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The prairie pothole region ranges from central Iowa to the northwest into Montana and south-central Canada, totaling around 700,000 km². This area contains millions of potholes, or enclosed topographical depressions, which often inundate with rainfall. Many are located in areas that have been converted to agricultural land through installation of artificial drainage. However, even with drainage, potholes pond or remain saturated during and after significant rain events. In this two-year study, surface water depth was collected hourly (typically from after planting through harvest) from eight farmed potholes (drained and under corn-soybean rotation) on the Des Moines Lobe in central Iowa. Nutrient data were collected daily and tested for nitrogen (N) and phosphorus (P) when inundation depth exceeded 10 cm. The data were analyzed in two ways. First, seasonal differences were investigated using samples from the first day of each inundation event. Surface water concentrations were higher in the early growing season than late season for total N (TN), NO3-N, NH3- N, total P (TP), and total suspended solids (TSS). Secondly, average event concentration changes were determined. Nitrate reductions occurred in 85% of multiday events, but these reductions were offset by increases in P. Total P and dissolved reactive P (DRP) had significant increases that averaged 0.51 and 0.46 mg L-1 per event, respectively, with event lengths of 2 to 19 days. This study demonstrates that inundated farmed potholes reduce NO3-N but serve as in-field hotspots, contributing elevated TP and DRP to drainage waters. When a surface intake directly connects inundated farmed potholes to drainage, new strategies, such as field management or engineered technologies, are needed to mitigate P export. This study is useful in informing policy regarding field management and conservation of farmed potholes. [ABSTRACT FROM AUTHOR]

Grassed waterways (GWWs) are an effective conservation practice for preventing ephemeral gully erosion resulting from channelized surface runoff in agricultural fields. However, field reconnaissance to identify areas of channelized erosion within a watershed can be time-consuming and labor-intensive. Recent advances in precision conservation and light detection and ranging (LiDAR) technologies can provide valuable information on environmentally sensitive areas that cause soil degradation. The objective of this study was to demonstrate that a compound topographic index (CTI) model supplemented with LiDAR data can be used to identify potential GWW locations and inform design recommendations. A LiDAR digital elevation model with a spatial resolution of 3 m was used to derive terrain attributes (slope, drainage area, and plan curvature). The GWW identification and design process was automated in the ArcGIS Python environment. The plan curvature identified erosion channels, but discontinuity in the model output was observed. The CTI model was calibrated to a field with GWWs installed under USDA-NRCS guidelines, which yielded a CTI threshold of 30. The calibrated model (CTI ≥-30) was able to identify all 14 existing GWWs in the watershed. Field surveys were conducted in the watershed, and areas exhibiting evidence of channelized erosion were identified by the model for GWW placement. Furthermore, the CTI model overestimated (PBIAS = -23.34%) the lengths of predicted GWWs, suggesting a need to further extend the existing GWWs. The total surface area of the predicted GWWs was 29.3 ha in the study watershed, with depth of GWWs reaching 0.3 m. The design process provides an estimate of land to be set aside for conservation practices. The terrain analysis was effective in targeting conservation practice placement and improves the accuracy of field assessments. [ABSTRACT FROM AUTHOR]

This study involved field observations in Squaw Creek watershed, located in central Iowa, to investigate the impact of a heavy rain event (rainfall of 71 mm in 24 h) on E. coli levels in the streambed sediment and overlying water. We assessed relationships between streamflow and E. coli and nutrient levels in the water column and streambed sediment. The results showed that during a heavy rain event, E. coli levels in the water column varied considerably, ranging from 360 to 37,553 CFU per 100 mL with a mean of 7,598 CFU per 100 mL. Elevated streamflow resulted in greater levels of E. coli in the water column. Streambed sediment E. coli levels ranged from 896 to 6,577 CFU per 100 g with a mean of 3,355 CFU per 100 g. Regression analysis found exponential relationships between streamflow and E. coli levels in the water column (R² = 0.56) and between streamflow and E. coli levels in the streambed sediment (R² = 0.45). R² values of the exponential relationship between streamflow and water column E. coli levels increased considerably when regressions for the rising and falling limbs of the hydrograph were performed separately (R² = 0.64 and 0.94, respectively). The exponential relationship between total suspended solids (TSS) and water column E. coli levels yielded an R² of 0.38, while TSS and streamflow yielded an exponential relationship with an R² of 0.64. The results presented here provide information on in-stream bacteria dynamics of an agricultural watershed during the first heavy rain of the season. We anticipate that the results will improve the understanding of in-stream E. coli transport during rain events and provide insight for policy makers to allocate E. coli loads in impaired water bodies. [ABSTRACT FROM AUTHOR]

