Nutrient regeneration and oxygen consumption by sediments along an estuarine salinity gradient

Abstract

ABSTRACT: Nutrient fluxes and oxygen consumption (SOD) across the sediment-water interface were measured in situ along with vertical profiles of dissolved and particulate-phase nutrients in sediments and overlying water at 8 locations along the salinity gradient of Chesapeake Bay during spring and summer. Strong spatial and temporal patterns were evident. Highest rates of sediment NH: regeneration and SOD occurred in summer at mid-salinity (12 to 17 %a) stations. Sediment fluxes of dissolved inorganic phosphorous (DIP) were always low, possibly due to relatively oxidized conditions in surficial sediments. Nitrate (NO;) fluxes generally were directed into the sedirnents in spring and from the sediments during summer, and in both seasons fluxes were proportional to NO3 concentrations in overlying waters. Seasonal shifts in sediment 0:N flux ratios suggest that denitrification may have been important in spring but not summer. Significant relations were inferred between C:N:P composition of suspended materials and surficial sediments and the magnitude and direction of sediment-water fluxes. Although accretion of particulate nitrogen in sediments was less than 6 % of NH: regeneration in the lower bay, it was similar to rates of NH: flux in the low salinity region, suggesting that burial represents a significant sink for N in some estuarine zones. SOD constituted an important term in water column O2 budgets at all stations (1G50 % of total respiration), and sediment regeneration of NH: was capable of supplying 13 to 40 % of calculated phytoplankton N requirement, being more important during the summer period of higher productivity.