.
Given these factors, a prudent approach in setting eutrophication management goals is to determine the m i n i m u m water quality and trophic conditions
acceptable for the primary use or uses of the lake or reservoir (Table 1), and attempt to manage the waterbody so that these conditions are achieved. In a given
situation, if the primary use or uses of a waterbody is hindered by existing water
quality, or else requires water quality or trophic conditions not being met in the
waterbody, this signals the need for remedial or control programmes to achieve
the necessary in-lake conditions.
21
T A B L E 3. Intended lake andreservoirwater uses as related to trophic conditions.
Trophic state
Desired utilization
Required
Drinking water production
Bathing purposes
L o w - w a t e r improvement
with long distance supply line
without long distance supply line
Fish culture
salmonid waterbodies
cyprinid waterbodies
Providing process water
Cooling water production
W a t e r sports (without bathing)
Landscaping in recreation areas
Irrigation (by m e a n s of channels)
Energy production
oligotrophic
mesotrophic
Still tolerable
mesotrophic
slightly eutrophic
mesotrophic
slightly eutrophic
oligotrophic
mesotrophic
mesotrophic
mesotrophic
eutrophic
slightly eutrophic
eutrophic
eutrophic
slightly eutrophic1
strongly eutrophic
strongly eutrophic2,3
1. Within the scope of landscaping, a eutrophic state caused by the natural ageing process, can even be
desirable.
2. Without consideration of the eventual water quality requirements for the receiving canal.
3. Not valid for river power plants, which m a y be impaired by macrophyte and algal growths.
[Source : Adapted from Bernhardt 1981.]
W h o should be involved in addressing
the problem?
The governmental role
It is recognized that a range of different forms of government, as well as economic conditions, exist around the world. Consequently it is difficult to provide
general guidelines regarding the role of the government in environmental protection efforts that will cover all possible situations. However, virtually all nations also contain some type of civil service infrastructure which, if properly
used, can be an effective instrument with which to address governmental concerns. Even so, as noted earlier, not all concerns identified in this chapter will
receive the same degree of attention in all countries, in part because of differing governmental priorities and national perspectives.
Eutrophication management programmes usually are developed and implemented by a governmental entity. Consequently, all affected governmental
agencies should be consulted.
22
T A B L E 4. O E C D boundary values for open trophic classification system1.
Mesotrophic
Eutrophic
Oligotrophic
Parameter
Hypertrophic
(annual meari values)
Total
phosphorus
(|ig P/l)
Total
nitrogen
(ugN/1)
Chlorophyll a
(ug/1)
Chlorophyll a
peak value
(Ug/1)
Secchi
depth
(m)
X
8.0
x±lSD
x±2SD
range
4.9-13.3
2.9-22.1
3.0-17.7
26.7
14.5-49
7.9-90.8
10.9-95.6
n
21
19 (21)
X
661
753
x±lSD
x±2SD
range
371-1180
208-2103
307-1630
485-1170
313-1816
361-1387
n
11
8
84.4
48-189
16.8-424
16.2-386
71 (72)
X
1.7
4.7
14.3
x±2SD
0.8-3.4
0.4-7.1
3.0-7.4
1.9-11.6
6.7-31
3.1-66
range
0.3-4.5
3.0-11
n
22
16 (17)
2.7-78
7 0 (72)
X
4.2
16.1
x±lSD
x±2SD
range
2.6-7.6
1.5-13
1.3-10.6
8.9-29
4.9-52.5
4.9-49.5
42.6
16.9-107
6.7-270
9.5-275
n
16
12
46
2.45
1.5-4.0
0.9-6.7
0.8-7.0
70 (72)
X
9.9
4.2
2.4-7.4
x±2SD
range
5.9-16.5
3.6-27.5
5.4-28.3
n
13
20
1.4-13
1.5-8.1
2
1875
861-4081
395-8913
393-6100
37 (38)
x±lSD
x±lSD
750-1200
100-150
2
0.4-0.5
1. The geometric means (after being transformed to base 10 logarithms) were calculated after removing
values which were greater than, or less than, two times the standard deviation obtained (where applicable)
in the first calculation.
x = geometric mean.
S D = standard deviation.
( ) = the value in brackets refers to the number of variables (n) used in the first calculation.
[Source : Modified from Organization for Economic Cooperation and Development 1982.]
23
In this w a y , one can obtain the perspectives of the individual agencies involved, as well as bring their collective wisdom and experience to bear on the
problem. Relevant agencies can include governmental units concerned with environmental quality, water quality, water supply, resource management, fisheries or aquaculture, power production, agriculture, commerce and/or public
health. This interagency consultation also is a good planning strategy, since cooperation between governmental units, rather than confrontation, will concentrate more energy and resources on solutions to environmental problems.
The selection of effective eutrophication control measures depends on a n u m ber of scientific/engineering, socio-economic and political factors. Furthermore, lakes and reservoirs are complex aquatic environments. Consequently,
eutrophication is a problem which the policy-maker need not face alone. T o attempt to obtain an understanding of the eutrophication process, a multidisciplinary approach is highly desirable. Eutrophication policy and management decisions usually are best m a d e in consultation with individuals in the following
areas of expertise:
Municipal wastewater treatment engineer/consultant engineer. This expert can
provide knowledge of the nutrient contributions of, and control strategies for,
municipal wastewaters in the drainage basin.
Municipal chemist/consultant chemist. The chemist can supply information on
nutrient concentrations in municipal wastewaters and industrial effluents, as
well as other important point sources of nutrients.
Agriculturalist. The agricultural expert will have necessary knowledge of soils,
land-use activities, feedlot and fertilizer practices, and other relevant farm
operations, as well as methods for the control of soil erosion and associated
nutrient runoff.
Hydrologist. Water movement and water balances play an important role in dictating the pathways of nutrients through the landscape. These factors can affect the nature and magnitude of the nutrient loads and concentrations reaching surface waters. The hydrologist can give guidance on these topics.
Economist. M a n y eutrophication problems and control strategies require an
economic evaluation as part of the assessment of alternative management
strategies. The economist is essential for such endeavours.
Limnologist. The limnologist can assess the impacts of excessive nutrient inputs on the aquatic environment with respect to plant growth, deteriorating
water quality, fishery development, and general effects on the aquatic ecosystem. Relevant individuals include experts in the fields of algal physiology, fisheries, aquatic chemistry and water quality modeling.
Other professionals. The advice of legal, health and planning experts can be extremely valuable in the development of effective eutrophication control
programmes.
24
The public role
Where it is feasible, it can also be very helpful to seek the public's view regarding eutrophication problems and solutions. If the public's view is sought in a
given situation, a readily usable forum for obtaining this viewpoint should be
clearly identified. O n e example is the creation of a citizen's advisory committee. This type of committee can provide additional insight about the extent of a
given eutrophication problem, and what the social and political consequences
might be if the problem was left uncorrected. A s noted earlier, the policy-maker
often must balance the interests of advocates of long-term benefits against those
wishing more politically expedient solutions.
Interested citizens can be an asset in the development of effective eutrophication management programmes. A s an example of the potential benefit of public input, actual water quality data from a lake m a y be scarce at the beginning
of a control programme. In such cases, narrative descriptions of prior conditions, remembered by elder citizens and leaders, can be used as an initial reference point against which the potential effectiveness of a control programme
can be assessed.
In the broad sense, such interactive communication can have at least two
beneficial effects: (1) knowledge gained through lifetime observations of a
waterbody can be documented for use in developing management programmes;
and (2) persons encouraged to participate in the development of a programme
are more likely to become advocates of the programme.
Knowledge gained in this manner by governmental personnel can be disseminated a m o n g the general population, preparing them for more informed future
judgements and actions. Effective public participation requires that government
officials be honest in their presentation of information and responsible to the
views expressed in them. Nothing can be more damaging to public confidence
in a new government initiative than a feeling by the public that the government
did not listen to those participating in the process.
In some developing countries, in particular, financial constraints m a y limit
the use of large structural solutions to eutrophication problems (e.g. municipal
wastewater treatment plants). In such situations, the governmental entity m a y
wish to make m a x i m u m use of community-based information and educational
programmes on eutrophication control measures, especially those in which the
public can most directly participate. In such cases, a communications specialist can be a valuable asset.
25
A S S E S S THE E X T E N T OF
INFORMATION AVAILABLE
THE W A T E R B O D Y
ABOUT
Before a eutrophication monitoring or management programme is developed,
one should attempt to determine the full scope of the problem. Previous studies
and relevant case histories should be reviewed prior to development of a m a n agement programme. Likely sources of such information include drinking water
and wastewater treatment agencies, universities and other types of research centres (including national, regional and local government laboratories), and the
scientific and engineering literature dealing with aquatic ecosystems. While
some control measures can be initiated in the absence of such knowledge, further refinement of management alternatives usually requires more knowledge.
There are several reasons for collecting adequate monitoring data in regard
to any environmental assessment or management programme: (1) to establish
past and present baseline conditions in order to confirm the problem, and to provide a reference against which progress can be assessed; (2) to identify significant information gaps; and (3) to develop a cost-effective monitoring programme.
Necessary information for the assessment and control of lake or reservoir eutrophication normally includes such items as the depth, volume and water-flushing rate, the in-lake concentrations of nutrients and algae, the occurrence of
nuisance growths of algae and other aquatic plants, the occurrence of oxygendepleted bottom waters in the lake and related fish kills, the annual nutrient
loadings to the lake, and the population and land use characteristics of the drainage basin.
If existing data are not sufficient to provide the necessary information for assessment or management purposes, it will usually be necessary to implement a
27
drainage basin and/or in-lake monitoring programme. A n initial monitoring prog r a m m e can be modest. However, the monitoring network should be designed
to allow progressive expansion and revision, if necessary, to meet changing
needs. Ryding and Rast (1989) provide detailed information on developing effective in-lake monitoring programmes, as well as methodologies for determining the nutrient load. In addition, Cale and M c K o w n (1986) present a methodology for estimating the anticipated costs of monitoring programmes.
Data and documentation should be sufficient to support the undertaking of
corrective measures. There probably will never be sufficient scientific understanding to convince every technical expert that a given management action is
the ideal or timely one to be taken. N e w knowledge inevitably raises new questions. Nevertheless, if the policy-maker delays implementation of any corrective actions until all questions are completely answered, the problem can
become extremely difficult to correct.
28
IDENTIFY A V A I L A B L E O P T I O N S
FOR M A N A G E M E N T OF
EUTROPHICATION
Should one treat the causes or the symptoms?
There are several approaches for assigning a priority to alternative eutrophication control programmes. The programmes can be directed either toward treating the basic causes or the symptoms (e.g. reducing aquatic plant nutrient inputs from the drainage basin versus periodic harvesting of excessive aquatic
plant growths). In some cases, a combination of the two will be most useful. Alternatively, programmes can focus on treating primarily point sources or nonpoint sources of nutrients. Examples would be limiting 'pipeline' nutrient inputs from municipal wastewater treatment plants and controlling runoff from
farms and urban areas, respectively. Further, the programme can be either structural or non-structural in form (e.g. building a municipal wastewater treatment
plant versus changing agricultural fertilizer application practices). In a given
case, the basic approach should be tied as closely as possible to the overall eutrophication management goals.
