Nitrogen Contamination of Groundwater from Barnyards in the Central Sand Plain Aquifer of Wisconsin
Travis, Micheal J.
University of Wisconsin-Stevens Point, College of Natural Resources
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Nitrogen contamination of groundwater by barnyards was monitored at five study locations in the Central Sand Plain of Wisconsin. The study areas differed in size from 0.04 to 1.0 hectare. Cattle densities on these yards ranged from 10 to 300 m^2 per animal. Management of the yards' surfaces included: complete manure removal at the smallest site; high organic accumulation at the three midsize sites; and low accumulation on a vegetated surface at the largest yard. Peizometers and multilevel wells installed upgradient and downgradient of each barnyard were used to monitor groundwater movement and quality in the vicinity of the yard. Potassium proved to be an excellent indicator of animal waste influence in the shallow groundwater. Concentrations of K+ were low or undetected in upgradient water. Downgradient concentrations up to 725 mg/1 K+ were observed in upper ports of downgradient multilevel monitoring wells. Groundwater flow analyzed at one of the study sites indicated a complex system. Interaction of impermeable and permeable areas affected recharge in the farmyard altering local flow. In addition, variation in hydraulic conductivity affected rate of flow and dispersion. Vertical gradients were noted and further complicated the interpretation of contaminant flow. Three aspects of nitrogen contamination of groundwater by barnyards were noted: 1) direct infiltration within the yard; 2) runoff from the yard and infiltration to the groundwater in outlying areas; and 3) transformation of nitrogen forms within the soil/water environment of the barnyard. Groundwater nitrogen data was compared to soil data obtained within the yards (Bowen, 1987). The low use yard and the yard with regular manure removal contributed nitrate to the groundwater system by direct infiltration. The high use yards with manure accumulation restricted direct infiltration by a compacted soil/organic layer which encouraged runoff. Low density fencerows and areas surrounding these barnyards accepted this runoff and were suggested to be the most significant contributor to groundwater quality degradation in these compacted barnyard systems. Nitrate concentrations as high as 140 mg/1 NO3-N were detected in a well downgradient of one such ponding area. Denitrification of N within the groundwater was indicated at all sites by absence of 02 and detection of NO2- in the groundwater. Changes of N species within the contaminant plume indicated a dynamic chemical/ biological system established by a confined cattle facility.