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This data package is used in the manuscript entitled “Hydrological control of chemical weathering and rock-carbon fluxes”. The field study was conducted in a lower montane hillslope of the East River watershed, underlain by Mancos Shale, within the lower 140 m section of a transect that extends nearly 1 km to its local peak. The data in this package, in CSV file format, were collected from Fall 2016 to fall 2021, including depth-resolved dynamic water table depths, subsurface water fluxes, solid phase (soil to bedrock) chemical compositions, geochemical properties of porewater and pore-gas, including radio carbon concentrations. The detailed methods of field studies, laboratory chemical analyses, and calculations are described in the Methods section and in the dataset file: Wan_et_al_Methods.pdf. The dataset additionally includes a file-level metadata (flmd.csv) file that lists each file contained in the dataset with associated metadata; and a data dictionary (dd.csv) file that contains column/row headers used throughout the files along with a definition, units, and data type.

Permafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw-induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO₂) is relatively unconstrained. Resolving this uncertainty is important as thaw-driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean-atmosphere system and increase pCO₂, producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate (SO₄^2-) sulfur (³⁴S/³²S) and oxygen (¹⁸O/¹⁶O) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO₂. Calculations found that approximately 80% of SO₄^2- in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, ³⁴S/³²S ratios, ¹³C/¹²C ratios of dissolved IC, and sulfur X-ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO₂ over timescales shorter than carbonate compensation (~10⁴ yr) and, for mainstem samples, higher values of pCO₂ over timescales longer than carbonate compensation but shorter than the residence time of marine (~10⁷ yr). Furthermore, the absolute concentrations of and Mg²⁺ in the Koyukuk River, as well as the ratios of SO₄^2- and Mg²⁺ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale-dependent feedback on warming.

Fungal mineral weathering regulates the bioavailability of inorganic nutrients from mineral surfaces to organic matter and increase the bioavailable fraction of nutrients. Such weathering strategies are classified as biomechanical or biochemical. In the case of fungal uptake of mineral nutrients through biochemical weathering, it is widely hypothesized that uptake of inorganic nutrients occurs through organic acid chelation, but such processes have not been directly visualized. This is in part due to challenges in probing the complex and heterogeneous soil environment. Here, using an epoxy-based, mineral-doped soil micromodel platform, which emulates soil mineralogy and porosity, we visualize the molecular mechanisms of mineral weathering. Mass spectrometry imaging revealed differences in the distribution of fungal exudates, citric acid, and tartaric acid on the soil micromodels in presence of minerals. Citric acid was detected closer to the nutrient-rich inoculation point, whereas tartaric acid was highly abundant away from inoculation point. This suggested that the organic acid exuded by the fungi depended on the proximity from the carbon-rich organic substrate at the point of inoculation. Using a combination of X-ray fluorescence and X-ray near edge structure analysis, we identified citric acid- and tartaric acid-bound K within fungal hyphae networks grown in the presence of minerals. Combined, our results provide direct evidence that fungi uptake and transport mineral derived nutrient organic acid chelation. The results of this study provided unprecedented visualization of fungal uptake and transport of K⁺, while resolving the indirect weathering mechanism of fungal K uptake from mineral interfaces.

Terrestrial enhanced weathering (EW) through the application of Mg- or Ca-rich rock dust to soil is a negative emission technology with the potential to address impacts of climate change. The effectiveness of EW was tested over 4 years by spreading ground basalt (50 t ha^–1 year^–1) on maize/soybean and miscanthus cropping systems in the Midwest US. The major elements of the carbon budget were quantified through measurements of eddy covariance, soil carbon flux, and biomass. The movement of Mg and Ca to deep soil, released by weathering, balanced by a corresponding alkalinity flux, was used to measure the drawdown of CO₂, where the release of cations from basalt was measured as the ratio of rare earth elements to base cations in the applied rock dust and in the surface soil. Basalt application stimulated peak biomass and net primary production in both cropping systems and caused a small but significant stimulation of soil respiration. Net ecosystem carbon balance (NECB) was strongly negative for maize/soybean (–199 to –453 g C m^–2 year^–1) indicating this system was losing carbon to the atmosphere. Average EW (102 g C m^–2 year^–1) offset carbon loss in the maize/soybean by 23%–42%. NECB of miscanthus was positive (63–129 g C m^–2 year^–1), indicating carbon gain in the system, and EW greatly increased inorganic carbon storage by an additional 234 g C m^–2 year^–1. Our analysis indicates a co-deployment of a perennial biofuel crop (miscanthus) with EW leads to major wins—increased harvested yields of 29%–42% with additional carbon dioxide removal (CDR) of 8.6 t CO₂ ha^–1 year^–1. EW applied to maize/soybean drives a CDR of 3.7 t CO₂ ha^–1 year^–1, which partially offsets well-established carbon losses from soil from this crop rotation. EW applied in the US Midwest creates measurable improvements to the carbon budgets perennial bioenergy crops and conventional row crops.

As plastics degrade in the environment, chemical oxidation of the plastic surface enables inorganics to adsorb and form inorganic coatings, likely through a combination of adsorption of minerals and in situ mineral formation. The presence of inorganic coatings on aged plastics has negative implications for plastics fate, hindering our ability to recycle weathered plastics and increasing the potential for plastics to adsorb contaminants. Here, inorganic coatings formed on terrestrially weathered polyethylene were characterized using synchrotron spectroscopy and microscopy techniques across spatial scales including optical microscopy, nano-X-ray-fluorescence mapping (nano-XRF), nano-X-ray absorption near edge structure (nano-XANES), and high-energy resolution fluorescence detected-XANES (HERFD-XANES). Results indicate a heterogeneous elemental distribution and speciation which includes inorganics common to soil terrestrial environments including iron oxides and oxyhydroxides, aluminosilicates, and carbonates.

