Izffects of Waste Disposal OH Groundwater and Surface Water (Proceedings of
the Exeter Symposium, July 1982). IAIIS Publ. no. 139.
Case study on non-point source plant nutrient
load calculations
G.G. PINTER & G. JOLÂNKÂI
Vituki Institute for Water Pollution Control
H-1095 Budapest, Kvassay, J.u.l., Hungary
ABSTRACT
The possibilities of modelling non-point
source runoff contribution to the pollution load of
recipient surface water bodies has been analyzed using
the data from a regular water quality monitoring network
and also that of objective oriented field studies. The
relevant literature is also briefly reviewed and evaluated from the point of view of practical applicability.
Experimental regression type approaches are discussed in
detail.
INTRODUCTION
Models, methods and formulae facilitating the quantitative estimation of the non-point source runoff contribution of pollutants
from drainage basins to recipient water bodies are of outstanding
significance from the view point of water qualtiy management. Data
serving for the development of reliable generalized yield rate (or
pollutant export rate) models are scarce since for this purpose very
detailed field measurements for many sites have to be coupled with
extensive data collection programmes. On the other hand non-point
source pollution forms a significant and, in certain cases, the
larger part of the total pollution input, and thus generalizable
quantitative estimation methods are very much needed.
The main conclusion coming from a detailed review of the methods
offered by the relevant literature - made by Jolânkai & Pinter
(1981) - was that regression type models also taking into consideration factors that allow generalization are rather scarce. In other
words it means that most of the expressions and formulae are site
specific and the comparison of them with a given set of data will
result in contradicting yield rates.
The use of more complex non-point source watershed models, such
as ARM or CREAMS (Donigian et al. , 1976) for load predicting purposes were found much too cumbersome to use with many essential, but
undefinable or hardly definable, model parameters.
In the framework of the complex Lake Balaton eutrophication
modelling and control programme, detailed analysis of available data
(regular water quality monitoring network data) were carried out,
together with field studies, aimed at the determination of the
effects of runoff events on the loading rates of plant nutrients.
207
208 G.G.
Pinter
& G.
Jolânkai
The objective of this programme was to provide reliable estimates of
plant nutrient loads entering into the lake including short and long
term dynamics (flood effects and seasonal changes), long term
trends, etc. The development of generalizable approaches involving
annual runoff and other watershed parameters, such as slope, were
also considered important.
Some fragments of the results of this complex study will be
presented in this paper focusing on the possibilities of developing
models of more or less general validity, namely on results that
could be used for projects other than Lake Balaton.
THE STUDY AREA AND DATA AVAILABILITY
Lake Balaton (figure 1), the largest shallow lake in Europe, is
situated in the middle of the so-called Transdanubian part of
Hungary. Its area is 593 sq km with an average depth of 3.14 m.
The total watershed of 5185 km2 is composed of the subwatersheds of
about 50 permanent and temporary tributary water courses, of which
the River Zala is the largest, draining about half of the total
watershed. The major land use form is agriculture and the lake side
is one of the most frequented recreational regions in Europe, where
the peak summer population exceeds 600 000.
FIG. 1 Lake Balaton and its watershed.
Although not apparent yet to the visitors for recreation, there
are clear signs of eutrophication. Open water phytoplankton is the
most important primary producer. Usually there are two peaks of
algae growth: diatoms in spring and a mixed phytoplankton dominated
by Creatium hirundinella in summer.
Wide spreading national and international cooperative research
programmes have established for the eutrophication control of Lake
Balaton in which eutrophication modelling and nutrient input modelling plays a significant role.
Plant
nutrient
load calculations
209
For the determination of nutrient inputs the folloiwing data and
information are available.
- The data of the regular water quality monitoring network that
includes the 20 largest tributaries, and covers 87% of the total
watershed.
The usual sampling frequency is 12-24 per year excluding the River Zala where an extraordinary daily monitoring
programme for Total P and Total N components is carried out since
1975 and this is completed by weekly full chemical analysis
including also dissolved nutrient components.
The length of
water quality records is about 12 years, however data in the
first half of this period were rather scarce.
In addition to the data of discharge measurements carried out
simultaneously with the sampling more detailed discharge data on
the basis of recording flow meters are available for the ten
largest tributaries (measuring 70% of the total inflow).
- Hydrometeorological records for more than 50 years are available
for many stations in the surroundings of the lake.
