三峡工程调蓄水对长江口外海浮游植物生态动力过程影响的数值模拟

基于海洋模式ECOM-si,建立长江口外海包含环流场、温盐、泥沙和NPZD型生态模型的物理-生态耦合数值模式。利用历次定点、断面观测资料对模拟结果进行验证,表明模型具有一定的模拟精度,且稳定性良好,可用于研究长江口外浮游植物生物量的季节变化规律,以及长江入海径流量受三峡工程调蓄前后,不同月份下泄水量的增减分别在丰水年、平水年和枯水年对长江口外营养盐和浮游植物月平均生物量的影响。模拟结果表明:长江口外营养盐增减的绝对量由近河口区向远河口区递减;且调蓄引起的营养盐增减峰值时间上自西向东推迟、峰值滞后。枯水年受径流调蓄的影响最大,径流调蓄导致的营养盐增量在各区均是枯水年明显大于丰水年和平水年,而在过渡区和远河口区10月后因蓄水导致的减量则相反。浮游植物生物量的情势与营养盐较为一致,枯水年影响最大,且自西向东峰值滞后;此外,由于硅藻和甲藻的竞争作用,硅藻在流量增加季节的生物量增幅大于流量减少季节的生物量减幅,而甲藻则相反。三峡工程的径流调蓄有利于增加长江口外海域的年均浮游植物生物量,但年平均增幅较小。

Numerical study of the effect of the Three Gorges Project on the ecological dynamics of phytoplankton off the Changjiang Estuary

Based on the ECOM-si, a physical-ecological coupled numerical ocean model off the Changjiang Estuary with modules of circulation, thermohaline, sediment simulation and NPZD type of ecological model was established.The model was validated by observed data of several sites and sections, and the simulated results show a certain precision and stability.Therefore, the model can be applied to seasonal variation study of the phytoplankton biomass off the Changjiang Estuary, and the influences of increase-decrease of water discharge in different months and during high, normal and low flow years, on the nutrients and the monthly mean biomass of the phytoplankton,after the runoff of Changjiang regulated by Three Gorges Project(TGP). The modeling results showed that, the absolute value of nutrients variation was decreased from the nearly estuary to the far estuary,and the peak value of nutrients variation occurred successively from west to east. Low flow year was influenced greatly by runoff regulation, and the nutrients increment during low flow year was significantly greater than during high and mean years caused by runoff regulation in the estuary, while the nutrients decrement was on the contrary in the transition area and the far estuary after October.The distribution of phytoplankton biomass was relatively consist with that of nutrients, with a greatest effect during the low flow year andthe peak value also occurred successively from west to east.In addition, due to the competition between diatoms and dinoflagellates, the increased absolute amplitude of diatom biomass in flow increased season was higher than the decreased amplitude of diatom biomass in flow reduced season, while dinoflagellates was on the contrary.Runoff regulation of TGP was beneficial to the growth of phytoplankton off the Changjiang Estuary, but the annual mean increased biomass was small.