Underway profiling of photosynthesis and dissolved oxygen in Narragansett Bay, Rhode Island

Comparisons of primary productivity measured by 14C uptake and a fast repetition rate fluorometer (FRRF) for samples taken from Massachusetts Bay and Narragansett Bay demonstrated a linear relationship between the two techniques. The slope of the regression for different phytoplankton samples varied by over a factor of 4 ranging between 0.23 and 1.04 with the 0.4–0.5 being the most common range. The r2 was usually high, with r2 greater than 0.9 in the best cases. The results indicated that the FRRF typically underestimated primary productivity relative to 14C. The variability. An additional comparison of 14C and the FRRF techniques was conducted during a diurnal experiment performed in a 13 m 3 mesocosm with a contained phytoplankton population. The slope differed from the laboratory comparisons with values of 9.32 at 1 m depth and 5.14 at 2 m depth. An estimate of annual carbon fixation in Narragansett Bay for 2001 using the FRRF deployed in a towed undulating sensor platform was performed and compared with an earlier 14C study by Oviatt et al. (2001) from 1997–1998. 14C calibrated FRRF field results produced an annual production estimate of 238 g C m−2 y−1 for Narragansett Bay. Dissolved oxygen was also studied during cruises with a towed sensor performed by NMFS as well as by URI monitoring buoys and NBEP volunteer oxygen surveys in 2001. Widespread hypoxia occurred in upper parts of Narragansett Bay during the summer. Hypoxia below the EPA acute criteria (2.3 mg/L) was observed frequently during the summer months, primarily north of Prudence Island and into the Providence River. The area covered by acute hypoxia in the Providence River approached 40% of the region during neap tides