News – Page 9 – Narrabay

June 25-July 1, 2023

Phytoplankton samples were collected on June 28, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. Sondes data revealed the surface water temperature was 22.945⁰C, salinity was 23.18 psu, and chlorophyll a was 4.71 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a green- brown 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 5,670,000 cells per Liter. The micro flagellates were found at 25,000 cells/L. The most predominant phytoplankton genus was Skeletonema spp.at 4,400,000 cells/L. Other representative genera include Chaetoceros spp., Gonyaulax spp., and Leptocylindrus spp.

100x phase contrast micrograph of the qualitative tow net sample.

July 25-July 1, 2023

Nutrient samples were collected from 14 river stations and nine bay stations on June 28th. 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 and the morning of, there were 1.51 inches of rainfall recorded at T.F. Green.

Among the river stations sampled, the highest total nitrogen (TN) concentration was observed at Warren Reservoir/Kickemuit River (1,590 ppb), while the highest total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN) concentrations were observed at Ten Mile River @ Central Ave. (TDN = 1,310 ppb, DIN = 970 ppb). The lowest TN and TDN was observed at Moshassuck River @ Higginson Ave. (TN = 505 ppb, TDN = 479 ppb, average of duplicates), while the lowest DIN was at Coles River @ Milford Rd. (109 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Phillipsdale Landing (TN = 1,120 ppb, TDN = 772 ppb, DIN = 522 ppb). The lowest surface TN was observed at Conimicut Point (600 ppb), the lowest surface TDN was at Edgewood Yacht Club (206 ppb), and the lowest surface DIN was at Pomham Rocks (14.8 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 12.34 μg/L overall with a maximum of 22.3 μg/L at Edgewood Yacht Club.

The next scheduled sampling date is July 12, 2023.

June 25-July 1, 2023

Water column profiles were conducted at eight locations in the Providence and Seekonk River estuaries on June 28, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey and the morning of, there were 0.92 inches of precipitation recorded at T.F. Green. Strong density stratification was observed at most sites surveyed this week, with Bullock Reach Buoy and Conimicut Point West exhibiting moderate density stratification.

Dissolved oxygen (DO) conditions remained above the hypoxia threshold (2.9 mg/L) at most sites this week but were below the hypoxia threshold in the bottom waters of Phillipsdale Landing (1.01 mg/L) and Edgewood Shoal (0.57 mg/L). Fluorescence was low to moderately elevated this week, with the highest value (32.52 mg/m³) observed at the surface of Phillipsdale Landing.

June 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 June 6th and June 20th.

June was relatively wet, with 3.1 inches of precipitation recorded at T.F. Green. The largest storm occurred on June 17th (1.3 inches). Blackstone River flows were elevated for June 18th (i.e., above the 18-year median statistic of USGS data) in response to the precipitation. Salinity at Phillipsdale averaged 14.0 ppt at the surface (range 1.7 – 26.1 ppt) and 24.4 ppt at the bottom (range 8.3 – 29.5 ppt). Temperatures increased from May, averaging 20.4°C at the surface and 18.0°C at the bottom. Surface temperatures ranged 14.9 – 26.7°C, while bottom temperatures ranged 14.9 – 24.5°C.

The surface dissolved oxygen (DO) concentrations remained above the hypoxia threshold (2.9 mg/L) while the bottom waters were hypoxic periodically throughout the month. The longest sustained period of hypoxic conditions (~13 hours) occurred during the late morning of June 22nd into the early morning of June 23rd. DO averaged 8.3 mg/L at the surface with a minimum of 3.6 mg/L, while bottom waters averaged 3.6 mg/L with a minimum of 0.01 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 20.6 µg/L and 19.8 µg/L, respectively. The maximum surface reading of 86.6 µg/L occurred on June 27th and the maximum bottom reading of 118.2 µg/L occurred on June 7th. Also, please note that data from the bottom sonde between June 23rd and the 29th was excluded due to mud compromising the results. Minor data gaps also occurred periodically between June 11th to the 29th on the surface and bottom due to potential sediment interference (common at this site), fouling, and when the surface sonde was tangled and reporting at an incorrect depth.

Bullock Reach

The Bullock Reach buoy was deployed June 1st for the 2023 season. Sondes were changed out for routine maintenance on June 13th and 27th. Please note that minor data gaps occurred in the surface, middle and bottom on June 1st, 8th, 16th and 27th and is potentially due to equipment failure.

