Accounting for the Three-Dimensional Distribution of <i>Escherichia coli</i> Concentrations in Pond Water in Simulations of the Microbial Quality of Water Withdrawn for Irrigation

• Main Authors: Matthew D. Stocker, Dong Jin Jeon, Ekaterina Sokolova, Hoonsoo Lee, Moon S. Kim, Yakov A. Pachepsky
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Water
• Subjects: microbial water quality; irrigation; EFDC; 3D distribution; <i>E. coli</i>
• Online Access: https://www.mdpi.com/2073-4441/12/6/1708

Evaluating the microbial quality of irrigation water is essential for the prevention of foodborne illnesses. Generic <i>Escherichia coli</i> (<i>E. coli</i>) is used as an indicator organism to estimate the microbial quality of irrigation water. Monitoring <i>E. coli</i> concentrations in irrigation water sources is commonly performed using water samples taken from a single depth. Vertical gradients of <i>E. coli</i> concentrations are typically not measured or are ignored; however, <i>E. coli</i> concentrations in water bodies can be expected to have horizontal and vertical gradients. The objective of this work was to research 3D distributions of <i>E. coli</i> concentrations in an irrigation pond in Maryland and to estimate the dynamics of <i>E. coli</i> concentrations at the water intake during the irrigation event using hydrodynamic modeling in silico. The study pond is about 22 m wide and 200 m long, with an average depth of 1.5 m. Three transects sampled at 50-cm depth intervals, along with intensive nearshore sampling, were used to develop the initial concentration distribution for the application of the environmental fluid dynamic code (EFDC) model. An eight-hour irrigation event was simulated using on-site data on the wind speed and direction. Substantial vertical and horizontal variations in <i>E. coli</i> concentrations translated into temporally varying concentrations at the intake. Additional simulations showed that the <i>E. coli</i> concentrations at the intake reflect the 3D distribution of <i>E. coli</i> in the limited pond section close to the intake. The 3D sampling revealed <i>E. coli</i> concentration hot spots at different depths across the pond. Measured and simulated 3D <i>E. coli</i> concentrations provide improved insights into the expected microbial water quality of irrigation water compared with 1D or 2D representations of the spatial variability of the indicator concentration.