Temporal and spatial variability of photosynthetic parameters and community respiration in Long Island Sound

Photosynthetic parameters and community respiration were measured throughout 3 seasons at 8 stations in central and western Long Island Sound during 2002 and 2003. Light-dark bottle oxygen change was measured in a photosynthesis-irradiance (P-I) series for water from the mixed layer, and respiration was measured for surface, pycnocline, and near bottom water. P-I curves were fitted numerically to calculate biomass-specific rates of maximum photosynthesis at light saturation (Pm), photosynthetic efficiency at low irradiance (alpha(B)) and plankton community respiration (R-c). The temporal and spatial variability of these fitted parameters, the derived parameter I-k, and the concentration of phytoplankton pigments were described in relation to each other and to environmental factors. Concentrations of chlorophyll (chl) and phaeopigments(phaeo), and R-c reached maxima in summer and significantly decreased seaward along the length of the Sound. Photosynthetic parameters also reached maxima in summer, however there was no significant spatial variability. In surface waters, the average (+/- SD) of P-m(B) (1.3 +/- 0.4 mmol O-2 [mg chl](-1) h(-1)) demonstrated the lowest variability, compared to chl (6.9 +/- 4.9 mg m(-3)), phaeo (3.5 +/- 2.5 mg m(-3)), alpha(B) (10.9 +/- 5.4 mu mol O-2 [mg chl](-1) h(-1) [mu E m(-2) s(-1)](-1)), I-k (132.6 +/- 71.9 mu E m(-2) s(-1)), and R-c (1.4 +/- 0.9 mmol O-2 m(-3) h(-1)). Chl and P-m(B) both varied with total daily insolation and with average irradiance of the photic zone, while P m was also correlated with temperature. Although P m and chl increased during summer, their peaks did not occur simultaneously. Temporal trends in alpha(B) were less clear-cut than for P-m(B) and chl, but alpha(B) was correlated with light properties of the water column. Plankton community respiration was high in surface waters and decreased with depth. Based on the relationship between R-c and chl, algal-related rates of respiration (R-a) were estimated at similar to 50 % of total plankton community respiration. Our results do not support the common method of estimating algal respiration based on P-m(B).