Campbell, DavidSperanskaya, Leeza2023-12-152023-12-152023https://hdl.handle.net/10289/16269Peatlands store disproportionately large amounts of carbon (C) per unit area compared to other ecosystems, a function that depends on maintaining a high and stable water table. Water table levels are in turn influenced by evaporation (E), which consists of surface E, transpiration, and interception loss (Eint) components. In boreal peatlands, E rates have been predicted to increase due to climate change-induced increases in vapour pressure deficit (VPD), potentially causing water table drawdown and threatening the ability of peatlands to store C. However, the response of E to VPD has not yet been quantified for Aotearoa New Zealand peatlands dominated by a very water-conservative vegetation species, Empodisma robustum. In addition, the Eint component of E has not been extensively investigated in these peatlands. Therefore, to gain a better understanding of the E regimes of this peatland type, this thesis firstly investigated the extent of E restrictions by E. robustum and the response of E to increasing VPD at Kopuatai bog, using an 11-year eddy covariance (EC) dataset. This analysis was replicated on a 20-year dataset from Mer Bleue bog, a ‘typical’ shrub and moss-dominated Northern Hemisphere peatland. Mean annual E was 45% lower than mean annual equilibrium E (Eeq) at Kopuatai but only 16% lower at Mer Bleue, demonstrating much greater limitations on E at the former. The mean midday (10:00–14:30) dry canopy Bowen ratio (β) at Kopuatai was 1.96, compared to 0.77 at Mer Bleue, as the sensible heat flux (H) dominated over the latent heat flux (LE) at Kopuatai, and vice versa at Mer Bleue. In addition, the response of E to VPD at Kopuatai indicated that more water was conserved at high VPD than at Mer Bleue. This likely occurred due to stronger stomatal limitation of transpiration at Kopuatai, while at Mer Bleue the effect of stomatal limitation by shrubs may have been offset by a high moss E. The second component of this thesis determined the magnitude of Eint at Kopuatai using two Eint modelling approaches and a canopy water balance field experiment. The field data overestimated Eint, while modelling produced much lower and more realistic estimates. Therefore, the models likely provided the best estimates of Eint as a proportion of gross rainfall (Eint/Pg) and total E (Eint/E), with annual-scale values of 15.5–18.3% and 31.3–36.6%, respectively, and a canopy storage capacity of 1.5 mm. Controls on Eint/Pg were rain event size, net radiation, and canopy height/density. This research has shown that, during dry canopy conditions, E. robustum enables a much more conservative E regime at Kopuatai compared to Mer Bleue, potentially enabling greater “hydrological resistance” to increased VPD under future climate warming compared to Northern Hemisphere peatlands. This may be a crucial factor in ensuring resilience of the C sink function at Kopuatai under a warming and drying climate. During wet canopy conditions, however, Eint enables much greater water loss from Kopuatai than when the canopy is dry.application/pdfenAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis2023-12-11