三门湾近五十年来富营养化的沉积记录

Sedimentary Records of Eutrophication for the Last 50 Years in Sanmen Bay

沿海(特别是河口港湾)富营养化已成为当前海洋环境的一个突出问题。以人类活动影响下的典型海湾——三门湾为研究对象,对三门湾湾内(SM-3)及湾口(SM-17)沉积物柱状样品进行研究,采用210Pb对SM-17沉积柱进行年代测定,建立年代标尺。通过对两个沉积柱多化学指标变化特征(有机碳、总氮、总磷和生物硅分布特征、生源要素的比值、生源要素的埋藏通量)同沉积柱的年代标尺有机结合,从沉积物中提取水体富营养化发生的高分辩率沉积记录,剖析了三门湾近五十年来富营养化沉积演变历史。从柱状样TOC、TN变化趋势来看,SM-17和SM-3都大致经历了三个阶段,但SM-17变化趋势较明显,即自下而上呈上升趋势。SM-3和SM-17沉积柱中TOC与TN和BSi都呈正相关,两个柱子沉积物来源都表明是陆源和海源的混合。从上世纪50年代初到80年代中旬,TOC的埋藏通量其间虽有波动,基本上变化不大;从上世纪80年代中旬开始到本世纪初,各大指标的埋藏通量呈上升趋势;从本世纪初,TOC、TN的埋藏通量有下降的趋势。综合分析各项环境指标,提出了三门湾近五十年来三门湾富营养化沉积环境演变经历了3个阶段,即人类活动干预下的自然演化阶段(建国以来到改革开放前);人类活动不断增强阶段(改革开放前夕到本世纪初);人类活动开始协调阶段(本世纪初以后)。

Estuarine and coastal eutrophication has been one of the prime environmental problems worrying the coastal countries,because of human frequent activities in the recent years.Sanmen Bay is a typical bay under the influence of human activities.On the basis of the present eutrophication analysis and combined 210Pb age data,sedimentary age records is constructed.Through the organic tight combination of more chemical indexes（The vertical distribution of TOC,TN,TP and BSi;the ratios and burial fluxes of biogenic elements.） and age records from sedimentary pole and historical data,sedimentary records are extracted from the sedimentary pole,the sedimentary history of Sanmen Bay eutrophication in the past fifty years are presented.From varied trends of TOC and TN,the cores of SM-17and SM-3 also experience approximately three stages and show an increase from bottom to top,but the former relatively more obvious than the latter.The relationship between TOC,TN and BSi in the two cores show positive correlation.Organic matter within the two cores is of aquatic and terrestrial sources deduced from the ratio of C/N.Although a few fluctuation burial flux of TOC for core SM-17 basically vary little from the early 1950s to middle 1980s.The fluxes of various indexes have also an increasing trend from the middle 1980s to early 20th century.The fluxes of TOC and TN do not increase.＂three stages theory＂ on sedimentary history of Sanmen Bay eutrophication is put forward from comprehensive analyses of environmental indexes,namely natural evolution stage under the interference of human activities（from the establishment of the People＇s Republic of China to the beginning of reform and opening up）;increasing stage under the interference of human activities（from the beginning of reform and opening up to early 20th century）;slow coordination stage under the interference of human activities（since early 20th century）.