title: Volatility Spillovers between New Zealand  Stock Market Returns and Exchange Rate Changes before and after the 1997 Asian Financial Crisis

authors: Choi, Daniel F.S.

subjects: New Zealand

abstract: Researchers in the last decade have been investigating the interdependence of stock returns and exchange rate changes within the same economy. Kanas (2000) and Yang and Doong (2004) find that for the G-7 countries, in general, the volatility of the stock market spills over to the exchange rate market but that volatility spillovers from the exchange rate market to the stock market are insignificant. Chen, Naylor, and Lu (2004) find that NZ individual firm returns are significantly exposed to exchange rate changes. This study complements their work by investigating the volatility spillover between the stock market and the foreign exchange market within the NZ economy.

text: Volatility Spillovers between New Zealand  Stock Market Returns and Exchange Rate Changes before and after the 1997 Asian Financial Crisis Researchers in the last decade have been investigating the interdependence of stock returns and exchange rate changes within the same economy. Kanas (2000) and Yang and Doong (2004) find that for the G-7 countries, in general, the volatility of the stock market spills over to the exchange rate market but that volatility spillovers from the exchange rate market to the stock market are insignificant. Chen, Naylor, and Lu (2004) find that NZ individual firm returns are significantly exposed to exchange rate changes. This study complements their work by investigating the volatility spillover between the stock market and the foreign exchange market within the NZ economy.

year: 2009

title: Impact of black swan grazing and anthropogenic contaminants on New Zealand seagrass meadows

authors: Dos Santos, Virginie

subjects: Zostera muelleri

abstract: Seagrass is the only marine angiosperm (flowering plant) and decline of seagrass meadows has been reported worldwide. The important ecological and economic values of this marine habitat make it essential to preserve. Seagrass meadows of New Zealand are composed of only one species, Zostera muelleri. They are mainly present in sheltered, intertidal sand flats in harbours. Seagrass decline has been recorded in many New Zealand estuaries during the last century. Grazing by the black swan (Cygnus atratus) and anthropogenic contaminants resulting from catchment development are postulated to contribute to seagrass meadow loss in New Zealand and these factors have been assessed in this study. The aim of this study was to quantify black swan grazing pressure and examine effects of potential anthropogenic contaminants (specifically nutrient enrichment, sedimentation and herbicide residues) on seagrass meadows in New Zealand. The impact of current levels of these anthropogenic contaminants on seagrass resilience to swan grazing was also assessed in situ. To quantify black swan grazing pressure on seagrass meadows and to evaluate the potential relationship between swan grazing pressure and seagrass standing stock, observations and measurements were conducted in Tauranga Harbour where more than a third of the seagrass meadows disappeared between 1959 to 1996. Observations have shown that black swans graze intensively on Zostera muelleri meadows during high tide and were most numerous in the harbour during autumn. Black swan grazing resulted in the formation of circular devegetated patches (0.28 m2), where 92 % of shoots, 25 % of roots and 99 % of rhizomes are removed. The consumption rate was estimated to be 394 g dry weight (DW) swan-1 day-1. Significant seagrass loss on an annual basis was detected at the most swan populated site, which also had the highest swan grazing pressure (19-20 % of biomass consumed annually). This suggests a potential threshold of 19-20 % of annual seagrass biomass removal above which black swan grazing may contribute to substantial damage on seagrass meadows. Applied at the harbour scale, where there is a total of ~29 km2 of seagrass meadows, this corresponds to a swan population (i.e. grazing pressure) > 4630 birds. To identify the potential environmental stressors affecting seagrass condition, two contrasting harbours (Tauranga and Aotea) were surveyed where a range of environmental parameters, including parameters indicative of anthropogenic contamination, and seagrass condition metrics were measured. The survey showed that many of the seagrass condition metrics were positively correlated with sediment porewater ammonium (NH4-N) concentrations suggesting that nitrogen availability regulates seagrass growth. The presence of higher porewater nitrate (NO3-N) concentrations was linked to higher proportions of urban and crop land use in subcatchments, these latter parameters being negatively correlated with light availability during high tide. In spite of this, current levels of nutrient enrichment were apparently not detrimental to seagrass condition with evidence of N-limited plant growth and abundant light availability. Herbicide compounds were detected in seagrass sediment and at consistently higher concentrations in Tauranga harbour, which is the harbour more exposed to developed land use. The seagrass photosynthetic potential was lower in more herbicide contaminated sediments, although there was no evidence of any impact on seagrass biomass or morphometry. In a final experiment, black swan grazing was simulated in situ at four sites in Tauranga Harbour differing in exposure to potential anthropogenic contaminants and environmental characteristics. Grazing was simulated by removing seagrass biomass from patches (0.25 m2) in the meadow equivalent to natural swan removals (see above). Two levels of grazing intensity were applied to these patches; ~100 % of biomass removed (high) and ~ 40% of biomass removed (low). Results showed that the cover and the biomass of the low grazing intensity patches were not significantly different to controls (0 % of biomass removed) during the entire experiment. For the high grazing intensity patches, although the cover was restored after 9 months, biomass recovery was incomplete with only 30 % of total biomass regenerated, after one year. This suggests that swan grazing at high intensity can cause long-lasting damage to seagrass meadows, and that > 3 years is probably needed for a devegetated patch to fully recover from grazing (assuming a constant plant regeneration rate). The resilience response was similar across all sites examined in this harbour, suggesting that the current magnitude and range of environmental variability and potential contaminant levels within the seagrass meadows do not affect the ability of seagrass to regenerate from grazing. In conclusion, from these results, I can not conclude that anthropogenic contaminant or black swan grazing pressure are by themselves responsible for seagrass decline in Tauranga Harbour. However, the study suggests that herbicide residues have the potential to detrimentally affect the seagrass photosynthetic activity as do high grazing pressure by the black swan on the seagrass meadow condition. Overall, this study contributes to the understanding of impacts of black swan grazing pressure combined with potential contaminant effects on seagrass ecosystems. It emphasizes the importance of herbivory in temperate seagrass systems, which it is often underestimated and highlights the seagrass habitat contamination due to coastal development. It provides crucial information that will assist resource management agencies to preserve this valuable natural ecosystem.

