title: Evaporation at Kopuatai bog: An investigation of dry and wet canopy evaporation regimes

authors: Speranskaya, Leeza

abstract: Peatlands 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.

text: Evaporation at Kopuatai bog: An investigation of dry and wet canopy evaporation regimes Peatlands 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.

year: 2023

title: Olsemwanem kastom blong tring kava i save afektem tingting blong man mo wei we man i draev (Traditional kava-drinking, cognition and driver fitness)

authors: Aporosa, S. 'Apo'

abstract: Kava, we oli singautem tu se ‘plant blong ol god’, hemi gro plante long ol tropikol aelan blong Pacific.  Ol man oli yusum kava olsem lokol meresin. Mo tu, oli kranem rus blong hem, afta strenem long wota blong oli save tring blong mekem oli fil rilaks. Long saed blong kastom, kava i kat impotent mining, be naoia we man i stap tring tumas kava, i kat wari i kamaot from ifekt blong hem long saed blong seifti taem man i draev. Dokta ‘Apo’ Aporosa, we hemi stap karem aut risej long Waikato University long Aotearoa New Zealand, hemi bin stadi wei we kava i afektem tingting blong man taem man i draev. 

(Kava, or ‘the plant of the gods’, grows widely across tropical Moananuiākea (the Pacific). Used in traditional medicine, its roots are also pounded and strained through water to make a drink with relaxant effects. Kava has deep cultural significance, but because it is drunk in large quantities over several hours, concerns have been raised about its effects on driver safety. Dr ‘Apo’ Aporosa, a Research Fellow at the University of Waikato in New Zealand, has studied the impact of traditional kava use on cognition and its implications for driver fitness. The findings of that research are presented here in Bislama/Pidgeon language.)

text: Olsemwanem kastom blong tring kava i save afektem tingting blong man mo wei we man i draev (Traditional kava-drinking, cognition and driver fitness) Kava, we oli singautem tu se ‘plant blong ol god’, hemi gro plante long ol tropikol aelan blong Pacific.  Ol man oli yusum kava olsem lokol meresin. Mo tu, oli kranem rus blong hem, afta strenem long wota blong oli save tring blong mekem oli fil rilaks. Long saed blong kastom, kava i kat impotent mining, be naoia we man i stap tring tumas kava, i kat wari i kamaot from ifekt blong hem long saed blong seifti taem man i draev. Dokta ‘Apo’ Aporosa, we hemi stap karem aut risej long Waikato University long Aotearoa New Zealand, hemi bin stadi wei we kava i afektem tingting blong man taem man i draev. 

(Kava, or ‘the plant of the gods’, grows widely across tropical Moananuiākea (the Pacific). Used in traditional medicine, its roots are also pounded and strained through water to make a drink with relaxant effects. Kava has deep cultural significance, but because it is drunk in large quantities over several hours, concerns have been raised about its effects on driver safety. Dr ‘Apo’ Aporosa, a Research Fellow at the University of Waikato in New Zealand, has studied the impact of traditional kava use on cognition and its implications for driver fitness. The findings of that research are presented here in Bislama/Pidgeon language.)

year: 2023

title: Te ao hurihuri : iwi identification in the census

authors: Kukutai, Tahu

abstract: As the flagship of official statistics, the national population census is an important forum for the recognition of indigenous peoples in their homelands and territories (United Nations, 2008). While most governments worldwide count and classify their populations by ethnicity, New Zealand is rare in enabling multiple expressions of indigenous identity in the census. Since 1991, it has been possible to identify as Māori in three ways: by descent, ethnicity and iwi (tribal) affiliation (see Figure 1). The Māori descent population is the largest— in 2013, just under 669,000 individuals ticked the Māori descent box. The number identifying as Māori by ethnicity - intended as a measure of cultural belonging - was substantially lower at just under 600,000. Most of the remaining 69,000 Māori descendants identified solely as NZ European. In 2013 nearly 83 per cent of Māori descendants (n=535,941) reported belonging to at least one iwi. Of those that did not report an iwi affiliation, 40 per cent did not identify as Māori by ethnicity either.

text: Te ao hurihuri : iwi identification in the census As the flagship of official statistics, the national population census is an important forum for the recognition of indigenous peoples in their homelands and territories (United Nations, 2008). While most governments worldwide count and classify their populations by ethnicity, New Zealand is rare in enabling multiple expressions of indigenous identity in the census. Since 1991, it has been possible to identify as Māori in three ways: by descent, ethnicity and iwi (tribal) affiliation (see Figure 1). The Māori descent population is the largest— in 2013, just under 669,000 individuals ticked the Māori descent box. The number identifying as Māori by ethnicity - intended as a measure of cultural belonging - was substantially lower at just under 600,000. Most of the remaining 69,000 Māori descendants identified solely as NZ European. In 2013 nearly 83 per cent of Māori descendants (n=535,941) reported belonging to at least one iwi. Of those that did not report an iwi affiliation, 40 per cent did not identify as Māori by ethnicity either.

year: 2015