Department of Geography
University of Colorado Boulder
Apr 22, 2022, 3:30 PM
Sidney Bush Abstract:
"Investigating spatiotemporal shifts in hydrologic connectivity within a montane headwater catchment in central Colorado"
Within United States (US) western montane regions, headwater, intermittent, and ephemeral streams play an important role in the delivery of water, sediment, and nutrients downstream, and are vital to maintaining ecosystem health. Despite their importance, catchments in these regions are typically understudied compared to higher elevation alpine catchments with persistent snowpack, as they contribute less downstream discharge per unit drainage area than high alpine regions and are therefore viewed as less vital for water resource management. However, in the western US, alpine regions with high snow persistence only constitute 14% of the land surface compared to lower elevation areas with lower snow persistence that cover almost 30% of the land surface. Thus, although these lower elevation catchments yield less stream discharge per unit drainage area than those in alpine regions, their cumulative contributions to discharge in downstream rivers can be significant. In addition, because future climate projections suggest that areas with high snow persistence will decline substantially in the coming decades, it is increasingly important to understand the hydrologic processes controlling stream flow in lower elevation montane regions where precipitation inputs can be dominated by summer rain-events rather than snowpack. To address this, we collected geochemical and hydrometric data over three years to quantify hydrologic connectivity of uplands to a montane headwater stream at the Manitou Experimental Forest in central Colorado. We use a combined approach of end-member mixing analysis, paired with high resolution measurements of soil moisture, precipitation, and groundwater levels to characterize source areas to the stream in 3-dimensions: longitudinal, lateral, and vertical. Samples were collected and measurements were recorded along the stream profile (longitudinal), from groundwater wells and soil lysimeters installed with increasing distance from the stream (lateral), and from shallow versus deep groundwater wells and soil moisture measured at different depths (vertical). Our analysis suggests spatiotemporal differences in shallow and deep vertical source areas, and between riparian and upland sources to the stream. These results provide a promising step towards quantifying the expansion and contraction of runoff source areas for a montane headwater stream, which will become increasingly important to water resource management in light of climate driven shifts in precipitation.