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Research papers, University of Canterbury Library

The Avon-Heathcote Estuary is of significant value to Christchurch due to its high productivity, biotic diversity, proximity to the city, and its cultural, recreational and aesthetic qualities. Nonetheless, it has been subjected to decades of degradation from sewage wastewater discharges and encroaching urban development. The result was a eutrophied estuary, high in nitrogen, affected by large blooms of nuisance macroalgae and covered by degraded sediments. In March 2010, treated wastewater was diverted from the estuary to a site 3 km offshore. This quickly reduced water nitrogen by 90% within the estuary and, within months, there was reduced production of macroalgae. However, a series of earthquakes beginning in September 2010 brought massive changes: tilting of the estuary, changes in channels and water flow, and a huge influx of liquefied sediments that covered up to 65% of the estuary floor. Water nitrogen increased due to damage to sewage infrastructure and the diversion pipeline being turned off. Together, these drastically altered the estuarine ecosystem. My study involves three laboratory and five in situ experiments that investigate the base of the food chain and responses of benthic microalgae to earthquake-driven sediment and nutrient changes. It was predicted that the new sediments would be coarser and less contaminated with organic matter and nutrients than the old sediments, would have decreased microalgal biomass, and would prevent invertebrate grazing and bioturbation activities. It was believed that microalgal biomass would become similar across new and old sediments types as the unstable new sediments were resuspended and distributed over the old sediments. Contact cores of the sediment were taken at three sites, across a eutrophication gradient, monthly from September 2011 to March 2012. Extracted chlorophyll a pigments showed that microalgal biomass was generally lower on new liquefied sediments compared to old sediments, although there was considerable site to site variation, with the highly eutrophic sites being the most affected by the emergence of the new sediments. Grazer experiments showed that invertebrates had both positive and negative site-specific effects on microalgal biomass depending on their identity. At one site, new sediments facilitated grazing by Amphibola crenata, whereas at another site, new sediments did not alter the direct and indirect effects of invertebrates (Nicon aestuariensis, Macropthalmus hirtipes, and A. crenata) on microalgae. From nutrient addition experiments it was clear that benthic microalgae were able to use nutrients from within both old and new sediments equally. This implied that microalgae were reducing legacy nutrients in both sediments, and that they are an important buffer against eutrophication. Therefore, in tandem with the wastewater diversion, they could underpin much of the recovery of the estuary. Overall, the new sediments were less favourable for benthic microalgal growth and recolonisation, but were less contaminated than old sediments at highly eutrophic sites. Because the new sediments were less contaminated than the old sediments, they could help return the estuary to a noneutrophic state. However, if the new sediments, which are less favourable for microalgal growth, disperse over the old sediments at highly eutrophic sites, they could become contaminated and interfere with estuarine recovery. Therefore, recovery of microalgal communities and the estuary was expected to be generally long, but variable and site-specific, with the least eutrophic sites recovering quickly, and the most eutrophic sites taking years to return to a pre-earthquake and non-eutrophied state. changes in channels and water flow, and a huge influx of liquefied sediments that covered up to 65% of the estuary floor. Water nitrogen increased due to damage to sewage infrastructure and the diversion pipeline being turned off. Together, these drastically altered the estuarine ecosystem. My study involves three laboratory and five in situ experiments that investigate the base of the food chain and responses of benthic microalgae to earthquake-driven sedimen tand nutrient changes. It was predicted that the new sediments would be coarser and less contaminated with organic matter and nutrients than the old sediments, would have decreased microalgal biomass, and would prevent invertebrate grazing and bioturbation activities. It was believed that microalgal biomass would become similar across new and old sediments types as the unstable new sediments were resuspended and distributed over the old sediments. Contact cores of the sediment were taken at three sites, across a eutrophication gradient, monthly from September 2011 to March 2012. Extracted chlorophyll a pigments showed that microalgal biomass was generally lower on new liquefied sediments compared to old sediments, although there was considerable site to site variation, with the highly eutrophic sites being the most affected by the emergence of the new sediments. Grazer experiments showed that invertebrates had both positive and negative site-specific effects on microalgal biomass depending on their identity. At one site, new sediments facilitated grazing by Amphibola crenata, whereas at another site, new sediments did not alter the direct and indirect effects of invertebrates (Nicon aestuariensis, Macropthalmus hirtipes, and A. crenata) on microalgae. From nutrient addition experiments it was clear that benthic microalgae were able to use nutrients from within both old and new sediments equally. This implied that microalgae were reducing legacy nutrients in both sediments, and that they are

