Hydrologic: Land Use Relationship to Non Point Pollution of the Big Eau Pleine River

Abstract

Nitrogen and phosphorus loading characteristics of the Big Eau Pleine River, Marathon County, Wisconsin, were investigated from a run­off study of Hamann and Noisy Creeks over a two year period (1975 and 1976). The study was initiated because the Big Eau Pleine River and Reservoir was experiencing a deteriorating water quality. Dense algae blooms and periodic fish winterkills had occurred prior to the study. To more precisely examine the affects of land use, fanning practices and hydrological behavior on nutrient loading to the Big Eau Pleine River, Hamann Creek was divided into six drainage basins, each having differenct physical characteristics. The hydrologic behavior was determined by employing the USDAHL-74 Revised Model of Watershed Hydrology developed by the Agricultural Research Service of the U.S.D.A. Hydrologic simulation showed three periods of high overland flow and resulting transport energy: snowmelt, spring rain, and fall. Basin contributions to surface flow varied by season and by watershed, but the alluvial area contributed the largest protion of the overland flow in each basin. Land use and soil types were found to significantly affect runoff volumes and total water yield. Overland flow volumes from all basins ranged from 4.11 to 6.89 inches in 1975. In 1976 overland flow ranged from 2.46 to 6.85 inches despite severe drought conditions experienced during the summer and fall. Nitrogen and phosphorus losses in 1975 averaged 3.84 lbs/ac (4.30 kg/ha) TN and .310 lbs/ac ( .347 kg/ha) TP for all basins. The majority of the nutrient loading occurred during the high runoff periods of spring rain and fall. The Major source of N and P was manure disposed during the winter months and pasture disposal during the summer. Cattle densities, frequency of cattle on streamside pasture also affected N and P discharge. Sediment loss influenced TP loading during 1975. Losses of N and P increased substantially in 1976; a result of high surface flows during the Snowmelt period. TN losses averaged 6.77 lbs/ac (7.58 kg/ha) and ranged from 4.20 lbs/ac (4.70 kg/ha) to 9.72 lbs/ac (10.89 kg/ha) TN. TP losses were also increased, but to a much lesser degree. Average P loads were 377 lbs/ac (.422 kg/ha). Manure runoff was the major contributing element to the nutrient load. Sediment and other organic sources contributed lesser amounts. Land uses were evaluated as to the impact on nutrient loads. Pasturing the streambanks increased TN and TP losses. Cultivated crops on the alluvial plain correlated with suspended solids concentrations and indicated a higher sediment load. Alfalfa fields near the stream channel apparently increased the levels of nitrate-N during spring and fall runoff periods.