Transport and Fate of Nutrients and Indicator Microorganisms at a Dairy Lagoon Water Application Site: An Assessment of Nutrient Management Plans

摘要

The Environmental Protection Agency (EPA) currently requires that application of Concentrated Animal Feeding Operation (CAFO) wastes to agricultural fields follow an approved Nutrient Management Plan (NMP). The tacit assumption is that a well designed and executed NMP ensures that all lagoon water contaminants (nutrients and pathogens) are retained or taken up in the root zone, so that groundwater is inherently protected. Recent research by the EPA, however, has demonstrated that land application of CAFO lagoon water can cause nitrate contamination of groundwater at significant depths in short time frames. The research outlined in this report was designed to test the assumption that a well designed and executed NMP is protective of groundwater from nutrients, salts, and indicator microorganisms, and to address potential weaknesses in the land application design and operation processes of NMPs. The report is divided into seven chapters. Chapter 1 provides a detailed review of the literature examining the reuse of CAFO wastewater on agricultural fields, with special emphasis on nutrients and pathogens. A dairy farm in San Jacinto, California, was selected for our NMP research experiments. Chapter 2 provides a description of our field site and extensive experiments that were conducted to characterize the flow and transport properties at this site. Chapter 3 provides a detailed description of the NMP implemented at this site and results pertaining to the fate of nutrients and salts. Chapter 4 describes field and laboratory research that was conducted to study the fate of indicator microorganisms under NMP conditions. Many gaps still exist with regard to our understanding of microorganism transport and retention in the field. Laboratory experiments and mathematical model development were therefore initiated to overcome some of these limitations. Chapter 5 outlines results from laboratory studies that examined the coupled effects of pore structure, solution chemistry, and water velocity on colloid retention in saturated and unsaturated porous media, whereas Chapter 6 describes the development and application of the mathematical models for colloid transport and retention. Chapter 7 provides a summary of the research, and the main conclusions and recommendations.