Water Column Clarity
Water clarity was measured at six locations in the Providence and Seekonk Rivers on November 21, 2018. Light rainfall (0.2 inches) occurred on the day prior to sampling. Five days before sampling, there was 0.94 inches of recorded precipitation. Average water clarity increased from the previous week, from 1.1 m to 1.6 m.
Water clarity increased at India Point Park, Pomham Rocks, Pawtuxet Cove, Bullock Reach, and Conimicut Point. Largest increases in clarity (≥ 1 m) occurred at Conimicut Point and Bullock Reach. Secchi depth ranged from 0.90 m at Edgewood Yacht Club to 2.50 m at Conimicut Point and Bullock Reach. There was evidence of a slight north to south water clarity gradient.
Data was collected on November 21, 2018 while the R/V Monitor was underway collecting nutrient samples and performing vertical profiles in the Providence River estuary. The chlorophyll concentrations were mostly low in areas surveyed. From north to south, average chlorophyll concentrations were as follows: Upper Providence River (16.00 µg/l), Edgewood Shoals area (1.63 µg/l), Pawtuxet River area (1.54 µg/l), and the Lower Providence River (1.06 µg/l). Overall, chlorophyll ranged between non-detectable and 69.90 µg/l with an overall average of 6.08 µg/l. The chlorophyll data from this date is presented in the map below:
Five bay stations and twelve river stations were sampled for nutrients on October 24, 2018. Surface and bottom waters were sampled at all bay stations. Light rainfall occurred in the five days prior to sampling, with 0.2 inches of recorded precipitation.
Among the river stations sampled, highest total nitrogen (TN), total dissolved nitrogen (TDN), and dissolved inorganic nitrogen (DIN) values were measured in the Ten Mile River at Central Avenue, with reported values of 1380 ppb, 1550 ppb, and 1108 ppb, respectively. The Moshassuck River at Higginson Avenue had the lowest measured TN (496 ppb) and TDN (510 ppb) values. Lowest DIN concentrations were observed in the Palmer River at Route 6, at 317 ppb.
Highest bay surface nutrient concentrations occurred at Phillipsdale Landing, with TN, TDN, and DIN concentrations of 927 ppb, 761 ppb, and 640 ppb, respectively. Conimicut Point demonstrated the lowest nitrogen values, at 803 ppb TN, 441 ppb TDN, and 313 ppb DIN. Chlorophyll a averaged 1.7 ug/L, ranging from 1.0 ug/L at Conimicut Point to 3.2 ug/L at Edgewood Yacht Club.
Results from nutrient sampling completed on November 7 and November 21 are pending final analysis from the NBC Laboratory. The next anticipated date of sampling is December 5, 2018.
Water Column Profiles
Water column profiles were measured at three sites in the Seekonk and Providence Rivers on November 7, 2018. A total of 2.41 inches of precipitation was recorded in the five days prior to sampling; the day before sampling, 0.72 inches of rainfall occurred. Some salinity-driven stratification was evident, as recent precipitation enhanced surface freshwater inputs.
Highest water column salinity was observed at Edgewood Shoal, where surface salinity measured 15.6 psu and bottom salinity measured 27.5 psu. Lowest surface salinities (around 2.5 psu) were observed at Phillipsdale Landing and Pawtuxet Cove. Phillipsdale Landing and Pawtuxet Cove had bottom salinities of 14 and 13 psu, respectively.
Surface water temperatures were approximately 12.5°C at all sites. Lowest bottom water temperatures (around 12°C) were observed at Phillipsdale Landing. Water temperature at depth was highest at Edgewood Shoal, at 13.3°C.
Hypoxic conditions (dissolved oxygen <2.9 mg/L) were not present at the sites sampled. The maximum dissolved oxygen (DO) concentration, 9.89 mg/L, was observed at Phillipsdale Landing. The minimum DO concentration, 5.65 mg/L, occurred at Edgewood Shoal. Fluorescence was low (<3 mg/m3) at all sites, and maximum fluorescence values (2.0 - 2.2 mg/m3), were observed at Phillipsdale Landing.
Water Column Clarity
Water clarity was measured at seven locations in the Providence and Seekonk Rivers on November 7, 2018. In the five days prior to sampling, 2.41 inches of precipitation was recorded, with 0.72 inches of rain falling on the day prior to sampling. In light of the recent rainfall, average water clarity decreased from the previous week, from 1.9 m to 1.1 m.
Decreases in water clarity were observed at Phillipsdale Landing, India Point Park, Pomham Rocks, Pawtuxet Cove, Bullock Reach and Conimicut Point. Water clarity increased at Edgewood Shoals. Secchi depth ranged from 0.63 m at Pawtuxet Cove to 1.50 m at Bullock Reach. A slight north to south water clarity gradient was present.