- water quality;
- water quantity;
- flooding regime; and,
The state of freshwater ecosystems can be assessed according to the current output and quality of the good or service currently produced by the ecosystem compared with the output and quality of 20 to 30 years ago. According to the World Resources Institute, freshwaters now rate poor for water quality, fair for water quantity and bad for biodiversity.
Trends in freshwater ecosystems can be viewed in terms of the underlying biological ability of the ecosystem to continue to provide a specific good or service. In this regard, water quality has a mixed trend, and water quantity and biodiversity are on decreasing trends and flooding regimes are for many river systems greatly modified.
The state of inland aquatic ecosystems is very much reflected in the condition of upstream terrestrial systems located in the same watershed or basin. For instance, soil degradation causes soil erosion that, in turn, increases sediment loads and reduces biological production in lakes and rivers.
Outlook and trend
The general situation and near-future outlook of terrestrial ecosystems from an inland fisheries perspective is not encouraging. FAO's Inland Water Resources and Aquaculture Service points out that biodiversity loss and habitat fragmentation, land degradation, and forest loss and degradation are among the salient problems of terrestrial systems.
Examples of negative conditions and trends for specific aquatic ecosystems include:
- half the world's wetlands are estimated to have been lost during the twentieth century as land was converted to agriculture and urban use or filled to combat diseases such as malaria.
- the number of large dams has increased sevenfold since the 1950s and now impound 14 percent of the world's runoff.