Research On Distributed Pattern And Sources Of Nitrate In Groundwater Of Shandong Province

With the rapid development of industry and agriculture, the nitrate (NO3--N) contamination of groundwater has been a worldwide environmental problem. The excessive NO3--N in groundwater will be directly or indirectly endanger people's health. There are a lot of sources of nitrate in groundwater and once the contamination has happened, the treatment was very expensive.The most fundamental solution is to identify the sources of nitrate and cut off them which are moved to the groundwater. In this paper, we studied the concentration and the distributed pattern of nitrate in groundwater in the rural areas of Shandong province. We also preprocessed groundwater samples of which NO3--N is above 10mg/L by the method of ion exchange chromatography in order to determine the source furtherly. At the same time, adding and improving the database of existing NO3--δ15N value in order to provide a theoretical basis for identifying and controlling the nitrate contamination in groundwater.The results are as follows:1 The AG1-X8(Cl-, 200-400mesh) anion resin produced by Bio-rad3 Corporation had a relatively high affinity for nitrate which made the sorption efficiency achieve more than 98 percent and the elution recovery achieved more than 94 percent by using 15ml of 6 M HCl, which had met the requirements of isotopic analysis. There were many advantages of it which was worth applying in hydrological studies. AgNO3 converted from different concentrations (10,30,50,100 mgN/L) of KNO3 standard solution was transformed into N2 and CO directly by TC-EA avoiding the complicated conversion steps in the past and the reproducibility ofδ15N andδ18O values was good. The testing accuracy is 0.22‰forδ15N and 0.4‰forδ18O, which has reached the level of similar studies abroad and met the requirements of identifying the sources and hydrogeological applications.2 Among the groundwater samples studied in this paper, the proportions of typeⅠ,typeⅡ, typeⅢ,typeⅣand typeⅤwater according to the concentration of NO3--N were 28.89 percent, 10.67 percent, 31.56 percent, 11.11 percent, 17.78 percent respectively. 71.12 percent of the groundwater samples could be consumed directly, 28.89 percent of them were not drinkable. There were higher proportions of exceeding NO3- in groundwater under fruit and vegetable cropping systems and there were relatively lower proportions of exceeding NO3- in groundwater under grains-cropping systems. This was mainly caused by the higher application rate of N-fertilizer under vegetable and fruit cropping systems and lower application rate of N-fertilizer under grain-cropping systems. Overall, the conditions of NO3- concentration in groundwater of Shandong Province was not optimistic, certain measures such as rational fertilization and improving the fertilizer efficiency must be taken to protect the groundwater from being contaminated, avoiding the serious consequences caused by it.3 Take the urban area as a unit, the levels of average concentrations of NO3--N in groundwater were as follows: the average concentrations of NO3--N about Binzhou, Liaocheng, Dezhou and Heze were lower than 10mg/L.As to Laiwu, Zibo, Yantai and Weifang, the average concentrations of NO3--N were higher than 20mg/L. Jinan, Qingdao, Zaozhuang, Linyi, Weihai, Rizhao, Jining and Tai'an had the moderate levels of NO3--N concentrations .The nitrate concentrations of the groundwater had no obvious regularity along with the burying depth in our study areas, which might be affected by textures of local soil or recharge ways of groundwater. It also might be associated with places and numbers of sampling points. The orders from small to large according to the average concentration of NO3- in groundwater under different cropping systems were as follows: grains, open field vegetables, fruit, greenhouse vegetables. In addition, we also found that the concentrations of sulfate were significantly correlated with the concentrations of nitrate and the sulfate concentration increased with the nitrate concentration.4 There was no significant denitrification in aquifers of Shandong, due to which we could use NO3--δ15N values of groundwater to reflect the characteristics of the sources.Take the whole study region as a unit, the rate of nitrate-sources coming from manure contamination was 35.45 percent, 27.1 percent of the groundwater samples were contaminated by N-fertilizers and 37.45 percent of the groundwater samples were contaminated by the mixture of fertilizer,manure and sewage. Take the areas whose average concentration of NO3--N in groundwater was above 20mg / L as a unit. As to Zibo, 22.22 percentage of nitrate contaminations came from manure, 22.22 percentage of them came from N-fertilizer, others were from the mixture of fertilizer,manure and sewage; with respect to Yantai , the ratios of nitrate contaminations came from manure, N-fertilizer and the mixture of fertilizer,manure and sewage were 55.56 percentage, 5.56 percentage and 38.88 percentage respectively; with regard to Weifang, the ratios of nitrate contaminations came from manure, N-fertilizer and the mixture of fertilizer,manure and sewage were 16.13 percentage ,48.39 percentage and 35.48 percentage respectively.