Snapshot of the Bay

Historical News

Week of June 16 - 22, 2019

Phytoplankton Sampling

Phytoplankton samples were collected on June 19, 2019 at Bullock's Reach and analyzed in the laboratory shortly after collection.

It was a cloudy and muggy day on Narragansett Bay. Sondes data revealed the surface water temperature was 20.62^oC, salinity was 17.42 psu, and chlorophyll a was 18.8 ug/L.

The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light brown color with a medium 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 2,784,000 cells per Liter.

The most predominant phytoplankton was Guinardia spp. at 1,672,000 cells/L. The flagellates were found at 568,000 cells/L. Representative genera include Chaetoceros, Thalassiosira spp., Leptocylindrus and Eucampia spp.

200x phase contrast micrograph showing Guinardia spp.

Week of June 2 - 8, 2019

Nutrients Sampling

Nutrient samples were collected at seven local river stations and seven bay stations (surface and bottom) on June 5, 2019. The three days prior to sampling had light rain, with just 0.07 inches of precipitation recorded.

Among the river stations, the highest total nitrogen (TN), total dissolved nitrogen (TDN), and dissolved inorganic nitrogen (DIN) values were measured at the Pawtuxet River at Broad St. site, with values of 946 ppb, 1,000 ppb, and 784 ppb, respectively. The lowest nitrogen results (440 ppb TN, 448 ppb TDN, and 238 DIN) were measured at the Moshassuck River at Higginson Ave. site.

At the bay sites, Phillipsdale Landing had the highest concentrations of TN (945 ppb) and TDN (607 ppb). The highest DIN concentration was observed at Pawtuxet cove, at 463 ppb. Conimicut Point had the lowest TN concentration at 420 ppb, while several stations had TDN concentrations below detection (i.e., <100 ppb; Conimicut Point, Edgewood Yacht Club, Pomham Rocks, and Bullock Reach). The minimum DIN concentration, 13 ppb, was measured in samples from Conimicut Point and Bullock Reach. Chlorophyll concentrations showed a slight increase since the last survey, with a maximum of 11.65 ug/L at Phillipsdale Landing and an overall average of 5.7 ug/L.

Week of June 23 - 29, 2019

Water Column Clarity

Water clarity was measured at eight locations in the Providence and Seekonk Rivers on June 26, 2019. Approximately 0.7 inches of rainfall was recorded in the area over the five days prior to sampling. Average Secchi depth increased from the previous week’s survey, from 1.3 m to 1.7 m. Water clarity increased at all locations, with the greatest increase (1.1 m) observed at Pawtuxet Cove; this station had the highest clarity overall: 2.7 m. Phillipsdale had the lowest water clarity with a Secchi depth reading of 1.1 m. Generally, water clarity increased with distance down-bay.

Week of June 23 - 29, 2019

Water Column Profiles

Water column profiles were measured at eight sites in the Seekonk and Providence Rivers on June 26, 2019. Moderate rainfall of 0.3 inches was recorded the day before the survey, and low surface salinities were observed at sites close to river inputs. Overall, density stratification was observed at Phillipsdale, India Point Park, Pawtuxet Cove, and Conimicut Point, while the water column was relatively well-mixed at the remaining sites. The lowest surface salinity (7 psu) was measured at Phillipsdale Landing; surface salinity reached a maximum of 26 psu at Bullock Reach. Bottom salinity was highest (28 psu) at Conimicut Point, Pomham Rocks, and India Point Park. Surface temperatures were warm, around 20-21°C at most sites, up to 22°C at Pawtuxet Cove, Point St. Bridge, and Edgewood Yacht Club; bottom temperatures ranged from 17.7°C at India Point to 21°C at Point St. Bridge.

Dissolved oxygen (DO) was moderate to good at most sites, except for Phillipsdale Landing where the bottom waters were severely hypoxic. Dissolved oxygen below 3 meters depth at this site averaged 0.7 mg/L. Phytoplankton bloom activity was evident at several sites, with maximum fluorescence around 36 mg/m³ at 1 m depth at Phillipsdale Landing.

Week of June 23 - 29, 2019

Bacteria Sampling

Twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers on June 26, 2019. There was 0.73 inches of rain in the five days prior to sampling.

The fecal coliform geometric mean for all sites was 165 MPN/100 mL. Elevated fecal coliform geometric mean results were measured in both the Seekonk River (323 MPN/100 mL) and the Providence River (120 MPN/100 mL). The maximum fecal coliform concentration (9,300MPN/100 mL) was measured at the Point Street Bridge. Geometric mean results indicate both rivers exceeded state primary contact and shellfishing standards.

The enterococci geometric mean for the Seekonk and Providence Rivers decreased from the previous sampling, from 48 MPN/100 mL to 35 MPN/100 mL. Enterococci concentrations ranged from <10 MPN/100 mL at Conimicut Point and Save the Bay to 1,063 MPN/100 mL at Point Street Bridge. These results are not within the state criteria for primary contact.

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.