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

Key words: 
• Sanmen Bay /
• eutrophication /
• sedimentary records

Abstract: 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 210Pb 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 20th 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 20th century）; slow coordination stage under the interference of human activities（since early 20th century）.