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					                                    AQUATIC ECOSYSTEMS


        Rivers, lakes, wetlands, and estuaries are an important part of the global ecosystem. Rivers
connect the land surface and atmosphere to the ocean, delivering about 40,000 km3 of water per
year from land to ocean. Water en route to the oceans forms wetlands, lakes, and eventually coastal
estuaries. Together these surface waters represent about 5-10% of the global terrestrial surface area.
The aquatic ecosystems that have developed in these surface waters provide habitat for diverse flora
and fauna species (much of which is endemic to very small regions), transport nitrogen, carbon,
phosphorus, sediments and numerous other elements, and support diverse biogeochemical activity.
Together the aquatic ecosystems provide services, both to humans and the natural system, far
beyond their limited boundaries.
        Fresh water is vital to human life and economic well-being. Humans currently are believed
to use more than 50% of the available global runoff (Postel 1996). Societies extract vast quantities
of water from rivers, lakes, wetlands, and aquifers to supply the requirements of power generation,
flood control, irrigation, and urban, industrial, and agricultural uses. Traditionally, this human use
of water has been at the expense of equally vital benefits of water in sustaining healthy aquatic
ecosystems. For example, at present 30% of the world’s population does not have access to clean
water, as a result of poor water management, and under current trends of global change and
population growth two thirds of the population may be subject to moderate to high water stress
(WHO 2000, UNFPA 2003).
        There is growing recognition, however, that the many economically valuable commodities
and services to society provided by functionally intact and biologically complex aquatic ecosystems
have not been included in evaluation of the importance of aquatic ecosystems. These services
include flood control, transportation, recreation, purification of human, industrial, and agricultural
wastes, habitat for plants and animals, and production of fish and other foods and marketable goods.
        Aquatic ecosystems have evolved to the rhythms of natural hydrologic variability, requiring
a range of variation or disturbance, on long and short time-scales, to maintain viability and
resilience. They are also tightly linked to their watersheds or catchments; water flowing to the sea
moves in three dimensions, linking upstream to downstream, stream channels to floodplains, and
riparian wetlands and surface waters to ground water. Therefore, materials generated across the
landscape ultimately make their way into rivers, lakes, and other aquatic ecosystems and they are
thus, greatly influenced by human activities proximate and distant.
        Failure to provide adequate water, proper timing of flows, and suitable water quality to
aquatic ecosystems results in loss of species and ecosystem services in wetlands, rivers, and lakes,
and over the long-term results in a loss of the adaptive capacity of aquatic ecosystems to sustain
production of these important goods and services in the face of future environmental disruptions,
such as climate change. These ecosystem benefits are costly and often impossible to replace when
aquatic systems are degraded.
        The ecological consequences that arise from aquatic ecosystem degradation often become
apparent to people only after the degradation begins to interfere with societal uses of fresh water.
Nuisance algal blooms and loss of commercial or sport fisheries are examples of failures in
ecosystem processes that were often years in the making. Some ecosystems naturally experience
wide swings in environmental and ecological conditions from one year to the next that can mask
gradual changes in physical and chemical factors. Most systems are inherently resilient to a
particular pattern of disturbance, and their plant and animal communities will persist as long as
conditions fluctuate within a certain range. Once a threshold is reached, however, these ecosystems
may change rapidly to a new stable state that is very difficult to reverse. The collapse of a fishery
and permanent cultural eutrophication from nutrient inputs are two examples of conditions that,
once reached, make it difficult to restore the integrity of an aquatic system.
        Therefore, it is imperative that the minimum requirements of aquatic ecosystems be
maintained in order for them to continue as functioning systems under future land use and climate
changes and for humans to continue to enjoy the goods and services provided by these ecosystems.
The traditional view that the requirements of healthy aquatic ecosystems are at odds with human
activity must be altered. The challenge is to determine how society can extract the water resources
it needs while protecting the important natural complexity and adaptive capacity of aquatic
ecosystems. Therefore, an important component of the GLP is to develop a better understanding of
the linkages between terrestrial and aquatic ecosystems and how humans are altering these linkages.
This better understanding of the functions, requirements, and services of aquatic ecosystems can
help us better value and preserve ecosystem functions while simultaneously meeting human needs.

Application to Global Land Project

         The research goals of the GLP should be to increase knowledge, understanding, and
appreciation of aquatic ecosystem functions and services, as an integral part of the terrestrial
landscape. Questions to address include: 1) what are the functions, goods, and services of aquatic
ecosystems; 2) how these vary in time and space; 3) how they are affected by land use/management
decisions and climate changes; 4) how feedbacks may occur between aquatic ecosystems and the
Earth System (land, ocean, and atmosphere); and 5) how can water use be optimized for multi-
criteria decision-making (and for sustainability), simultaneously providing for humans and
ecosystems. Accordingly, five classes of key questions have been identified that explore the
importance of aquatic ecosystems in the context of the GLP.

1) Quantification of goods and services provided by aquatic ecosystems.

       Providing for the health and maintenance of aquatic ecosystems requires a thorough
understanding of the goods and services provided to humans and the global environment by the
ecosystems. Therefore, it is imperative that the GLP foster local and regional research into the
magnitude of the goods and services provided by aquatic ecosystems. Questions under this topic
may include (but not be limited to):

A) How can the scale of aquatic ecosystem monitoring and access to data be increased? Are there
other technologies (satellite) that can augment ground-based data? Can the GLP foster more open
data access?
B) How can aquatic ecosystems be better valued? Can metrics be developed to better quantify the
importance of aquatic ecosystems to humans?
C) What is the role of wetlands in greenhouse gas production? What is the scale of the methane flux
from natural wetlands and rice paddies? What is the inter-annual variability?
D) What is the role of aquatic ecosystems in the provision of fresh drinking water?
E) What is the role of permafrost in the global trace gas budget? How might climate changes impact
this flux?

