Climate and Land Use Influences on Bacteria Levels in Stormwater

Abstract

The influence of climatic variables and land use on fecal coliform (FC) levels in stormwater collected from outfalls throughout southern Vancouver Island between 1995 and 2011 are examined through statistical analyses, Fourier analysis, Multiple Linear Regression (LR) and Multivariate Logistic Regression (MLR). Kendall’s τ-b demonstrated that FC levels were significantly and positively correlated with the amount of residential area within a drainage catchment generating the runoff, and that FC levels were location dependent. Climatic variables of temperature and antecedent dry period length were significantly and positively correlated with FC levels at both the sampling location level and across the region overall. Precipitation and flowrates were negatively correlated with FC levels. Fourier analysis showed that monthly FC levels shared the same 12 month cycle (peaking in July) as precipitation and temperature. MLR modelling was applied by aggregating the LogFC data by order of magnitude. The MLR model shows that the data are subject to different influences depending on the season and as well, the month of the year. The land use and climate analyses suggest that future climate change impact studies attempted on nearshore bacterial water quality should be conducted at the urban catchment scale.

Rotational grazing can mitigate ecosystem service trade‐offs between livestock production and water quality in semi‐arid rangelands

“…The significant effect of the smoothing term in our selected GAMM shows that there is strong seasonal variation in E. coli concentrations that are somewhat independent of grazing treatment. Past studies have found E. coli and faecal bacteria concentrations can increase cumulatively due to reduction of stream flow in the summer (Roche et al., 2013; Xu et al., 2019), or can undergo short escalations due to rain events that flush bacteria into streams or re‐suspend bacteria from stream sediments (Cha et al., 2016; Pachepsky & Shelton, 2011). These processes, however, do not explain the hump‐shaped pattern in E. coli concentration that we observed between May and October.…”

“…These processes, however, do not explain the hump‐shaped pattern in E. coli concentration that we observed between May and October. A growing number of studies examining climate effects on water quality have found E. coli levels in streams and other waterbodies are correlated with ambient air temperature (Whitman & Nevers, 2008; Xu et al., 2019). Maximum bacterial concentrations often occur during the warmest part of the year (Cha et al., 2016; Derose et al., 2020), potentially driven by the ability of E. coli to reproduce rapidly in warmer waters (Guber et al., 2015).…”

Urban stormwater characterization, control, and treatment

“…Escherichia coli median concentrations were well above regulatory/advisory levels at 3.7 × 104 and 8.6 × 104 CFU/100 ml for the two sites. A 16‐year study of fecal coliform levels in stormwater throughout southern Vancouver Island, Canada, demonstrated high concentrations of fecal coliform with annual periodicity and positive correlations with residential area, temperature, and antecedent dry period (Xu, Valeo, Valeo, He, & Xu, 2019). Given the length of the study, a positive test ratio was used to screen out the influence of the number of tests per month to account for nonuniform sampling.…”

Urbanization under a Changing Climate–Impacts on Hydrology

“…While at first glance the submissions to this special issue may seem disparate, they are however, all intimately connected to urban hydrology and most importantly, they span the wide range of scales of observation and consequences of urban hydrology. From the near microscopic scale [2] to meter scale [3,4] to km scale [5][6][7][8], this special issue effectively brings awareness and attention to the range of scales at which these phenomena manifest, and the responses that are necessary if societies are to truly become resilient. Spatial scale is not the only variant-temporal scales also vary across the study of urbanization and climate change impacts.…”

“…Further increasing the spatial scale is an examination of the impacts of climate and land-use on bacterial concentrations in stormwater. Xu, et al [6] looked at the relationship between observations of fecal coliform concentrations in urban stormwater runoff from the lower Vancouver Island region in Canada. The work demonstrated a clear relationship historically between increases in fecal coliform (FC) concentrations and minimum temperatures (positive), antecedent dry period (positive), and higher urban area proportions (positive,) and with negative relationships to precipitation volumes.…”