Phillipsdale Landing
Sondes were swapped this week on the morning of August 20th. Overall, the water quality at Phillipsdale Landing was good to fair this week. Weather conditions included sporadic rain events, with 0.49 inches of precipitation recorded at T.F. Green. The Blackstone River flow declined over the week, dropping below the 20-year daily median at midweek. Surface salinity averaged 20.1 ppt and ranged from 12.4 ppt to 25.2 ppt. At the bottom, salinity averaged 23.6 ppt and ranged from 17.4 ppt to 26.7 ppt. Temperatures continued to increase this week, averaging 23.3°C at the surface and ranging 21.7°C – 24.9°C. At the bottom, temperatures averaged 23.1°C and ranged 22.1°C – 24.8°C.
Dissolved oxygen (DO) at Phillipsdale Landing dropped below the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week. Surface DO average 6.6 mg/L and ranged from 2.7 mg/L to 13.7 mg/L. Bottom DO concentrations averaged 4.2 mg/L and ranged from 1.7 mg/L to 10.3 mg/L. The longest period of hypoxic conditions (6 hours, 30 minutes) occurred at the bottom depth between the night of August 20th to the morning of August 21st. During this period, bottom DO averaged around 2.52 mg/L. Chlorophyll readings decreased from last week, averaging 20.76 µg/L at the surface and 15.9 µg/L at the bottom. Maximum chlorophyll at the surface reached 126.5 µg/L on August 21st around midday. Please note that tidal fluctuations and Blackstone River flows greatly influence water column salinity, temperature, and DO at this location.
Bullock Reach
Overall, the water quality was good to fair at Bullock Reach this week. Salinity averaged 26.9 ppt, 28.2 ppt, and 29.2 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged 24.9 – 28.3 ppt, mid salinity ranged 25.8 – 29.6 ppt, and bottom salinity ranged 28.0 – 30.4 ppt. Surface temperature averaged 22.9°C and ranged from 21.3°C to 24.2°C. Mid temperatures averaged 22.5°C and ranged from 21.5°C to 23.9°C. Bottom temperatures averaged 21.9°C and ranged from 20.6°C to 23.3°C.
DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week at the surface and middle depths. Bottom DO dropped below the hypoxia threshold infrequently throughout the week. Surface DO averaged 7.1 mg/L and ranged 4.5 – 11.3 mg/L. In the mid waters, DO averaged 5.5 mg/L and ranged 3.6 – 8.4 mg/L. At the bottom, DO averaged 4.3 mg/L and ranged 2.3 – 7.3 mg/L. The longest period of hypoxic conditions (1 hour, 15 minutes) occurred at the bottom depth on the morning of August 19th. During this period, bottom DO averaged around 2.58 mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 17.4 µg/L at the surface, 13.0 µg/L at mid-depth, and 9.0 µg/L at the bottom. The maximum surface chlorophyll was 42.1 µg/L on the afternoon of August 23rd.