Review of Wildfire Effects on Chemical Water Quality

Abstract

The Cerro Grande Fire of May 2000 burned almost 43,000 acres of forested land within the Pajarito Plateau watershed in northern New Mexico. Runoff events after the fire were monitored and sampled by Los Alamos National Laboratory. Changes in the composition of runoff water were noted when compared to runoff water composition of the previous 20 years. In order to understand the chemical water quality changes noted in runoff water after the Cerro Grande Fire, a summary of the reported effects of fire on runoff water chemistry and on soils that contribute to runoff water chemistry was compiled. The focus of this report is chemical water quality, so it does not address changes in sediment transport or water quantity associated with fires. Within the general inorganic parameters, increases of dissolved calcium, magnesium, nitrogen, phosphorous, and potassium and pH in runoff water have been observed as a result of fire. However, the dissolved sodium, carbon, and sulfate have been observed to increase and decrease as a result of fire. Metals have been much less studied, but manganese, copper, zinc, and cesium-137 have been observed to increase as a result of fire.

Wildfire Induces Changes in Receiving Waters: A Review With Considerations for Water Quality Management

“…For cations generally, this pattern of a general increase occurred across biomes (Bayley et al., 1992; Beche et al., 2005; Betts & Jones, 2009; Bitner et al., 2001; Burke et al., 2013; Murphy et al., 2018), but not in all cases. Boreal streams in Alaska, for instance, exhibited a calcium decline downstream of a fire, even though potassium increased (Betts & Jones, 2009).…”

“…Cations contribute to water hardness, which can influence the toxicity of certain metals to aquatic life (e.g., cadmium, chromium III, copper, lead, nickel, and zinc), and to total dissolved solids, for which there is a secondary drinking water standard. Cations like calcium, potassium, and magnesium generally follow nutrient trends, increasing after post‐fire precipitation events as a function of burned area and burn severity (Bitner et al., 2001; Rust et al., 2018; Smith et al., 2011) as they are primarily generated from ash (Ranalli, 2004). Such responses are consistent with the ash‐alkaline hypothesis reviewed in Bayley and Schindler (1991), whereby alkaline fire ash, high in base cations like potassium and calcium, generally leads to an increase in calcium carbonate alkalinity and other associated base cation complexes.…”

“…Wildfires have been shown to condense and mobilize radionuclides in soils. In burned plots in Colorado and New Mexico, soils had concentrations of 137 Cesium 400%–2,200% of those in unburned plots (Bitner et al., 2001). Although the article did not specify, the presumed mechanism for radionuclide release is combustion of contaminated organic matter or vegetation.…”

Stream chemical response is mediated by hydrologic connectivity and fire severity in a Pacific Northwest forest

“…In the absence of fire, biogenically derived constituents have been shown to increase during the first rain events after a summer dry period or drought (Hood et al, 2006; Mosley, 2015), and this may play a role in the heightened concentrations of biogenic solutes during the September and October rain events (Figure 5). Prior studies show that cations generally follow nutrient trends, increasing post‐fire as a function of burned area and burn severity (Bitner et al, 2001; Rust et al, 2018; Smith et al, 2011) and a t HJA we measured post‐fire increases in Ca 2+ , Mg 2+ and K + . Variability in cation concentrations that we observed between watersheds could be attributed to differential subsurface flow paths associated with soil hydrophobicity and decreased infiltration or related to more moderate burn severity in WS9 relative to WS1.…”