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, (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
Recent studies have shown that stream bottom sediments can harbor large numbers of E. coli. During rainfall events, these bottom sediments are suspended, resulting in high E. coli concentrations in the water. Experiments were conducted to simulate runoff of dilute manure into sediments and the subsequent growth and survival of E. coli strains. A dilute dairy manure slurry containing fresh E. coli was added to sediments with different textures, organic matter contents, and indigenous E. coli concentrations, and incubated in chambers with flowing creek water at 4ºC, 14ºC, and 24ºC. The highest die-off rates were observed in sandy sediments with low organic carbon and low indigenous E. coli concentrations, while the lowest die-off rates were observed in silty sediments with high organic carbon content and high indigenous E. coli concentrations. In another series of experiments, methods of E. coli extraction from sediments were compared. The progress of the work has been monitored by monthly meetings with the UMD counterparts, and weekly group meetings. Results are relevant for research scientists investigating the dynamics of water-borne bacteria and to regulatory agencies tasked with minimizing surface water contamination.