| Groundwater is the primary component of water resource, and is the importantnatural resource for people’s living and social development. Along with the rapiddevelopment of social economy, groundwater pollution has become more serious thanbefore as lacking of enough attention to environmental protection. Groundwater pollutionhas become one of the most serious problems aroused general concerns in the worldnowadays. Nitrate is one of the main pollutants in groundwater. In Beijing, the output ofsupplying groundwater accounts for2/3of the water totally supplied, which results in thesituation that Beijing’s water supply mainly depends on the groundwater resource.Therefore carrying out the investigation and assessment of groundwater nitrate in Beijinghas very practical and important significances for rational utilization and protection ofwater resources and for guarantee resident drinking water security.In this paper groundwater samples were collected from intensive agriculturalregions of13districts in Beijing from2005to2012to determine the status of nitratenitrogen （N） contamination in groundwater. Based on the monitoring data, this paperaimed at investigating the situation, analyzing the distribution regularity andspatial-temporal dynamic change, and analyzing the influence factors of groundwaterpollution. In addition, the groundwater vulnerability was evaluated according to the realsituation of the study area. The main results were summarized as the following:1. The results indicated that the mean concentration of nitrate-N of all samplesanalyzed in the study area was6.42mg·L-1. There were19.35%of the samples exceeding10mg·L-1, and7.03%of the samples exceeding20mg·L-1. The annual averageconcentration of nitrate-N varied from5.85mg·L-1to6.93mg·L-1, which met thecategory III national water quality standard. Nitrate leaching was enhanced by rainfalland higher concentrations of nitrate-N in groundwater were observed after rainy seasons.The nitrate-N concentration in groundwater decreased with increasing groundwater depth,and the average concentration within30m was12.94mg·L-1, exceeding the WHOdrinking water guideline. The nitrate-N concentration in groundwater was affected by theland use system in the following order: vegetable field> grain crop field> other landuses> orchards, with the mean nitrate-N concentration being7.75mg·L-1,6.16mg·L-1,5.63mg·L-1and5.04mg·L-1, respectively. The concentration of nitrate-N in groundwater varied significantly among13districts, the highest value was observed in Fengtai Districtfollowed by Miyun County, and the lowest value was in Daxing District.2. The spatial distribution and variation regularity of nitrate-N concentration ofgroundwater under intensive agricultural regions of Beijing were studied using GIStechnology and geostatistics analysis methods. The results showed that nitrate-Nconcentration of groundwater in this study area mainly met the category Ⅱand Ⅲ ofthe national groundwater quality standard from2006to2012.The highest concentrationof nitrate-N in groundwater was distributed in east of Fengtai District, north of DaxingDistrict and north of Miyun County, and the lowest concentration was on the borderamong Chaoyang, Changping and Shunyi District, and also distribuated in south ofDaxing and south of Tongzhou. The concentration distribution of nitrate-N ingroundwater in the study area varied significantly in different monitoring time during2006to2012. The distribution area which concentration of nitrate-N increased after rainyseasons was much larger than that concentration of nitrate-N decreased, and variation ofnitrate-N concentration after rainy seasons was mostly in the range of-2.00mg·L-1to2.00mg·L-1. In part of Yanqing, Changping, Shunyi and Pinggu District which accountedfor2.48%of study area were the distribution area where nitrate-N concentration ingroundwater increased persistently after rainy seasons during seven years. Thespatial-temporal dynamic variation of nitrate-N contamination in groundwater canobjectively reflect the groundwater nitrate situation of the study area.3. From two aspects of natural factors and socioeconomic factors, the causes ofconcentration distribution of nitrate-N in groundwater in the study area were revealed.The correlation analysis had been studied to find out correlation between influencefactors and nitrate-N concentration in groundwater every monitoring period. The resultsshowed that there were five main influence factors which were population density, theproportion of grain planting area accounting for cultivation area, the proportion oforchard area accounting for cultivation area, topographic slope and accumulationprecipitation.4. By referencing DRASTIC model, the assessment model of groundwatervulnerability is defined according to the real situation of the study area. The quantitativeevaluation of groundwater vulnerability was carried out, and the assessment results couldapproximately reflect the groundwater vulnerability of the study area. The results showedthat there was a regular pattern on spatial distribution of groundwater vulnerability underintensive agricultural regions of Beijing. The higher degree of groundwater vulnerabilitywas distributed in southeastern plain area, and lower degree of groundwater vulnerabilitywas in western and northern mountain area. On the whole, groundwater antipollutionfunction of the study area was relatively worse, particularly Beijing plain area. |
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