Assessing Linkages between E. coli Levels in Streambed Sediment and Overlying Water in an Agricultural Watershed in Iowa during the First Heavy Rain Event of the Season

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

Relating Watershed Characteristics to Elevated Stream Escherichia coli Levels in Agriculturally Dominated Landscapes: An Iowa Case Study

Fecal Indicator Bacteria (FIB) such as Escherichia coli (E. coli) are a leading cause of surface water impairments in the United States. However, the relative impacts of different watershed characteristics on microbial water quality in agriculturally dominated watersheds are unclear. Spatial and statistical analyses were utilized to examine relationships between watershed characteristics and FIB and a multiple regression model was created. Geometric mean E. coli concentration data were obtained for 395 ambient water quality monitoring locations in Iowa. Watersheds were delineated for thirty randomly selected monitoring locations and drainage areas ranged from 93 to 1.1 million hectares. Watershed characteristics examined include area, presence of animal units (open feed lots and confinements), percent of watershed area receiving manure application, presence of point-source discharges, and land cover. The results from the analyses reveal that the presence of animal feeding operations and agriculture, wetland, and woody vegetation land covers are the most influential watershed characteristics regarding E. coli concentration. A significant positive correlation was identified between E. coli concentration and agriculture while significant negative correlations were identified with animal feeding operations and wetland and woody vegetation. Establishing relationships between watershed characteristics and presence of E. coli is needed to identify dominant watershed characteristics contributing to pathogen water impairments and to prioritize remediation efforts

Escherichia coli inactivation kinetics in anaerobic digestion of dairy manure under moderate, mesophilic and thermophilic temperatures

Batch anaerobic digestion experiments using dairy manure as feedstocks were performed at moderate (25°C), mesophilic (37°C), and thermophilic (52.5°C) temperatures to understand E. coli, an indicator organism for pathogens, inactivation in dairy manure. Incubation periods at 25, 37, and 52.5°C, were 61, 41, and 28 days respectively. Results were used to develop models for predicting E. coli inactivation and survival in anaerobic digestion. For modeling we used the decay of E. coli at each temperature to calculate the first-order inactivation rate coefficients, and these rates were used to formulate the time - temperature - E. coli survival relationships. We found the inactivation rate coefficient at 52.5°C was 17 and 15 times larger than the inactivation rate coefficients at 25 and 37°C, respectively. Decimal reduction times (D10 ; time to achieve one log removal) at 25, 37, and 52.5°C, were 9 -10, 7 - 8 days, and \u3c 1 day, respectively. The Arrhenius correlation between inactivation rate coefficients and temperatures over the range 25 -52.5°C was developed to understand the impacts of temperature on E. coli inactivation rate. Using this correlation, the time - temperature - E. coli survival relationships were derived. Besides E. coli inactivation, impacts of temperature on biogas production, methane content, pH change, ORP, and solid reduction were also studied. At higher temperatures, biogas production and methane content was greater than that at low temperatures. While at thermophilic temperature pH was increased, at mesophilic and moderate temperatures pH were reduced over the incubation period. These results can be used to understand pathogen inactivation during anaerobic digestion of dairy manure, and impacts of temperatures on performance of anaerobic digesters treating dairy manure

Near shore beach volume modeling approach for setting beach bacteria TMDLs: A case study, Hickory Grove Lake, Iowa

A novel approach to set bacteria Total Maximum Daily Load (TMDL) using a Near-Shore Beach Volume (NSBV) model was described along with recommendations for design of a monitoring network to support this method. Sources of fecal bacteria in the Hickory Grove Lake watershed include unpermitted septic systems, manure applications in the watershed, livestock access to streams, waterfowl, and wildlife. The Lake Inlet, Lake Outlet, and Lake Beach were monitored for E. coli concentrations from 2010-2012, this monitoring data was used to assess relationships between watershed bacteria loads and the beach bacteria levels. Fecal bacteria from waterfowl were identified as the major source to the Lake Beach causing the water quality impairment. The bacteria TMDL for the Hickory Grove Lake beach was set at 1.87E+11 orgs/day for the single sample maximum target and 1.01E+11 orgs/day for the geometric mean target, which correlates to the presence of fewer than five resident geese. Monitoring recommendations to support this approach include weekly beach water quality monitoring and post-event sampling; periodic spatial sampling of the lake; weekly and post-event grab sampling of the water quality at the lake inlet mixing zones; and weekly and post-event grab sampling of the water quality at the lake outlet

