Historical News
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 20.62oC, 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.
Nutrients Sampling
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.
Water Column Profiles
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.