Modeling the effects of wildfire on sediment and nutrient loads in the southeastern U.S.
SUMMARY: Fire plays a significant role in runoff, sediment yield, and nutrient transport in aquatic and terrestrial ecosystems in mountain watersheds. In the southern U.S., about one million hectares of forestlands are subjected to prescribed burning annually to reduce fuel loads, enhance stand health, and release preferred forest species from competition. The negative impacts of this practice on forest communities include reduction of total ecosystem nitrogen as a result of volatilization, leaching, and increased sediment loading. The magnitude of effects of this practice varies greatly and depends on fuels, soil properties, topography, climate, weather, and fire frequency and intensity. The objective of this study is to evaluate the effect of prescribed burning practices across the mountain (Nantahala National Forest–Wayah Ranger District), piedmont (Uwharrie National Forest–Uwharrie Ranger District), and coastal plain (Alligator Wildlife Refuges and Croatan National Forest–Croatan Ranger District ) physiographic regions in the southeastern U.S. Researchers will also test several field, watershed-scale, distributed hydrology models for their performance in predicting hydrology both at the watershed outlet and in-stream locations.
EFETAC's ROLE: EFETAC scientists and partners are conducting research with funding support through the Joint Fire Science Program.
PROGRESS: Researchers tested a field-scale soil chemistry model, NuCM (nutrient cycling model), and watershed-scale hydrology model, MIKE SHE. Combination of low intensity and severity fires and the rapid flush of spring growth resulted in no measurable changes in soil, soil solution, or stream nitrogen (N) for both of the upland sites. The NuCM model simulations suggest that those systems would have limited responses even under severe fires. Overland flow rarely occurred in any of the three topographic conditions, thus soil erosion and sediment movement were limited. Prescribed fires have limited effects on forest leaf area and soil infiltration capacity, thus simulations suggest little hydrologic response, especially in the coastal plain watersheds. Based on the study and literature review, researchers conclude that existing prescribed burning practices are not likely to greatly elevate inorganic stream and soil solution nitrogen levels (NO3-N and NH4-N) and sediments in the study region. However, scientists caution that catastrophic fires may cause water quality concerns when combined with extreme hydrologic conditions (e.g., flooding) that cause severe soil erosion even in forested watersheds. Data are being compiled, and results have been presented at national and international conferences.
Crumbley, T., G. Sun, S. McNulty, and J. Vose. 2007. Modeling Soil Erosion and Sediment Transport from Fires in Forested Watersheds of the South Carolina Piedmont. In: Proceedings of Emerging Issues along Urban-Rural Interface: Linking Land Use Science and Society. D.N. Laband (ed). April 9-12, 2007, Atlanta. GA. Pp 196-199.
Vose, J.M., S.H. Laseter, G. Sun, S.G. McNulty. 2005. Stream nitrogen responses to fire in the Southeastern U.S. In:Proceedings of the 3rd International Nitrogen Conference. Nanjing, China. Contributed Papers:577-584.
CONTACT: Ge Sun, EFETAC Research Hydrologist, firstname.lastname@example.org or 919-549-4070
Updated May 2010