Soil profile sampled in the Hautes Fagnes area, where soil water samplers are installed.

The study on soil-water-vegetation dynamics was realised in the scope of the LandSense project, and it is focused on a disturbed peatland in the Belgian Hautes Fagnes. The site was previously drained and planted with spruce. In the study led by Maud Henrion, we aimed to elucidate the use of Ground-penetrating radar (GPR) and Electromagnetic induction (EMI) techniques in characterizing peatlands, with a specific focus on their implications for peat depth and electrical conductivity assessment, related to peatland degradation.

In the study led by Yanfei Li, we aimed to establish links between the above- and below-ground factors that control soil carbon status of the peatlands, and identify the key environmental variables associated with carbon storage. The study also explored the potential for using Unmanned Aerial Vehicle (UAV) remote sensing for spatial mapping of peatlands. Our results indicated that both peat thickness and soil organic carbon (SOC) stock (top 1 m) are spatially heterogeneous and that the contributions from the surface topography to peat thickness and SOC stock varied from micro- to macro-scales.

More information :

Henrion, M., Li, Y., Koganti, T., Bechtold, M., Jonard, F., Opfergelt, S., Vanacker, V., Van Oost, K., Lambot, S.: Mapping and monitoring peatlands in the Belgian Hautes Fagnes: Insights from Ground-penetrating radar and Electromagnetic induction characterization. Geoderma Regional 37, e00795 (2024)

Li, Y., Henrion, M., Moore, A., Lambot, S., Opfergelt, S., Vanacker, V., Jonard, F., Van Oost, K.: Factors controlling peat soil thickness and carbon storage in temperate peatlands based on UAV high-resolution remote sensing. Geoderma 449, 117009 (2024)

We use a compiled dataset of 99 detrital ¹⁰Be measurements, 63 of which are new, covering more than 30% of the country and a wide range of topographic, bioclimatic and geologic characteristics. Overall, ¹⁰Be erosion rates are low (2.4–51.1 mm kyr⁻¹), with clear differences between regions. The lowest rates are measured on the central highlands ( 8 mm kyr⁻¹), in the Alaotra–Ankay graben ( 11 mm kyr⁻¹) and in the large north-central catchments ( 11 mm kyr⁻¹). Higher rates are found on the steep eastern escarpment ( 20 mm kyr⁻¹), in the northwest ( 31 mm kyr⁻¹) and in the southwest ( 29 mm kyr⁻¹).

Figure shows the ¹⁰Be erosion rates organised from north to south for the different regions. Marker size represents the catchment area. Boxplots are included for regions that contain sufficient sampled catchments. Hollow dots represent outliers (id = 30, 32, 37, indicated by grey boxplot dots) and catchments in the east that encompass more than one region (id = 94, 95) and are not included in statistical analysis.

Higher ¹⁰Be erosion rates were associated with lower river concavity (more convex shaped rivers) and higher seismic activity both at the level of individual catchments as well as at the regional level, while higher lavaka densities explain regional variations. No relationship between ¹⁰Be erosion rates and slope gradient or river steepness was observed, which brings into question the general applicability of fluvial metrics to constrain vertical incision rates in a slowly eroding landscape such as Madagascar.

While ¹⁰Be concentrations suggest that rates of landscape change in Madagascar are low, there are indications that chemical weathering rates may outpace CRN-derived denudation rates, pointing to the importance of deep weathering and removal of dissolved materials. In thick regolith-mantled landscapes, mass losses by deep weathering and sub-surface dissolution should be considered alongside with mass losses by physical erosion.

More information : Brosens, L., Cox, R., Campforts, B., Jacobs, L., Vanacker, V., Bierman, P. et al. (2023) The slow downwearing of Madagascar: Inferring patterns and controls on long-term basin-averaged erosion rates from in situ ¹⁰Be at the catchment and regional level. Earth Surface Processes and Landforms, 1– 18. Available from: https://doi.org/10.1002/esp.5586

References

Cox, R., Bierman, P., Jungers, M.C., Rakotondrazafy, A. F. M. (2009) Erosion rates and sediment sources in Madagascar inferred from ¹⁰Be analysis of lavaka, slope, and river sediment. The Journal of Geology, 117(4), 363– 376. Available from: http://www.journals.uchicago.edu/doi/10.1086/598945

Wang, Y., Willett, S.D., Wu, D., Haghipour, N. & Christl, M. (2021) Retreat of the great escarpment of Madagascar from geomorphic analysis and cosmogenic ¹⁰Be concentrations. Geochemistry, Geophysics, Geosystems, 22(12), e2021GC009979. Available from: https://onlinelibrary.wiley.com/doi/10.1029/2021GC009979

Summary

The influence of vegetation on soil water balance and solute fluxes is restricted to the A horizon. Evapotranspiration is 1.7 times higher and deep drainage 3 times lower under cushion-forming plants than under tussock grass. Likewise, cushions transmit about 2-fold less water from the A to lower horizons. This is attributed to the higher soil water retention and saturated hydraulic conductivity associated with a shallower and coarser root system.

