The CO 2 consumption potential during gray shale weathering: Insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory

Jin, Lixin; Ogrinc, Nives; Yesavage, Tiffany; Hasenmueller, Elizabeth A.; Ma, Lin; Sullivan, Pamela L.; Kaye, Jason P.; Duffy, Christopher; Brantley, Susan L.

doi:10.1016/j.gca.2014.07.006

Cited by 59 publications

(73 citation statements)

References 85 publications

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“…Soil CO 2 represents the largest flux of carbon (C) from terrestrial ecosystems, affects carbonate speciation within calcareous soils, and contributes to the acidity that drives silicate weathering (e.g., Amundson et al, 1998; Davidson et al, 1998; Jin et al, 2014). In soils, C resides in both organic and inorganic forms within soil organic matter, biota, minerals, and pore water, with respiration by roots and heterotrophic organisms being the largest flux of C from soils (Chapin et al, 2011).…”

Section: Reactions In Soil With Ratio That Could Results In a Change mentioning

confidence: 99%

“…Silicate weathering has been documented in the soil of the SSHCZO and accounts for some of the consumed CO 2 in the soils of Garner Run and Shale Hills (Angert et al, 2015; Jin et al, 2014). However, the rate of these weathering reactions is slow, ranging from 0.001 to 0.005 mol Si m −2 yr −1 (Sullivan et al, 2019), and at most could only consume about 0.3 mg C m −2 d −1 (Jin et al, 2014). Although model results indicate that the silicate dissolution rate is fastest in the early growing season when we observe ARQ <1, this relatively small consumption potential could not explain our observations.…”

Section: Discussionmentioning

confidence: 99%

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Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Hodges

Kim

Brantley

et al. 2019

Soil Science Soc of Amer J

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Soil CO2 and O2 cycles are coupled in some processes (e.g., respiration) but uncoupled in others (e.g., silicate weathering). One benchmark for interpreting soil biogeochemical processes affected by soil pCO2 and pO2 is to calculate the apparent respiratory quotient (ARQ). When aerobic respiration and diffusion are the dominant controls on gas concentrations, ARQ equals 1; ARQ deviates from 1 when other processes dominate soil CO2 and O2 chemistry. Here, we used ARQ to understand lithologic, hillslope, and seasonal controls on soil gases at the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. We measured soil pCO2 and pO2 at three depths from the soil surface to bedrock across catenas in one shale and one sandstone watershed over three growing seasons. We found that both parent lithology and hillslope position significantly affect soil gas concentrations and ARQ. Soil pCO2 was highest (>5%) and pO2 was lowest (<16%) in the valley floors. Controlling for depth, pCO2 was higher and pO2 was lower across all sites in the sandstone watershed. We attribute this pattern to higher macroporosity in sandstone lithologies, which results in greater root respiration at depth. We recorded seasonal variation in ARQ at all sites, with ARQ rising above 1 during July through September, and dipping below 1 in the early spring. We hypothesize that this seasonal fluctuation arises from anaerobic respiration in reducing microsites July through September when the soils are wet and demand for O2 is high, followed by oxidation of reduced species when the soils drain and re‐oxygenate. We estimate that this anaerobic respiration in microsites contributes 36 g C m−2 yr−1 to the soil C flux. Our results provide evidence for a conceptual model of metal cycling in temperate watersheds and point to the importance of anaerobic respiration to the carbon flux from forest soils. Core Ideas Hillslope position and lithology affect soil CO2 and O2 in humid temperate forests. The ratio of CO2 and O2 (ARQ) fluctuates over the growing season. The ARQ fluctuations indicate seasonal metal redox cycling at all hillslope positions. Anaerobic respiration is important to soil CO2 flux during the late growing season.

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Section: Reactions In Soil With Ratio That Could Results In a Change mentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Hodges

Kim

Brantley

et al. 2019

Soil Science Soc of Amer J

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“…(2); see Jin et al, 2010) consumes dissolved CO 2 (Eq. (3)) as evidenced by the 13 C of DIC and positive correlations between soil pCO 2 and DIC concentrations in porewaters (Jin et al, 2014). Carbonates in the Silurian Rose Hill Formation shale, including calcite and ankerite, have been completely weathered out of surface soils.…”

Section: Introductionmentioning

confidence: 96%

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

Hasenmueller

Jin

Stinchcomb

et al. 2015

Applied Geochemistry

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a b s t r a c tAccurate measurements of soil CO 2 concentrations (pCO 2 ) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO 2 , most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO 2 distribution can predictably vary with topographic position. We measured soil pCO 2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO 2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO 2 generally at 0.1e0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO 2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO 2 diffusive fluxes. The highest pCO 2 values were observed in the valley floor and swales where soils are deep (!0.7 m) and wet, resulting in low CO 2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO 2 because they are shallower ( 0.6 m) and drier, resulting in high CO 2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO 2 : the north (i.e., south-facing) swale generally had lower soil moisture content and pCO 2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO 2 was similar across the watershed, the amplitude of the pCO 2 peak was higher in the deep soils due to more variable moisture content. The high pCO 2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO 2 alone. CO 2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO 2 dynamics would be improved by including landscape controls on soil pCO 2 .

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“…Compared with silicate catchments, however, the carbon sink flux in karstic catchments is much higher. Results from a Susquehanna Shale Hills catchment, USA, show that silicate weathering consumes CO 2 at a rate of only 1.94 t km À2 a À1 (Jin et al, 2014). The silicate weathering carbon sink is only 7.3% of the karst sink flux in this comparison, emphasizing the control of lithology on the rock weathering-related carbon sink.…”

Section: Comparison With Carbonate and Non-carbonate Catchments Elsewmentioning

confidence: 65%

A groundwater conceptual model and karst-related carbon sink for a glacierized alpine karst aquifer, Southwestern China

Zou

Liu

Yang

et al. 2015

Journal of Hydrology

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The CO 2 consumption potential during gray shale weathering: Insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory

Cited by 59 publications

References 85 publications

Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

A groundwater conceptual model and karst-related carbon sink for a glacierized alpine karst aquifer, Southwestern China

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The CO 2 consumption potential during gray shale weathering: Insights from the evolution of carbon isotopes in the Susquehanna Shale Hills critical zone observatory

Cited by 59 publications

References 85 publications

Soil CO2 and O2 Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Soil CO2 and O2 Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

A groundwater conceptual model and karst-related carbon sink for a glacierized alpine karst aquifer, Southwestern China

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Product

Resources

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Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Soil CO₂ and O₂ Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations