长江口及邻近海区营养盐结构与限制

Nutrient structure and limitation in Changjiang River Estuary and adjacent East China Sea

通过研究长江口及邻近海域溶解无机氮(DIN=NO3-+NO2-+NH4+)、磷酸盐(PO34-)、硅酸盐(SiO23-)所表征的营养盐区域结构特征及影响因素,在分析营养盐绝对限制情况的基础上,划分了潜在相对营养限制区域。结果表明,123°E以西近岸表层区域DIN/P比值全年均高于16,而Si/DIN除秋季外基本小于1,显示出长江冲淡水影响下"过量氮"的特征。春夏季河口锋面区(31°～32.5°N,122.5°～124°E)硅藻的大量生长可使DIN/P异常升高和Si/DIN异常降低。秋季研究区域北部DIN/P西低东高且Si/DIN西高东低是由于在高DIN、低PO34-的长江冲淡水影响下,近岸受相对低DIN、高SiO23-的苏北沿岸流南下入侵影响而被分割而成。冬季长江口门东北部存在的高DIN/P和低Si/DIN区则主要由于寡营养盐的黑潮水深入陆架,向东北输送的部分长江冲淡水和增强的苏北沿岸流共同作用造成DIN升高所致。利用Redfield比值进行了不同站位表层潜在相对营养限制情况的区分。近岸123°E以西受高DIN、SiO23-长江冲淡水影响,四季多呈现PO34-潜在相对限制,而在春夏季由于浮游植物的大量吸收PO34-,造成局部PO34-绝对限制及潜在相对限制。春夏季氮限(DIN潜在相对限制)一般发生在外海部分站位,但较为零散。秋季除了东南外海大部分站位外,受苏北沿岸流影响在长江口北部近岸也存在氮限。随着低DIN/P的黑潮表层水(KSW)的入侵加强,冬季外海氮限站位增多。硅限(SiO23-潜在相对限制)在夏季发生在赤潮高发区,而冬季南部存在较多硅限站位表明KSW中SiO23-相对较为缺乏。

The spatial distribution of nutrients structure and its controlling factors indicated by the dissolved inorganic nitrogen（DIN=NO3-＋NO2-＋NH4＋）,PO34-,SiO23-were studied on the basis of four cruises in the Changjiang（Yangtze River）Estuary and the adjacent East China Sea（ECS）,nutrients absolute limitation was presented,after that the relative potential limitation was analyzed.The results showed,controlled by the Changjiang dilution water and offshore seawater mixing,DIN/P was usually above 16in the coast east of 123°E all year round,Si/DIN was below 1except in autumn,indicating＂excess nitrogen＂influenced by the Changjiang River dilution water.The water DIN/P were increased and Si/DIN decreased abnormally when phytoplankton bloomed in the riverine plume area（31°～32.5°N,122.5°～124°E）in spring and summer.In autumn DIN/P was low west and high east and Si/DIN was high west and low east in the north estuary,because high DIN low PO34Changjiang River dilution water was separated by relatively low DIN and high SiO23-Subei Coastal Water coming from the north.In winter the oligotrophic Kuroshio water intrudes deeply into the ECS continental shelf,the high DIN/P and low Si/DIN area was attributed to elevated DIN resulting from northeast transporting Changjiang Dilution Water and enhanced Subei Coastal Water.The relative potential nutrients limitation was discriminated based on Redfield ratio：The coastal area west of 123°E presented PO34-potential limitation under the influence of Changjiang Dilution Water with high DIN and SiO23-all year round,while regional PO34-absolute limitation and relative potential limitation occurred in spring and summer as a result of massive PO34-uptake by phytoplankton.N limitation stations（DIN relative potential limitation）scattered offshore in spring and summer.In autumn N limitation existed in north coastal area as well as offshore stations.Strengthened intrusion of KSW（Kuroshio Surface Water）with lower DIN/P caused more N limitation stations in winter.The estuary plume area showed Si limitation（SiO23-relative potential limitation）because of diatom blooms in summer,whereas in winter Si limitation existed in most southern offshore stations,indicating SiO23-relative deficit in KSW.