Primary Production in Long Island Sound

Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak rates, $\pm 95%$ confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, $1,730 \pm 610 mmol O_{2} m^{-2} d^{-1}$), community respiration ($R_{c}, 1,660 \pm 270 mmol O_2 m^{-2} d^{-1}$), and net community production (NCP, $1,160 \pm 1,100 mmol O_{2} m^{-2} d^{-1}$) occurred during summer at the western end of the Sound. Lowest rates of GPP ($4 \pm 11 mmol O_{2} m^{-2} d^{-1}$), Rc ($-50 \pm 300 mmol O_{2} m^{-2} d^{-1}$), and NCP ($-1,250 \pm 270 mmol O_{2} m^{-2} d^{-1}$) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, Rc, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (Ra) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of $R_{a} : R_c$. From this range, we established that the estimated Ra accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from $2 to 870 mmol O_2 m^{-2} d^{-1}$ throughout cwLIS during the study. Annual NPP averaged $40 \pm 8 mol O_{2} m^{-2} yr^{-1}$ for all sampled stations, which more than doubled along the main axis of the Sound, from $32 \pm 14 mol O_{2} m^{-2} yr^{-1}$ at an eastern station to $82 \pm 25 mol O_{2} m^{-2} yr^{-1}$ at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound. Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems.