College of Forestry
paired-catchment
Beyond the Paired-Catchment Approach: Isotope Tracing to Illuminate Stocks, Flows, Transit Time, and Scaling
Dec-19-2011
This dissertation integrates a process-based hydrological investigation with an ongoing paired-catchment study to better understand how forest harvest impacts catchment function at multiple scales. This is done by addressing fundamental questions related to the stocks, flows and transit times of water. Isotope tracers are used within a top-down catchment intercomparison framework to investigate the role of geology in controlling streamwater mean transit time and their scaling relationships with the surrounding landscape. We found that streams draining catchments with permeable bedrock geology at the Drift Creek watershed in the Oregon Coast Range had longer mean transit times than catchments with poorly permeable bedrock at the HJ Andrews Experimental Forest in the Oregon Cascades. We also found that differences in permeability contrasts within the subsurface controlled whether mean transit time scaled with indices of catchment topography (for the poorly permeable bedrock) or with catchment area (for the permeable bedrock). We then investigated the process-reasons for the observed differences in mean transit time ranges and scaling behavior using a detailed, bottom-up approach to characterize subsurface water stores and fluxes.
Local and Downstream Effects of Contemporary Forest Harvesting on Streamflow and Sediment Yield
Nov-19-2008
This dissertation is a collection of three manuscripts that serve to fill the knowledge gaps and advance methods of detecting the effects of contemporary forest harvesting in experimental catchment studies. The objective of this research was to develop change detection models using time-series records to detect and quantify the effects of forest harvesting on streamflow and sediment yield. To accomplish this, it was necessary to characterize streamflow and sediment processes at a temporal scale capable of describing daily, monthly, and seasonal dynamics following forest harvesting; increase sample sizes used to construct regression-based change detection models; and develop alternative methods to the paired-catchment approach in order to discern changes in streamflow and sediment using highly variable time-series data. The paired-catchment approach was used to detect and quantify relative changes in streamflow and sediment yield in 5 harvested catchments. The ability to detect statistically significant changes at certain time-steps was a function of accounting for all sources of variability in change detection models. In this study, we aimed to develop robust change detection models using time-series data to increase sample size and decrease false/missed detections of true treatment effects.