Occurrence and Movement of Antibiotic Resistant Bacteria, in Tile-Drained Agricultural Fields Receiving Swine Manure

The use of tylosin at subtherapeutic levels by the swine industry provides selective pressure for the development of antibiotic resistance in gastrointestinal bacteria. The land application of swine manure to drained agricultural fields might accelerate the transport of pathogen indicators such as enterococci as well as antibiotic-resistant bacteria. The objective of this study was to develop an understanding of the occurrence and transport of antibiotic-resistant enterococci in tile-drained chisel plow and no-till agricultural fields that have received multi-year application of liquid swine manure through injection. Enterococci resistance to tylosin in manure, soil and water samples was investigated phenotypically and compared with samples from control plots treated with urea and ammonium nitrate (UAN). The analysis found that 70% of the enterococci in manure samples were resistant to tylosin. Concentrations of enterococci in tile water were low, and only exceeded the geometric mean for recreational waters 9 times, with 33% of these exceedences occurring in tile flow from the control plots. The results of this study indicate that the occurrence of tylosin-resistant enterococci in tile water is low, found in only 16% of samples, in both control plots and plots receiving fall manure application

Impacts of Temperatures on Biogas Production in Dairy Manure Anaerobic Digestion

Batch anaerobic digestion of dairy manure was performed at low (25ºC), mesophilic (37ºC), and thermophilic (52.5ºC) temperatures to determine the influences of temperatures on biogas production. The experiment was runfor 76, 40 and 29 days at 25, 37, and 52.5ºC, respectively. The biogas production was measured daily at each temperature. To estimate the solid reductions, we measured total solids (TS) andvolatile solids (VS) over time. The biogas production at 52.5ºCand 37ºC were 49 and 17 times higher than that at 25ºC. Over incubation periods, the TS reduction at 25, 37, and 52.5ºC were5.6, 57, 34%, respectively. The VS reductions were 127, 58.4, 42.5%, respectively. At 25 and 37 ºC, pH was reduced, while at52.5 ºC pH was increased. The Oxidation Reduction Potential (ORP) values at 37 and 52.5ºC were negative over the incubation period. But at 25ºC, however, the ORP values were positive after Day 19. Findings from this study are useful for enhancing anaerobic digesters’ performance

Sediment E. coli as a Source of Stream Impairment

In the U.S., 74,863 surface water quality impairments are on the EPA‘s list of impaired waters, and the leading cause is high levels of pathogens or fecal indicator bacteria (FIB) in streams and lakes. To understand E. coli contamination in an agricultural stream, we monitored streambed sediment and the overlying water for E. coli concentrations over a range of flow conditions during storm events and characterized the impact of sediment E. coli on stream water quality. Data collected in the field were used to develop and test a model of E. coli resuspension that uses sediment transport theory to calculate the release of E. coli from the streambed sediment to the water column

Transport and Persistence of Tylosin-Resistant Enterococci, erm Genes, and Tylosin in Soil and Drainage Water from Fields Receiving Swine Manure

Land application of manure from tylosin-treated swine introduces tylosin, tylosin-resistant enterococci, and erythromycin resistant rRNA methylase (erm) genes, which confer resistance to tylosin. This study documents the persistence and transport of tylosin-resistant enterococci,erm genes, and tylosin in tile-drained chisel plow and no-till agricultural fields treated with liquid swine manure in alternating years. Between 70 and 100% of the enterococci in manure were resistant to tylosin and ermB concentrations exceeded 108 copies g−1 manure, while the mean ermF concentrations exceeded 107 copies g−1 manure (ermT was not detected). The mean concentration of tylosin was 73 ng g−1 manure. Soil collected from the manure injection band closely following application contained \u3e109 copies g−1 soil of both ermB and ermF in 2010 and \u3e108 copies g−1 soil after the 2011 application compared to 3 × 103 to 3 × 105copies g−1 soil in the no-manure control plots. Gene abundances declined over the subsequent 2-yr period to levels similar to those in the no-manure controls. Concentrations of enterococci in tile water were low, while tylosin-resistant enterococci were rarely detected. In approximately 75% of tile water samples, ermB was detected, and ermF was detected in 30% of tile water samples, but levels of these genes were not elevated due to manure application, and no difference was found between tillage practices. These results show that tylosin usage increased the short-term occurrence of tylosin-resistant enterococci, erm genes, and tylosin in soils but had minimal effect on tile drainage water quality in years of average to below average precipitation

Characterization of Bacterial Endophytes Isolated from Brassica Carinata and their Potential Use to Decrease Nutrient Requirements in Crops

Bacterial endophytes have the capability to enhance plant growth by producing plant growth hormones, solubilizing phosphates, suppressing pathogenic fungi, and reducing plant stress hormones. These capabilities make them desirable limiting the amount of nutrients and pesticides that are applied to crops. Through these assays and isolations, it is possible to identify novel bacterial species. In-vitro testing had shown 9 of the 20 isolates possess the ability to produce indole-3-acetic acid (IAA) with Pantoea agglomerans BC09 producing a concentration of 30.2 ng/μl over 4 days. BC09, Bacillus subilis BC10, and Pantoea sp. BC12 were able to solubilize calcium phosphate, 7 endophytes exhibited amplification of the 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase) gene (acdS), and the plant pathogen Fusarium proliferatum had shown suppression from 17 endophytes. In-planta studies with wheat show differences between spring wheat genotypes, with BC12 and Bacillus cereus BC14 increasing Boost’s root volume more than 80% and Enterobacter sp. BC05 increasing root volume of Prevail 87%. The corn genotype 5126RR was significantly increased 72% in root volume with Bacillus pumilis BC07 applications. Brookings soybean variety increased most across endophyte applications with BC07 increasing seedling mass and root volume more than 71%. Greenhouse trial responses did not always respond to the same endophytes as root architecture with Bacilus thuringiensis BC15 drastically increasing root dry biomass of Boost 102% under low nitrogen conditions and Prevail showing a significant increase in shoot under low or high nitrogen from 9 endophytes. Corn genotype 9714/G root and shoot biomass responded positively to Bacillus safensis BC16 inoculation under high nitrogen conditions. Codington soybean genotype significantly increased root biomass 23% after BC15 inoculation. When testing endophytes ability to increase yields under field conditions, all 3 crop species did not show a significant increase. Concentration of nitrogen in plant tissue was similar to controls for both soybean and corn while phosphorus concentrations only differed in Codington at R3 after Bacillus sp. BC20 applications. Additionally, isolation of endophytes leads to previously unsequenced and uncharacterized novel bacteria belonging to Methylorubrum under the proposed species M. endophytica

Modelling animal waste pathogen transport from agricultural land to streams

The transport of animal waste pathogens from crop land to streams can potentially elevate pathogen levels in stream water. Applying animal manure into crop land as fertilizers is a common practice in developing as well as in developed countries. Manure application into the crop land, however, can cause potential human health. To control pathogen levels in ambient water bodies such as streams, improving our understanding of pathogen transport at farm scale as well as at watershed scale is required. To understand the impacts of crop land receiving animal waste as fertilizers on stream\u27s pathogen levels, here we investigate pathogen indicator transport at watershed scale. We exploited watershed scale hydrological model to estimate the transport of pathogens from the crop land to streams. Pathogen indicator levels (i.e., E. coli levels) in the stream water were predicted. With certain assumptions, model results are reasonable. This study