News – Page 8 – Narrabay

July 9-15, 2023

Phytoplankton samples were collected on July 12, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. Sondes data revealed the surface water temperature was 25.529⁰C, salinity was 21.40 psu, and chlorophyll a was 11.25 ug/L. Small sea jellies were observed today on Narragansett Bay. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a green- tan color and had a medium 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 1,124,000 cells per Liter. The micro flagellates were found at 198,000 cells/L. The most predominant phytoplankton genus was Skeletonema spp.at 772,000 cells/L. Other representative genera include Chaetoceros spp., Thalassiosira spp., and Eutreptiella spp.

200x phase contrast image of Protoperidinium spp.

July 9-15, 2023

Surface chlorophyll data were collected on July 12, 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, Northern Providence River Channel, and Pawtuxet River areas and as fair in the Edgewood Shoals and Southern Providence River areas. Overall, chlorophyll ranged from 0.94 to 18.55 µg/L with an average of 6.07 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

July 9-15, 2023

Nutrient samples were collected from seven river stations and seven bay stations on July 12th. All bay stations were sampled at the surface and bottom. In the five days prior to sampling, there were 1.91 inches of rainfall recorded at T.F. Green, all from a rain event on July 10th.

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 = 1,140 ppb, TDN = 1,080 ppb, DIN = 796 ppb). The lowest TN and TDN were observed at Woonasquatucket River @ Manton Ave. Bridge (TN = 664 ppb, TDN = 633 ppb, average of duplicates), while the lowest DIN was at Blackstone River @ Stateline (357 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Pawtuxet Cove (TN = 1,100 ppb, TDN = 882 ppb, DIN = 640 ppb, average of duplicates). The lowest surface TN and DIN were observed at Conimicut Point (TN = 577 ppb, DIN < 13.0 ppb), while the lowest surface TDN was at Bullock Reach Buoy (181 ppb). Chlorophyll a concentrations at the surface bay stations were relatively low at most sites and moderately elevated at Edgewood Yacht Club and Pawtuxet Cove; concentrations averaged 5.46 μg/L overall with a maximum of 15.7 μg/L in one of the duplicate samples at Edgewood Yacht Club.

The next scheduled sampling date is July 26, 2023.

July 9-15, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on July 12, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey, there were 1.91 inches of precipitation recorded at T.F. Green. Strong density stratification was observed at all sites surveyed this week.

Dissolved oxygen (DO) conditions were above the hypoxia threshold (2.9 mg/L) at Conimicut Point West; all other sites surveyed had hypoxic conditions in the middle and/or lower half of the water column. Fluorescence was moderately elevated at the surface of Conimicut Point West this week and relatively low at all other sites.

July 2-8, 2023

Water clarity was measured at eight locations in the Providence River and Seekonk River estuaries on July 5. Rainfall totaling 1.25 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.1 meters, compared to 1.4 meters on the previous survey (June 28). The lowest clarity this week (0.8 meters) was measured at Bullock Reach, while the greatest clarity (1.3 meters) was measured at India Point Park and Point St. Bridge. There was no clear north-to-south gradient in water clarity among the sites this week.

July 2-8, 2023

Surface chlorophyll data were collected on July 5, 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 the Seekonk River, Northern Providence River Channel, and Pawtuxet River areas and as fair in the Edgewood Shoals and Southern Providence River areas. Overall, chlorophyll ranged from 0.71 to 20.65 µg/L with an average of 5.56 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

July 2-8, 2023

On July 5, 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 1.25 inches as recorded at TF Green, most of which occurred on July 4.

The geometric mean of fecal coliform results for all sites was 3472 MPN/100 mL compared to 31 MPN/100 mL on June 21. Overall, bacteria counts were higher in both the Seekonk and Providence Rivers this week than during the previous sampling event on June 21. Fecal coliform counts were geomeans of 3160 MPN/ 100 mL in the Seekonk River and 3629 MPN/ 100 mL in the Providence River. The maximum count (46,000 MPN/100 mL) was measured at Off FP Outfall in the Providence River.

Enterococci results had an overall geometric mean of 1250 MPN/100 mL. Enterococci counts ranged from 246 MPN/100mL at a Conimicut Point duplicate to 5475 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.

July 2-8, 2023

Water column profiles were conducted at eight locations in the Providence and Seekonk River estuaries on July 5, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey, there were 1.25 inches of precipitation recorded at T.F. Green. Strong density stratification was observed at all sites surveyed this week.

Dissolved oxygen (DO) conditions were above the hypoxia threshold (2.9 mg/L) at Bullock Reach Buoy and Conimicut Point West; all other sites surveyed had hypoxic conditions in the lower half of the water column. Fluorescence was moderately elevated at the surface of Bullock Reach Buoy and Conimicut Point West this week and low at all other sites.

June 25-July 1, 2023

Water clarity was measured at eight locations in the Providence River and Seekonk River estuaries on June 28. Rainfall totaling 1.51 inches was recorded at TF Green in the five days prior to the survey, with 0.44 inches occurring on the day of sampling. Secchi depth averaged 1.4 meters, compared to 1.6 meters on the previous survey (June 21). The lowest clarity this week (0.9 meters) was measured at India Point Park while the greatest clarity (1.9 meters) was measured at Bullock Reach and Conimicut Point. There was a general north-to-south gradient of increasing water clarity among the sites this week.

June 25-July 1, 2023

Surface chlorophyll data were collected on June 28, 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 poor in the Seekonk River and Northern Providence River Channel, fair in the Edgewood Shoals area, and good in the Pawtuxet River and Southern Providence River areas. Overall, chlorophyll ranged from 0.53 to 43.90 µg/L with an average of 17.24 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.