Analysis Of Sources Of Groundwater Contaminants In Paddy

The pressure of food supply increased as the population growth these years, and increasing the nitrogen application is the most important way to improve the grain output. But increasing the nitrogen application blindly would lead to low efficiency, and redundant nitrogen fertilizer caused a lot of environmental problems through volatilize, leaching and runoff.The current study aimed to analyze hydrochemical data and their vertical spatial variations collected in paddy cropping system, and consequently clarify the origin of NO3-and biogeochemical processes (NH4+-N, NO3--N, NO2--N) in an agricultural region of Shuanglin town in Huzhou city.The conclusions as followed:(1) In0-90cm depth soil, the concentration of organic matter was3.78～54.16g/kg. The concentration of total nitrogen was0.14-1.90g/kg. The concentration of total phosphorus was0.20～0.78g/kg. The concentration of potassium was1.78～3.41g/kg. Compared with the results of the second soil survey, all the nutrients had decreased, and formula fertilization by soil testing had certain effect. The concentration of total nitrogen was proportional to the concentration of organic matter. In the cultivation period, the NH4+-N was32.15mg/kg, and the NO3--N was2.99mg/kg. In the fallow period, the NH4+-N was22.45mg/kg, and the NO3--N was1.13mg/kg. The NH4+-N content was higher than that in other regions. (2) The shallow groundwater had been contaminated. Based on China’s groundwater quality standards (GB714848-93), the groundwater samples showed that SO42-and NH4were the major contaminants, and the average concentrations of them were191.30mg/L and0.28mg/L, and the main sourses of them were soil N and manure. The Pollution of groundwater in farmland was closely related to fertilization in the region. The space-time change of NH4+-N and NO3--N showed the same trend, and irrigation had a great effect on the distribution of NO3--N, NH4+-N in groundwater.(3) The δ15N of groundwater sampled in the fallow period was5.5～13.6‰, and the δ18O was-2.3～8.3‰. The δ15N of groundwater sampled in the cultivation period was0.2～15.4%o, and the δ18O was-1.4～17.2%o. It was found that the NO3--N and815N were both low in the deep layer, and the NO3--N and δ15N were both higher in the shallow layers. No correlations were observed between the ions in the groundwater and the well depth. The δ15N data showed that manure and soil N were the NO3-sources in the groundwater sampled in the fallow period, and soil N and chemical fertilizer were the NO3-sources in the groundwater sampled in the cultivation period.