Characterization of Water Quality in the Sakonnet River, Rhode Island, 2018-19

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Sections of Narragansett Bay and its eastern arm, the Sakonnet River, are considered impaired for shellfishing, aquatic habitat and recreational use by the State of Rhode Island. Aquatic habitat and water quality in the western portions of Narragansett Bay are relatively well understood, but there is comparably limited information available in the Sakonnet River. To address concerns about the lack of data on water-quality conditions, the USGS New England Water Science Center, in cooperation with EPA Region 1, conducted water-quality monitoring in the Sakonnet River during 2018-19.

Location of the Sakonnet River, Rhode Island

Figure 1. Location of the Sakonnet River, Rhode Island. (Credit: Jason Sorenson, U.S. Geological Survey. Public domain.)

The Sakonnet River is a tidal strait that flows approximately 14 miles between Mount Hope Bay and Rhode Island Sound, in Rhode Island (Figure 1). Seasonal algal and nuisance plant growth and other indicators of ecological impairment have raised concerns about the health of this important coastal resource. Some areas of the Sakonnet River are already permanently closed to shellfishing due to elevated bacteria concentrations. The shoreline along the Sakonnet River and the larger watersheds draining to Narragansett Bay are densely developed. Consequently, inputs of nutrients and other constituents from point- and nonpoint-source wastewater disposal and stormwater runoff are likely the primary causes of observed water-quality impairments. Detailed characterization of water-quality conditions in the Sakonnet River is important for developing an improved understanding of the effects of spatially and temporally distributed inputs to eastern Narragansett Bay and the Sakonnet River and informing associated management actions.

Low dissolved oxygen conditions are of particular concern for aquatic habitat and the overall ecological health of the system.

Data-collection locations for the 2018 monitoring program, Sakonnet RI

Figure 2. Data-collection locations for the 2018 monitoring program in the Sakonnet River, Rhode Island. Continuous and discrete water-quality data were collected at three fixed stations (413642071125701, near Gould Island; 413252071131501, near Fogland Beach, and 412932071124701, near Church Point) where monitoring buoys were deployed. Continuous data were collected during three moving-boat surveys on July 26, August 28, and September 25, 2018 to characterize the spatial distribution of near-surface water quality; the line represents an example moving boat track from the August 28. 2018 survey. Vertical water-quality profile data were also collected at the fixed stations and an additional 15 stations (RI-Sakonnet-001 through -015) during the moving boat surveys. (Credit: Jason Sorenson, U.S. Geological Survey. Public domain.)

To address concerns about water-quality conditions in the Sakonnet River, the U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency (EPA) Region 1 Southeast New England Program for Coastal Watershed Restoration (SNEP) and the Rhode Island Department of Environmental Management (RIDEM), conducted a comprehensive monitoring program during 2018-19. Data were collected from April 28 to November 11, 2018 and from June 19 to November 26, 2019. 

Continuous and discrete data collection were done in accordance with standard USGS sample-collection procedures. All continuous and discrete water-quality data from top and bottom water locations were collected with calibrated multi-parameter probes. All continuous water-quality data records were analyzed and approved by using USGS data-management procedures for continuous data (USGS, 2010; Wagner and others, 2006). Discrete water-quality data and samples collected from top and bottom locations were also analyzed and approved by using USGS data-management procedures for discrete data (USGS, variously dated; Wilde and others, 2004a; 2004b; 2014). Final, approved data are stored in the USGS National Water Inventory System (NWIS) database (National Water Information System (NWIS) Mapper) or the project data release (Sorenson and others, 2021) as described below.

 

Components of the 2018 monitoring program

1. Continuous records of water-quality were collected at fixed locations for the duration of the 2018 monitoring period. Continuous data were collected from three monitoring buoys (Figure 2):

413642071125701, Sakonnet River near Gould Island;

413252071131501, Sakonnet River near Fogland Beach; and

412932071124701, Sakonnet River near Church Point.

Examples of multi-parameter probes and temperature and dissolved oxygen sensors used for 2018-19 monitoring program

Figure 3. (A) Examples of the multi-parameter water-quality probes used for continuous fixed-station monitoring, moving boat surveys, and vertical water-quality profiles. (B) Example of smaller temperature and dissolved oxygen sensors with and without a wiper unit. (Credit: Jason Sorenson, U.S. Geological Survey. Public domain.)