Compared to conventional cage laying-hen houses, aviary hen houses generally have much higher concentrations of airborne dust and bacteria due to generation of bioaerosols by the hens' access to and activities on the litter floor. Hence, reducing these airborne agents is important to safeguard the health of the animals and workers in such housing systems. Spraying slightly acidic electrolyzed water (SAEW) is a novel approach to reducing airborne culturable bacteria (CB) and particulate matter (PM) levels in hen houses. The objective of this study was to evaluate the efficacy of reducing airborne CB and PM in an experimental aviary chamber by periodic spraying of SAEW (Trt), as compared to no spraying (Ctrlns) or spraying of tap water (Ctrlw). The hens were provided 16 h light and 8 h dark (lights on at 6:00 h and off at 22:00 h) and were given access to the litter floor from 12:00 h to 22:00 h. The Trt regimen sprayed SAEW at 14:00 h for 15 min at a dosage of 80 mL m-2; the Ctrlns regimen had no spraying; and the Ctrlw regimen sprayed tap water following the same procedure as with Trt. Concentrations of airborne CB and PM in six aerodynamic size ranges (0.65-1.1, 1.1-2.1, 2.1-3.3, 3.3-4.7, 4.7-7.1, and >7.1 µm) were measured at 1.5 m above the floor in the center of the room during the periods of 13:45-14:00 h and 14:45-15:00 h. Compared to Ctrlns, spraying SAEW significantly reduced airborne CB (>2.1 µm) by up to 49% ±10% (p < 0.05), while Ctrlw did not show a reduction effect. No significant difference was found between Trt and Ctrlw in reducing airborne PM, although both reduced or tended to suppress PM >7.1 µm in size. The results show that spraying SAEW can inactivate airborne CB attached to PM. Thus, this is a promising technique for alleviating the adverse health impacts of bioaerosols in aviary laying-hen housing systems. [ABSTRACT FROM AUTHOR]

A long-term study (1998 to 2009) was initiated on eleven tile-drained field plots, ranging in size from 0. 19 to 0.47 ha, to investigate the effects of poultry manure application on subsurface drainage water quality in Iowa under a corn-soybean rotation system. The experimental treatments included poultry manure at rates of 168 kg N ha-1 (PM) and 336 kg N ha-1 (PM2), each with three replications; nitrogen application from chemical fertilizer, urea ammonium nitrate (UAN), at a rate of 168 kg N ha-1 with four replications," and a control treatment that received 0 kg N ha-1. Subsurface drainage (tile) flow volume was monitored, and drainage samples were collected and analyzed for nitrate-nitrogen (NO3- N). The results from this 12-year study show that NO3-N losses with tile drainage were more likely to occur during the early stages of crop production (April to June) and were more related to the monthly distribution of precipitation than the total rainfall amount. The overall results of this study indicate that applying poultry manure at 168 kg N ha-1 resulted in significantly lower flow-weighted nitrate concentrations (PM < UAN < PM2) and the lowest nitrogen losses to subsurface drain water compared to UAN and PM2 application(PM < (JAN < PM2), as well as higher crop yields compared to UAN application. Therefore, it can be concluded that poultry manure application at a rate of 168 kg N ha-1 is an environmentally sound N application practice with good yield potential for corn and soybean production systems with poorly drained soils in the upper Midwest. Future work is recommended to identify new practices and technologies to reduce nitrate loss to water systems. [ABSTRACT FROM AUTHOR]

