气候变化与土地利用对东江流域河流碳氮营养物浓度的影响

The Dongjiang River basin in the southern China shoulders the duty to provide water resources for big cities -- such as Guangzhou, Shenzhen and Hong Kong -- in the Pearl River delta. Climate change and human land-use activity without doubt affect land-surface ecological and hydrological processes as well as the formation of terrigenous carbon and nitrogen and their transportation to nearby rivers, which further impact the quantity and quality of available water resources. This explains why the quantification of effects of climate change and human land-use on land-surface ecological and hydrological processes as well as how the coupling between ecological and hydrological processes impacts the formation and transportation of terrigenous carbon and nitrogen are not only the key scientific issues and challenges in the field of environment and water resources but also the necessity for the sustainability of society and economy at the regional scale. The proposed study aims to assimilate different and multi-scale observational and laboratory data into mechanistic and distributed eco-hydrological model to explore (i) effects of climate change and human land-use in the Dongjiang River basin on its land-surface eco-hydrological processes and (ii) how the coupling between ecological and hydrological processes further affects the formation of terrigenous carbon and nitrogen and their transportation to nearby rivers. The novelty of the proposed study lies in (i) its dynamic simulation of terrestrial vegetation under climate change and its impacts on land-surface hydrological processes, and (ii) a full consideration of the coupling between land-surface ecological and hydrological processes. The successful fulfillment of the proposed study will lead to an improved understanding of mechanisms of coupling between land-surface ecological and hydrological processes in hot-and-humid region, a more accurate quantification of carbon and nitrogen budget in terrestrial ecosystems, and an enhancement of our ability to analyze and predict the dynamics of water and terrestrial ecosystems under climate change. Eventually, these improvements will build scientific basis for protecting the safety of water resources and terrestrial ecosystems as well as sustaining the development of society and economy in the Pearl River delta.

东江流域肩负着给珠三角州内城市及香港供水的重大任务。气候变化与土地利用势必影响陆地生态水文过程、陆源碳氮营养物的形成迁移，进而影响可利用水资源的数量。探讨气候变化与土地利用对东江流域生态水文过程的影响和两者之间的耦合如何影响陆源碳氮营养物的形成迁移不仅是当前资源环境研究面临的重点科学问题和挑战，也是区域社会经济发展的重大科技需求之一。本项目拟把多源和不同尺度的观测、实验分析数据融入机理性分布式生态水文模型来定量探讨东江流域气候变化与土地利用对流域生态水文过程和陆源碳氮营养物形成迁移的影响。本项目的创新点在于动态地模拟植被的时空变化对流域水文的影响和充分考虑陆地生态与水文过程的耦合对陆源碳氮营养物的调控。本项目的执行可增进我们认识陆地生态水文过程耦合的机理和改进对陆地碳氮通量的估算，提高我们分析和预测流域水与生态系统演变的能力，为区域水安全、生态安全以及社会经济的可持续发展提供基础理论。

当前人类面临着严重的水危机，水问题是影响社会经济发展的重大问题。陆地的生态过程与水文过程相互耦合，探讨气候与土地利用变化对河流碳氮营养物浓度的影响有助于我们深入认识陆地生态系统的功能和精确地估算区域碳氮平衡，具有重大应用和科学价值。. 本项目旨在探讨东江流域自然环境要素的变化特征；流域气候与土地利用变化对流域水文过程的影响；流域溶解性碳氮营养物的特征及与环境要素间的关系；气候与土地利用变化对溶解性碳氮的影响。. 研究发现：. 东江流域土地利用/覆被变化的空间差异明显，表现在上游耕地面积减少显著；相比较，中、下游用地的幅度逐渐增大。同自然要素比较，人口增长、城市化、技术革新和政府决策是造成土地利用和覆被变化的主要驱动力。其次，径流年内分配季节性明显，主要集中在4-9月份，年径流极值比下游小于上游。. 不同土地利用类型对流域水文过程的影响存在差异，按对流域实际蒸散量、产流量和蒸腾量贡献率大小排序依次是常绿阔叶林>草地>耕地。森林覆盖度的变化与年径流量变化呈强相关。此外，退耕还林能有效提高流域水源涵养的能力，对水土保持产生积极意义。. 河水有机碳、硝态氮的含量存在明显的空间差异。当河流位于人类聚集、活动频繁的子流域时，河水有机碳和硝态氮的含量都比较高。硝态氮浓度与耕地、建筑用地面积存在正相关关系。此外，硝态氮的含量具有周期性，其浓度6月达到峰值后下降，春季后又回升，这与流域内植被的净初级生产力变化相吻合。. 极端降水可改变土壤水分状况，加快有机氮的矿化、硝化反应速率，进而影响河水中硝态氮的浓度，且这种影响大于土地变化的影响。造成这种差异的原因可能是土地变化方案中，林地面积仍然占据流域总面积的80%以上，其他覆被类型占比小。. 总体来说，本项目所采集的河流碳氮营养物数据和发现极端降水能增加河水中溶解性碳氮的浓度，这提高了我们分析、预测和预报流域水生态系统演变的能力，也为区域水安全、生态安全提供基理论和科技支撑。