|MadSci Network: Earth Sciences|
Joe - Rivers are important parts of healthy ecosystems and preserving them is an important job. It is a difficult one too because rivers are influenced by a very large area - their watershed. The watershed (or catchment) includes all of the area which eventually supplies water to a river. The watershed of most rivers contains all sorts of different land-uses from urban land to farms to forests. Anything that happens in the watershed can eventually have an impact on the river. Fertilizers and pesticides applied to fields can run off the surface or seem into groundwater which eventually enters the river. Large areas of "impervious surface" like pavement and roofs prevent storm water from seeping into the soil; this can cause much more rapid and frequent flooding of the river. Likewise, rivers occur in networks and impacts in small tributaries can all add up to a much larger impact on the main river. Thus, to really protect a river, you have to have to carefully protect and manage everything upstream! Over the last few decades policy work has shifted towards managing rivers at the scale of watersheds but there is still a lot of progress to be made. Of all the area in a river's catchment, the habitat nearest to the river can be critical. This riparian habitat is important to many organisms which live in or around the river. It can serve to slow the runoff of water or sediment into the river. Riparian wetlands can even remove some pollutants, like excess nitrogen, from water before it reaches the river. This is why one of the first steps in river conservation and protection is to secure and protect strips of land adjacent to the river. Another important part of conserving rivers involves recognizing their dynamic nature. Heraclitus once said that you cannot step into the same river twice - because they are always changing. Natural river systems experience a wide range of flow conditions from low flows during drought to high flows during floods. These variations in flow play important roles in affecting the structure of the river including the shape of channels and the distribution of sediment (which are in turn important for many of the organisms which live in the river). Dams are one example of an anthropogenic (human-caused) disturbance which can reduce important high flow events. There is considerable debate in the Northwestern US about what to do about dams' influence on rivers. On a smaller scale, attempts to prevent the river from naturally drifting in it's path (by installing concrete embankments or other measure) can also alter flows away from natural conditions. You might want to check the websites of the Environmental Protection Agency or US Geological Survey for more information. You can learn about the river watershed where you live at: http://www.epa.gov/surf3/ Please feel free to contact me if I can help more, Alex
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