Freshwater ecosystem

Freshwater ecosystems are a subset of the aquatic ecosystems of Earth that include the biological communities living in freshwater bodies such as lakes, ponds, rivers, streams, springs, bogs and wetlands. They contrast with marine ecosystems, which have much higher salinity, and can be classified by temperature, light penetration, nutrients and vegetation. There are three basic types: lentic systems of slow moving water, lotic systems of faster moving streams and rivers, and wetlands where the soil is saturated or inundated for at least part of the time. Freshwater ecosystems contain about 41 percent of the world known fish species. Threats to their biodiversity include overexploitation, pollution, flow modification, habitat loss and invasive species, and the Living Planet Index recorded an 83 percent decline in freshwater vertebrate populations between 1970 and 2014.