西南喀斯特地区水体硝态氮时空分布特征及其来源解析

由于人类活动影响,水体硝态氮污染已经成为世界范围内的环境问题。硝态氮污染不仅会造成水体富营养化,长期摄入过量硝酸盐还会严重威胁人体健康,控制并解决水体硝态氮污染是我国经济社会发展过程中亟待解决的重要环境问题。我国西南喀斯特地区是世界上面积最大、发育最典型和人地矛盾尖锐的岩溶连续分布带,具有十分脆弱且高度敏感的生态系统。与非喀斯特地区相比,这里水体硝态氮污染情况更为复杂和严重。因此,明确西南喀斯特地区内硝态氮的时空分布特征并对其来源进行解析是有效治理的前提。本研究梳理了近几十年来西南喀斯特地区水体硝态氮的现代监测结果,探讨了水体硝态氮时空分布特征、来源及受控机制等问题,发现:(1)区域内地表水硝态氮平均检出质量浓度不高,地下水检出质量浓度波动范围较大;(2)近几十年来,地表水硝态氮质量浓度整体呈现小幅增长趋势,而地下水检出质量浓度随时间的变化存在地域差异;(3)降水的稀释和冲携作用对区域内硝态氮质量浓度及分布的影响不容忽视,而人类活动导致的土地利用变化带来的影响可能成为未来的主控因素;(4)区域内水体硝态氮主要来源于铵态化肥、土壤有机氮、粪肥及污水,硝化作用是主要的转化过程。研究结果将为进一步认识喀斯特地区氮循环过程及促进地区可持续发展提供理论基础。

Spatial-temporal distribution and sources of nitrate-nitrogen in karst water,Southwest China

Water nitrate contamination is a global environmental problem because of intensive human activities.Excessive nitrate can cause eutrophication,reduce water quality and even threaten human health.Controlling nitrate pollution is an urgent issue for social and economic development in China.The karst area of southwest China(KASC)is the largest karst landscape on the earth and has a fragile ecosystem;therefore,the nitrate pollution state in the KASC is serious and complicated.Thus,the premise of pollution control is to clarify the distribution,sources,and influencing factors of nitrate in the water of KASC.This review summarizes the recent monitoring results of nitrate to assess the spatial-temporal distribution characteristics and identify the sources of nitrate-nitrogen in the waterbodies of the KASC in recent years.The results indicate that the average detected concentration of nitrate in the surface water is not high,and the range of concentrations detected in groundwater in the KASC fluctuates greatly.The concentration of nitrate in surface water showns a slight upward trend overall,while the changes in groundwater concentrations over time have regional differences in recent decades.Human activities have a strong influence on the concentration and distribution of nitrate in the region,and the dilution and carryover effects of precipitation cannot be ignored.Nitrate dual isotopes suggest that nitrate in KASC mainly comes from NH₄⁺ in fertilizers,soil organic nitrogen(SON),domestic waste,and manure,and that nitrification is the key transformation process.This study provides scientific support for further understanding the nitrogen cycling process in the karst areas and promotes the sustainable development of KASC.