W h e r e possible, it usually is most effective to attempt to treat the underlying
and most readily-controllable causes of eutrophication, rather than attempt
merely to alleviate the symptoms. In most cases, this means reduction or elimination of the excessive nutrient inputs that stimulate the excessive growths of
aquatic plants in the first place. This approach will work to eliminate the basic
problem, and usually is the most effective strategy over the long term.
The alternative strategy is to treat the specific symptoms of eutrophication.
This is the logical and perhaps only option if the costs of treating the basic cause
(excessive nutrient inputs) are too high, or if additional treatment is necessary
29
in a given case. Other possible reasons for using this approach are the absence
of an institutional framework for treating the cause or an inability to formulate
and/or implement an effective management programme directed toward nutrient
reductions. In such cases, several 'in-lake' treatment options (discussed in a following section) can offer temporary relief in varying degrees from the symptoms of eutrophication.
Consider full range of available control options
Reduction of nutrient Inputs
The first control priority usually is to limit or reduce nutrient inputs to the waterbody from the sources in the drainage basin that contribute the largest quantities
of the 'biologically available' forms of the nutrients (Rast and Lee, 1978,1983;
Lee et al. 1980, Sonzogni et al. 1982). The control effort can be directed to both
the point ('pipeline') and/or non-point (diffuse) nutrient sources in the drainage
basin. For example, human and animal wastewaters contain large quantities of
phosphorus and nitrogen, in chemical forms easily used by algae and other aquatic plants. Treatment to reduce the level of the nutrients in these wastewaters
usually is a cost-effective approach to keep them from reaching surface waters
(at least up to a certain advanced level of treatment). Examples of some approximate costs for sewage treatment in Sweden is provided in Table 5. O f course,
the costs can vary, dependent upon such factors as the age of the plant, the degree of treatment and the population served.
T A B L E 5. Approximate costs for sewage treatment in Sweden, 19781.
N u m b e r of
person
equivalents (P.E.)
2,000
5,000
20.000
50,000
Costs for post-precipitation plants
(including sludge treatment)
Capital costs2 Operating costs2
130
100
60
45
100
70
50
40
Additional costs for
deep-bed filtration
Capital costs2 Operating costs2
—
25
10
7
—
8
4
3
1. Swedish crowns(krona)/capita.a (1 Swedish crown = $0.11 U . S ) .
2. The annuity used in calculation of capital costs is 10 per cent for post-precipitation plants and 13 per
cent for deep-bed filters.
[Source : Forsberg and Ryding 1981.]
30
Phosphorus and nitrogen are not the only nutrients needed by aquatic plants
for growth. However, they are the most important nutrients from the management perspective, because their input to lake waters can be controlled significantly with existing technology (e.g. phosphorus removal from effluents at m u nicipal wastewater treatment plants). Further, reduction of the quantities of
phosphorus in phosphate-containing detergents can be an effective supplemental measure, especially in areas where the removal of phosphorus at municipal
wastewater treatment plants is not practised, or where there are a large number
of septic tank disposal systems in a drainage basin.
Another method of reducing nutrient inputs to a waterbody is to divert m u nicipal sewage wastewaters from the drainage basin of concern into a d o w n stream basin. This latter method can be effective for the affected waterbody.
However, it does not eliminate the basic problem; it merely shifts it to another
waterbody which m a y or m a y not be more capable of handling it. There also are
obvious social and political problems associated with this type of 'solution'.
A large number of nutrient control options also exist for non-point sources
of nutrients in the drainage basin. These various measures exhibit a wide range
of costs and effectiveness ( P L U A R G 1978a, Monaghan Ltd 1978, Skimin et al.
1978, Monteith et al. 1981, Ryding and Rast 1989).
In-Lake control measures
S o m e treatment measures can be applied directly in a lake or reservoir to attempt to alleviate the symptoms of eutrophication (Table 6). They also can be
used to augment other treatment methods, or to provide temporary relief from
eutrophication symptoms while a long-term control strategy is being formulated
or implemented.
Examples of in-lake methods include the harvesting of aquatic plants, the use
of algicides, in-lake nutrient inactivation or neutralization, artificial oxygenation of bottom waters, dredging or covering of bottom sediments, increasing the
water flushing or circulation rates, and 'biomanipulation' (Cooke et al. 1986,
Ryding and Rast 1989). Although such measures usually are less effective over
the long term than external nutrient control programmes, they do offer an effective means of combatting, at least temporarily, the negative impacts of eutrophication.
Valuable sources of relevant information regarding both point and non-point
source eutrophication control measures include Monaghan Ltd (1978), Skimin
et al. (1978), P L U A R G (1978a), Johnson et al. (1978), Phosphorus Management
Strategies Task Force (1980), Welch (1980), United States Environmental Protection Agency (1980), Bernhardt (1983) and Lester and Kirk (1986). In addi-
31
T A B L E 6. Water quality problems treatable by in-lake restoration measures.
Water quality problem
Control meaaure
Odoun
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Hxceealve
algal
blooms
X X X
Dredging
Hypolimnetic aeration
Nutrient inactivaüon
Altered circulation
Algicides
Biomanipulation
Dilution/flushing
Removal of hypolimnetic waters
Lake drawdown
Harvesting
Covering sediments
Fiahkilla Toxic algae
InterrercncB
Reduced
Bxcesaiw Poordrinkâig
withcommercial- macrophyte
water
awimroing
flatting
growth
quality
X
X
X
X
tion, Cooke et al. (1986) provide a comprehensive summary of in-lake treatment measures. These various reports discuss both the relative effectiveness and
costs of the control measures considered.
The option of doing nothing
The environmental, social and economic consequences of doing nothing also
should be considered prior to developing or evaluating eutrophication management options, and even in deciding whether or not to implement such programmes in the first place. The consequences of doing nothing offer a basis for
comparison with the potential impacts of initiating control programmes.
However, doing nothing is not usually a satisfactory solution to eutrophication problems. A n inevitable consequence of human settlement of a drainage
basin is a deterioration of water quality in the drainage basin over time, especially if such deterioration continues to be ignored. A n untreated waterbody exhibiting eutrophication symptoms sufficiently severe that control programmes
are being considered likely will become even worse over the long term. This
can necessitate even more expensive control programmes at a later date, as well
as the loss of an increasing number of water-use options. Further, while cultural eutrophication is largely reversible, a lake cannot be allowed to deteriorate
indefinitely without diminishing the chances for a timely and successful rehabilitation.
32
In addition, it is pointed out that doing nothing when corrective actions are
called for also can be a costly alternative over the long term since it even can
create costs. For example, long-term and presumably beneficial water uses m a y
have to be curtailed or eliminated as a result of eutrophication-related water
quality deterioration. The number of sources of good or acceptable water also
m a y decrease over time. A s noted earlier, the occurrence of parasitic diseases
can be enhanced in some cases. Such impacts potentially could result in higher
environmental, socio-economic and/or political costs over the long term than
initiation of appropriate remedial programmes at an earlier stage. Furthermore,
some eutrophication prevention or control measures actually m a y result in m o n etary savings, or even profits, over time. A n example is the use of nutrient-rich
waters for irrigation or aquaculture purposes (Figure 3). Such possibilities can
be an attractive part of an effective eutrophication control programme. Ryding
and Rast (1989) present a summary of eutrophication control case studies of
lakes and reservoirs around the world.
River water
Fishpond
I Aquatic
plants
Agricultural
areas
— < u « i Fodder I
Feed for pigs
FIG. 3. Schematic representation of different possibilities for the integrated management of
nutrient-rich waterbodies in tropical settings (China and Indochina).
[Adapted from various sources.]
33
A N A L Y Z E ALL C O S T S A N D
E X P E C T E D BENEFITS OF
ALTERNATIVE M A N A G E M E N T
STRATEGIES
Consider relative costs of control options
The costs of specific eutrophication control options vary substantially. The
costs of phosphorus removal at municipal wastewater treatment plants, for
example, will vary as a function of the treatment process used, the age of the
plant, the number of people served, etc. Non-point source control measures also
exhibit a wide range of costs and effectiveness. However, the long-term costs
of some non-point source measures can be minimal (e.g. the use of sound land
management practices). Furthermore, some non-point source control measures
actually can result in a monetary saving over the long term, even considering
the initial costs of implementing the programmes. It was determined, in the
North American Great Lakes Basin, that beyond a certain advanced degree of
point source control, it was less expensive to implement some non-point source
control measures (Table 7) than to implement further, more stringent point
source control measures ( P L U A R G 1978a, Johnson et al. 1978). In addition, some
non-point source control measures can be relatively simple in concept. A n
example is the application of fertilizers in quantities which do not exceed the
actual needs of the soil. Applying fertilizers in excess of soil needs can result
in their transport to surface waters via agricultural runoff. Soil nutrient requirements can be readily determined with appropriate soil tests.
The costs of some eutrophication control measures (e.g. building and operating municipal wastewater treatment plants for nutrient removal) are sufficiently well-known by civil and sanitary engineers that reliable cost estimates can
35
be obtained. Nevertheless, because of local conditions, eutrophication control
alternatives still can show a wide range of costs. For example, the local costs
of such factors as labour, energy, materials, etc., can vary in different regions
and impact the ultimate costs of eutrophication control alternatives. Such factors will have to be considered individually in each situation.
T A B L E 7. Example of least expensive combination of
phosphorus control options for Lake Erie1.
Remedial measures
Phosphores
removal (t)
Annual cost2
450
minimal
Rural level 1 measures
0.5 mg/1 effluent phosphorus
limitation for municipal
wastewater treatment plants
Rural level 2 measures
Urban level 1 measures
1,305
350
445
2,550
TOTALS
$
$
$
$
10.5
22.5
36.5
69.5
million
million
million
million
1. Assumes an effluent phosphorus concentration of 1 mg/1 has already
been achieved at municipal wastewater treatment plants discharging
3,800 m ' / d .
2. Based on 1975 U . S . dollars.
[Source : adapted from PLUARG 1978a; Johnson et al. 1978.]
Compare available resources and
management goals
There is little practical value in designing or developing a substantial eutrophication control programme if the available resources or administrative structure
are not adequate to carry out the programme. Consequently, the available resources should be identified and compared with the needs of the task to be
undertaken. Such resources would include such items as technical expertise, financial resources and manpower.
A n initial assessment of resources also can help identify what resources must
be m a d e available before an effective programme can be carried out. A wellformulated statute or regulation, for example, is of little value if it is not supported with an adequate administrative apparatus. The responsible agency must
have sufficient funds to hire qualified staff, purchase necessary supplies, equipment and instruments. Responsible personnel must be able to travel within their
country and examine similar problems, and to attend meetings (both inside and
outside their native country) to learn of current approaches and practices a m o n g
their fellow professionals elsewhere.
36
The initial control programme should not be so elaborate as to be unattainable. Rather, it should be designed and have sufficient scope that it has a realistic chance of achieving its management goals. A small, successful programme
can be expanded as knowledge is gained and resources m a d e available, building upon the success already achieved.
