三江源地区河流生源物质的迁移及其通量变化规律

The Three Rivers’ Headstream Region, where the Changjiang River, Lancang River and Huanghe River originate from, is a large area with high sensitivity to environment changes. The effects of global change and hydropower development determine the designation of the multi-objective for the water resource utilization and environment protection. One of the basic scientific issues for the knowledge of the aquatic environment and its potential change caused by development of dam construction is to study the transport of the nutrient substances and changes of their fluxes. The present project will select the Three Rivers’ Headstream Region as study area. About 100 rivers will be surveyed during summer. The particle and dissolved nitrogen, phosphorus and organic carbon will be analyzed, as well as the water flux will be recorded. The topographic partition of watersheds of major rivers such as Tuotuohe River, Chumaerhe River, Beiluhe River, will be created using digital elevation models. The regression analysis will be employed to explore the relationship between nutrient substances concentrations and water fluxes. The area of watershed, vegetation types will be used to calculated to ascertain the contribution of vegetation types and areas to the nutrient substances fluxes. Typical watersheds in permafrost regions will be selected to monitor the water-heat processes continuously, and further used to study the possible effects of changes of permafrost conditions on nutrient concentrations and its possible mechanisms. Based on these result, the vegetation changes under global change scenarios will be modeled and further were used to assess the possible effects on nutrient substances. In addition, the possible changes of permafrost will be modeled using permafrost model and the vegetation changes will be modeled with the bio-climatic parameters provided by IPCC using decision tree rules, and future the possible effects on dissolved organic carbon, nitrogen and phosphorus will be evaluated. The present project will provide the basic information for the temporal and spatial transport and fluxes of nutrient substances, and also will be helpful to understand their possible changes in the future.

三江源地区河流生源物质浓度及通量变化是西南水电开发和水环境保护必须要考虑的重要因素。本项目以该区域为研究对象，对其境内约100条河流进行逐月采样，分析颗粒态和溶解态碳氮磷的含量，同步测定流量，研究生源物质含量的时空变化及其与流量的关系；选择主要河流如沱沱河、楚玛尔河、北麓河，通过数字高程模型划分流域范围，通过回归分析，以对应流域中植被和多年冻土为环境变量，建立生源物质浓度与植被及多年冻土的定量关系；选择典型的多年冻土区域,同步测定水热过程变化,研究多年冻土变化对水体生源物质浓度的影响及其机理;利用决策树方法和多年冻土模型，根据IPCC提供的未来变化情景，分析未来植被和冻土的变化，进而根据冻土、植被和生源物质浓度的定量关系，计算生源物质的变化。本研究可揭示三江源地区河流生源物质迁移和通量的时空规律，为西南水电开发和水环境保护提供科学依据，并有助于了解未来情景下该地区河流生态系统的可能变化。

本项目对三江源地区的陆地和河流生态系统的碳氮进行了研究。研究了高寒沼泽草甸、高寒草甸、高寒草原、高寒荒漠和裸地几种植被覆盖类型下土壤及对应河流中碳氮磷浓度变化特征；探讨了流域面积、流量大小与河流碳氮磷浓度的相互关系。主要结论如下：.1）三江源地区中，土壤碳氮磷浓度与植被类型密切相关，沼泽草甸和草甸最高，荒漠草原和裸地最低。不同环境因子之间存在着复杂的相互作用关系，其中土壤质地解释的方差最大。地形因素及多年冻土也对土壤碳氮含量有着重要的影响。在三江源地区，不同的植被类型对于气候变化的呈类似的变化响应。.2）不同植被类型下河流DOC的浓度存在较大的差异且与土壤有机碳含量相一致。河流DOC含量依次为高寒沼泽草甸>高寒草甸>高寒草原>高寒荒漠和裸地；河流DOC浓度与流域内高寒沼泽草甸覆盖的比例呈显著正相关，而与高寒草原、高寒荒漠和裸地覆盖面积比例显著负相关；流域内植被覆盖率越低，河流DOC浓度越小，土壤侵蚀越严重，河流pH值越高；河流DOC浓度与采样点的流量及流域面积呈显著负相关关系，表明在输移过程中，河流DOC的部分活性碳被快速分解，导致其浓度下降。.3）在青藏高原三江源多年冻土区，流域内的植被类型是影响河流生物可利用溶解性有机碳（BDOC）浓度的主要因素。在不同植被类型之间，高寒草甸和高寒沼泽草甸为主的流域内河流BDOC浓度较大，高寒草原和裸地覆盖面积比例较高的流域内，河流BDOC浓度较小。在不同的植被类型之间，DOC可降解程度（BDOC%）的变化范围在11.72%~23.66%，且与DOC和BDOC的含量正相关。.4）总体而言，三江源地区DOC的浓度(四分位: 3.96-4.62 mg L-1)比环北极地区(通常 >10 mg L-1)要低，溶解总氮和总磷(四分位: 1.07-1.12 mg N L-1, 0.037-0.040 mg P L-1)浓度则高于环北极地区s (0.77 mg N L-1, 0.01 mg P L-1)。单位面积的输移方面，碳的输移量低，而氮的输移量与环北极地区相当。气温与DOC的浓度正相关，但是碳氮磷的输移都取决于流量。在气候变化会导致三江源的地区更暖更湿更绿的背景下，三江源地区的碳氮磷输移会呈增加趋势。