Abstract
Wildfires can change ecosystems by altering solutes in streams. We examined major cations in streams draining a chaparral-dominated watershed in the Santa Ynez Mountains (California, USA) following a wildfire that burned 75 km2 from July 8 to October 5, 2017. We identified changes in solute concentrations, and postulated a relation between these changes and ash leached by rainwater following the wildfire. Collectively, K+ leached from ash samples exceeded that of all other major cations combined. After the wildfire, the concentrations of all major cations increased in stream water sampled near the fire perimeter following the first storm of the season: K+ increased 12-fold, Na+ and Ca2+ increased 1.4-fold, and Mg2+ increased 1.6-fold. Our results suggested that the 12-fold increase in K+ in stream water resulted from K+ leached from ash in the fire scar. Both C and N were measured in the ash samples. The low N content of the ash indicated either high volatilization of N relative to C occurred, or burned material contained less N.
Highlights
Depending on the ecosystem and climate [1,2], wildfires occur with varying frequency and severity, and have the potential to perturb the cycling of major cations (Mg2+, Ca2+, K+, and Na+ ) [1,3] and other elements that are essential for metabolic processes in plants [4,5,6,7,8,9,10], animals [11], fungi [12], and microbes [13]
Our findings suggested that wildfires increase the concentrations of all major cations in streams
We further propose a chief pathway for K+ outflux from the fire scar associated with leaching of ash and export via stream discharge
Summary
Depending on the ecosystem and climate [1,2], wildfires occur with varying frequency and severity, and have the potential to perturb the cycling of major cations (Mg2+ , Ca2+ , K+ , and Na+ ) [1,3] and other elements that are essential for metabolic processes in plants [4,5,6,7,8,9,10], animals [11], fungi [12], and microbes [13]. Major cations and other nutrients can be volatilized during combustion, or removed from fire scars via erosion or leaching after burning [17]. Destruction of vegetation during burning enables the removal of nutrients from topsoil that were formerly held in place by plant coverage and shallow roots [18,19] and reduces biological uptake. Water-soluble components can leach into the soil and be transported through runoff, and particulate residues can be transported via runoff and erosion [22,23] following precipitation
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