The retention of water in man-made and natural lakes creates an area wherein sediment and nutrients drop out of river water before it continues on its path. The relatively stagnant water of lakes is characteristically much warmer than running river water. lake The combination of warm water and nutrient deposition is the primary causal factor of unsightly algal blooms. As time progresses, sedimentation increases, depth decreases, and the lake environment grows warmer still. The algal blooms cause increases in algal predators and detritovores (organisms that break down dead organic material). In extreme cases, the amplification of these populations results in low levels of dissolved oxygen in the water. Possible consequences of low dissolved oxygen levels include fish kills. Native fish inhabitation is also impacted by the changes associated with warmer temperatures and habitat fragmentation (dams).
Much of the origin of poor lake water quality is from the contributing watershed. The eroded sediments and nutrients generated by upstream sources are washed into the river and trapped in the lake causing decreases in depth and turbidity. Few substantial efforts have been made to curb such pollution. In 1977, the Federal Water Pollution Control Act (FWPCA) was substantially amended and renamed the Clean Water Act (CWA). The 1972 and 1977 amendments implemented an extensive permit system that focused on control of pollutants from individual sources. While this "end of the pipeline" method has met with some success, it noticeably left the control of pollutants from runoff (non-point source pollution) residing in the States or other authorities. Without upstream controls in place, downstream water quality has deteriorated and management attempts have been transient in nature.
Wetlands serve as a source of groundwater recharge and discharge, flood storage, erosion and shoreline anchoring, sediment trapping, food chain support, and nutrient retention and removal. One of the most important hydrologic functions of wetland is this provision of water retention and prevention of flooding and sedimentation. Studies have shown that increased proportions of wetlands in a watershed reduce flood flows and improve water quality downstream (Johnston, Detenbeck, and Niemi 1990). Given the cost of dredging, I wonder if filling those wetlands and farming to the edge of the riverbank really made money?
Cristen, algae are protists and fish are vertebrates, and why are you using environmental law acronyms?
I know algae are protists and I know that this is the Native Plant Society Newsletter. Remember Clements' interactive theory of ecology! Disturbance can have all kinds of effects throughout an ecosystem as evidenced by the prominence of invasive species in highly disturbed areas. Minimization of disturbance via control of non-point source pollution, reestablishment of wetland zones, and establishment of buffer strips around lakeshores and river edges can work wonders in the preservation and restoration of native species. That's why this newsletter is about watersheds.