Effective design of peatland restoration: insights from studying how hillslope lengths change with drainage network structure

The restoration of peatlands taking place worldwide is a remarkable case of implementation of nature-based solutions at large spatial scales. It is often suggested that peatland restoration may contribute to climate adaptation goals by attenuating the hazard of floods and improving water quality. However, approaches to evaluate such benefits beyond single case studies and account for them in the planning of restoration are lacking.

Peatland restoration is often realized by filling in or damming drainage ditches, thereby increasing the distance of land parcels to the drainage network. In this work we leverage recent advances in the relationship between drainage network structure and the mean distance to the nearest drainage (i.e., the mean hillslope length, a key metric for ecosystem services like flood mitigation and solute degradation) in the context of peatland restoration. We analyze how this metric changes with different ways of realizing peatland restoration (i.e., by intervening on all ditches - as it is mostly done now - or only on some of them) in four catchments located across Norway.

We find that effects comparable to those obtained by erasing all ditches can be achieved by only erasing some of them. This means that peatland restoration may be realized at lower costs, while obtaining similar results for the ecosystem services mentioned above.

Results indicate that the contributing area of a ditch is the fundamental criterion determining the benefit of its removal, and ditches with larger contributing areas should therefore be prioritized in restoration. When the restoration goal is to achieve a target mean hillslope length and the related ecosystem services, implementing restoration from down to upstream consistently minimizes ditch removal, making it the most economically convenient option.

The proposed approach can support effective planning of nature-based solutions such as peatland restoration, thus reducing costs linked to their large scale implementation.