Nitrogen pollution and variation of chemical composition of shallow groundwater in Lubei Plain

Based on the inorganic analysis and field testing of 1084 groundwater samples in Lubei Plain, using the method of single factor evaluation, this paper discussed nitrogen pollution and chemical composition variation of shallow groundwater influenced by human activities in the region. The influence included the fertilizer used in agriculture, the discharge of industry and domestic sewage in downtown, and the septic tanks with inadequate impermeable measures. The evaluation result showed that 35% was polluted by nitrogen. Nitrogen pollution caused the increasing of total hardness, TDS, and variation of chemical composition. The average amount of total hardness of the nitrogen polluted samples was 1.1 times-3.9 times than the non-nitrogen polluted ones. Compared to the non-nitrogen pollution samples, the average concentration of Ca²⁺+Mg²⁺,K⁺+Na⁺ and TDS of the polluted ones was 1.22 times-1.57 times higher. There was no obvious relation between the depth and nitrogen pollution where depth of wells was less than 45 meters. Nitrogen pollution was the main reason the concentration of Ca²⁺+Mg²⁺ increased.