Measuring The Water And Energy In An Alpine Peatland

Peatlands are wetlands with at least a 30-40 cm thick peat layer and are highly dependent on water. In these waterlogged, anaerobic soils, the dead plant material does not decompose and accumulates.

Over many thousands of year, peatlands have accumulated carbon in the form of peat. Currently, it accounts for around 30% of the organic carbon that is globally stored in all the soil. This amount is approximately half the amount of greenhouse gas carbon dioxide (CO₂) in the atmosphere. The particularly close interdependence of the carbon and water cycles in peatland ecosystems signal that understanding the water cycle is crucial to the functioning of peatlands.

In the Alps, small peatlands formed in lakes in mountain saddles when the glaciers retreated. The fact that the peatlands are small in area does not make these peatlands less important. It is, therefore, important to understand how these small-scale peatlands function to see what their current state is and to identify their threats. Only, in this case, it is possible to understand how these alpine peatlands will respond to the current climate change.

In “Assessment of the water and energy budget in a peatland catchment of the Alps using the process based GEOtop hydrological model” a paper recently published in the Journal of Hydrology, J.W.M. Pullens, M. Sottocornola, G. Kiely, D. Gianelle, and R. Rigon implemented the process-based hydrological model GEOtop to assess the water and energy balance of a peatland in the Italian Alps.

Peatland on Monte Bondone, Autonomous Province of Trento, Italy. Credit: Roberto Zampedri

To assess the health of the Italian peatland, the researchers looked at the complete carbon balance. Based on the carbon balance the researchers can see if the peatland is taking up carbon, and is, therefore, healthy, or losing it. A full carbon balance entails both the amount of carbon that is leaving the peatland via gas (CO₂ and CH₄) and via dissolved organic carbon (DOC) in runoff and drainage water. The greenhouse gas balance of the peatland has been studied over 3 years (2012-2016) and indicated that although the weather in the three years was very variable, the peatland was a carbon source, so losing carbon in the form of CO₂ and CH₄ (previously published research article: Carbon fluxes of an alpine peatland in Northern Italy).

A model was used to study the complete water and energy cycle of the alpine catchment. The catchment was studied using the process-based hydrological model GEOtop over 4 years (2012-2015). The model has never been used for such a complex catchment. The catchment does not only entail the peatland but also areas with grassland, scree, and bare rock in a mountainous area. The energy and water fluxes that were measured in the peatland were accurately replicated by the model. This was also the case for the volumetric water content and soil temperature of over the four years for which the model was run. Because of these results, the researchers can conclude that a process-based hydrological model is capable of simulating the water and energy dynamics of a peatland in a complex catchment.

Based on the modeled discharge and the in the field-measured DOC values, an initial estimation of DOC export of the peatland was made through extrapolation. The DOC concentration in the stream water was low, but the high stream flows lead to similar DOC values compared to other peatlands. For the peatland at Monte Bondone, of which in 1914 the top peat layer of 0.35 ha was harvested for fuel, this resulted in the estimate of four years of carbon balance (CO₂, CH₄ fluxes and DOC losses combined), which indicated that the peatland was a carbon source for all four subsequent years. To the authors’ knowledge, the carbon dynamics has been studied continuously over multiple years in only this particular Italian alpine peatland, which indicates that although the alpine peatlands are small, they should not be overlooked since much carbon is stored in them that can potentially be released into the atmosphere when the peatlands are permanently damaged.

These findings are described in the article entitled Assessment of the water and energy budget in a peatland catchment of the Alps using the process based GEOtop hydrological model, recently published in the Journal of Hydrology.

This work was conducted by Johannes Pullens, currently working at the Department of Agroecology of Aarhus University, and previously affiliated to the Department of Sustainable Agro-Ecosystems and Bioresource of Fondazione Edmund Mach in San Michele Italy and the Department of Civil and Environmental Engineering and Environmental Research Institute of University College Cork, Ireland, Matteo Sottocornola from the Department of Science of Waterford Institute of Technology, Ireland, Gerard Kiely from the Department of Civil and Environmental Engineering and Environmental Research Institute of University College Cork, Ireland, Damiano Gianelle from the Department of Sustainable Agro-Ecosystems and Bioresource of Fondazione Edmund Mach in San Michele Italy and the Foxlab Joint CNR-FEM Initiative, Italy and Riccardo Rigon from the Department of Civil, Environmental and Mechanical Engineering, University of Trento, Italy.