2 Materials and Methods

2.1 Site description

In 2002, the Hayman Fire burned more than 554 km2 of ponderosa pine (Pinus ponderosa ) and Douglas-Fir (Pseudotsuga menziesii ) forest in the Pike San Isabel National Forest (Graham, 2003) (Figure 1). This was one of the largest wildfires in Colorado’s recorded history and 35% of the fire burned at high severity (Robichaud et al., 2003). The fire burned the contributing area of Cheesman Reservoir, a primary drinking water supply to the city of Denver (Graham, 2003). In combination, the 2002 Hayman and 1996 Buffalo Creek fires cost Denver’s public water utility tens of millions of dollars on water quality treatment, sediment and debris removal, and reclamation (Hall, 2017). Watersheds within the Hayman Fire burn perimeter receive an annual average of 40 cm of precipitation (WRCC, 2021) and 60-75% of that comes from summer monsoonal rains (Wilson et al., 2018). Mean elevation within the fire perimeter is 2462 m which is within the intermittent snow zone that does not maintain snow cover throughout the winter (Richer et al., 2013). The parent material underlying our study area is dominated by Pike’s Peak Formation granite (Ruleman et al., 2011) which weathers to form coarse, sandy loam soils (Cipra et al., 2003). Ambient Na+ concentrations are relatively low in granitic basins in our study area. There were no reported post-fire increases in stream Na+ and measured post-fire increases in other geochemical ions (i.e., calcium, acid neutralizing capacity, and conductivity) recovered to pre-fire levels 2 years after the Hayman Fire (Rhoades et al., 2011).