渤海中部营养盐季节变化及限制统计分析

根据2013年7月（夏季），11月（秋季）和2014年5月（春季）渤海中部海域营养盐数据以及温盐等数据，以浮游植物对营养盐的吸收阈值和化学计量关系为判断标准，对研究海域营养盐分布、限制状况以及季节变化特征进行分析，结果表明：调查海域内各营养盐组分变化均呈现明显季节性特征，表现为夏季低秋季上升春季下降的趋势.夏季受冲淡水影响，海水存在层化现象，溶解无机氮（DIN）、PO₄^3--P和SiO₃^2--Si含量分别为（10.33±7.75）、（0.05±0.03）和（3.94±3.19）μmol/L，DIN/P较高，Si/DIN远低于1，其中表层和10m层存在P和Si限制站位分别达93%、93%和40%、20%，限制状况严重.秋季受底层沉积物扰动再悬浮及营养盐矿化释放等因素影响，各种营养盐含量迅速上升，DIN、PO₄^3--P和SiO₃^2--Si含量为（16.44±6.51）、（0.54±0.20）和（16.94±6.37）μmol/L，分别升高了1.6、10.8和4.3倍，垂向分布差异较小，且仅存在P潜在限制现象.春季由于陆源输入相对较少，同时受浮游植物吸收等因素影响，各营养盐含量急剧下降，DIN、PO₄^3--P和SiO₃^2--Si含量分别为（9.04±8.06）、（0.06±0.04）和（2.47±1.90）μmol/L，分别降低了45%、89%和85%，其中部分站位PO₄^3--P和SiO₃^2--Si含量低于阈值，在表层和10m层海水中存在P和Si限制站位分别达70%、65%和55%、50%，对海域内硅藻作为优势种的浮游植物生长和初级生产力产生影响.

Spatial distributions and seasonal variations of nutrients and statistical analysis of nutrient limitation in the center of the Bohai Sea,China

Based on nutrients and hydrological data collected in the center of the Bohai Sea in July 2013, November 2013 and May 2014, nutrient spatial distributions and seasonal variations were examined in this study, and the nutrient limitation conditions for phytoplankton growth were also analyzed according to the minimum threshold of nutrients required by phytoplankton and their stoichiometric compositions. Results showed that nutrient concentrations and compositions varied significantly with a seasonal cycling. Nutrient concentrations were high in the autumn but relatively low in the summer and spring. In the summer, influenced by diluted water influx, seawater stratification was formed. Concentrations of dissolved inorganic nitrogen (DIN), reactive phosphate (PO₄^3--P) and reactive silicate (SiO₃^2--Si) were (10.33±7.75), (0.05±0.03) and (3.94±3.19) μmol/L, respectively. And DIN/P ratios were high and Si/DIN ratios were far below 1. In the surface and 10-m layers, stations with P limitation accounted for 93% of all stations, stations with Si limitation accounted for 40% and 20%, respectively, revealing serious limitation status of P and Si for phytoplankton growth. Due to the sediment resuspension and organic matter decomposition in the autumn, concentrations of DIN, PO₄^3--P and SiO₃^2--Si increased dramatically by 1.6, 10.8 and 4.3times, relative to the summer, to be (16.44±6.51), (0.54±0.20) and (16.94±6.37)μmol/L, respectively. The vertical variations of nutrients were small and only PO₄^3--P showed potential limitation to phytoplankton growth. In the spring, concentrations of DIN, PO₄^3--P and SiO₃^2--Si decreased by 45%, 89% and 85%, compared to those in the autumn, to be (9.04±8.06), (0.06±0.04) and (2.47±1.90)μmol/L, respectively, because of the decreasing of riverine outflow and increasing phytoplankton uptake. At some stations, concentrations of PO₄^3--P and SiO₃^2--Si were below the nutrient threshold of 0.03μmol/L and 2μmol/L for phytoplankton growth, respectively. In the surface and 10m layers, 70% and 65% of surveyed stations were in the status of P limitation, meanwhile 55% and 50% of stations were in the status of Si limitation, therefore, the primary production and diatom-dominant phytoplankton structure might be affected in the study area.