Sewage discharge data are also available, but only for the larger
sewage treatment plants and effluent outfalls.
The regular
sampling frequency is only 2-6 annually, but more detailed occasional observations were made several times at the larger plants
along the shore-line.
Other data on natural and economical factors (such as topography,
land use activities, water uses, etc.) are also available.
Field Experiments
Earlier researches have proved that in the contribution of nutrients
by the tributary inflows, the runoff events (i.e. flood waves) play
an outstanding role.
For most of the components concerned, the
contribution of the larger flood waves exceeds half of the total
input, while the corresponding time (duration of floods) is only a
minor fraction of the year.
It follows from the above conditions
that the regular observation programme - mentioned above - will not
be able to follow these dynamics in loading, that is with monthly
one or two observations, the effect of flood waves of durations
varying between a few hours to a few days, cannot be determined.
This fact necessitated field measurements where the objective was to
obtain measurement data corresponding to such extreme flow conditions .
Experiments were made on two subwatersheds (Cr.Tetves and
Cr.Orvényes - shaded areas on figure 1) each equipped with continuous flow measuring gauges. Samples were taken at intense runoff
(storm) events with intervals of about four to ten a day depending
on the character of the runoff event concerned. Samples were analyzed within a few hours or at least filtered and kept in a cool,
dark place. Analyses were made for Total P, P0 -P, NO -N, Total-N
and suspended solids. Hydrometeorological data were also collected.
It may be mentioned that experiments are being continued at the
present on both watersheds with daily regular observations with even
more frequent observations during runoff events.
210 G.G,
Pinter
& G.
Jolânkai
DATA EVALUATION
The data set provided by the regular monitoring network and the
special field measurement and data collection programme was evaluated to yield the following results:
(a)
annual and monthly average nitrogen and phosphorus balances,
(b)
nutrient yield rate-runoff relationships developed on the
basis of annual total load and total runoff data pairs
for five years and 20 tributaries,
(c)
tri-variate nutrient yield rate-runoff average slope
relationship for the same set of data as in item b,
(d)
long term concentration trends in the inflowing streams,
(e)
flow-loading rate relationships developed on the basis of
both the data of regular network and that of special
flood measurements,
(f)
nutrient loading rate probability distributions developed
on the basis of runoff statistics and flow-load relationships .
DISCUSSIONS OF RESULTS
From the results referred to in the foregoing paragraph, only those
offering some general use will be discussed here. Annual nutrient
yield rates expressed in kg ha-1 were related to corresponding
runoff values in figures 2 and 3. In the figures, curves derived on
the basis of published literature values are also shown. Considering these figures and other literature data the following general
conclusions (relationships and export rate ranges) may be drawn.
FIG. 2 Phosphorus export rates from drainage basins of
different character based on literature data and on a
Lake Balaton study.
Plant nutrient
load calculations
211
Phosphorus Export Rates from Watersheds of Different Character
Forest land and welands:
where Y
Lp
Y
= 0.00059 L
P
is the export rate of phosphorus in kg ha-1, and
is the runoff in mm
Literature values range between 0.02-0.11 kg P ha-1yr-1.
Agriculural land:
Y
= 0.0031 L
P
Reported annual total export rates (without giving runoff values)
are covering a wide range of 0.09-4.2 kgP ha-1yr-1. Curves representing Lake Balaton sub-watersheds in figure 2 are described by the
equations
Y
= 0.0245 expO.0233 L
(r = 0.89) and
Y P = 0.00134 L
(r = 0.86)
P
are enveloping the literature derived equation: i.e. the rocky and
forested northern sub-watershed yields less and the more erodible,
mostly agricultural southern sub-watershed yields more than that
estimated on the basis of literature values.
Literature export rate values for pasture range between 0.20.5 kg P ha^yr- 1 .
It has to be emphasized that from vineyards phosphorus export
rates as high as 11 kg P ha-1yr-1 have been reported.
Urban Land
The model developed on the basis of literature data is in the form
of
Y
= 0.00545 L
P
while
reported
annual
export
5.6 kg P ha-Vr- 1 -
rates
range
between
Nitrogen Export Rates (figure 3) from Watersheds of Different
Character
Forest land and marshland:
Literature values resulted in
Y
n
=
0.0137 L
while annual export rates range between 2-8 kg N ha-'yr-1.
