榆神矿区地下水和干旱指数对植被耗水的联合影响

Joint effects of groundwater and aridity index on the transpiration of vegetation: A case study in the Yushen mining area

为研究干旱矿区地下水位下降和气侯变化对典型植被耗水的联合,选择榆神矿区优势植被沙柳为研究对象,以干旱指数表征气候变化,在野外调查、室内测试及原位试验的基础上,采用有限元算法分析不同地下水位埋深和干旱指数组合条件下的植被耗水特征。研究结果表明:植被生长受干旱指数和地下水位埋深的双重影响,当地下水埋深为1.0～2.0 m处,植被耗水主要受地下水控制;地下位水埋深为2.0～2.5 m时,植被耗水受地下水和干旱指数的双重影响;地下水位埋深大于2.5 m时,植被耗水主要受干旱指数影响;单指数模型可以很好的拟合地下水埋深和植被实际蒸腾量(T_a)与潜在蒸腾量(T_p)比值(T_a/T_p)的关系曲线,其相关系数高达0.99,利用单指数模型和T_a/T_p的比值可以反求出枯水年、平水年和丰水年条件下的植被生态临界地下水位,不同水文年的植被生态临界水位有差异性,认为当地下水位埋深大于1.24 m(平均),植被生长受到水分胁迫,当地下水位埋深大于2.06 m(平均),植被出现退化现象;同时,采煤引起地下水位下降对植被生态的影响是有限的,只有当采前地下水位埋深为1.0～2.5 m时,地下水位下降才会引发植被生态退化;当采前地下水位埋深大于2.5 m时,采煤引起地下水位下降基本对沙柳的生长不产生影响,此时植被生态退化主要受气候变化影响。目前,榆神矿区采前地下水位埋深普遍大于2.5 m,影响矿区生态环境的主要控制因素是气候变化(降水量),考虑到近年来榆神矿区降水量有增大趋势,因此出现"虽然地下水位明显下降,但是生态环境局部转好"的现象。

Hydrus-1D software was used to simulate the joint influences of groundwater and aridity index on the transpiration of Salix psammophila based on field investigation,laboratory test and in-situ test.The results showed that the transpiration receives joint influence from the groundwater and aridity index.The transpiration is mainly controlled by groundwater when the water table depth is 1.0-2.0 m,and controlled by groundwater and aridity index when the water table depth is 2.0-2.5 m,but only controlled by aridity index when the water table depth is more than 2.5 m.The monoexponential decay function can fit the cave between the groundwater and T a/ T p,whose correlation coefficient is above 0.99.On this basis,the critical water table depths are determined in normal,low and high flow year.The critical water table depths vary in different hydrological years and the vegetation will suffer from water stress when the water table depth is more than 1.24 m (average),and degenerate when the water table depth is more than 2.06 m (average).Meanwhile,the effects of the decline in the water table caused by coal mining on the transpiration of typical vegetation is limited.The decline in the water table caused by coal mining has effect on vegetation when the initial pre-mining water table depth is less than 2.5 m.However,there has little effect on vegetation when the initial pre-mining water table depth is more than 2.5 m,the transpiration is only controlled by climate change at this moment.At present,the main factor that affects the vegetation coverage is climate change (precipitation) because the initial pre-mining water table depth is generally greater than 2.5 m in Yushen mining area.Therefore,the vegetation coverage increases although the water level decreases obviously considering the increasing trend of precipitation in recent years.