Week of June 28 - July 4, 2020
Fixed Site Network
Phillipsdale Landing
Water quality was poor to fair this week at Phillipsdale Landing. Heavy rainfall at the end of last week caused surface salinity to drop substantially as Blackstone River flows increased. Bottom salinity was also reduced; note that approximately 12 hours of problematic bottom salinity data on June 28 were excluded from this summary.
Surface salinity averaged 9.2 ppt (range 3.0 - 23.3 ppt), while bottom salinity averaged 19.8 ppt (range 6.0 - 28.4 ppt). Water temperatures cooled slightly from the previous week; surface temperatures averaged 23.4°C and bottom temperatures averaged 22.2°C. Surface temperatures ranged from 21.2°C to 26.8°C, while bottom temperatures ranged from 20.1°C to 25.1°C. Dissolved oxygen (DO) concentrations were fair at the surface and poor in bottom waters most of the week. Surface waters remained above the hypoxia threshold of 2.9 mg/L, averaging 7.4 mg/L with a minimum of 3.3 mg/L. Bottom DO averaged 3.0 mg/L with a minimum of 0.2 mg/L; bottom waters were hypoxic for approximately 58% of the week. Please note, calculation of DO in mg/L utilizes information from the salinity probe; the problematic salinity data on June 28th were so far out of range that the DO data have also been excluded for that period prior to summarizing here. Surface chlorophyll averaged 29.0 ug/L this week with evidence for phytoplankton bloom activity, particularly on June 29th. Note that tidal fluctuations and Blackstone River flow greatly influence water column salinity, temperature, and DO at this location.
Bullock Reach
Bullock Reach sondes were changed-out for maintenance on the morning of June 30. The mid-depth sonde retrieved on June 30 had recorded erroneous depth readings; though there are no precise depth data for the deployment period (June 16-June 30), the position of the sonde in the water was good and all other parameters recorded normally. The bottom sonde retrieved on June 30 exhibited excessive drift in specific conductivity and salinity toward the end of the deployment; bottom salinity data from June 28 through 10am on June 30 have been excluded from the following summary.
Water quality at Bullock Reach was fair to good this week. Water temperatures continue to warm, averaging 23.5°C at the surface, 22.2°C at the mid depth, and 20.1°C at the bottom. Surface salinity averaged 24.8 ppt, ranging from 20.8 ppt to 28.0 ppt. Salinity values at the mid and bottom sondes averaged 28.7 ppt and 32.5 ppt, respectively. Salinity at the surface decreased over the course of the week, impacted by river runoff following rains the previous week. Mid and bottom waters remained just above the hypoxia threshold this week, reaching DO minima of 2.9 mg/L and 3.0 mg/L, respectively. Average DO for surface, mid, and bottom waters was 7.0 mg/L, 4.9 mg/L, and 4.1 mg/L, respectively. Please note, calculation of DO in mg/L utilizes information from the salinity probe; as a result of the drift in the salinity probe, bottom DO readings may be overestimated during this reporting period. Chlorophyll was slightly elevated this week, particularly at the surface, averaging 16.4 ug/L and reaching a maximum of 56.4 ug/L; mid-depth chlorophyll averaged 10.3 ug/L and bottom chlorophyll averaged 3.6 ug/L.
Week of July 19 – 25, 2020
Water Column Clarity
Water clarity was measured at six locations in the Providence and Seekonk Rivers on July 22, 2020. Within the five days prior to the survey, 0.16 inches of precipitation was recorded. On the morning of the survey, 0.06 inches of precipitation occurred. Average Secchi depth increased by 0.17 m since the last survey, from 1.54 m to 1.70 m. The greatest increase in water clarity was observed at Phillipsdale Landing, which increased by 1.13 m, from 0.83 m to 1.97 m. Water clarity also exhibited increases at Pomham Rocks, Bullock Reach, and Conimicut Point. Water clarity decreased at Edgewood Yacht Club (-0.40 m). The greatest water clarity was observed at Phillipsdale Landing, which had a measured Secchi depth of 1.97 m. Lowest water clarity was observed at Edgewood Yacht Club, with a measured Secchi depth of 1.43 m. Generally, water clarity decreased along a north-to-south gradient in the Upper Bay.
