黄、东海西部营养盐浓度近几十年来的变化

Changes of nutrient concentrations in western areas of Yellow Sea and East China Sea in recent several decades

通过对以往调查资料和研究成果的总结,发现黄、东海西部海域在近40～50年中NO3-、SiO32-和PO43-浓度均发生了显著的变化,NO3-浓度快速上升,而SiO23-和PO34-浓度显著下降。NO3-浓度的上升和SiO23-浓度的下降均与它们在长江等河流中的变化趋势一致;PO34-浓度的下降在河流以及长江口海域并不明显,而更多地体现在较为封闭的渤海、黄海。作者推测,NO3-陆源输入的增加,提高了海洋生产力,加强了浮游植物对PO43-的吸收可能是造成PO43-在研究区域平均水平下降的一个原因。基于这个假设,设计了一个简单的数学模型,用以计算为了满足目前PO43-的下降量,外界NO3-输出通量所需的增长速率。结果表明,如果增长的氮通量全部是由长江等河流输出的NO3-提供,这些河流NO3-的平均浓度在近几十年中至少增加了7.8μmol/L。

Based on historical data and previous researches, significant concentration variations of nutrients （i. e. , NO3^- , SiO3^2- , and PO4^3- ）, in the western Yellow Sea and the East China Sea and during the recent 40-50 years, were studied, in which [NO3^-] showed a rapid increase whereas [SiO3^2-] and [PO4^3-] displayed considerable decreases. The increase of [NO3^-] and decrease of [SiO3^2- ] were consistent with their concentration changes in the Changjiang Estuary; however, the [PO4^3- ] decrease was obscure in the Changjiang Estuary and appeared more evidently in the enclosed areas, such as the Bohai Sea and the Yellow Sea. It was speculated that marine primary productivity was enhanced by the increasing NO3^- fluxes and as a result, POa uptakes by phytoplankton were greatly simulated, which led to the observed [PO4^3-] decrease in the study area. According to the above assumption, a simple box model was established, through which the required increase rate of NO3^- outputs was calculated to satisfy the [PO4^3-] decrease. The calculation results showed that, if the increase of nitrogen flux was completely ascribed to NO3^- transports via rivers, the increase of average NOa concentrations in these rivers was at least 7.8 μmol/L during the recent several decades.