浅埋水位下降的温度效应及其对表生植被生态的影响

Water level declines of shallow groundwater table has induced the regional heat island effect in the arid and semi-arid areas, where air temperature is much difference by day and night. It not only leads to redistribution of water and heat on surface energy balances system due to forming soil dry layer and even accelerates regional climate change,in the meantime,the negative effects on the surface vegetatition eco-system has been caused. However, groundwater has a regulate and control function on surface temperature and soil temperature and influence on vegetation ecology has much more complex dynamic process. This project, bases on the porous media fluid dynamics theory and theory of thermodynamics. combines the laboratory physical experiment, in-situ monitoring with numerical simulation methods. The study area chooses groundwater ecosystem of bottomland in Ordos basin. In this project we will analysis the soil temperature and surface temperature variation trend because of groundwater level declines of shallow groundwater table, and discuss the methods of soil moisture and heat parameters under the condition of temperature changes, build water-heat coupled model on the unsaturated zones,analysis the indexes and quantitative assessment method of surface soil and surface temperature field change impact on vegetation ecological succession. This research result is not only beneficial supplement to the relationship between groundwater environment and regional climate change. And also has an important theoretical and practical application value to restoration the groundwater dependent ecosystems in arid and semi-arid areas.

昼夜温差大的干旱半干旱区，浅埋水位下降形成区域性"热岛效应"。地层的干化不仅导致地表能量、水分的再分配甚至局部气候改变，同时对依赖地下水生长的表生植被产生诸多不利影响。然而浅埋地下水对近地表温度、土壤温度的温度调控过程及其对表生生态的影响机理却十分复杂。本项目运用多孔介质流体动力学、热力学相关理论，采用室内物理模拟、原位定点监测及数值模拟等方法，选择鄂尔多斯盆地滩地地下水生态系统为研究区，分析浅埋水位下降引起的土壤温度及地表温度变化规律，探讨温度变化下土壤水分运移参数、土壤热属性参数的获取方法。构建非等温条件下包气带水热耦合动力学模型，揭示水位下降的温度效应与机制。研究土壤热量、水分改变对表生植被生态的影响指标体系与定量评价方法。该成果是对地下水环境与区域气候变化相结合研究的有益补充。对于修复旱区地下水生态系统，丰富生态水文地质学理论具有重要的理论和应用价值。

主要成果如下：1热传导对流法和谐波法计算结果表明，土壤热扩散率与水通量密度均随深度增加而增加。热传导对流法预测试验场地土壤热通量精度更高。2毛乌素湖盆滩地土壤饱和渗透系数随着土壤温度的升高不断增大。随着温度的升高均呈下降趋势，土壤水分特征曲线整体下移。土壤的非饱和渗透系数K(s) 随着温度的升高缓慢增大进而趋近稳定。利用赵贵章模型和Campbell模型能够较好模拟不同质地、含水率、温度下的导热率；获得土壤含水率和温度共同影响下的导热率模型，可以用于试验场地土壤热导率的预测。3降雨条件下, 降雨前温度梯度导致〖qVT〗和q_LT发散面和聚集面存在30至40cm之间，基质势梯度导致q_LH从潜水面向包气带运移；降雨中，白天q_VT为混合面，q_LT由混合面转变为向上的发散面，分别位于30和40cm处；晚上，q_LH受降水的作用向下运移， q_VT和q_LT受温度梯度影响恢复到降雨前。降水停止后的白天，q_VT和q_LT变为和前一天白天相同的混合面，q_VH和q_LH变为向上，晚上q_LT向下运移，q_VT的发散面存在30至40cm之间；蒸发条件下，凌晨到早上，q_VT和q_LT的发散面和聚集面在35至45cm之间，q_LH为位于10cm的聚集面，之后变为发散面；白天，q_VT为发散面，q_LT为聚集面，均位于30cm，q_LH和q_VH为从潜水面向上的发散面。4能量平衡方程中，净辐射通量、土壤热通量、潜热通量与水位埋深均呈负相关，感热通量与水位埋深呈正相关；感热通量与潜热通量受水位埋深影响的变幅要比净辐射通量以及土壤热通量的显著；随着地下水位埋深的增大对地表温度的调节能力减弱。5土壤温度与穗数的回归模型可以作为土壤温度对寸草苔生长的影响预测。试验场地上生物量与5 cm土壤温度，地下生物量与20 cm土壤温度负相关性最高。表层微生物总数相对最多，细菌在5cm处、固氮菌在20cm处与地下生物量相关性都较大。40cm处真菌与水位埋深有显著正相关，20cm处反硝化细菌与地下水位埋深呈正相关。6通过解析法（Vflux2）、数值法（VS2DH模型）、水动力学三种方法对比，温度传感器的精度，传感器间距都会对湖水-地下水垂向渗透速度评估结果有影响。湖床沉积物热量运移方式主要以热对流为主，热传导弥散作用相对很小。