Freshwater Ecosystems in Crisis
A Synopsis of Decline
2007 Pacific Rivers Council
The Pacific Rivers Council gratefully acknowledges the following
foundations for making this publication possible:
The Brainerd Foundation
The Bullitt Foundation
The Firedoll Foundation
The Flintridge Foundation
The General Service Foundation
The Harder Foundation
The Lazar Foundation
The Giles W. & Elise G. Mead Foundation
The Weeden Foundation
The Wilburforce Foundation
Freshwater Ecosystems in Crisis
A Synopsis of Decline
Introduction
Freshwater ecosystems – the biologically complex rivers, lakes and wetlands
that sustain our lives and that of thousands of species – are in a state of
emergency. Compared with the attention given to the clearing of tropical
rainforests and the plight of the oceans, the ongoing devastation of freshwater
ecosystems has gone relatively unnoticed. Yet of all the major ecosystems,
freshwater ecosystems have suffered the most calamitous decline in recent
years and are likely the Earth’s most imperiled.1
Freshwater species are undergoing widespread and accelerated population
decline and extinction. Freshwater ecosystems have lost a greater proportion
of their species and habitat than any other ecosystem on land or in the
oceans.2 Of course, native fish and frogs are not the only species at risk when
freshwater ecosystems are imperiled. Humans, too, depend on the health of
rivers and streams for our continued existence.
The impairment and loss of freshwater ecosystems has many causes, but
experts agree that habitat alteration and destruction are the primary culprits.
Logging, road building, mining, dams, diversions, grazing — all of these
activities have detrimental effects on our waters, not just when they occur
adjacent to streams, lakes and wetlands, but even when they occur far from
surface water bodies.
For the past 20 years, the Pacific Rivers Council has worked to bring attention
to the rapid degradation of our nation’s freshwater ecosystems and to help
implement solutions to reverse the decline.
Life in Freshwater Ecosystems
While 70 percent of the earth’s surface is water, only 2.5 percent of that
water is fresh. Of that 2.5%, just 0.3 % is found in rivers and lakes; the rest is
groundwater or is frozen in ice sheets and glaciers.3 But although occupying
less than one percent of the Earth’s surface, freshwater ecosystems support an
estimated 12 percent of all animal species.4
Freshwater ecosystems in their natural state are densely packed with life. Per
unit area or volume, freshwater ecosystems are richer in species than the more
expansive terrestrial and marine ecosystems.5 There is on average one species
per 15 km3 of freshwater, as compared to one species per 100,000 km3 of
seawater.6
Seven major groups of organisms depend upon freshwater ecosystems:
vertebrates (e.g., fish, amphibians, reptiles, birds, and mammals), invertebrates
(e.g., protozoans, myxozoans, rotifers, worms, mollusks, insects, crustaceans),
plants, algae, fungi, bacteria, and other microbes.7 Forty percent of known fish
species (10,000 of 25,000) live in fresh water,8 and freshwater fishes comprise
more than half of all vertebrate species on Earth.9
Species Richness by Ecosystem
Ecosystem
Habitat extent
Percent known
species*
Relative Species
richness**
Freshwater
0.8%
2.4%
3
Terrestrial
28.4%
77.5%
2.7
Marine
70.8%
14.7%
0.2
*Sum does not add to 100 percent because 5.3 percent of known symbiotic species are
excluded.
**Calculated as the ratio between the percent species known and the percent area occupied by
the ecosystem.
Source: Revenga, C., and G. Mock. 2000. Freshwater Biodiversity in Crisis. Adapted from PAGE: Freshwater
Systems 2000 and World Resources 1998-99. World Resources Institute. http://earthtrends.wri.org/pdf_
library/features/wat_fea_biodiversity.pdf Note: “percent” for “proportion” heading error corrected.
