A plot scale study was conducted to determine bacterial transport in runoff from cropland treated with poultry litter and dairy manure applied at phosphorus (P) agronomic rates. Treatments included surface application of dairy manure, surface application of poultry litter, incorporation of dairy manure and control. A rainfall simulator was used to induce runoff 1 and 2 days after manure application. Runoff was analyzed to determine the concentration of indicator bacteria-fecal coliform, Escherichia coli, and Enterococcus. Observed edge-of-field bacterial concentrations were 10 2 to 10 5 times higher than Virginia's in-stream bacteria criteria for primary contact recreation waters. No significant treatment effects were observed on edge-of-field bacteria concentration or yield. Results suggest that the manure application based on agronomic P rates may yield significant bacterial loading to downstream waterbodies if rainfall occurs soon after manure application. This research underscores the need for BMPs that reduce runoff volumes and filter pollutants associated with animal manures.

A field-scale plot study was conducted at Virginia Tech's Prices Fork Research Farm, to evaluate the transport of nutrients in runoff from manure and fertilizer applied at P-based agronomic rates to cropland planted to corn. Simulated rainfall events representing 2-to 10-year storms in southwest Virginia, occurring 1 and 2 days following manure and fertilizer application were used to generate runoff. Plots were treated with surface applied poultry litter, surface applied and incorporated dairy manure, incorporated inorganic fertilizer, and no fertilizer (control). Application rates were based upon agronomic phosphorus (P) requirements of corn. The concentration of total suspended solids and nutrients decreased from the first to the second simulated rainfall event; however, the edgeof-field mass loss or yield increased due to increased runoff volume. Surface application of dairy manure resulted in 25-50% lower runoff volumes and 35-60% lower total suspended solid yields when compared to surface applied poultry litter. Surface applied poultry litter produced the greatest total P and dissolved reactive P losses. Results of this study suggest that manure applied based on crop P requirements can still yield significant edge-of-field nutrient losses, if rainfall occurs soon after application.

This study presents a probabilistic framework that considers both the water quality improvement capability and reliability of alternative total maximum daily load (TMDL) pollutant allocations. Generalized likelihood uncertainty estimation and Markov chain Monte Carlo techniques were used to assess the relative uncertainty and reliability of two alternative TMDL pollutant allocations that were developed to address a fecal coliform (FC) bacteria impairment in a rural watershed in western Virginia. The allocation alternatives, developed using the Hydrological Simulation Program-FORTRAN, specified differing levels of FC bacteria reduction from different sources. While both allocations met the applicable water-quality criteria, the approved TMDL allocation called for less reduction in the FC source that produced the greatest uncertainty (cattle directly depositing feces in the stream), suggesting that it would be less reliable than the alternative, which called for a greater reduction from that same source. The approach presented in this paper illustrates a method to incorporate uncertainty assessment into TMDL development, thereby enabling stakeholders to engage in more informed decision making.

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