Insight into watershed hydrodynamics using silica, sulfate, and tritium: Source aquifers and water age in a mountain river

Nested Recharge Systems in Mountain Block Hydrology: High-Elevation Snowpack Generates Low-Elevation Overwinter Baseflow in a Rocky Mountain River

“…Manning et al [11] demonstrated that low vertical permeability produces distinct stratification in mountain groundwaters, with the majority of younger circulation occurring in the upper 20 m. Paznekas and Hayashi [15] showed that the winter baseflow rate in several Rocky Mountain watersheds is not dependent on the volume of precipitation from the previous year, suggesting a "fill and spill" model for the aquifers, and Campbell et al [12] demonstrated that in an eastern slopes Rocky Mountain river, up to 20% of winter baseflow is derived from the previous winter s snowmelt, implying relatively rapid cycling through the hydrogeologic system. Similarly, Campbell et al [16] found an average groundwater residence time of~4 years for streamflow. Somers and McKenzie [2] highlight the 'buffering capacity that groundwater storage provides for streamflow in dry seasons and drought and suggest that it may provide some resilience to climate change.…”

“…Numbers indicate sampling locations (named in Table 1). [16] used this characteristic, along with dissolved silica and sulfate concentrations, to confirm distinct water types in a three end-member mixing model for the Elbow River. The same approach, based on silica and sulphate concentrations, and dissolved sulphate isotopes are used in the present study to analyze aquifer contributions to streamflow.…”

“…The longitudinal streamflow samples were collated with the analytical results for tributary and summer samples collected in July 2017 and previously reported in Campbell et al [16]. In this previous sampling program, every 10th set of samples was taken in triplicate to ensure analytical consistency, and the same quality assurance and consistency is assumed to apply to the samples in the current study, since these data were collected mid-way through that sampling program.…”

“…Precipitate collected on 0.45 µm Millipore filters was air dried for at least 24 h, then weighed and analyzed in an a Thermo Finnigan Delta+ XL elemental analyzer (analytical error ± 0.2‰ for δ 34 S in SO 4 and ±1‰ for δ 18 O in SO 4 ). 34 S is reported relative to Troilite from Canyon Diablo meteorite (CDT) and 18 O/ 16 O ratios are reported relative to Vienna Standard Mean Ocean Water (VSMOW), both in standard delta notation.…”

“…Dissolved silica has been used with water oxygen isotopes to evaluate transit times [23][24][25] and can also provide insight about rock-water interaction and therefore host aquifers [26][27][28]. Campbell et al [16] used silica and sulfate, along with sulfur isotopes in sulfate, to define a three-end-member mixing model that differentiated spring and summer aquifer contributions to the Elbow River. This method can be further applied to assess source-aquifer contributions to overwinter baseflow, and these findings used to assess resilience of the Elbow River watershed to climatic change.…”