The Nitrogen And Oxygen Isotopic Composition Of Nitrate In The Daya Bay And The Jiaozhou Bay

The nitrogen and oxygen isotopic compositions of nitrate in the Daya Bay and the Jiaozhou Bay were studied,funded by the National Basic Research Program of China(973 program).The spatial and temporal variations of nitrate concentration,NO3--?15N and NO3--?18O were revealed.Based on the characteristics of NO3--?15N and NO3--?18O,the SIAR model was applied to calculate the proportion of nitrate contributed from different sources.The factors affecting the sources of nitrate were discussed also.The conclusions were as follows:According to the distributions of nitrate concentration,NO3--?15N and NO3--?18O,four different sources of nitrate were identified in the Daya Bay,namely sewage,river,atmospheric deposition and seawater.The results from the SIAR model indicated that nitrate in the Daya Bay in four seasons was mainly came from sewage(41.4-53.7%),followed by river(22.3-29.4%),and the contributed proportion of atmospheric deposition was minimum(1.5-9.4%).The nitrate concentration in the Jiaozhou Bay was mainly affected by sewage discharge in spring,autumn and winter,while it was also affected by riverine source and atmospheric deposition in summer.Based on the results of the SIAR model,the contributed proportion of sewage in the Jiaozhou Bay showed a seasonal pattern with:autumn(80.4%)>winter(48.7%)>summer(41.5%)>spring(6.2%).The nitrate in the Daya Bay and the Jiaozhou Bay was mainly derived from the terrestrial input,while the influence of anthropogenic activity on the Jiaozhou Bay was more significant.The annual average values of NO3--?15N and NO3--?18O in two bays were close to each other,reflecting the similarity of nitrogen and oxygen isotopic compositions in the sewage entering the two bays.The influence of sewage on nitrate in the Jiaozhou Bay was stronger than that in the Daya Bay,while the effect of riverine input in the Daya Bay was stronger than in the Jiaozhou Bay.The influence of atmospheric deposition in the Daya Bay was minimum in summer,while its impact on the Jiaozhou Bay was most important in summer.Nitrification played a significant role in regulating the nitrogen and oxygen isotopic compositions of nitrate in the Daya Bay and the Jiaozhou Bay,and NH4+concentration was one of the major factors affecting this process.In the Daya Bay,the influence of temperature and particle concentration on nitrification was much significant due to its high NH4+concentration in summer and autumn.In the Jiaozhou Bay,the low NH4+ concentration weakened the effect of temperature and particle concentration in spring and summer,thus the strongest nitrification was observed in winter when the NH4+concentration was high.