基于水土保持的流域生态环境需水研究

Study on Eco-environmental Water Requirement of Drainage Basin Aiming for Water and Soil Conservation

针对现有生态环境需水量的计算主要基于现状而导致其实用性不足的特点,提出了根据流域或区域对生态环境功能的需求来确定其生态建设规模并计算其生态环境需水量的思想。以位于黄土高原的安塞纸坊沟流域为例,针对该流域以水土流失为首要生态环境问题的特点,在已有的土壤侵蚀与土地利用结构关系研究的基础上,基于水土保持目标确定土地利用结构,进而计算出该流域的生态环境需水量,并对不同土地利用情景以及不同水土保持目标进行了对比分析。研究表明,综合考虑水土保持效益与生态环境用水代价,纸坊沟流域以允许土壤流失量1 000 t/(km2.a)为目标为宜,此时该流域生态环境需水量约为1.77×106m3,占该流域年降水总量的39.0%。通过与基于生态系统现状的计算结果相比较,说明提出的思想更为合理。

Usually the calculation of eco-environmental water requirement （EWR） is based on the status quo of ecosystems in most researches, thus leading to little practicability to water allocation practice. Therefore, this paper advanced an idea based on the calculation of EWR on a proper ecosystem status determined by the demand of a region or a watershed for eco-environmental functions and services. Zhifanggou watershed, which is located in Ansai county on the Loess Plateau and suffering from serious water and soil loss, was chosen as the study area. Based on the existent study of the relationship between soil erosion and land use structure, the land use structure of Zhifanggou watershed was determined according to the objective of water and soil conservation, and then the EWR of Zhifanggou watershed was calculated according to the determined land use structure. EWRs corresponding to different scenarios of land use structure and different objectives of water and soil conservation were compared and discussed. The result shows that the proper objective of water and soil conservation for Zhifanggou Watershed is 1000 t/（km^2 · a） of soil loss tolerance, and the corresponding EWR is 1.77×10^6m^3, which occupies 39.0% of the total annual precipitation. By the comparison between the calculation result based on the status quo of ecosystems and that of ours, our idea was proved more practical.