摘要
有机地球化学指标可以有效地区分沉积物中有机物的来源,进而分析人类活动对三角洲演变的影响。文章对珠江三角洲洪奇沥水道附近2个钻孔(HP和MZ,它们的研究深度分别是18.00 m和45.00 m)全新世沉积物进行了AMS^(14)C测年和全样有机地球化学分析,同时收集和对比了已有表层及钻孔沉积物的研究成果。结果表明,珠江三角洲平原全新世地层中有机质来源以陆源输入为主,反映了半封闭的古珠江河口湾内径流作用强盛,陆架高盐水难以入侵。晚全新世、尤其是近2000年以来,δ^(13)C迅速增大,反映了流域内C_(4)植物贡献的显著增加,推测是珠江流域自汉代以来甘蔗种植业发展的体现,也证实了珠江流域近2000年以来农业活动对三角洲建造的影响日益加剧。
Organic geochemical proxies can effectively distinguish the sources of organic matter in sediments,and thus reflect the human impacts on delta evolution.The natural vegetation in the Pearl River basin is dominated by C;plants.But with the development of agriculture in the historical period,sugarcane has been cultivated in the Pearl River basin from Han dynasty,which possibly changed the composition of vegetation in the river basin and increased sediment load into the river mouth.In this study,we collected two boreholes HP(22°43’54.92″N,113°25’41.86″E)and MZ(22°38’9.69″N,113°32’24.23″E)along the Hongqili Channel in the Pearl River Delta,and the sediments above 18.00 m in borehole HP and 45.00 m in borehole MZ were analyzed.We carried out measurement of organic carbon,nitrogen and δ^(13)C values for the bulk sediments and AMS^(14)C dating in the two boreholes.The organic geochemical analysis was carried out on 102 samples containing no gravel in borehole HP and 160 samples containing no gravel in borehole MZ.Two charcoals and four shells were selected from borehole HP,and one charcoal,four plant fragments,two woods and six shells were selected from borehole MZ for AMS^(14)C dating.The age of borehole HP at 18.00 m was about 8700 cal.a B.P.and that of borehole MZ at 45.00 m was about 13000 cal.a B.P.In order to better explain the source of organic matter,we also collected the C/N and δ^(13)C dataset of surficial and borehole sediments in previous studies for comparison.The results show that C/N varied from 2.09 to 28.05 andδ;C values are in the range of -29.4‰~-21.6‰.The organic geochemical compositions in the two boreholes indicate the dominance of terrestrial organic matter in the Holocene sediments,suggesting the prevalence of fluvial function in the sheltered inner bay of palaeo-Pearl River mouth.However,the δ^(13)C values in borehole MZ increased to mostly higher than -28.0‰ from about 4900 cal.a B.P.and the C/N decreased to about 8.00 from about 2800 cal.a B.P.,which indicates the increase in the contribution of marine organic matter,possibly induced by the enhancement of tidal function as a response to the topographic changes.An abrupt increase in the δ^(13)C values over past 2000 years was widely observed in the sediment sequences of the Pearl River Delta,for example,mostly being between -26.0‰ and -21.0‰ in boreholes HP and MZ.This reflects the significant increase in the organic carbon contribution from C_(4) plants and associated sugarcane cultivation in the drainage basin since the Han Dynasty.This finding also supports the increased impact of agriculture on the construction of the Pearl River Delta over past 2000 years.
作者
时硕
吉俊熹
王张华
SHI Shuo;JI Junxi;WANG Zhanghua(State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200241;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519080,Guangdong)
出处
《第四纪研究》
CAS
CSCD
北大核心
2022年第2期397-411,共15页
Quaternary Sciences
基金
南方海洋科学与工程广东省实验室(珠海)创新团队项目“高强度扰动下粤港澳大湾区环境承载力与生态修复”(批准号:311020003)资助。
