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:
The research included experiments and data analysis to establish survival and release parameters for E. coli deposited with manure. Rainfall simulation experiments were performed at plots with land-applied bovine manure on different times after application. Samples of runoff, soil, and manure were collected and analyzed. All experiments were performed with participation of USDA employees. We also acquired data of analogous experiments from New Zealand, Virginia, Nebraska, and Tennessee. We developed the model of temperature effect on E. coli survival in manure and tested the validity of this model with above experimental data. The preliminary results show that the model is valid after the E. coli die-off begins to dominate growth of the organism. More work is needed to understand and predict the initial E. coli growth phase that may increase the E. coli concentration in manure up to two orders of magnitude, and therefore can affect the accuracy of the E. coli load estimates which are commonly used in microbial water quality forecasts for surface waters. Consecutive E. coli concentrations in runoff were analyzed to evaluate three models of E. coli release kinetics. The preliminary results show that the E. coli concentrations in runoff do not change much during one hour of intensive rainfall. This is a critical observation indicating the need in revision of the exponential release model that is currently used to evaluate manure management policies and practices.