基于营养盐分布特征的长江口附近海域分区研究

A nutrient-distribution-based partition method in the Yangtze Estuary

基于长江口海域2005年夏季、秋季和2006年春季三期调查数据,对盐度、无机氮、活性磷酸盐、活性硅酸盐、悬浮物和溶解氧浓度进行了聚类分析,并依据聚类结果对长江口附近海域进行分区.结果表明,长江口海域可分为4个区域.受陆地径流和海洋环流的影响,4个分区的范围随着季节略有变化.各区域水体的水文、化学特征和控制因素各不相同.一区是淡水控制区,受淡水影响表现出低盐、中沙、高营养盐、氮磷比远高于Redfield比值等特征;二区处于悬沙锋控制区域,最突出的特征是悬浮物含量高,悬沙锋内外含沙量相差3倍以上;三区在羽状锋控制范围,具有明显的盐度水平梯度,表层盐度和底层盐度差异较大;四区处于长江冲淡水外缘,受外海陆架水控制,盐度较高.

Based on in-situ observations in summer and autumn 2005 as well as in spring 2006, a regional partition over the Yangtze estuary area was performed. Cluster analysis was used to identify the divisions considering parameters like salinity, inorganic nitrogen, phosphate, silicate, suspended sediment and dissolved oxygen concentration. As a result, four zoning areas bearing specific hydrological and chemical characteristics were finally generated. The first zone was regarded as a freshwater controlled area with relatively low salinity, moderate suspended sediment and high nutrient concentration. In this area, the nitrogen ：phosphorus ratio was higher than the Redfieid ratio under freshwater influence. The second zone was a suspended sediment front controlled area, where the suspended sediment concentration was very high. A three-fold concentration difference was observed between this area and its surroundings. The third zone was a plume front controlled area, which exhibited a horizontal sahnity gradient and a clear difference between the surface and the bottom of the water body. The fourth zone was eventually recognized on the outer fringe of the freshwater body and was controlled mainly by the continental shelf water. Further analysis indicated that along with the seasonal alternation, the scope of the above zoning areas was correspondingly changing on account of the seasonal impact of river runoff and the continental shelf circulation.