The oxidation of organic carbon in sedimentary bedrock (petrogenic OC, OC_petro) is increasingly recognized as a potential source of CO₂ to the atmosphere. Recent studies provide evidence for the mobilization and oxidation of OC_petro in sedimentary bedrock during rock weathering. However, the mechanisms and rates remain uncertain, particularly where overlying soils and vegetation drive contemporaneous oxidation of recently fixed organic carbon. Here, in this study, we quantify OC_petro weathering across a 16 m shale depth profile in a steep, rapidly eroding forested hillslope in the Northern California Coast Ranges. We report solid and gas phase radiocarbon and stable isotope analyses of samples extracted from specialized in-situ samplers, and a supporting laboratory incubation experiment of the shale regolith. OC_petro is removed from the weathered bedrock at a rate of approximately 0.12 gC/m³yr, which is orders of magnitude lower than the rate of OC_petro oxidation we achieved in the laboratory with crushed samples (557.1 gC/m³yr). This disparity occurs despite high O_2(g) content across the depth profile, indicating that physical accessibility of OC_petro can regulate oxidative weathering. There is no direct radiocarbon evidence of OC_petro oxidation in CO_2(g) across the upper 13 m of the weathering profile during both wet and dry seasons. Instead, vadose zone CO_2(g) production at the site is dominated by respiration of recently fixed carbon associated with deep rooting. OC_petro is clearly mobilized across the vadose zone during weathering in this rapidly eroding, oxygen-rich, biologically dynamic hillslope, but at rates far below what can be measured given the contribution of root-derived CO_2(g).

Earth’s biosphere is thought to exert a substantial influence on regolith evolution and chemical weathering rates. However, ecosystems are also highly efficient at retaining and recycling nutrients. Thus, when the ecological demand for rock-derived nutrients (e.g., P, Ca, K) exceeds the rates of regolith supply, ecological retention and recycling strategies can minimize nutrient limitations. To evaluate the balance between nutrient recycling and new nutrient input, we combined a plant model that drives growth according to foliar P levels with a weathering model that includes regolith rejuvenation via erosion and export via chemical weathering according to water flow, regolith thickness, mineral dissolution rates, secondary minerals, and nutrient storage in organic and mineral phases. We find that plant growth is strongly dependent on the total regolith nutrient inventory, resulting in a strong correlation between plant productivity and erosion. Increased water export or decreased regolith thickness diminish the total inventory of nutrient corresponding to lower rates of recycling and lower plant growth. In contrast, purported biogenic drivers of weathering, such as enhanced mineral dissolution, only support higher growth rates at high erosion rates. At erosion rates typical of the global land surface, more rapid mineral dissolution combined with enhanced formation of secondary minerals, depletes the inventory of mineral P, resulting in no benefit for plant growth. We also find that the increased chemical weathering export does not scale directly with plant growth. For example, accelerated mineral weathering does increase chemical weathering export but not potential plant growth. Conversely, thicker regolith is associated with a small increase in weathering export, but a large increase in potential plant growth. Collectively, when plant growth is coupled to regolith weathering our calculations suggest that plant productivity is not directly correlated with silicate weathering fluxes, and that biotic drivers of silicate weathering may only be effective at high erosion rates not typical at the Earth’s surface.

Soil supports life by serving as a living, breathing fabric that connects the atmosphere to the Earth's crust. The study of soil science and pedology, or the study of soil in the natural environment, spans scales, disciplines, and societies worldwide. Soil science continues to grow and evolve as a field given advancements in analytical tools, capabilities, and a growing emphasis on integrating research across disciplines. A pressing need exists to more strongly incorporate the study of soil, and soil scientists, into research networks, initiatives, and collaborations. This review presents three research areas focused on questions of central interest to scientists, students, and government agencies alike: 1) How do the properties of soil influence the selection of habitat and survival by organisms, especially threatened and endangered species struggling in the face of climate change and habitat loss during the Anthropocene? 2) How do we disentangle the heterogeneity of abiotic and biotic processes that transform minerals and release life-supporting nutrients to soil, especially at the nano- to microscale where mineral-water-microbe interactions occur? and 3) How can soil science advance the search for life and habitable environments on Mars and beyond- from distinguishing biosignatures to better utilizing terrestrial analogs on Earth for planetary exploration? This review also highlights the tools, resources, and expertise that soil scientists bring to interdisciplinary teams focused on questions centered belowground, whether the research areas involve conservation organizations, industry, the classroom, or government agencies working to resolve global challenges and sustain a future for all.

To understand geological systems that are important to our national well-being -- such as nuclear waste repositories or hydraulically fractured rocks -- requires the ability to make quantitative projections of the evolution of rock-water systems forward in time. A fundamental goal of much of our geochemical research was focused on development of numerical models of reactive transport to simulate the evolution of natural water-rock systems. The geochemical community has provided such models and they are rapidly being improved with field-model cross-testing. This project was especially impactful in field-model testing for well-constrained weathering systems to provide new conceptual understanding of how these systems function.

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model. This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coating on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. In conclusion, this work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.