Week of August 18 - 24, 2019
Bacteria Sampling
Twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers on August 21, 2019. Five stations were also sampled for enterococci. In the five days prior to sampling, 0.51 inches of precipitation was recorded.
The geometric mean of fecal coliform results for all sites was 70 MPN/100 mL; counts were higher at the Seekonk River sites than the Providence River sites (geometric means of 316 and 35 MPN/100 mL, respectively). The maximum count (2,300 MPN/100 mL) was measured at the Point St. Bridge site. Overall, the Providence River results were within state standards for primary contact.
The enterococci results decreased from the previous sampling event on August 7, from 19 MPN/100 mL to 14 MPN/100 mL. Enterococci results ranged from <10 MPN/100 mL at most sites to 86 MPN/100 mL at Point St. Bridge. These results met 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 August 25 - 31, 2019
R/V Monitor's Blog
The crew of the R/V Monitor was out on the upper Bay twice this week. First, on Tuesday, August 27th, the crew deployed equipment for the temporary buoy to be installed next week in the Bullock's Reach area. They then conducted 3 profiling transects across the upper Bay using the Seabird instrument. The transects were done at India Point, Pomham Rocks, and Bullock's Reach. Jeff captained the boat while monitoring professionals Mike and Bekki deployed the buoy equipment and conducted the transects. NBC scientist Eliza joined the crew in the afternoon for the transects. It was a calm partly sunny day with a breeze out of the southeast. On Wednesday, August 28th, the crew was out collecting nutrients and plankton samples, taking Secchi Disk and Par sensor water clarity measurements, conducting water column profiles using the Seabird instrument, and conducting real-time surface mapping of water quality parameters, including dissolved oxygen, chlorophyll, water temperature, salinity pH, all in an effor to document water quality improvements associated with NBC construction projects. Jeff captained the boat, while monitoring professionals Sara and Mike collected the samples and data. The day began sunny but became cloudy by late morning. There was no wind and very calm waters. Monitoring was only conducted in the morning due to stormy weather predicted for the afternoon. The Block Island Ferry was observed outbound by the Port of Providence this day.
Week of August 11 - 17, 2019
Water Column Clarity
Water clarity was measured at eight locations in the Providence and Seekonk Rivers on August 15, 2019. Light rain fell two days prior to the survey, totaling 0.13 inches. Average Secchi depth decreased very slightly since the previous week’s survey, from 1.5 m to 1.4 m. Three sites exhibited decreased clarity since the previous survey, with the greatest drop observed at India Point Park (-0.9 m). Three sites exhibited increased clarity, with the greatest increase observed at Pomham Rocks (+0.8 m); the remaining two sites were either unchanged from the previous survey or had not been surveyed for several weeks before, making such comparisons inappropriate. Overall, there was no gradient in water clarity up or down bay. The lowest clarity was measured at India Point Park and at Pawtuxet Cove: 0.8 m. The highest water clarity was observed at Pomham Rocks, at 1.9 m.
Week of August 4 - 10, 2019
Water Column Profiles
Water column profiles were measured at seven sites in the Seekonk and Providence Rivers on August 7, 2019. The weather during the week leading up to the survey was warm and dry, with no precipitation recorded in the five days prior to water column profiling. Most sites were relatively well-mixed, with some evidence of slight stratification, particularly at Phillipsdale Landing and India Point Park.
Lowest water column salinity this week was observed at Phillipsdale Landing, with a surface salinity of 18 psu and bottom salinity of 24 psu. Water column salinity was highest at Conimicut Point, ranging from 26 psu at the surface to 30 psu in bottom waters.
Water column temperatures averaged 24.5°C this week. Highest water temperatures were observed at Point St. Bridge, with temperatures ranging from 27°C in bottom waters to 29°C in surface waters. Waters were coolest at Conimicut Point, ranging from bottom temperatures of 22°C to surface temperatures of 24°C.
