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Kantola et al. (2023) (K23) report data on carbon dioxide removal (CDR) via enhanced weathering (EW) after applying ground basalt to agricultural plots. Here, we argue that their methodology does not allow them to assess whether EW fluxes are significantly different from zero at the 1 standard error level (≈83% CI). 

Perez-Fodich AGU 2019 

Volcanic landscapes begin with high permeability, but with time develop a weathered surface that reduces permeability and diverts increasing amounts of water to stream runoff. On the island of Hawai’i the young volcanoes have no permanent streams; stream incision becomes important the older surfaces (more than about 20,000 years). By treating the weathered surface as a porous-plastic medium we find that weathering can induce compaction of the soil that reduces permeability. The reduction in infiltration and initiation of stream incision fundamentally changes the hydrologic and geomorphic evolution of the landscape. Weathering affects both the chemistry and material properties of the surface and strongly influences landscape development, in ways that can be predicted with reactive transport and mechanical modeling. Geochemical tracers can be used to identify and quantify weathering processes and constrain these models. Chadwick et al. 2003 Chem Geol 202 195-203; Gurson 1977, Trans ASME 99 1-25. 

Fernandez EGU 2019 

Grant Goldschmidt 2018 

Richardson Derry Richter GSA NE 2017 

Abstract Silicon stable isotope ratios (³⁰Si) of over 150 stream water samples were measured during seven storm events in six small critical zone observatory (CZO) catchments spanning a wide range in climate (sub‐humid to wet, tropical) and lithology (granite, volcanic, and mixed sedimentary). Here we report a cross‐site analysis of this dataset to gain insight into stream³⁰Si variability across low‐order catchments and to identify potential climate (i.e., runoff), hydrologic, lithologic, and biogeochemical controls on observed stream Si chemical and isotopic signatures. Event‐based³⁰Si exhibit variability both within and across sites (−0.22‰ to +2.27‰) on the scale of what is observed globally in both small catchments and large rivers. Notably, each site shows distinct³⁰Si signatures that are preserved even after normalization for bedrock composition. Successful characterization of observed cross‐site behavior requires the merging of two distinct frameworks in a novel combined model describing both non‐uniform fluid transit time distributions and multiple fractionating pathways in application to low‐order catchments. The combined model reveals that site‐specific architecture (i.e., biogeochemical reaction pathways and hydrologic routing) regulates stream silicon export signatures even when subject to extreme precipitation events.