Continuous (15-minute interval) temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected within the top 0.5 meters (m) of the water column with calibrated multi-parameter probes (Figure 3) at all three stations. Continuous (15-minute interval) temperature and dissolved oxygen data were also collected 0.5 m from the bottom of the water column at two of the stations (413642071125701, near Gould Island; and 413252071131501, near Fogland Beach) (Figure 2) by using two smaller internally logging sensors (Figure 3). These bottom sensors were not equipped with wiper units and resulting in some sensor biofouling. As a result, a portion of the dissolved oxygen data needed to be deleted from the record. A fourth clean and calibrated multi-parameter probe was used as the reference probe for all station visits associated with sample collection and sensor maintenance activities. Monitoring buoy platforms are shown in Figure 4. The continuous data from these fixed stations are stored in the NWIS database.

2. Continuous (5-second interval) records of water-quality were collected from moving boat surveys on July 26, August 28, and September 25, 2018. These surveys were designed to characterize the spatial distribution of near-surface water-quality conditions in the river during snapshots in time. Temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected with a calibrated multi-parameter probe equipped with a flow-through cell and pump designed to draw water from through-hull fittings in the boat. Water-quality results and survey tracks are provided in the project data release (Sorenson and others, 2021) and an example boat track from August 28, 2018 is shown in Figure 2. 

3. During the moving boat surveys, vertical profiles of water quality were collected at the 18 stations shown on Figure 2 (RI-Sakonnet-001 through RI-Sakonnet-015 and the three fixed, buoy stations). On July 26, 2018, data were collected at only 16 of these stations due to high winds. Temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected from depths ranging from 3 to 39 feet (1 to 15 m) with an additional calibrated multi-parameter probe by using a constant rate of descent through the water column and recording data at 1-2 second intervals. Near-surface results were compared to the moving boat survey results at these locations as a check on the agreement between the two multi-parameter probes used in these surveys. Water-quality results are provided in the project data release (Sorenson and others, 2021). 

Examples of monitoring buoys used for 2018-19 monitoring program

Figure 4. Examples of monitoring buoys deployed in (A) 2018 and (B) 2019 and (C) example of a bottom cage containing a sensor. (Credit: Jason Sorenson, U.S. Geological Survey. Public domain.)

4. Discrete samples were collected for laboratory analysis from the three fixed stations (413642071125701, near Gould Island; 413252071131501, near Fogland Beach; and 412932071124701, near Church Point) (Figure 2) during the monitoring period. Eleven rounds of samples were collected from the top and bottom of the water column at the three fixed stations, for a total of 66 environmental and 10 quality-assurance samples.  Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) for the following constituents:  ammonia nitrogen; nitrate+nitrite nitrogen; nitrite nitrogen; total nitrogen, filtered;  total particulate nitrogen; total phosphorus, unfiltered; total phosphorus, filtered; orthophosphate phosphorus; total particulate carbon; and chlorophyll a. Suspended sediment concentrations were analyzed at the USGS Sediment Laboratory in Kentucky. These water-quality results are stored in the NWIS database.

 

Data-collection locations for 2019 monitoring program, Sakonnet RI

Figure 5. Data-collection locations for the 2019 monitoring program in the Sakonnet River, Rhode Island. Continuous and discrete water-quality data were collected at one fixed station (413642071125701, near Gould Island) where a monitoring buoy was deployed. Continuous data were collected during three moving-boat surveys on August 15, 2019 to characterize the spatial distribution of near-surface water quality over a 14-hour tidal cycle. The lines represent the moving boat tracks from August 15, 2019 survey. Vertical water-quality profile data were also collected at the fixed station and an additional two stations (RI-Sakonnet-007 and RI-Sakonnet-016) during the moving boat surveys. (Credit: Jason Sorenson, U.S. Geological Survey. Public domain.)

Components of the 2019 monitoring program

1. Continuous (15-minute interval) records of water-quality were collected at a single fixed location for the duration of the 2019 monitoring period (413642071125701, near Gould Island; Figure 5). 

Continuous temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected within 0.5-m of the top and bottom of the water column with calibrated multi-parameter probes; additional measurement were made periodically during the monitoring period with a third calibrated multiparameter probe. These water-quality results are stored in the NWIS database.