Dissolved oxygen (DO) concentrations were low at several sites this week. Waters were hypoxic (i.e., <2.9 mg/L DO) below 3 m at India Point Park and throughout the water column at Point St. Bridge and Phillipsdale Landing. The lowest bottom DO (<0.1 mg/L) was measured at Phillipsdale Landing. DO at the surface was in the 5 - 7 mg/L range at most sites. Fluorescence was slightly higher than the previous week, with a maximum reading of 35 mg/m3 at 1.25 m at Phillipsdale Landing.
Week of August 4 - 10, 2019
Fixed Site Network
Phillipsdale Landing
Water quality was fair to poor this week at Phillipsdale Landing. Sonde change-out for maintenance occurred during the morning of August 6. Salinity at the surface and bottom decreased over the course of the week following about 0.4 inches of rainfall August 8. Both the Blackstone River and Ten Mile River had relatively high flows for several days following the rainy weather, bringing a large influx of freshwater to the site. Surface salinity averaged around 19 ppt prior to the rain then dropped to the single digits in the days that followed. The overall average surface salinity for the week was 13.8 ppt. Bottom salinity averaged 20.8 ppt for the week, fluctuating with the tides and following the rainfall and increased river flow. Before the rain, bottom salinity ranged from 20 ppt to 26 ppt; following the rain, the range was much greater: <13 ppt at low tide to >23 ppt at high tide. Water temperatures remained warm, similar to the previous week. Surface temperatures averaged 25.0°C and ranged from 23°C to 28.2°C; bottom temperatures averaged 24.7°C, ranging from 23.6°C to 26.1°C. Hypoxic conditions (dissolved oxygen, DO <2.9 mg/L) were observed periodically in both surface and bottom waters and overall DO concentrations were lower than the previous week. Surface water DO averaged 6.5 mg/L, while bottom oxygen averaged 2.2 mg/L. The lowest DO concentrations, <0.5 mg/L, occurred at both depths. Overall, the rain and increased river flows led to improved DO at the surface but worsened DO at the bottom; this is likely due in part to the density stratification that set up with the influx of freshwater, resulting in less mixing of surface and bottom waters. Chlorophyll came down slightly since the previous week, averaging 31.4 ug/L in surface waters; peaks in chlorophyll concentrations >200 ug/L occurred in the evenings on August 6th and 8th.
Note that tidal fluctuations and Blackstone River flow greatly influence water column DO, temperature, and salinity at this location.
Bullock Reach
This week at Bullock Reach, water quality was good to fair. Average water temperatures were 24.8°C at the surface, 24.2°C at the mid sonde, and 23.2°C at the bottom. Overall, water temperature at all depths was stable across the whole week with no strong trends increasing or decreasing. The greatest difference in temperature between surface and bottom waters (approximately 3.5°C) was observed on August 4. Surface salinity ranged from 23.7 ppt to 28.3 ppt, averaging 26.5 ppt. Salinity values at the mid sonde and bottom sondes averaged 28.1 and 28.4 ppt, respectively. The greatest difference in salinities between the surface and bottom occurred two days following the rains and subsequent increased river flows starting August 8; prior to the rain effect there was actually a period where the water column was well-mixed over the night of August 7 until the evening on August 8. DO showed some improvement compared to the previous week at the deeper depths. There were no recorded measurements of hypoxia (DO <2.9 mg/L) at the surface or middle sondes; DO at the bottom sonde dipped below the hypoxia threshold for less than two hours during the morning of August 4. Surface DO averaged 7.3 mg/L with a minimum of 5.1 mg/L; the mid depth had an average of 5.6 mg/L, and a minimum of 3.9 mg/L; the bottom sonde had an average DO of 4.5 mg/L and a minimum of 2.4 mg/L. Water column chlorophyll was variable throughout the week and hit the highest concentrations in bottom waters. Surface chlorophyll averaged 10.7 ug/L, chlorophyll at the mid sonde averaged 9.5 ug/L, and chlorophyll at the bottom sonde averaged 12.0 ug/L.
