A Study On The Accumulation And Transfer Processes Of Nutrients At The Sediment-water Interface In The Pearl River Estuary

Three cruises were launched in the Pearl River estuary during 2005-2006 to investigate the biogeochemical cycling of nutrients associated with early diagenetic degradation of sediment organic matter. Nutrient fluxes at the sediment-water infterface estimated based on the nutrient gradients were compared with those measured by sediment incubation experiments, based on which the accumulation and bio-transformation processes of nutrients at the sediment-water interface were discussed.Anaerobic conditions below the sediment-water interface are evidenced by the gradual increase of NH₄-N and the rapid decrease of NO3⁺-N concentrations with depth. Although positive fluxes (from sediment to overlying water) for NH₄-N and negative fluxes for NO₃-N were suggested by the nutrient profile data, negtive fluxes of NH₄-N positive NO₃-N fluxes were commonly observed in the sediment incubation experiments, indicating the nitrification of NH₄⁺—N at the sediment-water interface. Seasonal and spatial variations of porewater nutrient content and profile pattern were observed, with the nutrient content generally decreases from the Pearl River outlets toward the open sea. The fluxes of phosphate and silicate are relatively high compared with other estuaries in the warld. The primary production in the Pearl River estuary is limited by phosphate, not by silicate or nitrogen.The fluxes calculated based on the porewater profiles are not only much smaller in magnitude than those measured by the incubation experiments, but they may indicate contrary migration directions. The calculate fluxes are obtained assuming diffusive transport of nutrients across the sediment-water interface, while the measured fluxes result from the coupling of diffusion, bio-disturbation and biochemical reaction.