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Modeling inactivation of indicator microorganisms is a necessary component of microbial water quality forecast and management recommendations. The linear semi‐logarithmic (LSL) model is commonly used to simulate the dependencies of bacterial concentrations in waters on time. There were indications that assumption of the semi‐logarithmic linearity may not be accurate enough in waters. The objective of this work was to compare performance of the LSL and the two‐parametric Weibull inactivation models with data on survival of indicator organism Escherichia coliin various types of water from a representative database of 167 laboratory experiments. The Weibull model was preferred in >99% of all cases when the root mean squared errors and Nash–Sutcliffe statistics were compared. Comparison of corrected Akaike statistic values gave the preference to the Weibull model in only 35% of cases. This was caused by (i) a small number of experimental points on some inactivation curves, (ii) closeness of the shape parameter of the Weibull equation to one, and (iii) piecewise log–linear inactivation dynamic that could be well described by neither of the two models compared. Based on the Akaike test, the Weibull model was favored in agricultural, lake, and pristine waters, whereas the LSL model was preferred for groundwater, wastewater, rivers, and marine waters. The decimal reduction time parameter of both the LSL and Weibull models exhibited an Arrhenius‐type dependence on temperature. Overall, the existing E. coliinactivation data indicate that the application of the Weibull model can improve the predictive capabilities of microbial water quality modeling.

Vegetated filter strips (VFS) have become an important component of water quality improvement by reducing sediment and nutrients transport to surface water. This management practice is also beneficial for controlling manure‐borne pathogen transport to surface water. The objective of this work was to assess the VFS efficiency and evaluate the uncertainty in predicting the microbial pollutant removal from overland flow in VFS. We used the kinematic wave overland flow model as implemented in KINEROS2 coupled with the convective‐dispersive overland transport model which accounts for the reversible attachment‐detachment and surface straining of infiltrating bacteria. The model was successfully calibrated with experimental data obtained from a series of simulated rainfall experiments at vegetated and bare sandy loam and clay loam plots, where fecal coliforms were released from manure slurry applied on the top of the plots. The calibrated model was then used to assess the sensitivity of the VFS efficiency to the model parameters, rainfall duration, and intensity for a case study with a 6‐m VFS placed at the edge of 200‐m long field. The Monte Carlo simulations were also performed to evaluate the uncertainty associated with the VFS efficiency given the uncertainty in the model parameters and key inputs. The VFS efficiency was found to be <95% in 25%, <75% in 23%, and <25% in 20% of cases. Relatively long high‐intensity rainfalls, low hydraulic conductivities, low net capillary drives of soil, and high soil moisture contents before rainfalls caused the partial failure of VFS to retain coliforms from the infiltration excess runoff.

Attachment of bacteria to soil is an important component of bacterial fate and transport. Escherichia coliare commonly used as indicators of fecal contamination in the environment. Despite the fact that E. coliare derived exclusively from feces or manure, effect of the presence of manure colloids on bacteria attachment to agricultural soils was never directly studied. The objective of this work was to evaluate the magnitude of the effect of manure on E. coliattachment to soil. Escherichia coliattachment to soil was studied in batch experiments with samples of loam and sandy clay loam topsoil that were taken in Pennsylvania and Maryland. Escherichia colicells were added to the water–manure suspensions containing 0, 20, and 40 g L−1of filtered liquid bovine manure, which subsequently were equilibrated with air‐dry sieved soil in different soil to suspension ratios. The Langmuir isotherm equation was fitted to data. Manure dramatically affected E. coliattachment to soil. Attachment isotherms were closer to linear without manure and were strongly nonlinear in the presence of manure. The maximum E. coliattachment occurred in the absence of manure. Increasing manure content generally resulted in decreased attachment.

The objective of this study was to develop a method that could be applied to investigations of soil/environmental factors influencing the spatial and temporal variability of carbofuran hydrolysis in field soils. Two factors were considered: (i) soil handling and pesticide application, and (ii) the method of data summarization. Three soil handling/pesticide treatments were evaluated: (i) sieved soil/sprayed pesticide application, (ii) injected pesticide application/sieved soil, and (iii) injected pesticide application/intact core incubation. This last method was developed to mimic field conditions where high localized concentrations of carbofuran (2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl methylcarbamate) occur as a result of banded application of granular carbofuran at planting time. For all three treatments sigmoidal 14CO2production kinetics were observed. Several mathematical models for describing sigmoidal product appearance data were evaluated and a general saturation model was found to yield the best fit. Using parameter estimates obtained from this model in statistical tests, we found that the intact core soil treatment yielded significantly longer half lives for carbofuran degradation. Additional experimental evidence suggests that soil structure of the intact cores retarded diffusion of the 14CO2produced from carbofuran degradation and influenced the kinetic pattern observed.