LRES M.S. Thesis Defense: Florence Miller
- Tuesday, August 7, 2018 at 9:00am
- Animal Biosciences Building, 134 - view map
STRONTIUM AND URANIUM ISOTOPES REVEAL INTERACTIONS OF STREAM WATER AND GROUNDWATER ACROSS THE TRANSITION FROM MOUNTAIN HEADWATERS TO AN INTERMOUNTAIN BASIN (GALLATIN RIVER WATERSHED, MT)
A repeated landscape pattern in the inter-mountain west is convergent mountain headwater streams supplying water to divergent flow systems within intermountain basins. Patterns in the character and flux of water across these transitions in geomorphological process domains are subject to projected changes in both mountain headwater snowpack dynamics and water use in rapidly developing inter-mountain basins. Here, we evaluate controls on water/substrate and stream water/groundwater interactions within a mountain headwater (Hyalite Creek) and an intermountain basin (Gallatin Valley). We used geochemical tracers (87Sr/86Sr, and [234U/238U]), as well as solute loads as indicators of such interactions. Stream water in Hyalite Creek had 87Sr/86Sr values that varied dramatically based on interaction with different lithologic groups. The [234U/238U] values were consistent with groundwater inflows from aquifers in the Madison Group Limestones and Archean gneiss fracture flow. We used mixing models to estimate the fractional contribution of the Madison and Archean aquifers to local streamflow. Mountain headwater streams carry diverse geochemical signals of water/rock interaction at the mountain front transition. In the intermountain basin, groundwater and surface water geochemistry is influenced by mixing of water sources, infiltration through soils, and anthropogenic contamination, likely including septic outflows. Our results provide a novel approach to quantification of the groundwater contribution to streamflow in mountain headwaters, and conceptualize water quality and quantity controls at the mountain front to intermountain basin transition.
- Department of Land Resources and Environmental Sciences