Week of August 20 – 26, 2023

​Water clarity was measured at four locations in the Providence River estuary on August 23rd, 2023. Rainfall totaling 2.16 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 1.7 meters, compared to 2.8 meters on the previous survey (August 18th). The lowest clarity this week (1.3 meters) was measured at Pawtuxet Cove, while the greatest clarity (2.0 meters) was measured at Edgewood Yacht Club. There was no clear north-to-south gradient in water clarity among the sites this week.

August 2023

​Phillipsdale Landing

The Phillipsdale Landing sondes have been deployed for the season since May 9th, 2023 utilizing a new setup allowing staff access to the equipment from the boat instead of standing on the dock. During the month of August, sondes were changed out for routine maintenance on August 1st, 16th, and 29th. 

Surface DO remained mostly above the hypoxia threshold, dropping briefly below the threshold for approximately an hour and a half on August 2nd and again on August 3rd. The bottom waters were hypoxic periodically throughout the month, with the longest sustained hypoxic periods (11 hours) occurring overnight between August 16th and 17th, and again overnight August 17th to 18th. DO averaged 6.4 mg/L at the surface with a minimum of 1.6 mg/L, while bottom waters averaged 3.0 mg/L with a minimum of 0.6 mg/L. 

Chlorophyll readings were generally low with intermittent periods of elevated readings through the month, suggestive of minor phytoplankton blooms. The surface and bottom readings averaged 4.3 µg/L and 4.1 µg/L, respectively. The maximum surface reading of 43.6 µg/L occurred on August 8th and the maximum bottom reading of 30.0 µg/L occurred on August 24th. 

Bullock Reach

The Bullock Reach buoy was deployed June 1st for the 2023 season. During the month of August, sondes were changed out for routine maintenance on August 8th and 22nd.

Surface DO remained above the hypoxia threshold all month. There were a few brief periods of hypoxic conditions in the middle waters, with the longest duration at 2 hours on August 18th. The bottom waters had hypoxic conditions on and off all month, with the longest sustained period of hypoxic conditions at 2.5 days between the 16th and 19th. Surface, middle, and bottom DO averaged 7.3 mg/L, 5.1 mg/L, and 3.5 mg/L, respectively.

Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the month. Readings averaged 13.8 µg/L at the surface, 11.1 µg/L at mid-depth, and 3.3 µg/L at the bottom. The maximum surface reading of 70.0 µg/L occurred on August 21st. Please note that data gaps occurred between the 1st and 2nd and between the 28th and 29th on the middle sonde due to equipment failure.​

August 20-26, 2023

​Surface chlorophyll data were collected on August 22, 2023 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 the Seekonk River, Northern Providence River Channel, and Edgewood Shoals and as fair in all other areas. Overall, chlorophyll ranged from 1.56 to 44.70 µg/L with an average of 5.72 µg/L. The chlorophyll concentrations from this date are presented in the map below using Inverse Distance Weighting (IDW) interpolation.

August 20-26, 2023

Phytoplankton samples were collected on August 23, 2023 at Bullock Reach and analyzed in the laboratory shortly after collection. Sonde data revealed the surface water temperature was 21.0°C and salinity was 26.5 psu. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light brown color and had a quick filter time. The tow net sample was analyzed qualitatively for microorganisms using 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 1,866,000 cells per Liter. The micro flagellates were found at 348,000 cells/L. The most predominant phytoplankton genus was Leptocylindrus spp.at 948,000 cells/L. Other representative genera include Skeletonema spp., Chaetoceros spp. (see 200x phase contrast image below), and Guinardia spp.

August 1, 2024

​Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on August 1, 2024 using a Seabird Electronics profiler. In the five days leading up to the survey, 1.34 inches of precipitation were recorded at T.F. Green. Water column stratification at the sites varied from well-mixed at Edgewood Yacht Club, to strongly stratified at Point Street Bridge. 

