利用水體中溶解性硝酸根離子中的氮氧同位素組成來識別中國太湖和巢湖水體中氮污染源的研究.pdf

1、The technique of using nitrogen and oxygen isotopic compositions to identify nitrogen sources and assess the nitrogen cycle process has been extensively applied in
　　 fresh water research in the last few decades.Nitra

2、te pollution in fresh water has
　　 caused concern worldwide:if nitrate sources could be identified,this major form of
　　 pollution could be combated.Thus,this technique provides much-needed scientific help with the

3、 remediation of fresh water.As the method of determining nitrogen and
　　 oxygen isotopic ratios has become more precise,many deficiencies in earlier methods of determination have been overcome.Moreover,each kind of ni

4、trate source and some isotopic fractionation processes have also been well studied;all these factors
　　 play an important role in research into the use of isotopic tools in tracing nitrate sources.The joint use dual i

5、sotopes with water chemistry are indeed providing very detailed and useful information relating to the identification of nitrate sources and the tracking of nitrate transformation in freshwater systems.Surface water samp

6、les were collected from Taihu Lake and Chaohu Lake in three different periods.The current study can be divided into three parts to discuss,such as Taihu Lake (collected in December,2007);Taihu Lake (collected in January

7、and July of 2009,respectively);Chaohu Lake (collected in January and July of 2009,respectively).Theδ15N and δ18O- NO3- values,as well as major ions tracers,from collected water samples in Taihu Lake and Chaohu Lake were

8、investigated to identify the primary nitrate sources and assess nitrogen biogeochemical process in the present study.
　　 The results of Taihu Lake (collected in December,2007) showed that the nitrate
　　 concentrat

9、ion in North Taihu Lake (WTL) was generally higher than those in East Taihu Lake (ETL) and its upstream inflow rivers.The NO3-/Cl- value combined with
　　 mapping of δ15N-NO3-and NO3- concentration [There was a positiv

10、e correlations (R2=0.83,0.63 respectively) between Cl- and NO3- levels can be observed in WTL]
　　 suggested that mixing process should play a major effect in WTL,and denitrification was the dominant nitrogen transform

11、ation process in WTL.A linear relationship of
　　 close to～1∶2 was observed between δ15N-NO3- and δ18O-NO3- values in NTL, confirming the occurrence of denitrification in NTL.The nitrogen isotopic composition of local

12、nitrate sources were comparable with previously published values.The δ15N-NO3- in ETL ranged from 3.32‰ to 6.17‰ (n=5,mean=5.1‰),and the δ15N-NO3- in WTL and rivers ranged from 5.69‰ to 10.35‰ (n=7,mean=8.79‰) and from 7

13、.33‰ to 10.11‰ (n=5,mean=9.35‰),respectively.The δ15N-NO3- data implied that sewage and manure were the principal nitrate sources in WTL and its feeder rivers,while the nitrate in ETL might derive from soil organic nitro

14、gen and atmospheric deposition.The range of determined δ18O-NO3- value in the current study varied from 4.0‰ to 12.4‰(n=17,mean=7.9‰).The δ18O-NO3- data indicated most of nitrate from microbial nitrification of organic n

15、itrogen matter could possibly make a significant contribution to the lake.
　　 In January and July of 2009,the Cl- concentrations in Taihu Lake basin were found to range from 58.33 to 85.72 mg/L in winter and from 30.

16、52 to 69.22 mg/L in summer,with average values of 66.68 and 56.21 mg/L,respectively.This seasonal variation was also observed in SO42- and NO3- concentrations,in which the mean values of SO42- and NO3- in summer (73.54 a

17、nd 3.87 mg/L,respectively) were lower than those in winter (84.49 and 5.53 mg/L,respectively),which clearly suggested a dilution effect by rain water in summer months The relationship between No3- and Cl- suggested that

18、a mixing effect dominated the nitrate transformation process in Taihu Lake in winter.The δ15N-NO3- values in watersheds varied from +5.3‰ to +22.2‰ (n=6,mean value = +15.1‰) in winter,and from十0.5‰ to +20.6‰ (n=8,mean va

19、lue = +9.2‰) in summer.The δ15N-NO3- values in NTL varied from +4.0‰ to +17.8‰(n=7,mean value = +8.7‰) in winter,and from +5.2‰ to +11.1‰(n= 7,mean value = +9.7‰) in summer.Moreover,the δ15N-NO3- values in ETL varied fro

20、m +1.8‰ to +5.9‰ (n=5,mean value = +4.4‰) in winter,and from +8.1‰ to+10.2‰ (n= 7,mean value = +9.4‰) in summer.The δ15N-NO3- values suggested that: In winter,sewage and manure were the primary nitrate sources in major i

21、nflow rivers and NTL,while nitrate sources in ETL probably derived from soil organic nitrogen.In summer,atmospheric deposition and swage/manure inputs appeared to play an important role in controlling the distribution of

22、 nitrates in the whole Lake. The δ18O-NO3- values in Taihu Lake basin ranged from +0.4‰ to +17.9‰ in winter and from +0.4‰ to +17.9‰ in summer,with average value of +6.3‰ and +6.6‰, respectively,suggesting that the nitra

23、te produced from microbial nitrification was another major nitrate sources during both winter and summer months.The variations in isotopic values in nitrate suggested that denitrification enriched the heavier isotopes of

24、 nitrate in NTL in winter and in ETL in summer.
　　 About the results of Chaohu Lake (collected in January and July of 2009,respectively).The nitrate concentrations and their nitrogen and oxygen isotopic compositions

25、in the water samples were analyzed.The nitrate concentration ranged from 0.30 to 13.94 mg/L in winter and from 0.08 tO 5.14 mg/L in summer,with average values for 6.72 and 2.10 mg/L,respectively,which exhibited a large s

26、easonal variation,suggesting the dilution effect of rainwater.There was a positive correlation (y = 0.2x + 4.0,R2=0.74) between NO3- and Cl- in WCL in summer,indicating the occurrence of mixing process in WCL in summer.I

27、n the current study,the δ15N-NO3-values in the water samples ranged from +5.8 to +16.1‰ in winter with a mean value of+10.9‰ (n=8),and from +5.2 to +9.9‰ in summer with a mean value of +6.7‰ (n=15),and the δ15N-NO3- valu

28、es for the rivers in summer (mean value = 13.7‰,n=5) were evidently lower than those in winter (mean value = 6.9‰,n=5).The data conceming δ15N-NO3- values in winter suggested that the nitrate sources of inflow rivers der

29、ived mainly from sewage and manure inputs,while the nitrate sources in the southern part of Chaohu Lake were possibly influenced by chemical fertilizer or plant derived nitrogen; in summer,seasonal fertilizer application

30、 in the lake watersheds and rainwater probably contributed more nitrates into the rivers and the lake.Theδ18O-NO3- values did not exhibit distinct seasonal variations in rivers and Chaohu Lake,and the δ18O-NO3- values of

31、 collected water samples in both winter and summer scatted from +0.7 to +13.5‰,with a mean value +7.1‰(n=23).The δ18O-NO3- values suggested that nitrate produced from microbial nitrification could also be a significant

32、r>　　 nitrate source in the Chaohu Lake basin.The slope of the linear regression between
　　 δ15N and δ18O-NO3- values supported the hypothesis that the denitrification process may control the isotopic composition of ni