News – Page 39 – Narrabay

Week of October 8 – 14, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on October 11, 2023 using a Seabird Electronics profiler. In the five days leading up to the survey, 0.36 inches of precipitation were recorded at T.F. Green. All sites were strongly stratified this week.

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the Edgewood Yacht Club site. The highest fluorescence readings for the week were measured around 2 meters below the surface at Conimicut Point.

Week of October 1 – 7, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on October 4, 2023 using a Seabird Electronics profiler. In the five days leading up to the survey, 1.27 inches of precipitation were recorded at T.F. Green. All sites were strongly or moderately stratified this week, other than Pomham Rocks, which was weakly stratified.

Dissolved oxygen (DO) conditions were not observed to be below the hypoxia threshold (2.9 mg/L) at any site profiled this week. The highest fluorescence readings for the week were measured around 2 meters below the surface at the Bullock Reach Buoy.

Week of September 24 – 30, 2023

Water column profiles were conducted at six locations in the Providence and Seekonk River estuaries on September 27, 2023 using a Seabird Electronics profiler. In the five days leading up to the survey, 2.77 inches of precipitation were recorded at T.F. Green. All sites were strongly or moderately stratified this week.

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the India Point Park site, and in the lower and middle portions of the water column at Point Street Bridge. The highest fluorescence readings for the week were measured around 3 meters below the surface at the Bullock Reach Buoy.

Week of September 17 – 23, 2023

Water column profile data was collected at seven sites on September 20, 2023. However, due to an equipment deployment issue, only the data from the Phillipsdale Landing site was usable. In the five days leading up to the survey, 1.55 inches of precipitation were recorded at T.F. Green.

At the Phillipsdale Landing, the water column here was strongly stratified. Dissolved oxygen (DO) conditions were not observed below the hypoxia threshold (2.9 mg/L), but approached this threshold near the very bottom of the water column. Fluorescence readings at this site were relatively low, but reached a maximum value approximately 2 meters below the surface.

Week of September 10 – September 16, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on September 14, 2023 using a Seabird Electronics profiler. In the five days leading up to the survey, 1.23 inches of precipitation were recorded at T.F. Green. All sites were strongly stratified this week.

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the Bullock Reach Buoy and Phillipsdale Landing sites, in the lower and middle portions of the water column at Conimicut Point and Point Street Bridge, and in all portions of the water column (upper, middle, and lower) at India Point Park, Pomham Rocks, and Edgewood Yacht Club. The highest fluorescence readings for the week were measured around 1.5 meters below the surface at Edgewood Yacht Club.

Week of August 6 – 12, 2023

Nutrient samples were collected from seven river stations and seven bay stations on August 9th, 2023. All bay stations were sampled at the surface and bottom. In the five days prior to sampling, there were 0.48 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 = 1,390 ppb, TDN = 1,520 ppb, and DIN = 1244.2 ppb). The lowest TN and TDN were observed at Moshassuck River @ Footbridge at Mill Street (TN = 741.5 ppb, TDN= 680.5 ppb, average of duplicates), while the lowest DIN was at Blackstone River @ Bikepath Bridge (DIN = 484.7 ppb).

Among the bay stations sampled, the highest surface TN, TDN, and DIN concentrations were observed at Phillipsdale Landing (TN = 1,050 ppb, TDN = 919 ppb, DIN = 561 ppb). The lowest surface TN, TDN, and DIN concentrations were observed at Conimicut Point (TN = 738 ppb, TDN = 360 ppb, DIN = 143.2 ppb). Chlorophyll a concentrations at the surface bay stations averaged 4.16 μg/L overall with a maximum at the Bullock Reach Buoy (6.94 μg/L, average of duplicates).

Week of September 3 – September 9, 2023

Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on September 6, 2023 using a Seabird Electronics profiler. In the five days leading up to the survey, no precipitation was recorded at T.F. Green. Most sites were moderately to weakly stratified this week.

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the Pomham Rocks, India Point Park, and Phillipsdale Landing sites. The highest fluorescence readings for the week were measured around 1.5 meters below the surface at Edgewood Yacht Club.

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.

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 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.