Sampling Methods

From June 2018 to July 2019, twelve sites were sampled in and around Lake Montauk yielding 35 surface-water samples, 3 groundwater samples (including one replicate), and 1 sediment sample. Of the surface-water sites, five were considered to be source sites (waters flowing directly into Lake Montauk from the land), and four were considered to be receptor sites (the lake itself). Seventeen surface-water samples were collected under wet conditions, and eighteen, under dry conditions; seventeen surface-water samples were collected in the summer, and eighteen, in the winter. Quality control samples from the larger MST assessment represent the sample collection and laboratory methods for the Lake Montauk area; quality assurance procedures are presented in Tagliaferri and others (2021). All water-quality and sediment data collected in the field and those analyzed in laboratories as part of this study are available from the U.S. Geological Survey (USGS) National Water Information System (NWIS) database (U.S. Geological Survey, 2020a).

Sampling and laboratory methods used for this study are detailed in Tagliaferri and others (2021). All groundwater and sediment samples in Lake Montauk were collected in June 2019 (with the exception of one groundwater sample collected in July 2019). Wet conditions were defined as more than 0.25 inch of precipitation in 24 hours or 0.50 inch in 48 hours. Dry conditions were defined as less than 0.25 inch of precipitation in 72 hours. Rainfall totaled 0.02 inch on September 9, 2018, and 0.25 inch on September 10, 2018, designating samples collected on September 10, 2018, in Lake Montauk as summer wet samples (more than 0.25 inch within 24 hours). Winter, wet, receptor samples were collected in Lake Montauk on April 17, 2019, with 0.47 inch of precipitation falling on April 15, 2019, 0.12 inch falling on April 16, 2019, and no precipitation on April 17, 2019. Winter, wet, source samples were collected on April 30, 2019, with 0.03 inch of precipitation falling on April 29, and 0.28 inch falling on April 30. Rainfall values were obtained from the Montauk Airport weather station (KMTP; Weather Underground, 2021).

Laboratory Methods

Laboratory methods used for this study are detailed in Fisher and others (2020). Samples for fecal coliforms were analyzed at Suffolk County Department of Health Services Public Environmental Health Laboratory (PEHL). Samples for MST markers were analyzed by the USGS Ohio Water Microbiological Laboratory in Columbus, Ohio. Additional information was either observed or compiled to facilitate interpretation of data. Precipitation measurements from the Montauk Airport weather station (Weather Underground, 2021) were used to determine whether weather conditions were considered dry or wet. Quality assurance for samples collected at Montauk Airport weather station are unavailable. Relative tide stage as noted by USGS field personnel and verified based on tidal predictions available (National Oceanic and Atmospheric Administration, undated) was documented along with the sample information in NWIS (U.S. Geological Survey, 2020a). Land-cover and sewer district geographic information system (GIS) coverages (Nassau County, 2015; Suffolk County, 2020; U.S. Geological Survey, 2020b) were used for data interpretation. These data support the MST results to increase confidence in the geographical source of the water and likely transport mechanisms of fecal contamination to Lake Montauk.

Microbial Source Tracking

The human-associated Bacteroides (HF183) marker was the only marker detected at surface-water receptor sites, and both HF183 and waterfowl Helicobacter (GFD) markers were detected at surface-water source sites. The human marker was detected five times throughout the Lake Montauk landscape, with four positive detections in receptor site samples and one in a source site sample (Stepping Stones Pond; fig. 3). There were three detections for the waterfowl marker, all in source site samples (fig. 4; table 1). The canine-associated Bacteroides (BacCan) markers and ruminant Bacteroides (Rum2Bac) markers were not detected, suggesting minimal contribution from domestic dogs and the resident deer population. There were no positive MST marker detections in the groundwater samples collected at the South West Lake Drive and West Lake Drive near Star Island sites or in the sediment sample collected at the South Beach site.

Host Specific Markers

Reporting limits for the two predominant MST markers (HF183 and GFD) detected in Lake Montauk varied slightly because of analytical processes, such as dilutions required because of matrix interferences. Understanding occurrence of the predominant MST markers in Lake Montauk can help prioritize locations for additional investigation and infrastructure improvement and provide a baseline for host contributions when prioritizing sites of concern for assessing FC and after total maximum daily load implementation.