Week of July 12 – 18, 2020
Water Column Profiles
Water column profiles were measured at seven sites in the Providence and Seekonk Rivers on July 15, 2020. The NBC's Seabird profiling instrument was sent to the manufacturer for routine servicing over the winter; due to the COVID-19 pandemic, the return of the instrument has been greatly delayed. In the absence of this instrument, the NBC Environmental Monitors utilized a YSI EXO sonde to collect data on surface and bottom conditions at seven typical Seabird sites on July 15. Settings on this instrument were not optimized for measurements of a true profile, rather the goal was stable estimates of conditions at the surface and bottom only. These data are summarized here, and raw data are available upon request. The three days prior to the survey date were moderately wet, with approximately 0.82 inches of total rainfall recorded. Evidence of salinity stratification was observed at all sites; the strongest stratification was observed at Phillipsdale Landing (bottom salinity 12 ppt > surface), while the weakest was observed at Edgewood Yacht Club (bottom salinity 4 ppt > surface).
Estimated surface salinities were highest at Pomham Rocks and Edgewood Yacht Club (25 ppt), and lowest at Phillipsdale Landing (15 ppt). The highest estimated bottom salinity (31 ppt) was observed at Conimicut Point and Bullock Reach, while the lowest (27 ppt) was observed at Phillipsdale Landing. The warmest waters overall were observed at Pawtuxet Cove, from approximately 26.3°C at the surface to 25.2°C at the bottom. The coolest surface waters (23.8°C) were observed at India Point Park, while the coolest bottom waters (21.3°C) were observed at Conimicut Point.
Dissolved oxygen (DO) concentrations were low at most sites this week. Hypoxic (i.e., DO <2.9 mg/L) conditions were observed at the bottom waters of all sites except for Bullock Reach and Conimicut Point. Surface DO ranged from 3 to 7 mg/L across all sites. The estimated surface chlorophyll averaged 27.6 ug/L among all sites, with a maximum of 100.8 ug/L observed at Conimicut Point.
Week of July 19 – 25, 2020
Bacteria Sampling
Twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers on July 22, 2020. Five stations were also sampled for enterococci. In the five days prior to sampling, 0.22 inches of rainfall was recorded, while 0.06 inches of precipitation occurred on July 22 prior to sample collection.
The geometric mean of fecal coliform results for all sites was 13 MPN/100 mL; counts were higher at the Seekonk River sites than the Providence River sites (geometric means of 58 MPN/100 mL and 6 MPN/100 mL, respectively). The maximum count (2300 MPN/100 mL) was measured at Division St. Dock. Results from the Providence River were within the state standards for primary contact and shellfishing, however, results from the Seekonk River exceeded these state standards.
The enterococci results decreased slightly from the previous sampling event, from an overall geomean of 16 MPN/100 mL to 14 MPN/100 mL. Enterococci results ranged from <10 MPN/100 mL measured at four sites (Phillipsdale Landing, South FP East, Gaspee Point, and Conimicut Point) to 86 MPN/100 mL at Point St. Bridge. These enterococci results were within the state standards for primary contact.
Please note: the results of NBC's fecal coliform and enterococci monitoring are for informational/research purposes only and are not intended to suggest official state compliance with bathing or shellfishing standards.
Week of July 19 - 25, 2020
R/V Monitor's Blog
On Wednesday, July 22nd, the crew of the R/V Monitor was out on the upper Bay collecting bacteria samples, taking Secchi Disk water clarity measurements, conducting water column profiles using a profiling sonde, and conducting real-time surface mapping of water quality parameters, including dissolved oxygen, chlorophyll, water temperature, salinity, and pH, all in an effort to document water quality improvements associated with NBC construction projects. The crew also changed out the sonde at the temporary buoy at Pawtuxet Cove and collected a chlorophyll sample while there. Sara captained the boat while monitoring professionals Fern and Mike collected the samples and data. The day began cloudy but cleared by the afternoon. There was a slight breeze all day but the water remained calm. This day's featured photo was taken at India Point Park of paddle boarders.