2. Discrete samples were collected for laboratory analysis at the fixed station (413642071125701, near Gould Island; Figure 5) during the monitoring period. Eight rounds of samples were collected from near the top and bottom of the water column at approximately bi-monthly intervals, for a total 16 environmental and 6 quality-assurance samples at this location (as described below, additional discrete samples were collected at this station on August 15, 2019). Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) for the following constituents:  ammonia nitrogen; nitrate+nitrite nitrogen; nitrite nitrogen; total nitrogen, filtered; total particulate nitrogen; total phosphorus, unfiltered; total phosphorus, filtered; orthophosphate phosphorus; total particulate carbon; and chlorophyll a. Suspended sediment concentrations were analyzed at the USGS Sediment Laboratory in Kentucky. These water-quality results are stored in the USGS National Water Inventory System (NWIS) database.

3. Discrete samples were also collected for laboratory analysis over a 14-hour tidal cycle at the fixed station (413642071125701, near Gould Island; Figure 5) on August 15, 2019. Samples were collected near that top and bottom of the water column five times over the tidal cycle for a total of 10 environmental and 1 quality-assurance sample. Samples were analyzed at the USGS National Water Quality Laboratory (NWQL) for the following constituents: ammonia nitrogen;  nitrate+nitrite nitrogen; nitrite nitrogen; total nitrogen, filtered;  total particulate nitrogen; total phosphorus, unfiltered; total phosphorus, filtered; orthophosphate phosphorus; total particulate carbon; and chlorophyll a. Suspended sediment concentrations were analyzed at the USGS Sediment Laboratory in Kentucky. These water-quality results are stored in the NWIS database.

5. Continuous (15-minute interval) records of water-quality were collected from three moving boat surveys conducted along a roughly East-West transect across the Sakonnet River, intersecting three sampling stations (RI-Sakonnet-007, RI-Sakonnet-016 and 413642071125701, near Gould Island; Figure 5), on August 15, 2019. These surveys were designed to characterize the spatial distribution of near-surface water-quality conditions in the river at various times over the tidal cycle. Temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected with a calibrated multi-parameter probe equipped with a flow-through cell and pump designed to draw water from through-hull fittings in the boat. Water-quality results and survey tracks are provided in the project data release (Sorenson and others, 2021) and boat tracks are shown on Figure 5. 

6. During the moving boat surveys on August 15, 2019, three vertical profiles of water quality were collected at the three stations (RI-Sakonnet 007, RI-Sakonnet 016 and 413642071125701, near Gould Island; Figure 5). Temperature, pH, specific conductance, salinity, dissolved oxygen concentration and saturation, turbidity, and chlorophyll a data were collected from depths ranging from 0.5 to 41 feet (0.2 to 12.5 m) with an additional calibrated multi-parameter probe by using a constant rate of descent through the water column and recording data at 1-2 second intervals. Near-surface results were compared to the moving boat survey results at these locations as a check on the agreement between the two multi-parameter probes used in the survey. Water-quality results are provided in the project data release (Sorenson and others, 2021). 

 

References

Sorenson, J.R., Spaetzel, A.B., and Campo, K.W., 2021, Physical and Chemical Data to Characterize Water-Quality Conditions in the Sakonnet River, Rhode Island, 2018-2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9R6HRPS.

U.S. Geological Survey [USGS], 2010, USGS real-time water quality data for the nation: U.S. Geological Survey National Real-Time Water Quality web page, accessed March 15, 2015, at https://nrtwq.usgs.gov/.

U.S. Geological Survey, [variously dated], National field manual for the collection of water-quality data, section A of Handbooks for water-resources investigations: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, 10 chap. (A0–A8, A10), accessed July 31, 2018, at https://pubs.water.usgs.gov/twri9A.

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continuous water-quality monitors—Station operation, record computation, and data reporting: U.S. Geological Survey Techniques and Methods, book 1, chap. D3, 51 p. [Also available at https://pubs.er.usgs.gov/publication/tm1D3.]

Wilde, F.D., Sandstrom, M.W., and Strobialowski, S.C., ed., 2014, Selection of Equipment for water sampling (ver. 3.1, April 2004): U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A2, accessed July 27, 2017, at 2https://water.usgs.gov/owq/FieldManual/chapter2/Ch3_contents.html.

Wilde, F.D., ed., 2004a, Cleaning of Equipment for water sampling (ver. 2.0, April 2004): U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A3, accessed July 27, 2017, at https://water.usgs.gov/owq/FieldManual/chapter3/Ch3_contents.html.

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., eds., 2004b, Processing of water samples (ver. 2.2): U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A5, accessed July 11, 2017, at https://water.usgs.gov/owq/FieldManual/chapter5/html/Ch5_contents.html.