News – Page 6 – Narrabay

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.

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.

July 30-August 5, 2023

Surface chlorophyll data were collected on August 2, 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 1.49 to 18.92 µg/L with an average of 6.48 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

July 2023

Phillipsdale Landing

The Phillipsdale Landing sondes have been deployed since May 9th, 2023 utilizing a new setup allowing staff access to the equipment from the boat instead of standing on the dock. Sondes were changed out for routine maintenance on July 6th and July 18th. July was a wet month, with 8.37 inches of precipitation recorded at T.F. Green. The largest storm occurred on July 16th (3.35 inches). Blackstone River flows were elevated due to the frequent precipitation throughout the month of July. Salinity at Phillipsdale averaged 4.3 ppt at the surface (range 0.2 – 18.8 ppt) and 42.0 ppt at the bottom (range -0.6 – 108.9 ppt). Temperatures increased from June, averaging 25.4°C at the surface and 24.0°C at the bottom. Surface temperatures ranged 22.6 – 30.0°C, while bottom temperatures ranged 21.0 – 26.7°C.

The surface dissolved oxygen (DO) concentrations remained mostly above the hypoxia threshold (2.9 mg/L), only briefly dropping below the threshold for a half hour the morning of July 10th. The bottom waters were hypoxic periodically throughout the month. The longest sustained period of hypoxic conditions (~1.5 days) occurring from the morning of July 9th until the night of July 10th. DO averaged 7.3 mg/L at the surface with a minimum of 2.2 mg/L, while bottom waters averaged 3.3 mg/L with a minimum of -0.1 mg/L.

Chlorophyll readings were generally low with periods of moderately elevated chlorophyll intermittently through the month, suggestive of moderate phytoplankton blooms. The surface and bottom readings averaged 8.3µg/L and 8.6 µg/L, respectively. The maximum surface reading of 112.8 µg/L occurred on July 9th and the maximum bottom reading of 130.9 µg/L occurred on July 22nd. Please note that data from the bottom sonde between July 23rd and the 29th was excluded due to mud compromising the results. Also, gaps occurred in the bottom on July 4th to the 6th potentially due to equipment failure.

Bullock Reach

The Bullock Reach buoy was deployed June 1st for the 2023 season. Sondes were changed out for routine maintenance on July 11th and 25th. Overall, water quality was fair at Bullock Reach Buoy throughout the month of July 2023. Surface, middle, and bottom DO averaged 7.5 mg/L, 4.8 mg/L, and 2.6 mg/L, respectively. Hypoxic conditions were not observed at the surface. However, hypoxic conditions occurred sporadically in middle waters beginning July 19th. Bottom waters periodically fell below the hypoxia threshold (2.9 mg/L) throughout the month and the longest duration of hypoxic conditions occurred for 5.5 days between the 22nd and the 28th.

Surface salinity at Bullock Reach ranged 9.5 – 27.2 ppt and averaged 21.1 ppt. Mid-depth salinity ranged 16.4 – 30.0 ppt and averaged 25.7 ppt. Bottom salinity ranged 23.5 – 31.3 ppt and averaged 30.1 ppt. Water column temperatures averaged 25.7°C, 25.1°C, and 22.1°C at the surface, middle, and bottom, respectively. Temperatures ranged 23.2°C – 28.6°C at the surface, 21.6°C – 27.4°C at mid-depth, and 19.4°C – 25.7°C at the bottom.

Chlorophyll readings were moderately elevated, averaging 25.7 µg/L at the surface, 15.0 µg/L at mid-depth, and 2.8 µg/L at the bottom. Periods of elevated chlorophyll occurred around July 6th – 10th. The maximum surface reading of 81.2 µg/L occurred on July 22nd. Please note that minor data gaps occurred between the 8th to the 25th on the surface and bottom due to potential equipment failure and fouling.

Please note that the data exclusions mentioned in the above text for Phillipsdale Landing and Bullock Reach does not affect the raw data, and any exclusions occurred during a QC process, prior to the average, maximum, and minimum calculations discussed.

July 23-29, 2023

Water clarity was measured at eight locations in the Providence River and Seekonk River estuaries on July 27. Rainfall totaling 0.47 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.1 meters, compared to 1.0 meters on the previous survey (July 12). The lowest clarity this week (1.1 meters) was measured at India Point Park, Edgewood Yacht Club, Phillipsdale Landing, Conimicut Point, and Edgewood Shoal, while the greatest clarity (1.3 meters) was measured at Pawtuxet Cove. There was no clear north-to-south gradient in water clarity among the sites this week.