Potential climate change effects on water tables and pyrite oxidation in headwater catchments in Colorado

A water, energy, and biogeochemical model (WEBMOD) was constructed to simulate hydrology and pyrite oxidation for the period October 1992 through September 1997. The hydrologic model simulates processes in Loch Vale, a 6.6-km² granitic watershed that drains the east side of the Continental Divide. Parameters describing pyrite oxidation were derived sulfate concentrations measured in pore water and stream water in Handcart Gulch, a naturally acidic watershed in the Colorado Mineral Belt. Average monthly differences in precipitation and temperature between current and future climates, as predicted by using six global circulation models and three carbondioxide emission scenarios, were input into WEBMOD to identify possible shifts in the quantity and quality of the water flowing from the watershed for the period 2005 through 2100. Initial results suggest that increased air temperatures will result in earlier snowmelt compared to current conditions. Average sulfate concentrations and acidity in streams draining hydrothermally altered terrain may decrease as water tables rise in response to greater overall precipitation and earlier snowmelt, although a net increase of sulfate load was simulated as a result of greater overall discharge. Evapotranspiration is expected to increase but not enough to offset the increase in precipitation.