Research Progress in Area 1 方向 ( 一 ) 課題進展 103 Abstract The sediments’ contributions to the water column biogeochemical cycles in the Pearl River Estuary (PRE) remain uncharacterized. We combine field sampling andmeasurements, laboratory analyses and experiments, as well as diagenetic modeling to characterize the sediment diagenetic pathways and sediment-water exchanges in this dynamic system across oceanic gradient, investigate their geochemical controls, and elucidate the response of sediments to changes in water column chemistry and biological productivity. Research Activities and Progress • Developed methods for sampling, set up a whole-core incubation system, and tested methods for chemical analyses of solid, liquid, and gas species in sediments; • Participated in the cruise organized by HKBDirection One to collect sediment and water samples at five locations in the South China Sea; • Characterized porewater and solid geochemistry of samples collected; • Analyzed water column phosphorus species including soluble reactive phosphorus, total dissolvable phosphorus, dissolved organic phosphorus, and total particulate phosphorus; • Established collaborations with local and international researchers to study sedimentwater geochemistry in the region. Key Findings • Sediment Oxygen is depleted within the upper 0.25 - 1 cm and is consumed at rates of 6 - 30 mmol/m2/d (Fig. 1); • The concentrations of ammonium and phosphate increase sharply into the anoxic sediments, generating large effluxes across the sediment-water interface (Fig. 1); • Large differences between diffusive and total oxygen uptake suggest active benthic burrowing; • Vertical distributions of particulate organic carbon suggest non-steady state sedimentation (Fig. 2). Research Output Publication 0 Trained personnel 5 Sediment Diagenesis and Sediment-water Exchange at a Dynamic Land-sea Interface, the Pearl River Estuary Prof. Jiying Li The Hong Kong University of Science and Technology Fig 1. The vertical distributions of dissolved oxygen, ammonium and phosphate in sediment porewaters at twolocations in the coastal waters off the Pearl River Estuary.
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