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Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E. coli isolates from streams draining 15 small (

Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E. coli isolates from streams draining 15 small (

We present a simple modular landscape simulation model that is based on a watershed modeling framework in which different sets of processes occurring in a watershed can be simulated separately with different models. The model consists of three loosely coupled submodels: a rainfall-runoff model (TOPMODEL) for runoff generation in a subwatershed, a nutrient model for estimation of nutrients from nonpoint sources in a subwatershed, and a stream network model for integration of point and nonpoint sources in the routing process. The model performance was evaluated using monitoring data in the watershed of the Patuxent River, a tributary to the Chesapeake Bay in Maryland, from July 1997 through August 1999. Despite its simplicity, the landscape model predictions of streamflow, and sediment and nutrient loads were as good as or better than those of the Hydrological Simulation Program-Fortran model, one of the most widely used comprehensive watershed models. The landscape model was applied to predict discharges of water, sediment, silicate, organic carbon, nitrate, ammonium, organic nitrogen, total nitrogen, organic phosphorus, phosphate, and total phosphorus from the Patuxent watershed to its estuary. The predicted annual water discharge to the estuary was very close to the measured annual total in terms of percent errors for both years of the study period (≤2%). The model predictions for loads of nutrients were also good (20-30%) or very good (<20%) with exceptions of sediment (40%), phosphate (36%), and organic carbon (53%) for Year 1. [ABSTRACT FROM AUTHOR]

Summary: Recent advances in optimizing watershed model calibration have focused mainly on incorporating multiple objective measures of model performance and improving optimization algorithms. However, some parameters vary widely among different calibration locations. We present a watershed model calibration method that combines multi-objective optimization with averaging across multiple calibration sites. Model parameters were first estimated by multi-objective optimization at each calibration site, and then finalized by weighted averaging the parameter values across sites. The weight for each site was calculated from the prediction error at that site. The calibration framework was applied to estimate 16 hydrological and nutrient parameters of the General Watershed Loading Function (GWLF) watershed model at the Rhode River basin, in Maryland, United States of America. When calibrated to a single watershed, GWLF gave reasonable predictions for monthly streamflow (r 2 =0.71–0.78), monthly total nitrogen (TN) loads (r 2 =0.55–0.65), annual streamflow (r 2 =0.80–0.91), and annual TN loads (r 2 =0.67–0.86); but success for total phosphorus (TP) loads varied among watersheds (r 2 =0.41–0.68 for monthly TP loads and r 2 =0.47–0.79 for annual TP loads). In comparison to the single-site calibrations, the multi-site weighted average approach combined with multi-objective optimization reduced the relative cumulative error of predictions in validation watersheds by 3.5–7.4% for monthly streamflow, 3.2–6.3% for monthly TN loads, and 4.3–5.9% for monthly TP loads, respectively. [Copyright &y& Elsevier]

Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E. coli isolates from streams draining 15 small (<19 km2) watersheds of the Chesapeake Bay with contrasting levels of concentrated poultry operations. Total nitrogen and nitrate plus nitrite concentrations increased with poultry barn density with concentrations two and three times higher, respectively, in watersheds with the highest poultry barn densities compared to those without poultry barns. Analysis of N and O isotopes in nitrate by mass spectrometry showed an increase in the proportion of 15N associated with an increase in barn density, suggesting that the nitrate associated with poultry barns originated from manure. Phosphorus concentrations were not correlated with barn density. Antibiotic susceptibility testing of putative E. coli isolates was conducted using the disk diffusion method for twelve clinically important antibiotics. Of the isolates tested, most were completely susceptible (67%); 33% were resistant to at least one antibiotic, 24% were resistant to ampicillin, 13% were resistant to cefazolin, and 8% were multi-drug resistant. Resistance to three cephalosporin drugs was positively associated with an index of manure exposure estimated from poultry barn density and proportion of cropland in a watershed. The proportion of E. coli isolates resistant to cefoxitin, cefazolin, and ceftriaxone, broad-spectrum antibiotics important in human medicine, increased by 18.9%, 16.9%, and 6.2%, respectively, at the highest estimated level of manure exposure compared to watersheds without manure exposure. Our results suggest that comparisons of small watersheds could be used to identify geographic areas where remedial actions may be needed to reduce nutrient pollution and the public health risks of ABR bacteria. Unlabelled Image • Nitrogen concentrations in watersheds increased with numbers of poultry barns in and around the watershed. • Cephalosporin-resistant E. coli in streams was positively correlated with the estimated poultry manure exposure. • Studying small watersheds has the potential to reveal sources of antibiotic resistant bacteria and nutrient pollution. [ABSTRACT FROM AUTHOR]