HF183

There were five positive detections for human-associated Bacteroides (HF183) marker in Lake Montauk. Three of the five positive detections were in samples collected during the winter, and the other two, in the summer (table 1). The highest concentration of HF183 (and the only instance of HF183 at a source site) was in the sample collected at the Stepping Stones Pond site (3,200 copies per 100 milliliters [copies/100 mL]; table 1.2; U.S. Geological Survey, 2020a) during wet winter conditions, whereas the lowest concentration that was above the detection limit was in the sample collected at the Star Island North site (260 copies/100 mL) during dry winter conditions. The human marker was detected more frequently in samples from receptor sites and was exclusively detected in samples from receptor sites adjacent to marinas (Lake Montauk Inlet and Star Island North). The low detection frequency of HF183 in samples collected throughout Lake Montauk is indicative of minimal to no human-associated Bacteroides inputs from inland sources or sources from within the receptor (including boats and marinas) during this study. Additionally, there were no positive detections of HF183 in the groundwater or sediment samples collected for this study (fig. 3).

GFD

The waterfowl marker was detected in 3 of the 35 surface-water samples collected. All positive detections were in samples collected at source sites and under varying sampling conditions—one sample each in wet winter, dry winter, and dry summer conditions (fig. 4). The lowest concentration of the GFD marker that was above the detection limit was in the sample collected at the South Beach site during dry winter conditions (570 copies/100 mL; table 1.2; U.S. Geological Survey, 2020a). The low detection frequency of GFD in samples collected throughout Lake Montauk is indicative of minimal to no waterfowl-associated Helicobacter inputs from inland sources or sources from within the receptor during this study. There were no positive detections of GFD in the groundwater samples collected at the South West Lake Drive and Lake Drive near Star Island sites or in the sediment sample collected at the South Beach site.

Fecal Coliform Bacteria

Fifteen of 16 (94 percent) receptor site samples and 12 of 19 (63 percent) source site samples had concentrations that were at or below the FC reporting limit (less than [<] 18 or 20 MPN/100 mL). The single receptor sample with a positive FC detection (40 most probable number per 100 milliliters [MPN/100 mL]) was collected at the Lake Montauk Inlet site during wet, summer conditions. The sample with the highest fecal coliform concentration exceeded the upper concentration threshold (greater than [>] 16,000 MPN/100 mL) and was collected in wet, summer conditions at the Stepping Stone Pond Culvert site; this sample was negative for all MST markers (human, waterfowl, ruminant, and canine). All other samples collected at the Stepping Stones Pond Culvert site had concentrations that were at or below detection for FC. Seven of the 35 surface-water samples collected in and around Lake Montauk (20 percent) had concentrations that were above 49 MPN/100 mL (table 1.2; U.S. Geological Survey, 2020a), the 90th percentile concentration determined by the NYSDEC as part of the National Shellfish Sanitation Program (NSSP) closure criteria (U.S. Food and Drug Administration, 2019). Of these seven surface-water source samples, five were collected during the summer, and five under wet sampling conditions (table 1.1; U.S. Geological Survey, 2020a). In general, high FC concentrations were measured during the wet summer conditions.

The relation between FC and marker detection is not straightforward. Fecal coliform and specific host-associated markers may decay at different rates and be present in different abundances. Additionally, host-associated markers have been shown to decay more rapidly than FC (Drozd and others, 2013; Rogers and others, 2011). One of six sample sites with MST marker detections (Little Reed Pond Culvert) had high FC concentrations (110 MPN/100 mL) with the rest at or above the reporting limit for FC.

Nonpoint Sources of Fecal Coliform Bacteria

Potential, major nonpoint contributors of freshwater to Lake Montauk include groundwater seepage and direct stormwater runoff not conveyed by the municipal separate storm sewer system, particularly from ponds and road ends. Fecal coliform concentrations for groundwater samples collected at the South West Lake Drive and West Lake Drive near Star Island sites were below detection (<18 MPN/100 mL), indicating minimal to no contribution of FC to Lake Montauk from groundwater samples collected during these two sampling events. There were no MST markers associated with the groundwater samples.

