Rainfall runoff may be captured and stored for later use, but the quality of this water can be detrimental in some uses without the use of appropriately designed first-flush diverters. The rainfall runoff water quality was measured on nineteen new small-scale and two aged commercial roofs located near high traffic highways. Roof coverings included asphalt shingles, sheet metal, clay tiles, and tar and gravel. Runoff samples were evaluated for polycyclic aromatic hydrocarbons (PAHs), phosphorus flame retardants (PFRs), and pyrethroid insecticides. Eighteen small-scale roofs were subjected to a range of simulated rainfall events, while natural runoff was sampled on the commercial roofs and one small-scale roof. Runoff was analyzed for pH, conductivity, turbidity, total suspended solids, boron, iron, copper, zinc, manganese, sodium adsorption ratio, nitrate-nitrogen, seventeen PAHs, tris(2-chloroethyl) phosphate, tris(1,3-dichloro-2-propyl)phosphate, bifenthrin, cypermethrin, and lambda-cyhalothrin. Samples from four natural storm events were also analyzed for total coliforms and Escherichia coli. In addition, soils below seventeen existing gutter downspouts were sampled to determine long-term pollutant accumulation. Atmospheric deposition was the main contributor of pollutants in the roof runoff. A majority of samples fell within the U.S. EPA guidelines for non-potable urban and agricultural water reuse. Trace levels of PAHs, PFRs, and insecticides were detected, but all detections were three orders of magnitude below the USGS health-based screening level benchmark concentrations. Results indicate that diverting the first flush, based on turbidity, total suspended solids, or conductivity, can improve the overall water quality and reduce the concentrations of PAHs in harvested rainwater. Downspout soil sampling showed potential for the long-term accumulation of PAHs at concentrations exceeding the minimum human-health risk-based screening levels at these high runoff-loading locations.

Lake Thunderbird, which is located to the east and south of Oklahoma City, Oklahoma, is on the Army Corps of Engineers 303(d) list of impaired water bodies due to three limiting factors, one of which is turbidity. The lake has approximately 50 miles of shoreline with 83% having some degree of erosion. Over the years, shoreline erosion has resulted in significant loss of shoreline and deposition of the eroded material into the lake, effectively reducing the holding capacity of the lake and adversely affecting water quality. To reduce the erosive action of the waves, this project was completed to utilize floating wetland breakwaters (FWBs) anchored near the shoreline to reduce the energy from wave action. The three objectives of this study were: (1) Test multiple FWB frame designs to determine the best design for maximizing wave-energy reduction; (2) Complete laboratory-scale experiments on model FWB frames to determine the viability of using scale models to predict full-scale performance; and (3) Complete field testing of the selected design to determine in-situ wave reduction and the resulting impact on shoreline erosion. Overall, the project was successful in meeting the three project objectives. The full-scale mesocosm demonstrated that a frame design with 11 ballasts that were each 3-feet long per 10-foot section provided the most wave energy reduction per materials cost. Through the laboratory-scale experiments, we were able to utilize similitude concepts to demonstrate that, in general, we could predict full-scale wave-reduction performance using smaller scale models when similitude concepts are recognized in the design. Finally, our field implementation resulted in the best wave reduction performance of all of our tests at multiple scales, including comparisons to designs available in literature. Based on wind speed and fetch data for southerly winds and shear stress determination from the shoreline soils, we estimate that our FWB design is able to reduce 96% of the waves to heights smaller than what is required to cause detachment erosion on that bank. In addition, the materials‘ cost per foot was comparable to other shoreline erosion techniques.

