Climate projections suggest that snowfall-dominated areas will decline; substantially in the coming decades. Such climate impacts are already; being observed in Colorado where the dominant source of annual peak; discharge is shifting from snowmelt to rainfall, altering the paths by; which water flows through a landscape and is ultimately delivered to; streams. Observed climate driven shifts in stream flow dynamics and; permanence highlight the increasing importance of understanding the; hydrologic connectivity of uplands to streams in lower elevation,; montane ecoregions. 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 concentration-discharge relationships and; 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). Results indicate distinct; differences in stream chemistry along the longitudinal stream profile,; with highest concentrations at the most upstream sites and lowest; concentrations at the most downstream sites. Stream solute; concentrations increased with decreasing stream discharge values from; spring to late summer. However, the stream remained chemostatic during; all recorded rain storms, suggesting a difference in flow pathways; during individual summer storm pulses. End member mixing 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 to a montane headwater stream.