2) Dynamics of aquatic ecosystems.

        The dynamics of the biogeochemistry and species interactions of aquatic ecosystems and
their vulnerability to changes in land use/management and climate are, for the most part, still not
understood. Therefore, a second set of key questions is related to better understanding the
ecosystems and their sensitivities.

A) What are the basic requirements (nutrient, water, sediment, light) for individual aquatic
ecosystems? How must these requirements vary in time and space?
B) How sensitive are these systems to human induced changes? At what time of year are human-
induced deviations from optimal most damaging?
C) What is the impact of invasive species introduction on ecosystem function and service?
D) What are thresholds of ecosystem function caused by species removal/substitution?
E) What are the dynamics of nutrient cycling in aquatic ecosystems? How important are wetlands to
total nitrogen transport in rivers?

3) Providing for all parties.

        Growing population and water demands require that resource optimization be made a
priority. The GLP should help identify the ways in which water resources can be equitably provided
for human needs and aquatic ecosystem health, and to minimize conflict between differing parties.

A) What are minimum water quantity and quality requirements for maintenance of a healthy
B) How can wetlands be restored to simultaneously maximize goods and services and minimize
negative impacts (greenhouse gas emissions, disease, farmland loss)?
C) What are the inequities between supply and demand of water?
D) Who are the relevant stakeholders that use water, how much do they use, and how much access
do they have to this resource?
E) How much is left for ecosystem functioning and if not enough, how will the lack of water affect
ecosystem functioning?
F) What are the institutions that regulate human access to water at different spatial scales, how well
suited are they, what can be done to enhance them?
G) How can conflict among stakeholders, and those between stakeholders and nature’s needs, be
reduced and resolved?

4) Quantification of land use/management impacts.

        Because of the transient nature of water, aquatic ecosystems are simultaneously connected
to both local and distant landscapes. This connectivity leads to complex sensitivities to land
use/management and climate changes. A clearer understanding of the impacts of land
use/management on ecosystem functioning, goods, and services is required.

A) What are the connections between land and water quantity (land use/management change, large
dams, channelization, changes in evapotranspiration, discharge)? How does the conversion of land
to agriculture impact discharge timing and magnitude through energy and water balance changes?
How has irrigation impacted local and regional discharge and how is this likely to change with
more intensive agriculture and changing climate?
B) What are the connections between land and water quality (salinization caused by land use and
water diversions, eutrophication, nitrogen and phosphorus loading, toxins)? How do fertilizer
application practices and crop types affect the magnitude and variability of the flux of nitrogen in
river systems and to the ocean? How are those likely to fluctuate in the future?
C) How does water management impact coastal zones (loss of land from sediment starvation and
loss of habitat, saltwater intrusion, and altered biogeochemical fluxes) by reducing water flow
D) What are the ecological consequences of inter-basin transfers (species transfer, wetlands/estuary
E) What are the consequences of disruption of connectivity in time and space (upstream
downstream, riparian)?
5) Feedbacks.

        Changes in aquatic ecosystems initially derived from land use/management changes and
climate changes can in turn have feedbacks to the human and Earth Systems. Again, because of the
role of water in connecting the Earth System (land, ocean, and atmosphere), these feedbacks can be
local or distant, immediate or delayed.

A) What are the feedbacks between agricultural land management and aquatic ecosystem health?
How do biochemical changes impact habitat diversity?
B) How does wetland destruction/restoration impact greenhouse gas production (CH4, CO2)? C)
What are the feedbacks from water management to climate (frost date change in Florida, irrigation
leading to an increase in humidity, large dams affecting lake and coastal circulation)?
D) What are feedbacks between species loss (due to invasive species, pollution, ecosystem change)
and ecosystem health?
E) How might climate-induced changes in the cryosphere (glacial and snow) impact human and
aquatic ecosystems dependent on them?
F) What are the potential feedbacks to atmosphere, infrastructure, and ecosystems of future
permafrost changes?
G) What are the feedbacks to the planetary energy budget of future changes in snow and lake ice
H) What are the feedbacks between water scarcity for human purposes and mismanagement?


         Greater understanding of the connectivity between aquatic and terrestrial ecosystems, and
the rates by which aquatic systems are being altered by land use change, greater appreciation of the
amenities provided by functional aquatic ecosystems to society by policy makers, and greater
awareness of the crisis facing both human societies and natural ecosystems as fresh water supplies
become co-opted for one purpose over another, contaminated beyond use, or altered beyond their
ability to provide ecological services.


        The aquatic ecosystems section of the GLP will directly compliment the goals of the Global
Water System Project (GWSP), which are “to catalyze interdisciplinary understanding of the role of
water in the Earth System, the unique role that humans play in the Global Water System and the
reciprocal interactions between the biogeophysical and human components of the water system of
the planet.” The unique niche of the GLP will be in providing local and regional studies for
synthesis. This emphasis on local and regional scale studies compliments GWSP who’s
“fundamental focus… is on articulating the fully global-scale dimension of water system change,
developing the necessary tools/data sets required to address this issue; at the same time the GWSP
will draw from the established literature at local, case study, and regional scales”. Therefore, the
GLP can provide the local and regional analysis and understanding of aquatic ecosystem linkages to
the Earth System on which GWSP depends.


Postel, S.L., G.C. Daily, and P.R. Ehrlich. 1996. Human appropriation of renewable fresh water.
Science, 271, 785-788.

WHO. 2000:
UNFPA. 2003: Global population and water. Access and sustainability. Populations and
development strategies. UNFPA.

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