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)

Summary

Islands are particularly vulnerable to global change due to their limited size and remoteness. Sustainable land use practices based on nature-based solutions can help local communities to adapt their agricultural systems to climate change. This doctoral thesis research focused on Santa Cruz Island located in the Galapagos Archipelago-. About 72% of its continental surface area is nowadays protected. On the island’s windward side, the non-protected area was originally designated for the development of a self-sufficient rural community After characterising the land use dynamics over the last 60 years, this study analysed the potential impacts and benefits of agroforestry management practices on physical and hydraulic soil properties, and soil nutrient stocks . An intensive monitoring programme was implemented in 2019 to monitor hydrometeorology, soil moisture and temperature, and essential soil hydrophysical and biogeochemical properties, including soil nutrients.

Land use changed drastically in the central part of the island. While 94% of the non-protected area was still covered by native vegetation in 1961, the agricultural expansion converted the forests to an anthropogenic landscape having only 7% forest, 67% agricultural land and 26% invasive species. While the early settlements were large, isolated farmsteads, the average size of the farms decreased over time as the number of farms doubled. Over the last two decades, the rapid rise of tourism activities alleviated pressure on natural resources and led to the abandonment of agricultural land.

The agroforestry management practices have a significant effect on soil temperature, moisture availability, and nutrient contents. When forest vegetation protects the soil from direct solar radiation, the soil is about 12% cooler than in soils that were converted to agricultural land. Soil moisture is, on average, 20% higher under forest than under traditional agroforestry or abandoned farmland, and forest soils have a lower bulk density, lower saturated hydraulic conductivity, higher soil organic stocks and higher water retention capacity. The loss of soil organic carbon in agricultural sites is related to soil mixing due to tillage, which increases soil pore connectivity and facilitates the decomposition of soil organic carbon and leaching of base cations. At the same time, fertilization with organic manure and nitrogen-phosphorus-potassium changed the soil pH and enhanced soil nutrient leaching.

The present work illustrates how soil fertility, access to markets, and alternative incomes play an important role in land use decision making. Preserving forest remnants in an agricultural landscape has measurable effects with a reduction of soil warming by 12 %, a reduction of soil drying by 20%, and better preservation of soil organic carbon stocks compared to traditional agroforestry. Future land policy needs to account for the diversity in livelihoods in the rural communities, and the impacts and benefits of agroforestry management practices on soil and environmental health

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.

Summary

Cosmogenic radionuclides accumulate at the Earth’ surface as a function of time and depth. They can be used to constrain the age and the deposition mode of fluvial deposits.

Occupied by the braided channels of the Meuse during the Middle Pleistocene, the (eastern) Campine plateau resisted the overall erosion that affected the Campine area, and nowadays stands out of its environment.

In this study, we applied cosmogenic radionuclides on the eastern Campine plateau to constrain its depositional and post-depositional history. Main results show that the deposition occurred in different phases, interrupted by thousands of years long hiatuses that correspond to climatic fluctuations.

These first numerical ages of the eastern Campine plateau could be used in the future to better constrain the geomorphological evolution of the Campine region and the European Lowlands in general.

Required education: PhD in geoscience, geochemistry or a related discipline by the appointment start date.

The Earth and Life Institute invites applications for a 2-year postdoctoral position in the LandSense project. LandSense is a collaborative research effort on “Pushing the boundaries of Critical Zone research: Unravelling hydrological controls on carbon and nutrient fluxes by integrating proximal sensing, field measurements and smart modelling” funded by the Fédération Wallonie-Bruxelles. The project is directed by François Jonard, Sébastien Lambot, Sophie Opfergelt, Kristof Van Oost and Veerle Vanacker.

The LandSense project focuses on the spatio-temporal variation in soil hydrology and its controls on carbon and nutrients fluxes in hillslope-floodplain systems in both temperate and arctic regions. LandSense aims to improve the fundamental understanding of these key critical zone (CZ) processes and their interactions by collecting targeted measurements using advanced sensing methodologies across spatial and hydrological gradients. This will be complemented with state-of-the-art chemical and isotopic characterizations, giving insights into the genesis and dynamics of the soil mantle. The team is working in two study sites, one located in the Belgian High Fens region, and a second Arctic site located at the foothills of the Alaska Range.

Within the frame of the LandSense project, the postdoc will focus on the hydrological controls on soil processes controlling carbon- and nutrient-efflux in the Critical Zone at the landscape scale. Long-term patterns in critical zone structure, biogeochemical composition and soil residence time will be characterised, and their control on the spatial and temporal heterogeneity of soil nutrients and DOC fluxes will be studied in coupled floodplain-hillslope systems. The observational insights will then be used to study process-feedbacks and inform coupled and integrated models of the CZ.