text: Impact of black swan grazing and anthropogenic contaminants on New Zealand seagrass meadows Seagrass is the only marine angiosperm (flowering plant) and decline of seagrass meadows has been reported worldwide. The important ecological and economic values of this marine habitat make it essential to preserve. Seagrass meadows of New Zealand are composed of only one species, Zostera muelleri. They are mainly present in sheltered, intertidal sand flats in harbours. Seagrass decline has been recorded in many New Zealand estuaries during the last century. Grazing by the black swan (Cygnus atratus) and anthropogenic contaminants resulting from catchment development are postulated to contribute to seagrass meadow loss in New Zealand and these factors have been assessed in this study. The aim of this study was to quantify black swan grazing pressure and examine effects of potential anthropogenic contaminants (specifically nutrient enrichment, sedimentation and herbicide residues) on seagrass meadows in New Zealand. The impact of current levels of these anthropogenic contaminants on seagrass resilience to swan grazing was also assessed in situ. To quantify black swan grazing pressure on seagrass meadows and to evaluate the potential relationship between swan grazing pressure and seagrass standing stock, observations and measurements were conducted in Tauranga Harbour where more than a third of the seagrass meadows disappeared between 1959 to 1996. Observations have shown that black swans graze intensively on Zostera muelleri meadows during high tide and were most numerous in the harbour during autumn. Black swan grazing resulted in the formation of circular devegetated patches (0.28 m2), where 92 % of shoots, 25 % of roots and 99 % of rhizomes are removed. The consumption rate was estimated to be 394 g dry weight (DW) swan-1 day-1. Significant seagrass loss on an annual basis was detected at the most swan populated site, which also had the highest swan grazing pressure (19-20 % of biomass consumed annually). This suggests a potential threshold of 19-20 % of annual seagrass biomass removal above which black swan grazing may contribute to substantial damage on seagrass meadows. Applied at the harbour scale, where there is a total of ~29 km2 of seagrass meadows, this corresponds to a swan population (i.e. grazing pressure) > 4630 birds. To identify the potential environmental stressors affecting seagrass condition, two contrasting harbours (Tauranga and Aotea) were surveyed where a range of environmental parameters, including parameters indicative of anthropogenic contamination, and seagrass condition metrics were measured. The survey showed that many of the seagrass condition metrics were positively correlated with sediment porewater ammonium (NH4-N) concentrations suggesting that nitrogen availability regulates seagrass growth. The presence of higher porewater nitrate (NO3-N) concentrations was linked to higher proportions of urban and crop land use in subcatchments, these latter parameters being negatively correlated with light availability during high tide. In spite of this, current levels of nutrient enrichment were apparently not detrimental to seagrass condition with evidence of N-limited plant growth and abundant light availability. Herbicide compounds were detected in seagrass sediment and at consistently higher concentrations in Tauranga harbour, which is the harbour more exposed to developed land use. The seagrass photosynthetic potential was lower in more herbicide contaminated sediments, although there was no evidence of any impact on seagrass biomass or morphometry. In a final experiment, black swan grazing was simulated in situ at four sites in Tauranga Harbour differing in exposure to potential anthropogenic contaminants and environmental characteristics. Grazing was simulated by removing seagrass biomass from patches (0.25 m2) in the meadow equivalent to natural swan removals (see above). Two levels of grazing intensity were applied to these patches; ~100 % of biomass removed (high) and ~ 40% of biomass removed (low). Results showed that the cover and the biomass of the low grazing intensity patches were not significantly different to controls (0 % of biomass removed) during the entire experiment. For the high grazing intensity patches, although the cover was restored after 9 months, biomass recovery was incomplete with only 30 % of total biomass regenerated, after one year. This suggests that swan grazing at high intensity can cause long-lasting damage to seagrass meadows, and that > 3 years is probably needed for a devegetated patch to fully recover from grazing (assuming a constant plant regeneration rate). The resilience response was similar across all sites examined in this harbour, suggesting that the current magnitude and range of environmental variability and potential contaminant levels within the seagrass meadows do not affect the ability of seagrass to regenerate from grazing. In conclusion, from these results, I can not conclude that anthropogenic contaminant or black swan grazing pressure are by themselves responsible for seagrass decline in Tauranga Harbour. However, the study suggests that herbicide residues have the potential to detrimentally affect the seagrass photosynthetic activity as do high grazing pressure by the black swan on the seagrass meadow condition. Overall, this study contributes to the understanding of impacts of black swan grazing pressure combined with potential contaminant effects on seagrass ecosystems. It emphasizes the importance of herbivory in temperate seagrass systems, which it is often underestimated and highlights the seagrass habitat contamination due to coastal development. It provides crucial information that will assist resource management agencies to preserve this valuable natural ecosystem.

