强降雨对胶州湾生源要素补充和分布的影响

The Influence of Typhoon-Induced Precipitation on Biogenic Element Supplementary and Distribution of Jiaozhou Bay,China

台风带来的强降雨对地表的强烈冲刷作用可将大量淡水和生源要素从陆地输送到近海,从而在短时间内对近海的水文和生物地球化学过程造成显著影响。本文以胶州湾这一典型的半封闭海湾为研究对象,以2012年台风"达维"对青岛地区带来的强降雨事件为背景,通过降雨前后生源要素入湾河流和湿沉降输入及海上分布同步调查,考察了强降雨对胶州湾生源要素的输入、浓度及组成的影响。结果显示,在强降雨过程中,通过河流和湿沉降输入的生源要素DIN、SiO3-Si、PO4-P通量分别是降雨前的2.7、19.7和25.6倍。相应地,胶州湾表层海水中DIN、SiO3-Si、PO4-P平均浓度分别达到(37.90±26.72),(20.18±17.22)和(1.75±1.28)μmol·L-1,分别是降雨前的1.5、2.4和2.3倍;同时,胶州湾中生源要素的结构发生明显改变,N/Si/P的比例从降雨前的24∶8∶1变化为降雨后的19∶10∶1,更接近Redfield值和适宜浮游植物的生长。进一步运用富营养化指数(EI)分析表明,降雨后的富营养化程度加剧,整个海域EI指数平均值由降雨前的(4.35±6.40)升高到降雨后的(13.71±21.20),同时降雨后的EI>5的严重富营养化区域面积占比达到50%。以上分析表明台风带来的强降雨提供了大量适宜浮游植物生长的生源要素,这可能是导致胶州湾富营养化程度加剧的原因。

Typhoon-induced heavy rains often have great impact on coastal hydrology and biogeochemistry through the strong pulse input of biogenic elements.However,few studies have explored the impacts of heavy rains associated with typhoon on the ecosystem of the Jiaozhou Bay（JZB）,which is a typical semienclosed bay of China.In this study,two synchronous survey of the input,the concentrations and composition of biogenic elements as well as other physical-chemical parameters of the JZB were conducted,prior to and after Typhoon Damrey in August 2012.During the process of the typhoon,the flux of dissolved inorganic nitrogen（DIN）,silicate（SiO-3）andphosphate（PO3-4）,through both the bay catchments and atmospheric wet deposition was the 2.7,19.7and 25.6times than that of the previous heavy rain,respectively.Accordingly,the average concentration of DIN,SiO-3and PO3-4in surface seawater of the JZB elevated to（37.90±26.72）μmol·L^-1,（20.18±17.22）μmol·L^-1,（1.75±1.28）μmol·L^-1,which was the 1.5,2.4and 2.3times than that of the previous heavy rain,respectively.At the same time,the structure of biogenic elements of the JZB also changed significantly.The average values of the DIN/SiO-3/PO3-4ratio changes from 24∶8∶1before the typhoon to 19∶10∶1after 1day of the typhoon,which is closer to the Redfield ratio and is more optimal for phytoplankton growth.Further application of eutrophication index（EI）analysis showed that the level of eutrophication in the JZB become more serious after the strong rainfall.The average value of the EI increased greatly from 4.35±6.40 of the previous rainfall to 13.71±21.20 of the post rainfall,and the area proportion with severe eutrophication（EI5）reached 50%.These results indicate that typhoon-induced heavy rain not only could provide the sufficient nutrient elements,but also could vary nutrient ratio appropriately for the growth of phytoplankton,which might result in the occurrence of phytoplankton bloom in the JZB.