Intra-seasonal variation of E. coli and environmental covariates in two irrigation ponds in Maryland, USA

Authors: STOCKER, MATTHEW - Orise Fellow; Pachepsky, Yakov; HILL, R - University Of Maryland; SELLNER, K - Hood College; STAVER, K - University Of Maryland

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2019
Publication Date: 3/9/2019
Citation: Stocker, M., Pachepsky, Y.A., Hill, R., Sellner, K., Staver, K. 2019. Intra-seasonal variation of E. coli and environmental covariates in two irrigation ponds in Maryland, USA. Science of the Total Environment. 670:732-740.

Interpretive Summary: Microbial quality of irrigation water is commonly assessed by measuring concentrations of E. coli. Concentrations of E. coli in irrigation waters are variable in space and time and their determination is resource-demanding in the regular farm environment. E. coli concentrations are known to be affected by several factors affecting bacteria survival. These factors are characterized by water quality parameters that co-vary with E. coli concentrations and can be measured with currently available sensors. The objective of this work was to identify the most influential environmental covariates affecting E. coli concentration during a three month-long monitoring campaigns in two irrigation ponds in Maryland. We performed dense sampling of ponds biweekly during the summer of 2017. Water quality parameters as well as E. coli concentrations were measured. Regression tree algorithms were applied to determine the most influential water quality parameters for prediction of E. coli levels. Correlations between E. coli and water quality covariates were not strong and were inconsistently significant. On average, shoreline samples had higher E. coli concentrations than interior samples and significant differences were observed when comparing these two groups. Regression trees provided fairly accurate predictions of E. coli levels based on water quality parameters with R2 ranging from 0.70 to 0.93. Regression trees varied by sampling date but common leading covariates included cyanobacteria, organic matter, and turbidity. Results of this work indicate the opportunity to use environmental covariates sensed either remotely or in situ to delineate areas with different E. coli survival conditions across the irrigation ponds.

Technical Abstract: Fecal coliform bacteria (FCB) contamination of natural waters is a serious public health issue. Therefore, understanding and anticipating the fate and transport of FCB are important for reducing the risk of contracting diseases. The objective of this study was to analyze the impacts of climate change on the fate and transport of FCB. We modified both the soil and the in-stream bacteria modules in the soil and water assessment tool (SWAT) model and verified the prediction accuracy of seasonal variability of FCB loads using observations. Forty bias-correcting GCM-RCM projections were applied in the modified SWAT model to examine various future climate conditions at the end of this century (2076–2100). Lastly, we also compared the variability of FCB loads under current and future weather conditions using multi-model ensemble simulations (MMES). The modified SWAT model yielded a satisfactory performance with regard to the seasonal variability of FCB amounts in the soil and FCB loading to water bodies). The modified SWAT model presented substantial proliferation of FCB in the soil (30.1%–147.5%) due to an increase in temperature (25.1%). Also, increase in precipitation (53.3%) led to an increase in FCB loads (96.0%–115.5%) from the soil to water body. In the in-stream environment, resuspension from the stream bed was the dominant process affecting the amount of FCB in stream. Therefore, the final FCB loads increased by 71.2% because of the growing peak channel velocity and volume of water used due to an increase in precipitation. Based on the results of MMES, we concluded that the level of FCB would increase simultaneously in the soil as well as in stream by the end of this century. This study will aid in understanding the future variability of FCB loads as well as in preparing an effective management plan for FCB levels in natural waters.