消落带土壤黑碳的降解及环境效应

Many water transfer projects have been initiated to mitigate the crisis of water resource shortage. Micropollutants of freshwater systems is becoming a major public concern in almost all parts of the world. Water level fluctuation zone (WLFZ) have received considerable attention with a focus on reducing contamination in aquatic environments. Soil sorption/desorption is a key process in determining the fate of pollutants and quantifying the risk of contamination.Black carbon (BC) are ubiquitous in the environment and frequently occur in soils and sediments. They play important roles in sorption/desorption of hydrophobic organic contaminants (HOCs), such as polycyclic aromatic hydrocarbons (PAHs). The Danjiangkou reservoir, the water source area of the Middle Route of the South to North Water Transfer Project (SNWDP), will supply water to the North China Plain. Our previous results clearly show that water level fluctuation imposed on the reservoirs have altered BC decomposition and thus influence water quality. Up to now, the impacts of WLF on BC degradation have not been studied. Considering the absence of data on the influence of WLFZ on BC decomposition, as well as the role of the Danjiangkou reservoir, we selected soil BC from the WLF zone in the Danjiangkou reservoir. The purposes of this study were (1) to discover the decomposition process and mechanism of soil BC; (2) to investigate the impacts of water regime and temperature in the WLFZ on BC decomposition process; and (3) to discuss the processes of sorption/desorption of PAHs and OCPs to the BC decomposition products of in the WLFZ. Understanding the decomposition mechanisms, dynamics and environmental influences should provide new insights into BC degradation and cycling.

随着全世界调水工程的兴起，水体中的微污染物受到广泛关注。消落带作为水库水质安全的最后一道屏障，日益得到重视。土壤黑碳的吸附解吸对污染物迁移、转化及最终归趋发挥着重要作用，而黑碳的降解可改变这一过程。消落带的人类活动改变了河流原有的生物地球化学过程，在黑碳的降解中发挥着积极的保护作用，同时对水体水质产生了深刻影响。在人类活动加剧的影响下，这个过程正发生难以预见变化。本项目以南水北调中线工程丹江口库区作为研究区域，以该区消落带土壤黑碳为对象，拟通过野外调查与室内试验，运用分子生物学和现代结构表征分析等技术，从生物化学角度揭示土壤黑碳的降解途径和机制，阐明消落带的水分和温度耦合条件下土壤黑碳的降解过程，准确认知消落带在土壤黑碳降解中的保护作用，明确消落带土壤黑碳降解的环境效应，解析消落带在不同水文条件下的源汇效应，旨在为水体中污染物的归趋提供理论依据，同时为土壤全球碳汇效应等领域提供科学依据。

调水工程形成的消落带是水库水质安全的最后一道屏障，而消落带土壤黑碳的降解可影响水质安全。本项目以南水北调中线工程丹江口库区作为研究区域，以消落带土壤黑碳为对象，开展了消落带土壤黑碳的降解及环境效应研究。从生物化学角度探讨了消落带土壤黑碳降解过程中酶的动力学及热力学特征，阐明了消落带的温度变化对降解的影响，揭示了消落带土壤黑碳降解的主要环境因子和调控路径，明晰了消落带土壤黑碳降解的环境效应。重要研究结果如下：1）该区土壤黑碳降解的真菌以子囊菌（Ascomycota）中的粪壳菌纲（Sordariomycetes）和担子菌（Basidiomycota）中的伞菌纲（Agaricomycetes）为优势类群。2）消落带土壤中LiP、MnP和Lac的活性特征为：LiP＞MnP＞Lac。Fe(II)是影响LiP活性的主要因素；Mn(II)是影响MnP活性的主要因素；C/N、SWC是影响Lac活性的主要因素。3）消落带黑碳降解酶的Vmax为：LiP＞MnP＞Lac；Km为：Lac> LiP＞MnP；Vmax/Km为：MnP＞LiP＞Lac。不同的动力学参数对温度的响应不同：Vmax随温度升高呈上升趋势；Km随温度上下波动；Vmax/Km 随温度升高在低温区(5-15℃)保持不变，而高温区(25-45℃)升高或保持不变。4）土壤黑碳的降解属于非自发反应，是吸能过程，降解酶的Ea主要受控于C/N。5）消落带土壤DOM以CHO类化合物为主，木质素类化合物是其主要组成部分，芳香结构和缩合芳香结构都以CHO和CHON1类化合物为主，母核结构为一个苯环连有不同取代基。6）DOM进入水体后的光解使其芳香性和分子量降低，生物可利用性增加；生物降解使其芳香性增强、分子量减小。变化的结果都增加了对菲的结合能力。本项目获得的结果为认知消落带土壤在全球碳汇效应的作用和评价该区持久性有机污染的归趋提供了科学依据。