Compare available resources and
expected benefits
A s suggested earlier, if the management goal is to alleviate the negative impacts
of eutrophication, the most effective approach usually is to treat the most readily controllable cause of the problem - the input of excessive quantities of phosphorus and/or nitrogen from the drainage basin to the waterbody. The control
programme should be directed toward the major sources of these nutrients in
the drainage basin. These sources primarily are human and animal wastes (including municipal wastewater effluents and drainage from large animal feedlots). Non-point sources, especially runoff from urban and agricultural lands,
also offer important nutrient control targets.
Changes in land usage patterns and/or land management practices offer a
largely non-structural way of reducing nutrient loads associated with land runoff. However, the implementation of some non-point source methods m a y require basic public education and/or a change in public attitudes regarding m a n ' s
use of the land. For example, a farmer located a long distance from a lake m a y
not appreciate his role in causing or promoting nutrient runoff from his land to
the lake. In such a case, the farmer understandably m a y resist the suggestion
that a change in his fertilizer application practices or methods of ploughing can
help reduce the nutrient load to the lake by reducing the quantities of agricultural nutrient runoff. This is especially true if the suggested changes are more
expensive or time-consuming than his current farming practices, or if no direct
benefit to the farmer can be demonstrated. Obviously, if the suggested change
can be shown to have a beneficial effect on farm operations, its usefulness is
m u c h easier to demonstrate. A s suggested by P L U A R G (1978a), such individual
efforts m a y not seem impressive when viewed individually, but actually can be
very significant on a cumulative scale.
It is reiterated that the enhanced biological productivity associated with eutrophication also can be a beneficial aspect of the eutrophication phenomenon
in some situations. Examples are enhanced fish production (Figure 4) and other
forms of aquaculture for the production of needed food supplies. The use of harvested aquatic plants as a livestock food, or the use of nutrient-rich sewage
sludge or bottom waters as a soil fertilizer, also are economically beneficial in
37
50 _
Y = 0.072X + 0.792
r2 = 0.84
n = 21
40
jf 30
"&
JÉ
> 20
10
0
100
200
300
400
500
600
TPftig/l)
FIG. 4a. Relationship between total phosphorus CTP) andfishyield (FY).
[Source: Redrawn from Hanson and Leggett (1982).]
101 ,_
S
10°
_
•o
O)
>-
I
w
LL
(H9 P/l)
FIG. 4b. Relationship betweenflushing-correctedannual phosphorus load andfishyield.
[Source: Redrawn from Lee and Jones (1981). For definition of terms, see Fig. 5, page 52 of
this digest]
38
some situations. Such possibilities can be positive components of environmentally acceptable, long-term eutrophication management programmes in a region
or country.
Cost-benefit analysis
A s noted earlier, non-scientific concerns also must be taken into account in
m a n y cases when developing effective eutrophication control programmes. For
m a x i m u m public acceptance of environmental protection programmes, the
scientist or engineer cannot ignore economic and political realities, in favour of
a solely technical approach. Likewise, the policy-maker or manager cannot ignore environmental and engineering considerations. In fact, because of the
tremendous growth in the size, scope and expenditures of central governments,
the public reaction in some countries has been a reluctance to fund n e w environmental protection programmes without a thorough social and economic analysis of such programmes (in addition to environmental impact assessments).
O n e approach often used to assess the desirability or worthiness of alternative management programmes is cost-benefit analysis. Cost-benefit analysis has
its basis in a branch of economic theory called welfare economics. Little (19S7)
and B a u m o l and Oates (1975) provide a basic introduction to this topic.
In the broadest sense, cost-benefit analysis means a comparison of all the
positive and negative elements of a decision, even if not all of the elements are
measurable in strictly monetary terms. However, in practice, cost-benefit analysis usually means a comparison of the financial gains realized and the costs
incurred for a particular programme or activity. If a value unit (e.g. dollars) is
spent in a w a y that generates more wealth than is sacrificed, then the overall social welfare is increased. Thus, if the «price» of a necessary or desirable activity (e.g. eutrophication control programme) does not exceed the expected benefits (e.g. enhanced water quality or water uses), it usually is considered desirable
to proceed with the project. A s a practical example, a policy-maker using costbenefit analysis usually is asking whether or not the expected benefits of a eutrophication control programme are worth the investment of public funds.
It is obvious that, at the broadest scale, governments must choose between a
wide array of potential projects and programmes, from national defence, to food
subsidies, to environmental protection. Using solely economic criteria should
stress 'efficiency' in assessing competing alternatives (i.e. the most efficient
use of scarce resources is required to maximize their impact).
Unfortunately, a significant shortcoming of a strictly monetary-oriented approach is that it usually is done under the implicit assumption that a positive
benefit: cost ratio alone is sufficient rationale to proceed with a given pro-
39
g r a m m e or activity. However, while the cheapest solution to a eutrophication
problem m a y be economically pleasing, it also m a y be environmentally shortsighted. This is because some elements of a eutrophication control programme
m a y not be easily quantified, or else can be quantified only in an artificial or
unrealistic manner. Examples of such elements are cultural values, the longterm sustainability of natural resources, political realities, societal and/or governmental structure and stability, and the national or regional distribution of
wealth. It is because of such realities that the logical solution to an environmental problem is not always the most socially acceptable one.
Thus, using a strictly monetary-oriented cost-benefit analysis as the sole decision-making tool m a y preclude realistic consideration of the long-term environmental, social and/or public health consequences of a given control prog r a m m e . For example, if one cannot assign a realistic monetary value to the
desirability of maintaining a particular fish species or the achievement of enhanced water quality, such factors m a y be ignored as a benefit w h e n compared
to the use of a water resource for industrial purposes or municipal waste assimilation.
Non-scientific concerns also m a y require explicit consideration in development of effective eutrophication control programmes.
Because of these types of problems, one can use cost-benefit analysis in a
somewhat different manner in assessing management alternatives. Justification
of eutrophication control programme expenditures can be based on an analysis
of the expected benefits of alternative programmes, since different uses of m o n etary resources can be expected to yield different benefits. B y comparing the
expected benefits of alternative control programmes, one can attempt to select
the most preferrable option in a given situation. This can be done either by:
(1) Comparing the benefitxost ratios of alternative programmes and levels of
expenditure; (2) Comparing the absolute values of the expected benefits of alternative projects, using a fixed level of monetary and other resources; or (3)
Determining the m i n i m u m cost programme for achieving a specific goal or
benefit.
The remaining discussion in this particular section assumes that the basic decision to proceed with development of a eutrophication control programme has
been m a d e .
Social concerns
A s used here, social concerns are meant to cover the non-technical concerns related to development or implementation of an environmental protection or m a n agement programme. It is assumed that these concerns are measuable or defin-
40
able in some way. Accordingly, four broad categories of social impact can be
usefully distinguished, as follows:
Economic impacts. Includes the 'efficiency' concept identified above, as well
as such fiscal and social factors as employment rates, balance-of-trade, tax
revenues, and the national and/or regional distribution of wealth. Consideration of the latter factor must include the observation that the expected benefits m a y not be equivalent, or m a y have different economic significance, for
different income classes or occupational categories.
Demographic impacts. Involves population distribution characteristics, such as
shifts from urban to rural areas, whether self-sufficient or dependent on government agencies or from one region to another. A n example would be the
potential impacts of construction of a centralized marine fish processing facility to replace local fish stocks lost due to advanced eutrophication.
Changes in health parameters m a y also be an important consideration in some
cases.
Environmental impacts. Involves both natural (e.g. aesthetic appreciation of a
pristine lake) and 'created' concerns (e.g. urbanization, crowding and increased noise as the result of a tourist influx to an aesthetically pleasing area).
Real estate values sometimes reflect such concerns, especially within small
areas.
Cultural impacts. Involves the way that populations perceive and react to environmental changes. A n example is a cultural or religious attitude regarding
the sanctity of a pristine lake, as contrasted with a spartan work ethic supporting the notion that m a x i m u m use of a lake for economic productivity is
critical.
A hypothetical example serves to illustrate h o w these concerns can impact
the selection or implementation of a eutrophication control programme. It is assumed here that a lake or reservoir is exhibiting depleted oxygen levels in its
bottom waters due to excessive nutrient runoff from agricultural lands. T h e
oxygen depletion is having negative impacts on the recreational fishery of the
waterbody. It is the task of the policy-maker to determine whether or not a soil
erosion (and associated nutrients) control programme based on m i n i m u m tillage
farming methods should be implemented. T h e eutrophication control prog r a m m e possibly could result in increased levels of desirable g a m e fish species.
The types of concerns the policy-maker m a y have to consider in this example
include the following: (1) a possible increased overall farm production, but also
an increased number of failing, small family farms due to n e w required capital
investments. This could have the impact of promoting large-scale farming operations at the expense of small ones, and of changing prevailing farming practices; (2) a possible change in crop species, which could diminish the local pro-
41
duction of a culturally-significant commodity; (3) a possible increase in levels
of toxic substances in fish, due to the transport to the waterbody of the increased
quantities of herbicides used on the land surface. Increased herbicide use is
often necessary with this method of farming; (4) a possible increased health risk
from consumption of affected fish and ground water; (5) a possible increased
recreational fishery, with larger and more plentiful g a m e fish, but a decreased
commercial fishery; and (6) a possible increased tourist influx (with attendant
economic benefits), but accompanied by increased traffic noise, congestion, etc.
In analyzing the importance of such often-competing factors in development
of an effective eutrophication control programmes, some mechanisms for prioritizing, 'weighting' and/or integrating them into the decision-making process are
desirable.
O n e way to accomplish this, particularly when several control options are
being considered, is to develop a simple matrix which considers the relative 'social impact' of each control option. Since multiple control options m a y be available in a given situation, one can rank (even if subjectively) the major criteria
of concern for each of the control programmes or options being considered. For
example, if one assumes a ranking scale of - 5 to + 5 , with zero being 'no effect'
and ±3 being a large impact in a positive or negative direction, a social impact
ranking matrix of alternative control programmes can be developed. In this
example, Control programme A refers to phosphorus removal at municipal
wastewater treatment plants, programme B refers to in-lake nutrient inactivation and programme C refers to urban non-point source control measures.
The ranking numbers for each control programme can be generated on a
quantitative or qualitative basis. For example, using the occurrence of conjunctivitis (an eye infection associated with swimming in degraded waters), a ranking scale for health effects could be developed as follows:
Increase in conjunctivitis ranking
up to 5 %
up to 10 %
up to 25 %
up to 50 %
greater than 50 %
-1
-2
-3
-4
-5
The reverse would be true for a decrease in the occurrence of conjunctivitis.
If all criteria used in the ranking matrix above were of equal social value, the
overall rankings of the alternative control programmes could be summarized,
as illustrated in Table 8 (I).