Pacific Rivers Council
The number of described species that rely on freshwater habitats has
been estimated at 45,000; but many freshwater species worldwide remain
undescribed by science. In fact, between 130 to more than 300 new fish species
are described annually.10,11 The true count of the species throughout the world
that need fresh water to survive could well be more than one million.12
The Economics of Fresh Water
Putting a dollar amount to the value of ecosystem services is extremely
complex, and not the emphasis of this handbook. However, it is important
to recognize that healthy, biologically complex freshwater ecosystems play a
vital role in the global economy. The value of the Earth’s freshwater services
has been estimated in the several trillions of dollars.13 One study estimated the
total economic value of the planet’s wetlands alone at $70 billion per year.14
Rivers, lakes and wetlands provide us with drinking and irrigation water,
food, marketable goods, flood control, pollution filtration, drought mitigation,
recreation, and employment. In fact, the services of freshwater ecosystems
globally are valued at 85 per cent greater than the world total of gross national
products — a greater contribution to human welfare per unit area than any
other ecosystem.15 And the predicted shortfall of clean, fresh water is expected
to be a major factor in limiting the 21st century economy.16
Water purification is one example of an ecosystem service provided by intact
freshwater ecosystems. Municipalities around the world are realizing that
investing in the ecosystem is cheaper than building a filtration plant for their
drinking water. For example, New York City is spending $1.5 billion over 10
years on watershed protections to avoid building a $6 billion water filtration
plant that would cost an additional $300 million a year to operate. Portland,
Oregon spends $920,000 a year on watershed protections to avert the need for
a $200 million filtration plant.17
Healthy freshwater ecosystems provide essential services at less cost and with
greater consistency and equity than treatment technology alone could provide.
Even more importantly, there is simply no substitute for clean water.
Selected U.S. Cities That Have Avoided Construction
of Filtration Plants Through Watershed Protection
Metropolitan Area
Population
Avoided Costs Through Watershed Protection
New York City
9 million
$1.5 billion to be spent on watershed protection
over 10 years will avoid at least $6 billion in capital
costs and $300 million in annual operating costs.
Boston, MA
2.3 million
$180 million (gross) avoided cost.
Seattle, WA
1.3 million
$150–200 million (gross) avoided cost.
Portland, OR
825,000
$920,000 spent annually to protect watershed is
avoiding a $200 million capital cost.
Portland, ME
160,000
$729,000 spent annually to protect watershed has
avoided $25 million in capital costs and $725,000
in operating costs.
Syracuse, NY
150,000
$10 million watershed plan is avoiding $64–76
million in capital costs.
Auburn, ME
23,000
$570,000 spent to acquire watershed land is
avoiding $30 million in capital costs and $750,000
in annual operating costs.
Source: Postel, S. 2005. Liquid Assets: The Critical Need to Safeguard Freshwater Ecosystems.
WorldWatch Paper 170. The Worldwatch Institute. http://www.worldwatch.org/node/820, p. 29
Unlike other natural resources, such as gas, coal or metal, there are no feasible
alternatives to fresh water. Worldwide, less than 0.5% of current water use
comes from desalination.18 Desalination costs up to eight times more than the
average cost of urban water supplies; as of 1997, it would cost roughly 12
percent of the gross world product, or $3 trillion a year, to desalinate enough
water for human use.19
Because humans depend on the health of freshwater ecosystems, the decline
of these ecosystems is taking its toll. Currently, 2.3 billion people in more than
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80 countries – 41% of world population – live in river basins with serious
water shortages.20 By 2025 it is expected that 3.5 billion people, or nearly half
the world’s population, will not have enough fresh water for drinking and
irrigation. The resulting illness and death could be devastating.
Life-Support Services Provided by
Rivers, Wetlands, Floodplains,
and Other Freshwater Ecosystems
• Water supplies for irrigation, industries, cities, and homes
• Fish, waterfowl, mussels, and other foods for people and
wildlife
• Water purification and filtration of pollutants
• Flood mitigation
• Drought mitigation
• Groundwater recharge
• Water storage
• Wildlife habitat and nursery grounds
• Soil fertility maintenance
• Nutrient delivery to deltas and estuaries
• Delivery of freshwater flows to maintain estuarine salinity
balances
• Aesthetic, cultural, and spiritual values
• Recreational opportunities
• Conservation of biodiversity, which preserves resilience
and options for the future
Source: Postel, S. 2005. Liquid Assets: The Critical Need to Safeguard
Freshwater Ecosystems. WorldWatch Paper 170. The Worldwatch Institute.
http://www.worldwatch.org/node/820.
