Historical News
Phytoplankton Sampling
Phytoplankton samples were collected at Bullock Reach on May 24, 2017 and analyzed in the laboratory shortly after collection. It was a very breezy and overcast day on Narragansett Bay. The surface water temperature was 16.10oC (a balmy 61oF), salinity was 17.04 psu, and chlorophyll a concentration was 8.3 µg/L. Since the previous phytoplankton sampling on May 10, 2017, the water warmed by 3.5oC (6oF), and the chlorophyll a concentration decreased by 6 µg/L.
The plankton tow net sample was filterable with a 20 micron mesh. The filtrate was a light golden brown color with a short filter-ability time. The tow net sample was analyzed qualitatively for microorganisms using 100x 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 2,406,000 cells per liter, a large increase from the previous sampling date that was primarily due to a rise in diatom abundance. It is interesting to note that while the chlorophyll concentration decreased from May 10 to May 24, cell abundance increased. Since chlorophyll concentrations in individual cells vary between species, chlorophyll trends do not always reflect cell abundance trends.
The most predominant phytoplankton genus was the diatom Skeletonema at 1,814,000 cells/L. Skeletonema is the most common genus found at Bullock Reach and throughout much of Narragansett Bay, where it has been a key spring bloom component since records began in the 1950s. In addition to Skeletonema, other representative phyla included the flagellates and the diatom genus Leptocylindrus.
200x phase contrast micrograph of two Skeletonema spp. chains.
Bacteria Sampling
Twenty stations were sampled for fecal coliform bacteria in the Providence and Seekonk Rivers on June 14, 2017. Five of these stations were additionally sampled for Enterococci bacteria. Sampling occurred during a relatively dry week; only 0.02 inches of rain fell during the five days prior to sampling.
The overall fecal coliform geometric mean for both rivers was 43 MPN/100 mL, an increase compared to the previous sampling date. Fecal coliform concentrations were higher in the Seekonk River, which had a fecal coliform geometric mean of 107 MPN/100 mL in comparison to a geometric mean of 28 MPN/100 mL in the Providence River. The maximum fecal coliform concentration, 430 MPN/100 mL, was observed at Point Street Bridge. Fecal coliform concentrations for the Providence River were within state criteria for primary contact.
The geometric mean of Enterococci concentrations in both rivers was 15 MPN/100 ML. The highest Enterococci result, 86 MPN/100 mL, was observed at Point Street Bridge, the site with the maximum fecal coliform result. Due to this maximum result over 60 MPN/100 mL, enterococci result were not within state criteria 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.
Fixed Site Network
Phillipsdale
At Phillipsdale, sonde data revealed good conditions over the week with no instances of hypoxia evident at either depth. There was a 0.82 inches of rainfall this week and there was a considerable increase in flow from the Blackstone River. Surface salinities were again low this week due to the rainfall and increased river flow and were below 10.7 psu the entire week; salinity averaged 4.9 psu, and had a minimum of 0.6 psu. Bottom salinity was affected by tidal fluctuations this week, and seemed to be impacted by the rainfall/river flow as minimum salinities were below 10 everyday; average bottom salinity this week was 17.1psu and ranged between 3.0 psu – 26.1 psu. Some slight stratification was observed due to these salinity differences. Surface temperatures increased slightly over the course of the week with an average of 16.9oc and a range of 14.2oC – 20.2oC. Bottom temperatures also increased slightly from last week with an average of 15.6oC and ranging between 14.1oC – 19.7oC. Surface chlorophyll was still low this week with an average of 3.2 ug/L. Dissolved oxygen (DO) for the week was good at both depths, and generally increased throughout the week. The surface had an average of 8.7 mg/L and ranged from 6.2 mg/l to a 10.2 mg/L. Dissolved oxygen in the bottom waters had a weekly average of 5.8 mg/l and ranged from a minimum of 3.2 mg/L to a maximum of 10.0 mg/L. Note that tidal fluctuations greatly influence bottom DO, temperature and salinity at this location.
Bullocks Reach
Water quality equipment was deployed successfully at the buoy on May 30th, though communications were lost with the buoy on May 31st. On June 5th all Hydrocat Seabird equipment was removed in addition to the communications can and solar array from the buoy. It was found that the modem responsible for communications had failed. A new modem will be installed shortly. Data loss did not occur as a second set of internally logging backup instruments are currently deployed as well. Data from 5/30 – 6/5 showed good water quality at the surface and bottom; mid data was not available. Average temperatures were 16.4oC at the surface and 12.5oC at the bottom; salinity averaged 22.6 psu at the surface and 29.3 psu at the bottom. Dissolved oxygen was good with no hypoxic conditions observed; Surface DO averaged 8.8 mg/L with a minimum of 6.6 mg/L; bottom DO averaged 6.4 mg/L with a minimum of 5.2 mg/L. Surface chlorophyll averaged 7.9 ug/L
Water Column Profiles
Seven water column profiles were measured in the Providence River estuary on June 14, 2017. The three days leading up to the survey were hot and dry, though isolated thunderstorms occurred throughout the watershed. Moderate stratification was observed at several sites. At Phillipsdale Landing, the site with the most direct river influence, surface waters had the lowest salinities and highest temperatures of all sites, 7.3 psu and 22.6°C. Surface temperatures overall were warmer than the previous week, ranging 18.6-21.5°C among all sites. Bottom waters were cooler, hitting a minimum of 14.3°C at Pomham Rocks. These were also the most saline waters, hitting a maximum of 30.0 psu. Most surface salinities ranged 19.1-24.7 psu.
Dissolved oxygen levels were observed below the acute hypoxia threshold of 2.9 mg/L at Pomham Rocks, in the deepest waters profiled, at 2.6 mg/L. Dissolved oxygen in bottom waters at Bullock Reach and the entire water column at Phillipsdale Landing and Point St. Bridge was also low, around 4.0 mg/L. Surface waters at several sites ranged 8.0-10.9 mg/L; these sites, Edgewood Yacht Club, Bullock Reach, and Conimicut Point, also exhibited the highest fluorescence measurements, indicative of phytoplankton productivity. The highest fluorescence this week was measured as 35.2 mg/m3 at 1.75 m depth at Conimicut Point, and overall there was an increase in this indicator over the previous week.
Water Column Clarity
Water clarity was measured with a Secchi disk at seven locations in the Providence River Estuary on June 14, 2017. The week of sampling was mostly dry, with 0.02 inches of rainfall occurring during the five days prior to sampling. Secchi depth did not vary greatly, ranging from 1.2 meters at the Point Street Bridge and Edgewood Yacht Club stations to 1.6 meters at Phillipsdale. Overall, Secchi depth decreased from previous sampling weeks. The overall average was 1.4 meters, and the greatest decrease (1.6 meters) was observed at Bullock Reach in the lower Providence River. A north to south water clarity gradient was not apparent, and clarity was less than 2 meters at all sites.
