Restoring freshwater quality: an integrated environmental, economic and ecosystem services assessment of reducing nutrient loads to Lake Rotorua
Mueller, H. (2017). Restoring freshwater quality: an integrated environmental, economic and ecosystem services assessment of reducing nutrient loads to Lake Rotorua (Thesis, Doctor of Philosophy (PhD)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/11054
Permanent Research Commons link: https://hdl.handle.net/10289/11054
The management of freshwater resources is a global concern as anthropogenic pressures on these resources have intensified. A decline in the quantity and quality of freshwater urgently requires concerted restoration actions to reverse the decline. Restoration of lakes is impacted by complex relationships of ecosystem responses to management actions, economic constraints, societal pressures and policy contexts. Research in this thesis was aimed at an integrated assessment covering these aspects to inform future lake restoration action. The overarching objective of this thesis is to evaluate ecological and economic aspects of lake restoration, assessing the economic importance of ecosystems through exploring the costs of restoring and managing them, and assessing the ecological effectiveness of restoration actions. A focus was the evaluation of ecosystem services provided by a lake and its catchment, and uses quantitative analysis to study lake management dynamics to analyse what impedes successful lake restoration. This research uses a case study of Lake Rotorua, central North Island, New Zealand. Like many lake ecosystems, this lake has been subject to pressures from human activity for decades, driving eutrophication and decline in ecosystem health. Land use has played a major role in nutrient enrichment of this lake. Restoration actions have been targeted at limiting nutrient loss from land, and reducing internal loading of the lake through engineering solutions. The aim of the research here was to analyse historical management responses and current management options alongside economic values of the lake and the catchment. The interdisciplinary assessment is aimed at connecting the lake to the catchment, as well as ecological to economic and policy assessments; such an integrated approach provides insight not only on the restoration of Lake Rotorua, but can also contribute to the management of lakes throughout New Zealand. A main aim was to offer an integrated environmental, economic and policy assessment of the process of restoring water quality by reducing nutrient loads from the catchment alongside engineering options designed to reduce nutrients within the lake. The objectives for this thesis were to (1) explore a number of underlying drivers of lake management and the mechanisms for implementation of restoration initiatives, historically and in present times, (2) analyse ecosystem services and associated economic values of the lake ecosystem that are currently not valued by markets, and (3) evaluate cost-effectiveness of options to manage nutrient loads to the lake and internal loads through in-lake mitigation options, synthesising information on possible environmental outcomes and economic benefits for the lake and its catchment. Several different methods were used to address these research objectives. To analyse the drivers of ecosystem degradation and resulting management initiatives, water quality data and research publications on Lake Rotorua were collected from 1922 to 2012. These data were categorised using the Drivers-Pressures-State-Impact-Response (DPSIR) model. Important management and environmental changes were used as independent variables in the year of their occurrence. Results of a Generalised Maximum Entropy (GME) regression, a specialised multinomial regression that is suitable for small datasets with a diverse range of variables (binary and continuous), showed that management was reactive, and policy responses (followed by regulatory interventions) often took effect only when ecosystem decline was already well advanced. There was also a disconnect between land use intensification and its role in driving water quality change, and long social lag times between the recognition of the environmental issue and a policy response delayed implementation of restoration actions. To complement the historical study of lake restoration, the economic value of the lake and costs associated with degradation were evaluated to inform future management. Based on standard ecosystem services classification systems such as the Millennium Ecosystem Assessment in 2005, five different ecosystem services provided by the lake (habitat provision, food, nutrient processing, aesthetics, and recreation) were assessed. A range of direct and indirect valuation approaches, including existence value, hedonic pricing, and replacement cost, were used to assess the annual economic value of the lake ecosystem. A range of direct and indirect valuation concepts, including existence value, hedonic pricing and replacement cost, were used to assess the annual economic value of the lake ecosystem. A potential damage cost of the impacts of continued eutrophication was estimated as part of this economic assessment based on the current value of the lake and estimated reduction factors in ecosystem service provision and associated values. To assess the effectiveness of options to reduce nutrient loads to the lake, a range of nutrient load scenarios was analysed for their effect on lake water quality using a hydrodynamic-ecological lake model (DYRESM-CAEDYM). Options needed to meet nutrient reductions as key component of a lake water quality target set by policy included mitigation on land, mitigation in the lake, and land use change. Different costs were attributed to each option, including lake and land mitigation costs. Values of different land use types and ecosystem services values of the catchment were included in the analysis. Costs and changes in values were determined for each scenario, to integrate an analysis of environmental effectiveness and costs of management options. Costs associated with these options were determined to illustrate the environmental effectiveness and potential costs of management options. Main findings of this thesis are that freshwater management is subject to response lags between the recognition of environmental decline and the restorative action undertaken to address this decline. These lags relate to the visibility of environmental problems in the public sphere, with action often only undertaken once effects such as lake weeds, low water clarity and possibly toxic algal blooms impact the public. Social lag times also exist as part of the general bureaucratic management process, and within scientific research to inform management. Lags mean that ecosystem degradation can be allowed to proceed until impacts, at times, become irreversible. This research found that a better integration of science and policy could inform management decision making by providing a holistic framework integrating ecological knowledge, pursuits of economic growth and societal constraints. The ecosystem services value of Lake Rotorua based on the ecosystem services of food, habitat provision, nutrient processing, aesthetics and recreation was calculated to be $100-145 million per year. Ecosystem services provided by the catchment based on the current land use types were $176 million annually. A policy target for water quality was set for the lake. The ecological model was used to evaluate whether reduction scenarios meet such a water quality standard before assessing the management costs. The most cost-effective option to achieve the nutrient load reduction to the lake to meet this policy target was a combination of mitigation practices and land use change in the catchment. The current practice of alum dosing of two tributaries to the lake was instrumental in meeting water quality targets under current land use and resulting nutrient loads from the catchment. Best water quality outcomes were achieved by a conversion of intensive land use types to exotic or indigenous forest. This option also showed the best economic outcomes, when non-market values including ecosystem services values were considered. Results here show the importance of integrating ecological and economic assessments for best management outcomes. They also show the economic significance of preserving and restoring ecosystems. This thesis has revealed how environmental and social lag times can hinder the success of lake restoration actions, which at times can lead to irreversible degradation. It has shown the importance of making environmental decline visible in the public sphere, and the integration of science and policy to achieve effective management action. It has revealed how lake ecosystems are a major economic asset as well as being highly important for the provisioning of ecosystem services. The research has illustrated the economic potential of ecosystem services in the catchment. Response lags and ensuing degradation, as well as the economic importance of the lake ecosystem and its surrounding catchment mean that it is crucial to assess lake and land management in an integrated fashion. To restore the lake and maintain a resilient ecosystem, long term reduction of nutrient losses from intensive agriculture is an important component complementing in-lake restoration actions. This can be achieved through a combination of mitigation options reducing nutrient losses from intensive land use types, as well as land use change away from these types. This research analysed the management of both land and lake elements of a lake ecosystem. It has integrated analysis of ecological processes with an economic assessment of lake and catchment ecosystem services, and placed this within a policy and management context. The integration of lake and catchment, and ecology and economics in an applied context contributes to shifting research and management focus towards more integrated assessments, taking ecological, economic, social and cultural values into consideration.
University of Waikato
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