42
In m a n y situations, however, some factors m a y be more important than
others. In such cases, the policy-maker can assign a value to the ranking criteria which signifies its relative social importance, thereby integrating this value
into the ranking process. The relative importance could be assigned directly by
the policy-maker or manager based on personal experience or knowledge of the
particular situation, or can be obtained by other means (e.g. public opinion polls,
referendum votes, a canvass of opinion from scientific experts, etc.).
In this example, if health effects were the primary concern, and the policymaker had determined that the relative social importance of the three factors
considered above were 7 , 2 and 1 (out of a possible 10), respectively, then the
overall rankings of the alternative control options would change, as shown in
Table 8 (II).
T A B L E 8. Relative ranking of three alternative control programmes, based on three
different ranking criteria.
Ranking criterion
Control Programmes
Health
effects
Desirable
fishery
Aesthetic
quality
S u m of
criteria
Rank
I. Based on ranking criteria
of equal importance1
Control-Programme A 2
Control-Programme B 3
Control-Programme C
1
-3
-1
+
+
+
2
5
2
+
+
+
-5
-2
4
=
-2
0
5
3
2
1
+ 1 (-5)
+ 1 (-2)
+ 1 (+4)
=
=
=
6
-13
1
1
3
2
H . Based o n weighting
specific ranking criteria1
Control-Programme A 2
Control-Programme B J
Control-Programme C
7(+l)
7(-3)
7(-l)
+ 2 (+2)
+ 2 (+5)
+ 2 (+2)
1.1 = All ranking criteria assumed to be equally important. II = Reflects relative social importance of
ranking criteria.
2. Phosphorus removal from municipal wastewater-treatment plant effluents.
3. In-lake nutrient inactivation.
4. Urban non-point source control programme.
[Source: Taken from Rast and Holland 1988, T h o m b u r n 1986.]
Clearly, the relative weights (however assigned), as well as the specific ranking criteria used in this simple analysis, can significantly affect the eutrophication control programme ultimately selected. The monetary costs of a control
programme also can be included as one (but not the only) ranking criterion. The
primary difficulty with such an analysis is in establishing the relative weights
of the individual criterion, even if the necessary data can be obtained. This process often ends up a political one.
43
A s a practical matter, the policy-maker already implicitly performs simple
analyses of this type in choosing between management alternatives. The point
made here is that it usually is beneficial to perform such an analysis explicitly
(whatever form it m a y take), especially if socio-economic or political factors
are of significant concern in selecting between alternative eutrophication control programmes. In this way, individuals whose input to the selection process
is strictly technical can see w h y some of their recommendations m a y have to be
subordinated to non-technical ones. Such an approach would also educate the
scientist and engineer as to the additional factors which the policy-maker and/or
manager must consider, in addition to the strictly technical ones.
A n example of a simplified approach used to determine the minimum cost
nutrient control strategy for the North American Great Lakes Basin is provided
by P L U A R G (1978a) and Johnson et al. (1978).
The reader is referred to other reports for more details regarding the important topic of cost-benefit analysis in relation to development of effective pollution control programmes. Useful information sources include Organization for
Economic Cooperation and Development (1974), Henderson (1974), Krutilla
and Fisher (1975), Sinden and Worrell (1979), Pineau et al. (1985), Conn (1985)
and Thornburn (1986).
44
A N A L Y Z E A D E Q U A C Y O F EXISTING
LEGISLATIVE/REGULATORY
FRAMEWORK
FOR IMPLEMENTING
EUTROPHICATION CONTROL
PROGRAMMES
Institutional concerns
A s noted earlier, a range of different forms of government, national priorities,
customs and socio-economic conditions exist around the world. Consequently,
guidelines for addressing institutional and regulatory concerns in one country
m a y not be appropriate for other countries. Thus, the following concerns will
have different priorities in different countries.
The legislative and regulatory frameworks for addressing eutrophication
should be examined as a necessary component of an effective eutrophication
control programme. There is little point in developing a complex eutrophication monitoring network, for example, if the legislative or regulatory framework
for implementing or enforcing the eutrophication control programmes does not
exist. Conversely, a well-formulated statute is of little value if the necessary
monitoring or pollution-alert network for determining compliance with the
statute is inadequate.
It usually is most efficient at the central government level to assign environmental programmes to a single agency structured to manage multiple environmental concerns (e.g. air, water and land resources), than to create a separate
governmental unit to deal with each problem as it arises. Furthermore, the responsible agency or institution for carrying out such programmes should be
clearly identified. A s noted earlier, the public especially m a y have concerns or
suggestions about various aspects of eutrophication, but be frustrated by the
lack of a clearly-identified and readily-accessible forum for expressing such
concerns to the policy-maker or administrator.
A n effective eutrophication control programme also m a y contain elements,
or be involved with problems, which overlap political boundaries and/or gov-
45
emmental agency concerns. If there is an existing agency with which a new control programme is compatible, that agency is the logical one to carry out the
new function. However, care must be taken to prevent a new programme from
being assigned to an existing governmental unit having a conflicting purpose or
goal. For example, an agency responsible for promoting commercial fisheries
(thereby interested in enhancing the overall productivity of a waterbody) is not
necessarily the best agency to be given the task of protecting a lake as a drinking water supply (for which increased algal production is not desirable). The
optimal water quality for these two uses is markedly different. If a central
agency is charged with governmental programmes which have conflicting purposes, much effort can be expended in resolving the conflict rather than addressing the problem, or else one purpose will advance at the expense of the other.
If it is necessary to create a n e w programme for the management or control
of eutrophication, a definite term for the existence of the programme should be
enacted. Approximately five-ten years would be a reasonable period of time. At
the end of this time interval, the programme would either be terminated or reenacted. Even though this provision creates some risk that a beneficial agency
or programme might be terminated, this limited term provides an incentive for
governmental accomplishment, mandates timely attention by the policy-maker
and/or the public, and provides an opportunity for necessary updating and refinement of the programme.
Regulatory concerns
Lengthy, complex, detailed regulations should be discouraged, if not prohibited,
because of the potential difficulty both in understanding and administering
them. The proliferation of agency-oriented regulations that typically burden
many environmental programmes certainly should be avoided. M a n y environmental regulatory statutes adopted in the United States in the 1970's, for
example, were initiated without full appreciation of the magnitude of the duties
ultimately required of the relevant governmental regulatory body, usually the
Environmental Protection Agency. A s a result, the required duties often were
more than the available manpower and money could support or accomplish
within the prescribed deadlines. If a n e w statute cannot be implemented because
of unrealistic components, not only is achievement of the worthwhile objective
delayed, but respect for the timely compliance with laws also is generally
eroded. Over the long term, an orderly progression in statutory complexity and
development, from one legislative session (or its equivalent) to another, is
preferable to the confusion that can result from attempting to accomplish too
m u c h , too soon, with too little information, manpower and money.
46
The administering agency should record its significant decisions, especially
those that are controversial or strongly contested. These recorded decisions provide a mechanism for guiding the administering agency, as well as the affected
parties, in the future. In addition, eutrophication m a y be the only concern addressed in a given statute. However, in drafting such statutes, consideration also
should be given to relating eutrophication to other environmental problems (and
their solutions) in the future.
Initial regulatory statutes should contain provisions for securing sufficient
data and knowledge useful for periodically re-evaluating a eutrophication control programme. In the United States, for example, m a n y environmental improvement programmes began as attempts to assist local governmental units
(e.g. states, regions, counties or cities) in understanding and addressing their
specific needs. Such assistance as training grants to prepare technical staff,
money for personnel, assistance to develop monitoring networks, support for
students to secure advanced degrees in colleges and universities, and research
grants to study the issues and problems, contribute to future refinements in the
regulatory scheme. It also furthers our general scientific understanding of the
complexities of the eutrophication process.
The degree to which local and regional resources can be focused on solving
enviromental problems depends in part on the institutional framework, and in
part on the strengths and interests in a particular country. The size of the country
also impacts the choices to be made. A s an example, the United States has
learned that more effective programme administration within its large geographic area can be achieved in a cooperative hierarchial arrangement, with its
relevant federal, state, and local governmental entities.
47
SELECT EUTR0PH1CATI0N
CONTROL STRATEGY AND
DISSEMINATE S U M M A R Y TO
A F F E C T E D PARTIES PRIOR T O
IMPLEMENTATION
General considerations
N o single approach or control measure will successfully treat all cases. A s noted
earlier, the extent of present scientific knowledge is not sufficient to be able to
offer a completely fool-proof eutrophication control programme. Nevertheless,
our present knowledge is sufficient to develop a generalized approach which,
if used in conjunction with an adequate monitoring programme and continuing
scrutiny of the measured data, will usually work in the majority of cases likely
to be encountered. The use of statistically analyzed data bases and derived quantitative relationships (e.g. Organization for Economic Cooperation and Development 1982) allows for the development of a reasonable, generalized approach
for attempting to assess and control eutrophication of lakes and reservoirs. O f
course, one always should remain aware of the uncertainty and potential error
associated with such data bases, in order to use them effectively for predictive
purposes.
The most feasible control option in a given situation can vary from location
to location, depending on the circumstances. A s noted earlier, it is generally believed that the control of inputs of external nutrients (especially phosphorus)
represents the most effective, long-term strategy for attempting to control eutrophication of both natural lakes and reservoirs. Nevertheless, it is important
to be realistic in selecting specific control measures, both in terms of h o w m u c h
reduction in the phosphorus inputs can be expected and h o w m u c h such control
measures will be likely to cost. A n unrealistic management plan can undermine
popular support for phosphorus control efforts if it is observed that a given plan
will not achieve the desired phosphorus control goals, or that it is inappropriate from the point of view of cost-effectiveness.
49
It must be recognized that, in a given situation, the observed differences in
the characteristics of natural lakes and reservoirs m a y affect the selection of
control programmes based on reduction of the external phosphorus load. R y d ing and Rast (1989) discuss these differences, and h o w they should be considered in the development of effective eutrophication control programmes. It
also must be recognized that it m a y not be possible to achieve the desired water
quality and trophic conditions in all cases, even after implementation of the realistic phosphorus control efforts. If so, additional control efforts (often considerably more expensive) will be necessary to achieve the desired in-lake conditions. Otherwise, the in-lake conditions resulting from the achievable
phosphorus control efforts will have to be accepted as the best that can be obtained under the circumstances. This decision should be m a d e by those w h o are
most familiar with the specific circumstances.
Water quality as related to desired water use
A s noted previously, 'good' or 'bad' water quality often can be defined on the
basis of several in-lake parameters (Table 4). Furthermore, the trophic status of
a lake or reservoir can be related to specific boundary levels for several of these
parameters (Table 3). Because of such relationships, it is also possible to relate
desired water uses to the optimal (or minimally acceptable) water quality for
such uses. Therefore, a logical approach for establishing an effective eutrophication control programme is to determine the necessary water quality and/or
trophic conditions for a desired water use (or uses), and design the programme
to achieve these necessary conditions.
It is important to remember that one cannot always define the trophic status
or intended water use of a lake or reservoir in an unequivocal manner. Nevertheless, it is usually possible to identify ideal or acceptable water quality for
given water uses. For example, a lake or reservoir used as a drinking water supply ideally should have water of such good quality that it can be treated easily,
using standard inexpensive methods, to yield a water suitable for human consumption. The content of phytoplankton and their metabolic products in waterbodies used for such purposes should be as low as possible to facilitate this goal.
