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Reservoir NO3- pollution and chemical weathering: by dual isotopes of delta N-15-NO3-, delta O-18-NO3- and geochemical constraints
Herath, Imali Kaushalya; Wu, Shengjun; Ma, Maohua; Ping, Huang
2022-01-25
摘要Reservoir dams alter the nutrient composition and biogeochemical cycle. Thus, dual isotopes of delta O-18-NO3- and delta N-15-NO3- and geochemical signatures were employed to study the NO3- pollution and chemical weathering in the Three Gorges Reservoir (TGR), China. This study found that the TGR dam alters the delta N-15-NO3- composition and is enriched in the recharge period. Values of delta N-15-NO3- varied from 4.5 to 12.9 parts per thousand with an average of 9.8 parts per thousand in the recharge period, while discharge period delta N-15-NO3- ranged from 3.2 to 12.5 parts per thousand, with an average of 9.3 parts per thousand. delta O-18-NO3- varies (1.2-11.3 parts per thousand) with an average of 6.5 parts per thousand and (2.4-12.4 parts per thousand) with an average of 7.5 parts per thousand, in the recharge and discharge periods, respectively. Stable isotopic values sharply decreased from upstream to downstream, indicating the damming effects. delta O-18-NO3- and delta N-15 NO3- confirm that sewage effluents, nitrification of soil organic material, and NH4+ fertilizers were the primary sources of NO3- in the reservoir. Carbonate weathering mainly provides ions to the reservoir. HOC3- + SO42- and Ca2+ + Mg2+ represent 90% of major ions in the TGR. Downstream sampling sites showed low solute concentration during the recharge period, indicating the dam effect on solute concentration. Ca-Mg-Cl-, Ca-HCO3- and Ca-Cl- were the main water types in the TGR. The average percentage of solutes contribution revealed the carbonate weathering, evaporites dissolution, silicate weathering, and atmospheric input were 51.9%, 41%, 7.8%, and 1.7% for the recharge period. In contrast, the discharge period contributed 66.4%, 29.2%, 10%, and 4.3%, respectively. TGR water is moderately suitable for irrigation, and hardness is high in drinking water. This study provides new insight into the dual isotopic approach and geochemical signatures to interpret the NO3- cycle and chemical weathering process under dam effects in the TGR. However, this isotopic application has some limitations in source identification, isotope fractionation, and transformation mechanisms of nitrate. Thus, further studies need to be done on these topics for a better undestanding.
关键词Chemical weathering Nitrate pollution Dual isotopes Aquatic geochemistry Three Gorges Reservoir
DOI10.1007/s10653-021-01195-4
发表期刊ENVIRONMENTAL GEOCHEMISTRY AND HEALTH
ISSN0269-4042
页码22
通讯作者Herath, Imali Kaushalya(imalikaushalya@yahoo.com) ; Wu, Shengjun(wsg@cigit.ac.cn)
收录类别SCI
WOS记录号WOS:000746759300001
语种英语