UC Research Repository Collection:

Geomorphological and geophysical investigation of the effects of active tectonic deformation on the hydrogeology of North Culverden Basin, North Canterbury

Sat, 01 Jan 2000 00:00:00 GMT

Title: Geomorphological and geophysical investigation of the effects of active tectonic deformation on the hydrogeology of North Culverden Basin, North Canterbury Authors: Armstrong, Mark James Abstract: This thesis examines the complex interaction between the tectonic evolution of Culverden Basin and the Late Quaternary sediments, which form the aquifer-bearing deposits, using geological and geomorphological mapping as well as near-surface geophysical investigations. Along the eastern margin of Culverden Basin, the deformation associated with the actively widening Australian-Pacific plate boundary zone, has resulted in the evolution of Culverden Basin and the progressive inversion of the basin floor. The eastern margin of the basin is structurally controlled by a NE trending, complexly segmented range-front fault system and associated thrust-propagated anticlines forming the basin boundary. Basin inversion is driven by the westward propagation of footwall imbricate thrusts and associated folds. The inversion of the basin floor lead to the creation of sub-basins within the larger basin, which have controlled the distribution and architecture of the Late Quaternary stratigraphy. The Late Quaternary sedimentary record documents periods of climatically induced aggradation during cold conditions and degradation in the intervening warmer times. The interaction between the sedimentation and ongoing tectonic deformation has resulted in complex lithological relationships between the locally sourced alluvial fans and the glacial outwash deposits of the major rivers entering the basin. The architecture of the aquifers is therefore controlled by the changing fluvial regime and its interaction with the evolving sub-basins. The progressive evolution of the sub-basins leads to increasing complexities in the facies relationships and to the confinement of the deposits into progressively smaller portions of the sub-basins. Once the basin boundaries become emergent, the basin becomes isolated, and potentially cut-off from its groundwater recharge source. Leonard Mound is an actively evolving imbricate thrust system along the eastern margin of Culverden Basin that has isolated the Wynyard sub-basin from the central portion of Culverden Basin, during the Late Pleistocene and present. The emergence of Leonard Mound is preventing the recharge to the Wynyard sub-basin from the high yielding aquifers of the central portion of the basin. In the central portion of Culverden Basin, high natural recharge combined with an irrigation scheme has allowed for transformation of the basin into a major dairy farming centre. In contrast, the Wynyard sub-basin is still subjected to frequent summer droughts, making it desirable to find a better source of groundwater for the eastern margin of the basin. The hydrogeological model provided by the Culverden Basin almost certainly has wider implications to the groundwater resources of other basins in similar active tectonic settings.

The Impact of Edge Effects & Matrix Restoration on Dung Beetle Community Structure & Ecosystem Function

Sat, 01 Jan 2011 00:00:00 GMT

Title: The Impact of Edge Effects & Matrix Restoration on Dung Beetle Community Structure & Ecosystem Function Authors: Barnes, Andrew David Abstract: Land-use change has become a force of global importance and has gained status as the most important driver of ecosystem degradation. The resulting creation of habitat edges has pervasive impacts on the distribution and persistence of species in forest ecosystems. Responses of species to edge effects can be highly dependent on ‘response’ traits, which may in turn co-vary with ‘effect’ traits that determine rates of ecosystem functioning. Therefore, non-random loss of species due to traits conferring higher susceptibility to extinction may also result in the loss of functionally-important species across a habitat edge gradient. Likewise, response and effect traits may be important in determining reassembly of communities in regenerating habitats, which may provide insight into potential scenarios of functional responses to restoration efforts. To test for potential off-site effects of adjacent matrix habitat restoration on dung beetle communities, I compared dung beetle community structure and species trait composition across Afromontane forest edges adjacent to degraded and regenerating matrix habitat at Ngel Nyaki forest reserve in Nigeria. I also measured dung removal rates across habitat edge gradients to investigate the relative off-site impacts of matrix restoration on dung beetle-mediated ecosystem processes. I found significant effects of adjacent matrix condition on edge response functions in dung beetle abundance, species distributions, and trait composition. Beetle abundances were markedly higher in forests adjacent to regenerating matrix, whereas the largest differences in trait composition were found between degraded and regenerating matrix habitat, indicating the presence of ecological filtering processes in these areas. Furthermore, I found that species traits determined community structural responses to environmental change and this had strong flow-on effects to rates of dung removal. Shifts in trait distributions explained dung removal rates above and beyond total beetle mass, suggesting that neutral processes alone could not explain functional efficiency. In particular, habitat regeneration resulted in the assembly of communities with high total beetle mass and on-average smaller beetles, which was optimal for functional efficiency. In conclusion, the restoration of adjacent matrix habitat was shown to effectively mitigate edge effects on dung beetle community structure resulting in the re-establishment of important associated ecosystem processes.

