Abstract:

Sihu region locates in south of Hubei Province and between middle reaches of the Yangtze River and Dongjing River,which is the important agriculture area in Hubei Province.In Sihu region,groundwater is still the main drinking water source for resident’s life in rural area.In recent years,as the improvement of living standard and the development of industry and agriculture,the pollution in the rural groundwater environment in Sihu region has become a threatening problem.Groundwater circulation is a complex process,especially after the Three Gorge Project was finished.Ammonia (NH4+－N),nitrate nitrogen (NO3-－N) and nitrite nitrogen (NO2-－N) are the common contaminant in the groundwater.Based on monitoring of groundwater quality for four times in April,June,September and November of 28 samples,the seasonal and spatial changes in concentrations  NH4+－N,NO3-－N,NO2-－N were analyzed in phreatic water and shallow confined water as well as the influencing factors.The results show as follows:(1) The NH4+－N monitoring results in phreatic groundwater varied from 0.08-0.39 mg/L,0.14-0.39 mg/L,0.32-1.65 mg/L and 0.03-0.50 mg/L while in shallow confined water the monitoring results varied from 0.11-3.19 mg/L,0.10-8.77 mg/L,0.42-11.18 mg/L,0.17-5.27 mg/L.The groundwater NH4+－N concentration in Sihu region exceeds certain limit which is higher in phreatic water than shallow confined water and the exceeding standard rate of NH4+－N concentration in phreatic water is over 50%.(2) The concentrations of NO3-－N are low in phreatic water and generally exceed standards in confined water.The exceeding standard rate of NO3-－N reached to 83% in June.(3) The concentrations of NO2-－N of confined water in the monitoring year mostly reached the class II standards of GB/T14848-9.While in phreatic water the monitoring results which exceed the III class standards accounted 50%、83%、33% and 40%.(4) The results reveal obvious seasonal variability,the NH4+－N concentration in September is higher than the other months; the concentrations of NO3-－N and NO2-－N in confined water reached the maximum in June.(5) The groundwater NH4+－N concentration has higher spatial variability.The NH4+－N concentration that reaches the National Primary Drinking WaterStandard (≤05 mg/L ) are mostly in the phreatic water samples and distributed in the inter-channel plain.The high concentration mostly centralized in both sides of Neijing River near Honghu Lake.(6) Meteorological factors,agricultural activities,domestic pollution and redox environment have a synthetic impact on groundwater quality of the study area.The concentration of threenitrogen has a close relationship with the dynamic changes of precipitation.The seasonal variability of NO3-－N and NO2-－N shows that the annual variability of precipitation influenced the phreatic groundwater directly.The intensive use of pesticides and fertilizers as the nonpoint pollutant source and the unregulated sewage emissions as the point pollutant source are the two main pollutant source in the study area