Another nonpoint source that can contribute to fecal contamination in water samples is sediment during resuspension (O’Mullan and others, 2019). To better understand these contributions, one sediment sample was collected at the South Beach site. There are no fecal coliform data available for the sediment collected at the South Beach site, and there were no MST markers detected in the sediment sample (table 1.2; U.S. Geological Survey, 2020a); therefore, additional, targeted investigations would be needed to determine the degree of contribution to FC loads from sandy shoreline sediments in Lake Montauk.

Little Reed Pond Culvert—Class 4

Fecal coliform concentrations were highest in the dry summer and wet winter samples (110 MPN/100 mL in each sample). Waterfowl markers were detected in the wet winter sample; this sample contained the second highest waterfowl marker concentration of the three waterfowl marker detections in Lake Montauk samples (2,000 copies/100 mL). No markers were detected in the other samples collected at this site. Fecal coliform concentrations were not higher in samples from wet conditions than in dry, therefore, stormwater runoff from road ends or Little Reed Pond is not implicated as a source of FC to Lake Montauk during this study.

South Beach—Class 4

Two of four surface water samples collected at this site had FC concentrations above 49 MPN/100 mL but contained no MST markers. The sample collected in dry winter conditions had concentrations that were positive for the waterfowl marker (540 copies/100 mL) but was below detection for FC (<18 MPN/100 mL). Elevated FC concentrations were observed during wet sampling conditions, implicating stormwater influence on FC loads to Lake Montauk at this site during this study.

Little Reed Pond Outlet—Class 5

Little Reed Pond Outlet was the only surface water source site where samples contained no MST markers, most likely due to dilution by the receptor. Three of four samples collected at this site had concentrations that were below the reporting limit for FC (<18 or <20 MPN/100 mL). The dry summer sample had a concentration of FC that was 130 MPN/100 mL and was negative for all MST markers. Given the general absence of FC in wet conditions, stormwater runoff is not suspected to contribute FC to Lake Montauk at this site during this study.

Stepping Stones Pond—Class 5

Three of four samples collected at this site had concentrations that were at or below the reporting limit for FC and ranged from <18 to 220 MPN/100 mL in the wet summer sample. The human marker was detected in the wet winter sample at a concentration of 3,200 copies/100 mL, the highest concentration observed in all of Lake Montauk samples. Available data indicate that stormwater, particularly during the summer, is a source of FC to Lake Montauk.

Stepping Stones Pond Culvert—Class 5

Three of four samples collected at this site had concentrations that were at or below the reporting limit for FC (<18 or <20 MPN/100 mL). The wet summer sample exhibited the highest FC concentration observed in all of Lake Montauk (>16,000 MPN/100 mL). Stepping Stones Pond also had elevated FC detected during wet weather. The lack of human, canine, waterfowl, and ruminant markers coupled with the high FC concentration in the wet summer sample at this site may indicate fecal contamination from an untested source organism during this study. Stormwater flushing water from the pond through the culvert is a source of FC to Lake Montauk during the summer.

Sediment—Class 5

No human, waterfowl, or canine markers were detected in these samples, indicating minimal to no fecal contamination from the tested host organisms to Lake Montauk through the sandy shoreline sediment during this study. Fecal coliform concentrations are not available for sediment samples collected at the South Beach site. However, recent research (O’Mullan and others, 2019; Hassard and others, 2016) indicated that resuspension of sediment along natural shorelines and lakebeds can cause a spike in fecal indicator bacteria in the water column. Therefore, it is possible that, during conditions that result in high wave energy, sediment (particularly organic-rich material) can act as a source of FC when resuspended in the water column as a result of tidal movement, storms, or boat activity. Additional, targeted investigations would be needed to determine the degree of contribution to FC loads from sandy, shoreline sediments in Lake Montauk.

Groundwater—Class 5

The human MST marker was not detected at the West Lake Drive near Star Island or South West Lake Drive sites during this study, suggesting no septic influx to Lake Montauk on the days the two samples were collected. The lack of positive detections for FC in groundwater samples collected throughout Long Island for the island-wide MST study suggests that direct groundwater seepage is an unlikely contributor of FC to Lake Montauk.