Grand Lake O’The Cherokees, the third largest reservoir located in northeastern Oklahoma, provides recreational services, water supply, hydroelectric power, and flood control to residents of Oklahoma and neighboring states. Grand Lake has experienced major problems with eutrophication, harmful algal blooms, and dissolved oxygen (DO) depletion during summer. To better understand the dynamics of DO depletion in the hypolimnion of Grand Lake, a three-layer steady state vertical DO model for summer-stratified conditions was used to investigate dissolved oxygen profiles both above and below the thermocline. The DO model was used to determine the relative effects of atmospheric reaeration and phytoplankton production as a source of DO and phytoplankton respiration, decomposition of organic matter, and nitrification as loss terms for DO. Additionally, the importance of sediment oxygen demand (SOD) for hypolimnetic oxygen depletion was investigated at the sediment water-interface under stratified conditions. Observed water quality data, kinetic coefficients from the literature, and physical, biological, and chemical data collected throughout 2013 and 2015 along the spatial gradient of riverine, transition, lacustrine zones and a site close to the Grand Lake Pensacola Dam were used in the pre-processing calculations to derive estimates of kinetic rates as input parameters to the model. The estimated predictions from the model showed reasonable agreement with the observed vertical profiles of DO. Conclusions from this study indicate that phytoplankton production, high light limitation, and phosphorus were the major terms that controlled DO production in the surface layer, while nitrification and organic carbon decomposition were the major sinks of DO consumption in the bottom layer. Interestingly, SOD did not play a significant role in DO depletion in the water column.

A wide range of mathematical models are available for predicting phosphorus (P) losses from agricultural fields, ranging from simple, empirically based annual time-step models to more complex, process-based daily time-step models. In this study, we compare field-scale P-loss predictions between the Annual P Loss Estimator (APLE), an empirically based annual time-step model, and the Texas Best Management Practice Evaluation Tool (TBET), a process-based daily time-step model based on the Soil and Water Assessment Tool. We first compared predictions of field-scale P loss from both models using field and land management data collected from 11 research sites throughout the southern United States. We then compared predictions of P loss from both models with measured P-loss data from these sites. We observed a strong and statistically significant ( < 0.001) correlation in both dissolved (ρ = 0.92) and particulate (ρ = 0.87) P loss between the two models; however, APLE predicted, on average, 44% greater dissolved P loss, whereas TBET predicted, on average, 105% greater particulate P loss for the conditions simulated in our study. When we compared model predictions with measured P-loss data, neither model consistently outperformed the other, indicating that more complex models do not necessarily produce better predictions of field-scale P loss. Our results also highlight limitations with both models and the need for continued efforts to improve their accuracy.

Streambanks can be a significant source of sediment and phosphorus to aquatic ecosystems. Although the streambank-erosion routine in the Soil and Water Assessment Tool (SWAT) has improved in recent versions, the recently developed routine in SWAT 2012 has undergone limited testing, and the lack of site or watershed specific streambank data increases the uncertainty in the streambank-erosion predictions. There were two primary objectives of this research: (1) modify and test the 2012 SWAT streambank-erosion routine on composite streambanks, and (2) compare SWAT default and field-measured channel parameters and assess their influence on predicted streambank erosion. Three modifications were made to the SWAT 2012 streambank-erosion routine: (1) replacing the empirical effective shear stress equation with a process-based equation, (2) replacing bankfull width and depth measurements with top width and streambank height, and (3) incorporating an area-adjustment factor to account for non-trapezoidal cross-sections. The proposed streambank-erosion routine was tested on gravel-dominated streambanks on the Barren Fork Creek in northeastern Oklahoma. The study used data from 28 cross-sectional surveys, including streambank height and top width, side slope, thickness and texture of streambank layers, and an area-adjustment factor. Gravel d(50) and k(d)-t(c) relationships were used to estimate the critical shear stress (tau(c)) and the erodibility coefficient (k(d)), respectively. Incorporating the process-based shear stress equation, area-adjustment factor, or the top width and streambank height increased predicted streambank erosion by 85%, 31%, and 30%, respectively. Incorporating the process-based effective shear stress equation, sinuosity, radius of curvature, and measured bed slope improved the predicted versus observed streambank erosion Nash-Sutcliffe efficiency from -0.33 to 0.49 and the coefficient of determination (R-2) from 0.02 to 0.65 at the ten study sites. Although the process-based effective shear stress equation was the most influential modification, incorporating the top width, streambank height, and area-adjustment factor more accurately represented the measured irregular cross-sections.

