2010 Annual Report
1a.Objectives (from AD-416)
Objective 1: Determine dominant environmental parameters and processes involved in the fate and transport of manure-borne coliform bacteria at field and watershed scales in a hydrological context. Develop predictive models of the fate and transport of manure-borne coliform bacteria at field and watershed scales.
Objective 2: Determine prevalence and diversity of pathogenic E. coli and Salmonella in watersheds with different land uses (urban/suburban, forested, animal agriculture) in the mid-Atlantic area. Measure airborne dissemination and survival of pathogenic bacteria and endotoxin from manures, compost, and wastewater treatment plant sludge. Evaluate methods combining immunological and genetic techniques for detection of water-borne pathogenic E. coli.
1b.Approach (from AD-416)
An integrated laboratory research, field research at hillslope and watershed scales, and mathematical modeling will be used. The experimental research will include evaluating effect of manure particulates on transport of coliform microorganisms in soil, relating partitioning of coliform microorganisms between sediment and runoff to soil texture, manure properties and flow rate, establishing dependencies of coliform release rates from manure on rain intensity, manure type and composition, and manure application method, evaluating predictive efficiency of laboratory data on manure-borne coliform survival data for the field conditions, assessing phosphorus as a tracer of manure-borne transport in runoff; determining effect of background coliform populations and field manure application on coliform concentrations in runoff from fields and in a perennial creek in a riparian zone. Modeling research will include determining dominant mechanisms of manure-borne coliform transport at pedon, field, and watershed scales; develop and test models to simulate those mechanisms, performing uncertainty analysis to evaluate the reliability of coliform transport model predictions given available data on variation in input parameters, transforming model computers codes to make them compatible to existing and under-development user-friendly decision support tools.
To assess the effect of streambed E.coli reservoirs on surface water quality, we conducted field studies simulating high stream flow events (a large volume of water was introduced directly into the stream). These data reflect exclusively the processes of E. coli suspension during high flow (heavy rainfall events) and subsequent resettling as flow subsides. We observed that the release of E. coli from a single “hot spot” in the bottom sediment affected water quality far downstream. Results of this work will contribute to the development and validation of models of water quality to predict suitability for irrigation purposes.
We conducted studies to elucidate factors of E. coli survival in bottom sediments. Inactivation rates were temperature dependent; however, the sensitivity of inactivation rates to temperature was discovered to be dependent on sediment properties. These results will contribute to development of a model of E. coli survival in streambed sediments, the absence of which hampers predictions of water quality for irrigation purposes.
The efficiency of vegetated filter strips (VFS) was evaluated in experiments in which soil moisture status was controlled in plots with different vegetation conditions. The results of these studies indicate that the efficiency of VFS is substantially reduced when the soil column is saturated, due to low infiltration rates. These results will contribute to design and evaluation of VFS for the purpose of retention of manure-borne microorganisms.
Experiments were conducted to evaluate the uncertainty in predictions of manure-borne bacteria leaving manured fields in runoff. The variability of microorganism concentrations in manure (up to 6 orders of magnitude) was the dominant factor of uncertainty in predictions of microorganism concentrations at the edge of the field. Using the average concentration of fecal coliforms led to substantial overestimation of the bacteria leaving the field in runoff. These results are important for improving data collection for predicting pathogen fluxes to surface water sources.
To improve the predictability of transport of manure-borne E. coli to surface waters, we investigated the possibility of using data from public sources rather than field-specific information (which is frequently very hard to obtain). Our pedotransfer multimodeling technology was applied to convert public data on soils to input parameters for the model STWIR, developed to simulate overland transport of the manure-borne E. coli. These results will contribute to the dissemination of the STWIR model as the comprehensive tool to access the effect of manure application and grazing on the quality of surface water sources.
The database on microorganism inactivation in environmental media (DIMEM) was outfitted with the Graphic User Interface which was designed and implemented in Visual Basic. This improved the accessibility of the database for users, and simplified the database that currently contains 600 experimental datasets. The testing of the beta version is currently being conducted. These results will contribute to improvements in risk assessment and mitigation of manure-borne pathogens.
Microbiological water quality in streams and reservoirs can be significantly affected by the E. coli hot spots in bottom sediments. The concentrations of pathogens and indicator bacteria (E. coli) in surface waters are dependent on several processes, including transport to waters as well as within waters. Previous research has shown that E. coli runoff from fields accounts for a relatively small percentage of E. coli measured in the water column after rainfall events. Consequently, ARS researchers in Beltsville, MD, conducted an artificial high flow event in a stream by introducing a large volume of water directly into the stream (simulating a heavy rainfall event) in order to quantify in-stream transport. The suspension of E. coli from bottom sediments into the water-column and subsequent resettling as E. coli were transported downstream were monitored. In addition, a model of bacterial suspension and transport was developed applicable to small creeks/streams. Both measurements and modeling showed that the release of E. coli from a single “hot spot” in the bottom sediment affected microbiological water quality far downstream. These results are important in the evaluation of the role of bottom sediments in their impact on microbiological water quality degradation, which can be mistakenly attributed to agricultural practices. This information is useful for growers and regulators relying on water quality monitoring in identifying important environmental microorganism reservoirs that affects microbiological water quality for recreational and irrigation purposes.
Risk of manure-borne E. coli reaching surface water sources is evaluated. ARS researchers in Beltsville, MD, used the model STWIR to evaluate how the natural variation in soil, vegetation, weather, and manure properties affects variations in E. coli transport from fields and through vegetated filter strips (VFS). VFS are widely used to mitigate the transport of contaminants from fields to surface waters; however the efficacy of VFS in mitigating microbial contaminations is poorly understood, in large measure due to lack of information regarding the numbers of E. coli present in runoff. Our studies demonstrated that the dominant factor contributing to uncertainty in model predictions was the extreme variability in spatial distribution of bacteria concentrations in the applied manure and subsequently on the field; the variability in fecal coliform concentrations in manure was up to 6 orders of magnitude. This research emphasizes the need for characterization of pathogen and indicator concentrations in manures, and concludes that multiple placements of manure have to be simulated to quantify the uncertainty of manure-borne bacteria transport. This information is useful for policy makers and researchers in indicating how margins of safety can be used for risk assessment related to pathogen and indicator delivery from manured field and pastures to streams and reservoirs.
Guber, A.K., Pachepsky, Y.A., Shelton, D.R., Yu, O. 2009. Fecal Coliform Interaction with Soil Aggregates: Effect of Water Content and Bovine Manure Application. Soil Science. 174(10):543-548.
Mikayilsoy, F., Pachepsky, Y.A. 2010. Average concentration of soluble salts in leached soils inferred from the convective-dispersive equation. Irrigation Science. 28(5):431-434.
Garzio-Hadzick, A.M., Shelton, D.R., Hill, R., Pachepsky, Y.A., Guber, A.K., Rowland, R.A. 2010. Survival of manure-borne E. coli in streambed sediment: effects of temperature and sediment properties. Water Research. 44:2753-2762
Kim, J., Pachepsky, Y.A., Shelton, D.R., Coppock, C.R. 2010. Effect of streambed bacteria release on E. Coli concentrations: Monitoring and Modeling with the Modified Soil and Water Assessment Tool (SWAT). Ecological Modeling. 221:1592:1604.