Use Of Multi-isotope And Microbial Technology(E.Coli) For Evaluating Sources And Transformation Of Nitrate In The Groundwater In Handan Area In The North China Plain

With the development of industrialization, urbanization, modernization, the emission of industrial and life wastes lead to soil, surface water and groundwater pollution is increasing. Nitrate is one of the most common components of pollution in the groundwater, and for people, excessive intake of nitrate is easy to cause methemoglobinemia, but also lead to esophageal cancer, gastric cancer and colon cancer. The nitrate contamination of groundwater with multi-sources, hidden and difficult control properties. In order to combat nitrate pollution, it is critical to judge the source of nitrate, determine the nitrogen cycle transformation process of the nitrification and denitrification, only to determine the source of nitrate and its migration transformation rule, the control measures can suit the problem, achieving a multiplier effect. However, due to the complex pgysical, chemical and biological processes of nitrogen cycle in nature, traditional hydrogeochemical methods is difficult to identify the source of nitrate pollution.Nitrate δ15N values of difficult nitrogen sources is overlap, making the results exist multiple solutions, using only the nitrogen isotope tracing nitrate contamination still can not accurately determine the nitrate pollution sources, especially for the NO3-formed from organic matter. With isotope test technology development, use the isotopic N and18O isotopes of NO3-to study NO3-source, pollution mechanism and nitrogen cycle, to a certain extent make up for the weaknell of using δ15N value to identify the sources, but there are still large limitations for complex system. Therefore, funded by National Natural Science Fund Project "The online testing new technology of nitrate triple oxygen isotope and its application in the study of groundwater contamination"(NO.40972157) by the Supervisor professor Aiguo Zhou and "The testing technology of the nitrate nitrogen and oxygen in the natural water and its application in hydrogeology"(NO. 40802057) by the associate professor Chuanming Ma, in the high incidence of esophageal cancer-Handan area in the north China plain, the multi-isotope (N> O, C, Cl) and microbial technology (E.coli) is tried to study groundwater quality characteristics and their evolution, the distribution characteristics of nitrogen and oxygen isotope of nitrate, carbon isotope of dissolved organic carbon and chlorine isotopic composition of chloride, to identify the sources of groundwater nitrate, and to provide a scientific basis for prevention and treatment of nitrate pollution of groundwater and safe drinking water in esophageal high incidence area.The study area is located in the southern part of Hebei Province, the west close to the low mountain and hilly area of Taihang Mountains, the east is piedmont and Zhang River alluvial plain, the strata exposed than the whole. The aquifer groups can be divided into the karst fissure aquifer, clastic rock pore fissure aquifer, and the loose rock pore aquifer group.Groundwater is mainly recharged by atmospheric precipitation, river infiltration, lateral flow, canals, irrigation seepage, the overall flow from west to east, and discharged mainly by the lateral runoff, evaporation, and labor exploitation. The object of this study is mainly for the loose rock pore aquifer group.Ground surveys in the study area, from west to east along the direction of groundwater flow, select the difficult landforms, stratigraphy, lithology and hydrogeology units, collect32groups groundwater samples, all samples are tested the pH value, temperature, conductivity, major ions, trace elements, oxygen and deuterium isotope (δ18OH2O、δ2H), nitrate nitrogen and oxygen (δ15N、 δ18O), carbon isotope of dissolved organic carbon (δ13C), chlorine isotope composition of chloride (δCl) and microbial technology (E.coli). Comprehensive comparative analysis of test results, we achieved the following understanding:(1)Hydrochemical characteristics of groundwater with apparent regularity in Handan area in the North China PlainThe type of water chemistry of the western mountains is HCO3-Ca and HCO3-Ca·Mg, the large area of HCO3·SO4-Ca, HCO3·Cl-Ca·Mg, HCO3·Cl-Na·Mg, HCO3·Cl·SO4-Na·Mg and HCO3·Cl-Na type water appeared in the Quaternary pore water, due to the slight pollution. The major iron content progressively from west to east, with the loal existence of industrial, life and mining pollution.(2)The main recharge of groundwater is atmospheric precipitationThe δ18O and δ2H values of groundwater samples fall near the meteoric water line, indicating that the main sources of groundwater is atmospheric precipitation.