河口区DOM生物可利用性的时空演变及其调控机制

The biolability of dissolved organic matter (DOM) is a key scientific issue in global carbon cycle. In the estuarine critical zone, the spatial and temporal variations of the biolability of DOM and their major biogeochemical controlling factors are still unclear. This is due to the quite different properties of multiple allochthonous and autochthonous sources of DOM discharging into this dynamic system, and the complex biogeochemical processes between river-sea, sea-atmosphere interfaces and the submarine groundwater-seawater reaction zone. The Jiulong River Estuary is a suitable place for studying such issues as it is highly coupled with its watershed and is also strongly influenced by rainstorm events. In this project, the chemical properties and the biolability of DOM from different sources (terrestrial river discharge, atmospheric deposition, submarine groundwater discharge and in situ biological production) into this estuary will be characterized comprehensively by spectroscopy, stable isotopic analysis and chromatography. The effect of differences in sources and chemical compositions on the lability of DOM will be analyzed and the fluxes of DOC, labile DOC (LDOC) and refractory DOC (RDOC) into the estuary will be estimated based on long-term monitoring data. The DOM properties and its biolability between normal and rainstorm event conditions will be also compared. These results will provide the scientific basis for better understanding the influence of natural and anthropogenic perturbations on the biolability of terrestrial DOM, and to better evaluate the ecological role played by allochthonous DOM. It will also be helpful for the estimate of the long-term storage of terrestrial DOM in coastal environments.

溶解态有机物（DOM）的生物可利用性是全球碳循环研究的关键科学问题之一。在河口临界带，由于DOM来源多样，各种界面过程复杂，陆-海相互作用中从源到汇的DOM 生物可利用性的时空演变及其关键控制过程尚不清晰。本研究选取暴雨频发、与流域高度耦合的九龙江河口为研究对象，综合运用光谱学及稳定同位素、色谱分析等多种表征手段，研究输入到该河口区的陆地河流、大气干湿沉降、地下水及自生源DOM的化学特征和生物可利用性，探讨来源和化学组成差异对DOM生物可利用性影响的化学机理，估算各种来源的DOM通量及其中活泼与惰性组分的相对贡献，并对比常态和暴风雨条件下流域-河口-近海系统DOM化学组成与生物可利用性的变化。通过上述研究，为评价外部自然及人为扰动对陆源DOM 生物可利用性的影响提供科学依据，揭示河口与近海的微生物对DOM 的利用与转化，评估陆源DOM 入海后的环境生态效应及其长期储存潜力。

本项目以河口区DOM的生物可利用性及其关键控制过程为主线，选取九龙江口和长江口作为主要研究区域，系统探讨了河流、大气干湿沉降和海底地下水等外源DOM的化学特征和生物可利用性。结果发现，九龙江和长江输送入海的DOM的生物可利用性总体较低，特别是长江输送入海的DOM尤为惰性，这种差异与流域背景、水循环过程（暴雨事件）及河流内部改造等因素有关。与地表水相比，地下水中的DOM总体上更为惰性，因此通过海底地下水排泄途径进入海洋的DOM生物可利用程度不高。但是，通过大气沉降途径进入厦门湾的雨水却具有非常高的生物可利用性，其活泼DOC占DOC总量的相对百分比高达47±17%。通量估算表明，通过湿沉降输入海洋的活泼DOC通量基本与河流途径相当。因此，大气沉降途径对河口近海的次级生产过程有重要影响，而河流途径对海域有机碳的长期储存有更大贡献。在青藏高原冰川中开展的对比研究也发现，大气沉降途径是冰川中有机质的重要来源，而冰川DOM的生物可利用性也非常高，反映出大气有机质在组成和结构上的特殊性。此外，水母代谢释放的自生源DOM和污染湿地中的DOM也具有较高的生物可利用性，因此水母暴发和污水排放对近海及污染水域的碳循环过程也有重要影响。