论文部分内容阅读
The impoundment of the Three Gorges Dam (TGD) has altered downstream hydrological characteristics and sediment discharge,and it has caused ecological impacts,such as changes in chlorophyll-a (Chl-a) in estuaries and coastal oceans.To investigate the TGD's influence on Chl-a's interannual and seasonal variations in the Changjiang Estuary and the adjacent coastal East China Sea,a physical-biogeochemical model was developed with numerical experiments covering a decade,including TGD's preperiod (pre-TGD,1999-2003) and post-period (post-TGD,2004-2008).The modeling results demonstrate an annual increase in the regional average Chl-a from pre-to post-TGD,with the largest increase reaching up to 20.8％ in spring in the nearshore region beyond the Changjiang mouth.The spatial variations in Chl-a are high,with the largest variation being observed around the 20-40 m isobaths.The increase in Chl-a is influenced by improved light and nutrient conditions,which is attributed to dam construction and fertilization by human activities.A decline in nitrogen-phosphorus fertilizer usage ratio along the Changjiang River watershed after the TGD's impoundment is another factor that influences the Chl-a's variation.The modeling results also show severe NO3 and PO4 imbalances with a larger N/P ratio during the post-TGD period,especially in regions with large Chl-a increases.Moreover,the greater increase in the usage of phosphorus fertilizer than nitrogen fertilizer influences Chl-a's variation and has potential promotion effects on the outbreak of harmful algal bloom events.