(3)The relationship between nitrate concentration and the incidence and mortality of esophageal cancer is positiveThe groundwater nitrate content in west is higher than eastern plains, and high rate of esophageal cancer in western is also higher than the east proved that the incidence and mortality of esophageal cancer was positively correlated with groundwater nitrate content; The NO3-content in the groundwater of Qianshi village in Cixian is higher than the drinking water health standards (≤30mg/L), with of38.66mg/L.The NO3-content in confined water is generally low. The eastern plains located in micro-confined and confined water zone, and the impermeable roof of confined groundwater can be anti-fouling, while the deep confined water is anaerobic reductive environment, conductive to denitrification and thus the content is generally low.The NO3-content of groundwater in Songjiajing village in Wuan city, and there is mine area near this place, and the main sources of nitrate pollution may be applied by industry and mining companies discharge of waste water. The antifouling performance of the surface lithology plays an important role of nitrate pollution in shallow groundwater, because the surface lithology is coarse, the infilitration is good, and the autifouling performance is poor, the various sources of nitrate is easy to access to groundwater pollution.(4)Characteristics of δ13CDOC values and microbial (E-coli)①There is a generally negative correlation between DOC and δ13CDOC value, and as the concentration of DOC decrease, the δ13CDOC values are more positive, and the reason may be the carbon isotope of DOC is effected by animal manure and seawage.②The δ13CDOC values of the samples detected by E-coli (27,19,4) are more negative, and the reason may be that the microbial activity in groundwater is serious due to the input of animal manure and city pollution, that to enhance the proportion of biogenic carbon.(5)The characteristics of37Cl isotopic①The chlorine and nitrate distribution lawStudy area Cl-and NO3-with a high consistency in the spatial distribution, the high-value area distributes around Cixian, mainly impact of the industrial and mining wastewater discharge; The relationship of Cl-and NO3-distribution is basically a positive correlation in the piedmont area (unconfined water zone), while that of Cl-and NO3-distribution in he eastern plains (confined water zone) is high Cl-and low of NO3-.②The correlation between δ37Cl and Cl-, δ18OH2O, δ2HH2O, groundwater depthThe δ37C1value in Quaternary pore water and Karst water get smaller or become megative with the concentration of Cl-increases; The δ37C1value in②The correlation between δ37Cl and Cl-, δ18OH2O δ2HH2O, groundwater depthThe δ37C1value in Quaternary pore water and Karst water get smaller or become negative with the concentration of Cl-increases. The δ37Cl vaiue in groundwater is not correlated with δ18OH2O and δ2HH2O value, because the37C1isotope fractionation mechanism is different from δ18OH2O and δ2HH2O. The relationship of Cl-,δ37C1and depth is obviously negative correlation in Karst water in the western mountains, meaning the Cl-concentration decrease with the depth increase; the δ37Cl value become negative with the depth increase. There is no correlation between the Cl-,δ37Cl and depth in Quaternary pore water, and the Cl-concentration has no change with the depth increase.③Relationship between δ37Cl and δ15N Combination of δ15N values and837C1values can be distinguished from nitrate from the precipitation and nitrate from the soil, which taking advantage of the differences of837C1values to judge springs exposed strata are carbonate or non-carbonate; using the differences of δ15N values and relationship of837C1values to identify δ15N values from fertilizer or animal manure; The δ37C1values and δ18O values in carbonate distribution area are higher, and may be subject to fertilizer pollution; Quaternary distribution δ37C1low and δ18O values higher, may be by the breeding faecal contamination.(6)Source identification of NO3-Use the relationship between NO3-and δ15N, combined with the hydrogeological conditions and other information, to identify NO3-sources of in groundwater.①Nitrogen from atmospheric: the characteristics is NO3--N content less than25mg/L, and the δ15N value is negative, its main source is the organism (decaying vegetation), and fractionation mechanism is biological nitrogen fixation.②Nitrogen from natural soil sources:the characteristic is NO3-N content less the10mg/L, and the δ15N value in the range of0～+8%o, its main source is nitrification or degradation of natural soil organic nitrogen or humans.③Nitrogen from fecal sources:the characteristic is that the range of NO3--N content change a lot,24.86to72.16mg/L, and the δ15N value is high, with the range of15.78～18.35%o, the main source is pollution caused by livestock manure and ammonia volatilization is strong.