Research project P7/24 (Research action P7)
Human interventions on the soil system, mainly as a result of land use and land management, have now reached a level that soil forming processes are influenced on the decadal timescale. Soil erosion entrains lateral fluxes of C resulting in burial of C in colluvia and replacement of soil C on eroded hillslopes to such an extent that these lateral fluxes are now considered as a small but significant C sequestration in the global C cycle. Following deposition of the eroded soil, reactions between the fresh reactive mineral surfaces with organic matter have the potential to control C sequestration due to the strong influence of complexing cations and reactive soil minerals. Silica fluxes to the rivers are significantly lower in catchments under cropland compared to forested catchments but major gaps in the fundamental understanding of the silica cycle, particularly the effects of human activities, remain. These examples demonstrate that soil forming processes have now reached such rates that they can no longer be considered to be in a steady state and that we need to include both dynamic soil properties and lateral fluxes for a better understanding of the role of soils in the biogeochemical cycles even at the scale of decades.
The objective of our research consortium is the understanding and quantification of the feedbacks between the soil system and sediment, nutrient, water and carbon fluxes in response to anthropogenic forcings over timescales ranging from the decade to the millennium. Before this can be achieved at the global scale, the interaction between the soil components over different temporal and spatial scales should be identified in case study areas with clear and different types of human interventions. The approach will consist in (i) using novel techniques for the analysis of soils, the sediment record, chronosequences and modern day fluxes at the catchment scale, and ii) in building models that formalize these interactions. The overall hypothesis that we would like to propose is that the anthropogenic pressure has now reached the point that many soil properties including their distribution over the landscape change significantly within decades to centuries. Hence, we can no longer ignore the interactions between the forcing and the changing soil properties for the future development of ecosystems and the services they provide to mankind.
The project is designed to achieve a consistent flow of information and tools towards and integrated prediction and analysis of the feedbacks between the soil system and fluxes of sediment, C, nutrients and water in response to anthropogenic forcings over decadal to millennial timescales. We will employ four different, but highly interrelated, approaches.
1. A network of 4 Soil Observatories will be established at which systematic and interdisciplinary observation of the soil system will lead to the quantification of the current state of the soil system and understanding of its past evolution. Groenland is an ideal site to investigate the impact of climate change on microbial activity leading to changes in SOC dynamics through effects on decomposition rates. The Belgian loam belt has high rates of soil erosion in thick sediments without depletion of available material and is adequate to demonstrate the effects of lateral sediment, C and nutrient fluxes on the biogeochemical cycles. The other two sites will be instrumental to integrate soil processes over larger spatial and temporal scales but are characterized by a contrasting soil-landscape setting: high rates of soil erosion on thin soils where the erosion is limited by supply of soil material in Almeria, Spain, and combination of high rates of soil erosion and weathering in Brazil. Significant improvements in process understanding are now possible due to the emergence of new tools and we aim to bring state-of-the-art technologies to bear in this consortium. The unique combination of expertise that is available in the current consortium will allow studying simultaneously the cycles of sediment, water, nutrients, C and Si in landscapes in an integrated way thereby providing a unique opportunity to understand their interactions at different spatial and temporal scales. Important items to be quantified include Si cycling, water flow structures, soil organic carbon dynamics, microbial physiology and physico-chemical and mineralogical soil characterization. A key focus, distinguishing this project from many current efforts is that is explicitly aiming at the quantification of both current and past lateral fluxes of sediments, water, carbon, nutrients and Si within the study catchments using fallout and cosmogenic nuclides, geochemical tracers, compound specific stable isotope analyses of biomarkers, radiocarbon tools and sedimentary records, so that the impact of these fluxes on both soil evolution and the role of soils in global cycles can be fully understood. This approach is covered in work package 1: Biogeochemical characterization of soils, work package 3: Current sediment and biogeochemical fluxes, and work package 4: Past sediment and biogeochemical fluxes.
2. Experimental studies will be employed that elucidate the response of key soil processes to disturbances by human activities and climate warming. We focus on the sensitivity of SOC to temperature change and soil degradation (erosion and burial) and the response of soil microbial communities to climate warming. These disturbances are potentially large but at present relatively unknown. We aim to improve process understanding by applying and further developing stable isotope tools, biomarkers, radiocarbon tools and soil respiration measurements. This approach is covered in work package 2: Sensitivity to disturbances.
3. The data that will be acquired during this project will be a significant step forward but will not fully capture the dynamic evolution of the soil system in response to human activities. The information acquired from the experimental studies and soil observatories will therefore be translated into integrated models. Process-based profile models will be refined and validated with observational data and processes for which at present no model parameterization exists will be implemented (e.g. microbial community-T response and erosion-soil weathering feedbacks). These models will be integrated into simplified but integrated catchment models that will have the capacity to simulate soil functioning (ecosystem productivity, carbon, nitrogen, silicon and water exchange), lateral fluxes and mineral precipitation/dissolution in response to human activities. This approach is covered in work package 5: Interactions between element cycles during weathering and pedogenesis, work package 6: hydrology as driver for biogeochemical fluxes, and work package 7: Integrated landscape models.
4. By using the data and models from the other WP’s, we aim to integrate the biogeochemical, hydrological and soil formation related services studied in this project into an ecosystem service evaluation platform that allows assessing how various ecosystems may be affected by changes in soil functioning. However, the explicit analysis of ecosystem service response will be limited to a number of key services within this project (work package 8: Integrated assessment of soil ecosystem services).
The network driven training activities are central to the integration of the work the young researchers (work package 9: Training). Two summer schools will be organised: the first on novel analytical and proximal sensing techniques and the second on the different model approaches. Clearly defined milestones and deliverables under the responsibility of a work package leader will ensure a smooth and timely management of the project. In summary, this project will result in a unique dataset and a quantitative framework for an improved and integrated analysis of the feedbacks between the soil system and fluxes of sediment, C, nutrients and water in response to anthropogenic forcing over decadal to millennial timescales and its translation into ecosystem services.
