News – Page 15 – Narrabay

April 30-May 6, 2023

Water column profiles were conducted at eight locations in the Providence and Seekonk River estuaries on May 3, 2023 using a Seabird Electronics profiler. There were 2.68 inches of precipitation recorded at T.F. Green in the three days leading up to the survey, almost all from a large rain event on April 30th. Evidence of moderate density stratification was observed at Edgewood Yacht Club; all other sites had strong density stratification.

Surface salinities ranged from 0.55 psu at Phillipsdale Landing to 16.9 psu at Edgewood Yacht Club; bottom salinities ranged from 21.1 psu at Phillipsdale Landing to 29.9 psu at Conimicut Point West. Surface temperatures ranged from 12.4°C at Pawtuxet Cove to 13.7°C at Bullock Reach Buoy, while bottom temperatures ranged from 10.5°C at Conimicut Point West to 12.9°C at Pawtuxet Cove.

Dissolved oxygen (DO) conditions remained above the hypoxia threshold (2.9 mg/L) at all sites this week; the lowest DO observed was approximately 5.05 mg/L near the surface (1.5 m deep) at Pomham Rocks. Fluorescence was low this week, with the highest value (5.38 mg/m3) observed 1.75 m deep at Bullock Reach Buoy.

April 30-May 6, 2023

Surface chlorophyll data were collected on May 3, 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 areas surveyed. Overall, chlorophyll ranged between 1.39 and 3.08 µg/L with an average of 2.14 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

April 23-29, 2023

On April 26, 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 0.91 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 29 MPN/100 mL compared to 10 MPN/100 mL on April 13, 2023. Overall, bacteria counts were higher in the Seekonk River and Providence River this week than during the previous sampling event on April 13. Fecal coliform counts were 68 MPN/ 100 mL in the Seekonk River and 19 MPN/ 100 mL in the Providence River. The maximum count (430 MPN/100 mL) was measured at Point St. Bridge in the Providence River.

Enterococci results had an overall geometric mean of 14 MPN/100 mL. Enterococci results ranged from non-detect at Phillipsdale Landing, South FP East, and one of the Conimicut Point duplicates to 52 MPN/100 mL at the Point St. Bridge site.

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.

April 23-29, 2023

Surface chlorophyll data were collected on April 26, 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 fair in the Edgewood Shoals area and good in the other areas surveyed. Overall, chlorophyll ranged between 0.79 and 11.19 µg/L with an average of 2.60 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

April 16-23, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on April 19, 2023 using a Seabird Electronics profiler. There were 0.17 inches of precipitation recorded at T.F. Green in the three days leading up to the survey. Evidence of strong density stratification was observed at Phillipsdale Landing, Pomham Rocks, and Pawtuxet Cove. Evidence of moderate density stratification was observed at India Point Park, Conimicut Point West, and Bullock Reach Buoy, while Edgewood Yacht Club showed signs of being well mixed.

Surface salinities ranged from 12.5 psu at Phillipsdale Landing to 25.9 psu at Conimicut Point West; bottom salinities ranged from 24.4 psu at Edgewood Yacht Club to 30.2 psu at Conimicut Point West. Surface temperatures ranged 10.6°C at India Point Park to 12.5°C at Pawtuxet Cove, while bottom temperatures ranged from 8.4°C at Pomham Rocks to 11.3°C at Pawtuxet Cove.

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) throughout the water column at Edgewood Yacht Club this week, averaging 2.6 mg/L. All other sites remained above the hypoxia threshold. Fluorescence was low to moderately elevated, with the highest value (8.42 mg/m3) observed near the middle of the water column at Pawtuxet Cove.

April 16-22, 2023

Nutrient samples were collected from eight local river stations, and seven bay stations on April 19, 2023. All bay stations were sampled at surface and bottom. In the five days prior to sampling, there was 0.17 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) were observed at Blackstone River at Stateline. The TN, TDN, DIN were 1,210 ppb, 1,220 ppb, and 951.4 ppb, respectively. The lowest TN, TDN and DIN were observed at the duplicate samples collected at Pawtuxet River at Broad Street. The TN, TDN and DIN averaged 535 ppb, 246.5 ppb, and 66.7 ppb, respectively.

Among the bay stations sampled, the highest TN, TDN, and DIN were observed at Ten Mile River at Central Ave. The TN, TDN, DIN were 2,300 ppb, 2,000 ppb, and 1,727 ppb, respectively. Among the bay stations sampled, the highest TN (1,290 ppb), TDN (1,060 ppb), DIN (818.9 ppb) were observed at Phillipsdale Landing. The lowest surface TN (378 ppb) and TDN (129 ppb) were observed at Conimicut Point. The lowest surface DIN (13 ppb) was observed at Bulluck Reach Buoy. Chlorophyll a concentrations at the bay stations increased from the previous sampling event, averaging 10.2 ug/L across all sites. The maximum result (15.17 ug/L) occurred at Bullock Reach Buoy.

Data from additional sampling dates (typically every two weeks) are pending analysis and writeup.

April 16-22, 2023

Surface chlorophyll data were collected on April 19, 2023 while the R/V Monitor was underway collecting nutrient samples in the Seekonk River, Upper Providence River, and Edgewood Shoals areas (chlorophyll data were not collected for the Pawtuxet River or Southern Providence River areas due to data logging issues). The average chlorophyll concentrations were categorized good in the areas surveyed. Overall, chlorophyll ranged between 0.00 and 9.34 µg/L with an average of 3.20 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

April 16-22, 2023

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on April 19. Rainfall totaling 0.17 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.5 meters, compared to 3.0 meters on the previous survey (April 13). The lowest clarity this week (1.6 meters) was measured at Phillipsdale Landing and Pawtuxet Cove while the greatest clarity (3.4 meters) was measured at Bullock Reach. There was no clear north-to-south gradient in water clarity among the sites this week.

April 9-15, 2023

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on April 13. No precipitation was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 3.0 meters, compared to 2.1 meters on the previous survey (April 5). The lowest clarity this week (2.0 meters) was measured at Phillipsdale Landing while the greatest clarity (3.3 meters) was measured at Pomham Rocks and Point St. Bridge. There was no clear north-to-south gradient in water clarity among the sites this week.

April 9-15, 2023

On April 13, twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers. Five of these stations were also sampled for enterococci bacteria. No precipitation was recorded at TF Green in the five days prior to sampling.

The geometric mean of fecal coliform results for all sites was 10 MPN/100 mL compared to 32 MPN/100 mL on March 29, 2023. Overall, bacteria counts were lower in both the Seekonk River and Providence River this week than during the previous sampling event on March 29. Fecal coliform counts were higher in the Seekonk River sites than in the Providence River sites (geometric means of 29 MPN/100 mL and 7 MPN/100 mL, respectively). The maximum count (430 MPN/100 mL) was measured at Point St. Bridge in the Providence River.

Enterococci results had an overall geometric mean of 11 MPN/100 mL. Enterococci results ranged from non-detect at Phillipsdale Landing, South FP East, Gaspee Point, and Conimicut Point to 20 MPN/100 mL at the Point St. Bridge site.

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.