News – Page 10 – Narrabay

June 11-17, 2023

Nutrient samples were collected from seven river stations and seven bay stations on June 14th. All bay stations were sampled at the surface and bottom. In the five days prior to sampling, there were 0.59 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 = 1,560 ppb, TDN = 1,360 ppb, DIN = 1,150 ppb). The lowest TN and TDN was observed at Woonasquatucket River @ Manton Ave. Bridge (TN = 796 ppb, TDN = 772 ppb), while the lowest DIN was at Blackstone River @ Bikepath Bridge (314 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Pawtuxet Cove (TN = 1,220 ppb, TDN = 984 ppb, DIN = 767 ppb). The lowest surface TN and TDN concentrations were observed at Conimicut Point (TN = 586 ppb, TDN = 153 ppb), while three locations – Conimicut Point, Edgewood Yacht Club, and Phillipsdale Landing – had surface DIN concentrations below the detection limit of 13.0 ppb. Chlorophyll a concentrations at the surface bay stations were relatively low, averaging 5.59 μg/L across all sites with a maximum of 11.9 μg/L at Phillipsdale Landing.

The next scheduled sampling date is June 28, 2023.

June 11-17, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on June 14, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey, there were 0.21 inches of precipitation recorded at T.F. Green. India Point Park exhibited strong density stratification and all other sites were moderately stratified.

Dissolved oxygen (DO) conditions remained above the hypoxia threshold (2.9 mg/L) at all sites this week; the lowest DO observed was approximately 4.05 mg/L in the middle waters of Phillipsdale Landing. Fluorescence was fairly low this week, ranging from 1.28 to 13.38 mg/m³.

June 4-10, 2023

Surface chlorophyll data were collected on June 7, 2023 while the R/V Monitor was underway collecting bacteria samples in the Providence and Seekonk River estuaries. The average chlorophyll concentrations were categorized as good in all areas surveyed. Overall, chlorophyll ranged between 0.35 and 3.45 µg/L with an average of 1.90 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

June 4-10, 2023

Water clarity was measured at six locations in the Providence River and Seekonk River estuaries on June 7. There was 0.14 inches of precipitation recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.5 meters, compared to 1.5 meters on the previous survey (May 31). The lowest clarity this week (2.1 meters) was measured at Phillipsdale Landing while the greatest clarity (3.1 meters) was measured at Conimicut Point. There was no clear north-to-south gradient in water clarity among the sites this week.

June 4-10, 2023

On June 7, 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 0.14 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 17 MPN/100 mL compared to 73 MPN/100 mL on May 24. Overall, bacteria counts were lower in the Seekonk River and Providence River this week than during the previous sampling event on May 24. Fecal coliform counts were geomeans of 41 MPN/ 100 mL in the Seekonk River and 12 MPN/ 100 mL in the Providence River. The maximum count (210 MPN/100 mL) was measured at Point St. Bridge in the Providence River.

Enterococci results had an overall geometric mean of 15 MPN/100 mL. Enterococci counts ranged from non-detect at South FP East and Gaspee Point to 52 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.

June 4-10, 2023

Water column profiles were conducted at six locations in the Providence and Seekonk River estuaries on June 7, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey, there were 0.12 inches of precipitation recorded at T.F. Green. Phillipsdale Landing exhibited moderate density stratification and all other sites were weakly stratified.

Dissolved oxygen (DO) conditions remained above the hypoxia threshold (2.9 mg/L) at all sites this week; the lowest DO observed was approximately 4.65 mg/L in the bottom waters of Phillipsdale Landing. Fluorescence was low this week, ranging from 1.06 to 4.64 mg/m³.

May 28-June 3, 2023

Surface chlorophyll data were collected on May 31, 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 Southern Providence River area and fair in all the other areas surveyed. Overall, chlorophyll ranged between 3.01 and 16.90 µg/L with an average of 7.96 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

May 28-June 3, 2023

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on May 31. There was no precipitation recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.5 meters, compared to 1.3 meters on the previous survey (May 24). The lowest clarity this week (0.8 meters) was measured at Edgewood Shoal while the greatest clarity (2.2 meters) was measured at Pawtuxet Cove. There was no clear north-to-south gradient in water clarity among the sites this week.

May 28-June 3, 2023

Phytoplankton samples were collected on May 31, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. Sondes data revealed the surface water temperature was 18.11⁰C, salinity was 21.04 psu, and chlorophyll a was 4.88 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light tan/brown color and had a quick filter time. 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 16,860,000 cells per Liter. The micro flagellates were found at 525,000 cells/L. The most predominant phytoplankton genus was Skeletonema spp. at 15,585,000 cells/L. These plankton were found in chains of 6 cells. Other representative genera include Guinardia spp., Chaetoceros spp., and Leptocylindrus spp.

200x phase contrast micrograph of Skeletonema spp.

May 28-June 3, 2023

Nutrient samples were collected from 14 river stations and eight bay stations on May 31st. 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 was no rainfall recorded at T.F. Green.

Among the river stations sampled, the highest total nitrogen (TN) concentration was observed at Warren Reservoir/Kickemuit River (1,770 ppb), while the highest total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN) concentrations were observed at Ten Mile River @ Central Ave. (TDN = 1,650 ppb, DIN = 1,360 ppb). The lowest TN was observed at Moshassuck River @ Footbridge at Mill St. (790 ppb), the lowest TDN was at Palmer River @ Rt. 6 (715 ppb), and the lowest DIN was at Coles River @ Milford Rd. (122 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Phillipsdale Landing (TN = 1,250 ppb, TDN = 903 ppb, DIN = 570 ppb). The lowest surface TN and TDN concentrations were observed at Conimicut Point (TN = 444 ppb, TDN = 167 ppb), while several locations – Conimicut Point, Edgewood Yacht Club, Bullock Reach Buoy, and Edgewood Shoal – had surface DIN concentrations below the detection limit of 13.0 ppb. Chlorophyll a concentrations at the surface bay stations were relatively low at most sites but elevated at Edgewood Yacht Club, Pomham Rocks, and India Point Park; concentrations averaged 12.1 μg/L overall with a maximum of 26.6 μg/L at Pomham Rocks.

The next scheduled sampling date is June 14, 2023.