Clearly, the need for naturally functioning freshwater ecosystems is critical to
maintaining the Earth’s biodiversity, as well as essential to human health and
economic well-being. Yet freshwater ecosystems have lost a larger proportion
of their species and habitat than land or ocean ecosystems.21
Scientists have documented a 50% decline in populations of freshwater
species over the past 30 years — much greater than the 30% population
drop for terrestrial and marine species.22 Of the 10,000 known species of
freshwater fish, 20 percent are threatened, endangered or have become
extinct in recent decades.23 At least ninety-one freshwater fish species are
known to have gone extinct in the last century.24 The following chart tracks
the trajectory of freshwater fish extinctions in the 20th century.
Source: WWF Living Planet Report 2004
The World Conservation Union (IUCN) announced the 2006 IUCN Red
List of Threatened Animals proclaiming, “Freshwater fish assumes top slot on
extinction list.”25
The IUCN also found that another freshwater group – amphibians – is
suffering massive population declines. Today, one in three amphibians
is threatened. Since the IUCN first began tracking threatened species
worldwide in 1996, the number of threatened amphibian species has grown
from 124 in 1996 to 1,811 just a decade later.26
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Freshwater Species Decline in the North America
In North America, 40 percent of freshwater species are extinct or at risk of
extinction27 — twice the global average endangerment of 20 percent.28 In the
20th century, at least 123 North American species of freshwater fish, mollusks,
crayfish and amphibians became extinct.29
In fact, freshwater mussels, called “living filters” because they purify water so
effectively,30 are considered to be the most endangered group of animals in
North America.31 Mussel declines reflect loss of habitat, deterioration of water
quality, loss of native fishes that serve as biological hosts for many mussel taxa,
and invasion of non-native mollusks.32
Based on recent extinction trends, an estimated 3.7 percent of
freshwater animal species will be lost in North America each
decade, a rate nearly five times that of terrestrial animals.33
In the United States, more than one-third of threatened or endangered
species inhabit only wetlands, and nearly half depend on wetlands at some
point in their life-cycle.34 Below are more sobering statistics on threatened and
endangered freshwater species in the U.S.35
•
38 percent of freshwater fishes are threatened or endangered;
•
68 percent of mussels are threatened or endangered, and almost
1 in 10 may already have vanished forever;
•
51 percent of crayfish are threatened or endangered;
•
40 percent of amphibians are threatened, endangered, or already
extinct;
•
18 percent of dragonflies and damselflies are threatened or
endangered;
•
Over 40 percent stoneflies are threatened or endangered;
•
Almost 50 percent of freshwater snails in the Southeastern
United States are now endangered or extinct due to
channelization and impoundment of rivers.
The map below shows, state by state, the number of freshwater fishes
considered imperiled as compared to the total number of native freshwater
fishes in that state.36 For example, 39 of 43 freshwater fish species native to
Nevada (91%), 22 of 26 in Arizona (85%), 42 of 58 in California (72%) and
25 of 57 in Oregon (44%) are in jeopardy.
