Freshwater ecosystems are a subset of Earth's aquatic ecosystems that include the biological communities inhabiting freshwater waterbodies such as lakes, ponds, rivers, streams, springs, bogs, and wetlands.[1] They can be contrasted with marine ecosystems, which have a much higher salinity. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation.
There are three basic types of freshwater ecosystems: lentic (slow moving water, including pools, ponds, and lakes), lotic (faster moving streams, for example creeks and rivers) and wetlands (semi-aquatic areas where the soil is saturated or inundated for at least part of the time).[2][1] Freshwater ecosystems contain 41% of the world's known fish species.[3]
Freshwater ecosystems have undergone substantial transformations over time, which has impacted various characteristics of the ecosystems.[4] Original attempts to understand and monitor freshwater ecosystems were spurred on by threats to human health (for example cholera outbreaks due to sewage contamination).[5] Early monitoring focused on chemical indicators, then bacteria, and finally algae, fungi and protozoa. A new type of monitoring involves quantifying differing groups of organisms (macroinvertebrates, macrophytes and fish) and measuring the stream conditions associated with them.[6]
Threats to freshwater biodiversity include overexploitation, water pollution, flow modification, destruction or degradation of habitat, and invasion by exotic species.[7] Climate change is putting further pressure on these ecosystems because water temperatures have already increased by about 1 °C, and there have been significant declines in ice coverage which have caused subsequent ecosystem stresses.[8]
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