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[Impacts of reclaimed water irrigation of urban lawn on groundwater quality].

Based on long-term monitoring of groundwater and irrigation water quality, the dynamics of the main physicochemical property and pollutant concentration of groundwater influenced by reclaimed water irrigation were examined in this study. The results of our five-year continuous study showed that the ammonium nitrogen concentration in reclaimed water ranged 0.05-65.4 mg x L(-1) with an average of 12.0 mg x L(-1), which exceeded the urban miscellaneous water quality standards for urban greening (GB/T 18920-2002). The total nitrogen in reclaimed water averaged at 28.3 mg x L(-1), ranging from 2.56 mg x L(-1) to 78.0 mg x L(-1), which was also relatively high. The groundwater quality indexes were normal with small fluctuations under tap-water irrigation. The influence of lawn irrigation with reclaimed water on the groundwater water quality was significant in the shallow well with a depth of 6 m, but not obvious in the deep well with a depth of 20 m. The greatest change was found in the enhanced value of nitrate concentration. The nitrate nitrogen concentration in shallow underground water had significantly positive correlation but lagging with the concentration of dissolved nitrogen in the irrigation reclaimed water, which indicated that lawn irrigation with reclaimed water might cause nitrate nitrogen pollution in shallow underground water. Therefore, considering the huge water consumption for the urban greening, it is suggested that the criteria of reclaimed water reuse should be further improved to avoid the risk of environmental pollution.