I Estimating soil C stock in a peatland is highly dependent on accurate measurement of the peat volume. In this study, we evaluated the uncertainty in calculations of peat volume using high-resolution data to resolve the threedimensional structure of a peat basin based on both direct (push probes) and indirect geophysical (ground-penetrating radar) measurements. We compared volumetric estimates from both approaches, accounting for potential sources of error, with values from the literature. Approximate uncertainty of 14 to 23% was observed in the basin volume, and the total uncertainty roughly doubled when incorporating peat properties to derive the estimated C pool. Uncertainties in final C stock values are based on the uncertainty of the basin volumes and the variability in the peat properties and range between 31 and 38%. The results indicate that the well-established ground-penetrating radar technique that is scalable to larger peatlands can be used to ohtain estimates of peat basin volumes at uncertainty levels similar to those for invasive direct probe surveys. This investigation demonstrated that ground-penetrating radar can quantify peat basin volumes at uniquely high spatial resolution without the need for extensive and invasive direct probing.
[1] Northern peatlands contain vast amounts of organic carbon. Large-scale datasets have documented spatial patterns of peatland initiation as well as vertical peat accumulation rates. However, the rate, pattern, and timing of lateral expansion across the northern landscape remain largely unknown. As peatland lateral extent is a key boundary condition constraining the dynamics of peatland systems, understanding this process is essential. Here we use ground penetrating radar (GPR) and peat core analysis to study the effect of local slope and topography on peatland development at a site in south-central Alaska. The study site is unique in that a thick tephra (volcanic ash) layer, visible in the GPR data, interrupted the peatland development for about one thousand years during the mid Holocene. In our analysis, this tephra layer serves as a re-initiation point for peatland development. By comparing the initial mineral basin vs. the post-tephra surfaces, the influence of topography and slope on peatland expansion rate and peat-carbon sequestration was analyzed. Our results show that (1) peatland surface slope becomes progressively shallower over the Holocene, (2) slope affects peatland lateral expansion nonlinearly, (3) the relationship between lateral expansion rate and slope follows a power-law behavior, and (4) peatland expansion becomes slope-limited above a threshold (0.5 ). Furthermore, we propose a conceptual model linking slope to peatland lateral expansion where slope gradient and basin topography exert deterministic controls on peatland lateral expansion directly or through hydrology and vertical accumulation rates.
The distribution of shallow frozen ground is paramount to research in cold regions, and is subject to temporal and spatial changes influenced by climate, landscape disturbance and ecosystem succession. Remote sensing from airborne and satellite platforms is increasing our understanding of landscape-scale permafrost distribution, but typically lacks the resolution to characterise finer-scale processes and phenomena, which are better captured by integrated surface geophysical methods. Here, we demonstrate the use of electrical resistivity imaging (ERI), electromagnetic induction (EMI), ground penetrating radar (GPR) and infrared imaging over multiple summer field seasons around the highly dynamic Twelvemile Lake, Yukon Flats, central Alaska, USA. Twelvemile Lake has generally receded in the past 30 yr, allowing permafrost aggradation in the receded margins, resulting in a mosaic of transient frozen ground adjacent to thick, older permafrost outside the original lakebed. ERI and EMI best evaluated the thickness of shallow, thin permafrost aggradation, which was not clear from frost probing or GPR surveys. GPR most precisely estimated the depth of the active layer, which forward electrical resistivity modelling indicated to be a difficult target for electrical methods, but could be more tractable in time-lapse mode. Infrared imaging of freshly dug soil pit walls captured active-layer thermal gradients at unprecedented resolution, which may be useful in calibrating emerging numerical models. GPR and EMI were able to cover landscape scales (several kilometres) efficiently, and new analysis software showcased here yields calibrated EMI data that reveal the complicated distribution of shallow permafrost in a transitional landscape.
Direct measurements of soil moisture are extremely diffi cult to obtain between the spaal scales of point measurements and remote sensing. Nevertheless, the spa otemporal distribu on of soil moisture remains a key variable in hydrology. In this study, we explored the use of mul point direct-current resis vity to examine spa otemporal changes in soil moisture following a rapid infi ltra on event into a large macropore. The methodology was selected because the me scale of fl ow processes in the homogeneous isotropic sand prevented the use of imaging techniques. Selec on of an appropriate electrode array was cri cal for collec ng the required high-resolu on spa otemporal resis vity measurements in a 1.44-m-diameter tank. Direct placement of a dense array of electrodes in the sand allowed us to use geosta s cal methods for spa al interpola on, thereby removing the inherent uncertainty resul ng from inversion mechanics (i.e., smoothness constraints for underconstrained problems). Instead, conversion of resis vity to satura on was directly performed using Archie's law. We compared the observa ons to a two-dimensional, axisymmetric, numerical solu on of the system using the HYDRUS 2D/3D so ware, and to a semianaly cal solu on to es mate soil hydraulic proper es. We found sa sfactory comparisons among the observa ons and the numerical and semianaly cal solu ons of the system, which indicates that these techniques may be applicable to fi eld-scale es mates of eff ec ve hydraulic proper es. Subject to limi ng ini al condi ons, boundary condions, and material proper es, the results of the semianaly cal solu on are encouraging for capturing general hillslope-scale dynamics at longer temporal scales toward a greater understanding of emergent pa erns in dryland ecosystems.Abbrevia ons: TDR, me domain refl ectometry.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.