Research papers, University of Canterbury Library

The city of Christchurch and its surrounds experienced widespread damage due to soil liquefaction induced by seismic shaking during the Canterbury earthquake sequence that began in September 2010 with the Mw7.1 Darfield earthquake. Prior to the start of this sequence, the city had a large network of strong motion stations (SMSs) installed, which were able to record a vast database of strong ground motions. This paper uses this database of strong ground motion recordings, observations of liquefaction manifestation at the ground surface, and data from a recently completed extensive geotechnical site investigation program at each SMS to assess a range of liquefaction evaluation procedures at the four SMSs in the Christchurch Central Business District (CBD). In general, the characteristics of the accelerograms recorded at each SMS correlated well with the liquefaction evaluation procedures, with low liquefaction factors of safety predicted at sites with clear liquefaction identifiers in the ground motions. However, at sites that likely liquefied at depth (as indicated by evaluation procedures and/or inferred from the characteristics of the recorded surface accelerograms), the presence of a non-liquefiable crust layer at many of the SMS locations prevented the manifestation of any surface effects. Because of this, there was not a good correlation between surface manifestation and two surface manifestation indices, the Liquefaction Potential Index (LPI) and the Liquefaction Severity Number (LSN).

Research papers, University of Canterbury Library

This paper provides a summary of the ground motions observed in the recent Canterbury, New Zealand earthquake sequence. The sequence occurred in a region of relatively moderate seismicity, 130km to the east of the Alpine Fault, the major plate-boundary in the region. From an engineering perspective, the sequence has been primarily comprised of the initial 04/09/2010 Darfield earthquake (Mw7.1) followed by the 22/02/2011 Christchurch earthquake (Mw6.3), and two aftershocks on 13/06/ 2011 (Mw5.3 and 6.0, respectively). The dense spacing of strong motions in the region, and their close proximity to the respective causative faults, has resulted in strong ground motions far exceeding the previous catalogue of strong motion observed in New Zealand. The observed ground motions have exhibited clear evidence of: (i) near-source directivity; (ii) sedimentary basin focusing, amplification and basin effect refraction; (iii) non-linear site response; (iv) cyclic mobility postliquefaction; and (v) extreme vertical ground motions exceeding 2g, among others.

Research papers, University of Canterbury Library

Science education research shows that a traditional, stand-and-deliver lecture format is less effective than teaching strategies that are learner-centred and that promote active engagement. The Carl Wieman Science Education Initiative (CWSEI) has used this research to develop resources to improve learning in university science courses. We report on a successful adaptation and implementation of CWSEI in the New Zealand university context. This two-year project at Massey University and the University of Canterbury began by using perception and concept surveys before and after undergraduate science courses to measure students’ attitudes towards science as well as their knowledge. Using these data, and classroom observations of student engagement and corroborating focus groups, the research team worked with lecturers to create interventions to enhance student engagement and learning in those courses. Results show several positive changes related to these interventions and they suggest several recommendations for lecturers and course coordinators. The recommendations include:1. Make learning outcomes clear, both for the lecturer and the students; this helps to cull extraneous material and scaffold student learning. 2. Use interactive activities to improve engagement, develop deeper levels of thinking, and improve learning. 3. Intentionally foster “expert-like thinking” amongst students in the first few semesters of the degree programme. 4. Be flexible because one size does not fit all and contextual events are beyond anyone’s control.In addition to these recommendations, data collected at the Canterbury site during the 2010 and 2011 earthquakes reinforced the understanding that the most carefully designed teaching innovations are subject to contextual conditions beyond the control of academics.