Inland aquatic ecosystems
Inland aquatic ecosystems include a variety of natural (streams, rivers, floodplains, lakes, swamps, etc.) and manmade (reservoirs, rice fields, irrigation canals, etc.) inland water bodies. In spite of only covering about one percent of the total land surface inland waters are home to around 100 000 aquatic species, including for instance 10 000, or 40 percent, of all fish species.
Production cycles in inland aquatic ecosystems closely track seasonal changes in temperature and precipitation in the surrounding terrestrial environment which create a dynamic environment, where the availability of aquatic habitats are constantly changing and where nutrients are released in pulses; for aquatic organisms this divides the year into a period of intense production and a time of high mortality. The close linkages with the terrestrial ecosystems also imply that inland aquatic ecosystems are strongly affected by land use practices and are vulnerable to human activities. Since water is needed for a range of purposes, human settlements have always been located near inland water bodies.
These water bodies have, however, provided much more than just water, for example food, medicine and building materials are easily available because of the ubiquitous presence of living aquatic resources. But water is increasingly needed for a range of competing purposes and because people comprise an integral part of these ecosystems, many human activities have a direct or indirect impact on inland aquatic ecosystems which are under much more pressure from these activities than their marine counterparts. Fish and other living aquatic resources from inland waters nevertheless continue to constitute an essential role in people’s livelihoods on rural areas in many parts of the world, especially in developing countries.
However, human activities have also created new aquatic habitats such as irrigation canals, rice fields and reservoirs, which to varying degrees supplement the services provided from the natural ecosystems.
Linkages between inland and marine ecosystems
Marine and inland aquatic ecosystems are interconnected. Some inland aquatic ecosystems are linked to the ocean ecosystems which they affect for example through nutrient inflows that causes the high productivity in many coastal fisheries, but also negatively by pollutants carried by the water. In addition, a number of marine fishery resources (anadromous and catadromous species, salmons, eels, sturgeons and shrimps) need inland water ecosystems including estuaries and lagoons to complete their life cycles.
In developed countries, industrialization has lead to increased pressure on inland waters and aquatic habitats degraded with negative consequences for the associated ecosystems. Many developing countries are now following the same path. Drainage, flood protection and extraction of water have lead to the disappearance and fragmentation of aquatic habitats. It is likely that around 50 percent of the inland water area (excluding large lakes) has been lost globally. The reduction in area, combined with pollution and eutrophication, have caused the disappearance of species and changed the species composition in many places. The biodiversity of inland waters now appears to be in a worse condition than that of any other ecosystem. Land-based sources of pollution and degradation are also among the main sources of negative changes in the coastal zone. Excess fertilizers and livestock wastes in the runoff from farmland have caused eutrophication and harmful algal blooms. Deforestation in coastal mountains is a major source of excess sedimentation in the coastal areas, affecting coral reefs and seagrass beds.
However, the situation is gradually changing and many developed countries are trying to reverse the long standing adverse impacts and the international community and FAO with the Code of Conduct for Responsible Fisheries have acknowledged the value of understanding ecosystem processes, the bio-physical-chemical qualities of aquatic habitats, nutrient cycling and the interactions of non-target species in maintaining the productivity of fisheries.