Freshwater systems

Abstract

This chapter discusses the extent and modification of freshwater ecosystems. The chapter also assesses goods and services based on the conditions and changing capacity of water quantity, groundwater sources, and biodiversity of freshwater ecosystems. Freshwater ecosystems in rivers, lakes, and wetlands contain just a fraction of the earth's water and occupy less than 1 percent of the earth's surface. Freshwater ecosystems provide many crucial goods and services such as habitats for fish, mitigation of floods, maintenance of biodiversity, assimilation and dilution of wastes, recreational opportunities, and a transportation route for goods. Harnessed by dams, freshwater ecosystems also produce hydropower—one of the world's most important renewable energy sources. Freshwater systems, particularly wetlands, play an essential role in maintaining water quality by removing contaminants and helping to break down and disperse organic wastes. In Malawi, the freshwater catch provides about 70–75 percent of the animal protein for both urban and rural low-income families. Freshwater systems harbor a diverse and impressive array of species. Physical alteration, habitat loss and degradation, water withdrawal, over-exploitation, pollution, and introduction of non-native species contribute directly or indirectly to declines in freshwater species. The best measure of the actual condition of freshwater biodiversity is the extent to which species are threatened with extinction.