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Abstract
Agricultural filter strips are commonly used to treat runoff from agricultural farmstead areas. Many filter strips have been assessed in terms of surface water quality impacts but have failed to determine the fate of pollutants once they have infiltrated the soil subsurface. Two side-by-side filter strips plots were installed to assess the performance of and determine the fate of contaminants in a filter strip system. One of the two plots also contained a pretreatment system to facilitate nitrogen removal in an attempt to reduce nitrate leaching. Both plots were lined with an impermeable membrane to collect subsurface leachate as well as surface runoff. A mass balance could then be determined for these filter strip systems to assess the fate of nutrients and the ability of a low cost pretreatment system to reduce nitrate leaching.
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Why Is It Important to Prevent Runoff from Silage Piles from Reaching Water?
Silage runoff, or the flow of surface excess water over an area containing silage or silage leachate, contains nutrients harmful to watersheds. A filter-strip, a long narrow buffer strip used in agriculture as a BMP, could be used to reduce nutrient concentrations within silage runoff. A study that investigates design storm loading and seasonal operation could benefit producers and their surrounding watershed. A pre-treatment design consisting of an aerobic and anaerobic section, is also analyzed to quantify improvements in pollutant reduction.
What Did We Do?
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Two experimental filter-strips, one control and one pre-treatment design, were applied with silage runoff at volumes and rates corresponding to a 25 year – 24 hour and a 2 year – 24 hour design storm. Design storm rates and volumes were determined from the runoff modeled from a 1:1 dairy bunker to filter strip area. Three runs of each design storm were accomplished throughout the months of October, November, and early December 2012.
What Have We Learned?
The pre-treatment filter strip design distributed higher BOD5 reduction however, nitrite concentrations increased in the effluent. Application in November and December had lower infiltration and changes in ammonia reduction were illustrated.
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Future Plans
Applications in the spring and summer will determine further seasonal variation. Expanding design storms applied will help determine prescriptive loading and aid in modeling.
Authors
Michael Holly, Master’s Candidate Biological System Engineering, University of Wisconsin – Madison, maholly@wisc.edu
Dr. Rebecca Larson, Assistant Professor and Extension Specialist, University of Wisconsin – Madison
Acknowledgements
Zach Zopp, Lab and Field Tech
Shayne Havlovitz, Undergraduate Research Assistant
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