长江三角洲地区全新世环境变化与人类活动的影响

HOLOCENE ENVIRONMENTAL CHANGES AND HUMAN IMPACT IN THE YANGTZE RIVER DELTA AREA,EAST CHINA

长江三角洲地区全新世气候和环境曾发生过大的变迁,新石器时代文化伴随着全新世气候最暖期的到来,以及三角洲的形成和发展而出现,并由此向前推衍,奠定了以稻作农业为基础的经济形态。通过研究本区与农作物相关的现代植物花粉形态和代表性表土花粉,揭示出部分用于指示人类活动的综合指标、不同植被带表土花粉的组合特征和用于半定量界定不同植被类型的E/D比值区间。研究区自然区域全新世孢粉反映当时植被3个主要发展阶段,即亚热带常绿-落叶阔叶混交林(11000～9500cal.aB.P.)、中亚热带常绿阔叶林(9500～3900cal.aB.P.)和次生性质的亚热带针阔叶混交林(3900cal.aB.P.以来),其中8000～3900cal.aB.P.为全新世大暖期的鼎盛期,3900cal.aB.P.以来人类活动明显增强。人类活动区绰墩遗址孢粉植物群,反映新石器各主要文化期都以亚热带含针叶植物的常绿-落叶阔叶混交林为地带性植被,遗址周围一般都有较大面积的水域分布;人类对植被的干预只是在后期才开始明显增强。区内人类文化几经兴衰,主要受制于环境的变迁,包括气候和地理状况的变化,以及由此产生的海平面升降和植被变化等。与此同时,人类活动的影响随着时间的推移而日趋加重,成为一种新的环境影响因素。

With the accumulation of new data on early agriculture, especially on the cultivated rice in the Yangtze River Delta area,this area has become one of the most important places in the study of Holocene human-environment interface in China. On the basis of some related studies,this paper focuses on the pollen study of Holocene natural sequence and human induced site, in combination with pollen morphology study on some regular crops and their related weeds, and surface pollen analysis from some representative vegetation zones, in order to extract the possible anthropogenic indicators in pollen diagrams,and further assess the human impact on environment. Pollen morphology study and surface sample pollen investigation reveal some integrated anthropogenic indicators, such as poaceous pollen with 34 - 38 μm in diameter holding a majority probability of rice pollen,which occurs in high frequency in paddy fields, and declines quickly in the nearby lake surface samples. Surface sample pollen assemblages well reflect their represented vegetation zones with E/D ratio （the ratio between broad-leaved evergreen and deciduous trees） as a practical proxy. Three main developing stages of local vegetation are recognized from the Holocene natural sequence, i. e. subtropical mixed evergreen and deciduous broad-leaved forest （11000 9500cal. aB. P. ） , central subtropical evergreen broad-leaved forest （ 9500 - 3900cal. aB. P. ） and secondary subtropical mixed coniferous and broad-leaved forest（since 3900cal. aB. P. ）. Among the second stage,pollen flora in 8000 - 3900cal. aB. P. corresponds to the maximum Holocene Megathermal, while distinctive human impact is recognized in the third stage. Pollen analysis from Chuodun Neolithic site demonstrates that during the Neolithic period, the surrounding highlands and hills were covered by the subtropical mixed evergreen and deciduous broad-leaved forest accompanied with coniferous elements, revealing a warm and humid climate with well-developed wetlands, swamps, ponds and lakes near the relic sites. The presence of abundant possible poaceous rice pollen suggests that the rice agriculture initiated at the very beginning of the Majiabang Culture. In contrast to the pollen data derived from the natural sites,pollen floras from archaeological sites are generally dominated by a majority of herbaceous pollen, with secondary forest increased upward, indicating an enhanced disturbance or deforestation as a result of intensified human activities.