year: 2011

title: Carbon dioxide and methane emissions from the Te Arawa lakes of Rotorua, New Zealand

authors: Santoso, Arianto Budi

subjects: global carbon cycle

abstract: One of the biggest issues confronting humankind today is global warming due to the rapidly increasing greenhouse gas (GHG) emissions, namely CO₂, CH₄ and N₂O. The Intergovernmental Panel for Climate Change (IPCC) has prepared an emission reduction strategy. So far, inland waters, including lakes and reservoirs, have not been included in the global carbon cycle. However, the contribution of inland waters to global CO₂ and CH₄ emissions has been identified to be important. Inland waters are also known to be a major sink for GHG emissions by attenuating carbon that would otherwise be transported from the terrestrial landscape to the ocean. Lakes are also very sensitive to climate change as well as to human impacts generally, and these effects will need to be considered in understanding the future role of lakes in the global carbon cycle.
This study aimed to improve understanding of CO₂ and CH₄ emissions from lakes, and to quantify these emissions under changing climate and nutrient loading regimes in a regionally discrete group of lakes of volcanic origin in North Island of New Zealand. It included a comprehensive field study of one lake, application of process-based numerical modelling to the lake, and collation and critical analysis of existing datasets for the group of lakes. The primary study site was Okaro, a monomictic eutrophic lake where a major restoration program has been in place for more than one decade. The study also extended to 10 other lakes in order to give insights into effects of different nutrient and mixing regimes on carbon sources and sinks
Based on observations over a one-period (September 2013 – October 2014), Lake Okaro accumulated CO₂ and CH₄ in the hypolimnion during summer stratification. These gases were entrained into surface waters as lake started to turnover just prior to complete mixing in winter. As recorded in many other eutrophic lakes, the net CO₂ flux was mostly from the atmosphere to the lake. However, CO₂, together with CH₄, escaped from the lake as a pulsed emission in winter.  Using a simple annual mass balance model it was calculated that, ~31% of CH₄ sourced from the sediment escaped to the atmosphere through diffusive flux. The remainder was likely to be oxidized in the water column. The model also showed that on an annual basis the net CO₂ emission is out of the lake. These findings suggest that eutrophic lakes may actually be net emitters of greenhouse gases and that pulsed emissions may be an important contributor to the direction of the flux. This study did not account for CH₄ ebullition, however, and therefore the magnitude of GHG emissions from this lake is likely to be lower than predicted. 
The effects on CO₂ and CH₄ emissions from Lake Okaro of a warming climate and changes in nutrient loads was simulated using a coupled hydrodynamic-ecological model (GLM-AED2). Future possible changes were simulated by altering model forcing data, increasing air temperature by 2.5 °C. Internal and external nutrient (nitrogen and phosphorus) loads were also either halved or increased by one half. Model simulations showed that annual CO₂ uptake by the lake was enhanced under a warmer climate, but emissions of CH₄ increased during lake overturn as a result of greater diffusive fluxes. Total GHG emissions, as CO₂ equivalent (kg CO₂-eq m⁻² y⁻¹), from the lake were predicted with model simulations to increase by 27% under a warming climate, relative to present conditions. This increase would be reduced to 19% if nutrient loading was halved.
A first-order diagenesis model was used to estimate the carbon deposition in the 11 Te Arawa lakes. The most productive lakes, using chlorophyll a as a proxy, had higher rates of carbon deposition in the bottom sediments than the less productive lakes. However, burial efficiency (buried carbon: deposited carbon) was lower in productive lakes meaning that most of the deposited carbon in these lakes is remineralized back into the water column. This remineralization process can be associated with CO₂ and CH₄ emissions from the lake.
The results of this study highlight that eutrophic lakes may contribute emit higher levels of GHGs to the atmosphere than has previously been estimated, primarily as a result of pulsed emissions associated with the onset of seasonal mixing, at least in monomictic lakes.  Eutrophication and climate warming are likely to enhance GHG emissions from lakes. The findings from this study have important implications for global GHG fluxes and indicate that fluxes into or from lakes need to be included in inventories. Reducing nutrient loads to lakes could offset some of the predicted increases in emissions of GHGs that are likely to occur with climate warming.