Overall, water quality was good at Bullock Reach Buoy throughout the month of June 2023. Surface, middle, and bottom DO averaged 8.8 mg/L, 7.3 mg/L, and 5.6 mg/L, respectively. Hypoxic conditions were not observed at Bullock Reach this month; the minimum DO observed was 3.1 mg/L measured in bottom waters.

Surface salinity at Bullock Reach ranged 20.6 – 29.1 ppt and averaged 25.9 ppt. Mid-depth salinity ranged 19.7 – 30.5 ppt and averaged 28.1 ppt. Bottom salinity ranged 17.6 – 31.2 ppt and averaged 29.8 ppt. Water column temperatures averaged 19.7°C, 19.0°C, and 17.4°C at the surface, middle, and bottom, respectively. Temperatures ranged 14.6°C – 25.1°C at the surface, 15.2°C – 23.9°C at mid-depth, and 13.6°C – 22.5°C at the bottom. Chlorophyll readings were generally low, averaging 12.2 µg/L at the surface, 11.4 µg/L at mid-depth, and 4.0 µg/L at the bottom. The maximum reading of 38.9 µg/L occurred on June 15th in the surface waters.

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.

June 18-24, 2023

On June 21, 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 1.30 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 31 MPN/100 mL compared to 17 MPN/100 mL on June 7. Overall, bacteria counts were higher in the Seekonk River this week than during the previous sampling event on June 7. Fecal coliform counts were geomeans of 256 MPN/ 100 mL in the Seekonk River and 12 MPN/ 100 mL in the Providence River. The maximum count (4300 MPN/100 mL) was measured at Bishop Point in the Seekonk River.

Enterococci results had an overall geometric mean of 12 MPN/100 mL. Enterococci counts ranged from non-detect at Conimicut Point, Phillipsdale Landing, South FP East, and Gaspee Point to 41 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 18-24, 2023

Water clarity was measured at eight locations in the Providence River and Seekonk River estuaries on June 21. Rainfall totaling 1.30 inches was recorded at TF Green in the five days prior to the survey, all of which occurred on June 17. Secchi depth averaged 1.6 meters, compared to 1.9 meters on the previous survey (June 14). The lowest clarity this week (1.2 meters) was measured at Phillipsdale Landing while the greatest clarity (2.0 meters) was measured at Conimicut Point. There was a general north-to-south gradient of increasing water clarity among the sites this week.

June 18-24, 2023

Surface chlorophyll data were collected on June 21, 2023 while the R/V Monitor was underway collecting bacteria samples in the Providence and Seekonk River estuaries. Unfortunately, only limited data between Field’s Point and Conimicut Point were collected due to an instrument logging error. The average chlorophyll concentrations were categorized as fair in the Northern Providence River Channel, Edgewood Shoals, and Pawtuxet River areas. Overall, chlorophyll ranged from 2.07 to 25.68 µg/L with an average of 12.64 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

June 18-24, 2023

Water column profiles were conducted at eight locations in the Providence and Seekonk River estuaries on June 21, 2023 using a Seabird Electronics profiler. In the three days leading up to the survey, there was no precipitation recorded at T.F. Green. Density stratification was moderate to strong at the sites surveyed.

Dissolved oxygen (DO) conditions remained above the hypoxia threshold (2.9 mg/L) at most sites this week; the lowest DO observed was approximately 3.76 mg/L near the surface of Phillipsdale Landing. Fluorescence was low to moderately elevated this week, with the highest value (21.44 mg/m³) observed at Pawtuxet Cove.

June 11-17, 2023

Surface chlorophyll data were collected on June 14, 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, Upper Providence River Channel, and Pawtuxet River areas and as fair in the Edgewood Shoals and Southern Providence River areas. Overall, chlorophyll ranged between 0.98 and 15.51 µg/L with an average of 5.09 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

June 11-17, 2023

Water clarity was measured at six locations in the Providence River and Seekonk River estuaries on June 14. There was 0.59 inches of precipitation recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.9 meters, compared to 2.5 meters on the previous survey (June 7). The lowest clarity this week (1.5 meters) was measured at Pawtuxet Cove while the greatest clarity (2.3 meters) was measured at Edgewood Yacht Club. There was no clear north-to-south gradient in water clarity among the sites this week.