Effect of stockpiling time on donor-peat hydrophysical properties: Implications for peatland restoration

Northern peatlands are an important global climate regulator storing approximately one-third of the global carbon pool, however the degradation of these ecosystems from land-use change can switch peatlands to persistent and long-term sources of atmospheric carbon dioxide. Active restoration is often required to return degraded peatlands to a net carbon sink. The peat-block restoration technique, where intact peat blocks are extracted from a donor peatland and transferred to restore peatlands where the remnant peat is non-existent, contaminated, and/or undergoes seasonal flooding is increasingly being adopted as a peatland restoration technique given the carbon sequestration that can occur immediately post-restoration. However, donor peat blocks often need to be temporarily stockpiled during the restoration process due to logistical constraints. The dewatering of the peat blocks during this stockpiling period may alter hydrophysical peat properties that sustain critical peatland ecohydrological functionality and ultimately affect peatland restoration success. Yet, the hydrophysical evolution of stockpiled peat blocks remains unknown. Here, we examine how peat block stockpiling time (3, 7, 11, and 14 months and a reference site) impacts peat hydrophysical properties and sphagnum moss photosynthesis, both of which are critical for peatland restoration success. Stockpiling peat differentially impacted the hydrophysical properties between the shallower and deeper peats, where little to no impact from stockpiling was observed in the shallower peats, regardless of stockpiling time. Rather, as stockpiling time increased, there was a marked decrease in macroporosity (pores >75 mu m) and mobile porosity (drainable porosity at approximately -100 hpa) at depths below 20 cm but the water conducting matrix porosity (defined as mobile porosity minus macroporosity) was not significantly different than the reference samples. However, stockpiling created inhospitable conditions for sphagnum mosses., as chlorophyll fluorescence ratio was below 0.3, indicating little to no photosynthesis of the stockpiled peat during summertime drought conditions. Taken together, we suggest limiting stockpiling time as much as possible would be advantageous for using the stockpiled peat blocks for the peat-block restoration technique or other restoration efforts, such as floating mat creation.