4/47
WA
6/57
MT
25/57
OR
5/36
ID
8/49
WY
39/43
NV
11/26
UT
42/58
CA
22/26
AZ
4/49
ME
5/76
ND
7/135
MN
8/144
WI
5/87
SD
9/47
CO
12/188
IL
9/118
KS
10/151
OK
20/66
NM
7/131
MI
7/134
IA
6/81
NE
14/197
MO
9/148 21/201
WV
VA
40/257
TN
14/200
MS
23/143
TX
8/166
PA
8/153
OH
9/188
IN
18/220
KY
18/189
AR
11/150
LA
10/155
NY
30/257
AL
2/88
VT NH
3/55
2/62
MA
2/43
RI
2/55
CT
2/77
NJ
2/70
DE
4/99
MD
21/182
NC
8/119
SC
20/219
GA
No. imperiled / no. native freshwater fish
Northwest
Southwest
Midwest
Central
Northeast
Southeast
10/119
FL
Source: James E. Johnson, “Imperiled Freshwater Fishes,” National Biological Service
As if the current population decline isn’t startling enough, consider this:
species not currently considered at-risk are likely to decline or even disappear
because of “future biological invasions…and the cascading effects of keystone
extinctions,” 37 in which species decline in response to declines or extinctions of
other (“keystone”) species on which they somehow depend. For example, one
reason so many mussel species are threatened is that their life cycles depend on
a limited number of particular fish species, which serve as hosts for their brief
parasitic larval stage. If host fish are reduced or eliminated from a non-mobile
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mussel population’s range by, for example, habitat degradation or dams that
block the host fish’s migrations,38 the mussels cannot reproduce and become
“functionally extinct” even though living individuals remain. This is, in fact,
the alarming current situation for populations of over 40% of Tennessee River
mussel species.39
Concern over the decline of freshwater ecosystems should start well before
species extinction occurs or becomes imminent. The decline of individual
stocks and populations within freshwater species is dangerous as well. A large
body of science illuminates how local populations of freshwater fish, for
example, hold unique genetic and ecological adaptations to particular localities,
ensuring the health, persistence, and future resilience of the species over its
historical range and the long-term.40 Loss of this diversity among populations
within species diminishes the capacity of those species to maintain both their
productivity and resilience, and this will likely become increasingly critical as
freshwater ecosystems respond to global climate change.
Human activities such as draining wetlands, constructing dams, and diverting
and channelizing rivers contribute to 71-73% of freshwater fish extinctions.
Other major factors in the extinction of freshwater fishes include: the
introduction of non-native species, which compete with or prey on native
species (54-68%), hybridization (38%), pollution (26-38%), and over-fishing
(15-29%). Multiple factors contribute to most (82%) native freshwater fish
extinctions.41
Freshwater Habitat Degradation42
Habitat alteration and/or destruction are the biggest single threat to freshwater
ecosystems and species.43 Land and watershed conversion and degradation
are widespread. Up to half of the wetlands worldwide have been lost to
development.44 The “lower 48” United States lost an estimated 53% of its
original wetlands area from the 1780s to the 1980s; 22 states lost more than
50%; California, 91%.45 More than 45,000 large dams worldwide now disrupt
35% of all river flows46 and can impound about 15% of global runoff,47 while
an estimated 800,000 smaller dams48 may impound three to four times that
Human Activity
Impact on Aquatic Ecosystems
Values/Services at Risk
Dam construction
Alters timing and quantity of river flows,
water temperature, nutrient and sediment
transport, delta replenishment; blocks fish
migrations
Habitat, sports, and commercial
fisheries; maintenance of deltas
and their economies
Dike and levee
construction
Destroys hydrological connection
between river and floodplain habitat
Habitat, sports, and commercial
fisheries; natural floodplain
fertility; natural flood control
Excessive river
diversions
Depletes streamflows to ecologically
damaging levels
Habitat, sports, and commercial
fisheries; recreation; pollution
dilution; hydropower;
transportation
Draining of wetlands
Eliminates key component of aquatic
environment
Natural flood control, habitat
for fisheries and waterfowl,
recreation, natural water filtration
Deforestation/poor
land use
Alters runoff patterns, inhibits natural
recharge, fills water bodies with silt
Water supply quantity and
quality, fish and wildlife habitat,
transportation, flood control
Uncontrolled pollution
Diminishes water quality
Water supply, habitat,
commercial fisheries, recreation
Overharvesting
Depletes living resources
Sport and commercial fisheries,
waterfowl, other living resources
Introduction of exotic
species
Eliminates native species, alters
production and nutrient cycling
Sport and commercial fisheries,
waterfowl, water quality, fish and
wildlife habitat, transportation
Release of metals and
acid-forming pollutants
to air and water
Alters chemistry of rivers and lakes
Habitat, fisheries, recreation
Emission of climatealtering air pollutants
Has potential to make dramatic changes
in runoff patterns from increases in
temperature and changes in rainfall
Water supply, hydropower,
transportation, fish and wildlife
habitat, pollution dilution,
recreation, fisheries, flood
control
Population and
consumption growth
Increases pressure to dam and divert more
water, drain more wetlands, etc., increase
water pollution, acid rain, and potential
for climate change
Virtually all aquatic ecosystem
services
Source: Postel, S., and S. Carpenter. 1997. Freshwater Ecosystem Services. Pages 195-214 in G.
