荒漠绿洲湿地盐分累积过程及其水热驱动机理

Wetland is an important part of inland river basin in arid regions of Northwest China, and soil salinization in wetland has been become a serious threat to the stability of oasis ecosystem and the development of agriculture. The accumulation of soil salinity occurs as a result of changes in the process of exchange between water and energy. Therefore, a deep investigation on the process of exchange between water and energy has vast importance to the research work about driving mechanism of salt accumulation in desert-oasis wetland. In this project, a case study on the shrub, swamp and meadow wetlands will been conducted to intensively discuss the dynamic characteristics and distribution pattern of the salinity in arid regions of Northwest China. Based on stable isotope analysis, combined with micro-meteorological method, we will accurately distinguish between plant transpiration and soil evaporation, determine the main sources of water and salt, and quantify the contribution rates of precipitation, evapotranspiration, groundwater and surface water to salt accumulation. The project will further analyze the control effects of water and energy gradient on the salt movement, and discuss the influences of water and energy to the salt movement in desert-oasis wetland. As a result, we will establish coupled models on water-energy-salinity, clarify the driving mechanism of water and energy in the accumulation process of soil salinity, which can provide the theoretical basis for the management, salinity control and revegetation at desert-oasis wetland in arid regions of Northwest China.

荒漠绿洲湿地是干旱区内陆河流域的重要组成部分，其土壤盐碱化严重威胁着干旱区绿洲稳定和农业发展。土壤盐分累积过程是水分运移和热量传输过程发生变化的结果与产物，因此深入探讨水热传输过程对荒漠绿洲湿地盐分累积的驱动机理研究具有重要意义。本项目以河岸灌木湿地、沼泽湿地和草地湿地为例，深入研究荒漠绿洲湿地盐分动态变化特征与时空分布格局；基于稳定同位素技术，结合微气象法准确区分植物蒸腾和土壤蒸发，确定湿地水盐来源并量化降水、蒸散发、地下水和地表水对土壤盐分累积的贡献率；分析水热梯度对盐分运移及其分布格局的控制作用，探讨湿地水热过程对盐分运移的影响；建立水热盐运移的耦合数值模型，阐明土壤盐分累积过程的水热驱动机理，为荒漠绿洲湿地管理、盐碱化治理和植被恢复提供科学依据。

湿地是干旱区内陆河流域的重要组成部分，湿地土壤盐碱化严重威胁着干旱区绿洲生态系统的稳定和农业发展。土壤盐分累积是水热传输过程发生变化的结果与产物，因此深入探讨水热传输过程对荒漠绿洲湿地盐分累积的驱动机理具有重要意义。本项目在黑河中游选取典型河岸灌木湿地、沼泽湿地和草地湿地作为研究区，通过水热盐长期定位监测，土壤水热参数野外测定，水化学与氢氧同位素实验室分析以及Hydrus模型模拟等实验手段；应用氢氧同位素示踪、波文比-微型蒸渗仪区分蒸散以及水热盐模型模拟等关键技术探讨荒漠绿洲湿地水热驱动下的盐分累积机理。研究表明：1)湿地多年平均降水125.3 mm，蒸散量587.5 mm，土壤水变化量为-12.5 mm，补给量为474.5 mm；在能量分配中，感热占50.42%，潜热占40.56%，地热流占9.02%；河岸湿地的地下水位和土壤盐分分别为85.4±5.4 cm、29.80 g/kg，盐沼湿地则分别为129.7±15.1 cm、63.64 g/kg。2)湿地水分主要来源于地下水和河水，且地下水占比超过60%，降水对湿地水分贡献较小且降水对地上生产力的贡献随着地下水位的降低逐渐减小；湿地水化学类型为SO42--Na型，阳离子均以Na+为主，阴离子以SO42-为主，阴离子浓度大小顺序为SO42->Cl->HCO3-，阳离子浓度大小顺序为Na+>Ca2+>Mg2+>K+。3)湿地土壤呼吸速率、总硝化速率与反硝化速率的季节变化均呈单峰变化趋势，且表层土壤温度和土壤电导率是影响湿地土壤呼吸的关键因子；总硝化速率与反硝化速率与土壤含水量、温度呈显著正相关，与盐分含量呈负相关；水分利用效率为：河岸湿地>荒漠湿地>草地湿地>湖泊湿地，光能利用效率为：湖泊湿地>河岸湿地>荒漠湿地>草地湿地。4)湿地表层水热盐运移规律较深层复杂，净辐射对荒漠绿洲湿地土壤水热盐影响较大；降水与蒸散的相互作用是河岸湿地的脱盐和积盐过程的影响因素，盐沼湿地的盐分累积是地下水、蒸散和降水的综合作用的结果。研究成果将为荒漠绿洲湿地管理、盐碱化治理和植被恢复提供科学依据。