| Abstrakt: |
The U.S. Geological Survey worked in cooperation with the Concerned Citizens of Montauk and the New York State Department of Environmental Conservation to assess the potential sources of fecal contamination entering the Lake Montauk embayment as part of a study of seven estuarine embayments across Long Island, New York, from June 2018 to July 2019. Water samples are routinely collected by the New York State Department of Environmental Conservation in Long Island embayments and analyzed for fecal coliform bacteria (FC), an indicator of fecal contamination, to determine the closure of shellfish beds for harvest and consumption. Concentrations of fecal coliform signify the potential for pathogenic (disease-causing) bacteria to be present. Indicator bacteria alone cannot determine either the biological or geographical sources of contamination. Microbial source tracking (MST) is a method used to determine these sources of contamination. Microbial source tracking laboratory techniques can ascertain whether genetic material obtained from Bacteroides or Helicobacter bacteria in water or sediment is consistent with humans, canines (dogs), ruminants (deer, sheep), or waterfowl (water birds). Bacteroides and Helicobacter are genera of bacteria found in the gut of most warm-blooded animals. These techniques can also quantify the concentration of genetic markers found. Information such as sample location, weather and season, surrounding land use, and additional water-quality data for the location where the sample was collected help determine the geographical source and conveyance of land-based water to the embayment. The presence of genetic material and FC in samples collected at the same time is important to show that the fecal coliform is likely from the host source detected. It is possible for waters with waste infiltration to have genetic material present but no fecal indicators, such as disinfected water from a wastewater treatment plant or from groundwater that has passed through a sandy aquifer Water samples were collected in the summer and winter seasons. In each of the two seasons, one sample was collected in dry weather, and one, after substantial rainfall. Two groundwater samples and one sediment sample were also collected during this study. Surface-water source sites sampled for Lake Montauk include the Little Reed Pond Culvert, Little Reed Pond Outlet, South Beach, Stepping Stones Pond, and the Stepping Stones Pond Culvert sites. Human and waterfowl fecal contributions to Lake Montauk were detected across the landscape. Among the potential sources of fecal-contaminated water contributing to Lake Montauk--groundwater, pond drainage, stormwater runoff, and marinas (boats)--stormwater runoff and pond drainage were identified as the most likely transport mechanism of fecal contamination to Lake Montauk. Additionally, 15 of 16 samples collected throughout this study at receptor sites (the lake itself) had FC concentrations that were all at or below the FC reporting limit (less than 18 or 20 MPN/100 mL). The highest frequency of FC detections in source site samples was found to be under wet summer conditions at the South Beach, Stepping Stones Pond, and Stepping Stones Pond Culvert sites (300, 220, and more than 16,000 MPN/100 mL, respectively). Samples from receptor sites adjacent to marinas (Lake Montauk Inlet and Star Island North sites) had a higher frequency of human marker detections but were associated with FC concentrations at or below the reporting limit, indicating minimal human influence on FC loads from the sampled receptor sites to Lake Montauk during this study. The absence of FC and the human MST marker in all groundwater samples indicated limited transport of bacteria in the subsurface groundwater through the sandy aquifer material, which is consistent with results throughout Long Island. It is unlikely that water from septic systems influenced the lake given the available data. Although data for FC concentrations are unavailable for the sediment sample at the South Beach site, this sample was negative for all MST markers and is unlikely to contribute FC from the tested host organisms during resuspension events caused by tidal shifts or boat wakes Targeted sampling of the sediment and groundwater would be needed in and around Lake Montauk to fully determine the potential of fecal contamination from these sources. A classification scheme was developed that considered conditions such as high FC concentrations (particularly during dry weather samples) and contributions from human and canine waste based on detection of MST markers. The sites were assessed to assist stakeholders and resource managers in prioritizing which source sites are consistently contributing fecal coliforms to Lake Montauk throughout the year. The Little Reed Pond Culvert and South Beach sites were classified as locations most likely to contribute fecal contamination to Lake Montauk. [ABSTRACT FROM AUTHOR] |
