Historical News
Bacteria Sampling
Twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers on February 16. Five of these stations were also sampled for enterococci bacteria. Precipitation in the five days prior to sampling totaled 0.65 inches, with the majority of this precipitation (0.60 inches) occurring in the morning hours prior to sample collection on the day of the sampling event.
The geometric mean of fecal coliform results for all sites was 50 MPN/100 mL, with Seekonk River sites having higher counts than Providence River sites (geometric means of 734 MPN/100 mL and 14 MPN/100 mL, respectively). The maximum count (24,000 MPN/100 mL) was measured at Bishop Point in the Seekonk River. Overall, fecal coliform results from both the Providence and Seekonk Rivers exceeded state primary contact and shellfishing standards.
Enterococci results also increased since the last sampling event, from 18 MPN/100 mL in early January to 37 MPN/100 mL in mid-February. Enterococci results at all sites ranged from <10 MPN/100 mL to 1,145 MPN/100 mL, with the highest results at Point St. Bridge. Like fecal coliform, these enterococci results exceeded the primary contact criteria.
Please note: the results of NBC's fecal coliform and enterococci monitoring are for informational/research purposes only and are not intended to suggest official state compliance with bathing or shellfishing standards.
Water Column Profiles
NBC Environmental Monitoring staff utilized a YSI EXO sonde to collect data on surface and bottom conditions at six typical Seabird profiling sites on March 10. Staff utilized a small boat to conduct surveys as the larger R/V Monitor remains out of service, and the Seabird instrument is too large to deploy from this smaller boat. Settings on the EXO sonde were not optimized for measurements of a true profile, rather the goal was stable estimates of conditions at the surface and bottom only. These data are summarized here, and raw data are available upon request. Conditions leading up to sampling were dry, with no recorded rainfall at T.F. Green in the 5 – 6 days leading up sampling. Minor salinity and temperature stratification was evident at India Point Park and Bullock Reach Buoy, with the remaining sites appearing more well-mixed.
Surface salinity ranged from approximately 19 ppt at India Point Park to 29 ppt at Pomham Rocks. Bottom salinities were higher, ranging from approximately 22 ppt at Edgewood Shoals to 31 ppt at Conimicut Point Park. Overall, water temperatures were cool this week, ranging from approximately 4°C at Pomham Rocks surface to 6°C at Edgewood Shoal surface, and bottom waters ranging from approximately 3°C observed at Conimicut Point to 4°C at Edgewood Shoal. Dissolved oxygen concentrations in bottom waters measured between 10 and 12 mg/L at all sites. Surface chlorophyll was generally low, averaging approximately 3.12 ug/L across all sites with a maximum value of 29.23 ug/L observed at Pomham Rocks.
Phytoplankton Sampling
Phytoplankton samples were collected on February 24, 2021 at Bullock Reach and analyzed in the laboratory shortly after collection. It was a sunny, calm, and mild day on Narragansett Bay. Sondes data revealed the surface water temperature was 2.99°C, salinity was 20.19 psu, and chlorophyll a was 0.3 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a golden color and had a quick filter time. The tow net sample was analyzed qualitatively for microorganisms using 100x 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 476,000 cells per Liter. The flagellates were found at 91,000 cells/L. The most predominant phytoplankton was Skeletonema spp. at 247,000 cells/L. Representative genera include Chaetoceros spp., Thalassionema spp. and Leptocylindrus spp.
200x phase contrast image of Chaetoceros socialis.
Fixed Site Network
Water quality at Phillipsdale Landing was good this week. Sondes were removed for the season on the morning of December 16. Less than 0.25 inches of rainfall occurred prior to the mid-week removal of the sondes. Water column salinity increased from the previous week. Surface salinity averaged 9.1 ppt with a maximum value of 20.2 ppt, while bottom salinity averaged 20.9 ppt with a maximum value of 29.9 ppt.
Surface and bottom temperatures were warmer than those measured the previous week. Surface temperatures averaged 5.8°C, while bottom temperatures averaged 7.6°C and ranged from 4.4°C to 8.8°C. Dissolved oxygen (DO) remained above the hypoxia threshold (2.9 mg/L) in surface and bottom waters this week. Surface DO averaged 11.3 mg/L, with a minimum of 9.1 mg/L, while bottom DO averaged 9.0 mg/L, with a minimum of 7.9 mg/L. Chlorophyll concentrations averaged 2.1 ug/L at the surface and 1.6 ug/L at the bottom. Please note that tidal fluctuations and Blackstone River flow greatly influence water column salinity, temperature, and dissolved oxygen at this location.
Bullock Reach
The Bullock Reach sondes were removed for the 2020 monitoring season on November 17.
Nutrients Sampling
Nutrient samples were collected from seven local and border river stations on December 30. Due to adverse weather concerns, bay nutrient samples were not collected as scheduled. In the three days prior to sampling there was no rainfall recorded at T.F. Green.
Among the river station samples, the highest total nitrogen (TN), total dissolved nitrogen (TDN), and dissolved inorganic nitrogen (DIN) were all observed at Pawtuxet River at Broad Street. At this site, concentrations for TN, TDN, and DIN were 1,230 ppb, 1,250 ppb, and 1,015.6 ppb, respectively. The lowest TN (691 ppb) was observed at Woonasquatucket River at Manton Avenue Bridge, while the lowest TDN (714 ppb) and DIN (470.3 ppb) were observed at Blackstone River at Stateline.
Results from nutrient sampling on January 13 and 27 are pending analysis. The next scheduled date of sampling is February 24, 2021.
