放牧对荒漠化草原垂向水循环过程的影响与机制研究

Grazing is the most important development and utilization method of natural grassland, but overgrazing causes grassland degradation, surface soil infiltration rate decline and other underlying conditions to change, thus affecting the grassland water cycle evolution process. At present, how does desertification steppe change under the conditions of grazing and infiltration, soil water migration, recharge groundwater, and evapotranspiration ? What is the mechanism between hydrological cycle and grazing intensities, and the process of mutual collapse among various factors ? The study of these issues has not received enough attention. Therefore, this project quantitatively studies the characteristics of soil change of grassland vegetation in desertification steppe and hydrological cycle under different grazing intensity in order to find out the mechanism of grazing, vegetation and grassland water cycle in desertification grassland ecosystem, and simulates the process of hydrological cycle dynamics under different combinations of grazing intensity and rainfall, in order to predict the rainfall infiltration recharge and groundwater precipitation infiltration. Finally, through the assessment of groundwater rainfall infiltration recharge under different conditions, the reasonable carrying capacity of desertification grassland based on the coupling of water cycle and productivity will have been obtained.

放牧是天然草原最主要的开发利用方式，但过度放牧导致草地退化、表层土壤入渗率下降等下垫面条件改变，从而影响草地水循环演化过程。目前，荒漠化草原在这种放牧利用条件下降雨入渗、土壤水运移、补给地下水、蒸散发的转化过程如何变化？垂向水循环与放牧强度之间的作用机制及各因子之间的互馈过程如何？这些问题研究尚未受到足够重视。因此，本项目通过定量研究不同放牧强度下荒漠化草原区草地植被土壤变化特征和垂向水循环变化规律，阐明荒漠化草原生态系统中放牧、植被与草地水循环之间的作用机理；模拟不同放牧强度和降雨量组合条件下垂向水循环动力学过程，预测不同条件地下水降雨入渗补给量及地下水降雨入渗补给系数推求；最终提出基于水循环和生产力耦合响应的荒漠化草原的合理载畜量。

放牧是天然草原最主要的开发利用方式，但过度放牧导致草地退化、表层土壤入渗率下降 等下垫面条件改变，从而影响草地水循环演化过程。本研究针对荒漠化草原在不同放牧利用条件下水循环演化问题，采用原位控制试验及模型分析开展研究，具体结论如下：1、研究了不同放牧强度条件下草地植被和土壤的变化特征，研究结果表明随放牧强度增加，植被高度、盖度、地上生物量和地下生物量均有不同程度降低，表层土壤容重增加，表层土壤砂粒含量增加，导致表层土壤粗粒化；2、采用Hydrus-1D模型开展天然草地垂向水循环动力学过程模拟，揭示了不同放牧强度下各水循环分项变化，结果表明随放牧强度增加，植被截留量、土壤入渗量有所减少，增散发量变化不显著，分析可能由于植被腾发与土壤散发影响相互抵消造成；3、采用通径分析法分析了水循环过程分项变化的主要驱动因素分析，提出各分项量的直接影响因素、间接影响因素及决定性变量和限制性变量。4、针对典型家庭牧场，考虑人工草地灌溉及天然草地放牧对水循环过程的干扰，从地下水循环角度入手，在考虑饲草料质量的前提下通过人工草地和天然草地耦合配置，以现状水土草畜平衡评估结果为基础，提出了基于水循环和生产力耦合响应的荒漠化草原家庭牧场用水策略调整方案和合理载畜能力。