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Title: Fate of Indicator Microorganisms Under Nutrient Management Plan Conditions

item Bradford, Scott

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2008
Publication Date: 6/23/2009
Citation: Bradford, S.A., Segal, E. 2009. Fate of Indicator Microorganisms Under Nutrient Management Plan Conditions. Journal of Environmental Quality. 38:1728-1738.

Interpretive Summary: The USEPA currently requires that application of wastewater and manure to agricultural fields follow an approved Nutrient Management Plan (NMP). An implicit assumption of NMPs is that disease causing microorganisms in animal wastes will be retained and die-off in the root zone. This manuscript reports on results from field and laboratory experiments that were designed to test this hypothesis. Results support this hypothesis and indicated that indicator microorganisms were retained and died-off in the root zone of our NMP site. This information was used to develop management recommendations for improved NMP performance to protect groundwater from microorganism contamination, and should be use to farmers and regulators who are concerned with maximizing crop productivity and protecting groundwater under NMP conditions.

Technical Abstract: Nutrient management plans (NMPs) for application of wastewater from concentration animal feeding operations are designed to meet crop water and nutrient requirements, but implicitly assume that pathogenic microorganisms in the wastewater will be retained and die-off in the root zone. A NMP was implemented on a small-scale field plot to test this assumption by monitoring the fate of several fecal indicator microorganisms (Enterococcus, fecal coliforms, somatic coliphage, and total E. coli). When well-water and wastewater were applied to meet measured evapotranspiration, little advective transport of the indicator microorganisms occurred below the root zone and the remaining microorganisms rapidly died-off (within 1 month). Additional experiments were conducted in the laboratory to better quantify microorganism transport and survival in the field soil. Batch survival experiments revealed much more rapid die-off rates for the bacterial indicator microorganisms in native than in sterilized soil, suggesting that biotic factors controlled survival. Saturated column experiments with packed field soil, demonstrated much greater transport potential for somatic coliphage than bacterial indicators (Enterococcus and total E. coli) and that the retention rates for the indicator microorganisms were not log-linear with depth. A worst case transport scenario of ponded infiltration on a large undistributed soil column from the field was also initiated and indicator microorganisms were not detected in the column outflow or in the soil at a depth of 65 cm. All of these observations support the hypothesis that a well-designed and implemented NMP at this site will protect groundwater supplies from microorganism contamination.