title: Parameterisation of sediment geochemistry for simulating water quality responses to long-term catchment and climate changes in polymictic, eutrophic Lake Rotorua, New Zealand

authors: Özkundakci, Deniz

subjects: DYRESM-CAEDYM

abstract: Numerical models of aquatic ecosystems that couple physics and biogeochemistry are valuable tools in aquatic ecosystem research. These models provide opportunities to test theories and to inform environmental management. In this study, we used the dynamic, process-based hydrodynamic-ecological model DYRESM-CAEDYM to simulate key ecosystem processes of Lake Rotorua, New Zealand, for six 8-year periods between 1920 and 2100 in order to evaluate the potential effects of future changes in land use and climate. Longterm variations in external boundary conditions (e.g. inflows) to the lake ecosystem are incorporated by varying the relevant input files in the DYRESMCAEDYM model. However, quantification of internal lake processes, specifically those at the sediment-water interface, presents a major challenge for long-term simulations. The sediment model within CAEDYM is ‘static’, with assumed constant sediment composition and a relatively simplistic process representation for nutrient and oxygen fluxes between sediment and water. Specifically, the model regulates sediment phosphate and ammonium release according to concentrations of oxidising species (i.e. oxygen and nitrate), and temperature in the overlying water layer. Sediment oxygen demand is controlled by dissolved oxygen concentrations and temperature in the water layer overlying the sediments. We used a ‘trial and error’ approach to estimate parameters for calibrating and validating the model, and regression modelling to infer the parameters beyond the calibration/validation simulation period (2001–2009). We observed a significant relationship in historic monitoring data between the external nitrogen load to the lake and its hypolimnetic oxygen demand as well as the bottom-sediment nitrogen concentrations. This relationship was used to hindcast and forecast model parameters for sediment nutrient release and oxygen demand in the six model simulation periods. The inclusion of a dynamic response of sediment nutrient release and oxygen demand parameters to changes in external nutrient loads enabled a more conceptually concise simulation of water quality for the simulations. This model is currently being used by regional environmental management authorities for developing an Action Plan for the restoration of Lake Rotorua.

text: Parameterisation of sediment geochemistry for simulating water quality responses to long-term catchment and climate changes in polymictic, eutrophic Lake Rotorua, New Zealand Numerical models of aquatic ecosystems that couple physics and biogeochemistry are valuable tools in aquatic ecosystem research. These models provide opportunities to test theories and to inform environmental management. In this study, we used the dynamic, process-based hydrodynamic-ecological model DYRESM-CAEDYM to simulate key ecosystem processes of Lake Rotorua, New Zealand, for six 8-year periods between 1920 and 2100 in order to evaluate the potential effects of future changes in land use and climate. Longterm variations in external boundary conditions (e.g. inflows) to the lake ecosystem are incorporated by varying the relevant input files in the DYRESMCAEDYM model. However, quantification of internal lake processes, specifically those at the sediment-water interface, presents a major challenge for long-term simulations. The sediment model within CAEDYM is ‘static’, with assumed constant sediment composition and a relatively simplistic process representation for nutrient and oxygen fluxes between sediment and water. Specifically, the model regulates sediment phosphate and ammonium release according to concentrations of oxidising species (i.e. oxygen and nitrate), and temperature in the overlying water layer. Sediment oxygen demand is controlled by dissolved oxygen concentrations and temperature in the water layer overlying the sediments. We used a ‘trial and error’ approach to estimate parameters for calibrating and validating the model, and regression modelling to infer the parameters beyond the calibration/validation simulation period (2001–2009). We observed a significant relationship in historic monitoring data between the external nitrogen load to the lake and its hypolimnetic oxygen demand as well as the bottom-sediment nitrogen concentrations. This relationship was used to hindcast and forecast model parameters for sediment nutrient release and oxygen demand in the six model simulation periods. The inclusion of a dynamic response of sediment nutrient release and oxygen demand parameters to changes in external nutrient loads enabled a more conceptually concise simulation of water quality for the simulations. This model is currently being used by regional environmental management authorities for developing an Action Plan for the restoration of Lake Rotorua.

year: 2012

title: Making Sense of the Census: Classifying and Counting Ethnicity in Oceania, 1965-2011

authors: Broman, Patrick David

subjects: Ethnicity

abstract: As the flagship government effort to count and classify its population, censuses are a key site for rendering and making visible group boundaries. Despite claims to objective rationality, however, census taking is a political and inherently subjective exercise. Censuses help shape the very categories they claim to capture: censuses do more than reflect social reality, they also participate in the social construction of this reality (Kertzer and Arel, 2002b, p. 2). While ethnicity – as a social construct – is imagined, its effects are far from imaginary, and census categorisations may have significant material consequences for the lives of citizens.

