Hydrological processes in undisturbed northern peatlands: Relative impact on water conservation and streamflow

The hydrology of peatlands is a crucial control on peatland ecosystem functions, including greenhouse gas emission, biogeochemistry, biodiversity and energy balance partitioning. Undisturbed peatlands contain numerous hydrological feedbacks that stabilize the internal water balance, hence ecosystem functioning. Besides affecting the peatland water balance internally, peatlands are renowned for their capacity to regulate streamflow. Nevertheless, the impact of peatlands on flow regulation remains inconclusive. Some studies suggest that peatlands reduce floods, whereas others conclude that there is no impact or even increased risk of flooding. Such contrasting results can largely be explained by the wide range of peatland ecosystem characteristics, or differences in local geohydrology, climate, and landscape configuration that control hydrological response. No two catchment are the same, making it difficult to discern whether observed differences between catchments originate from peatland hydrological processes or catchment dissimilarities. This seriously hampers understanding the effect of peatlands on streamflow in general and also the setting of priorities in peatland restoration projects.

In this research we take a modelling approach to quantify the relative impact of hydrological self-regulating processes in undisturbed northern peatlands on the internal peatland water balance and streamflow. By doing so, the confounding effects of local hydroclimatological settings can be excluded. Specifically, we set up a modular model to quantify the relative impact of (1) reduced lateral groundwater losses at deeper groundwater levels and (2) elastic storativity owing to the high compressibility of peat and (3) reduced evapotranspirative water losses at deeper groundwater levels. Landscape position was accounted for by adding or subtracting an extra efflux of water.

Our results indicate that hydrological self-regulation in natural peatlands is an important means to maintain the functionality of peatland vegetation in the face of changing hydroclimatological conditions. Part of the stored water is used for evapotranspiration. A significant part, however, is slowly released as discharge, resulting in maintaining downstream streamflow.

This study provides insight on the relative importance of hydrological processes and properties in northern peatlands in affecting internal peatland hydrology and downstream water availability. This information can be used for effective and targeted hydrological restoration of peatlands. With this research we contribute to a more solid scientific basis for the impact of peatlands on streamflow. Moreover, this work highlights the importance of undisturbed peatland processes for catchment behaviour.