Walker Point
Sondes were swapped this week on August 25th. Overall, water quality at Walker Point was poor to good this week. Weather conditions were mildly rainy this week, with a total of 0.44 inches recorded at T.F. Green, and the majority of rainfall occurring on the 30th. Blackstone River flow was highest on August 24th, where the flow was similar to the 20-year daily median flow. Flow dropped throughout the week, remaining below the 20-year daily median value. Salinity at the surface averaged 21.2 ppt and ranged from 7.6 ppt to 27.3 ppt. At the bottom, salinity averaged 27.2 ppt and ranged from 23.3 ppt to 29.3 ppt. Temperatures this week averaged 24.2 °C at the surface and 23.5 °C at the bottom. Surface temperatures ranged from 22.3 °C to 26.8°C, while bottom temperatures ranged from 23.5 °C to 24.7 °C.
Dissolved oxygen (DO) at Walker Point remained above the hypoxia threshold (i.e., DO >2.9 mg/L) at the surface during the entire week, but below the hypoxia threshold at the bottom for much of the time, especially towards the beginning of the week. Hypoxic conditions were observed at the bottom for extended periods from August 24th – 27th, but only briefly from August 28th – 30th (morning of August 30th). Surface DO averaged 9.5 mg/L and ranged from 4.2 to 22.9 mg/L. Bottom water DO concentration averaged 3.2 mg/L and ranged from 0 mg/L to 7.9 mg/L. Chlorophyll ranged from low to elevated levels throughout the week, averaging 14.1 ug/L at the surface and 8.7 ug/L at the bottom, with evidence of substantial phytoplankton blooms occurring throughout the week. Maximum surface chlorophyll readings reached 110.6 ug/L on the afternoon of August 26th. 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 ranged from poor to good at Bullock Reach this week. Salinity averaged 28.2 ppt, 29.7 ppt, and 31.1 ppt at the surface, middle, and bottom sondes, respectively. Surface salinity ranged from 26.4 to 29.3 ppt, mid salinity ranged from 27.6 to 30.7 ppt, and bottom salinity ranged from 29.9 to 32.2 ppt. Surface temperature averaged 23.7 °C and ranged from 22.3 °C to 25.3 °C. Mid temperatures averaged 23.2 °C and ranged from 22.1 °C to 24.7 °C. Bottom temperatures averaged 22.2 °C and ranged from 20.7 °C to 23.8 °C.
DO at Bullock Reach experienced hypoxic conditions (i.e., DO < 2.9 mg/L) briefly in mid waters on the morning of August 24th. Bottom waters experienced hypoxic conditions for a majority of the time from the morning of August 24th to the afternoon of August 25th, with hypoxic conditions also observed intermittently from August 26th– August 29th. Surface DO averaged 8.1 mg/L and ranged from 5.0 to 11.9 mg/L. In the mid waters, DO averaged 6.1 mg/L and ranged from 2.5 to 9.4 mg/L. At the bottom, DO averaged 3.7 mg/L and ranged from 2.1 to 7.0 mg/L. Chlorophyll readings ranged from low to moderate, with evidence of moderate phytoplankton blooms occurring throughout the week. Readings averaged 9.7 µg/L at the surface, 12.7 µg/L at mid-depth, and 3.8 µg/L at the bottom. The maximum surface chlorophyll was 19.6 µg/L on the morning of August 26th.