Spatial distribution and traceability analysis of nitrate in karst water system in Jinan spring basin
Nitrate pollution caused by human activities is one of the most common environmental problems in karst spring areas in north China.A total of 30 groundwater and surface water samples were collected in Jinan Spring Basin in September 2020.The source and spatial distribution of nitrate pollution in the study area were analyzed by using hydrochemical analysis method coupled with nitrate nitrogen and oxygen double isotope tracer technology.The results show that the sequences of major anions and cations in water were HCO3-＞SO42-＞Cl-＞NO3- and Ca2+＞Na+＞Mg2+＞K+,respectively.And the main water chemistry type was HCO3·SO4-Ca.The average NO3-concentration in groundwater(37.93 mg·L-1)was higher than that in surface water(10.15 mg·L-1).Waters of 7 sampling sites were obviously polluted by nitrate,exceeding standard rate was 27％,and the concentration of NO3--N in groundwater at the sampling points of upstream recharge area and downstream drainage area was higher than from runoff area.The concentration of NO3-was mainly affected by the mixing process,while no obvious denitrification occurred.The values of δ15NNO3 andδ18ONO3 ranged from 1.05 ‰ to 14.43 ‰ and-7.92 ‰ to 22.94 ‰,respectively.According to the calculation results of Bayesian isotope mixing model(MixSIAR),manure and sewage was mainly nitrate source of the groundwater and surface water,accounting for 39.3％and 52.3％of the total contribution,respectively.Soil nitrogen and NH4+in rainfall and fertilizer were the second,and the contribution rate of atmospheric deposition was the lowest.The results indicated that manure and sewage was the main source of nitrate pollution in this area,and there may be a mixture of soil organic nitrogen and chemical fertilizer.
karst water systemhydrochemical characteristicsnitratespatial distributionpollution source
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万方数据