Under cushion-forming plants, dissolved organic carbon (DOC) and metals (Al, Fe) are mobilized in the A horizon. Solute fluxes that can be related to plant nutrient uptake (Mg, Ca, K) decline with depth, as expected from biocycling of plant nutrients. Dissolved silica and bicarbonate are minimally influenced by vegetation and represent the largest contributions of solute fluxes. Soil chemical weathering is higher and constant with depth below tussock grasses but lower and declining with depth under cushion-forming plants.

This difference in soil weathering is attributed mainly to the water fluxes. Our findings reveal that vegetation can modify soil properties in the uppermost horizon, altering the water balance, solute fluxes, and chemical weathering throughout the soil profile.

More information here:

Páez-Bimos, S., Molina, A., Calispa, M., Delmelle, P., Lahuatte, B., Villacís, M., Muñoz, T., and Vanacker, V.: Soil–vegetation–water interactions controlling solute flow and chemical weathering in volcanic ash soils of the high Andes, Hydrol. Earth Syst. Sci., 27, 1507–1529, https://doi.org/10.5194/hess-27-1507-2023, 2023.

https://doi.org/10.5194/gchron-4-713-2022

Authors

Nathan Vandermaelen, Koen Beerten, François Clapuyt, Marcus Christl, and Veerle Vanacker

Citation

Vandermaelen, N., Beerten, K., Clapuyt, F., Christl, M., and Vanacker, V.: Constraining the aggradation mode of Pleistocene river deposits based on cosmogenic radionuclide depth profiling and numerical modelling, Geochronology, 4, 713–730, https://doi.org/10.5194/gchron-4-713-2022, 2022.

Abstract

Pleistocene braided-river deposits commonly represent long periods of non-deposition or erosion that are interrupted by rapid and short aggradation phases. When dating these sedimentary sequences with in situ-produced cosmic radionuclides (CRNs), simple concentration depth profiling approaches often fall short, as they assume that the alluvial sedimentary sequence has been deposited with a constant and rapid aggradation rate and been exposed to cosmic radiations afterwards. Numerical modelling of the evolution of CRNs in alluvial sequences permits one to account for aggradation, non-deposition and erosion phases and can simulate which scenarios of aggradation and preservation most likely represent the river dynamics. In this study, such a model was developed and applied to a Middle Pleistocene gravel sheet (Zutendaal gravels) exposed in NE Belgium.

The model parameters were optimised to the observed ¹⁰Be and ²⁶Al concentrations of 17 sediment samples taken over a depth interval of 7 m that constitutes the top of a gravel sheet up to 20 m thick. In the studied sedimentary sequence, (at least) three individual aggradation phases that were interrupted by non-deposition or erosion can be distinguished, each interruption lasting ∼ 40 kyr. The age for the onset of aggradation of the upper 7 m of the gravel sheet was further constrained to  ka. This age, within error limits, does not invalidate previous correlations of the gravel sheet with the Cromerian Glacial B and Marine Isotope Stage (MIS) 16. The deposition of the entire gravel sheet likely represents more than one climatic cycle and demonstrates the importance of accounting for the depositional modes of braided rivers when applying in situ cosmogenic radionuclide techniques.

To reconstruct multitemporal land cover change from existing land cover products, a multisource data integration procedure was followed to reduce imprecision and inconsistencies that may result from comparing heterogeneous datasets. The conversion of native forests and grasslands into agricultural land was the principal land cover change in the non-protected area. In 1961, about 94% of the non-protected area was still covered by native vegetation, which decreased to only 7% in 2018. Most of agricultural expansion occurred in the 1960s and 1970s, creating an anthropogenic landscape where 67% of the area is covered by agricultural land and 26% by invasive species. Early clearance of native vegetation occurred in the more accessible, less rugged areas with deeper-than-average and well-drained soils. The first wave of settlement consisted of large and isolated farmsteads, with 19% of the farms larger than 100 ha and specializing in dairy and meat production.

Over the period of 1961–1987, the number of farms doubled from less than 100 to more than 200, while the average farm size decreased from 90 to 60 ha/farmstead. Due to labour constraints in the agricultural sector, these farms opted for less labour-intensive activities such as livestock farming. New farms (popping up in the 1990s and 2000s) are generally small, with <5 ha per farmstead, and settled in areas with less favourable biophysical conditions and lower accessibility to markets. From the 1990s onwards, the surge of alternative income opportunities in the tourism and travel-related sector reduced pressure on the natural resources in the non-protected area.

More information in https://www.mdpi.com/1711014

Alomía Herrera, I.; Paque, R.; Maertens, M.; Vanacker, V. History of Land Cover Change on Santa Cruz Island, Galapagos. Land 2022, 11, 1017. https://doi.org/10.3390/land11071017