News – Page 20 – Narrabay

Week of August 20 – 26, 2023

Nutrient samples were collected from fourteen river stations and eight bay stations on August 23rd, 2023. Edgewood Shoal was sampled at the surface and bottom; all other bay stations were sampled at the surface only. In the five days prior to sampling, there were 2.16 inches of rainfall recorded at T.F. Green due to a heavy rain event on August 18th.

Among the river stations sampled, the highest total nitrogen (TN) concentration was observed at Pawtuxet River @ Broad Street (TN = 1,815 ppb, average of duplicates), while the highest total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN) concentrations were at Ten Mile River @ Central Ave. (TDN = 1,480 ppb, DIN = 1,013.9 ppb). The lowest TN and TDN were observed at Ten Mile River @ Roger Williams Ave. (TN = 510 ppb, TDN = 666 ppb), while the lowest DIN was at Coles River @ Milford Rd. (97.4 ppb, average of duplicates).

Among the bay stations sampled, the highest surface TN, TDN, and DIN were observed at Pawtuxet Cove (TN = 1,020 ppb, TDN = 892 ppb, DIN = 662.3 ppb). The lowest surface TN and DIN were observed at the Bullock Reach Buoy (TN = 540 ppb, DIN = 119.5 ppb), while the lowest surface TDN was at Conimicut Point (276 ppb). Chlorophyll a concentrations at the surface bay stations averaged 3.95 μg/L overall with a maximum of 7.02 μg/L at Conimicut Point.

August 13-19, 2023

Water clarity was measured at five locations in the Providence River and Seekonk River estuaries on August 16. Rainfall totaling 0.61 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.8 meters, compared to 1.8 meters on the previous survey (August 9). The lowest clarity this week (1.9 meters) was measured at Phillipsdale Landing, while the greatest clarity (3.6 meters) was measured at Point St. Bridge. There was no clear north-to-south gradient in water clarity among the sites this week.

August 13-19, 2023

On August 16, twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers. Five of these stations were also sampled for enterococci bacteria. Precipitation in the five days prior to sampling totaled 0.61 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 149 MPN/100 mL compared to 41 MPN/100 mL on August 2. Overall, bacteria counts were higher in both the Seekonk and Providence Rivers this week than during the previous sampling event on August 2. Fecal coliform counts were geomeans of 435 MPN/ 100 mL in the Seekonk River and 90 MPN/ 100 mL in the Providence River. The maximum count (9300 MPN/100 mL) was measured at Bullock Reach Buoy in the Providence River.

Enterococci results had an overall geometric mean of 35 MPN/100 mL. Enterococci counts ranged from non-detect at a Gaspee Point and Conimicut Point to 238 MPN/100 mL at Point St. Bridge.

The table below lists the Rhode Island bacteria standards for primary contact and shellfishing established by the Rhode Island Department of Environmental Management (RIDEM). RIDEM defines primary contact as any recreational activities in which there is prolonged and intimate contact with water, involving considerable risk of ingesting water (e.g., swimming, diving, water skiing and surfing). Please note that the RIDEM bacteria standards are provided here for informational purposes only and are not intended to indicate official state compliance with primary contact or shellfishing standards.

Summary of Rhode Island Bacteria Standards for Saltwater Primary Contact and Shellfishing

	Fecal Coliform	Enterococci
Primary Contact¹	Geometric mean ≤50 MPN/100 mL <10% of samples >400 MPN/100 mL	Geometric mean ≤35 colonies/100 mL All samples ≤104 colonies/100 mL²
Shellfishing	Geometric mean ≤14 MPN/100 mL <10% of samples >49 MPN/100 mL³	NO ENTEROCOCCI CRITERIA

¹Fecal coliform primary contact criteria applied only when adequate enterococci data are not available; ²Single sample maximum criterion for determining beach swimming advisories at designated beaches as evaluated by the Rhode Island Department of Health; ³For a three-tube decimal dilution

Table adapted from Rhode Island Water Quality Regulations (250-RICR-150-05-1); see regulations for complete details.

August 13-19, 2023

Surface chlorophyll data were collected on August 16, 2023 while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuaries. The average chlorophyll concentrations were categorized as good in the Seekonk River and Northern Providence River Channel and as fair in all others. Overall, chlorophyll ranged from 1.46 to 17.84 µg/L with an average of 5.21 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

*Due to file error the lowest portion of the boat path for this survey is not displayed.

August 6-12, 2023

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on August 9. Rainfall totaling 0.48 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.8 meters, compared to 2.3 meters on the previous survey (August 2). The lowest clarity this week (1.2 meters) was measured at Phillipsdale Landing, while the greatest clarity (2.1 meters) was measured at Pomham Rocks. There was no clear north-to-south gradient in water clarity among the sites this week.

