华北平原不同类型农田深层包气带水盐运移及其对地下水影响机理研究

Irrigated agriculture has leaded to continuous water table decline and a large amounts of slats accumulated in the deep vadose zone, which even has caused local groundwater contamination in the North China Plain. Investigation of the downward water movement and solute accumulation and transport in the deep vadose zone under croplands is essential for clarifying the impact of various irrigated agricultural land-use types on groundwater quantity and quality. However, current studies focus on the related process only in winter wheat and summer maize land, ignoring the other four agricultural land-use types (summer maize land, orchards, cotton land and vegetable land) that account for 40% of area of the agricultural lands. Therefore, the project intends to carry out in situ observations on soil water content and matric potential and soil sampling in the deep vadose zone and groundwater sampling under the above-mentioned four types of croplands. Based on observations, soil water dynamics in deep vadose zone will be illustrated and the rate of wetting front propagation will be estimated. Soil water budget and chloride will be used to calculate the soil water flux (groundwater potential recharge) and the average soil pore water velocity in the deep vadose zone. Then, the accumulation and leaching of salts in deep vadose zone and the salts in groundwater under different agricultural land-use types will be investigated. The lag-time of groundwater recharge (both water quantity and quality) will be further evaluated. From the perspective of groundwater recharge processes in deep vadose zone, the mechanism that agricultural land-use types impact on groundwater quantity and quality will be illuminated. The results of the study will broaden the knowledge of regional hydrological cycle and provide a scientific basis for sustainable groundwater management.

在灌溉农业影响下，华北平原地下水位持续下降，大量盐分累积于根系层以下的深层包气带，导致局部地区地下水严重污染。研究农田深层包气带水盐运移过程，是认识灌溉农业对地下水影响机理的重要前提。不同类型农田的深层包气带水盐运移过程存在较大差异。然而，当前的相关研究集中于冬小麦夏玉米农田，对占农田总面积近40%的其他类型农田（单季玉米农田、果园、棉田和菜地）关注甚少。本项目以华北平原地下水深埋区不同类型农田厚包气带为研究对象，开展水分定位监测，对包气带和地下水进行采样与测定分析，利用水量平衡法和氯离子示踪法，查明深层包气带水分运动速率、盐分累积与淋洗特征，分析不同农业土地利用类型对地下水盐分的影响，评估地下水位下降条件下地下水垂向补给（水量和水质）滞后时间，从地下水补给过程角度揭示农业土地利用类型对地下水水量和水质的影响机理。研究结果可深化对区域水文循环的认识，并为地下水资源可持续管理提供理论依据。

本项目以华北平原地下水深埋区（地下水位埋深大于10 m）不同类型农田（粮田、菜地、果园、棉田）的深层包气带水盐运移过程为研究对象，按计划完成了项目计划书的预定任务。通过本项研究，首次观测到40m厚农田包气带中的湿润锋传递过程，发现水分传导速度极快，湿润锋在7个月左右可达38m深处；农田区深层包气带水分维持在（或高于）田间持水量水平，为水分和盐分向下运移提供的良好的动力条件；估算了深层包气带水分通量、盐分累积与淋洗特征，发现深层包气带累积了大量的硝酸盐，粮、菜、果三种类型下最大值分别为6000、9000和23000kg/ha，远超以往的报道；部分蔬菜种植区的水分通量和盐分淋洗量最大、运移速率最快，已造成地下水硝酸盐污染；在其它大部分区域，由于包气带硝酸盐滞留时间长于40年，表明近几十年（1980s以来）大量施用的化肥尚未大规模地进入浅层地下水。.通过开展上述研究，不仅丰富并发展了地下水深埋区农田关键带水盐运移机理，而且进一步深化了对农业种植活动与地下水量质关系的机理认识。在本项目的资助下，共发表了SCI论文4篇、中文期刊论文4篇，先后组织和参加学术会议6次，培养博士研究生2名和硕士研究生1名。同时，依托该项目申请获得了河北省创新能力提升计划项目1项。综上，本项目已按计划完成，取得了预期成果。