变化环境下荒漠草原型小流域水文过程演变与植被生态最优性表现的响应机制

Grasslands are green ecological barriers for conservation of water sources and maintenance of carbon and nitrogen cycles in northern China. As fragile water-limited ecosystems, arid desert grasslands have dry climates and inadequate water sources with strong rainfall fluctuations, high soil moisture variability and frequent human interference, resulting in complex hydrological processes. In addition, changes in hydrological processes exert significant influences on distribution and succession of vegetation communities, vegetation net primary productivity and water use efficiency. During the hydrological processes of arid desert grasslands, various elements are unknown; soil moisture heterogeneity, occurrence and development conditions of subsurface flows as well as their migration patterns are unclear; the ecological optimality of grasses to environment collaboration is to be revealed. Accordingly, small watershed hydrological processes were investigated to quantify rainfall - evapotranspiration - infiltration - runon - runoff to analyze effective rainfall and soil moisture migration patterns; responses of the ecological optimality of vegetation to hydrological processes were characterized to determine the range of soil moisture threshold for changes of dominant vegetation communities; hydrological processes were simulated based on the eco-hydrological model of ecological optimality distribution to further predict small watershed eco-hydrological processes under climate change and further degradation, which has important significance for vegetation restoration and reconstruction of damaged arid desert grassland ecosystems, biodiversity conservation, sustainable management and regulation of water resources and sustainable development of regional social economy.

草原是我国北方涵蓄水源、维持碳氮循环的绿色生态屏障。荒漠草原气候干旱，水资源匮乏，是水分限制型脆弱生态系统，降雨脉动性强，土壤水变异性高，加之人为干扰，导致水文过程复杂化，而水文过程的改变又会对该区植被群落分布与演替、植被初级生产力及水分利用效率等产生显著影响。荒漠草原水文过程各环节要素不明了；土壤水分异质性、壤中流的发生发展条件及其运移规律尚不明晰；草原禾本植物对环境协同生态最优性表现尚待刻画。据此研究其小流域水文过程，将降雨-蒸散发-入渗-产流-汇流定量化，分析有效降雨与土壤水运移规律；研究植被生态最优性对水文过程响应的刻画，确定植被优势群落变化的土壤水阈值区间；利用生态最优性分布式生态水文模型进行水文过程模拟，进一步预测气候变化与植被退化下小流域生态水文过程。对荒漠草原受损生态系统植被恢复与重建、生物多样性保护、水资源可持续管理与调控及区域社会经济可持续发展具有重要意义。

草原是我国北方涵蓄水源、维持碳氮循环的绿色生态屏障。荒漠草原气候干旱，水资源匮乏，是水分限制型脆弱生态系统，水文过程复杂又与植物群落生态特征之间相互作用显著。据此本项目研究其小流域水文过程，将降雨-蒸散发-入渗-产流-汇流定量化，分析降雨与土壤水运移规律，研究植物生态最优性表现对水文过程响应的刻画，模拟预测气候变化与植物退化下小流域生态水文演变。研究得出蒸散量受到降雨补给的影响程度远大于群落差异的影响程度；小流域植物生长季（4月15日-9月15日）蒸散比介于92%—94%，降雨的补给绝大部分用来提供植物生长的耗水；小流域径流系数（α）与坡度（i）及群落盖度（C）的关系式为：α = -62.26C+2.472i+15.775；当雨强为20mm/h至60mm/h之间时，降雨历时60min后，土壤水分入渗深度在20cm以内，说明该区土壤水分入渗速率较低，降雨产流为超渗产流，场次降雨后一周内土壤水分入渗深度基本在20cm以内；建立了上东河小流域的水量平衡方程，分析得出小流域降雨补给主要用于植物群落的蒸散发，3个年份的降雨深层渗漏量介于9.8-19mm之间；降雨梯度对植物的比叶面积产生影响，增雨后地下生物量总体呈增加趋势，根系体积也随着增雨呈增加的趋势；运用SWAT模型模拟了荒漠草原塔布河流域径流过程，模型参数多次校验后相对误差、Nash-Sutcliffe效率系数和相关系数分别为-12.6%、0.75和0.78，SWAT模型能够较好的模拟预测荒漠草原内陆河径流过程。本项目研究对荒漠草原受损生态系统植被恢复与重建、生物多样性保护、水资源可持续管理与调控及区域社会经济可持续发展具有重要意义。