C. Daily, editor. Nature’s Services: Societal Dependence on Natural Ecosystems. Island Press,
Washington, D.C., p. 208.
Pacific Rivers Council
volume.49 Forty thousand of these large dams have been built since 1950 — a
rate of two constructed per day.50 Dams now strongly or moderately impair
172 of the world’s 230 major rivers (59%), with remaining free-flowing systems
mostly concentrated in the far north.51
Groundwater
Degradation of freshwater ecosystems also results from depletion of
subsurface water (groundwater) or the disruption of natural exchanges
between subsurface and surface waters. Groundwater is not only important
as a source of freshwater for human use, but the natural upwelling of
groundwater buffers temperatures and sustains habitat diversity in streams,
wetlands, rivers and lakes. For example, spring flooding in many rivers and
wetlands replenishes floodplain or wetland groundwater aquifers, which then
gradually discharge water back to the surface as flow levels recede later in the
year. Groundwater stays cooler than surface flows in summer and warmer
in winter, maintaining critical survival flows and suitable thermal habitat for
many species through summer, fall and winter.52
Groundwater entering streams and lakes often creates localized refuges from
extreme or intolerable conditions for fish and other species. For example,
juvenile bull trout can survive winter in the shallow groundwater flowing
through spaces among streambed particles in a stream completely dewatered of surface flow. 53 Many forms of land and water management or
development can sever this important connection: diking and revetment; road
encroachment; channel straightening and infilling of sloughs and channel
branches; disturbance of floodplain vegetation and soils by logging, grazing,
or industrial development; and flow modification by dams, reservoirs, and
diversions.
The inflow of groundwater to surface streams increases the quality of
spawning habitat for bull trout54 and other trout and salmon species.55
Observed and anticipated effects of climate warming 56 make it even more
critical to preserve and restore conditions that favor groundwater-surface
water exchange to buffer temperatures and maintain habitat diversity in
freshwater ecosystems.
11
Importance of Headwater Streams
Headwater streams – even those that do not support fish or hold water all
year – are vital to freshwater ecosystems. They are the capillaries that supply
water to connected larger streams, rivers, wetlands, ponds and lakes. The
critical functions of headwater streams are widely overlooked and insufficiently
protected by existing land management regulations and planning. Generally,
only buffers are provided, (primarily for larger waters and those with sport fish),
offering insufficient protection for smaller streams and those with seasonally
intermittent flow. Science, however, continues to underscore the crucial role of
headwater streams in sustaining water quality and freshwater habitat.
Even small and seasonally dry streams provide critical habitat (e.g., seasonal
habitat for juvenile coho salmon)57 and are the primary source of clean, cold
water to downstream reaches.58 Headwater channels are the primary point of
entry for the suspended and bedload sediment that determines conditions in
downstream rivers and lakes, and recent research exposes the failure of current
policy and regulations to protect the sediment mediation function of headwater
streams.59 The chart below shows the importance of headwater streams to a
number of amphibian populations.60
Stream Amphibian Relative Abundance and Management History in Olympic
Peninsula Headwater Streams (adapted from Raphael et al. 2002)
120
100
Tailed frog
Cope’s giant salamander
Olympic torrent salamander
Abundance
80
60
40
20
0
Old, unmanaged
Old, clearcut, 10-30m buffers
Mature 2nd growth
(35-100 yrs old)
Mature 2nd growth,
clearcut, 10-30-m
buffers
Mature 2nd growth,
commercially thinned,
no buffer
Adjacent Forest Site Condition
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Young 2nd growth,
logged 0-35 years
earlier, no buffers
Global Climate Change & Freshwater Ecosystems
Overlaying these well-documented threats is the increasingly confirmed
influence of global climate change on all ecosystems, including freshwater
ecosystems. For example, scientists estimate that by 2050 the Columbia River
will no longer be able to accommodate water releases for both hydropower
generation and salmon runs.61 In California, as in other places in the western
U.S., scientists are predicting changes in snowpack and snowmelt patterns (less
snowpack melting earlier in the year) which will lead to reduced streamflow
in the summer — exactly the time of year when needs of fish, farmers
and hydropower for sufficient water are at their highest.62 In addition, field
researchers are beginning to document alarming trends, such as increases in
