三峡水库三期蓄水前后长江口硅酸盐分布及其比值变化

Distribution of dissolved silicate and changes of Si∶N and Si∶P ratio in Yangtze River estuary before and after impoundment of Three Gorges Reservoir

河口SiO2-3-Si浓度的变化直接影响到水体的营养盐结构和生态系统.根据2010年8月、11月和2011年5月的现场调查资料,对长江口区域一个水文年(跨三峡水库三期蓄水)硅酸盐的分布特征和变化趋势进行了分析.结果表明,长江口及其邻近海域硅酸盐分布与盐度分布极其相似,整体呈现近岸高、外海低的特点;截取一断面分析发现存在上升流,硅酸盐等值线有抬升趋势.3个季节硅酸盐平面分布各有其季节性特点,但总体浓度夏季高于秋季,秋季高于翌年春季;在整个调查区域SiO2-3-Si/DIN值是10月>8月>5月,而SiO2-3-Si/PO3-4-P值是5月>8月>10月;3个季节SiO2-3-Si浓度与盐度都呈显著负相关关系.与历史资料比较得出,2010—2011年长江口海域营养盐比值小于2004年,也小于1985—1986年,可见三峡工程蓄水对长江口SiO2-3-Si/DIN、SiO2-3-Si/PO3-4-P降低的影响.

Yangtze River estuary is a transitional zone between land and the East China Sea, which plays an important role in land and ocean interaction. Analysis of the silicate dynamics in time and space is essential to understand the ecosystem changes, especially diatom dynamics. This paper analyzes the spatio-temporal dynamics of silicate as well as its affecting factors in the Yangtze River estuary based on the data of three surveys conducted in August and November 2010 and May 2011. The seasonal variations of silicate after the impoundment of stage-Ⅲ of the Three Gorges Dam are discussed. The results showed that the silicate distributions are characterized by a decreasing feature from inshore to offshore, and the concentration is mainly influenced by the discharge from Yangtze River. The silicate （SiO^2-_3-Si concentratmn m summer exhibits an eminent double tongue pattern. The distribution in autumn is relatively simple and only stretches towards northeast frontal zone. The isolines are sparser in spring than in summer, and they move more towards to the shore. The spatial features in the bottom layers are much simpler than the surface layer. Analyses on the silicate concentrations along a transect indicates that there is upwelling in the Yangtze River estuary, thus the isolines show an uplifting trend in summer; however, the upwelling is not strong. In average, the silicate concentration is higher in summer than in autumn and spring. Regarding to nutrient ratio, the Redfield values of SiO^2-_3-Si/DIN and SiO^2-_3-Si/PO^3-_4 -P are lower than 1 and 16, respectively. The rate of SiO^2-_3-Si/DIN is higher in October than May and August, while the rate of SiO^2-_3- Si/PO^3-_4 -P is higher in May than August and October. Comparing to the historical data, the Redfield values of SiO^2-_3 -Si/DIN and SiO^2-_3 -Si/PO^3-_4 -P are lower in 2010-2011 than 2004 and 1985-1986.