Chris Robert Rehmann

Disparities exist for marginalized populations ( i.e. , low-income populations) when it comes to potential exposure to elevated nitrate in drinking water.

**Abstract Text** Many methods for estimating turbulent kinetic energy (TKE) from an acoustic Doppler current profiler (ADCP) have require assump | ORAL

**Abstract Text** An accurate contaminant transport model is an important tool for coordinating remediation and response after spills occur. The | ORAL

An expression for the transverse mixing coefficient in a rectangular channel is derived to evaluate the importance of transverse turbulent diffusion. Although some formulas for the transverse mixing coefficient account for both turbulent diffusion and shear dispersion, most calculations of the transverse dispersion coefficient do not include the effect of transverse turbulent diffusion on shear dispersion. Both vertical and transverse turbulent diffusion contribute appreciably to transverse shear dispersion, and the direct contribution of transverse turbulent diffusion to transverse mixing is important for a range of conditions commonly observed in natural channels. A comparison of predicted and measured transverse mixing coefficients supports including turbulent diffusion in analyses of transverse mixing – both in its effect on shear dispersion and as a direct mechanism of transport.

A saturated riparian buffer (SRB) is an edge‐of‐field conservation practice that intercepts tile drainage and reduces nitrate flux to nearby streams by redistributing the flow as shallow groundwater. In this study, a three‐dimensional, finite‐difference groundwater model representative of SRBs in central Iowa was developed to assess the flow of groundwater and implications for nitrate removal during spring conditions, when flow to the SRB is highest. The model reproduces field observations of water level with Nash–Sutcliffe efficiency of 0.68, which is deemed acceptable for hydrologic models. The modeling shows that groundwater flow is three‐dimensional near the distribution pipe and the stream and primarily one‐dimensional in the rest of the buffer. The path the water takes in flowing toward the stream depends on where it exits the distribution pipe. When nitrate is not limiting, the potential for nitrate removal depends on the length of the path—and thus travel time—and depth because denitrification potential varies with depth. Travel time T_t can be estimated well with slight modifications to a one‐dimensional approximation: T_t = 1.11L_x/v_x, where L_x is the buffer width and v_x is a one‐dimensional approximation of the average linear velocity of groundwater. Refining knowledge of SRB function is an important step toward enhancing design for improving water quality.

Vegetative filter strips (VFS) have shown promising results in reducing the downstream transport of many agroecosystem contaminants. A recently developed type of VFS, prairie strips, has been shown to significantly reduce the impact of corn and soybean production systems on water quality in terms of sediment, nitrogen, and phosphorus losses. This study assessed potential additional benefits of prairie strips to include the reduction of pathogens. To assess the impact of prairie strips on manure‐laden agricultural runoff, we utilized a physical model of prairie strips in a laboratory flume to conduct highly controlled overland flow experiments. Escherichia coli and Enterococcus concentration reductions of up to 45% and 65% were observed for runoff and infiltration flows, respectively, while mass load reductions of up to 65% were observed for surficial runoff flows. The degree of concentration or mass load reductions was dependent on the residence time of the flow within the strip and the partitioning of overland flow running onto the strip to infiltration and runoff flows. Based on our results and a review of the literature, we developed a design method to provide guidance on the width of prairie strip buffer needed to achieve a user‐defined reduction of fecal bacteria concentration.