Multi-scale analyses of watershed ecosystems across a coastal temperate rainforest region

Coastal watersheds create vital freshwater habitats while also linking land and sea in important ways. However, the spatial heterogeneity and functional diversity of watersheds is poorly understood at regional scales, hindering our ability to steward these ecosystems. In this thesis, I used a combination of watershed characterization and riverine field observations to examine spatial controls on watershed-ecosystem pattern and process in the Northeast Pacific Coastal Temperate Rainforest. Beginning at the regional scale, I developed a watershed classification that predicts streamflow regimes and dissolved organic carbon (DOC) dynamics at the coastal margin. This revealed a high diversity of watershed types, ranging from glacierized mountains with peak flow in summer and dilute DOC, to rain-dominated lowlands with high flows in fall/winter and very high DOC concentrations, to rainshadow watersheds with lower summer-flows and intermediate DOC. At a meso scale, I assessed how a spatial gradient from inlets to islands generated contrasting watershed ecosystems, from a broader water quality perspective (e.g., considering nutrients, temperature, etc.). At a local scale, I evaluated the relative importance of different landcover types, as well as topography and climate, in controlling the spatial variation in DOC concentrations among watersheds of an area known as a global hotspot of DOC yields to the ocean. This work showed that maximum watershed elevation was a powerful predictor of DOC concentrations because it acted as a surrogate for watershed topography, climate, and landcover. Together, these studies provided a new framework for understanding what controls the spatial mosaic of coastal watershed ecosystems at regional to local scales. I explored how this framework could be used to understand the consequences of spatially variable and temporally dynamic watershed ecosystems from an ecosystem management perspective. For example, a spatially explicit watershed-ecosystem model of this nature could be used to design terrestrial and marine protected areas, to assess local watershed health against appropriate reference conditions, and to design the spatially representative observation networks needed for both science and stewardship. Multi-scale analyses of coastal watershed ecosystems offer new tools to study and steward the linkages between land and sea in an era of rapid environmental change.