Phillipsdale Landing
Sondes were swapped this week on the morning of July 23rd. Overall, water quality at Phillipsdale Landing was good to fair this week. Weather conditions included sporadic rain events, with 0.46 inches of precipitation recorded at T.F. Green. The Blackstone River flow fluctuate through the week in response to rain, while remaining below the 19-year daily median. Surface salinity averaged 20.9 ppt and ranged from 0.0 ppt to 25.4 ppt. At the bottom, salinity averaged 23.3 ppt and ranged from 14.7 ppt to 27.4 ppt. Temperatures continued to increase this week, averaging 24.6°C at the surface and ranging 23.6°C – 26.2°C. At the bottom, temperatures averaged 23.9°C and ranged 22.3°C – 25.6°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 5.7 mg/L and ranged from 1.9 mg/L to 14.1 mg/L. Bottom DO concentrations averaged 3.4 mg/L and ranged from 0.7 mg/L to 9.5 mg/L. The longest period of hypoxic conditions (15 hours, 15 minutes) occurred at the bottom depth between the afternoons of July 24th and July 25th. During this period, bottom DO averaged around 2.28 mg/L. Chlorophyll readings decreased from last week, averaging 23.8 µg/L at the surface and 18.3 µg/L at the bottom. Maximum chlorophyll at the surface reached 132.3 µg/L on the afternoon of July 25th. 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 to fair at Bullock Reach this week. Salinity averaged 25.6 ppt, 27.4 ppt, and 29.2 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged 23.4 – 27.5 ppt, mid salinity ranged 13.3 – 29.3 ppt, and bottom salinity ranged 27.1 – 30.1 ppt. Surface temperature averaged 24.2°C and ranged from 22.9°C to 26.1°C. Mid temperatures averaged 23.4°C and ranged from 21.2°C to 25.8°C. Bottom temperatures averaged 21.4°C and ranged from 19.9°C to 24.1°C.
DO at Bullock Reach remained above the hypoxia threshold (i.e., DO >2.9 mg/L) throughout the week at the surface. Middle and Bottom DO dropped below the hypoxia threshold frequently throughout the week. Surface DO averaged 6.5 mg/L and ranged 3.7 – 10.3 mg/L. In the mid waters, DO averaged 4.6 mg/L and ranged 2.7 – 8.9 mg/L. At the bottom, DO averaged 3.1 mg/L and ranged 1.9 – 4.9 mg/L.
The longest period of hypoxic conditions (1 day, 2 hours, and 45 minutes) occurred at the bottom depth between the morning of July 22nd and the afternoon of July 23rd. During this period, bottom DO averaged around 2.44 mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 12.7 µg/L at the surface, 9.5 µg/L at mid-depth, and 5.6 µg/L at the bottom. The maximum surface chlorophyll was 42.4 µg/L on the morning of July 28th.