Historical News
Phytoplankton Sampling
Phytoplankton samples were collected on November 4, 2020 at Bullock's Reach and analyzed in the laboratory shortly after collection. It was a windy and brisk day on Narragansett Bay. Sondes data revealed the surface water temperature was 10.23oC, salinity was 25.96 psu, and chlorophyll a was 2.0 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light tan color and had a short 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 222,000 cells per Liter. The flagellates were found at 16,000 cells/L. The most predominant phytoplankton was Skeletonema spp. at 105,000 cells/L. Representative genera include Leptocylindrus spp., Thalassiosira spp. and pennate diatoms.
200x phase contrast micrograph of a pennate diatom
Fixed Site Network
Phillipsdale Landing
Water quality was good this week at Phillipsdale Landing. Precipitation totaled 0.73 inches at TF Green this week, with all the rainfall occurring on November 1. Blackstone River flows increased at the beginning of the week in response to the precipitation, with freshwater flows reducing through the week. This week, surface salinity averaged 10.1 ppt and ranged from 2.0 ppt to 20.4 ppt. Bottom salinity averaged 22.2 ppt and ranged from 4.9 ppt to 29.3 ppt. Both surface and bottom water temperatures continued their seasonal decline, averaging 10.9°C and 12.8°C, respectively. Surface temperatures ranged from 7.2°C to 13.6°C, while bottom temperatures ranged from 8.2°C to 15.3°C.
Dissolved oxygen (DO) remained above the hypoxia threshold (2.9 mg/L) in surface and bottom waters this week. Surface DO averaged 9.4 mg/L, with a minimum of 6.6 mg/L, and bottom DO averaged 6.9 mg/L, with a minimum 5.4 mg/L. Chlorophyll concentrations were low, averaging 2.0 ug/L at the surface and 1.6 ug/L at the bottom. Maximum surface chlorophyll concentrations reached 4.4 ug/L, measured on November 1. Please note that tidal fluctuations and Blackstone River flow greatly influence water column salinity, temperature, and dissolved oxygen at this location.
Bullock Reach
Bullock Reach sondes were changed out for routine maintenance during the morning on November 3. Following the deployment of the sondes, the mid-sonde salinity data are not reported in this summary due to suspected probe drift. Water quality was good this week at Bullock Reach. Surface salinity averaged 27.6 ppt and ranged from 24.0 ppt to 30.1 ppt, while bottom waters averaged 30.7 ppt and ranged from 26.8 ppt to 32.8 ppt. Temperatures averaged 12.0°C at the surface, and 12.1 ppt at the mid depth and bottom waters. Surface temperatures ranged from 10.0°C to 13.8°C, mid depth temperatures ranged from 10.2°C to 14.0°C, and bottom temperatures ranged from 10.3°C to 14.4°C.
Dissolved oxygen (DO) concentrations remained above the hypoxia threshold (2.9 mg/L) throughout the water column. Surface DO averaged 8.3 mg/L for the week, while mid and bottom DO averaged 8.0 mg/L and 7.7 mg/L, respectively. Chlorophyll concentration remained low at this site, averaging 1.4 ug/L at the surface and mid waters, while bottom waters averaged 2.0 ug/L. The maximum water chlorophyll concentrations was 7.7 ug/L, measured in surface waters on November 1.
Bacteria Sampling
Water Column Clarity
Water clarity was measured at seven stations in the Providence and Seekonk Rivers on November 25, 2020. Heavy rainfall of 1.37 inches was recorded at TF Green two days prior to the survey, likely impacting clarity in the Bay. Overall, Secchi depths averaged 3.02 m, compared to 3.91 m on November 4; note that comparisons to the survey on November 18 are limited, since only three sites were visited on that day. The greatest clarity was observed at Edgewood Yacht Club, at 3.70 m. This was the only site that exhibited an increase in clarity compared to previous surveys: 2.70 m on November 4 and 2.97 m on November 18. The greatest decrease in clarity occurred at Conimicut Point; clarity at this site decreased by 2.70 m since the survey on November 4. The lowest water clarity this week was observed at India Point Park, at 2.50 m. There was a weak spatial gradient in clarity this week, with slightly higher clarity at southern sites than northern.
Water Column Clarity
Water clarity was measured at three stations in the Providence River on November 18, 2020; additional sites were abandoned due to rough conditions. Moderate rainfall occurred over the five days prior to the survey, with a total of 0.65 inches recorded at TF Green. Secchi depth was lowest, 2.37 m, at Pawtuxet Cove, representing a slight decline in clarity compared to the prior survey on November 4 (2.70 m). Clarity at Edgewood Yacht Club increased slightly since November 4, from 2.70 m to 2.97 m in the current survey. The greatest water clarity this week was observed at Edgewood Shoal, at 3.10 m; this site was not visited during the prior survey in November. Overall, clarity averaged 2.81 m this week.