河套灌区地下水氮污染状况

N pollution of groundwater in Hetao Irrigation District.

河套灌区浅层地下水氮浓度和地下水埋深的季节变化规律调查结果表明:3月地下水NO3--N和TN浓度显著高于5、7和9月,地下水埋深也比5月和7月深。不同类型的井水N浓度差异较大:农田与庭院的井水NO3--N浓度显著高于村庄附近的井水,而NH4+-N和TN则表现为庭院井水浓度显著高于农田和村庄。地下水氮形态以NO3--N为主,全年17.1%的水井地下水NO3--N浓度高于10 mg.L-1,最高达184.4 mg.L-1。在灌溉量和其他生产条件相同的情况下,沙壕渠试验站农场内施肥区井水NO3--N浓度[(17.55±15.02)mg.L-1]明显高于未施肥区[(7.67±4.48)mg.L-1],且65.5%的水样NO3--N浓度超过WHO规定的生活饮用水NO3--N浓度上限值(10 mg.L-1),而未施肥区仅有27.6%的水样超标。井水NO3--N的来源主要为农田氮肥与动物粪肥,当地地下水NO3--N污染已不容忽视。

Seasonal changes in nitrate concentration and table of groundwater in Hetao Irrigation District were investigated. Results show that in March the concentrations of NO3^- -N and TN were significantly higher than those in May ,July and September and the groundwater table was also lower than those in May and July. Sharp difference was found in N concentration between wells different in type. The NO3^- -N concentration in the wells in farmlands and courtyards was significantly higher than those near villages, whilst the concentrations of NH4^＋ -N and TN in the wells in courtyards were higher than those in farmlands and near villages. The major N component of the N pollution in the groundwater was NO3^- -N and about 17.1% of the groundabuter samples investigated were above 10 mg· L^-1 in NO3^- -N concentration throughout the year with the highest reaching 184.4 mg · L^ -1. When similar in irrigation rate and farming practice, 65.5% of the groundwater samples in the fertilized zone were over 10 mg · L^-1 in NO3^- -N concentration, whereas only 27.6% of the groundwater samples in the non-fertilized zone. In the former, the concentration of NO3^- -N averaged （17.55 ± 15.02 ） mg · L^- 1 , which was much higher than that in the latter [ （7.67 ± 4.48） mg · L^- 1 ]. Higher NO3^- -N concentration came from N fertilizer and animal manure applied in fanning production and courtyard economy production. Therefore, the problem of NO3^- -N contamination of groundwater that occurred with the current local N application rate can＇t be ignored.