Historical News
Fixed Site Network
Phillipsdale Landing
Water quality at Phillipsdale Landing was fair-to-poor this week. Conditions this week were mostly dry with 0.16 inches of rainfall recorded at TF Green. However, Blackstone River flows remained elevated above historical median levels, based on the heavy rainfall (2.39 inches) in the week prior. Water column salinity this week was higher than last week. Surface salinity averaged 12.2 ppt, with a maximum value of 21.3 ppt. Bottom salinity averaged 21.2 ppt, with a maximum value of 27.1 ppt. Water temperature averaged 24.3°C on the surface and 23.1°C on the bottom. Temperatures ranged from 22.3°C to 28.3°C at the surface and from 21.3°C to 25.7°C at the bottom.
This week, surface dissolved oxygen (DO) averaged 5.4 mg/L, with a minimum of 2.8 mg/L. Bottom DO increased slightly over the course of the week, averaging 2.4 mg/L and ranging from 1.2 mg/L to 2.4 mg/L; bottom hypoxia (DO≤2.9 mg/L) was persistent through a majority of the week. Chlorophyll concentrations were lower than the previous week, averaging 10.0 ug/L at the surface and 6.3 ug/L on the bottom. At the surface, chlorophyll ranged from 2.0 ug/L to 29.3 ug/L. Please note that tidal fluctuations and Blackstone River flow greatly influence waster column salinity, temperature, and DO at this location.
Bullock Reach
Water quality at Bullock Reach was poor this week. Sondes were changed out for routine maintenance on August 12. Over the course of the week, bottom salinity generally increased while mid-water and surface salinity remained similar. Overall, salinity averaged 24.4 ppt at the surface, 28.5 ppt at mid-depth, and 30.2 ppt in bottom waters. Salinity ranged from 19.4 ppt to 27.2 ppt at the surface, 25.2 ppt to 31.8 ppt at the mid-depth, and 25.8 ppt to 31.8 ppt at the bottom. Surface temperature averaged 24.3°C and ranged 22.6°C – 26.8°C, mid temperatures averaged 23.2°C and ranged 20.5°C – 26.2°C, and bottom temperatures averaged 21.2°C and ranged 19.9°C – 23.5°C.
This week, DO averaged 7.4 mg/L at the surface, 4.8 mg/L at mid-depth, and 2.5 mg/L at the bottom. Hypoxic conditions (DO ≤ 2.9 mg/L) were observed intermittently at mid-depth, while hypoxic conditions were persistent in the bottom waters throughout the week. The minimum DO value, 1.7 mg/L, occurred in bottom waters. Chlorophyll concentrations averaged 10.0 ug/L at the surface, 5.1 ug/L at mid-depth, and 3.3 ug/L at the bottom. The maximum chlorophyll value in surface waters was 22.5 ug/L.
Fixed Site Network
Phillipsdale Landing
Phillipsdale Landing sondes were changed out for routine maintenance during the morning on August 3. Overall, water quality at Phillipsdale Landing was poor this week. Rainfall this week totaled 2.39 inches at TF Green, with a majority (1.48 inches) occurring on August 5. Impacted by the large rain event on August 5, Blackstone River flows increased towards the end of the week and flows remained elevated over historical median levels. Please note, the bottom sonde salinity and pH data appeared suspect from August 1 to August 3; per an internal review, these data are excluded from this summary. Water column salinity this week was lower at the surface while higher in the bottom waters. Surface salinity averaged 5.4 ppt, with a maximum value of 11.6 ppt, while bottom salinity averaged 20.4 ppt, with a maximum value of 28.5 ppt. Water temperatures averaged 22.6°C on the surface and 21.9°C on the bottom. Temperatures ranged from 20.5°C to 25.1°C at the surface and from 20.6°C to 23.3°C at the bottom.
This week, surface dissolved oxygen (DO) averaged 7.8 mg/L, with a minimum of 4.9 mg/L. Bottom DO was mostly low throughout the week, averaging 1.7 mg/L and ranging from <1 mg/L to 5.9 mg/L. Persistent periods of hypoxia (DO ≤ 2.9 mg/L) were mostly observed in the bottom waters earlier in the week, with bottom DO generally increasing as the week progressed. Chlorophyll concentrations were higher than the previous week, averaging 17.4 ug/L on the surface and 7.5 ug/L on the bottom, with a surface maximum of 86.2 ug/L. Please note that tidal fluctuations and Blackstone River flow greatly influence waster column salinity, temperature, and DO at this location.
