Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and...Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.展开更多
Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate chan...Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores（#34： 28.5°N, 122.272°E; CJ12-1269： 28.861 9°N, 122.515 3°E） from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970 s and increased rapidly after the late 1990 s at Site #34; and it started to increase gradually from the middle 1960 s and increased rapidly after the late 1980 s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B（dinosterol/brassicasterol） ratio of Core #34 since the 1960 s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950 s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios.展开更多
基金The work is supported by the National Natural Science Foundation of China(Grant Nos.430100203 and 49801018)the Foundation for University Key Teachers by the Ministry of Education of China.
文摘Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.
基金The National Basic Research Program of China(973 Program)under contract No.2010CB428901the National Natural Science Foundation of China under contract Nos 41020164005,40976042 and 41076036
文摘Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores（#34： 28.5°N, 122.272°E; CJ12-1269： 28.861 9°N, 122.515 3°E） from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970 s and increased rapidly after the late 1990 s at Site #34; and it started to increase gradually from the middle 1960 s and increased rapidly after the late 1980 s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B（dinosterol/brassicasterol） ratio of Core #34 since the 1960 s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950 s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios.