In response to increased nutrient loads in surface waters, scientists and engineers need to identify critical nutrient source areas and transport mechanisms within a catchment to protect beneficial uses of aquatic systems in a costeffective manner. It was hypothesized that hydrologic heterogeneities (e.g., macropores and gravel outcrops) in the vadose zone play an integral role in affecting flow and solute transport between the soil surface and shallow alluvial aquifers. The objective of this research was to characterize phosphorus (P) leaching through silt loam soils to alluvial gravel aquifers in the floodplains of the Ozark ecoregion at the plot scale. Solute injection experiments used plots (1 m  1 m, 3 m  3 m, and 10 m  10 m) that maintained a constant head for up to 52 h. Solutes in the injection water included P (highly sorptive), Rhodamine WT (slightly sorptive), and chloride (conservative). Electrical resistivity imaging identified zones of preferential flow. Fluid samples from observation wells indicated nonuniform subsurface flow and transport. The surface soil type, ranging from silt loam to clean gravel outcrops, had a significant impact on P leaching capacity, with gravel outcrops resulting in high infiltration rates and rapid solute detection in wells (e.g., 4 min). Even in silt loam soils without gravel outcrops, macropore flow resulted in rapid transport of P. Maximum transport velocity for soluble reactive P in one silt loam plot was 810 cm h-1, compared with a mean pore water velocity in the range of 25 to 130 cm h-1. Soluble reactive P concentrations in observation wells reached up to 0.54 mg L-1 in silt loam plots and 1.3 mg L-1 in gravel outcrop plots, demonstrating that a highly sorbing solute can be mobile.

Due to a shortage of available phosphorus (P)-loss datasets, simulated data from an accurate quantitative P transport model could be used to evaluate a P Index. The objective of this study was to compare predictions from the Texas Best Management Practice Evaluation Tool (TBET) against measured P-loss data to determine whether the model could be used to improve P Indices in the southern region. Measured P-loss data from field-scale study sites in Arkansas, Georgia, and North Carolina were used to assess the accuracy of TBET for predicting field-scale loss of P. We found that event-based predictions using an uncalibrated model were generally poor. Calibration improved runoff predictions and produced scatterplot regression lines that had slopes near one and intercepts near zero. However, TBET predictions of runoff met the performance criteria (Nash-Sutcliffe efficiency ≥ 0.3, percent bias ≤ 35%, and mean absolute error ≤ 10 mm) in only one out of six comparisons: North Carolina during calibration. Sediment predictions were imprecise, and dissolved P predictions underestimated measured losses. In North Carolina, total P-loss predictions were reasonably accurate because TBET did a slightly better job of predicting sediment losses from cultivated land. In Arkansas and Georgia, where the experimental sites were in forage production, the underprediction of dissolved P led directly to the underpredictions of total P. We conclude that TBET cannot be used to improve southern P Indices, but a curve number approach could be incorporated into P Indices to improve runoff predictions.

Core Ideas WEPP rangeland model was evaluated using spatial erosion data for the first time. WEPP and 137Cs methods predicted similar low soil erosion rates. Spatial erosion patterns predicted by WEPP and 137Cs methods agreed well. WEPP predicted soil erosion patterns well along rangeland hillslopes. Lack of spatially distributed soil erosion data has greatly hampered the development and improvement of process‐based soil erosion models. The 137Cs method has been widely used to estimate soil erosion and redistribution but has seldom been used to evaluate process‐based erosion models. This study evaluated spatial erosion patterns predicted by the Water Erosion Prediction Project (WEPP) model using 137Cs‐estimated spatially distributed erosion data and quantified the effects of slope length on erosion along rangeland hillslopes. Eight rangeland hillslopes in midwestern Oklahoma were selected. The WEPP rangeland model was parameterized with observed soil and vegetation data. One downslope transect was sampled for each hillslope. At each sampling position, seven samples along a contour line were composited to represent the 137Cs inventory for that slope position to reduce random spatial variation. Both methods predicted low soil erosion rates, with the maximum erosion rates being near 2 Mg ha−1 yr−1. The erosion rates predicted by the two methods were significantly correlated at P = 0.01, and the medians were not significantly different; however, a paired t‐test showed that WEPP predicted significantly lower erosion rates than the 137Cs method. More importantly, the WEPP‐predicted soil erosion patterns in response to slope length agreed very well with those predicted by the 137Cs method. The loci of the maximum and minimum erosion rates were similar between the two methods for seven transects. The WEPP rangeland model predictions for the spatial patterns of relative soil erosion intensity along a hillslope compared favorably with 137Cs method estimates.