temperature at high elevations facilitating the spread of a disease deadly to
many amphibians.63
Global climate change is associated with increasing stresses on freshwater
ecosystems, but managing ecosystems to sustain the processes that provide
clean water, complex natural habitat, and diverse biological communities
also confers resilience to fresh waters to resist or rebound from many of the
stresses of climate change. For example, maintaining floodplain function and
the surface-subsurface flow exchange found in natural alluvial rivers can help
sustain their flow and buffer their temperature in the face of climate change.64
The Solution Begins with Responsible Land Management
Fortunately, the leading cause of freshwater species decline is also one of the
more manageable problems. Habitat destruction and alteration are potentially
both more preventable and more correctible than many other recognized
threats, such as invasion by introduced fish species.65 The connection between
land management, the quality of aquatic habitat, and the health of freshwater
species is indisputable, yet although the damage to freshwater ecosystems from
dams and exotic species is widely acknowledged, the role of land management
is largely overlooked unless the activity is taking place right next to an aquatic
feature such as logging in riparian areas or livestock grazing in wet meadows.
13
Scientists agree that land use activities – even those not adjacent to water
bodies – have direct, indirect, and cumulative impacts on the health of
freshwater species and ecosystems.66 The failure to recognize that land
management throughout the watershed’s land surface67,68 plays a crucial role in the
health of freshwater ecosystems and the vitality of freshwater species is a
common flaw in the majority of national and state land management laws and
policies.
As the trend of freshwater species decline makes obvious, current conservation
measures are not adequate to maintain, much less restore, freshwater
ecosystems and their dependent aquatic species. The existing legal framework
for protection of freshwater systems is not biologically based, and while the
protections offered by mechanisms such as Wilderness and Wild and Scenic
River designations are important, they provide no systematic relationship
between the quality of the resource and the level of protection or restoration.
What is needed is a new approach to taking care of freshwater ecosystems
that builds on and enhances existing land use laws and policies, and focuses
on protecting and maintaining the most biologically functioning watersheds,
then concentrates restoration resources where they can do the most good for
ecosystems and their inhabitants — including humans. Responsible water
management must also be part of the solution, but land management that
helps watersheds produce high-quality fresh water in the first place is a critical
starting point.
Conclusion
The state of our nation’s freshwater ecosystems is alarming. The future,
however, need not be. We possess the scientific knowledge and tools to reverse
the decline. The key to the recovery of our rivers, lakes, and wetlands is to
connect this knowledge with public policy on freshwater issues.
The Pacific Rivers Council has developed the following watershed restoration
strategy, which has ultimately become the guiding vision of our organization.
Pacific Rivers Council
First, Protect the Best. It is far more ecologically and financially efficient
to protect relatively intact and healthy habitats than attempt to recover and
restore highly degraded areas. The importance of healthier areas lies in
their role as “anchor habitat,” providing stable habitat to sustain populations
through environmental extremes. These areas of refuge are most beneficial
when they are large, well dispersed, and interconnected to the maximum
extent possible so that a full suite of habitats are represented to support a wide
range of aquatic species, ecotypes and populations. It is critical that these
last remaining areas of intact habitat, and the stream reaches that sustain
these areas, are protected from destructive land use activities such as logging,
mining, road building and diversions to ensure that no further harm is done.
Then, Restore the Rest. Once anchor habitat is identified and protected,
restoration of more degraded habitats should proceed by identifying the key
insults to these habitats and removing them. Roads are a prime example.
Roads must be improved, relocated or decommissioned where necessary
to minimize their impact on affected aquatic habitat. In most cases, stream
crossings that are blocking fish passage should be replaced with passable
culverts or bridges, or the roads should be removed. Logging, grazing and
other such habitat-altering activities should be suspended or ceased in more
sensitive areas. Where dams and diversions exist but cannot be removed,
stream flows need to be regulated as close to natural levels as possible.
