The Evolution and Environmental History of Wainono Lagoon, New Zealand (2016)
AuthorsNorman, Makishow all
Coastal lagoons are dynamic environments that are sensitive to climate change, sea level rise and anthropogenic activities, including the use of catchment water resources and land. Their management is of high public and scientific interest at present, both locally and internationally, not least due to widespread water quality declines associated with resource use in feeder catchments. However, despite its importance for sustainable lagoon management, consideration of the lagoon morphology and long-term stability appears to have been neglected in the decision making processes to date. This thesis provides the evolutionary and environmental history as well as a comprehensive understanding of the lagoon system and assessment of the long-term stability status of Wainono Lagoon, a coastal hydrosystem located in the South Island of New Zealand. The main objectives of the research are to: (i) reconstruct a history of the lagoon environment and morphological evolution over the historical time, (ii) identify the components that influence the lagoon system and morphology, (iii) assess the long-term stability of Wainono Lagoon and (vi) develop a generic evolutionary model for waituna-type lagoons. The evolutionary and environmental history of Wainono Lagoon is reconstructed using a number of techniques including analyses of sediment cores, foraminiferal assemblages and anisotropy of magnetic susceptibility. Analyses of barrier beach profiles, aerial images and bathymetry of the lagoon were also used to establish the recent trends in lagoonal sedimentation and barrier beach morphology. A generic evolutionary model was developed which can be used to assess the long-term stability of waituna-type lagoons on a transgressive coast. This study has found that Wainono Lagoon has experienced an estuarine phase for a prolonged period of time at least once since the closure of the barrier. Today, despite the chronic erosion of the Canterbury Bight, the coast of Wainono Lagoon is relatively stable, with very slow translation of the southern part of the Wainono barrier. The lagoonal sedimentation rates are high relative to the rate of sea level rise meaning that if the current trends continue the lagoon will become filled with sediments over time. This highlights the necessity of monitoring of the sedimentation regime in the lagoon, which is hardly understood at present. Translation of the barrier further south along the Waihao Dead Arm will cause blockages and management of this issue will also affect the future stability of Wainono Lagoon. Management intervention can result in accommodation or hindrance in the natural evolution of waituna-type lagoons. At Wainono Lagoon, inadequate understanding of human impacts on the lagoon’s geomorphology and a lack of adequate strategy may result in accelerated infilling of the lagoon. In development of a long-term policy and management strategies, it is critical that the morphological evolution and long-term stability status is taken into consideration in order to avoid undesirable outcomes such as human induced infilling of the lagoon. This study provides a better understanding of the dynamics of Wainono Lagoon as a basis for development of such a management policy and strategies.