News – Page 14 – Narrabay

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.

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 9-15, 2023

Surface chlorophyll data were collected on April 13, 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 areas surveyed. Overall, chlorophyll ranged between 0.44 and 81.81 µg/L with an average of 1.76 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation

April 2-8, 2023

Water clarity was measured at six locations in the Providence River and Seekonk River estuaries on April 5. Rainfall totaling 0.50 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.1 meters, compared to 3.2 meters on the previous survey (March 29). The lowest clarity this week (1.6 meters) was measured at Pomham Rocks while the greatest clarity (2.4 meters) was measured at Edgewood Shoal. There was a general north-to-south gradient of increasing water clarity among the sites this week.

April 2-8, 2023

Water column profiles were conducted at six locations in the Providence and Seekonk River Estuaries on April 5, 2023 using a Seabird Electronics profiler. There was no 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, Edgewood Shoal, and Pawtuxet Cove; all other sites showed signs of moderate density stratification.

Surface salinities ranged from 4.3 psu at Pawtuxet Cove to 22.1 psu at Pomham Rocks; bottom salinities ranged from 23.9 psu at Pawtuxet Cove to 28.0 psu at Pomham Rocks. Surface temperatures ranged 9.0°C at India Point Park to 10.8°C at Pawtuxet Cove, while bottom temperatures ranged from 7.3°C at Pomham Rocks to 9.0°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 8.5 mg/L in the bottom waters at Pawtuxet Cove. Fluorescence was fairly low, with the highest value (5.05 mg/m3) observed near the middle of the water column (3.25 meters deep) at Pomham Rocks.

April 2-8, 2023

Nutrient samples were collected from six bay stations and 15 local and border river stations on April 5th, 2023. Most bay stations were sampled at the surface only; one station, Edgewood Shoal, was sampled at the surface and bottom. In the five days prior to sampling, there was 0.5 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 Ten Mile River at Central Ave. The TN, TDN, DIN were 2,300 ppb, 2,000 ppb, and 1,727 ppb, respectively. The lowest TN was observed at Moshassuck River at Higginson Ave as 500 ppb. The lowest TDN and DIN were observed in the duplicates at Palmer River at Route 6. The lowest TDN and DIN were averaging 404.5 ppb and 92.4 ppb, respectively.

Among the bay stations sampled, the highest surface nitrogen concentrations were observed at Pawtuxet Cove. The TN, TDN, and DIN were 1,200 ppb, 990 ppb, and 847.3 ppb, respectively. The lowest surface TN (722 ppb) was observed in one of the duplicate samples collected at Edgewood Yacht Club; the duplicate was higher at 740 ppb. The lowest TDN and DIN were observed at Pomham Rocks as 361 ppb and 241.5 ppb, respectively. Chlorophyll a concentrations at the bay stations have increased (averaging 3.4 ug/L over all sites) since the March 22nd sampling event. The maximum result (6.13 ug/L) occurred at India Point Park.

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

April 2-8, 2023

Surface chlorophyll data were collected on April 5, 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 0.80 and 7.87 µg/L with an average of 2.28 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

April 2-8, 2023

Phillipsdale Landing

The sondes were removed this week on April 3rd after remaining deployed from March 7th due to safety concerns regarding the structural integrity of the dock. The site will be suspended until further noticed due to these safety concerns.

Due to the Phillipsdale Landing sondes being removed on April 3rd, we only have data from the first 3 days of April; all three days are discussed here rather than only discussing the two days of the focal week. The first of April saw 0.47 inches of precipitation recorded at T.F. Green, but the next two were dry. Blackstone River flows responded to the precipitation but remained below the 18-year median statistic of USGS. Surface salinity remained well below bottom salinity. Salinity at the surface averaged 3.4 ppt and ranged from 1.8 ppt to 6.2 ppt. At the bottom, salinity averaged 14.5 ppt and ranged from 2.3 ppt to 27.3 ppt. Temperatures averaged 9.4°C at the surface and 8.3°C at the bottom. Surface temperatures ranged from 7.0°C to 10.8°C, while bottom temperatures ranged from 7.0°C to 10.2°C.

Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold of 2.9 mg/L for these days. Surface DO averaged 11.1 mg/L and ranged 10.2-13.0 mg/L. Bottom water DO concentration averaged 9.9 mg/L and ranged from 8.6 mg/L to 12.4 mg/L. Chlorophyll concentrations were generally low (i.e., <20 µg/L), with no strong signs of phytoplankton bloom activity. Also, please note that portions of chlorophyll data from the bottom sonde from April 1st, 2nd, and 3rd are not included in the summary due to potential sediment interference which is common at this site.

Bullock Reach

Bullock Reach sondes will be deployed later this spring for the 2023 monitoring season.

March 26-April 1, 2023

On March 29, 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 0.67 inches as recorded at TF Green.

The geometric mean of fecal coliform results for all sites was 32 MPN/100 mL compared to 60 MPN/100 mL on March 16, 2023. Overall, bacteria counts were lower in the Seekonk River and Providence River this week than during the previous sampling event on March 16. Fecal coliform counts were similar in the Seekonk River and Providence River sites (geometric means of 32 MPN/100 mL and 33 MPN/100 mL, respectively). The maximum count (750 MPN/100 mL) was measured at Point St. Bridge in the Providence River.

Enterococci results had an overall geometric mean of 12 MPN/100 mL. Enterococci results ranged from non-detect at Point St. Bridge, South FP East, and one of the Conimicut Point duplicates to 20 MPN/100 mL at the Phillipsdale Landing 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

Table adapted from Rhode Island Water Quality Regulations (250-RICR-150-05-1); see regulations for complete details.

March 26-April 1, 2023

Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on March 29. Rainfall totaling 0.74 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 3.2 meters, compared to 2.2 meters on the previous survey (March 22). The lowest clarity this week (2.7 meters) was measured at India Point Park, while the greatest clarity (3.7 meters) was measured at Point St. Bridge. There was a general north-to-south gradient of increasing water clarity among the sites this week.

March 26-April 1, 2023

Surface chlorophyll data were collected on March 29, 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 areas surveyed. Overall, chlorophyll ranged between 0.63 and 8.23 µg/L with an average of 1.43 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.