广西海岸带近百年来人类活动影响下环境演变的沉积记录

Sedimentary Records of Environmental Evolution During the Recent 100 Years in the Coastal Zone of Guangxi Province

基于2007年在广西海岸带采集的6根短柱状样(64～97 cm),在210Pb年代框架构建的基础上对沉积物中的生源要素(C、N、P)、常量元素以及重金属(Hg、Cu、Pb、Zn、Cd、Cr和As)等指标进行了综合分析,并依此重建了广西海岸带近百年来人类活动影响下沉积环境的演变历程。研究发现,近二十年来重金属和总磷的表层富集和埋藏通量有明显的上升趋势,但整体污染程度依然较轻;总氮的年埋藏通量虽保持相对稳定,但总体高于引起最低级别生态风险效应的下限;而有机质年埋藏通量的逐年减少应与潮间带红树林生态系统的衰退有关。据此可将近百年来广西海岸带的环境演变大致分为两个阶段:即20世纪80年代初以前、80年代初至现在,分别经历了未污染期和轻度污染期。

Six sediment cores were collected during 2007 from the coastal zone of Guangxi province.The temporal evolution of biogenic elements（C,N and P） and metal（Hg,Cu,Pb,Zn,Cd,Cr and As） inputs was clearly recorded by high 210Pbxs-derived sedimentation rates（0.25~1.68 cm y-1）,especially in the estuary of Qinjiang river and Nanliu river（1.68 cm·y-1 and 0.70 cm·y-1,respectively）,which could be attributed to high rates of river sediment transport.Based on the vertical distributions of enrichment factors and excess fluxes,heavy metals and total phosphorus were obviously enriched in the recent 20 years,but do not exceed the quality standard for marine sediment.The results indicated that the natural inputs prevailed up to the early 1980s except Cu.After this period,the excess metal fluxes could be associated with the intensive use of phosphate fertilizers and the combustion of fossil fuels,which caused a slight enrichment.However,total organic carbon showed decreasing trends toward the surface,which could be associated with the decreases of the mangrove forest derived from tidal flat reclamation recently.According to all indicators,environmental evolution of the Guangxi coast during the recent 100 years can be divided into two stages：（1） before the early 1980s characterized by the relatively low heavy metal pollution and scarce eutrophication;（2） after the early 1980s,the concentrations of heavy metals and total phosphorus are significantly increasing,indicating of the anthropogenic inputs.