土地利用变化下湛江市地下水硝酸盐含量评估

Assessment of groundwater nitrate content under land use changes in Zhanjiang City

随着城市化进程的加快,密集的工、农业生产等人类活动使得地下水硝酸盐污染问题突出。基于土地利用变化评估湛江市地下水中硝酸盐的含量,运用ArcGIS分析不同土地利用变化下硝酸盐的空间分布特征,结合GeoSOS-FLUS模拟软件,分析未来土地利用变化下硝酸盐的变化趋势。结果表明,2005—2015年,湛江市耕地面积减少12.75 km^(2),居民用地增加了9.58 km^(2),分布更加集中;研究区浅层含水层中硝酸盐浓度为(51.13±48.72)mg·L^(−1),由北部与南部的超标区域,向中部地区递减,垂直方向上NO_(3)^(−)浓度随埋深增加而大幅降低;近十年来,研究区浅层含水层中NO_(3)^(−)污染减轻,超标区面积缩小,但局部地区污染加剧;不同土地利用类型中耕地区浅层地下水硝酸盐平均浓度最大,居民用地与草地最小,结合NO_(3)^(−)与九个主要离子的相关性分析可知,地下水硝酸盐可能来源于农业化肥,生活污水与工业废水;基于模拟结果,未来30年间硝酸盐浓度随耕地面积的增长可能呈现上升的趋势,未来80年期间,硝酸盐污染整体将可能会有所下降,但以工业园区为主的居民用地区域仍保持在较高浓度。

With the acceleration of urbanization,the problem of nitrate pollution in groundwater is prominent due to the intensive human activities such as industrial and agricultural production.Based on the land use changes,we assessed the nitrate content in groundwater of Zhanjiang City,analyzed the spatial distribution characteristics of nitrate under different land use changes using ArcGIS,and combined with GeoSOS-FLUS simulation software to analyze the change trend of nitrate under future land use changes.The results show that:1)From 2005 to 2015,the farmland area of Zhanjiang city decreased by 12.75 km^(2),and urban area increased by 9.58 km^(2),besides the distribution was more concentrated.2)The mass concentration of nitrate in the shallows groundwater of the study area was(51.13±48.72)mg·L^(−1),which was decreased from the over-standard area in the north and the south to the central area.In the vertical direction,the mass concentration of NO_(3)^(−) decreased greatly with the increase of the buried depth.3)In the past decade,the pollution of NO_(3)^(−) in shallow aquifer of the study area has been alleviated,and the area of the exceedance zone has reduced,while the pollution in some areas has been intensified;4)The average concentration of nitrate in shallow groundwater was the largest in the middle cultivation area of different land use types,and the smallest in residential land and grassland.By analyzing the correlation between NO_(3)^(−) and nine main ions,the nitrate in groundwater might come from agricultural fertilizers,domestic sewage and industrial wastewater.5)Based on the simulation results,in the next 30 years,the concentration of nitrate may increase with the growth of farmland area,and the overall nitrate pollution would probably decline in the next 80 years,but that of urban area mainly in industrial parks still remain at a high concentration.