PRC continues to promote the long-held conviction that what we do to the land,
we do to the water; the ultimate strategy for reversing the decline of aquatic
ecosystems must recognize the cumulative watershed effects of land use
activities — even when these activities are conducted far from the stream.
PRC is dedicated to ensuring that the best available science informs policy
decisions that affect our nation’s rivers and native aquatic species, applying
sound science where it exists and further research where it is needed.
To learn more about PRC’s watershed restoration strategy and projects, log on
to our website: www.pacrivers.org.
15
Pacific Rivers Council
Endnotes
1 World Wildlife Fund. 2006. Freshwater Losses. http://www.panda.org/about_wwf/
what_we_do/freshwater/problems/freshwater_losses/index.cfm.
2 Revenga, C., and G. Mock. 2000. Freshwater Biodiversity in Crisis. Adapted from
PAGE: Freshwater Systems 2000 and World Resources 1998-99. World Resources
Institute. http://earthtrends.wri.org/pdf_library/features/wat_fea_biodiversity.pdf
3 UNESCO. 2005. International Year of Freshwater 2003 website. Facts and Figures.
http://www.wateryear2003.org/en/ev.php-URL_ID=1462&URL_DO=DO_
TOPIC&URL_SECTION=201.html.
4 Abramovitz, J. 1996. Imperiled Waters, Impoverished Future: The Decline of
Freshwater Ecosystems. Worldwatch Paper #128. The Worldwatch Institute. http://
www.worldwatch.org/node/862.
5 Revenga, op. cit. note 2.
6 Groombridge, op. cit. note 6.
7 Groombridge, B., and M. Jenkins. 1998. Freshwater biodiversity: a preliminary
global assessment. WCMC Biodiversity Series No. 8. http://www.unep-wcmc.
org/information_services/publications/freshwater/. United Nations Environment
Programme-World Conservation Monitoring Centre. WCMC - World Conservation
Press, Cambridge; Table 7.
8 World Wildlife Fund. Living Planet Report 2004. http://assets.panda.org/downloads/
lpr2004.pdf.
9 Groombridge, op. cit. note 6, Table 7.
10 Berra, T. M. 1997. Some 20th century fish discoveries. Environmental Biology of
Fishes 50:1-12. http://www.springerlink.com/content/g126520l126556w120512/.
11 Revenga, op.cit. note 2, citing Nelson, J. S. 1976. Fishes of the World. Wiley, New
York; Nelson, J. S. 1984. Fishes of the World (2d ed.). Wiley, New York; and Nelson,
J. S. 1994. Fishes of the World (3d ed.). Wiley, New York.
12 IUCN-The World Conservation Union. Introduction to the Freshwater Biodiversity
Assessment Programme. http://www.iucn.org/themes/ssc/our_work/freshwater/
indexfreshwater.htm.
13 Postel, S., and S. Carpenter. 1997. Freshwater Ecosystem Services. Pages 195-214 in
G. C. Daily, editor. Nature’s Services: Societal Dependence on Natural Ecosystems.
Island Press, Washington, D.C.
14 Schuyt, K., and L. Brander. 2004. The Economic Values of the World’s Wetlands.
http://assets.panda.org/downloads/wetlandsbrochurefinal.pdf. WWF, Gland,
Switzerland/Amsterdam, The Netherlands.
17
15 WWF-UK. 2007. Freshwater Facts and Key Issues. http://www.wwf.org.uk/
researcher/issues/freshwater/0000000195.asp (citing Costanza, R, R. d’Arge, R.
de Groot, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R.V. O’Neill, J.
Paruelo, R.G. Raskin, P. Sutton, and M. van den Belt. 1997. The value of the world’s
ecosystem services and natural capital. Nature 387:253-260).
16 United Nations Development Programme, United Nations Environment
Programme, World Bank, and World Resources Institute. 2000. World Resources
2000-2001: People and ecosystems: The fraying web of life. http://www.wri.org/
biodiv/pubs_description.cfm?pid=3027.
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23
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