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Watershed
Degradation
Given the
ecological importance of watersheds and the extent of human dependence
on the services provided by them, watershed degradation has potentially
enormous environmental and socio-economic costs. Yet efforts to
develop and use the services provided by watersheds have not been
well integrated with efforts to protect and manage watershed ecosystems.
For example, vital economic resources, such as water, are usually
managed with policies, institutions, and practices that are disconnected
from, or even in direct conflict with, those designed to protect
forests, wetlands, and other habitats from which the water comes.
Moreover, watersheds face growing stress from rapid economic development,
increasing human populations, and often wasteful use of natural
resources. The result is to put watersheds at increasing risk
of degradation and hence to jeopardize water supplies and other
vital ecosystem services beneficial to human societies -- services
that can be extremely costly to replace.
The lack
of connection between economic development policies and sustainable
management policies stems in part from the failure to consider
watersheds as integral social-ecological units. What happens upstream
in a watershed, for example, can have a profound impact on conditions
downstream. Removal of forests or other vegetation can sharply
reduce water retention and increase erosion, resulting in reduced
water availability in dry seasons and more siltation downstream.
Dams are often a barrier to migratory fish and can degrade fisheries,
disrupt aquatic ecosystems, and prevent the renewal of soil by
flooding and siltation, reducing food supplies.
Pollution
from human activities can degrade water quality and even make
water unusable for human needs, as well as threatening other species.
Excessive withdrawal of water can damage or even destroy aquatic
ecosystems and surrounding regions. Changes in river flow and
sediment and pollutant loadings resulting from activities far
inland can degrade downstream coastal ecosystems, such as mangroves
and coral reefs. Sometimes downstream activities can even affect
upstream conditions, as when alien species introduced into watersheds
migrate upstream and threaten fisheries or economic activities.
These linkages illustrate how watershed development can have unplanned
and inadvertent effects -- sometimes with devastating consequences
-- and underscore the importance of managing watersheds as integral
social-ecological units and planning development with the entire
watershed in mind.
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