Search

Seagrasses are angiosperm plants that are completely adapted to life in seawater. They are distributed widely across the climatic regions, ranging from the tropics to temperate regions, in both inter-tidal and sub-tidal zones. Multiple ecosystem services are recognized as being supported by seagrass meadows, which recently has included appreciation role in carbon sequestration. Seagrass meadows, however, have been degraded in both terms of area and habitat quality across the globe, leading to a significant loss of ecosystem services and human livelihood support. This ongoing degradation has resulted in an urgent need to develop tools for assessing the temporal changes of extant meadows and accurate estimation of seagrass biological parameters, which will contribute to a sustainable conservation strategy into the future. This thesis describes the use of a range of freely available Earth observation products, including multi-spectral imagery from Landsat and Sentinel-2, and synthetic aperture radar (SAR) products from Sentinel-1, coupled with a range of machine learning (ML) and meta-heuristic optimization algorithms, to develop novel and advanced techniques for remote sensing of seagrass. The work used field validation data from Tauranga Harbor, New Zealand, and specifically targeted mapping, change detection, and estimation of seagrass distribution and biomass. The relatively small and patchy meadows of Zostera muelleri in this harbor can be mapped using a three-category classification (dense, sparse and none) with up to 91% accuracy for dense and 75% for sparse meadows using the machine learning algorithm Rotation Forest with Sentinel-2 imagery. Despite a slightly lower accuracy (90%), the algorithm Canonical Correlation Forest also shows merit for categorical seagrass mapping. Historic Landsat multispectral satellite data used with ML models was able to map accurately the change in distribution of seagrass meadows over 29 years (1989 - 2019). For this binary mappi

Seagrasses are ecosystem engineers that provide important ecological functions and societal economic values. Examples of the services that seagrasses provide are: sediment and coastal stability; maintenance of water quality; primary productivity for coastal ecosystems; fisheries nursery habitat; food for large herbivores; food-webs for complex marine communities; fisheries habitats; and carbon sink. They help minimise the costs of foreshore protection and maintain and support both tourism and fisheries economies. Different factors are implicated in causing the decline of seagrass ecosystems, but human activities are clearly identified as one of the major causes of seagrass decline in the world. Humans affect this ecosystem via physical damage (e.g., harbour developments, trawling, aquaculture), introduced species, global change, and pollution (e.g., sediments, nutrients, wastewaters, herbicides, heavy metals, petrochemicals). In New Zealand, sediment is the most pervasive seagrass stressor and the most prominent cause of seagrass decline. The goal of this PhD was to determine sediment effects on the seagrass Zostera muelleri in terms of light attenuation and substrate physico-chemical alteration. Within this research framework, provision of assistance for successful seagrass restoration was also considered. The principal research question for this project was to evaluate how sediment affects seagrasses and the project hypothesis was that sedimentation affects seagrass by altering the light climate, physically smothering the plants and modifying substrate physico-chemical composition. An extensive global literature review was undertaken to improve understanding of the international body of knowledge on the effects of sediment upon seagrass. Field surveys, field experiments and mesocosm experiments were used to evaluate the research objective. Field experiments were undertaken in Pāuatahanui Inlet, New Zealand. This inlet provides a wide range of seagrass cover, histo

Granular and biological activated carbon (GAC and BAC) filters are widely used to remove organic compounds from drinking water sources during municipal drinking water treatment. Common uses of GAC filters include removal of taste and odour (T&O) causing compounds such as geosmin and 2-methylisoborneol and reducing the concentration of dissolved organic matter (DOM) which contributes to the formation of disinfection by-products. GAC filters were installed at the Hamilton Drinking Water Treatment Station (HDWTS) in 2006 to address T&O issues and provide protection against cyanobacterial bloom events, and their effectiveness after such a long operational period was unknown. This study aimed to determine whether bacteria had colonised the GAC surface, compare full-scale GAC filters of different ages in their effectiveness in removing T&O compounds and different fractions of the DOM pool, and assess whether bacterially colonised GAC was able to remove high concentrations of T&O compounds during simulated, transient events after being subjected to steady state influent conditions. Results indicated that bacteria colonise the GAC surface quickly, and that T&O compounds and the humic fraction of the DOM are effectively removed. However, the extent to which humic substances were removed appeared to diminish relatively quickly as filters aged, and the protein fraction of the DOM appeared to be resistant to treatment across the entire treatment train.

Seagrass meadows form healthy near-coastal marine environments that provide a wide range of ecosystem services in New Zealand and Australia. However, seagrass habitats are declining regionally and globally. It is therefore essential that research fills the current knowledge gaps associated with seagrass disturbance-response regimes and develops standardised methods to measure seagrass health and resilience. Sedimentation associated with increased human activity is a major environmental stressor to seagrass; yet little is known about how sedimentation affects New Zealand’s only seagrass species, Zostera muelleri. This thesis, therefore explores how Z. muelleri responds to catastrophic burial (acute) events in Tauranga Harbour, New Zealand. Non-structural carbohydrates (NSC) are synthesised and stored in seagrass tissues when photosynthetic outputs exceed metabolic demands and, in turn, are mobilised when photosynthesis is unable to meet metabolic demands. Hence, NSC reserves can be used to measure the impact of a disturbance and/or the resilience of seagrass. A literature review in Chapter 2 illustrates that multiple methods are used to estimate NSC reserves. Experimental comparisons of a selection of these methods demonstrate that NSC estimates by different analytical methods cannot be compared. The outcome of Chapter 2 is the development of a 5-step standard analytical protocol for the quantitation of NSC reserves in seagrass (specifically Z. muelleri). The implementation of a standardised protocol will enable researchers to compare and synthesise results and, thus, increase the application of NSC as a seagrass health measure. Chapter 3 investigates the effects of acute sedimentation (i.e. burial) on Z. muelleri. In situ manipulative experiments across three sites in Tauranga Harbour, New Zealand were used to assess the spatial variation in resilience (i.e. resistance and recovery) to burial. Resistance and recovery following burial varied significantly between the