中文摘要：

根据2013年~2014年四个季度的调查资料,结合历史数据并采用数理分析与经验模型计算相结合的方法,分析讨论了钱塘江河口溶解硅的分布、年代际变化和潜在影响。结果表明,研究区域受到河流冲淡水和东海海水混合的双重影响,溶解硅的分布与浓度呈现出明显的梯度变化与季节规律,其浓度在秋季最高,夏季次之,春季与冬季较低。近些年来溶解硅的浓度呈降低趋势,较历史水平降低了12%~25%,硅氮比也有大幅度的降低,比值自1.25降低到0.52。钱塘江河口溶解硅浓度降低主要是由于东海低溶解硅浓度海水的稀释造成的,而浮游植物量对溶解硅浓度影响有限。另外,河口叶绿素a含量与历史数据相比也存在明显降低,浮游植物细胞总量和种数都有显著下降;硅藻种类减少了近70%,并出现了绿藻、蓝藻和甲藻等非硅藻类生物,造成这几方面变化的原因很可大程度上与营养盐结构和浓度的变化有关。

英文摘要：

Based on the comprehensive investigations during 2013-2014, the concentrations of dissolved silicate （DSi）, phytoplankton and hydrological parameters were analyzed to examine the influence of both estuary processes and human activities on silica delivery, transformation and fate to the month of the Qiantangjiang River. Results indicated that the DSi concentrations were influenced by both the Qiangtangjiang River and East China Sea, with a fair trend and seasonal character. DSi in the Hangzhou Bay decreased significantly since 1981;.Approximately 12%~25% of DSi was cut down between 1981 and 2013 due to the DSi reduction of off-bay waters, which also re-sulted in a significant drop of the Si/N ratio from 1.25 to 0.52. Compared with the past, diatom species decreased about 70% from 1989 to 2014, while green algae, cyanobacteria and dinoflagellates were found recently, which were absent in the past. There were also great decreases for Chla and biomass in recent years, which may be largely caused by the variation of nutrient structure and its content.