Furthermore, water used for swimming and similar recreational pursuits should
be free of nuisance blooms of planktonic organisms, which can cause such
physical symptoms as allergic skin reactions and conjunctivitis. Excessive m a c rophyte growths in shallow, nearshore areas can affect recreational water uses.
If a waterbody has one primary use, the control measures for achieving the
necessary water quality can be based on this single use. In m a n y cases, h o w ever, there m a y be multiple competing uses for the same waterbody. In these
50
cases, determination of the desired water quality can still be based on the single
use of highest priority. This use m a y require the highest standards of water
quality in some situations, while less stringent water quality m a y be sufficient
in other cases. Thus, decisions on a primary water use of a waterbody used for
multiple purposes are best made on the basis of specific knowledge of the lake
or reservoir in question.
A simple approach for selecting
a eutrophication control programme
A logical sequence of decisions to be made by a water manager was outlined
previously in Figure 1. It is pointed out here that the final decision on an appropriate control strategy should be a 'multi-judgement', based on the relevant social, technical, economical and ecological aspects. It is also very important to
set up a responsive monitoring programme both for defining the necessary pretreatment condition of the waterbody and for properly evaluating the final outcome of the remedial measures enacted.
A point previously made is reiterated here; namely, that one is advised to
start with a simple approach, and then add more detail and complexity as further knowledge and experience are gained. In this way, one can build on one's
successes and generally reinforce one's goals.
A simplified and practical approach for selecting appropriate eutrophication
control measures is outlined in Figure S. A 'decision-tree' approach is taken
(Ryding and Rast 1990), with the answers to key questions dictating the direction to be taken.
This approach relies primarily on the control of phosphorus and nitrogen inputs to a lake or reservoir. The eutrophication models presented in Figure 5
focus on the nutrient status of a waterbody. This focus appears to be appropriate for both temperate and tropical lakes and reservoirs, and for sub-arctic lakes
based on initial evaluation (McCoy 1983, Rast et al. 1983, Smith et al. 1984).
Thornton (1979,1980, Thornton and Walmsley 1982), for example, has applied
the statistical phosphorus loading models of the type developed by Vollenweider (1976) and concluded that they generally worked for assessing African
lakes, although the boundary phosphorus concentrations denoting the transition
between mesotrophic and eutrophic waterbodies m a y be too low to describe accurately tropical lake systems. The similar model developed by Dillon and Rigler (1974) also appeared to work well for 31 southern African lakes (Thornton
and Walmsley 1982). Walmsley and Thornton (1984, Thornton et al. 1986) have
also evaluated the applicability of the models developed in the Organization for
Economic Cooperation and Development (1982) eutrophication study and con-
51
52
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eluded that they are reliable predictors for southern African impoundments.There is a logical sequence of events outlined in Figure 5 (Ryding and
Rast 1989), as described in the following paragraphs.
Assess eutrophication problem,
define eutrophication goals
O n e must first determine the nature of the eutrophication problem and decide
on the goals of a control programme. The eutrophication problem in a given
situation m a y be excessive growths of algae and/or macrophytes, decreased
water transparency, hypolimnetic oxygen depletion and related fish kills, nutrient regeneration or water quality deterioration due to the regeneration of reduced chemicals, taste and odour problems in drinking water supply reservoirs,
or a combination of these types of problems. In this manner, one can relate the
major water use (or uses) of the lake or reservoir to the necessary water quality
for such a use (Table 3). Obviously, if the existing trophic state of a waterbody
is compatible with the water use, no action is necessary in regard to phosphorus loading conditions. If not, both point and non-point phosphorus control
measures m a y be necessary.
A n important yardstick for assessing the efficiency of external phosphorus
control measures is the reply to the question of whether or not an economicallyfeasible reduction in the phosphorus content of an effluent results in a change
towards an oligotrophic or mesotrophic state. Once the problem is clearly understood and defined, one can then determine whether or not the problem is severe
enough (or will become severe enough) to consider the control programme.
Assess limiting nutrient
If a eutrophication control programme is necessary to achieve the desired water
quality goals for a lake or reservoir, one can then assess the logical measures to
take in a given situation. The strategy outlined in Figure 5 is based on simple
and readily accessible criteria provided by a routine sampling programme for
chemical and biological data. Since an effective, long-term control measure is
usually to control the external nutrient load, the next step is to determine the
likely nutrient to be controlled.
The trophic state of the waterbody must be considered in order to m a k e a realistic estimate of the role of nitrogen and phosphorus as potential algal growthlimiting nutrients. The absolute concentrations of the biologically available nutrients are especially important in this assessment. A s a rough rule-of-thumb, if
53
the biologically available nitrogen and phosphorus concentrations decrease
below approximately 20 ng N/1 or 5 p.g P/l, respectively, during an algal bloom
peak, that nutrient is likely the limiting one. If both nutrients decrease below
this value, both m a y be limiting.
The simple stoichiometric atomic ratio between C : N : P of 106:16:1 in plankton cells (which corresponds to a mass ratio of approximately 40:7:1) has also
proved to be useful in deciding whether nitrogen and/or phosphorus is the nutrient most limiting to algal growth. Under the assumption that the ratio in algal
cells reflects the relative proportion needed by algae for growth and reproduction, measurement of the quantities of these nutrients in the water column can
be used to determine which nutrient is not present in the needed proportions.
Ryding and Rast (1990) provide further information on this topic.
Assess need for control of nitrogen
Even if nitrogen is not the limiting nutrient, it m a y be necessary to take measures
to control nitrogen, if the critical concentration for drinking water supply is exceeded. Since drinking water supply is one of the principal uses of lakes and
reservoirs, excess nitrate levels require a high priority in the context of the m a n agement of lakes and reservoirs. Control measures should be implemented as
far as possible from the water treatment plant, and as close as possible to the nitrate sources. Obviously, the successful application of preventive measures
presupposes that the principal sources in the drainage basin have been correctly identified.
Assess alternative phosphorus control option.
Before adequate control programmes can be identified and implemented, it is
often necessary to use generally applicable predictive tools. Although the concept of trophic states m a y be difficult for decision-makers to appreciate, it is
possible to calculate the expected in-lake phosphorus concentration resulting
from a given control programme, based on knowledge of the phosphorus loading, water retention and mean depth of a lake (Figure 6). B y employing k n o w n
relationships between phosphorus and c o m m o n eutrophication variables found
in multi-lake studies, algal biomass (in terms of chlorophyll) and water transparency can be predicted (e.g. Organization for Economic Cooperation and D e velopment 1982). The transparency of the water is an easily understood parameter, and it is informative when explaining lake water quality data to laymen.
Ryding (1983) has presented a n o m o g r a m for transforming phosphorus values
54
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M E A N DEPTH, Z/HYDRAULIC RESIDENCE TIME, Tw
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[Source: Modified and redrawn from O E C D (1982).]
55
l II 1
1 000
to chlorophyll and transparency values (Figure 7), based on data from 30 Swedish lakes. Since this nomogram simply represents the correlation between the
in-lake, summer average total phosphorus and chlorophyll concentrations (top
of graph) and between chlorophyll concentration and Secchi depth (bottom of
graph), one can also develop a site-specific nomogram based on local data, if
adequate. Alternatively, one m a y choose to use a more detailed approach, such
as computer scenario analysis, to assess eutrophication control options (see
Benndorf andRecknagel 1982).
As an aid in the management policy-making process, there is often a use for
mathematical models for predicting future trends in water quality for a given
waterbody under a changing pattern of nutrient input. This assessment is not
only in terms of the 'average' values for a specific time period. Extreme situations (e.g. worst possible conditions) are also of special interest to both
lake/reservoir managers and the public. However, such situations can be hard
to define when conducting routine monitoring programmes. Consequently, relationships found between the average and m a x i m u m values of chlorophyll can
be very useful for making predictions for water management. A n estimation of
the annual peak chlorophyll value can be obtained by multiplying the annual
average by a factor of three or the average summer value by a factor of 1.5-2.0
(Organization for Economic Cooperation and Development 1982, Jones et al.
1979). Similar relationships have been developed for some eutrophication variables in Swedish lakes, both for standing and flowing waters (Table 9). Such
simple models provide sufficient information for many situations; nevertheless,
one m a y also wish to consider the use of a more temporally or spatially detailed
dynamic model.
With regard to standing waters, the main public interest in industrialized
countries is usually focused on the water quality during the summer period, the
period of maximal use. In flowing waters, recreational use m a y be prolonged
throughout the entire year.
Assess need for further (In-lake)
control measures
If the expected improvement in water quality and/or trophic conditions from external phosphorus control measures will not be sufficient (based on model predictions or post-treatment monitoring) to achieve the eutrophication control
goals, one can also consider in-lake control methods as supplemental measures.
The expected water quality improvement, for example, following a phosphorus
load reduction of 75-90 percent may still represent eutrophic conditions in some
cases, especially in shallow waterbodies. Shallow waterbodies can be especially
56
^
200-1
log Chi = 1 . 3 log T P - 1.00
t-H Chlorophyll a (Chi, ug/l)
log S D = - 0 . 5 7
log Chi + 0.85
Hypertrophic
Fio. 7. N o m o g r a m for transforming phosphorus values to chlorophyll and Secchi depth values.
[Source: Based on Swedish lake data, Ryding (1983).]
57
sensitive because their water mass is more susceptible to mixing by wind action, their algae biomass is more frequently present in the euphotic zone, etc.
In such cases, one m a y consider such options as alterations in the lake basin
morphometry (e.g. dredging) or initiation of in-lake nutrient control measures.
Such measures can be very useful when the primary method of external nutrient
control alone is either inadequate to achieve the goals, or is too expensive to be
implemented in a given situation. In-lake controls (Table 9) include such
measures as nutrient inactivation, hypolimnetic aeration, harvesting of macrophytes, application of algicides, etc. Biological controls (e.g. enhancement of
certain food chain pathways by introduction or replacement of specific food
chain organisms) m a y also be considered, although the long-term, ecological
effects of this approach are largely unknown at present.
T A B L E 9. Linear correlations between m a x i m u m (y) and mean (x) values for
c o m m o n water quality variables in Swedish lakes.
Flowing waters2
Lake waters'
Correlation
coefficient
Discharge
Transparency
Absorbance
suspended matter
PH
Conductivity
Suspended matter
NHrN
NCVN
NC-N
Organic-N
Total-N
PO4-P
Residual-P
Total-P
Organic matter
Chlorophyll a
Equation
+0.93
y = 0.73 x - 0 . 0 4
+0.96
+0.92
+0.99
+0.98
+0.84
+0.86
+0.82
+0.97
+0.96
+0.99
+0.98
+0.98
+0.97
+0.96
y
y
y
y
y
y
y
y
y
y
y
y
y
y
= 1.64
= 0.93
= 1.06
= 1.36
= 1.92
= 2.91
= 1.70
= 1.53
= 1.42
= 1.53
= 1.55
= 1.39
= 1.33
= 1.77
1. Average values, June-September, n = 2300.
2. Annual average values, n = 3640.
[Source : Ryding 1981.]
