Microbial quality of surface water and subsurface soil after wildfire

Renan Valenca; Kavita Ramnath; Timothy M Dittrich; Robert E Taylor; Sanjay K Mohanty

doi:10.1016/j.watres.2020.115672

Microbial quality of surface water and subsurface soil after wildfire

Water Res. 2020 May 15:175:115672. doi: 10.1016/j.watres.2020.115672. Epub 2020 Mar 2.

Authors

Renan Valenca¹, Kavita Ramnath¹, Timothy M Dittrich², Robert E Taylor³, Sanjay K Mohanty⁴

Affiliations

¹ Department of Civil and Environmental Engineering, University of California, Los Angeles, USA.
² Department of Civil and Environmental Engineering, Wayne State University, USA.
³ Department of Chemistry and Biochemistry, University of California, Los Angeles, USA.
⁴ Department of Civil and Environmental Engineering, University of California, Los Angeles, USA. Electronic address: mohanty@ucla.edu.

PMID: 32155487
DOI: 10.1016/j.watres.2020.115672

Abstract

Runoff from wildfire affected areas typically carries high concentrations of fine burned residues or eroded sediment and deposits them in surface water bodies or on subsurface soils. Although the role of wildfire residues in increasing the concentration of chemical contaminants in both environments is known, whether and to what degree wildfire residues may affect microbial contaminants is poorly understood. To examine the effect of wildfire residues on growth and die-off of Escherichia coli (E. coli) -a pathogen indicator, we mixed stormwater with E. coli and suspended particles from the pre- and post-wildfire area in batch reactors and monitored E. coli concentration. E. coli grew initially in the presence of all particles, but the relative E. coli concentration was 10 times lower in the presence of wildfire residues than in natural soil from unaffected areas. Wildfire residues also decreased the persistence of E. coli during a 15-day incubation period. These results indicate that the growth or persistence of E. coli in surface water in the presence of wildfire residues was less than that in the presence of unburned soil particles, potentially due to depletion of nutrient concentration and/or loss of viability of bacteria in the presence of wildfire residues. To examine the transport potential of wildfire residues and their ability to facilitate the transport of E. coli in the subsurface system, suspensions containing wildfire residues and/or E. coli were injected through unsaturated sand columns-a model subsurface system. Transport of wildfire residues in sand columns increased with decreases in the depth and increases in the concentration of particles, but increased transport of wildfire residues did not result in the increased transport of E. coli, suggesting wildfire residues do not facilitate the transport of E. coli. Overall, the results indicate that wildfire residues may not increase the risk of the microbial contamination of surface water or groundwater via subsurface infiltration.

Keywords: Black carbon; Climate change; Pathogen; Stormwater; Suspended particles; Wildfire.

MeSH terms

Escherichia coli
Groundwater*
Soil
Water
Wildfires*

Substances

Soil
Water