Agricultural Impacts on Lake and Stream Water Quality in Grand Lake St. Marys, Western Ohio

摘要

Agricultural activities release variable products into air, soil and water ecosystems. The study was conducted to evaluate the impact of agriculture and concentrated livestock operations on stream and lake water quality in Grand Lake St. Marys watershed of north-western Ohio. Temporal water samples from the lake and the 6 feeding streams were collected bimonthly from January 2005 to May 2007, processed and measured for temperature, turbidity, pH, electrical conductivity (E_C), ammonium (NH_4~+), nitrate (NO_3~-), dissolved phosphorus (P), ultra-violet (UV) light absorption, and dissolved oxygen (DO), employing standard methods of analysis. The measured data were normalized and integrated into a simple index (WQ_(Index)) to evaluate overall water quality. Results showed that over 90% of the area in the watershed was under cropland with associated livestock operations. With a land area equal to 195 km~2 represented by the six major tributaries, the average animal density was over 240 units km~(-2). As a result, land disposal of manure from confined feedings operations and direct deposit by grazing animals contributed to non-point sources of water pollution. While (NH+4~+) and P concentration, turbidity, and UV absorption peaked during the summer, the (NO_3~-) and DO concentration in both stream and lake water was lowest in the summer. Water sampled from the Coldwater, Beaver and Prairie creeks had higher turbidity, (NH_4~+), and P than other creeks. However, DO concentration and UV absorption of water did not change significantly by the influence of streams. The WQ_(Index) peaked in both streams and lake water with greater water quality degradation in Beaver and Coldwater creek than other creeks. A significant relationship of WQ_(Index) with UV absorption and P accounted 84 to 90% of the variations in stream and lake water quality degradation. However, a strong linear relationship (r~2=0.81; p<0.01) between UV absorption and P concentration suggested a major contribution of P to the degradation of stream and lake water quality through algal blooming and associated eutrophication.