Quantifying the variability in Escherichia coli (E. coli) throughout storm events at a karst spring in northwestern Arkansas, United States

Abstract

In northwestern Arkansas, karst aquifers have experienced degraded water quality due to impacts of landuse changes, such as increased urbanization or intensification of agriculture. Water quality at a karst spring was characterized by quantifying the variability of fecal-indicator bacteria, specifically Escherichia coli (E. coli), throughout base-flow periods and storm events. Waterquality change over time was assessed using an intermittent record of nitrate and chloride data since the 1990s. A Geographic Information System was used to quantify changes in land use over time and identify housing subdivisions using on-site septic systems. E. coli was significantly greater during storm events (649 CFU/100 mL or MP/ 100 mL) than base-flow periods (41 CFU/100 mL or MPN/ 100 mL). The increase in E. coli at the spring following storm events was interpreted to result from flushing of bacteria from the land surface, through the epikarst and karst conduits, and into groundwater. Nitrate and chloride have increased significantly since the 1990s, following the general pattern of increased urbanization in the recharge area. Septic-tank effluent may be degrading the water quality of the karst spring based on the dominance of on-site septic tank usage in the recharge area, unsuitable topography and soil type for septic tank absorption fields, increased nitrate and chloride concentrations concomitant with increased urbanization, and increase of the fecal-indicator bacteria E. coli following storm events.

Storm sampling to assess inclement weather impacts on water quality in a karst watershed: Sinking Creek, Watauga watershed, East Tennessee

“…Travel time for impaired runoff from upstream areas to the creek ranges from 30 min to 2 h, indicating the timing of the first flush. This agrees with Mallin et al (2001), who found fecal coliform had a strong correlation with precipitation within 24 h. The faster E. coli-precipitation response at the spring is likely related to the region's karst topography and was similarly observed at a spring in Arkansas (Knierim et al, 2015). Epikarst systems occur in carbonate rocks that are extensively weathered near the surface; they represent an area of the vadose zone in which groundwater or contaminants may be stored in a perched aquifer before infiltrating the carbonate rocks below (Klimchouk, 2004).…”

Comparative Microbial Community Dynamics in a Karst Aquifer System and Proximal Surface Stream in Northwest Arkansas

“…The presence of fecal contamination within Blowing Springs Cave was shown to be correlated to the increase of discharge within the cave, confirming the study by Knierim et al (2015). The source of the fecal contamination is unknown, though it is hypothesized to originate from septic tanks within the recharge area.…”

“…C and k are constants of 0.5779 and 0.002903 (USBR, 2007). Discharge for BSC was also estimated using data from a USGS station on Little Sugar creek (USGS 07188838) and the established relationship by Knierim et al (2015).…”

“…(Figure 3). The data from the current study were added to the data set by Knierim et al (2015) and a linear regression was conducted, which indicated that E. coli increased as discharge increased (Figure 4). The best fit line determined by the linear regression for the total data set was 10 ( .…”

Hydrogeology and hydrologic conditions of the Ozark Plateaus aquifer system

“…The control of these porosity types on permeability leads to two end-member flow types-diffuse flow (Alley and others, 2002;Ghasemizadeh and others, 2012), in which slower time-averaged flow through diffuse flow paths allows for sustained groundwater input to streams and springs and focused flow, which provides extremely rapid response and transit times during precipitation events. The Ozark system is susceptible to surface-derived contamination because focused flow paths-including karst features such as sinkholes, losing-stream segments, and dissolution-enlarged fractures-rapidly transmit surface water to groundwater aquifers (Adamski and others, 1997;Peterson and others, 2000;Knierim, Hays, and Bowman, 2015). Groundwater flow is ultimately controlled by lithologies exposed at the surface that receive recharge, stratigraphic relations among hydrogeologic units, geologic structure, and modification of carbonate bedrock during distinct periods of karstification over time (Kresse and others, 2014).…”