Microbial pollution in stormwater is a concern in urban areas across the U.S. and is a leading cause of water-quality impairment in the United States. This issue may be addressed through the use of best management practices (BMPs) and target limits for pathogenic indicator species. Bioretention is a commonly used low impact development strategy that addresses this growing pollution problem at the source. Bioretention removal efficiencies have been well studied when considering nutrients and heavy metals, but field-scale treatment data are limited for microbial indicators. The primary objective of this study was to quantify microbial removal by installed bioretention cells with fly-ash amended soils. Three bioretention cells in Grove, Oklahoma were monitored over one and a half years and the removal microbial efficiency was quantified. Overall, removal rates for E. coli, enterococci, and coliphage were highly variable, with mean and standard deviations for removals for each site respectively: E. coli 87%, 35%, and 43%; enterococci 97%, 95%, and 80%; and coliphage 38%, 75%, and 32%. The site with negative removal efficiency appears to have some groundwater intrusion during storm events. Based on this relatively limited data set, these fly-ash amended bioretention cells performed 49% better than those with a sand-only filter media layer currently reported in the literature. Based on this initial field study, it appears that fly-ash amended bioretention cells may be a viable option for enhanced microbial removal from stormwater runoff.

Process-based models can predict stream response to streambank stabilization. However, a framework does not exist on how to explicitly utilize these models to evaluate stabilization measures prior to implementation. This research developed a framework to evaluate stabilization practices using hydraulic and sediment transport models, landowner preferences, construction costs, and effectiveness. This framework produces sediment reduction graphs to determine the stabilization length as well as cost graphs. The methodology was applied to Fivemile Creek in western Oklahoma. A CONCEPTS simulation was developed for a 10.25-km reach and several stabilization techniques (grade control, riprap toe, and vegetation) were simulated. Incorporating multiple stabilization practices simultaneously resulted in higher sediment loads, but also higher costs which were quantifiable using the framework. Vegetation with 2:1 bank slopes was the most cost-effective stabilization technique. With that said, the framework provided a process-based understanding of the system that also highlighted the need for grade control for long-term effectiveness.

Classic agricultural-conservation practices may not address decades of phosphorus (P) accumulation, known as legacy P. Identifying and quantifying legacy P sources are necessary to identify the most costefficient conservation practices. A method was developed to identify and quantify legacy P at the watershed scale using a mass-balance approach and uncertainty analysis. The method was applied to two nutrient-rich watersheds in northeast Oklahoma and northwest Arkansas. Each P import and export to and from the two watersheds was identified and quantified using a probability distribution and uncertainty analysis. The P retained in the soils, reservoirs, and stream systems were estimated from 1925 to 2015. Over 8.5 and 6.1 kg/ha/year of P were added to the Illinois River and Eucha-Spavinaw watersheds with 53 and 55% from poultry production, respectively. Other major historical sources were attributed to human population and commercial fertilizer. Though currently the net addition of P in the watersheds is small due to the export of approximately 90% of the poultry litter, historically only 14-19% of all P imported to the Illinois River and Eucha-Spavinaw watersheds was removed via the reservoir spillways, poultry litter, and food exports. The majority of the retained P is located in the soil, 3.6-5.8 kg/ha/year, and stream systems, 0.01-3.0 per ha/year.