Tectonic Geomorphology and Paleoseismicity of the Northern Esk Fault, North Canterbury, New Zealand

Sat, 01 Jan 2011 00:00:00 GMT

Title: Tectonic Geomorphology and Paleoseismicity of the Northern Esk Fault, North Canterbury, New Zealand Authors: Noble, Duncan Paul Abstract: Geomorphic, structural and chronological data are used to establish the late Quaternary paleoseismicity of the active dextral-oblique Northern Esk Fault in North Canterbury, New Zealand. Detailed field mapping of the preserved c. 35 km of surface traces between the Hurunui River and Ashley Head reveals variations in strike ranging from 005° to 057°. Along with kinematic data collected from fault plane striae and offset geomorphic markers along the length of the fault these variations are used to distinguish six structural subsections of the main trace, four dextral-reverse and two dextral-normal. Displacements of geomorphic markers such as minor streams and ridges are measured using differential GPS and rangefinder equipment to reveal lateral offsets ranging from 3.4 to 23.7 m and vertical offsets ranging from < 1 to 13.5 m. Characteristic single event displacements of c. 5 m and c. 2 m have been calculated for strike-slip and reverse sections respectively. The use of fault scaling relationships reveals an anomalously high displacement to surface rupture length ratio when compared to global data sets. Fault scaling relationships based on width limited ruptures and magnitude probabilities from point measurements of displacement imply earthquake magnitudes of Mw 7.0 to 7.5. Optically Stimulated Luminescence (OSL) ages from displaced Holocene alluvial terraces at the northern extent of the active trace along with OSL and radiocarbon samples of the central sections constrain the timing of the last two surface rupturing events (11.15 ±1.65 and 3.5 ± 2.8 ka) and suggest a recurrence interval of c. 5612 ± 445 years and late Quaternary reverse and dextral slip rates of c. 0.31 mm/yr and 0.82 mm/yr respectively. The results of this study show that the Northern Esk Fault accommodates an important component of the c. 0.7 – 2 mm/yr of unresolved strain across the plate boundary within the North Canterbury region and affirm the Esk Fault as a source of potentially damaging ground shaking in the Canterbury region.

The Role of Bark Beetles as Vectors in the Colonisation of Windthrown Timber by Fungi

Sat, 01 Jan 2011 00:00:00 GMT

Title: The Role of Bark Beetles as Vectors in the Colonisation of Windthrown Timber by Fungi Authors: McCarthy, James Abstract: The increasing frequency and severity of windthrow events affecting the forestry industry in New Zealand have raised important management issues surrounding the rate of colonisation of fallen trees by sapstain fungi and the time available for salvage harvesting before sapstain degradation limits potential economic returns. These fungi are known to be spread by a multitude of factors including wind, rain splash, harvesting processes and insect vectoring. Apart from the ecological interest in these interactions between fungi, plants and insects, sapstain fungi are also economically important because their hyphae discolour the sapwood and reduce the overall quality of the timber. The amount of time available to salvage harvest damaged trees is unknown, especially on seasonal and regional scales. Manipulative experiments were established in Pinus radiata forests to examine this seasonal and regional variation in sapstain attack following windthrow, and to investigate the importance of bark beetles as vectors of sapstain fungi. A range of methods were implemented to assess the role of bark beetles as vectors and to ascertain which sapstain fungi are associated with them. Experimental billet logs were caged to exclude beetles and subsequently analyse fungal attack in comparison with identical logs left exposed to beetles. In addition, individual beetles were sampled directly to determine whether they carried spores of particular fungal species and to assess the degree of association in vector-fungal dynamics. Finally, a novel application of DNA melt peak analysis was developed to investigate variation among the fungal communities associated with beetles potentially involved in vectoring sapstain spores. The moisture content of fallen trees was found to be the main factor regulating sapstain development, and when moisture content drops below 100% (on dry weight basis) sapstain fungi grew rapidly. The speed at which this level drops depends on the season, with much faster drying occurring in the warmer months of spring and summer. As a result, trees that fell in the previous winter or autumn did not develop significant sapstain levels until temperatures rose in the following summer, suggesting that storm-damaged trees that fall in winter can be left safely until just before the next summer before they are no longer suitable for salvage harvest. In New Zealand, the bark beetle species acting as vectors of sapstain fungi are not behaviourally adapted to colonisation of logs that are not in contact with the ground. Following windthrow events in pine forests, trees generally lie with their stems suspended above the level of the ground by their branches. As a result, under these circumstances, beetle colonisation of windthrown timber was low, and bark beetles were not a significant vector of stain. The caged and un-caged experimental log billets, however, were in contact with the ground, resulting in colonisation of the un-caged logs. In this case, bark beetles did play an important role in contributing to sapstain intensity, and the stain distribution within the logs mirrored that of the stain distribution. However, this effect may be due to the provision of access points for wind- or water-borne spores of the non-insect vectored stain fungus Diplodia pinea, or to the spread of hyphae through the tunnelling and feeding activities of beetles within the tree, rather than by bark beetles acting as vectors of spores. Bark beetles were confirmed as sapstain vectors with the isolation of seven different ophiostomatoid stain fungi from them, five of which were also found in wood. Finally, the development of a laboratory based, rapid species identification method was developed to identify fungal DNA. Melt peak analysis allowed the species-specific DNA melt temperatures to be compared with the melt temperatures of known species to be able to rapidly, and cheaply, identify an unknown species. Bark beetles are vectors of sapstain fungi in P. radiata forests, however the bark beetle species naturalised in New Zealand prefer to colonise wood when it is in contact with the ground. Following windthrow, trees are generally not attacked by beetles as they are held from the ground by their branches, leaving them to be stained predominantly be wind and rain dispersed stain fungus D. pinea. Stain did not occur until the moisture content of fallen trees dropped below 100%, which only happens in the warm months of summer and spring. In New Zealand, there are interactions between trees and bark beetles, and bark beetles with fungal pathogens from all around the globe resulting in a unique novel assemblage of species together for the first time. Understanding the dynamics of these species in their novel environment is crucial to effectively responding to potential pest threats.