Within semi-arid landscapes, karst areas are among the most productive in terms of water supply-largely because of the high rates of groundwater recharge compared with those of other semi-arid areas. Recharge rates in karst regions may be affected by the type of vegetation cover. Understanding the interactions between recharge and vegetation is important at many levels, but the complex nature of karst hydrology makes this endeavour challenging. This paper presents the results of a set of hillslope-scale rainfall simulation experiments conducted within a juniper-oak woodland and over a shallow karst cave that was instrumented for drip-rate monitoring. The variables measured during these experiments include the amounts and timing of cave recharge, surface runoff, stemflow, and throughfall. The findings of this study provide insights into the importance of canopy interception during runoff-producing events, the nature and relative magnitude of rapid recharge, and the interplay between recharge and surface runoff. Key findings of the study were (1) for simulated rainstorms of around 50 mm, between 0 and 23% of the water applied was intercepted (depending on cloud conditions), and 4-9% of the water reaching the ground surface came from stemflow (which was highest under the wettest conditions); (2) surface runoff accounted for approximately 3% of the water applied; and (3) recharge accounted for between 8 and 17% of the water applied and typically reached its maximum level within 20 min of rainfall cessation, declining rapidly thereafter.
Gastrointestinal (GI) illness risks associated with exposure to waters impacted by human and nonhuman fecal sources were estimated using quantitative microbial risk assessment (QMRA). Microbial source tracking (MST) results had identified Escherichia coli (E. coli) contributors to the waterbody as human and unidentified (10%), cattle and domestic animals (25%), and wildlife (65%) in a rural watershed. The illness risks associated with ingestion during recreation were calculated by assigning reference pathogens for each contributing source and using pathogen dose–response relationships. The risk of GI illness was calculated for a specific sampling site with a geometric mean of E. coli of 163 colony forming units (cfu) 100 mL−1, and the recreational standard of E. coli, 126 cfu 100 mL−1. While the most frequent sources of fecal indicator bacteria at the sampling site were nonhuman, the risk of illness from norovirus, the reference pathogen representing human waste, contributed the greatest risk to human health. This study serves as a preliminary review regarding the potential for incorporating results from library-dependent MST to inform a QMRA for recreational waters. The simulations indicated that identifying the sources contributing to the bacterial impairment is critical to estimate the human health risk associated with recreation in a waterbody.
Storm water runoff is increasingly assessed for fecal indicator organisms (e.g., Escherichia coli, E. coli) and its impact on contact recreation. Concurrently, use of autosamplers along with logistic, economic, technical, and personnel barriers is challenging conventional protocols for sample holding times and storage conditions in the field. A common holding time limit for E. coli is 8 h with a 10 °C storage temperature, but several research studies support longer hold time thresholds. The use of autosamplers to collect E. coli water samples has received little field research attention; thus, this study was implemented to compare refrigerated and unrefrigerated autosamplers and evaluate potential E. coli concentration differences due to field storage temperature (storms with holding times ≤24 h) and due to field storage time and temperature (storms >24 h). Data from 85 runoff events on four diverse watersheds showed that field storage times and temperatures had minor effects on mean and median E. coli concentrations. Graphs and error values did, however, indicate a weak tendency for higher concentrations in the refrigerated samplers, but it is unknown to what extent differing die-off and/or regrowth rates, heterogeneity in concentrations within samples, and laboratory analysis uncertainty contributed to the results. The minimal differences in measured E. coli concentrations cast doubt on the need for utilizing the rigid conventional protocols for field holding time and storage temperature. This is not to say that proper quality assurance and quality control is not important but to emphasize the need to consider the balance between data quality and practical constraints related to logistics, funding, travel time, and autosampler use in storm water studies.
Escherichia coli contamination in surface water is a universal issue that signifies potentially increased human health risks from fecal loading. Nonpoint-source contamination contributes to instream fecal loading; however, land use and land cover can alter its effects on stream water quality. Different land uses and land covers yield various landscape factors that influence water quality. This study evaluated E. coli occurrence, movement, and distribution by monitoring soil and rainfall runoff from small, ungrazed, upland watersheds under native prairie, managed hay pasture, and cultivated cropland uses and land covers. Management strategies applied to each small watershed excluded anthropogenic E. coli input, thus yielding E. coli concentrations that are considered background sources. Significant differences in median E. coli loads in runoff were identified (1.47 ´ 10 9 -5.71 ´ 10 9 ) despite similar runoff volume among watersheds, suggesting that land use and land cover differences can significantly affect background pollutant load transport during runoff events. Estimated soilderived E. coli loads were significantly less (£0.0046%) than runoff loads, suggesting that recent fecal deposition is likely the primary source of E. coli loading in surface runoff. Results further demonstrate the complexity in understanding watershed E. coli fate and transport and highlight the challenges in modeling, managing, and assessing background and other nonpointsource E. coli loads. SURFACE WATER QUALITY TECHNICAL REPORTS Core Ideas• Land use and land cover differences can affect E. coli concentrations and loads.• Upland soils were not a significant contributor of E. coli in surface runoff.• Wildlife can contribute significant E. coli loading in edge-of-field runoff.
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