Ecosystem services
Ecosystems provide humanity with a broad range of fundamental
market and non-market benefits. These benefits,
known as ecosystem services, include provisioning services
such as food, water, and fiber; regulating services such as
wastewater treatment; cultural services that include recreation
and aesthetic and spiritual benefits; and supporting
services such as photosynthesis and nutrient cycling (MA
2005b). One influential study estimated the global value of
ecosystem services at roughly double the gross national
product of the global economy (Costanza et al. 1997).
The Millennium Ecosystem Assessment (2005a) found that
the total economic value of unconverted wetlands was
often greater than that of converted wetlands. The greatest
single service freshwater ecosystems provide – marshes
in particular – is water purification and the assimilation
of wastes, valued at US$ 400 billion (2008$) worldwide
(Costanza et al. 1997). For example, Uganda’s Nakivubo
swamp bestows an estimated US$ 363 million worth of
wastewater treatment services annually to the citizens of
Kampala (UN WWAP 2009).
People have long relied on these natural processes to clean
water, dumping agricultural, municipal, and industrial wastes
into freshwater ecosystems for hundreds and thousands of
years. Often, however, the magnitude and toxicity of these
wastes overwhelms the capacity and resilience of such
ecosystems, degrading water quality locally and regionally.
These degradations manifest themselves in impaired amenity