Accounting for the three-dimensional distribution of E. coli concentrations in pond water in simulations assessment of microbial quality of water withdrawn for irrigation

Authors: JEON, DONGJIN - Gwangju Institute Of Science And Technology; STOCKER, MATTHEW - Orise Fellow; SOKOLOVA, EKATERINA - Chalmers University Of Technology; LEE, HOON SOO - Chungbuk National University; BAEK, INSUCK - University Of Maryland; Kim, Moon; Pachepsky, Yakov

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2020
Publication Date: 6/15/2020
Citation: Jeon, D., Stocker, M.D., Sokolova, E., Lee, H., Baek, I., Kim, M.S., Pachepsky, Y.A. 2020. Accounting for the three-dimensional distribution of E. coli concentrations in pond water in simulations assessment of microbial quality of water withdrawn for irrigation. Irrigation Science. 12(6):1708. https://doi.org/10.3390/w12061708.
DOI: https://doi.org/10.3390/w12061708

Interpretive Summary: Microbial quality of irrigation water is the important factor of public and individual health. Irrigation water sources, such as ponds, are monitored for the indicator organism E. coli to evaluate microbial water quality. Concentrations of E. coli are variable across ponds. However, it was never studied how these concentrations vary with depth, and how such variations may affect the change of the irrigation water quality with time. We sampled water across a Maryland pond at several depths, and then used the hydrodynamic model EFDC to simulate changes in microbial water quality at the intake of the irrigation pump. We observed large increases of E. coli concentration with depth in the hot spot section of the pond close to the intake. The quality of the irrigation water strongly depended on time and on the location of the intake in the pond. Results of this work will be of use for irrigation water managers and consultants in that they underscore the need of characterizing both lateral and vertical distribution of E. coli concentrations in irrigation ponds, and taking several samples of irrigation water at the field during irrigation events.

Technical Abstract: Evaluating microbial quality of irrigation water is essential for prevention of foodborne illnesses. Generic Escherichia coli (E. coli) is used as an indicator organism to estimate microbial quality of irrigation waters. Monitoring E. coli concentrations in irrigation water sources is commonly done in water samples taken from a single depth. Vertical gradients of E. coli concentrations are typically not measured or are ignored however, E. coli concentrations in water bodies can be expected to have horizontal and vertical gradients. The objective of this work was to research 3D distributions of E. coli concentrations in an irrigation pond in Maryland and to estimate the dynamics of E. coli concentrations at the water intake during the irrigation event using hydrodynamic modeling. The study pond is about 22 m wide and 200 m long, with an average depth of 2.7 m. Three transects sampled at 50-cm depth intervals along with intensive nearshore sampling were used to develop the initial concentration distribution for application of the EFDC model. An E. coli concentration hot spot was found near the pond outlet. An eight-hour irrigation event was simulated using on-site data on wind speed and direction. Substantial vertical and horizontal variations in E. coli concentrations translated into temporally varying concentration at the intake. Additional simulations showed that the E. coli concentrations at the intake reflect the 3D distribution of E. coli in the limited pond section close to the intake. Only this section should be surveyed to estimate the dynamics of the microbial quality of water taken for irrigation. Measured and simulated 3D E. coli concentrations provide improved insight into expected microbial water quality of the irrigation water as compared with the 2D representation of spatial variability of the indicator concentration.