Water clarity was measured at seven locations in the Providence River and Seekonk River estuaries on March 22. Rainfall totaling 0.20 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.2 meters, compared to 1.6 meters on the previous survey (March 22). The lowest clarity this week (1.2 meters) was measured at Pawtuxet Cove, while the greatest clarity (2.6 meters) was measured at Bullock Reach, Conimicut Point, and Phillipsdale Landing. There was a general north-to-south gradient of increasing water clarity among the sites this week.
Phytoplankton samples were collected on March 22, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. It was a brisk day with some cloud cover. The current was very strong and some seals were spotted in Narragansett Bay. Sondes data revealed the surface water temperature was 7.03⁰C, salinity was 13.76 psu, and chlorophyll a was 1.26 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a deep 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 108,000 cells per Liter. The micro flagellates were found at 4000 cells/L. The most predominant phytoplankton genus was Thalassionema spp. at 36,000 cells/L. Representative genera in the tow net sample include Skeletonema spp., Leptocylindrus spp. and pennate diatoms.
Water column profiles were conducted at seven locations in the Providence and Seekonk River Estuaries on March 22, 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 sites near the middle of the bay (Pomham Rocks, Edgewood Yacht Club, and Pawtuxet Cove), with sites to the north and south of these showing signs of weak to moderate density stratification.
Surface salinities ranged from 3.2 psu at Pawtuxet Cove to 24.3 psu at Bullock Reach Buoy; bottom salinities ranged from 22.8 psu at Phillipsdale Landing to 28.8 psu at Conimicut Point. Surface temperatures ranged from 6.3°C at India Point Park to 7.2°C at Pawtuxet Cove, while bottom temperatures ranged from 5.8°C at Conimicut Point to 6.7°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 9.9 mg/L in the bottom waters at Edgewood Yacht Club. Fluorescence was higher than the previous survey, with the highest value (22.98 mg/m3) observed near the surface at India Point Park but many other areas remaining relatively low.
Nutrient samples were collected from seven local river stations, and seven bay stations on March 22nd, 2023. All bay stations were sampled at surface and bottom. In the five days prior to sampling, 0.02 inches of rainfall was 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 Blackstone River at Slater Mill. The TN, TDN, and DIN were 1,080 ppb, 1,160 ppb, and 885 ppb, respectively. The lowest TN (698 ppb) was observed at Woonasquatucket River at Manton Ave Bridge. The lowest TDN and DIN were observed at one of duplicate samples collected at the Moshassuck River at Footbridge at Mill Street; 697 ppb and 554 ppb, respectively.
Among the bay stations sampled, the highest TN (1,050 ppb) and TDN (978 ppb) was observed at Phillipsdale Landing. The highest DIN were observed at Pawtuxet Cove as 697.7 ppb. The lowest surface TN (485 ppb), TDN (328 ppb) and DIN (193 ppb) were observed at Conimicut Point. Chlorophyll a concentrations at the bay stations have decreased (averaging 2.66 ug/L over all sites) since the February 22nd sampling event. The maximum result of 4.78 ug/L occurred at India Point Park.
Data from additional sampling dates (typically every two weeks) are pending analysis and writeup.
Surface chlorophyll data were collected on March 22, 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 fair in the Seekonk River and good in the other areas surveyed. Overall, chlorophyll ranged between 0.89 and 43.56 µg/L with an average of 2.77 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.
Sondes remained deployed this week as there were safety concerns regarding the structural integrity of the dock. Overall, water quality at Phillipsdale Landing was good this week. Weather conditions were mostly dry , with only 0.31 inches recorded at T.F. Green. Blackstone River flow decreased all week, and salinity at Phillipsdale increased . Surface salinity this week averaged 6.2 ppt and ranged from 1.8 ppt to 16.1 ppt. At the bottom, salinity averaged 15.7 ppt and ranged from 3.8 ppt to 28.0 ppt. Temperatures increased this week, averaging 8.1°C at the surface and ranging 4.8°C – 10.1°C. At the bottom, temperatures averaged 7.2°C and ranged 5.7°C – 9.6°C.
Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold of 2.9 mg/L throughout the week. Surface DO averaged 11.4 mg/L and ranged 9.8-13.0 mg/L. Bottom DO concentrations averaged 10.6 mg/L and ranged from 9.2 mg/L to 12.7 mg/L. Chlorophyll concentrations slightly decreased from the previous week, averaging 3.6 ug/L at the surface and 12.2 ug/L at the bottom. Maximum chlorophyll at the surface reached just 38.5 ug/L on the morning of March 23rd. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location. Also, please note that isolated spikes of suspect chlorophyll data, between March 19th-25th, were excluded from the summary this week.
Bullock Reach
Bullock Reach sondes will be deployed later this spring for the 2023 monitoring season.
On March 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 3.2 inches as recorded at TF Green.
The geometric mean of fecal coliform results for all sites was 60 MPN/100 mL compared to 11 MPN/100 mL on March 1, 2023. Overall, bacteria counts were higher in the Seekonk River and Providence River this week than during the previous sampling event on March 1. Fecal coliform counts were higher in the Seekonk River sites than in the Providence River sites (geometric means of 79 MPN/100 mL and 52 MPN/100 mL, respectively). The maximum count (430 MPN/100 mL) was measured at Collier Point Park in the Providence River.
Enterococci results had an overall geometric mean of 32 MPN/100 mL. Enterococci results ranged from 10 MPN/100 mL at one of the Conimicut Point duplicates to 74 MPN/100 mL at the South FP East 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
Water clarity was measured at five locations in the Providence River and Seekonk River estuaries on March 16. Rainfall totaling 3.2 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.6 meters, compared to 2.8 meters on the previous survey (February 22). The lowest clarity this week (1.1 meters) was measured at India Point Park, while the greatest clarity (2.2 meters) was measured at Bullock Reach. There was no clear north-to-south gradient in water clarity among the sites this week.
Surface chlorophyll data were collected on March 16, 2023 while the R/V Monitor was underway taking benthic video footage in the Providence and Seekonk River estuaries. The average chlorophyll concentrations were categorized as good in the areas surveyed. Overall, chlorophyll ranged between 0.69 and 12.51 µg/L with an average of 1.63 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.
Overall, water quality at Phillipsdale Landing was fair to good this week. Weather conditions were wet this week, with a total of 2.93 inches recorded at T.F. Green, and the majority of rainfall occurring on the 13th and 14th. Blackstone River flow increased during the 13th and 14th and remained above the 18-year daily median for the majority of the week. Surface and bottom salinity dropped dramatically after the 13th -14th storm and increased river flows. Salinity at the surface averaged 4.7 ppt and ranged from 0.3 ppt to 13.0 ppt. At the bottom, salinity averaged 14.4 ppt and ranged from 0.4 ppt to 29.5 ppt. Temperatures this week averaged 6.3°C at the surface and 5.9 °C at the bottom. Surface temperatures ranged from 4.3°C to 9.1°C, while bottom temperatures ranged from 4.4°C to 7.3°C.
Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO remained similar to the previous week, averaging 12.4 mg/L and ranging 10.4-14.1 mg/L. Bottom water DO concentration averaged 11.0 mg/L and ranged from 8.1 mg/L to 13.7 mg/L. Chlorophyll concentrations rose from the previous week, averaging 4.5 ug/L at the surface and 12.4 ug/L at the bottom. Maximum surface chlorophyll readings reached 56.0 ug/L, recorded in the morning of March 13th. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location. Also, please note that portions of chlorophyll data from the surface sonde on March 13th and from the bottom sonde on March 14th and 16th were excluded from the summary this week due to suspected sediment interference.
Bullock Reach
Bullock Reach sondes will be deployed later this spring for the 2023 monitoring season.
