惠州黄洞水库沉积速率及孢粉的环境指示意义

Sedimentation Rate and Environmental Reconstruction Based on Grain-size and Pollen-spores Analysis from Huangdong Reservior, Huizhou

对惠州黄洞水库沉积钻孔(HD)进行了210Pb和137Cs测试,结合岩性、粒度分析和建库历史资料为佐证,以137Cs为主确定了研究区沉积物年代序列和沉积速率,同时对钻孔沉积物进行了孢粉和炭屑指标的实验分析。粒度分析结果表明,建库前沉积速率较快(约为1.5 cm/a),建库后(1960年以来)沉积速率降低(约为1.0 cm/a)。钻孔孢粉组合和炭屑记录揭示出与人类活动有关的孢粉种类为禾本科(Gramineae)花粉、芒箕(Dicranopteris dichot oma)、松属(Pinus)花粉等,孢粉绝对浓度和乔木与非乔木花粉比值(AP/NAP)是指示森林覆盖度的重要指标。同时出现乔木花粉减少、孢粉总浓度下降及禾本科相对含量上升,表明了裸地增加和水土流失严重,为人类砍伐和焚烧频率最高的时期。显著的大面积山火事件可以根据沉积物炭屑浓度与孢粉浓度比值(C/P)的峰值来判断。孢粉和炭屑记录揭示流域内建库前、大跃进-文革期、改革开放中后期3个时期不同的植被生态条件,反映了不同阶段人类活动方式和强度的变化,与历史文献记载的1958年大炼钢铁、1963年百年一遇大旱和1986年造林绿化工程等主要事件对比显示出一致的变化。

A sediment core was collected from the northeast of the Huangdong Reservoir in Huizhou, Guang dong province. Environmental 137Cs and ^210Pb dating techniques （mainly with^137Cs） were applied to determine the chronology and modem sedimentation rates of the Huangdong Reservoir, by combining with the sediment lithology, grain size and the historical data on the construction of the reservoir. Meanwhile, a lab analysis was conducted on the pollen analysis and charcoal to explore the significances to the environment and reveal the past environmental changes, vegetation and ecological conditions of the reservoir. The grain size analysis re sult showed that the sedimentation rate was faster （approximately 1.5 crn/a） before the construction of the reser voir; and it decreased （approximately 1.0 cm/a） after the construction of the reservoir（since 1960s）. The re cords on pollen assemblages and charcoal revealed that the pollens of herbs （such as Gramineae）, spores of fern （such as Dicranopteris dichotoma） and Pinus were relative with the human activities. The concentration of pollen and AP/NAP ratios （arboreal pollen/non-arboreal pollen） were the important indicators to reveal the changes of the forest coverage. Human activities＇ influence on vegetation was manifested in the decrease in pollens of tree, the drop in the total concentration of pollens, the increase in pollens of herbs. And it showed that the bare land or water and soil loss increased significantly if humans cut down and burned frequently. Sig nificant large areas of forest fire events could be according to peak value of charcoal concentration as well as the C/P value （ratio of charcoal and pollen）. This study revealed the vegetation ecological information of three different stages in the basin, i.e. the period before the construction of the reservoir, the period of Great Leap Forward and the Cultural Revolution, and the subsequent period of reform and opening up. Such information tmcovered the changes of human activities in modes and intensities indifferent historical periods. The results of pollen assemblages and charcoal index analysis were consistent with the main events of the great Steel-Mak- ing movement in 1958, the hundred-year drought in 1963, and the afforestation project in 1986 which were re corded in the historical documentsl