text: Carbon dioxide and methane emissions from the Te Arawa lakes of Rotorua, New Zealand One of the biggest issues confronting humankind today is global warming due to the rapidly increasing greenhouse gas (GHG) emissions, namely CO₂, CH₄ and N₂O. The Intergovernmental Panel for Climate Change (IPCC) has prepared an emission reduction strategy. So far, inland waters, including lakes and reservoirs, have not been included in the global carbon cycle. However, the contribution of inland waters to global CO₂ and CH₄ emissions has been identified to be important. Inland waters are also known to be a major sink for GHG emissions by attenuating carbon that would otherwise be transported from the terrestrial landscape to the ocean. Lakes are also very sensitive to climate change as well as to human impacts generally, and these effects will need to be considered in understanding the future role of lakes in the global carbon cycle.
This study aimed to improve understanding of CO₂ and CH₄ emissions from lakes, and to quantify these emissions under changing climate and nutrient loading regimes in a regionally discrete group of lakes of volcanic origin in North Island of New Zealand. It included a comprehensive field study of one lake, application of process-based numerical modelling to the lake, and collation and critical analysis of existing datasets for the group of lakes. The primary study site was Okaro, a monomictic eutrophic lake where a major restoration program has been in place for more than one decade. The study also extended to 10 other lakes in order to give insights into effects of different nutrient and mixing regimes on carbon sources and sinks
Based on observations over a one-period (September 2013 – October 2014), Lake Okaro accumulated CO₂ and CH₄ in the hypolimnion during summer stratification. These gases were entrained into surface waters as lake started to turnover just prior to complete mixing in winter. As recorded in many other eutrophic lakes, the net CO₂ flux was mostly from the atmosphere to the lake. However, CO₂, together with CH₄, escaped from the lake as a pulsed emission in winter.  Using a simple annual mass balance model it was calculated that, ~31% of CH₄ sourced from the sediment escaped to the atmosphere through diffusive flux. The remainder was likely to be oxidized in the water column. The model also showed that on an annual basis the net CO₂ emission is out of the lake. These findings suggest that eutrophic lakes may actually be net emitters of greenhouse gases and that pulsed emissions may be an important contributor to the direction of the flux. This study did not account for CH₄ ebullition, however, and therefore the magnitude of GHG emissions from this lake is likely to be lower than predicted. 
The effects on CO₂ and CH₄ emissions from Lake Okaro of a warming climate and changes in nutrient loads was simulated using a coupled hydrodynamic-ecological model (GLM-AED2). Future possible changes were simulated by altering model forcing data, increasing air temperature by 2.5 °C. Internal and external nutrient (nitrogen and phosphorus) loads were also either halved or increased by one half. Model simulations showed that annual CO₂ uptake by the lake was enhanced under a warmer climate, but emissions of CH₄ increased during lake overturn as a result of greater diffusive fluxes. Total GHG emissions, as CO₂ equivalent (kg CO₂-eq m⁻² y⁻¹), from the lake were predicted with model simulations to increase by 27% under a warming climate, relative to present conditions. This increase would be reduced to 19% if nutrient loading was halved.
A first-order diagenesis model was used to estimate the carbon deposition in the 11 Te Arawa lakes. The most productive lakes, using chlorophyll a as a proxy, had higher rates of carbon deposition in the bottom sediments than the less productive lakes. However, burial efficiency (buried carbon: deposited carbon) was lower in productive lakes meaning that most of the deposited carbon in these lakes is remineralized back into the water column. This remineralization process can be associated with CO₂ and CH₄ emissions from the lake.
The results of this study highlight that eutrophic lakes may contribute emit higher levels of GHGs to the atmosphere than has previously been estimated, primarily as a result of pulsed emissions associated with the onset of seasonal mixing, at least in monomictic lakes.  Eutrophication and climate warming are likely to enhance GHG emissions from lakes. The findings from this study have important implications for global GHG fluxes and indicate that fluxes into or from lakes need to be included in inventories. Reducing nutrient loads to lakes could offset some of the predicted increases in emissions of GHGs that are likely to occur with climate warming.

year: 2016