1a. Objectives (from AD-416):
To develop comprehensive experimental data sets for testing and improving manure-borne pathogen fate and transport models suitable for nutrient management planning and environmental risk assessment.
1b. Approach (from AD-416):
Field experiments will be performed at the OPE3 field site and the Patuxent runoff site to: (a) evaluate the effect of the buffer strip status on its retention efficiency, (b) develop model parameters and evaluate model performance, and (c) evaluate the phosphorus in runoff as a natural indicator of E. coli. The edge-of-the-field conditions will be simulated at the Patuxent site where the manure suspensions will be maniflolded to the simulated vegetated buffer strips with varying soil type, initial soil moisture content, vegetation status, and slope. The rainfall will be simulated to cause runoff that will be collected at the bottom of the strips. Concentrations of E. coli and P will be measured in the runoff transport. Appropriate complementary soil, hydrologic, and microbial measurements will be carried out. The field-scale transport will be studied at the OPE3 site after manure application in accordance with Maryland agronomic rates. E. coli contents will be monitored in manure, in soil, in runoff using automated samplers, in groundwater, and in the first order creek separated from the field with a riparian zone. All experiments will be performed with participation of USDA employees. Cooperator will participate in modeling, data analysis, and publication of results.
3. Progress Report:
This research included experiments and data analysis to establish survival and release parameters for E. coli deposited with manure. Rainfall simulation experiments were performed in plots with land-applied bovine manure at different times after application. Samples of runoff, soil, and manure were collected and analyzed. Consecutive E. coli concentrations in runoff were analyzed to evaluate three models of E. coli release kinetics. Preliminary results show that the E. coli concentrations in runoff did not change much during one hour of intensive rainfall. This is a critical observation indicating the need for revision of the exponential release model that has been developed with data on farmyard slurry application, but is currently used with farmyard manures to evaluate manure management policies and practices. We have also continued to populate the unique database DIMEM on inactivation of microorganisms, and compare the temperature dependencies of inactivation rates for E. coli, Salmonella and Enterococci in surface waters used for irrigation and recreation. Dependencies of the inactivation of the three organisms on temperature displayed similar response patterns. However, site-specific variability in the data was observed which illustrates the uncertainty encountered in estimating the risk of microbial contamination in surface waters. This study will be extended to provide additional guidance on the calibration of indicator fate and transport modeling systems that are used to support environmental management decisions regarding the use of surface water sources in agriculture, aquaculture, and recreation.