Quality analyses of surface runoff from agricultural lands

Soil erosion by water has an adverse effect on everyone. Users of water from receiving streams or reservoirs often suffer loss of unpolluted water as a result of turbidity and sediment. Farmers suffer loss of topsoil, loss of natural and applied fertility, and loss of income. The purpose of this study was to establish a relationship between the soil erosion process and selected parameters of water quality. The study was conducted on three watersheds at the Milan Field Station and two at the Middle Tennessee Agricultural Experiment Station near Spring Hill. Runoff samples were collected from each watershed by an automatic pumping sampler and analyzed for sediment concentration, total suspended matter, and turbidity. Work was done to develop a relationship between sediment concentration and selected hydrologic parameters. Sediment data were developed for runoff-producing rainstorms occurring on each watershed. Linear regressions produced a good relationship between sediment weight and the kinetic energy associated with rainstorms. Using sediment as the dependent variable and the rainfall-erosion index as the independent variable, an empirical sediment prediction equation was developed for three of the five watersheds. Using cropping-management and soil-erodibility factors, a single prediction equation applicable to all five watersheds was formed. The equation tested favorably with data from two test watersheds as well as with data derived from the universal soil-loss equation developed by Wischmeier and Smith. Sediment concentration, total suspended matter, and turbidity were related to various conditions of rainfall, runoff, and land use. Average monthly values of rainfall maximum 30-minute intensity, peak runoff rate, turbidity, total suspended matter, and sediment concen-tration were compiled from one watershed at Milan. The data were analyzed for trends over a period of one year. A poor relationship was found between the water quality parameters and rainfall-runoff values during the growing season. However, the analysis indicated a good relationship for the dormant season. Concentrations of the selected water quality parameters reached maximum values during months when maximum tillage and minimum vegetative cover were prevalent.