South Shore Estuary Reserve Total Maximum Daily Load Monitoring

 

Ongoing efforts to improve the health of  New York's South Shore Estuary Reserve  (SSER) require continuously recorded  water-quality data to understand the short-term  effects of stormwater runoff and other  pollution sources. To document the diel and  tidal variability of water quality in the western  bays of the SSER, the USGS monitors select  physical and chemical parameters at two sites  within the SSER. One site, station 01310740 on Reynolds Channel at Point Lookout, is near  the estuary mouth and operated in cooperation  with the New York State Department of  Environmental Conservation (NYSDEC) and  Town of Hempstead Department of  Conservation & Waterways. The second, station  01311143 on Hog Island Channel at Island  Park, is at a mid-bay location and operated in  cooperation with the New York Department of  State through an agreement with the NYSDEC.  This monitoring program (fig. 1) documents the  diel and tidal variability of water quality across  a gradient of eutrophication in the western bays;   compliments the water-quality grab sampling  efforts of the NYSDEC, other partners, and  stakeholders; and provides information critical  to the preparation and application of a nitrogen  Total Daily Maximum Load (TMDL) for this  system. 

 

 

Both monitoring stations collect continuous  data on tidal water elevations and select  water-quality parameters that are being  recorded at 6-minute intervals, and made  publicly available via the Internet.  Water-quality data on water temperature,  specific conductance (used to compute  salinity), dissolved oxygen, turbidity, and  chlorophyll are collected from about 0.5 m  above the seabed; at mid-bay station  01311143, data on pH and nitrate also are  collected (fig. 2). Tidal statistics (for  example, mean high and low water levels)  and water-quality statistics (for example,  maximum, minimum, and mean or median  values) are published (online) annually in the  USGS Water-Data Report for Long Island.

 

 

Continuous monitoring reveals conditions  and processes undetected by grab sampling,  and documents the short-term variability of  water-quality parameters. These data  fluctuate in response to semi-diurnal and  longer-period tides, reflecting differences in  estuarine water quality due to oceanic,  upland, and atmospheric influences. One  example is an often-observed inverse  relationship between nitrate and salinity over  individual tidal cycles at mid-bay station  01311143 (fig. 3), suggesting that nitrate is  predominantly supplied by freshwater inputs  to the estuary (such as aquifer discharge), an  implication supported by reports of elevated  nitrogen concentrations in groundwater  (typically as nitrate) discharging to the SSER  (for example, Schubert and others, 2010, and  Monti and Scorca, 2003). However, other  instances where the comparatively high  nitrate-low salinity relation is not apparent or  is even reversed (not shown in fig. 3) may  indicate the input (or loss) of nitrate is due to  other factors. These findings underscore the  need for more detailed information on freshwater inputs and nitrogen (nitrate) loads  from wastewater treatment plant effluent and aquifer discharge to the estuary.  Daily statistics illustrate seasonal and  longer-term changes in water-quality  parameters, and facilitate comparison of data  between the two monitoring stations along a  eutrophication gradient within the western  bays. An example of this is shown in figure  4, which displays daily maximum, minimum,  and mean values from calendar year 2011 for  dissolved oxygen (DO) and chlorophyll.  Figure 4 illustrates good to fair water quality  and ecological conditions at station  01310740 near the estuary mouth, where  daily mean DO always remained above the  NYS Chronic Water Quality Standard (4.8  mg/L) and daily mean chlorophyll often  remained below the U.S. Environmental  Protection Agency (EPA) Fair Ecological  Condition Criterion (5 μg/L) during this  period. In contrast, figure 4 generally shows  fair to poor water quality and ecological  condition at mid-bay station 01311143, where  daily mean DO sometimes approached the  NYS Chronic Water Quality Standard (4.8  mg/L), and daily mean chlorophyll often  exceeded the EPA Poor Ecological Condition  Criterion (>20 μg/L).

 

 

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