In addition, smaller animals that live and feed along this biologically vital corridor may include birds (like the ring-necked pheasant, grouse, geese, falcons, great blue herons, hummingbirds and warblers), small mammals (such as longtail weasel and striped skunk), reptiles (garter snake and the western painted turtle), and amphibians (red-legged frog and the Pacific giant salamander). The flora and fauna often include many threatened, endangered, or sensitive species, among which could be the bald eagle, peregrine falcon, and kit fox (The Columbia River Basin watershed and its ecosystems 2005).
The plant life along the river can also has an effect on the health of the species living in the river by maintaining the health of the river by influencing the amount and kind of sediment in the river. The vegetation along the side of the river achieves this by anchoring soil, catching silt, filtering out pollutants, and absorbing nitrogen and phosphorus. This vegetation also provides shade to cool the water and so makes a habitat for insects and their predators (The Columbia River Basin watershed and its ecosystems 2005).
When there is too much sedimentation, which may occur when vegetation along riverbanks is removed by flooding or any other means, the river can become obscured. This occurs as sediment washes back into the water to cause turbidity, meaning that the sediment is stirred up and suspended in water. A river in this condition can impair the respiration of fish or other aquatic organisms. Such conditions can also cause sediment to cover gravel used for fish-spawning, raise the temperature of the water, and bury submerged plants (The Columbia River Basin watershed and its ecosystems 2005). This is the situation along much of the Snake River, some of it caused or exacerbated by the damming of the river. However, it is not clear if breaching the dams, as has been suggested, would be sufficient to alter the situation significantly given that breaching the dams would change the sedimentation but perhaps add to the turbidity.
Changes to the River
Many of the hydroelectric projects along the river alter the balance and can contribute to the sedimentation process. It is really the dams built for this purpose that cause the problem, and this includes dams built for other reasons, of which there are many. Specific ecosystem impacts are possible and are influenced by several variables, as follows:
the size and flow rate of the river or tributary where the project is located, the climatic and habitat conditions that are current, the type, size, design, and operation of the project, and whether cumulative impacts occur because the project is located upstream or downstream of other projects.
Dams create reservoirs or lakes, and these can significantly slow the rate at which water moves downstream. Because surface temperatures tend to become warmer as the slower moving or "slack," water absorbs heat from the sun, this can affect the nearby ecosystem. At the same time, the colder water sinks to the bottom because it has a higher density, and this in turn causes a layering effect called stratification, with the bottom layer the coldest and the top layer the warmest. There is also an ecosystem effect because the colder water that sinks toward the bottom contains reduced oxygen levels, and when water is released from the colder, oxygen-depleted depths, downstream habitat conditions change because of the reduced oxygen level in the water (How a hydroelectric project can affect a river 2005).
A related problem is cased by the accumulation of sediments, which are fine organic and inorganic materials that are typically suspended in the water but that can collect behind a dam because the dam itself is a physical barrier. Man-made and natural erosion of lands adjacent to a reservoir may cause sediment build-up behind a dam. The ecosystem can then be affected by the fact that 1) downstream habitat conditions can decline because these sediments no longer provide important organic and inorganic nutrients; and 2) because where sediment builds up behind a dam, "nutrient loading" can cause the supply of oxygen to become depleted because more nutrients are now available so that more organisms populate the area to consume the nutrients, using more oxygen. Gravel can be trapped behind a dam in the same way as sediment, and this can affect the ecosystem if there is a movement of gravel downstream (How a hydroelectric project can affect a river 2005).
According to a study conducted in 1991 by the U.S. Geological Survey, the water and sediment in the Snake River contains contaminants, found in streambed sediment and aquatic biota tissue. In 1992, fourteen sites in the upper Snake River Basin in Idaho and western Wyoming were analyzed, and mercury was identified as a contaminant in aquatic biota, representing contamination from natural or anthropogenic sources. Mercury enters the system from natural sources, including through the weathering of minerals and rocks. It also comes from human activities associated with mining,
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