Spatially explicit pollutant load-integrated in-stream E. coli concentration modeling in a mixed land-use catchment

Abstract

Pathogen contamination is a major cause of surface water impairment in the United States, and fecal bacteria levels are typically used to evaluate microbial loading in bodies of water. Environmental models are considered a useful tool for evaluating watershed management practices. In this study, we assessed E. coli contamination of the Upper Stroubles Creek, Virginia, USA using the Soil and Water Assessment Tool (SWAT) model. The study area has been declared an impaired body of water due to recent bacterial contamination. Bacterial source characterizations play a critical role in such modeling exercises and especially in the case of non-point sources. As the SWAT model involves bacteria load estimation at a Hydrological Response Unit (HRU) level, we use the Spatially Explicit Load Enrichment Calculation Tool (SELECT) for our E. coli load estimations. We also evaluate current approaches to the measurement of bacterial interactions of the sediment-water interface using SWAT and the frequent measurements of streambed E. coli concentrations. For the simulation of in-stream E. coli concentrations using estimates drawn from SELECT without (with) sediment bacteria resuspension-deposition, Nash-Sutcliffe Efficiency (NSE) values of -0.41 to 0.34 (-0.19 to 0.36) are found. Moreover, in-stream E. coli concentrations measured at flow duration intervals show that the model frequently overestimates mid-range flows while underestimating low-range flows even with model improvements. The use of high-resolution E. coli loads and the consideration of sediment bacteria resuspension-deposition processes, generated higher E. coli concentrations for forested areas compared to those of urban and pasture lands, suggesting the importance of using detailed bacteria load estimations and land use information when assessing E. coli distribution in the environment.

Rainfall-driven E. coli transfer to the stream-conduit network observed through increasing spatial scales in mixed land-use paddy farming karst terrain

“…manure heaps prepared for land application, to become hydrologically connected to the groundwater system, via transfer from fresh manure heaps to sink holes or irrigation ditches. Evidence of increased loading of watercourses in mixed-land-use or agricultural catchments during growing seasons and associated organic fertiliser application further supports this (Sinclair et al., 2009; Thilakarathne et al., 2018). The presence of impervious surfaces (e.g.…”

“…The activation of overland flow during higher intensity events may contribute to the higher sediment loads observed during events, and is likely to be more significant than in non-karst catchments (Buckerfield et al., 2019). The resuspension of streambed, fissure, or conduit sediment stores may also contribute to the increasing strength of correlation with increasing discharge - indeed, the potential for survival of E. coli in karst conduits for several months has been demonstrated (Bradshaw et al., 2016; Thilakarathne et al., 2018).…”

Multiscale spatiotemporal variability of fecal indicator bacteria and associated particle size distributions in the sandy bottom sediments of a Pennsylvania creek

“…Trends in concentrations along the creek were not significant on many sampling dates. Such trends were expected due to substantial differences in land use among the sampling sites, as the animal and human waste management in different land use settings can strongly affect FIB concentrations (Antunes et al., 2022; Frak, 2013; Haack et al., 2016; Thilakarathne et al., 2018). It appears that more samples may be needed to reveal such differences for individual sampling dates.…”

Coupled effects of land-use patterns and hydrological regimes on fecal indicator bacteria in a coastal watershed

“…In urban areas, dense human populations and wastewater treatment plants can lead to high E. coli levels in the environment owing to an increased potential for fecal contamination. The effectiveness of wastewater treatment plants in disinfecting water and managing stormwater runoff is crucial for determining E. coli export (Thilakarathne et al, 2018). Improved infrastructure and proper urban management can also help reduce E. coli contamination and exports to downstream water bodies.…”