水库调控下黄河口沉积有机碳的分布、来源与输运特征

Distribution,source,and transport of particulate organic carbon in the Yellow River estuary as affected by the water-sediment regulation

黄河是全球输沙量最大的河流之一,陆源颗粒有机碳通量高。然而,近年来流域水库调控对黄河下游水文格局和颗粒有机碳输送产生了重要影响,小浪底水库调水调沙时期成为黄河水沙和有机碳入海的关键时段。为揭示水库调控对河口水动力和有机碳分布的影响机制,基于2020年7月调水期和调沙期黄河口的水动力观测结果,结合沉积物有机碳测试结果,研究了水库调控不同阶段下河口沉积物粒度参数和表层沉积物有机碳的时空分布。研究结果表明,水库不同阶段下悬浮颗粒物的物源和主要扩散、沉积区域的变化,使得黄河口表层沉积物的粒度组成特征发生明显变化;在高径流量的调水期期间,粗颗粒泥沙携带颗粒有机碳在河口距离口门12 km范围内大量埋藏,河口区域表层沉积物的有机碳含量相较于调沙期明显偏低。调水期黄河口陆源有机碳主要来自下游河床冲刷,颗粒较粗,调沙期则转变为水库释放的细颗粒有机碳和流域C3维管植物碎屑。水库调控的不同阶段使得黄河下游河流水动力格局和泥沙运输机制改变,从而引起黄河口沉积有机碳来源和分布的显著变化。因此,人类活动对调节有机碳向海洋的输送及其在近岸海域的分布具有主导性作用。

The Yellow River,one of the highest sediment-laden rivers,discharges a huge amount of terrestrial particulate organic carbon(POC)to the sea.However,the reservoir regulations over recent decades have significantly affected the downstream hydrology and POC delivery.The Water-Sediment Regulation Scheme(WSRS)has become a critical time window for the impulse discharges of water,sediment,and POC to the estuary.We investigated the impacts of the WSRS on the estuarine dynamics and POC distribution based on the sampling and observations in the Yellow River estuary in July 2020 corresponding to the two stages(water-regulation stage and sediment-regulation stage)of the WSRS.The distributions of grain-size composition and POC content of surface sediments were presented according to the datasets of in-laboratory analysis.Results indicated that there was a clear turning point of variation in sediment source,grain-size composition,and the POC distribution at the two stages.At the water-regulation stage,the water discharge was high and sediments were relatively coarser and mostly deposited nearshore(<12 km off the river mouth)with low POC content,while at the sediment-regulation stage,fine-gained sediments were delivered offshore with significant increase in POC content.POC in surface sediments at the water-regulation stage was sourced maily from the lower river erosion,while that at the sediment-regulation stage was composed of the dam-released soil carbon and C3 vascular plant debris.The rapid changes in POC source and distribution in the Yellow River estuary were controlled by the reservoir regulation,which significantly changed the downstream hydrology and sediment transport.Therefore,human intervention can play an important role in regulating the seaward POC delivery and distribution in the coastal sea.