Incorporation of soil nutrients and acidity into PROBE

The vegetation composition in freshwater natural ecosystems can be explained on the basis of the soil moisture, nutrient fertility and acidity. A reliable assessment of how the vegetation will react to climate change and to adaptation measures, requires the process-based modelling of these factors. In the PROBE vegetation model this was effectively done for moisture, but the simulation of the two other factors was not quite satisfactory, because it was based mainly on decision-making rules drawn from expert assessment. In this BTO research, phosphorus mineralisation, as an estimator for nutrient fertility, is process-based modelled and incorporated into PROBE 2.

Measuring and modelling

Phosphorus mineralisation is the most suitable measure of soil fertility. To calculate it, we connected a model for the composition and decomposition of organic matter, CENTURY, to a model for soil moisture, SWAP. This project received substantial support from a grant from the Knowledge for Climate programme and the CARE project. For soil acidity, we connected the soil chemistry model, ORCHESTRA, to SWAP. Results from both model pairings were compared using measurements.

Procesdiagram van de invloed van klimaatverandering op bodem, water en vegetatie. Bron: managementsamenvatting in rapport

Process diagram of the impact of climate change on soil, water and vegetation

Phosphorus mineralisation incorporated into PROBE 2; acidity requires follow-up research

Phosphorus mineralisation is incorporated into PROBE 2, making the model more suitable for climate projections. The process-based calculation of acidity can be done technically, but its incorporation into PROBE 2 requires a follow-up project. The way we have modelled acidity in terms of soil chemistry is very innovative, and can be implemented more broadly, beyond PROBE alone.

A process-based modelling of nutrient fertility and pH is needed to enable an assessment of the feasibility of nature objectives in a future climate. Moreover, such modelling makes well-founded derogations from legally established nature objectives possible, as well as the mapping future biodiversity hotspots.