西南森林凋落物分解介导的典型生物累积性有机污染物释放特征及模式化

Litter decomposition is the key process of the material geochemical cycles in forest ecosystems. It is closely related to the accumulation of bioaccumulative organic pollutants in the soil. The accumulation of pollution in ground surface over Southwest China, an ecologically sensitive area, may pose a potential threat to the local natural environment, rare animals and plants, and even economic development. The project is about to carry out in situ field experiments on bioaccumulative organic pollutants release during litter decomposition by isotope labelled passive exchange meters. The emission characteristics will be illustrated. Based on pollutants leaching and volatilization fluxes and their correlation with environmental factors, a litter module will be constructed and incorporated into a traditional multimedia environmental model. The contribution of forest litter in the geochemical cycle of bioaccumulative organic pollutants will be explored via the sensitivity and scenario analysis. Focusing on the surrounding pollution sources, vast expanse of forest and rapid turnover of litter in Southwest China, the program will provide scientific reference for ecological risk control and development of agriculture and forestry.

凋落物分解是森林生态系统中物质周转的核心环节，与生物累积性有机污染物在土壤中的累积息息相关。我国西南地区属于生态敏感地带，地表污染累积对当地自然环境、珍稀动植物乃至经济发展造成潜在威胁。本项目拟利用同位素加标的凋落物被动交换器进行凋落物分解介导的生物累积性有机污染物释放的野外原位实验，阐明其释放特征；根据污染物下渗和挥发通量特征及其与环境因子之间的联系构建相应模式，将其耦合在传统的多介质模型中；利用灵敏性和情景分析探讨森林凋落物在生物累积性有机污染物的地球化学循环过程中的贡献。本研究针对西南周边污染源众多、森林广袤、凋落物周转快速的特点开展相应研究，以期为生态风险管控和农林业开发提供科学参考。

凋落物分解是控制生物累积性有机污染物进入土壤储库的重要环节。本研究基于同位素加标的凋落物被动交换器进行了西南地区三种典型树种凋落物中生物累积性有机污染物释放的野外原位实验，发现凋落物呈现指数衰减特征，污染物释放也出现由强转弱的趋势。其释放速率与目标化合物和凋落物自身性质有关。周转较慢的凋落物可能形成一定规模的污染储库。基于逸度方法，本研究构建了凋落物分解模块，将其耦合至污染物的多介质模型(GhnPERM-veg)。以PCB-153为代表，对比不同种类森林的渗滤、储存、降解通量，发现常绿阔叶林的PCB-153的降解和渗滤显著高于其他森林，平均是常绿针叶林、落叶阔叶林、落叶针叶林的3倍以上。空间上，低纬度森林PCB-153随凋落物进入地表的通量更高。由于森林过滤效应的存在，西藏南部和四川北部PCB-153的残留量降低。有森林情境下南亚的大气PCB-153传输量下降了29%、东南亚下降55%、中西亚下降41%，总传输量减少31%，对减少污染长距离迁移起到了重要作用。值得注意的是，目前有证据表明位于西南边境的青藏高原已经出现了有机磷阻燃剂，PCB-11等多种新型生物累积性污染物污染或者大气输入西南的证据。低温度森林可以降低污染向我国的传输，让而森林表层凋落物在受到生物活动，如蚯蚓或采蘑菇等影响，可能会形成短期的污染排放事件。