Peatland evaporation across hemispheres: contrasting controls and sensitivity to climate warming driven by plant functional types

Speranskaya, Leeza; Campbell, David I.; Lafleur, Peter M.; Humphreys, Elyn R.

Peatlands store disproportionally large amounts of carbon per unit area, a function that is dependent on maintaining high and stable water tables. Climate change is likely to negatively impact carbon storage in peatlands, in part due to increases in vapour pressure deficit (VPD) driving higher evaporation (inline-formulaE) rates. However, the response of inline-formulaE to increasing VPD depends on the dominant vegetation type within peatlands. In this study, we used multiple years of eddy covariance (EC) measurements to compare inline-formulaE regimes at two peatlands with contrasting vegetation types – Kopuatai bog in Aotearoa / New Zealand, dominated by the vascular wire rush Empodisma robustum, and Mer Bleue bog in Canada, a “typical” shrub- and moss-dominated Northern Hemisphere peatland. We examined seasonal variability in inline-formulaE and equilibrium inline-formulaE (inline-formulaEeq), energy balance partitioning, and the response of inline-formulaE, evaporative fraction (EF), and canopy conductance (inline-formulagc) to VPD. Mean annual inline-formulaE was 45 % lower than mean annual inline-formulaEeq at Kopuatai but only 16 % lower at Mer Bleue, demonstrating much greater limitations on inline-formulaE at Kopuatai. In addition, the mean midday (10:00–14:30 local standard time) dry-canopy Bowen ratio (inline-formulaβ) at Kopuatai was 2.0 compared to 0.8 at Mer Bleue; therefore, the sensible heat flux (inline-formulaH) dominated over the latent heat flux (LE) at Kopuatai and vice versa at Mer Bleue. The responses of inline-formulaE, EF, and inline-formulagc to increasing VPD at Kopuatai demonstrated stronger limitations on evaporative water loss for VPD inline-formula> 0.7 kPa compared to Mer Bleue. The observed limitations at Kopuatai were attributed to strong stomatal control by E. robustum due to the rapid decrease in inline-formulagc with increasing VPD; however, surface inline-formulaE could also be limited by its dense standing litter. At Mer Bleue, however, inline-formulaE was only weakly limited at VPD inline-formula> 2 kPa, likely due to weak stomatal control over transpiration by the sparse shrub canopy and relatively large surface inline-formulaE from Sphagnum carpets. As such, the results of this study suggest that E. robustum drives a greater “hydrological resistance” to increasing VPD than the vegetation at Mer Bleue, leading to greater water retention at Kopuatai. This may enable greater resilience of the carbon sink function at Kopuatai to climatic warming and drying than at Mer Bleue.



Speranskaya, Leeza / Campbell, David I. / Lafleur, Peter M. / et al: Peatland evaporation across hemispheres: contrasting controls and sensitivity to climate warming driven by plant functional types. 2024. Copernicus Publications.


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Rechteinhaber: Leeza Speranskaya et al.

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