Phillipsdale Landing
Sondes were swapped this week on the morning of July 9th. Overall, water quality at Phillipsdale Landing was good this week. Weather conditions were dry, with only 0.48 inches on July 13th, recorded at T.F. Green. The Blackstone River flow declined this week, dropping below the 19-year daily median mid-week. Surface salinity averaged 9.0 ppt and ranged from 2.6 ppt to 18.0 ppt. At the bottom, salinity averaged 17.7 ppt and ranged from 5.1 ppt to 25.1 ppt. Temperatures continued to increase this week, averaging 26.8°C at the surface and ranging 24.8°C – 30.6°C. At the bottom, temperatures averaged 24.8°C and ranged 22.0°C – 28.7°C.
Dissolved oxygen (DO) at Phillipsdale Landing remained above the hypoxia threshold (i.e., DO >2.9 mg/L) at the surface throughout the week, while DO at the bottom waters remained below the hypoxic threshold for most of the week. Surface DO average 10.1 mg/L and ranged from 4.5 mg/L to 19.1 mg/L. Bottom DO concentrations averaged 4.1 mg/L and ranged from 0.8 mg/L to 13.3 mg/L. The longest period of hypoxic conditions (10 hours, 45 minutes) occurred at the bottom depth from the morning to afternoon of July 14th. During this period, bottom DO averaged around 1.68 mg/L. Chlorophyll readings rose from last week, averaging 85.8 µg/L at the surface and 46.4 µg/L at the bottom. Maximum chlorophyll at the surface reached 261.8 µg/L on the morning of July 9th. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.
Bullock Reach
Overall, water quality was good at Bullock Reach this week. Salinity averaged 23.4 ppt, 25.9 ppt, and 28.8 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged 19.9 – 26.2 ppt, mid salinity ranged 23.2 -28.2 ppt, and bottom salinity ranged 26.3 – 30.4 ppt. Surface temperature averaged 25.7°C and ranged from 23.6°C to 27.9°C. Mid temperatures averaged 24.7°C and ranged from 20.9°C to 26.2°C. Bottom temperatures averaged 21.6°C and ranged from 19.3°C to 25.3°C.
DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) at the surface and middle depths throughout the week. Bottom DO dropped below the threshold, with the longest hypoxic period (11 hours and 15 minutes) occurring between the night of July 13th and the morning of July 14th.
During this period, the bottom DO averaged around 2.52 mg/L. Surface DO averaged 7.3 mg/L and ranged 4.5 – 12.0 mg/L. In the mid waters, DO averaged 5.9 mg/L and ranged 3.2 – 8.2 mg/L. At the bottom, DO averaged 3.7 mg/L and ranged 2.1 – 6.5 mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 18.4 µg/L at the surface, 15.0 µg/L at mid-depth, and 4.1 µg/L at the bottom. The maximum surface chlorophyll was 52.8 µg/L on the afternoon of July 8th.