1.1-
212
G. G.
Pinter
& G.
Jolânkai
S-average slope in rnkm
l a k e Bataton, Southern drainage bosin
100
120
160
180
200
Runoff
mm
FIG. 3 Nitrogen export rates from drainage basin of
different character based on literature data and on a
Lake Balaton study.
Agricultural land
Reported literature runoff-yield rate data scatters along the linear
equation
Y
=
0.0824 L
where Y is the export rate of nitrogen in kg ha-1
while annual total specific yield rates reported in the literature
mostly fall between 10-20 kg N ha-1yr-1.
Corresponding Lake Balaton export rates are described by
Y
=
Y^J =
0.994 expO.0129 L
0.55 expO.0167 L
(r = 0.92) and
(r = 0.89)
for the northern and southern sub-watershed respectively.
Pasture nitrogen yield rates from the literature cover a range of
1.1-5.3 kg N ha-1yr-1, while the highest export rates from vineyards
and orchards fall between 30-260 kg ha-1yr-1.
Tri variate data analysis of 20 tributaries of Lake Balaton have
resulted in a model of
Y
n
=
0.022 L°- 9 7 S 0 " 3 9
(R2 = 0.72)
where S is the average slope of the watershed in a m km-1/ /oo.
Urban Land
The equation derived on the basis of literature data is
Plant
Y
n
=
nutrient
load calculations
213
0.034 L
Note that urban areas yield less nitrogen than agricultural areas,
while in the case of phosphorus yield rates the proportion is vice
versa.
Annual
total
export
rates
fall
between
6.010.0 kg N ha-^r - 1 •
Remarks on the Regression Models and Yield Rate Ranges
Described Above
(a)
(b)
Data presented in more than a hundred studies have been
utilized and consequently no complete reference list can
be given but they have been referred to elsewhere
(Jolânkai, Pinter, 1981).
Correlation coefficients r are not given for the equations derived from the data presented in the literature,
since only the data scattered along well definable curves
have been utilized, and thus r values were always high
(between 0.8-0.99).
CONCLUSIONS
Although on the basis of a well established water quality and hydrological monitoring network, special field measurements and an extensive literature review, meaningful quantitative relationships were
developed for the estimation of plant nutrient export rates from
drainage basins of different land use forms, there remains quite a
number of questions to be answered later. Such open questions are:
(a)
effects of fertilizer application on the yield rate
(literature values are scarce and contradicting),
(b)
effects of grazed and large scale animal husbandry and
manure application (very broad ranges scattering results,
no quantifiable relationship),
(c)
seasonal effects (effects of vegetation cover), available
regression equations such as given by Humenik et al.
(1980) do not conform with other literature yield ranges,
(d)
effects of rainfall - runoff intensity (it is known but
not yet quantified that high intensity rainfalls and the
resulting "peaky" floodwaves cause export rates much
higher than those derived by the above runoff-yield rate
equations).
These and such other unknown effects could be quantified on the
basis of experimental data of several sub-drainage basins by using
bi- and multi-variable regression techniques. International efforts
on the development of such quantifiable relationships are under way
in the framework of the UNESCO Man and Biosphery - 5 Working Group
on land use impacts on aquatic systems, and it is hoped that generalized quantitative relationships covering a broad range of human
activities and natural drainage basin characters will be available
in the near future.
214 G .G . Pinter
S G.
Jolânkai
REFERENCES
CREAMS (multi author project report, not published) (1979) Chemical
runoff and erosion from agricultural management systems.
Donigian, A.S. & Crawford, N.H. (1976) Modelling pesticides and
nutrient on agricultural land.
U.S. Environmental Protection
Agency, Report No. EPA 600/2-76-043.
Humenik, F.J. et al. (1980) Rural non-point source water guality in
a southeastern watershed.
J. Wat. Pollut. Control Fed., 52,
29-43.
Jolânkai, G. (1981) Modelling non-point source pollution. In:
Application of Ecological Modelling in Environmental Management
(éd. S. Jorgensen), Elsevier Scientific Publishing Co. (in
press) .
Jolânkai, G. & Pinter, Gy. (1981)
Teruleti (nem-pontszerii)
szennyezés es felszini bemosodâs. (Non-point source pollution
and surface runoff), VMGT-Series No. 131.VI2DOK, Budapest (in
press).