Geospatial Analyses of Terrestrial-Aquatic Connections Across New Zealand and their Influence on River Water Quality
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This dissertation presents new techniques for quantifying and mapping terrestrial-aquatic connections, as well as new approaches for assessing the effects of intensive land uses on river water quality. Chapter 1 describes the general format of the dissertation as well as the research questions that were the impetus for this research. Chapter 2 is a case-study that investigated the nonlinear changes in land cover and sediment runoff in a sub-tropical catchment in New Zealand. Sediment budgets and their analyses showed that exotic forests were the dominant source of sediment runoff in periods of forest harvesting, while grasslands assumed the dominant role once exotic forests recovered. Connected land disturbance and water clarity time-series exhibited similar temporal break points, suggesting that the former can be a good indicator of stream water quality. Last, the connectivity layer that was developed could serve as a guide for placing and prioritizing Best Management Practices. In Chapter 3, a more accurate nationwide stream network for New Zealand was developed, that included intermittent and ephemeral streams, based on physiographic characteristics and varying thresholds. Results showed that the use of 8 different thresholds produced a higher and wider range of drainage density values. The new modeled network performed very well and identified the mapped validation headwaters 83-95% of the time. In Chapter 4, a new prioritization scheme for the protection of unmapped headwater channels in the most sediment-impaired catchment was proposed. Results showed more than 8,000 km of headwater streams need prioritization, with around 60% of them being High-priority. These streams corresponded to more than 34,000 channel heads with 55.6% of them being High-priority. Using a conservative 10-m buffer on these headwaters produced an area of 175.4 sq. km that would need to be buffered or excluded from livestock. Last, Chapter 5 discusses the future work and broader impacts of this dissertation.