August 6-12, 2023

Surface chlorophyll data were collected on August 9, 2023 while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuaries. The average chlorophyll concentrations were categorized as good in the Northern Providence River Channel, Edgewood Shoals, and Pawtuxet River Area and as fair in all other areas. Overall, chlorophyll ranged from 1.21 to 16.01 µg/L with an average of 5.34 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

*Due to file error the lowest portion of the boat path for this survey is not displayed.

August 6-12, 2023

Phytoplankton samples were collected on August 9, 2023 at Bullock’s Reach and analyzed in the laboratory shortly after collection. Sonde data revealed the surface water temperature was 23.4°C, salinity was 24.1 psu, and chlorophyll a was 7.2 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light brown greenish color and had a long filter time. Lots of activity was present in the sample and comb jellies were detected. The tow net sample was analyzed qualitatively for microorganisms using phase contrast microscopy. The whole water sample was analyzed quantitatively under 200x phase contrast microscopy. A Hensen Stempel pipette was used to accurately deliver 1ml of sample to a Sedge-wick Rafter chamber. This analysis revealed a total of 89,000 cells per Liter. The micro flagellates were found at 70,000 cells/L. The most predominant phytoplankton genus was Dinophysis spp.at 4,000 cells/L. Other representative genera include Scripsiella spp., Guinardia spp., Eutreptiella spp., and Polykrikos spp., the featured plankton taxon in the 200x phase contrast micrograph below.

Week of August 6 – 12, 2023

Nutrient samples were collected from seven river stations and seven bay stations on August 9th, 2023. All bay stations were sampled at the surface and bottom. In the five days prior to sampling, there were 0.48 inches of rainfall recorded at T.F. Green.

Among the river stations sampled, the highest total nitrogen (TN), total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN) concentrations were observed at Pawtuxet River @ Broad St. (TN = 1,390 ppb, TDN = 1,520 ppb, and DIN = 1244.2 ppb). The lowest TN and TDN were observed at Moshassuck River @ Footbridge at Mill Street (TN = 741.5 ppb, TDN= 680.5 ppb, average of duplicates), while the lowest DIN was at Blackstone River @ Bikepath Bridge (DIN = 484.7 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Phillipsdale Landing (TN = 1,050 ppb, TDN = 919 ppb, DIN = 561 ppb). The lowest surface TN, TDN, and DIN concentrations were observed at Conimicut Point (TN = 738 ppb, TDN = 360 ppb, DIN = 143.2 ppb). Chlorophyll a concentrations at the surface bay stations averaged 4.16 μg/L overall with a maximum at the Bullock Reach Buoy (6.94 μg/L, average of duplicates).

July 30-August 5, 2023

Water clarity was measured at six locations in the Providence River and Seekonk River estuaries on August 2. Rainfall totaling 0.66 inches was recorded at TF Green in the five days prior to the survey, all of which occurred on July 29. Secchi depth averaged 2.3 meters, compared to 1.1 meters on the previous survey (July 27). The lowest clarity this week (1.4 meters) was measured at Phillipsdale Landing, while the greatest clarity (3.1 meters) was measured at India Point Park. There was no clear north-to-south gradient in water clarity among the sites this week.

July 30-August 5, 2023

On August 2, twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers. Five of these stations were also sampled for enterococci bacteria. Precipitation in the five days prior to sampling totaled 0.66 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 41 MPN/100 mL compared to 463 MPN/100 mL on July 19. Overall, bacteria counts were lower in both the Seekonk and Providence Rivers this week than during the previous sampling event on July 19. Fecal coliform counts were geomeans of 97 MPN/ 100 mL in the Seekonk River and 28 MPN/ 100 mL in the Providence River. The maximum count (930 MPN/100 mL) was measured at Point St. Bridge in the Providence River.

Enterococci results had an overall geometric mean of 13 MPN/100 mL. Enterococci counts ranged from non-detect at Gaspee Point, Conimicut Point, and a Phillipsdale Landing duplicate to 52 MPN/100 mL at Point St. Bridge.

Summary of Rhode Island Bacteria Standards for Saltwater Primary Contact and Shellfishing

	Fecal Coliform	Enterococci
Primary Contact¹	Geometric mean ≤50 MPN/100 mL <10% of samples >400 MPN/100 mL	Geometric mean ≤35 colonies/100 mL All samples ≤104 colonies/100 mL²
Shellfishing	Geometric mean ≤14 MPN/100 mL <10% of samples >49 MPN/100 mL³	NO ENTEROCOCCI CRITERIA

Table adapted from Rhode Island Water Quality Regulations (250-RICR-150-05-1); see regulations for complete details.