荒漠绿洲湿地水分补给过程及其对水环境演变的影响机制

In inland river basins of arid regions in Northwest China, ecological water transport and water saving irrigation can lead to the fundamental changes of water recharge and exchange process in desert oasis wetland, which has been become a main factor causing many ecological and environmental issues such as aggravation of wetland salinization and water pollution. Ion-exchanges of various water sources are the root causes of hydro-chemical characteristics, differences of isotopic compositions and evolvement of water environment in wetlands. Therefore, studies on the process of water recharge and evolution mechanism of water environment are of great significance to solve the problems of land salinization and water pollution in desert oasis wetlands. By using the methods of long-term field location and control experiments, hydro-chemical measurement, multi-isotopic analysis and simulations of water quantity and quality coupling models, this project will take the desert oasis wetland in arid areas as research object and focus on the following four research parts.. (1) The processes of water recharge, exchange between groundwater and surface water and the characteristics of water balance will be studied in depth.. (2) The contributions of water sources on water recharge in desert oasis wetland will be discussed. . (3) The sources and mixing processes of chemical components and their influencing mechanism on the evolvement of water environment will be clarified. . (4) The coupling models of water quantity and quality will be established to predict the evolution tendency of water environment in wetlands under uncertain sources of water and pollution.. These research work can provide scientific basis for the protection of water environment and ecological security in desert oasis wetland in Northwest China.

西北内陆河流域实施的生态输水、灌区节水等工程导致荒漠绿洲湿地水分补给与交换过程发生根本改变，引起湿地盐碱化加重和水环境污染等生态环境问题。各种水分来源的离子混合作用是湿地水化学类型、同位素组成差异及其水环境演变的根本原因。因此，研究水分补给过程和水环境演变机制对解决荒漠绿洲湿地盐碱化和水环境污染具有重要意义。本项目以干旱区荒漠绿洲湿地为研究对象，通过长期定位试验、野外控制试验、水化学测定、多元同位素分析以及水量-水质耦合模型模拟等方法深入研究水分补给、地表水-地下水交换过程及其水量平衡特征，探讨水分来源对荒漠绿洲湿地水分补给量的贡献，阐明化学组分来源、混合过程及其对水环境演变的影响机制，构建水量-水质耦合模型预测水分来源和污染源不确定条件下湿地水环境演变趋势，为荒漠绿洲湿地水环境保护和生态安全保障提供科学依据。

本项目以张掖国家湿地保护区临泽县境内河岸灌木湿地和绿洲草地湿地为研究对象，通过长期野外定位观测实验、水化学、亮蓝为染色剂进行野外染色示踪实验、挖掘法、野外双环连续入渗实验等研究方法，应用CT扫描技术与图像处理相结合、Hydrus-1D模拟土壤入渗、ET-watch模型模拟蒸散量等关键技术，探讨荒漠绿洲湿地水分补给过程及其对水环境演变的影响机制。研究表明：（1）荒漠绿洲湿地相邻景观单元土壤养分，土壤养分总体上均呈现从湿地到戈壁逐渐降低的变化趋势。总体上，土壤盐分中阴离子以SO42-、Cl-为主，阳离子以Ca2+、Mg2+、Na+为主，HCO3-和K+含量较低，土壤电导率、光学溶解氧、氧化还原电位和荧光可溶性有机物呈现随地下水位的降低而逐渐减小的变化趋势。（2）在荒漠绿洲湿地，柽柳灌丛和盐碱草地水流入渗深度较深，杨树群落和道路较浅。随土壤深度的增加，不同植被类型土壤剖面染色面积比波动变异程度均呈现先增大再减小的趋势，但波动变异程度存在显著差异。（3）盐沼湿地和河岸湿地的主要离子类型分别为Na+-Ca2+-SO42--Cl-。古寨湿地和黑河湿地主要离子浓度均随着土壤深度的增加而显著降低，但在60-100 cm土层深度处没有显著差异。在盐渍化过程中，干旱湿地中的盐分积累有利于STC、STN和STP的增加，这种变化增强了湿地作为C、N和P(尤其是C)的汇的功能。（4）荒漠绿洲湿地土壤孔隙各向异性大小依次为：盐碱草地(0.545±0.061)>杨树林(0.548±0.042)>柽柳灌丛(0.564±0.042)>道路(0.581±0.052)。（5）在荒漠绿洲湿地，土壤根系长度总体呈现随土壤深度增加呈现波动下降的趋势，但在50-60 cm土层杨树林根系长度出现急剧的增加。（6）土壤水分下渗速率大小为杨树林>柽柳灌丛>盐碱草地>道路。（7）总体来说，黑河下游尾闾区湿地植被和湖泊蒸散发量表现出先增大后降低的变化趋势。