October 23, 2024
Water Column Clarity
Water clarity was measured at seven locations in the Providence River estuary on October 23, 2024. No precipitation was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 5.0 meters. The lowest clarity this week (4.7 meters) was measured at Conimicut Point, while the greatest clarity (5.5 meters) was measured at Edgewood Yacht Club. There was no distinct north-to-south trend of water clarity among the sites this week. Overall, water clarity increased from the previous measurements (data collected October 17, 2024).
October 17, 2024
Surface Mapping
Surface chlorophyll data were collected on October 17, 2024 while the R/V Monitor was underway collecting nutrient samples in the Providence and Seekonk River estuaries. The average chlorophyll concentrations were categorized as good in all areas surveyed. Overall, chlorophyll ranged from 1.23 µg/L to 11.31 µg/L with an average of 3.05 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.
September 4, 2024
Phytoplankton Sampling
Phytoplankton samples were collected on September 4, 2024 at Bullock Reach and analyzed in the laboratory shortly after collection. It was a sunny, calm and cloudless day on Narragansett Bay. Sonde data was not analyzed on this day. The qualitative tow net sample had a quick filtration time, the filtrate was slightly cloudy and golden brown with some black particulates. The analysis of the quantitative whole water sample revealed a total of 874,000 cells/L. The microflagellates were found at 94,000 cells/L. The most predominant phytoplankton genera were Skeletonema spp. at 240,000 cells/L, Leptocylindrus spp. at 224,000 cells/L, and Cylindrotheca spp. at 188,000 cells/L. Pleurosigma, shown here in a 200x phase contrast micrograph, is a widely distributed genus of elongate, biraphid diatoms which glide and rotate in brackish to marine waters. They are pelagic and either float on the tides, sink to lower levels on top of the salt layer or attach to marine organisms. These diatoms contribute to essential oxygen levels in the ocean and also serve as a food source for animal larvae and dinoflagellates.
March 20, 2024
Water Column Profiles
Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on March 20, 2024 using a Seabird Electronics profiler. In the five days leading up to the survey, 0.08 inches of precipitation were recorded at T.F. Green. Most sites were strongly or moderately stratified this week, with the exception of Phillipsdale Landing, which was dominated by freshwater.
Dissolved oxygen (DO) conditions were not observed to be below the hypoxia threshold (2.9 mg/L) at any site profiled this week. The highest fluorescence readings for the week were measured around 2 meters below the surface at Bullock Reach Buoy.
Week of July 29 - August 4, 2024
Fixed Site Network
Phillipsdale Landing
Overall, water quality at Phillipsdale Landing was fair to poor this week. Weather conditions included sporadic rain events, with 1.16 inches of precipitation recorded at T.F. Green. The Blackstone River flow fluctuate through the week in response to rain, rising above the 19-year daily median mid-way through the week. Surface salinity averaged 17.8 ppt and ranged from 7.7 ppt to 24.4 ppt. At the bottom, salinity averaged 22.6 ppt and ranged from 14.3 ppt to 25.8 ppt. Temperatures continued to increase this week, averaging 25.5°C at the surface and ranging 23.4°C – 27.9°C. At the bottom, temperatures averaged 24.5°C and ranged 22.8°C – 26.8°C.
Dissolved oxygen (DO) at Phillipsdale Landing dropped below the hypoxia threshold (i.e., DO >2.9 mg/L) over the week. Surface DO average 6.5 mg/L and ranged from 0.8 mg/L to 17.3 mg/L. Bottom DO concentrations averaged 2.6 mg/L and ranged from 0.2 mg/L to 9.2 mg/L. The longest period of hypoxic conditions (1 day, 9 hours and 31 minutes) occurred at the bottom depth between the morning of July 29th and the morning of July 30th. During this period, bottom DO averaged around 1.51 mg/L. Chlorophyll readings increased from last week, averaging 33.5 µg/L at the surface and 22.6 µg/L at the bottom. Maximum chlorophyll at the surface reached 347.5 µg/L on the morning of August 4th. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.
Bullock Reach
Sondes were swapped this week on the morning of July 30th. Overall, water quality was good at Bullock Reach this week. Salinity averaged 26.5 ppt, 28.3 ppt, and 30.1 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged 15.7 – 28.3 ppt, mid salinity ranged 26.6 – 29.7 ppt, and bottom salinity ranged 28.4 – 31.3 ppt. Surface temperature averaged 24.7°C and ranged from 22.5°C to 27.7°C. Mid temperatures averaged 23.9°C and ranged from 21.8°C to 26.7°C. Bottom temperatures averaged 22.5°C and ranged from 20.8°C to 24.7°C.
DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) at the surface and mid depths throughout the week. Bottom DO sporadically dropped below the hypoxia threshold this week. Surface DO averaged 8.2 mg/L and ranged 4.7 – 14.4 mg/L. In the mid waters, DO averaged 5.8 mg/L and ranged 3.0 – 7.8 mg/L. At the bottom, DO averaged 3.7 mg/L and ranged 2.4 – 6.7 mg/L. The longest period of hypoxic conditions (3 hours and 30 minutes) occurred at the bottom depth during July 30th. During this period, bottom DO averaged around 2.76 mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 21.8 µg/L at the surface, 17.5 µg/L at mid-depth, and 4.9 µg/L at the bottom. The maximum surface chlorophyll was 49.7 µg/L on the morning of August 2nd.
