长江中游网湖百年花粉序列及其沉积动力和环境特征

100a pollen sequence and the sedimentary dynamics and environments in Lake Wanghu,middle reaches of the Yangtze River

本文研究长江中游网湖钻孔百年来的花粉沉积序列,分析花粉沉积近、现代过程以及其与沉积粒度、过去百年湖泊由开放水系到封闭湖泊的气候、水文动力变化的关系.研究表明,花粉浓度、类型与沉积粒度的变化特征以及聚类分析反映出网湖经历了湖泊水系通江与封闭两个重大阶段变化,其花粉序列变化与沉积粒度、区域降水以及长江流量在时间序列上也具有显著的相关性.主要孢粉类型,包括陆生松属、常绿栎/落叶栎、乔灌木花粉、湿生莎草科、水生和陆生草本花粉、以及蕨类孢子,与沉积物粒度和降水具有同步相关的年份占过去130年的27%-40%,与1960年湖泊封闭以前长江流量的同步相关达到47%-57%,反映出花粉沉积量的变化受到了沉积粒径和流域降水量的影响.花粉类型对沉积和气候具有不同的响应关系,表现出具有大于降水70百分点年份以粘土沉积为主、乔灌木花粉占优的多水年模式,和小于降水30百分点的年份以粉砂沉积为主、水生、湿生、陆生草类花粉增加的少水年模式.花粉沉积与水动力这个关系为认识湖泊碎屑和利用花粉沉积记录反演过去环境变迁、生物湖泊沉积机制提供科学依据.

This paper studied sedimentary pollen sequence for the last hundred years of Lake Wanghu, in the middle reaches of the Yangtze River, and analyzed the relationships of changes in pollen types and contents, sediment granularity, and climate-hydrology features during the past hundred years when the lake turned from an open water system into closed basin. Results showed that there were two major periods of lake-river connections and lake closing according to sediment and pollen features and to clustering analysis. Correlation analysis of time series from the pollen, granularity, catchment precipitation and river discharge, showed that they have significant linear relationships with 95% confidence interval. Major pollen types, including Pinus, ratio of evergreen tree Quercus to deciduous tree Quercus, sum of trees and shrubs, Cyperaceae, aquatics, upland herbs, and fern spores, showed 27% -40% synchronous changes with the time series of granularity and precipitation during the past 130 years, and 47% -57% synchronous changes with the time series of granularity and river discharge before 1960 when the lake naturally connected with the Yangtze River, suggesting pollen deposition was controlled by sediments and catchment precipitation. We found different responses of pollen to sediments and precipitation： tree and shrub pollen with clay sediments responding to greater than 70^th percentile precipitation changes, and aquatics and upland herds with silt sediments responding to less than 30th percentile precipitation changes. This study may provide scientific basis to reconstruct past environment changes by using sediment and pollen records, and to understand bio-sedimentology mechanicals in the lake sediments.