干旱荒漠绿洲区不同土地利用类型浅层地下水硝态氮变化趋势

Trend of nitrate-N concentration in shallow groundwater of different land use types in arid desert oasis

【目的】分析西北干旱区黑河中游绿洲农业区不同土地利用类型地下水埋深和NO_(3)^(-)-N含量时间变化规律。【方法】对研究区域近10 a(2005~2014年)地表水和地下水NO_(3)^(-)-N浓度变化情况进行分析,在垂直黑河河道方向设置9个观测井,对不同土地利用类型地下水埋深及NO_(3)^(-)-N含量进行连续监测和分析。【结果】2005~2014年荒漠绿洲边缘区地下水NO_(3)^(-)-N含量呈明显上升趋势;不同景观带地下水埋深及NO_(3)^(-)-N含量均存在显著性差异,垂直河道由近及远方向地下水位基本呈下降趋势,而NO_(3)^(-)-N含量无明显递增或递减趋势;位于黑河河漫滩(GW_(1))、老绿洲农田(GW_(2))及东沙丘(GW_(7))区域的地下水NO_(3)^(-)-N含量显著低于其他土地类型的地下水,新垦沙地农田(GW3、GW_(4)、GW_(5))地下水NO_(3)^(-)-N含量已经严重超出WHO饮用水标准,荒漠绿洲过渡带GW_(6)、GW_(8)和GW_(9)观测井NO_(3)^(-)-N浓度呈增加趋势。【结论】黑河中游绿洲农业区地下水NO_(3)^(-)-N含量变化对自然条件和人类活动敏感性较强,尤其是新垦绿洲农田对灌溉表现出较强的敏感性,是地下水硝酸盐污染的敏感区域,建议在新垦沙地农田区实施减少氮淋溶灌溉施肥管理方案。

【Objective】In order to analyze the temporal variation of groundwater depth and NO_(3)^(-)-N content under different land use types in oasis agricultural area in the middle reaches of Heihe River in arid northwest China.【Method】First of all,we analyzed the the changes of NO_(3)^(-)-N concentration in surface water and groundwater in the study area in recent ten years,and then,nine observation wells were set in the vertical direction of Heihe River to continuously monitor and analyzed the groundwater depth and NO_(3)^(-)-N content of different land use types.【Result】The results showed that the NO_(3)^(-)-N content of groundwater in desert oasis fringe area increased significantly from 2004 to 2014.Groundwater depth and NO_(3)^(-)-N content of different land use types were significantly different,and groundwater level of vertical river showed a decreasing trend from near to far,while NO_(3)^(-)-N content had no obvious increasing or decreasing trend.The NO_(3)^(-)-N content of groundwater located in the Flood plain of Heihe River(GW_(1)),Old oasis cropland(GW_(2))and Sand Dune in eastern(GW_(7))was significantly lower than that of other land types.The NO_(3)^(-)-N content of observation Wells GW_(6),GW_(8) and GW_(9) in the desert oasis transition zone showed an increasing trend,and the NO_(3)^(-)-N content of groundwater in Newly cultivated sandy cropland(GW_(3),GW_(4),GW_(5))was significantly higher than WHO drinking water standard.【Conclusion】The changes of groundwater NO_(3)^(-)-N content in the oasis agricultural area in the middle reaches of Heihe River are highly sensitive to natural conditions and human activities.Especially,the newly reclaimed oasis farmland shows strong sensitivity to irrigation,which is a sensitive area of groundwater nitrate pollution.Thus,we suggested that reduce the nitrogen application rate in newly cultivated sandy cropland.