Although an increasing number of studies have examined how and why governments in particular times or places count their populations by ethnicity, studies that are both cross-national and longitudinal are rare. Attempting to in part bridge this gap, this thesis studies census questionnaires from 1965 to 2011 for 24 countries in Oceania. In doing so, it explores three general questions: 1) how ethnicity is conceptualised and categorised in Oceanic censuses over time; 2) the relationship between ethnic counting in territories to that of their metropoles; and 3) Oceanic approaches towards multiple ethnic identities. Spread over an area of thirty million square kilometres of the Pacific Ocean, Oceania provides an interesting context to study ethnic counting. The countries and territories which make up the region present an enormous diversity in physical geography and culture, languages and social organization, size and resource endowment. As the last region in the world to decolonise, Oceania includes a mix of dependencies and sovereign states.

The study finds that engagement with ethnic classification and counting is near-ubiquitous across the time period, with most countries having done so in all five cross-sectional census rounds. In general terms, in ethnic census questions ‘racial’ terminology of race and ancestry has been displaced over the focal period by ‘ethnic’ terminology of ethnicity and ethnic origin. Overall, the concept of ethnic origins predominates, although interestingly it is paired with race in the US territories, reflecting the ongoing social and political salience of race in the metropole. With respect to ethnic categories provided on census forms (and thus imbued with the legitimacy of explicit state recognition) the study finds a shift away from the imagined and flawed Melanesian/Micronesian/ Polynesian racial typology and other colonial impositions to more localised and self-identified Pacific identities. It is theorised that these shifts are emblematic of broader global changes in the impetuses for ethnic counting, from colonially-influenced ‘top down’ counting serving exclusionary ends to more inclusive, ‘bottom up’ approaches motivated by concerns for minority rights and inclusive policy-making.

text: Making Sense of the Census: Classifying and Counting Ethnicity in Oceania, 1965-2011 As the flagship government effort to count and classify its population, censuses are a key site for rendering and making visible group boundaries. Despite claims to objective rationality, however, census taking is a political and inherently subjective exercise. Censuses help shape the very categories they claim to capture: censuses do more than reflect social reality, they also participate in the social construction of this reality (Kertzer and Arel, 2002b, p. 2). While ethnicity – as a social construct – is imagined, its effects are far from imaginary, and census categorisations may have significant material consequences for the lives of citizens.

Although an increasing number of studies have examined how and why governments in particular times or places count their populations by ethnicity, studies that are both cross-national and longitudinal are rare. Attempting to in part bridge this gap, this thesis studies census questionnaires from 1965 to 2011 for 24 countries in Oceania. In doing so, it explores three general questions: 1) how ethnicity is conceptualised and categorised in Oceanic censuses over time; 2) the relationship between ethnic counting in territories to that of their metropoles; and 3) Oceanic approaches towards multiple ethnic identities. Spread over an area of thirty million square kilometres of the Pacific Ocean, Oceania provides an interesting context to study ethnic counting. The countries and territories which make up the region present an enormous diversity in physical geography and culture, languages and social organization, size and resource endowment. As the last region in the world to decolonise, Oceania includes a mix of dependencies and sovereign states.

