Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; State Key laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin, 300072, China.
Sci Total Environ. 2021 May 10;768:144343. doi: 10.1016/j.scitotenv.2020.144343. Epub 2020 Dec 30.
Sulfuric acid formed by pyrite oxidation and nitric acid formed by oxidation of reducing nitrogen fertilizer through neutralization with carbonate minerals can rapidly perturb the carbon cycle. However, these processes and corresponding mechanisms have not been well documented due to the lack of information about both the sources of acids and the processes of oxidative weathering. Here, multiple isotopes (C-DIC, S and O-SO, N and O-NO, and O and D-HO), hydrochemistry and historical monitoring data were used to assess the roles of strong acids in chemical weathering and the carbon cycle in a karst river system. The variations in alkalinity and the δC-DIC signals, along with theoretical mixing models, indicated that strong acids were involved in carbonate weathering. However, the contribution of weathering driven by strong acids to the total weathering budget determined by mixing models was lower than that determined by assuming that all protons were neutralized by minerals. These protons were liberated from oxidation of pyrite and reducing nitrogen fertilizers constrained by isotope techniques and hydrochemistry with the use of a Bayesian isotope mixing model. The strong acid weathering could account for 66% of total weathering if all of the protons were neutralized by carbonate and silicate, which was not consistent with the result provided by mixing models. These results indicated that in addition to being neutralized by minerals, the protons might be largely neutralized by HCO derived from rock weathering driven by both carbonic and strong acids. The coupling cycles of carbon, nitrogen and sulfur would be boosted due to oxidation of pyrite and reducing nitrogen fertilizers. This study suggests that the CO uptake by terrestrial chemical weathering should be re-evaluated after adequately considering the effects of strong acids liberated by natural processes and anthropogenic activities.
黄铁矿氧化形成的硫酸和还原氮肥氧化形成的硝酸与碳酸盐矿物中和后，可迅速扰乱碳循环。然而，由于缺乏关于酸源和氧化风化过程的信息，这些过程和相应的机制尚未得到很好的记录。在这里，我们使用多种同位素（C-DIC、S 和 O-SO、N 和 O-NO 以及 O 和 D-HO）、水化学和历史监测数据来评估强酸在喀斯特河流系统中的化学风化和碳循环中的作用。碱度和δC-DIC 信号的变化，以及理论混合模型，表明强酸参与了碳酸盐风化。然而，由混合模型确定的强酸风化对总风化预算的贡献低于假设所有质子都被矿物中和时的贡献。这些质子是由硫铁矿和还原氮肥氧化释放出来的，同位素技术和水化学与贝叶斯同位素混合模型的使用对其进行了约束。如果所有质子都被碳酸盐和硅酸盐中和，那么强酸风化可以解释总风化的 66%，这与混合模型提供的结果不一致。这些结果表明，除了被矿物中和外，质子可能还被 HCO 大量中和，而 HCO 则是由碳酸和强酸驱动的岩石风化产生的。由于黄铁矿和还原氮肥的氧化，碳、氮和硫的耦合循环将得到加强。本研究表明，在充分考虑自然过程和人为活动释放的强酸对陆地化学风化的 CO 吸收的影响后，应重新评估陆地化学风化的 CO 吸收。
