Phillipsdale Landing
Overall, water quality at Phillipsdale Landing was good to fair this week. Weather was rainy, with 1.38 inches of precipitation recorded at T.F. Green. The Blackstone River flow fluctuated through the week in response to rain, but remained below the 20-year daily median for most of the week. Surface salinity averaged 20.2 ppt and ranged from 12.9 ppt to 24.4 ppt. At the bottom, salinity averaged 24.5 ppt and ranged from 18.9 ppt to 28.2 ppt. Temperatures continued to increase this week, averaging 24.0°C at the surface and ranging 21.0°C – 26.6°C. At the bottom, temperatures averaged 23.4°C and ranged 22.2°C – 25.0°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 dropped below the hypoxic threshold throughout the week. Surface DO average 7.70 mg/L and ranged from 2.96 mg/L to 16.08 mg/L. Bottom DO concentrations averaged 3.7 mg/L and ranged from 1.4 mg/L to 8.0 mg/L. The longest period of hypoxic conditions (9 hours) occurred at the bottom depth during the evening of August 29th. During this period, bottom DO averaged around 2.00 mg/L. Chlorophyll readings increased from last week, averaging 49.5 µg/L at the surface and 18.8 µg/L at the bottom. Maximum chlorophyll at the surface reached 108.3 µg/L on the afternoon of August 29th. 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 August 27th. Overall, water quality was good at Bullock Reach this week. Salinity averaged 26.6 ppt, 28.3 ppt, and 30.1 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged 24.8 – 28.1 ppt, mid salinity ranged 26.3 – 30.0 ppt, and bottom salinity ranged 28.3 – 31.2 ppt. Surface temperature averaged 23.4°C and ranged from 21.7°C to 24.5°C. Mid temperatures averaged 22.8°C and ranged from 21.5°C to 24.2°C. Bottom temperatures averaged 21.5°C and ranged from 20.1°C to 23.0°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 7.8 mg/L and ranged 5.5 – 9.5 mg/L. In the mid waters, DO averaged 5.7 mg/L and ranged 3.2 – 8.6 mg/L. At the bottom, DO averaged 3.9 mg/L and ranged 2.7 – 6.1 mg/L. The longest period of hypoxic conditions (1 hour and 30 minutes) occurred at the bottom depth during August 31st. During this period, bottom DO averaged around 2.83 mg/L. Chlorophyll readings ranged from low to elevated, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 16.2 µg/L at the surface, 11.6 µg/L at mid-depth, and 3.3 µg/L at the bottom. The maximum surface chlorophyll was 30.4 µg/L on the morning of September 1st.