Fecal contamination of surface waters is a critical water-quality issue, leading to human illnesses and deaths. Total Maximum Daily Loads (TMDLs), which set pollutant limits, are being developed to address fecal bacteria impairments. Watershed models are widely used to support TMDLs, although their use for simulating in-stream fecal bacteria concentrations is somewhat rudimentary. This article provides an overview of fecal microorganism fate and transport within watersheds, describes current watershed models used to simulate microbial transport, and presents case studies demonstrating model use. Bacterial modeling capabilities and limitations for setting TMDL limits are described for two widely used watershed models (HSPF and SWAT) and for the load-duration method. Both HSPF and SWAT permit the user to discretize a watershed spatially and bacteria loads temporally. However, the options and flexibilities are limited. The models are also limited in their ability to describe bacterial life cycles and in their ability to adequately simulate bacteria concentrations during extreme climatic conditions. The load-duration method for developing TMDLs provides a good representation of overall water quality and needed water quality improvement, but intra-watershed contributions must be determined through supplemental sampling or through subsequent modeling that relates land use and hydrologic response to bacterial concentrations. Identified research needs include improved bacteria source characterization procedures, data to support such procedures, and modeling advances including better representation of bacteria life cycles, inclusion of more appropriate fate and transport processes, improved simulation of catastrophic conditions, and creation of a decision support tool to aid users in selecting an appropriate model or method for TMDL development. [ABSTRACT FROM AUTHOR]

Nitrate (NO 3 - N) export from row crop agricultural systems with subsurface tile drainage continues to be a major water quality concern. Woodchip bioreactors are an effective edge-of-field practice designed to remove NO 3 - N from tile drainage. The NO 3 - N by concentration (7.5 mg L 3 ) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L - N removal in a set of nine pilot-scale woodchip bioreactors in Central Iowa. NO 3 N with a removal efficiency of 32.1%. The 2 h HRT removed an average of 1.3 mg L - N concentration reduction from the inlet to the outlet was significantly different for all HRTs (p < 0.05). The 16 h HRT removed the most NO 3 - N mass removal rate (MRR) at 9.0 g m -1 ) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L -1 , followed by the 8 h HRT at 8.5 g m 3 - , and the 16 h HRT at 7.4 g m -1 NO 3 - N with a removal efficiency of 9.0%. The 2 h HRT had the highest NO 3 - N mass removal rate (MRR) at 9.0 g m -3 day -1 , followed by the 8 h HRT at 8.5 g m -3 day -1 , and the 16 h HRT at 7.4 g m -3 day -1 , all of which were statistically different (p < 0.05). Significant explanatory variables for removal efficiency were HRT (p < 0.001) and influent NO 3 - N concentration (p < 0.001), (R 2  = 0.80), with HRT accounting for 93% contribution. When paired with results from a companion study, the ideal HRT for the bioreactors was 8 h to achieve maximum NO 3 - N removal while reducing the impact from greenhouse gas emissions., (Copyright © 2019. Published by Elsevier Ltd.)

Application of poultry manure (PM) to cropland as fertilizer is a common practice in artificially drained regions of the Upper Midwest United States. Tile-waters have the potential to contribute pathogenic bacteria to downstream waters. This 3-year study (2010-2012) was designed to evaluate the impacts of manure management and tillage practices on bacteria losses to drainage tiles under a wide range of field conditions. PM was applied annually in spring, prior to planting corn, at application rates ranging from 5 to 40 kg/ha to achieve target rates of 112 and 224 kg/ha nitrogen (PM1 and PM2). Control plots received no manure (PM0). Each treatment was replicated on three chisel-plowed (CP) plots and one no-till (NT) plot. Tile-water grab samples were collected weekly when tiles were flowing beginning 30 days before manure application to 100 days post application, and additional grab samples were obtained to target the full spectrum of flow conditions. Manure and tile-water samples were analyzed for the pathogen, Salmonella spp. (SALM), and fecal indicator bacteria (FIB), Escherichia coli (EC), and enterococci (ENT). All three bacterial genera were detected more frequently, and at significantly higher concentrations, in tile-waters draining NT plots compared to CP plots. Transport of bacteria to NT tiles was most likely facilitated by macropores, which were significantly more numerous above tiles in NT plots in 2012 as determined by smoke-testing. While post-manure samples contained higher concentrations of bacteria than pre-manure samples, significant differences were not seen between low (PM1) and high (PM2) rates of PM application. The highest concentrations were observed under the NT PM2 plot in 2010 (6.6 × 10(3) cfu/100 mL EC, 6.6 × 10(5) cfu/100 mL ENT, and 2.8 × 10(3) cfu/100 mL SALM). Individual and 30-day geometric mean ENT concentrations correlated more strongly to SALM than EC; however, SALM were present in samples with little or no FIB., (Copyright © 2016 Elsevier Ltd. All rights reserved.)