Hydrologic Impacts of Burn Severity on Nutrient Concentrations
in Surface Water, Jemez Mountains, NM
Anita Lavadie, Sara Brown, Joseph Zebrowski, Edward Martinez, New Mexico Highlands University, Las Vegas, NM
Abstract—Climate change is currently intensifying wildfire behavior and thus fire severity in the Southwest.
After a fire, surface water runoff may contribute high concentrations of nutrients to water bodies, which may
potentially impair surface water quality in the receiving aquatic systems. Although there is a considerable
amount of research on the effects of nutrients in streams following fire, conditions on nutrient levels transported from various fire severity classes on a small scale is not well researched. The purpose of this study
was to investigate the contributions of total suspended solids (TSS), nitrate-nitrogen (NO3-N) and orthophosphate (PO4) concentrations in surface water runoff originating from high, moderate, low, mixed, and control
(unburned site) fire severity types from the Las Conchas fire in the Jemez Mountains, New Mexico. Prior to
surface water runoff sampling, fire severity classification was determined for four (Control-unburned, Low,
Moderate, and High) sub-drainages within the Cerro del Medio area in the Valles Caldera Preserve using
fuel load measurements and remote sensing imagery. Once fire severity classification was confirmed, ISCO
automated water samplers and buried single stage water-samplers were used to collect surface water runoff
from ten precipitation events at each severity collection location during the 2012 monsoon season. Total
suspended solids were measured from surface runoff collected at a mixed severity (inclusive of all severities) site as well. TSS, NO3-N, and PO4 concentrations were determined following standard Environmental
Protection Agency (EPA) methodology. TSS was determined using a gravimetric method and nitrogen and
phosphate concentrations were determined using colorimetric methods using an OI Analytical Auto Analyzer.
Preliminary results show that TSS were highest from the mixed severity site and increased with fire severity from Low to Moderate, to High severity burn. Additionally, NO3-N concentrations in surface runoff also
increased with fire severity. TSS concentrations ranged from 3 mg/L to 28 mg/L; NO3 concentrations ranged
from 3.1 mg/L at the Control site to 7.8 mg/L at the High severity site. PO4 concentrations decreased with
fire severity, ranging from 0.35 mg/L at the Control site to 0.1 mg/L at the High severity site. Data from all
burned severity classes were collapsed and a t-test analysis determined that the average NO3-N, and PO4
nutrient concentrations between burned and unburned (Control) sites were significantly different (p<.001).
Results from the Las Conchas fire illustrate the potential for nutrient loading in runoff that may result from
high severity wildfires. Our findings suggest that large wildfires or “mega-fires” experience amplified nutrient modifications and can pose negative water quality effects on receiving aquatic systems. Additionally,
removal of nutrients from the landscape by surface runoff can result in nutrient-poor soils and may prolong
regeneration of vegetation, especially in areas burned at high severity. Quantifying the removal of nutrients from the landscape via TSS and surface runoff and their contribution to aquatic systems will provide
scientists, land managers, and policy makers with the empirical information to make well-informed land
management decisions in regard to the impacts and recovery from large wildfires.
Keywords: Las Conchas fire, Total suspended solids, Nutrients, Surface runoff, Fire severity
In: Keane, Robert E.; Jolly, Matt; Parsons, Russell; Riley, Karin. 2015. Proceedings
of the large wildland fires conference; May 19-23, 2014; Missoula, MT. Proc.
RMRS-P-73. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station. 345 p.
340
The content of this paper reflects the views of the authors, who are responsible for the
facts and accuracy of the information presented herein.
USDA Forest Service Proceedings RMRS-P-73. 2015.