Alkalinity generation from carbonate weathering in a silicate-dominated headwater catchment at Iskorasfjellet, northern Norway

• Published in: Biogeosciences
• Main Authors: N. Lehmann, H. Lantuit, M. E. Böttcher, J. Hartmann, A. Eulenburg, H. Thomas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Norway; Carbonic acid; Northern Norway; permafrost; Subarctic
• Online Access: https://doi.org/10.5194/bg-20-3459-2023; https://doaj.org/article/b24936be134e4af993f587e6a545411f

The weathering rate of carbonate minerals is several orders of magnitude higher than for silicate minerals. Therefore, small amounts of carbonate minerals have the potential to control the dissolved weathering loads in silicate-dominated catchments. Both weathering processes produce alkalinity under the consumption of CO 2 . Given that only alkalinity generation from silicate weathering is thought to be a long-term sink for CO 2 , a misattributed weathering source could lead to incorrect conclusions about long- and short-term CO 2 fixation. In this study, we aimed to identify the weathering sources responsible for alkalinity generation and CO 2 fixation across watershed scales in a degrading permafrost landscape in northern Norway, 68.7–70.5 ∘ N, and on a temporal scale, in a subarctic headwater catchment on the mountainside of Iskorasfjellet, characterized by sporadic permafrost and underlain mainly by silicates as the alkalinity-bearing lithology. By analyzing total alkalinity (AT) and dissolved inorganic carbon (DIC) concentrations, as well as the stable isotope signature of the latter ( δ 13 C-DIC), in conjunction with dissolved cation and anion loads, we found that AT was almost entirely derived from weathering of the sparse carbonate minerals. We propose that in the headwater catchment the riparian zone is a hotspot area of AT generation and release due to its enhanced hydrological connectivity and that the weathering load contribution from the uphill catchment is limited by insufficient contact time of weathering agents and weatherable materials. By using stable water isotopes, it was possible to explain temporal variations in AT concentrations following a precipitation event due to surface runoff. In addition to carbonic acid, sulfuric acid, probably originating from oxidation of pyrite or reduced sulfur in wetlands or from acid deposition, is shown to be a potential corrosive reactant. An increased proportion of sulfuric acid as a potential weathering agent may have resulted in a decrease in AT. ...