A 22-Site Comparison of Land-Use Practices, E-coli and Enterococci Concentrations

Abstract

Land-use practices can greatly impact water quality. Escherichia (E.) coli and Enterococcus are accepted water quality indicators. However, surprisingly little research has been conducted comparing both organisms' population density relationships to land use practices and water quality. Stream water grab samples were collected monthly (n = 9 months) from 22 stream monitoring sites draining varying land use practice types in a representative mixed-land-use watershed of the northeastern United States. E. coli and enterococci colony forming units (CFU per 100 mL) were estimated (n = 396) and statistically analyzed relative to land use practices, hydroclimate, and pH, using a suite of methods, including correlation analysis, Principal Components Analysis (PCA), and Canonical Correspondence Analysis (CCA). Correlation analyses indicated significant (p < 0.05) relationships between fecal indicator bacteria concentrations, water quality metrics and land use practices but emphasized significant (p < 0.05) negative correlations between pH and instream enterococci concentrations. PCA and CCA results indicated consistent spatial differences between fecal indicator bacteria concentrations, pH, and land use/land cover characteristics. The study showed that pH could be considered an integrated proxy variable for past (legacy) and present land use practice influences. Results also bring to question the comparability of E-coli and enterococci relative to dominant land use practices and variations in pH and provide useful information that will help guide land use practice and water pollutant mitigation decision making.

Keywords: Escherichia coli; acid-mine drainage; enterococcus; fecal indicators; land use practices; water quality.

Figure 1

Monitoring site locations (n = 22) and land use cover, in West Run Watershed, Morgantown (Latitude: 39.629524, Longitude: −79.955894, WV, USA).

Figure 2

Climate variables (30−min time series) collected during the current study period (3 March−3 November 2020) in West Run Watershed, WV, USA.

Figure 3

Box and whisker plots of E. coli and enterococci (CFU) at 22 stream monitoring sites during the study period (3 March–3 November 2020) in West Run Watershed, Morgantown, WV, USA. Colony Forming Units (CFU) are as per 100 mL water sample. Blue shaded boxes denote tributaries. Green shading denotes main stem West Run Creek. Log-scale is solely for purpose of improved visualization. Note: to reduce y-axis column heading label length, enterococci are abbreviated “Entero”.

Figure 4

Box and whisker plots reflecting pH sampled weekly at 22 stream monitoring sites during the study period (3 March–3 November 2020) in West Run Watershed, Morgantown, WV, USA. Blue shaded boxes denote tributaries. Green shading denotes main stem West Run Creek.

Figure 5

Results of Principal Components Analysis (biplot) for extracted principal components of stream fecal indicator bacteria and pH data, explaining 85% of the dataset cumulative variance during the study period (3 March−3 November 2020) and land use/land cover characteristics in West Run Watershed, WV, USA. Red labels denote study site #s; axis scale has been adjusted to maximize visibility.

Figure 6

Results of Canonical Correspondence Analysis of stream fecal indicator bacteria and pH data, explaining approximately 53% of the adjusted cumulative variation of site-level bacterial averages, during study period (3 March–3 November 2020) and land use/land cover characteristics in West Run Watershed, WV, USA.

Figure 7

Average E. coli and enterococci concentration (CFU per 100 mL) and relative land use (%) for each sampling location (n = 22) during the study period (3 March–3 November 2020) in West Run Watershed, Morgantown, WV, USA.

Figure 8

(Top) Land use type by area (km²) draining to main stem West Run Creek monitoring sites #3, #4, #6, #10, #13, #18, #19, #21 and #22, and elevation (m) for each monitoring site, relative to (Bottom) average (mean), median and maximum Escherichia coli and enterococci concentrations (CFU per 100 mL) in West Run Watershed, Morgantown, WV, USA.