历史时期黄河下游湖泊消亡过程与机制及沉积碳埋藏量估算

The disappearance of lakes in the lower Yellow River area during historic periods has had far-reaching influences on the function of hydrologic and ecosystems within the drainage basin, which in turn have driven the changes in the pattern of regional carbon cycling. The well-dated and well-preserved lacustrine sediments can help understand the changes of lake status and the history of carbon storage as well as the influxes of organic/inorganic carbon from the drainage basin. This proposed work plans to: 1) reconstruct the paleohydrological regime during historic periods by analyzing sediments from these paleolakes in the lower Yellow River area in combination with remote-sensing technology and historic archives; 2) reconstruct climatic and environmental changes of the lower Yellow River area and discuss the driving mechanism of natural changes versus human activities on the evolution of the lower Yellow River by using sedimentary geological records of typical lakes and various kinds of proxies. For understanding the carbon storage in paleolakes and the variations of organic/inorganic C ratios in lacustrine sediments during historic periods and demonstrating the process and mechanism of carbon influxes, the analysis of organic/inorganic carbon contents, element distributions and sedimentation rate will be conducted. In addition, the results will provide scientific basis for river diversion and lake restoration which in turn would provide reasonable regional policies for reducing carbon emissions in the lower Yellow River area.

历史时期黄河下游大量湖泊的消亡对流域水文系统调整和生态环境变迁产生了深远影响，也使区域碳循环模式发生了深刻变化。利用信息丰富、层序完整且确知年代的湖泊沉积物的研究，可以深入了解湖泊演化史及湖盆储碳历程。本项目拟通过对黄河下游古湖沉积信息的提取，结合遥感技术、历史文献记载等，恢复历史时期的湖泊格局；利用典型湖泊沉积地质记录及各种替代性指标方法，重建历史时期黄河下游气候与环境变迁史，探讨自然尤其人类活动对黄河下游湖泊演变的影响机理；通过对层序完整且确知年代的古湖沉积物中有机碳、无机碳、主要元素含量以及沉积物密度等的分析，估算历史时期黄河下游湖泊沉积碳埋藏总量，揭示沉积物储碳速率变化的过程与机制。以为黄河下游河道治理、河湖系统修复与重建以及制定合理的区域碳排放政策等提供科学依据。

黄河下游地味腴沃，气候宜人，自古以来就是中华民族生息繁衍的场所和人类文明的函毓之处。由于环境变化及人类活动的影响，历史时期黄河下游地区自然环境发生了巨大变化，大量湖泊消亡、流域水文系统发生根本调整、生态环境发生极大变迁、区域碳循环过程与机制也发生了深刻变化。针对历史时期黄河下游古湖消亡过程与机制问题以及区域沉积碳埋藏量问题进行了研究。研究结果如下：.1、历史时期黄河下游地区至少有136个湖泊，总面积多达16197.31 km2，主要沿黄河古河道分布，其中中小型湖泊为黄河下游古湖的主体，分别占历史时期湖泊总数、总面积的74.26%、30.23%；自宋朝以来黄河下游古湖整体呈萎缩消亡态势，消亡了47.06%；气候变化是古湖消亡的背景，黄河改道泛滥带来的泥沙淤积是促使古湖消亡的直接原因，而人类围湖造田等活动加速了这一进程。.2、黄河下游地区现存湖泊表层沉积物有机碳含量巨大，其中南四湖表层沉积物有机碳累积量约为15.34Tg C、洪泽湖有机碳累积量约为 3.86Tg C、东平湖有机碳累积量约0.56Tg C，反映了湖泊生态系统的重要碳汇功能。.3、近百年来东平湖有机碳埋藏速率的变化范围约为11.13-36.32 g•m-2•yr -1，整体呈逐渐加快的变化趋势。相关性分析结果表明湖区水位、水生经济植物产量、人口数量、农业生产总值亦是影响近百年东平湖有机碳埋藏的重要因素。近百年来洪泽湖沉积物有机碳的平均含量为0.69%~0.91%。从影响因素来看，有机碳含量主要与有机碳矿化程度、叶绿素a浓度、温度以及人类活动（如人口数量）有关。.4、历史时期大陆泽、荥泽和孟渚泽有机碳埋藏速率平均值分别为38.17g∙m^(-2)∙yr^(-1)、67.66g ∙ m−2 ∙ yr−1和36.54g ∙ m−2 ∙ yr−1，有机碳储量分别为 20.33Tg C、39.85Tg C、37.74Tg C。总体来看历史时期黄河下游古湖沉积碳埋藏速率均值约为61.30g∙m^(-2)∙yr^(-1)，总有机碳埋藏量约为851.62Tg C。研究揭示了黄河下游历史时期湖泊沉积物的重要碳汇意义。