Effects of Prescribed Fire on Wetland Water Quality

Research Team: Juliann M. Battle (Research Technician III) and Dr. Stephen W. Golladay (Associate Scientist)

A grass-sedge marsh being burned and the same wetland flooded.

On the southeast Coastal Plain, isolated wetlands are a natural feature of the longleaf pine-wiregrass ecosystem. Fire is an essential part of the longleaf pine forest with prescribed burns occurring in intervals of 1-3 y. In 2000 and 2001, we sampled wetlands whose uplands had been ‘burned’ and reference wetlands (i.e., no fire) to determine the short-term changes (<1 mo) in surface water quality. In 2000, pH, alkalinity and dissolved inorganic carbon (DIC) were higher in ‘burned’wetlands than reference sites based on ranked ANOVA. In 2001, apparent color, dissolved organic carbon (DOC) and NH4-N were higher in ‘burned’ wetlands than reference ones. Differences between years suggest that field conditions are very important in determining fire's affect on water quality. To clarify our findings we conducted a laboratory experiment where we looked at changes in water quality when exposed to material (wiregrass, dead pine needles and soil) that had undergone simulated fire (muffle furnace at 340 C for 1 hr). Results indicated that water exposed to burned soil had elevated pH, alkalinity, DOC, NH4-N and soluble reactive phosphorus (SRP) compared to unburned soil. Burned wiregrass and pine needles had elevated DOC and DIC levels, and burned wiregrass also had significantly higher NH4-N and SRP concentrations. A fire burning through a cypress savanna wetland.Overall our results suggest that the linkage of fire and water quality of wetlands is through fire's effect on soils rather than vegetation. In 2000, water quality changes we measured were the consequence of a drought where fire burned the surface soil and caused alkalinity and DIC levels to increase within the wetland. In 2001, wetlands were more flooded and the amount and timing of rainfall following the burn were probably most important in influencing water quality; although, burned soil still appeared key in affecting water quality by increasing levels of DOC and NH4-N. Although, the outcome of prescribed fire on water quality of wetlands is strongly determined by prior hydrologic conditions, fire is nevertheless one way for these nutrient-limited wetlands to get subsidies from their surrounding catchments.

Additional Information:

Battle, J.M. and S.W. Golladay. In review. How does Prescribed Fire Affect Water Quality of Isolated Wetlands in Southwest Georgia? American Midland Naturalist

Funded by: The Joseph W. Jones Ecological Research Center