Hydrometeorological and Physicochemical Drivers of Fecal Indicator Bacteria in Urban Stream Bottom Sediments

Abstract

High levels of fecal indicator bacteria (FIB) are the leading cause of surface water quality impairments in the United States. Watershed-scale models are commonly used to identify relative contributions of watershed sources and to evaluate the effectiveness of remediation strategies. However, most existing models simplify FIB transport behavior as equivalent to that of dissolved-phase contaminants, ignoring the impacts of sediment on the fate and transport of FIB. Implementation of sediment-related processes within existing models is limited by minimal available monitoring data on sediment FIB concentrations for model development, calibration, and validation purposes. The purpose of the present study is to evaluate FIB levels in the streambed sediments as compared to those in the water column and to identify environmental variables that influence water and underlying sediment FIB levels. Concentrations of and enterococci in the water column and sediments of an urban stream were monitored weekly for 1 yr and correlated with a variety of potential hydrometeorological and physicochemical variables. Increased FIB concentrations in both the water column and sediments were most strongly correlated with increased antecedent 24-h rainfall, increased stream water temperature, decreased dissolved oxygen, and decreased specific conductivity. These observations will support future efforts to incorporate sediment-related processes in existing models through the identification of key FIB relationships with other model inputs, and the provision of sediment FIB concentrations for direct model calibration. In addition, identified key variables can be used in quick evaluation of the effectiveness of potential remediation strategies.

Storm loads of culturable and molecular fecal indicators in an inland urban stream

“…The 15-km creek, classified as a recreational water, runs from northeastern Blacksburg, through the Virginia Tech campus, and then into the New River, which has been the region's main source of drinking water supply and home to various recreational activities since the 1950s. A segment of the creek is instrumented with real-time monitoring capacity for a variety of hydro-meteorological and physicochemical variables as described in previous studies (Thompson et al, 2012;Liao et al, 2014). The watershed that drains to the sampling site encompasses an area of 14.4 km 2 currently classified as 84% urban/residential, 13% agricultural, and 3% forested (Fig.…”

“…The majority of previous studies have relied upon the collection and analysis of single grab samples of surface waters during high-flow events to understand relationships with major environmental factors such as land use and hydro-meteorological variables (Reeves et al, 2004;Gentry et al, 2006;Vidon et al, 2008;Liao et al, 2014). However, samples collected at single time points do not account for concentration changes during the course of a storm and therefore provide limited information regarding how loading rates might fluctuate during storm events.…”

Fecal Indicator Bacteria Entrainment from Streambed to Water Column: Transport by Unsteady Flow over a Sand Bed

“…Studies have found that streambeds, especially those comprising fine sediments, are home to FIB (Bai and Lung, 2005; Jamieson et al, 2005; Pachepsky et al, 2009; Rehmann and Soupir, 2009; Chu et al, 2014; Liao et al, 2014). A study by Cho et al (2010) found that storms cause a substantial increase in stream FIB concentrations in water from FIB‐laden runoff and the release of bacteria from stream‐bottom sediments.…”

Long-Term Impacts of Bacteria-Sediment Interactions in Watershed-Scale Microbial Fate and Transport Modeling

“…Existing modeling practice commonly assumes bacteria behave as “free‐phase” contaminants with near‐neutral buoyancy, that is, governed only by die‐off and transport downstream with the bulk flow (Jamieson et al, 2004a). Several studies note, however, that stream bed sediments can harbor 10 to 10,000 times more FIB than the overlying water column in a variety of aquatic environments (Buckley et al, 1998; An et al, 2002; Pandey et al, 2012; Liao et al, 2014). In addition, bacteria can be released and resuspended into the water column if bottom sediments are disturbed (Jamieson et al, 2005; Cho et al, 2010; Pandey et al, 2012).…”

“…A primary limitation of the Russo et al (2011) study was the lack of sediment coliform concentrations for model calibration; these data are difficult to obtain as most water quality monitoring programs only record water FIB concentrations. The present study targeted an urbanizing stream in Virginia (USA) where a paired sediment and water column FIB monitoring effort recently concluded (Liao et al, 2014). With this dataset, we aimed to (i) augment HSPF with a bacteria–sediment association module, (ii) calibrate the HSPF model parameters using both water column and bed sediment concentrations of E. coli , and (iii) evaluate the potential significance of streambed E. coli release and deposition in long‐term (2‐yr) simulations of daily in‐stream E. coli concentrations using this augmented model, as compared to the traditional assumption that E. coli behave as dissolved constituents.…”