SOURCE RECHARGE TO CAVE POOLS IN THE ALPINE KARST OF TIMPANOGOS CAVE NATIONAL MONUMENT, UTAH

Weekly water samples collected from cave pools in the spring and summer of 2012 demonstrate the dynamic geochemical behaviors within the alpine karst of Timpanogos Cave National Monument in the Wasatch Mountains of Utah. The pools divide into thee types: 1) those with limited water flux and geochemical variation, 2) rapid water flux and geochemical stability, and 3) rapid water flux and significant changes in geochemistry. Broadly speaking, these three types define two sources of water in the epikarst, direct meteoric recharge and storage with piston flow, and third water source representing diffuse recharge through the matrix of the host limestone.

Dissolved solids associated with hydrothermal activity (e.g., SO₄^2- and F^-) characterize the chemistry of the first category of pools. Values of δ³⁴S and δ¹³C along with cation-anion ratios suggest that microbial dissimilatory sulfate reduction may play some role in modern dissolution of carbonate in the sources to these pools. In-situ geochemical reactions influence the concentration of some solutes (e.g., HCO₃^-, Ca²⁺, F^-) and may cause a shift in the isotopes of dissolved inorganic carbon. In contrast, the geochemistry of the other two pool categories is dominated by reactions along the flowpath in the epikarst. Occluded flowpaths homogenize the chemistry in a surficial aquifer in the colluvium, although the rate of flow may fluctuate greatly and be driven by piston flow. Water temperature is cooler by 0.5 C° in these pools, suggesting source waters at higher elevation near the canyon rim. In contrast, open and direct flowpaths contribute to geochemical trends that resemble nearby surface rivers. Changing water temperature in these pools perhaps indicates a shift in recharge from melt water near the canyon rim to that of the diffuse recharge in the matrix permeability of the carbonate.