Bullock Reach Buoy
Water quality at Bullock Reach was fair-to-poor this week. Please note, the mid sonde salinity and temperature data appeared suspect from August 1 to the morning of August 4; per an internal review these data are excluded from this summary. Salinity generally increased slightly over the course of the week, averaging 24.5 ppt at the surface, 28.5 ppt at mid-depth, and 30.8 ppt in bottom waters. Salinity ranged from 19.7 ppt to 27.1 ppt at the surface, 22.9 ppt to 32.3 ppt at the mid-depth, and 28.0 ppt to 32.0 ppt at the bottom. Surface temperatures averaged 22.8°C and ranged from 21.5°C – 24.6°C, mid temperatures averaged 22.1°C and ranged 20.0°C –24.1°C, and bottom temperatures averaged 20.5°C and ranged 19.4°C – 22.6°C.
This week, DO averaged 8.3 mg/L at the surface, 5.4 mg/L at mid-depth, and 3.0 mg/L at the bottom. Hypoxic conditions (DO ≤ 2.9 mg/L) were observed at the mid and bottom depths, with the minimum DO value (1.8 mg/L) observed in bottom waters. Bottom hypoxic periods of up to 15 hours occurred towards the end of the week. Chlorophyll concentrations averaged 12.9 ug/L at the surface, 7.4 ug/L at mid-depth, and 2.7 ug/l at the bottom. The maximum chlorophyll value in surface waters was 29.9 ug/L, which occurred in mid-day on August 7.
Phytoplankton Sampling
Phytoplankton samples were collected on August 25, 2021 at Bullock Reach and analyzed in the laboratory shortly after collection. Sondes data revealed the surface water temperature was 24.94°C, salinity was 21.18 psu, and chlorophyll a was 15.70 ug/L. The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light tan color and had a quick filter time. The tow net sample was analyzed qualitatively for microorganisms using phase contrast microscopy. The whole water sample was analyzed quantitatively under 200x phase contrast microscopy. A Hensen Stempel pipette was used to accurately deliver 1ml of sample to a Sedge-wick Rafter chamber. This analysis revealed a total of 4,628,000 cells per Liter. The flagellates were found at 2,236,000 cells/L. The most predominant phytoplankton genus was Leptocylindrus spp. at 2,092,000 cells/L. Other representative genera include Prorocentrum spp., Skeletonema spp., Chaetoceros spp., and Thalassiosira spp.
200x phase contrast micrograph of Akashiwo sanguineum.
Water Column Clarity
Water clarity was measured at eight locations in the Providence and Seekonk River estuaries on August 25, 2021. Conditions this week were wet, with 0.51 inches of rainfall recorded at T.F. Green three days prior to the survey on August 22, and an additional 0.40 inches on August 23. Despite the rain, there was a slight increase in water clarity since the previous week’s survey. Overall, sites averaged 2.0 meters Secchi depth, compared to 1.9 meters on August 18, 2021. The lowest clarity (1.7 meters) was measured at Phillipsdale Landing, while the highest (2.3 meters) was measured at Edgewood Shoal. There was no gradient of increasing clarity from north to south this week.
Bacteria Sampling
The geometric mean of fecal coliform results for all sites was 26 MPN/100 mL, compared to a geometric mean of 40 MPN/100 mL the prior sampling event. Seekonk River sites generally had higher counts than Providence River sites (geometric means of 161 and 11 MPN/100 mL, respectively). The maximum count (430 MPN/100 mL) was measured at Bishop Point in the Seekonk River. Overall, fecal coliform results from the Providence River were within the state criteria for primary contact and shellfishing, while fecal coliform results from the Seekonk River exceeded state criteria for primary contact and shellfishing.
Enterococci results decreased from an overall geometric mean of 17 MPN/100 mL during the previous sampling event to a geometric mean of 13 MPN/100 mL. Results were <10 MPN/100 mL at all sites except for Point St. Bridge. At Point St. Bridge, the enterococci result was 52 MPN/100 mL. Enterococci results from both rivers were within state primary contact standards.
Please note: the results of NBC's fecal coliform and enterococci monitoring are for informational/research purposes only and are not to intended to suggest official state compliance with bathing or shellfishing standards.