58
x-79.8
x +1.26
x +1.11
x +2.63
x +0.14
x +0.00
x + 0.10
x +0.00
x +0.11
x +0.02
x +0.00
x +0.02
x +0.13
x +7.62
Correlation
coefficient
Equation
+0.99
y = 2.73 x + 1 . 0 6
+0.92
+0.93
y = 1 3 5 x + 2.56
y = 2.52 x + 0.06
+0.95
+0.88
+0.93
+0.96
+0.96
+0.97
+0.89
+0.94
y
y
y
y
y
y
y
y
= 2.04
= 1.91
= 1.65
= 2.68
= 2.32
= 2.43
= 1.40
= 2.60
x +0.17
x-0.15
x +0.27
x-0.01
x-0.01
x - 0.03
x + 0.30
x +0.84
Assess effectiveness of control programme
In most of the cases studied so far, economic optimization with respect to water
quality is primarily concerned with control measures in three major areas: (1)
nutrient source control in the watershed (external control); (2) temporal detention in the waterbody (internal control); and (3) treatment plants (off-line control), in the case of water used as a water supply.
The ultimate benefit that can be realized will usually be substantially higher
if optimization is related to all three control categories as a whole. This integrated approach is useful for the control of both nitrogen and phosphorus. A s
noted earlier, it is preferable over the long term to reduce or eliminate the sources of the substances (e.g. phosphorus) causing eutrophication, rather than temporarily ameliorating the symptoms of eutrophication.
Finally, if neither the external nor internal control measures are sufficient to
achieve the eutrophication control goals, one m a y simply have to accept the
achievable water quality as the best that can be attained under the circumstances. However, while all the eutrophication control goals m a y not be achieved
in a given situation, practical experience suggests that the basic condition of the
aquatic ecosystem will usually be improved over the long term.
Other practical considerations.
A s a practical matter, a lake or reservoir usually does not respond instantaneously to a eutrophication control programme, especially those based on reducing
the external nutrient input. Rather, there usually is a time interval ('lag period')
between the implementation of the control programme and the observable results in the waterbody. The lag period represents the time necessary for a waterbody to flush itself, or otherwise neutralize the effects of its internal store of
nutrients, following implementation of a control programme based on reducing
the external nutrient supply to the waterbody. In contrast, in-lake methods, such
as harvesting aquatic plant growths, m a y show smaller or no lag periods, since
this latter approach directly addresses the symptoms of eutrophication, rather
than the underlying cause. However, as noted earlier, the symptoms often reappear within a short period.
Efforts should be m a d e to inform the public that such lag periods are not
unexpected. Otherwise, lack of an immediate response to a control prog r a m m e m a y be prematurely, and erroneously, interpreted to m e a n that a control programme has failed. Methods for calculating the expected duration of
the lag period are discussed by Sonzogni et al. (1976) and Rast and Lee
(1978).
59
Although control programmes have been successful in many cases in addressing the negative impacts of eutrophication, there is always some remaining element of uncertainty regarding the ultimate success of any individual control prog r a m m e . In most cases, however, this usually is not sufficient reason to delay
development and implementation of eutrophication control programmes.
Ryding and Rast (1989) discuss the sequence of steps to be taken if a lake or
reservoir does not respond to eutrophication control measures as expected.
If a control programme does not produce the desired results, the only reasonable alternatives are to consider further, usually more stringent control
measures, or to be satisfied with the results obtained with the original prog r a m m e . Fortunately, as noted earlier, even when a control programme is unsuccessful in achieving desired goals, such programmes usually still work to the
positive ecological benefit of the waterbody.
A n additional factor to consider in selecting a eutrophication control prog r a m m e is the expected duration of its effectiveness. Programmes designed to
be effective over the long term are usually preferrable (although often more
costly) to programmes effective only over the short term. Ryding and Rast
(1989) provide a detailed listing of case studies which illustrate various point
and non-point source eutrophication control measures which have been applied
to lakes and reservoirs around the world.
Summarize desired control strategy
Once a specific control programme is selected, it is useful and desirable to develop a detailed working plan of the chosen programme, in order that regulators, implementors and all other interested individuals/agencies will have adequate documentation of the tasks to be undertaken, and the goals and objectives
to be met. Such an approach usually will work to foster cooperation, rather than
confrontation, between involved governmental units and between governmental agencies and the public. A s a m i n i m u m , the working plan should identify the
specific goals of the control programme and the obligations of the involved governmental agencies.
A brief overview of the control programme also can be prepared for all interested parties, both inside and outside of government. This overview should
contain a clear re-statement of the goals of the control programme, and should
be disseminated widely prior to implementation of the programme. In countries
where such groups exist, members of some type of citizen's advisory committee can be a valuable link in disseminating such documentation.
T o foster a greater understanding of the complexities of the eutrophication
process, and the public's role in both causing and mitigating its negative im-
60
pacts, a clearly-articulated education programme can be valuable. Such a prog r a m m e can be administered by a governmental unit, a concerned community
group, or a component of the public education system. This education prog r a m m e should include a periodic evaluation of the general effectiveness of the
implemented control programme (based on collected monitoring data), and an
interactive communication between governmental officials and the public. It
also can be the basis for development of periodic progress reports to all interested parties.
Post-treatment monitoring
In order to obtain sufficient information for a judicious selection of eutrophication control measures, extensive studies of the chemical and biological conditions of the waterbody of concern and its tributaries are usually required. U p o n
completion of such studies, after control measures have been planned and carried out, one m a y then conclude that further studies are not necessary. Such a
conclusion is false. Even after eutrophication control programmes have been initiated (e.g. reducing the nutrient influx), post-treatment studies should be continued for at least several more years. This should be done to compare the condition of the waterbody before and after the start of eutrophication control
measures, and to ascertain whether or not the results expected from model calculations have actually been achieved. Only then can one be certain whether or
not (or to what degree) the corrective action taken was correct, and whether or
not the monetary investment was a financially responsible one.
Should it occur that, in spite of very careful planning and use of all available
knowledge, the results obtained fall short of those expected, post-treatment
measurements can still be used to improve the model predictions in question.
This will also work to decrease the uncertainty of model predictions for future
planning purposes.
The period of time necessary for carrying out such post-treatment measurements is dependent on the individual case. The longer the lake is expected to
take to recover, the longer the period of time such measurements will have to
be taken. Even after a prompt recovery of a given lake, it m a y still be necessary to continue monitoring studies for several years, in order to be sure that
the situation has been correctly assessed. This is necessary especially in those
cases in which large annual differences in water quality can occur before eutrophication control measures are initiated. Examples are lakes and reservoirs
with relatively short water retention times, and those located in regions characterized by rapid, dramatic shifts in weather conditions.
61
Post-treatment monitoring and evaluation also provide valuable information
to others concerned with similar eutrophication management problems, and help
guide future efforts (e.g. building the information and experience base for improved lake and reservoir management technology).
62
P R O V I D E PERIODIC P R O G R E S S
REPORTS ON CONTROL
P R O G R A M M E TO T H E PUBLIC A N D
OTHER INTERESTED PARTIES
The role of public awareness
Where it is feasible, public participation in developing an effective eutrophication control programme can be important, particularly with regard to lakes and
reservoirs used extensively for recreational purposes. M a n y individuals m a y
have experienced eutrophication-related problems in such waterbodies in the
past, or else m a y have been exposed to media coverage of such problems. The
result can be a 'collective m e m o r y ' of poor water quality conditions in certain
waterbodies, which can lead to a certain degree of public curiosity about
lake/reservoir management problems. Greater public awareness of water-related issues usually can be developed by making details of new eutrophication
control programmes, and expected improvements in water quality, available to
the public. Such communication efforts also can provide governmental feedback to the public in the form of answers to public questions regarding a given
lake or reservoir.
The type and extent of information, and the format used, likely will vary considerably with the target audience. Appropriate media for public information
purposes include the press, television and radio, and popular scientific publications. In view of the non-technical background of the lay audience, general information often is most informative (e.g. a new municipal wastewater treatment
plant is being built to reduce nutrient levels in Lake X ; this nutrient reduction,
in turn, should lead to the elimination of algal blooms and related water quality
degradation in the lake). Appropriately illustrated information can be very useful in such public communications, and the use of specific technical jargon
should be kept to a m i n i m u m . A more detailed technical discussion is appropriate for an audience of scientific and/or engineering peers. Water users such as
63
agriculturalists or industrialists likely would require information on a level
somewhere between these extremes.
The importance of public feedback
The management of water resources often is done at the local level, with little
recognition or appreciation given to the long-term needs of a region or country.
Furthermore, costs frequently are the only criterion used in developing and/or
choosing between management options. Consequently, where feasible, public
awareness and feedback can be an important component of effective eutrophication control programmes. If the public can be persuaded of the severity of a
eutrophication problem (and its environmental, health and/or economic consequences if left untreated), the public can appreciate more easily the need for eutrophication control programmes. The result can be the development of a proprietary interest by the public in the work involved, and even can m a k e the
public more amenable to the associated expenses. This is especially true if the
public's experiences with past pollution control programmes have been positive (i.e., if control programmes have been successful in the past). Thus, public
awareness and feedback can be an important part of eutrophication control.
The reader is referred to the informative and interesting experiences of the
P L U A R G (1978b, 1978c) public participation panels for details regarding the
possibilities of the public working together with the government in developing
effective environmental management strategies.
64
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Z . Kajak & A . Hillbricht-Ilkowska (Eds), Productivity Problems of Freshwaters, 563-571. Proceedings of the IBP-Unesco Symposium. Kazimierz
Dolny, 6-12 M a y 1970. P W N Polish Scientific Publishers, Warsaw and Krakow.
Wolverton, B . & R . C . McDonald. 1976. Don't waste waterweeds. New Scientist!1:318-320.
W o o d , G . 1975. An Assessment of Eutrophication in Australian Inland Waters.
Report N o . 15. Australian Water Resources Council, Canberra.
Yaksich, S . M . & F . H . Verhoff. 1983. Sampling strategy for river pollutant transport. American Society of Civil Engineers, Environmental Engineering Division 109:219-231.
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Young, T . C . , J.V. D e Pinto, S.E. Flint, M . S . Switzenbaum & J.K. Edzwald.
1982. Algal availability of phosphorus in municipal wastewaters. Journal of
Water Pollution Control Federation 54:1505-1516.
Zaret, T . M . , A . H . Devol & A . D . Santos. 1981. Nutrient addition experiment in Lago
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G L O S S A R Y OF T E R M S
Absorbance. The absorption of light by components in the water column of a
waterbody.
Acid rain. Rainfall which has become acidic, usually because of the emissions
of sulfur and nitrogen oxides into the atmosphere and their subsequent chemical reaction with rainwaters.
Agricultural runoff. The water, and the materials carried by the water, flowing from agricultural lands to waterbodies, following rainfall or snowmelt
events.
