Ecological Implications

Streamflow in the Mississippi River has increased about 30% during 1979-83 as a result of increased precipitation. The increase in nitrate flux to the Gulf is partially attributed to this increased precipitation, which leads to increased runoff and drainage of agricultural fields. Seasonal variance of precipitation, along with episodic events, such as the 1993 flood can cause great fluctuations in levels of runoff into the water and are directly associated with increases in the nutrient fluxes of rivers and streams. For instance, in years of low precipitation, nitrogen can be stored in soils and ground water systems, such as drain tiles underlying croplands. This store can then be released over a short period of time when precipitation returns and leaches the soil of its nutrients. Contrastingly, high precipitation causes higher amounts of nutrient leaching from the soil over long periods of time causing chronic exposure of waters to high nutrient influx. Combined with tilled soils that are easily erodable, precipitation becomes a vehicle for nutrient influx into the Gulf.