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Climate models project changing patterns of precipitation and increases in temperature that modify soil moisture dynamics. Land use and changing frequency and intensity of precipitation can induce changes in soil structure and rooting abundances at timescales shorter than commonly considered. Soil structure is a critical ecosystem that governs water flow through soil profiles and across landscapes, and can influence weathering rates and thus solute release and soil development. We hypothesize that the altered soil structure and modification of rooting depth distributions linked to land use change can influence soil solute concentrations, and that those shifts in solute release are dependent on patterns of precipitation. We installed suction lysimeters to collect soil water for ~3 y in two grassland regions with distinct mean annual precipitation (800 mm y-1, 1100 mm y-1) in native prairie, agriculture, and post-agriculture land uses at depths of 10, 40, and 120 cm. We linked solute concentrations to soil moisture, aggregate-size distribution, pore geometry, and rooting depth distributions to assess how land use change and the altered rooting abundance it imposes can modify soil structure and hydrologic fluxes, and to infer how soil weathering can shift deep in the subsurface. We reveal how soil moisture residence time and the soil pore network can govern solute production, and the importance of precipitation and thus of soil moisture accumulation over growing seasons for mineral weathering and solute production. Specifically, we find that the solubility potential of multiple weathering products and organic carbon increases with precipitation, dominance of relatively small aggregates at the surface, and fewer coarse roots. Enhanced solute concentrations at depth may also reflect transport down-profile. Our findings reveal unintended consequences of land use change that influence important hydrologic dynamics and nutrient cycling in the vadose zone and how deeply and how persistently unexpected consequences of changes in land cover can propagate.
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Multiscale Legacy Responses of Soil Gas Concentrations to Soil Moisture and Temperature Fluctuations
Abstract The sensitivity of soil carbon dynamics to climate change is a major uncertainty in carbon cycle models. Of particular interest is the response of soil biogeochemical cycles to variability in hydroclimatic states and the related quantification of soil memory. Toward this goal, the power spectra of soil hydrologic and biogeochemical states were analyzed using measurements of soil temperature, moisture, oxygen, and carbon dioxide at two sites. Power spectra indicated multiscale power law scaling across subhourly to annual timescales. Precipitation fluctuations were most strongly expressed in the soil biogeochemical signals at monthly to annual timescales. Soil moisture and temperature fluctuations were comparable in strength at one site, while temperature was dominant at the other. The effect of soil hydrologic, thermal, and biogeochemical processes on gas concentration variability was evidenced by low spectral entropy relative to the white noise character of precipitation. A full mass balance model was unable to capture high‐frequency soil temperature influence, indicating a gap in commonly used model assumptions. A linearized model was shown to capture the main features of the observed and modeled gas concentration spectra and demonstrated how the means and variances of soil moisture and temperature interact to produce the gas concentration spectra. Breakpoints in the spectra corresponded to the mean rate of gas efflux, providing a first‐order estimate of the soil biogeochemical integral timescale (∼1 min). These methods can be used to identify biogeochemical system dynamics to develop robust, process‐based soil biogeochemistry models that capture variability in addition to long‐term mean values.
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- PAR ID:
- 10449319
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 126
- Issue:
- 2
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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