Algae. Small, often microscopic, aquatic plants in a waterbody; they exist either
as phytoplankton (free-floating cells) or as periphyton (filamentous algae attached to rocks or other underwater structures).
Algal biomass. The mass (weight) of phytoplankton in a waterbody at a given
time; often measured indirectly as the concentration of chlorophyll in the
waterbody.
Algal bloom. The nuisance or excessive growth of phytoplankton in a lake or
reservoir which interferes with the aesthetic quality and/or h u m a n uses of the
water resource; often denoted by a 'pea-soup' green colour in the waterbody.
Algal species diversity. A measure of the number of different algal species
present in a waterbody; because the number of different algal species usually
decreases as a waterbody becomes more eutrophic, algal species diversity
often is used as an indirect measure of the degree of eutrophication.
Algicides. Chemicals used to kill phytoplankton in waterbodies, especially
when the algae are present in excessive quantities.
Allochthonous. Organic matter and other material which enters a lake or reservoir from outside the waterbody, usually from the drainage basin or the atmosphere.
73
Altered circulation. Artificially modifying the natural circulation patterns
and/or thermal stratification of a lake or reservoir, usually by artifically
pumping air or oxygen into the bottom waters of the waterbody.
A m m o n i a nitrogen. The chemical form of total nitrogen represented by a m monia, a biologically-available form of nitrogen for aquatic plants (often abbreviated as a m m o n i a - N ) .
Aquaculture. The artificial cultivation or growth offish,crayfish and other aquatic organisms for use as food, especially infishponds and similar structures.
Aquatic ecosystem. The sum of the living (biological) and non-living (chemical and physical) components of an aquatic system, such as a lake or reservoir, which interact to give the system its specific characteristics.
Artificial oxygenation. The artificial addition of air or oxygen to the bottom
waters (hypolimnion) of a waterbody, usually during the period of thermal
stratification (see 'Altered circulation').
Attached algae. Algae (periphyton) which grow attached to submerged rocks
and other underwater structures in a waterbody, in contrast to free-floating
phytoplankton.
Baseline. The background (undisturbed) conditions of a waterbody; often used
as the reference against which to compare the impacts of pollution or other
stresses to the waterbody.
Bathymétrie m a p . A topographic m a p of the floor of a waterbody.
Biological controls. See 'Biomanipulation'.
Biologically-available nutrients. The chemical forms of phosphorus and nitrogen in a waterbody which can be immediately taken up and utilized by phytoplankton for growth and reproduction.
Biomanipulation. The use of native or artificially-introduced biological organisms (e.g., algae-eating zooplankton) to treat eutrophication, as contrasted
with the use of chemicals or other non-natural control measures.
Bottom fauna. The animals which usually live at the bottom of a lake or reservoir, often in the sediments.
Bottom fauna diversity. A measure of the number of different species of animals
present in the bottom waters and sediment of a waterbody; because the number
of different animal species usually decreases as a waterbody becomes more eutrophic, it is often used as an indirect measure of the degree of pollution.
Bottom waters. The water layer at the bottom of a lake or reservoir; usually refers to the water in the hypolimnion ('hypolimnetic waters').
Bypass flow. Water which bypasses, overflows from, or is otherwise not subjected to a given treatment, control or natural process.
Capital costs. The costs usually associated with the initial construction of a
building or structure, in contrast to the costs of operating or maintaining it
after its construction (see 'Operating costs').
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Chlorophyll. T h e green pigment in phytoplankton, periphyton and aquatic
plants which is essential for the conversion of sunlight energy in the photosynthesis reaction to produce new cellular material (i.e. new organisms).
Commercial fishery. The fish populations produced and caught for the purpose
of selling them as a commercial product, in contrast to sporting purposes
alone (see ' G a m e fish').
Conductivity. See 'Electrical conductance'.
Confidence interval. A statistical term denoting data which fits within a prescribed range (e.g., the 95 percent confidence interval on a graph denotes the
area within which 95 percent of the data are likely to be found).
Correlation coefficient. A mathematical measure of the relationship between
two independent variables.
Cost-benefit analysis. A process of comparing the costs of a given action (e.g.,
pollution control programme) with the expected benefits of the action (better
water quality); the comparison usually is expressed in strictly monetary terms.
Cultural eutrophication. The artificial and accelerated nutrient enrichment of
a waterbody (lake or reservoir) as a result of human-induced activities in the
drainage basin, in contrast to the natural ageing process which occurs in the
absence of human-induced activities (see 'Eutrophication').
Cyprinid waterbodies. Lakes which primarily contain fish of the order C y priniformes, including minnows and carps; which are usually the less-desirable g a m e fish.
Decision-tree. A chart or graph of alternative options deemed necessary to
achieve specific goals; the specific options are chosen on the basis of 'yes'
or 'no' responses to specific questions asked sequentially in the chart.
Deep release. The release of waters from a reservoir from its deeper layers,
usually via outlet structures located at lower levels on the d a m .
Diatoms. The c o m m o n n a m e of the phytoplankton comprising the class Bacillariophyceae, characterized by a symmetrical structure and silicon-based cell
walls.
Discharge. A term used to denote the volume of streamflow or effluents.
Dissolved oxygen. The oxygen present in water column.
Dissolved reactive phosphorus. The chemical form of phosphorus represented
by dissolved reactive phosphorus, which is easily utilized by phytoplankton
for growth and reproduction (see 'Biologically-available nutrient').
Dissolved solids. The salts and other materials present in the water column in a
dissolved form; often measured via electrical conductance.
Diurnal variation. The variation of water quality and/or biological characteristics of a waterbody over a 24-hour period of day and night.
Domestic effluents. Discharges or releases of liquid wastes from sewage m a terials from municipal wastewater treatment plants to surface waters (lakes
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and reservoirs); usually contain high concentrations of biologically-available
phosphorus and nitrogen, thereby constituting a primary point source of these
aquatic plant nutrients.
Drainage basin. The land area surrounding a lake or reservoir from which the
water, and the suspended and dissolved materials carried in it, flow to the
waterbody.
Effluents. The liquid wastes from municipal sewage, industrial and septic sources which are released to surface waters (lakes and reservoirs) (see ' D o m e s tic effluents').
Electrical conductance. The ability of water to conduct an electrical current;
because conductance is a function of the concentration of dissolved salts in
the water, it provides an indirect measure of this parameter.
Epilimnetic oxygen supersaturation. Excessive concentrations of dissolved
oxygen in the surface waters of a lake above expected baseline levels, usually
due to excessive photosynthetic activity in the surface water layer.
Euphotic zone. The layer of water in a waterbody delineated by the depth to
which sufficient light penetration exists to allow photosynthesis to occur;
often the zone of m a x i m u m phytoplankton productivity.
Eutrophic. From the Greek ('well-nourished'), the most productive trophic
state of a waterbody; characterized by high nutrient loads, high photosynthetic activity and low water transparency (see 'Eutrophication').
Eutrophication. T h e natural ageing process of a lake, whereby it slowly
becomes filled with sediments from its drainage basin, usually on a geologic
time scale, eventually becoming a marsh system and, ultimately a terrestrial
system; when the process is accelerated by human-induced nutrient inputs, it
is termed 'cultural eutrophication'.
External nutrient supply. The nutrient load entering a waterbody from the
drainage basin and other sources outside the lake basin itself; major external
sources include municipal and septic system wastewaters, urban and rural
drainage, atmospheric inputs and ground water.
Fish culture. The artificial cultivation or growth of fish, usually in specially
treated fish ponds.
Fish kills. The unexpected death of large quantities of fish in a waterbody, often
due to oxygen depletion or the presence of toxic substances in the water.
Fish yield. A description of the quantity of fish expected to be produced or
caught in a waterbody, as a function of nutrient supply and other waterbody
characteristics.
Food chains. The feeding relationship described by lower trophic level organisms sequentially serving as food sources for higher trophic level organisms.
G a m e fish. Fish caught as a recreational or sporting pursuit, in contrast to fish
that are caught and sold as a commercial venture (see 'Commercial fishery').
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Ground water. Water which flows beneath the soil surface.
Growth-limiting nutrient. The nutrient (usually phosphorus or nitrogen)
which primarily controls or limits the m a x i m u m level of algal biomass in a
lake or reservoir.
Harvesting. The cutting or mowing of excessive growths of rooted aquatic
plants (macrophytes) from the shoreline areas, as an in-lake method of alleviating some eutrophication symptoms.
Herbicide. A chemical used to kill or control aquatic plants.
H u m u s . A mixture of the organic matter of plants, animals and microorganisms
present in soils which are most resistant to decomposition.
Hydraulic load. The volume of water entering a lake or reservoir, usually over
the annual cycle.
Hydrologist. A specialist in the science of hydrology, the science of the occurrence, circulation and distribution of the earth's waters and their reactions
with their environment.
Hypolimnetic aeration. The artificial addition of air or oxygen to the bottom
waters (hypolimnion) of a waterbody, usually during the period of thermal
stratification (see 'Artificial aeration').
Hypolimnetic oxygen deficit. The degree to which the dissolved oxygen concentration in the bottom waters (hypolimnion) of a stratified lake or reservoir
are depleted, usually during the summer period of m a x i m u m phytoplankton
growth in the waterbody.
Hypolimnetic oxygen depletion. The depletion of dissolved oxygen in the bottom waters (hypolimnion) of a lake or reservoir, usually during the summer
period of m a x i m u m phytoplankton growth in the waterbody.
Hypsographic curve. A chart or m a p showing the location of areas or objects
within a lake.
Impoundments. M a n - m a d e lakes, usually created by the construction of a d a m
across a river channel; in contrast to natural lakes, impoundments exist because they were constructed for a specific purpose or water use.
Inflow. The waters entering a lake or reservoir, usually from tributaries.
In-lake methods. Control measures applied within a lake or reservoir to treat
temporarily the symptoms of eutrophication, in contrast to methods used to
treat the basic problem of excessive nutrient inputs; examples include harvesting, dredging, nutrient inactivation, hypolimnetic aeration and biomanipulation.
Insolation. The solar energy received per unit area of surface (e.g., sunlight energy at the lake surface).
Institutional framework. The institutional apparatus necessary to develop and
implement effective management and control programmes for lake and reservoir eutrophication.
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Lag period. The period between the implementation of a eutrophication control measure and the visible signs of a waterbody's response (improvement)
to the measure; during this period, the waterbody is flushing itself of its previously-existing, internal phosphorus content.
Lake basin. The depression in the earth's surface constituting the actual basin of
a lake.
Lake d r a w d o w n . The artificial lowering of the water level, or emptying, of
a lake, after which several in-lake eutrophication control measures can be
applied, including dredging and covering of the lake-bottom sediments.
Legislative framework. The legislative apparatus necessary to develop and implement effective management and control programmes for lake and reservoir eutrophication.
Limnologist. A specialist in the study of freshwater lakes, especially their biological, chemical and physical characteristics.
Littoral vegetation. The plants that exist in the littoral zone, in contrast to the
deeper waters in the centre of the lake.
Littoral zone. The water in a lake that is closest to the shore, in contrast to the
deeper waters in the centre of the lake.
Longitudinal axis. The direction along the longest length of a lake or reservoir.
Macrophytes. Rooted andfloatingaquatic plants which grow in the littoral
zone of a lake or reservoir.
M a s s ratio. The carbon:nitrogen:phosphorus ratio in the water column, expressed in terms of the mass of each nutrient, in contrast to the number of
atoms (atomic ratio) of each nutrient.
Mathematical models. Mathematical representations of the real world; often
used as an assessment or predictive tool for water quality and other variables
in a waterbody.
M e a n depth. The average depth of a lake or reservoir, calculated as the ratio
of the lake volume to the lake surface area.
Mesotrophic. A n intermediate trophic state describing the transitional condition between high productivity (eutrophic) and low productivity (oligotrophic) waterbodies.
Methane. A gas formed by the decomposition of organic matter in the absence
of oxygen; sometimes called 'Marsh gas'.
Models. See 'Mathematical models'.
Monitoring p r o g r a m m e . A sampling programme for a waterbody and/or drainage basin; the purpose is to collect inflow or in-lake data for assessment or
predictive purposes.
Morphometry. A description of a lake's physical structure (e.g., depth, shoreline length).
78
Natural lakes. Naturally-formed waterbodies, in contrast to m a n - m a d e i m poundments (reservoirs).
Nitrate nitrogen. The chemical form of total nitrogen represented by nitrate, a
biologically-available form of nitrogen for aquatic plants (often abbreviated
as nitrate-N).
Nitrite nitrogen. The chemical form of total nitrogen represented by nitrite, a
biologically-available form of nitrogen for aquatic plants (often abbreviated
as nitrite-N).
Nitrogen. The sum of all organic and inorganic forms of nitrogen, a primary
aquatic plant nutrient (sometimes called total nitrogen).
N o m o g r a p h . A chart which illustrates an equation containing three different
variables; three scales are used simultaneously, and a straight line intersecting the three scales can simultaneously provide values for all three variables.
Non-point sources. Aquatic plant nutrient sources in a drainage basin which
are diffuse (non-pipeline) in nature, and usually difficult to identify or quantify (in contrast to point sources); examples include runoff from urban and
agricultural lands following storm events.
Non-structural solution. A eutrophication control measure that does not involve the construction of a plant, building or other structure; examples are
changes in farm fertilizer application practices and tillage conservation (see
'Structural solution').
N : P ratio. The nitrogen:phosphorus ratio in a waterbody.
Nutrients. Usually refers to phosphorus and nitrogen, the primary phytoplankton and aquatic plant nutrients in lakes and reservoirs.
Nutrient inactivation. Chemically binding or otherwise neutralizing in-lake
nutrients, thereby inhibiting their use for phytoplankton and aquatic plant
growth, by directly adding chemicals to a waterbody.
Nutrient regeneration. The release of phosphorus and nitrogen from the bottom sediments of productive lakes and reservoirs, to which it was previously
bound, back into the water column during periods of hypolimnetic oxygen
depletion; often called 'internal loading'.
Oligotrophic. From the Greek ('poorly-nourished'), the least productive state
of a waterbody; usually characterized by low nutrient loads, low photosynthetic activity, and high water transparency.
Operating costs. The expenses of maintaining and/or operating a plant, building or structure, in contrast to the initial costs of building it.
Organic matter. A n y molecules produced by plants and animals which contain
carbon.
Organic nitrogen. O n e of the chemical forms of total nitrogen, a primary aquatic plant nutrient; because all phytoplankton cells contain organic nitrogen,
79
it can be used as an indirect measure of phytoplankton biomass (often abbreviated as organic-N).
Outflow. The water leaving or draining from a lake or reservoir, usually via the
main outflow tributary.
Pathogens. A microorganism (e.g., bacteria) capable of producing disease.
Pheophytin a. The portion of the plant pigment chlorophyll a which constitutes
non-living phytoplankton cells.
Phosphate-P. The chemical form of total phosphorus represented by phosphate,
a primary biologically-available form of phosphorus.
Phosphorus. The sum of all organic and inorganic forms of phosphorus, a primary aquatic plant nutrient (sometimes called total phosphorus).
Phosphorus loading. The input of phosphorus to a lake or reservoir from point
and non-point sources in the drainage basin, as well as ground water and the
atmosphere.
Phosphorus loading models. Simple, graphical models used to predict the levels of several c o m m o n eutrophication-related water quality parameters
(chlorophyll, Secchi depth, etc.) as a function of the annual phosphorus and
hydraulic load to a waterbody.
Phytoplankton. Microscopic algae and microbes that float freely in lakes and
reservoirs.
Point sources. Aquatic plant nutrient sources in a drainage basin that are 'pipeline' in nature, and usually easy to identify and quantify (in contrast to nonpoint sources); examples include effluents from municipal and industrial
wastewater treatment plants.
Policy-maker. A n individual responsible for developing and/or implementing
specific courses of action (legislative, regulatory, etc.); usually functions as
a representative of government (e.g., executive, legislator, senior administrator, manager).
Primary production. The production of new organic matter (e.g. algal cells)
from inorganic materials by photosynthetic organisms using sunlight energy.
Recreational fishery. Fish caught as a recreational or sporting pursuit, in contrast
tofishcaught and sold as a commercial venture (see 'Commercial fishery').
Reduced chemicals. Chemicals existing in the bottom waters (hypolimnion) of
a lake or reservoir in a reduced chemical form, most frequently during periods of hypolimnetic oxygen depletion.
Regulatory framework. The regulatory apparatus necessary to implement and
enforce effective management and control programs for lake and reservoir
eutrophication.
Remedial p r o g r a m m e . A treatment programme for attempting to control lake
and reservoir eutrophication; the programme can consist of external nutrient
control measures, in-lake control measures or a mixture of both measures.
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Reservoir. A m a n - m a d e lake, usually constructed by the placement of a d a m
across a river channel; in contrast to natural lakes, reservoirs exist because
they were constructed for a specific purpose or water use (see 'Impoundment').
Residual-P. Phosphorus remaining after a water has received various types of
treatment or control measures.
Rural measures. Remedial programmes applied to agricultural and rural areas in
a drainage basin as a means of attempting to control cultural eutrophication.
Rural runoff. The water, and the nutrients and other materials carried by the
water, flowing from rural and agricultural lands to waterbodies, usually following rainfall or snowmelt events.
Salmonid waterbodies. Lakes which primarily contain fish of the suborder Salmonoidei, including trout, salmon, whitefish and graylings; usually considered the more-desirable game fish.
Scenario analysis. A method of analyzing alternative eutrophication control
options, using dynamic computer model simulations.
Secchi depth. A measure of the transparency of water obtained by lowering a
circular white, or alternate black-and-white, disk into the water until it is no
longer visible; because water transparency is inversely related to the phytoplankton biomass, Secchi depth is commonly used as an indirect measure of
lake and reservoir eutrophication.
Sediments. The bottom material in a lake or reservoir deposited after its formation; usually consists of the remains of aquatic organisms, precipitated minerals and erosion washed into the waterbody.
Sewage pond. A pond or lagoon, containing phytoplankton, microbes and other
organisms, used to treat municipal wastewaters (primarily for nutrient removal) prior to its discharge to surface waters.
Sewage sludge. The semiliquid material obtained from the purification of m u nicipal wastes.
Silicate. The generic term for a compound containing silica, oxygen, one or
more metals and possibly hydrogen; it has a major role as a component of the
cell walls of diatoms, the algae which comprise the class Bacillariophyceae.
Stoichiometric atomic ratio. The ratio in which the atoms of the primary nutrients are utilized by phytoplankton for growth and reproduction; the c o m monly-used stoichiometric atomic ratio for carbon, nitrogen and phosphorus
(C:N:P) is 106:16:1 (see 'Mass ratio').
Structural solution. A eutrophication control measure involving the construction and operation of a building, plant or other structure; an example is the
construction of a municipal wastewater treatment plant (see also 'Non-structural solution').
Substrate. A general term used to denote the food source for microbes.
81
Surface overflow. The outflow or discharge of waters from the surface layer
(epilimnion) of a waterbody, in contrast to the bottom layer (hypolimnion).
Suspended solids. The materials present in the water column in a particulate or
solid form, in contrast to materials dissolved in the water (see 'Dissolved solids').
Taste and odour problems. Unpleasant tastes and/or odours existing in drinking waters.
Taxonomic group. The specific group in the hierarchial classification of biological organisms to which a given organism is related.
Thermal stratification. The formation of a w a r m , surface layer of water, and
a cooler, deep layer of water, in a lake or reservoir, due to temperature differences which develop during the summer months; it can be a substantial
barrier to the movement of materials between these two layers, resulting in
very different biological and chemical conditions during the course of the
phytoplankton growing season.
Topography. The general configuration (usually surface contours) of a land or
lake bottom surface area.
Total dissolved phosphorus. The quantity of the chemical form of total phosphorus in a waterbody represented by dissolved phosphorus, a biologicallyavailable form of phosphorus for aquatic plants.
Total nitrogen. The sum of all chemical forms of organic and inorganic nitrogen, a primary aquatic plantriutrient,in a lake or reservoir (often abbreviated as total-N).
Total phosphorus. The sum of all chemical forms of organic and inorganic
phosphorus, a primary aquatic plant nutrient, in a lake or reservoir (often abbreviated as total-P).
Toxic substances. Chemicals which can cause toxic effects to aquatic plants
and animals.
Tributaries. Streams or rivers that flow into or out of lakes and reservoirs.
Trophic state. The degree of eutrophication or productivity of a lake or reservoir, often assessed in terms of such parameters as water transparency and
concentrations of phytoplankton chlorophyll and/or aquatic plant nutrients;
the most productive trophic state is called "eutrophic", while the least productive is called "oligotrophic".
Urban runoff. The water, and the nutrients and other materials carried by the
water, flowing from urban areas to waterbodies, usually following rainfall or
snowmelt events.
Wastewaters. The discharges or releases of liquid wastes from sewage materials from municipal wastewater treatment plants to surface waters (lakes and
reservoirs); usually contain high concentrations of biologically available
phosphorus and nitrogen, thereby constituting a primary point source of these
aquatic plant nutrients.
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Water column. The water in a lake or reservoir which exists between the interface of the surface waters and the atmosphere and between the interface of
the bottom waters and the bottom sediments; essentially describes the vertical distribution of water from the surface to the bottom.
Water quality. A description of the general chemical conditions existing in a
waterbody during a specific time interval.
Water renewal time. The amount of time required to completely replace a volu m e of water equal to the volume of a lake or reservoir (in contrast to c o m pletely replacing all the original molecules of water in the waterbody).
Water residence time. See 'Water renewal time'.
Water retention time. See 'Water renewal time*.
Water transparency. The clarity or transparency of lake and reservoir waters;
often measured with the Secchi disk.
Welfare economics. A branch of economics which serves as the basis for costbenefit analysis.
Zooplankton. Microscopic animals which float freely in the water column,
usually feeding on bacteria, phytoplankton (algae) and/or detritus; serve as
food for higher level organisms, including fish.
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