Hydrologic connectivity between landscapes and streams : transferring reach and plot scale understanding to the catchment scale

Abstract

Transferring plot and reach scale hydrologic understanding to the catchment scale and elucidating the link between catchment structure and runoff and solute response remains a challenge. To address this challenge, I pursued the following questions as part of this dissertation: How do spatiotemporal distributions of hillslope-riparian-stream (HRS) hydrologic connectivity influence whole catchment hydrologic dynamics and what are the implications of this for stream biogeochemistry? What are the implications of catchment structure for riparian buffering and streamflow source water composition? What are the hierarchical controls on hydrologic connectivity and catchment runoff dynamics across 11 diverse headwater catchments and across flow states? I addressed these questions through detailed hydrometric monitoring and analysis (160 recording wells across 24 HRS transects and stream discharge across 11 catchments), tracer sampling and analysis (groundwater, soil water, and stream water sampling of major ions, specific conductance and dissolved organic carbon (DOC)), and newly developed digital landscape and terrain analyses. I installed this unprecedented network of instrumentation to address these questions across 11 adjacent and nested catchments within the Tenderfoot Creek Experimental Forest (TCEF), Rocky Mountains, MT. I determined that 1) hillslope topography, specifically upslope accumulated area (UAA), was the first order control on the duration of transient water table connectivity observed across HRS landscape positions; 2) the intersection of HRS connectivity with riparian area extents determined the degree of riparian groundwater turnover, riparian buffering of upslope water, and the magnitude of DOC transport to streams; 3) 11 catchments' stream network hydrologic connectivity duration curves were highly correlated to streamflow duration curves and the variable slopes of these relationships were explained by vegetation, geology, and within catchment distributions flowpath length and gradient ratios. This dissertation consists of five key chapters / manuscripts that address how landscape structure/organization within and across catchments can control the timing and magnitude of water and solutes observed at catchment outlets.