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at Point Street Bridge and Pomham Rocks, and in the upper and middle portions of the water column at Phillipsdale Landing. The highest fluorescence readings for the week were measured around 1.5 meters below the surface at Phillipsdale Landing.​

July 24, 2024

​Water column profiles were conducted at eight locations in the Providence and Seekonk River estuaries on July 24, 2024 using a Seabird Electronics profiler. In the five days leading up to the survey, 0.06 inches of precipitation were recorded at T.F. Green. Water column stratification at the sites varied from well-mixed at Pawtuxet Cove and Phillipsdale Landing, to moderately stratified at sites such as Bullock Reach Buoy and India Point Park. 

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the Bullock Reach Buoy, and in the lower and middle portions of the water column at the Pomham Rocks, India Point Park, Edgewood Yacht Club, and Edgewood Shoals sites. The highest fluorescence readings for the week were measured around 1.5 meters below the surface at Pawtuxet Cove.

July 17, 2024

​Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on July 17, 2024 using a Seabird Electronics profiler. In the five days leading up to the survey, 0.48 inches of precipitation were recorded at T.F. Green. Water column stratification at the sites varied from weakly stratified at Point Street Bridge, to strongly stratified at a majority of sites, including Bullock Reach Buoy and Phillipsdale Landing. 

Dissolved oxygen (DO) conditions were below the hypoxia threshold (2.9 mg/L) in the lower portion of the water column at the Bullock Reach Buoy and Edgewood Yacht Club sites, in the lower and middle portions of the water column at the Pomham Rocks and Phillipsdale Landing sites, and in all portions of the water column (upper, middle, and lower) at India Point Park. DO conditions were below the hypoxia threshold at Conimicut Point only in the middle portion of the water column. The highest fluorescence readings for the week were measured around 1 meter below the surface at Phillipsdale Landing.

Week of August 20 – 26, 2023

​Nutrient samples were collected from fourteen river stations and eight bay stations on August 23rd, 2023. Edgewood Shoal was sampled at the surface and bottom; all other bay stations were sampled at the surface only. In the five days prior to sampling, there were 2.16 inches of rainfall recorded at T.F. Green due to a heavy rain event on August 18th.

Among the river stations sampled, the highest total nitrogen (TN) concentration was observed at Pawtuxet River @ Broad Street (TN = 1,815 ppb, average of duplicates), while the highest total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN) concentrations were at Ten Mile River @ Central Ave. (TDN = 1,480 ppb, DIN = 1,013.9 ppb). The lowest TN and TDN were observed at Ten Mile River @ Roger Williams Ave. (TN = 510 ppb, TDN = 666 ppb), while the lowest DIN was at Coles River @ Milford Rd. (97.4 ppb, average of duplicates).

Among the bay stations sampled, the highest surface TN, TDN, and DIN were observed at Pawtuxet Cove (TN = 1,020 ppb, TDN = 892 ppb, DIN = 662.3 ppb). The lowest surface TN and DIN were observed at the Bullock Reach Buoy (TN = 540 ppb, DIN = 119.5 ppb), while the lowest surface TDN was at Conimicut Point (276 ppb). Chlorophyll a concentrations at the surface bay stations averaged 3.95 μg/L overall with a maximum of 7.02 μg/L at Conimicut Point.

April 16, 2024

​Water column profiles were conducted at seven locations in the Providence and Seekonk River estuaries on April 16, 2024 using a Seabird Electronics profiler. In the five days leading up to the survey, 1.01 inches of precipitation were recorded at T.F. Green. Most sites were strongly 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 10 meters below the surface at Pomham Rocks.

August 13-19, 2023

​Water clarity was measured at five locations in the Providence River and Seekonk River estuaries on August 16. Rainfall totaling 0.61 inches was recorded at TF Green in the five days prior to the survey. Secchi depth averaged 2.8 meters, compared to 1.8 meters on the previous survey (August 9). The lowest clarity this week (1.9 meters) was measured at Phillipsdale Landing, while the greatest clarity (3.6 meters) was measured at Point St. Bridge. There was no clear north-to-south gradient in water clarity among the sites this week.

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