Streambank nutrient loading rates are a growing concern within many watersheds. Only a few studies exist on streambank soil chemistry and phosphorus (P) concentrations, spatial distributions in watersheds, and P loading rates with a consideration of the potential uncertainty associated with the estimates. More so, limited studies compare streambank P loading for streams within similar watersheds and with similar land use and management. The objectives of this research included (1)quantifying the magnitude and spatial distribution of soil pH, electrical conductivity (EC), total P concentration, dissolved P concentration, and the degree of P saturation of streambanks in a watershed; (2)quantifying whether water-soluble phosphorus (WSP) and total phosphorus (TP) loads entering the stream from streambanks are significant based on a combined mass balance and uncertainty analysis approach; and (3)contrasting streambank P concentrations and loadings between two similar streams: Spavinaw Creek (SC) versus Barren Fork Creek (BFC) in eastern Oklahoma. Both SC and BFC flow through the Ozark ecoregion, possess similar geomorphology, and are characterized by similar land uses. Following procedures conducted for BFC, streambank sampling occurred at five sites along SC, and samples were processed for pH, EC, WSP, and TP. Unlike BFC, there were no clear longitudinal trends in WSP, TP, pH, and EC; similar to BFC, no consistent vertical trends were observed. Using estimated sediment loading (727x106kg) from aerial images and Monte Carlo analysis, it was estimated from 2003 to 2013 there was 1.5x103kg WSP and 1.4x105kg TP loaded into SC from streambanks in Oklahoma. Average in-stream estimates were an order of magnitude larger for WSP and comparable for TP. Streambank P contributions and erosion rates along one stream cannot be used to accurately predict P loading along other streams even in similar watersheds with similar hydrology, geomorphology, and land use because of watershed-specific variability in streambank erodibility and streambank P concentrations. Due to the uncertainty associated with critical input parameters, the uncertainty in streambank P loads at the watershed scale can be large and therefore uncertainty analysis approaches should be used in future research.

ABSTRACT Floodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events. EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen

In some watersheds, streambanks are a source of two major pollutants, phosphorus (P) and sediment. P originating from both uplands and streambanks can be transported and stored indefinitely on floodplains, streambanks, and in closed depressions near the stream. The objectives of this study were to (1) test the modified streambank erosion and instream P routines for the Soil and Water Assessment Tool (SWAT) model in the Barren Fork Creek watershed in northeast Oklahoma, (2) predict P in the watershed with and without streambank-derived P, and (3) determine the significance of streambank erosion P relative to overland P sources. Measured streambank and channel parameters were incorporated into a flow-calibrated SWAT model and used to estimate streambank erosion and P for the Barren Fork Creek using modified streambank erosion and instream P routines. The predicted reach-weighted streambank erosion was 40kg/m vs. the measured 42kg/m. Streambank erosion contributed 47% of the total P to the Barren Fork Creek and improved P predictions compared to observed data, especially during the high-flow events. Of the total P entering the stream system, approximately 65% was removed via the watershed outlet and 35% was stored in the floodplain and stream system. This study successfully applied the SWAT model's modified streambank erosion and instream P routines and demonstrated that streambank-derived P can improve P modeling at the watershed scale. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

•SWAT a capable tool in the evaluation of numeric water-quality standards.•New in-stream routine adequately calibrated phosphorus.•SWAT used to evaluate a reservoir’s numeric water-quality standard.•Management practices must consider legacy phosphorus.

Mixing models are frequently used as part of sediment fingerprinting to quantify sediment source contributions. Much research effort has been devoted to improving these mixing models. The objective of this study was to develop and evaluate a new method using discriminant function analysis (DFA) to fingerprint sediment source contributions. It was hypothesized that the outcome of DFA, commonly used as a component of standard fingerprinting procedures, can potentially be used directly to quantify source contributions, avoiding mixing models altogether. This hypothesis was tested in the Bull Creek Watershed in Oklahoma State, USA. DFA results were compared with outcomes from the Collins mixing model and previous research. When conservative geochemical tracers were used, DFA results did not differ significantly from the mixing model results, indicating that DFA alone has the potential to accurately quantify sediment source contributions, while being simple to use. When using non-conservative tracers, however, the results from the two methods were significantly different. On the basis of a comparison with previous research, we suggest that DFA offers an intuitive method for characterizing sediment source contributions.