河岸带地下水营养元素和有机质变化及与洪水的响应关系研究

Relationship Between Groundwater Quality Index of Nutrition Element and Organic Matter in Riparian Zone and Water Quality in River

河岸带地下水和河水存在复杂的交互作用,地下水和地表水存在明显的补排关系,洪水事件是影响河岸带地下水水质波动的重要水文过程.以黄河湿地国家级自然保护区孟津湿地为研究对象,通过河岸带地下水营养元素指标(特别是小浪底水库调水调沙期间)野外定位观测,深入分析了河岸带地下水水质变化及其与洪水的响应关系.结果表明,河岸滩区的农业开发存在明显的氮、磷下渗流失风险.临近河岸的农耕旱作区,是河流与人工湿地之间一个特殊的氮污染物控制单元,对地下水和河流之间的氮迁移隔离起着极为重要的作用.在人工湿地,农家粪作为底肥加入可能是磷下渗流失的重要源头,进入地下水中的磷顺着水力坡度还发生着显著的横向迁移,尤其在调水期横向迁移更加明显.河岸滩区的开发类型及其耕作制度对地下水的硝氮含量产生重要的影响.在鱼塘区,常年的土壤厌氧环境加重了氮的下渗迁移和积累;在荷塘区,春夏季节,土壤淹没呈厌氧环境,氮迁移和硝化作用显著,在秋冬季节,土壤呈好氧环境,氮硝化作用显著发生,全年氮达到相对平衡的状态;距离河岸50～200 m之间氮的硝化-反硝化作用强烈,是一个高效的微生物氮净化单元.人工湿地施用的农家粪是有机物流失的重要源头,河岸滩区土壤质地呈沙性,渗透能力强,土壤保水保肥能力差,在此区进行农业活动,尤其是人工湿地开发中大量施用肥料,容易造成土壤表层有机质和氮磷养分因灌溉而导致的下渗流失,进而污染地下水与河水,较由降雨引起的地表径流流失显得更为突出.距离河道50～200 m的范围是重要的污染净化单元,为典型的滩区地下水-河流的水陆交错带.该区域的合理保护,对于保护河流水质和地下水水质十分重要.

Riparian zone hydrology is dominated by shallow groundwater with complex interactions between groundwater and surface water.There are obvious relations of discharge and recharge between groundwater and surface water.Flood is an important hydrological incident that affects groundwater quality in riparian zone.By observing variations of physical and chemical groundwater indicators in riparian zone at the Kouma section of the Yellow River Wetland,especially those took place in the period of regulation for water and sediment at the Xiaolangdi Reservoir,relationship between the groundwater quality in riparian zone and the flood water quality in the river is studied.Results show that there will be great risk of nitrogen,phosphorus,nitrate nitrogen and organic matter permeating into the groundwater if floodplain changes into farmland.As the special control unit of nitrogen pollution between rivers and artificialwetlands,dry farming areas near the river play a very important role in nitrogen migration between river and groundwater.Farm manureas base fertilizer may be an important source of phosphorus leak and loss at the artificial wetlands.Phosphorus leaks into thegroundwater and is transferred along the hydraulic gradient,especially during the period of regulation for water and sediment at theXiaolangdi Reservoir.The land use types and farming systems of the riparian floodplain have a major impact on the nitrate nitrogencontents of the groundwater.Nitrogen can infiltrate and accumulate quickly at anaerobic conditions in the fish pond area,and theannual nitrogen achieves a relatively balanced state in lotus area.In those areas,the soil is flooded and at anaerobic condition in spring and summer,nitrogen infiltrates and denitrification significantly,but soil is not flooded and at aerobic condition in the autumn andwinter,and during these time,a significant nitrogen nitrification process occurs.In the area between 50 m and 200 m from the riverbank,which is the efficient microbial nitrogen purification unit,nitrification-denitrification is intensive.Farm manure is an importantsource of organic matter loss at the artificial wetlands.Floodplain has sandy soil texture,with high infiltration capacity and low waterand fertilizer conservation ability.Such features are prone for the loss of surface soil nutrition and organic matter if agricultural activitiestaken place in these areas change the land use of wetlands and apply extensive fertilizer.The infiltrated nutrition elements and organicmatter can pollute the groundwater and the river.Compared with the losses of nutrition element and organic matter caused by surfacerunoff,the infiltrated process is even more prominent.As typical floodplain groundwater-river ecotone,the area between 50m and 200mfrom the river bank is a momentous pollution purification unit.Rational protection for this region is critical for the conservation of waterquality in the river and groundwater.