The study finds that engagement with ethnic classification and counting is near-ubiquitous across the time period, with most countries having done so in all five cross-sectional census rounds. In general terms, in ethnic census questions ‘racial’ terminology of race and ancestry has been displaced over the focal period by ‘ethnic’ terminology of ethnicity and ethnic origin. Overall, the concept of ethnic origins predominates, although interestingly it is paired with race in the US territories, reflecting the ongoing social and political salience of race in the metropole. With respect to ethnic categories provided on census forms (and thus imbued with the legitimacy of explicit state recognition) the study finds a shift away from the imagined and flawed Melanesian/Micronesian/ Polynesian racial typology and other colonial impositions to more localised and self-identified Pacific identities. It is theorised that these shifts are emblematic of broader global changes in the impetuses for ethnic counting, from colonially-influenced ‘top down’ counting serving exclusionary ends to more inclusive, ‘bottom up’ approaches motivated by concerns for minority rights and inclusive policy-making.

year: 2013

title: Materials for enhancing denitrification performance in partially saturated vertical flow wetlands for marae

authors: Liu, Lucian XiaoRan

abstract: There are upwards of 773 marae in New Zealand which are responsible for many key events for the indigenous people, Māori, many of which are located rurally and have inadequate on-site wastewater treatment mostly comprising of a septic tank followed by land application. Māori have many strong beliefs about water and subsequently criteria surround the treatment of wastewater due to the effects it can have on people and environment. One proposed solution that meets criteria are treatment wetlands, more specifically partially saturated vertical flow wetlands which require a smaller footprint and produce better effluent than traditional wetland designs. NIWA (National Institute of Water and Atmospheric Research) has experimented with mesocosm scale versions of this design and has encountered issues with denitrification in the saturated zone.

This research is therefore directed at enhancing denitrification in the saturated zone with materials that are able to supplement organic carbon for denitrification. Several woodchip materials (Eastern Cottonwood, Mahogany, Manuka, Eucalyptus, Crack Willow, Princess Tree and Pine) along with two industry by-product materials (Brewers Spent Grain and Slum gum) and Coir (Coconut derivative) were examined for denitrification capabilities and to serve in producing a leachate for dosing the proposed system to supplement organic carbon for denitrification.

The research is split into three phases; the first examines the ability of materials to release organic carbon into water over 60 days, the second examines the same but over three 10 day cycles, and the third quantifies denitrification performance of the materials at lab scale.

Results showed that producing a suitable leachate is not possible without the use of fresh material for each batch. By-product materials had great capacity for releasing organic carbon into water and denitrification (up to 85.5% nitrate removal) but had limited lifespans as media. While woodchip materials did not exhibit as great carbon release, they achieved comparable denitrification (74.2-74.5% nitrate removal) with long lifespans. Therefore, a woodchip and industry by-product mix could be the solution. Alternatively, there are many woodchip species, some which could have better denitrification capacity or suitable industry by-products with longer useful lifespans.

text: Materials for enhancing denitrification performance in partially saturated vertical flow wetlands for marae There are upwards of 773 marae in New Zealand which are responsible for many key events for the indigenous people, Māori, many of which are located rurally and have inadequate on-site wastewater treatment mostly comprising of a septic tank followed by land application. Māori have many strong beliefs about water and subsequently criteria surround the treatment of wastewater due to the effects it can have on people and environment. One proposed solution that meets criteria are treatment wetlands, more specifically partially saturated vertical flow wetlands which require a smaller footprint and produce better effluent than traditional wetland designs. NIWA (National Institute of Water and Atmospheric Research) has experimented with mesocosm scale versions of this design and has encountered issues with denitrification in the saturated zone.

This research is therefore directed at enhancing denitrification in the saturated zone with materials that are able to supplement organic carbon for denitrification. Several woodchip materials (Eastern Cottonwood, Mahogany, Manuka, Eucalyptus, Crack Willow, Princess Tree and Pine) along with two industry by-product materials (Brewers Spent Grain and Slum gum) and Coir (Coconut derivative) were examined for denitrification capabilities and to serve in producing a leachate for dosing the proposed system to supplement organic carbon for denitrification.

The research is split into three phases; the first examines the ability of materials to release organic carbon into water over 60 days, the second examines the same but over three 10 day cycles, and the third quantifies denitrification performance of the materials at lab scale.

Results showed that producing a suitable leachate is not possible without the use of fresh material for each batch. By-product materials had great capacity for releasing organic carbon into water and denitrification (up to 85.5% nitrate removal) but had limited lifespans as media. While woodchip materials did not exhibit as great carbon release, they achieved comparable denitrification (74.2-74.5% nitrate removal) with long lifespans. Therefore, a woodchip and industry by-product mix could be the solution. Alternatively, there are many woodchip species, some which could have better denitrification capacity or suitable industry by-products with longer useful lifespans.

year: 2023