[1] Distributions and fluxes of methane were determined during two surveys in March-May 2001 in the Yellow Sea and the East China Sea. Methane concentrations in the surface and bottom waters range from 2.52 to 5.48 and 2.81 to 8.17 nM, respectively. The distributions of methane are influenced obviously by the Yangtze River effluent and Kuroshio water. CH 4 input via the Yangtze River is estimated to be 3.17 mol/s, of which a considerable part may be lost by air-sea exchange during estuarine mixing. Net CH 4 flux exported from the shelf to the Kuroshio is about 1.84 mol/s. Methane enrichments in bottom waters occur widely, which reveals sediment sources of CH 4 . However, the CH 4 input from the sediments of the studied region in spring is lower than other shelf regions due to low organic carbon in the sediments and high O 2 contents in the water column. The sea-to-air methane fluxes are estimated to be 1.36 ± 1.45 and 2.30 ± 2.36 mmol m À2 d À1 using Liss and Merlivat [1986] and Wanninkhof [1992] relationships, respectively, and the estimated spring emission rate of methane ranges from 9.32 Â 10 À3 to 15.7 Â 10 À3 Tg CH 4 yr À1 . However, these estimations suffer from the neglect of seasonal variability and should be taken as a low limit. Therefore more measurement campaigns should be carried out to enhance our understanding of this particular oceanic region.

Abstract. Nutrient dynamics based on field observations made along the eastern Hainan Island during the period 2006–2009 were investigated to understand nutrient biogeochemical processes, and to provide an overview of human perturbations of coastal ecosystems in this tropical region. The rivers showed seasonal variations in nutrient concentrations, with enrichment of dissolved inorganic nitrogen and dissolved silicate, and depletion of PO43−. High riverine concentrations of nitrate mainly originated from agricultural fertilizer inputs. The DIN : PO43− ratios ranged from 37 to 1063, suggesting preferential depletion of PO43− relative to nitrogen in rivers. Chemical weathering in the drainage area might explain the high levels of dissolved silicate. Aquaculture ponds contained high concentrations of NH4+ and dissolved organic nitrogen. The particulate phosphorus concentrations in the study area were lower than those reported for estuaries worldwide. The particulate silicate levels in rivers and lagoons were lower than the global average level. Nutrient biogeochemistry in coastal areas was affected by human activities (e.g., aquaculture, agriculture), and by natural phenomena including typhoons. The nutrient concentrations in coastal waters were low because of dispersion of land-derived nutrients in the sea. Nutrient budgets were built based on a steady-state box model, which showed that riverine fluxes are magnified by estuarine processes (e.g., regeneration, desorption) in estuaries and Laoyehai Lagoon, but not in Xiaohai Lagoon. Riverine and groundwater inputs were the major sources of nutrients to Xiaohai and Laoyehai lagoons, respectively, and riverine inputs and aquaculture effluents were the major sources for the eastern coast of Hainan Island. Nutrient inputs to the coastal ecosystem increased with typhoon-induced runoff of rainwater, elucidating the important influence of typhoons on small tropical rivers.