④Nitrogen from mixed sources:the characteristic is that the range of NO3--N content varied greatly, because nitrogen isotope ratios of industrial effluent close to nitrogen fertilizer, thus it is difficult to identify the source is nitrogen fertilizer or industrial waste water or sewage only by the relationship between NO3-and ε15N, so the combining with other isotope to identify and distinguish is needed.The correlation between δ13CDOC values and δ15NNO3values showed that both the isotope fractionation in dissolved organic carbon and the oxygen isotope fractionation in nitrate obeyed the Rayleigh fractionation theory. The carbon isotopic compositions of different sources of dissolved organic carbon (DOC) have different range. The average value of δ13C is-25%o for terrestrial plants,-23‰for C3plants (such as trees, wheat, rice, etc.),-13‰for the C4plants (such as corn, sorghum, millet, sugar cane, etc.). The13C value of soil organic matter was associated with the regional plant type, and was about-27±5%o for peat humic soil organic matter, and was up to-40‰in the serious pollution areas such as landfill. The δ13CDOC value in groundwater varied from-30‰o to-38‰, with the maximum frequency of-32‰-33‰and the average of-32.37‰, which was more negative than the δ13CDOC values of C3plants and terrestrial plants. According to the different range of the carbon isotopic compositions of different sources of dissolved organic carbon (DOC), the dissolved organic carbon in the groundwater of the study area is mainly soil organic matter. The positive correlation between δ13CDOC values and δ15NNO3values could be used to justify the source of NO3-further, and the main source of NO3-in groundwater is soil organic matter nitrogen.The general trend of the relationship between δ37Cl values and δ15NNO3values in groundwater are:①There is positive correlation between δ15NNO3values and δ37C1values in Karst water;②There is negative correlation between δ15NNO3values and837C1values in Quaternary pore water;③The ε15NNO3value is high with low δ37C1value in the waste pollution area. Overall, the mainly source of nitrate in groundwater of the study area is animal manure and chemical fertilizer.According to the nitrogen and oxygen isotopic composition values from different nitrate source reported by Savard et al.(2010), the relationship between the δ18ONO3values and the δ15NNO3values shows that the nitrate sources in the drinking water in the study area are:①The nitrogen from soil organic matter;②The nitrogen from animal manure and sewage;③the nitrogen from chemical fertilizer, which is given priority to with soil organic matter nitrogen,43.47%, followed by animal manure nitrogen,34.78%,21.75%for chemical fertilizer nitrogen. Especially the source of animal manure by colony and E-coli bacteria detection confirmed.This research area in central western mountains, hills and piedmont plain in groundwater recharge area, happening in the organic matter mineralization and nitrification. Only in the eastern alluvial plain of shallow confined water denitrification effect, the NO3-content in groundwater is reduced. In addition, the nitrogen of soil organic matter, animal manure can also occur between nitrogen and nitrogen fertilizer mixing action. In this research area, the atmospheric nitrogen source has not be found.(7)The transformation of nitrate in the study areaThe nitrification of soil is closely related to aeration of soil, soil acidity, soil moisture, organic matter content; The supply of soil carbon source, soil moisture and humidity, soil oxygen supply is a significant impact on soil denitrification. Nitrification is the main form of the nitrogen cycle in the study area, start with rainfall, N from the atmosphere after vegetation into the rock (soil), under the nitrogen fixation, assimilation, ammonification, nitrification, and continue to from the NO3-; There are two types of denitrification occurred in the study area. First, it occurred in the area of δ15N and NO3-distribution (ammonia volatilization) which from the fecal source; Second, it occurred in NO3-distribution area of the production and application of nitrogen fertilizer or industrial sewage source; Esophageal high incidence is mainly distributed in the nitrification-dominated areas, and denitrification zone and more low-incidence area for esophageal cancer, but also occurs in high incidence.Closely integraied with the hydrogeological conditions of Handan area in Hebei Plain, this study set groundwater circulation evolution as the main line, using a variety of isotope techniques (N、O、C、Cl) and microbial technology (E-coli) to carry out a systematic study of isotope composition, distribution characteristics and fractionation mechanism of the nitrate and oxygen in nitrogen, carbon of dissolved organic carbon, chlorine of chloride and microbial technology (E.coli) in shallow groundwater in Handan area, comprehensive reveals the nitrate source in groundwater and its relationship with esophageal cancer. For the first time use the related relationship between815N and δ13C,δ15N and δ7C1to identify the nitrogen from nitrogen from soil organic matter source, the nitrogen from animal manure and sewage and the nitrogen from chemical fertilizer; provide a scientific basis for control nitrate pollution in the study area and safe drinking water in esophageal high incidence area, with a certain scientific value and application prospect.