We welcome applications from early career scientists having a Ph.D. degree in geoscience, geochemistry or a related discipline by the appointment start date. We look for a highly motivated postdoctoral researcher with experience with Critical Zone research, quantitative geomorphology, and soil geochemistry. Additional experience with cosmogenic radionuclides and soil-landscape evolution models are an asset. Successful applicants should be willing to work as part of a diverse and multidisciplinary team, and have excellent written and oral communication skills in English. The successful candidate will work under the supervision of Veerle Vanacker and Sophie Opfergelt. The target starting date is February 2023, but can be flexible.

Interested?
The application should be sent in one single PDF including a motivation letter, a curriculum vitae, two publications representative of previous work, and contact information for two referees. Review of applications will begin on January 15, 2023 and continue until the position is filled. Applications are accepted through email to Veerle.vanacker@uclouvain.be (and indicating ‘Postdoc LandSense’ as subject).

A major concern for sustainable development in the Tropical Andes is the growing imbalance between ecosystem service supply and demand, particularly with regard to freshwater ecosystem services. While the capacity of the Tropical Andes to provide freshwater ecosystem goods and services is already under pressure, the demand is rapidly increasing as a result of demographic growth, urbanization and evolving socio-economic conditions. Coupled with future projections of climate change, urban growth and continued socio-economic development, these environmental questions surrounding sustainable development in the Ecuadorian Andes call for urgent action.

This thesis contributed with evidence-based research on conservation and restoration of young volcanic ash soils through an analysis of soil-water-plant interactions at the pedon, toposequence and landscape scale. The empirical data were collected over a 5-year period in the Jatunhuaycu experimental station, located in the northern Ecuadorian Andes at 4200 m a.s.l. The monitoring programme was specifically designed to test for potential differences in soil hydrophysical and biogeochemical properties and their changes over time between topographic positions and vegetation types.

At the soil pedon scale, the soil water balance was different between soils covered by tussock grasses and cushion-forming plants. The vegetation type had a measurable effect on the solute concentrations and fluxes in the uppermost horizon, while this effect strongly decreased with depth. The higher water infiltration rates of soils under tussock grasses resulted in higher chemical weathering rates than in soils under under cushion-forming plants.

At the toposequence scale, the soil pore structure and hydraulic properties of the A horizon varied by vegetation type across the studied profiles, while the studied topographic positions did not show a significant effect. The higher soil moisture content at higher matric potentials and total available water under cushion-forming plants can enhance soil water storage in the topsoil during prolonged rainfall events. However, its strong decrease in saturated hydraulic conductivity with depth can promote subsurface lateral flow during large rainfall events.

The connectivity of the geomorphic units at the landscape scale is time-dependent: storm runoff was observed at the outlet of the catchment when the moisture content in the upper horizons of the hillslope profiles reached field capacity. The geochemical signature of the solute export strongly varied over time, as a result of changes in the hydrological connectivity of geomorphic units.

The existence of strong interlinkages between plant functional types, soil and surface hydrology, and nutrient export has important implications for sustainable management of high Andean ecosystems. The results of this thesis can contribute to assess the potential impacts of vegetation conservation and restoration programmes on water resources in the Tropical Andes.

More information:

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 transport in volcanic ash soils of the high Andes, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2022-294, in review, 2022.

Páez-Bimos, S., Villacís, M., Morales, O., Calispa, M., Molina, A., Salgado, S., de Bievre, B., Delmelle, P., Muñoz, T., & Vanacker, V. (2022). Vegetation effects on soil pore structure and hydraulic properties in volcanic ash soils of the high Andes. Hydrological Processes, 36( 9), e14678. https://doi.org/10.1002/hyp.14678

The 9th of November, Beatriz will publicly defend her PhD thesis, entitled “Monitoring forest degradation patterns using multi-resolution spatial approaches”.

Summary

The subtropical dry forests of South-America have been impacted by deforestation and degradation over the last two centuries. The forests still provide important ecosystem services but overexploitation of the forested ecosystems may lead to irreversible loss of provision and regulation services. Remote sensing techniques enable us to monitor changes in forest cover at regional scale. Field-based forest inventories remain essential to measure more specific forest attributes and functions. However, the scale at which such field-based forest inventories can be organized is limited for the detection of slow and subtle changes in the forest at regional scale. Therefore, this thesis analyzed the potential of 3D vegetation models based on low-cost stereo-photos taken from unpiloted aerial vehicles to map forest degradation in dry forests. The ecosystem of the Dry Chaco in Argentina, which is considered as one of the major hotspots of deforestation worldwide, was taken as a case study. Therefore, new data on surface and vegetation height were collected during UAV-flights. Flights were realized at 44 locations in contrasting ecological settings of the Dry Chaco. The results of this research show that structure-from-motion algorithms are capable of reconstructing high resolution 3D surface models of the forest cover and this at a much lower cost than LIDAR derived products. Furthermore, this thesis proposes a set of relevant forest attributes that can be derived from these 3D surface models and compares these with indicators from traditional field-based forest inventories. In a next step, the correspondence between the forest structural indicators and degradation states was examined. Finally, the indicators were compared with high resolution laser data from a recently launched spaceborne sensor, which facilitates the assessment of forest degradation patterns at sub-continental scale.

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