In this experiment we quantified pelagic metabolism in the Parker River/Plum Island Sound estuary, Massachusetts. BOD bottles were incubated to determine changes in dissolved oxygen over 14.45 and 24 hour periods. These measurements were used to calculate net daytime production (NDP), respiration (R), gross production (GP), and net community production (NCP).
Many spatial patterns are evident in the data. NDP and NCP are highest in the upper water column and decrease with depth. Riverine respiration remains relatively constant, but rises in the sound. NCP levels indicate that the water column is net autotrophic until conductivities greater than 46.5 mS cm-1, where it becomes net heterotrophic. Pelagic metabolism contributed 54 to 64% of total system respiration, the remainder being benthic respiration. Although chlorophyll levels are higher in the upper estuary, the pattern of increasing production per unit chlorophyll from upper to lower estuary suggests that production is light-limited. The light extinction coefficient, a measure of turbidity, decreases as conductivity increases