Trajectories of ecosystem functions after disturbances spanning terrestrial and aquatic domains in the Intermountain West

Kathleen A. Lohse, Department of Biological Sciences, Idaho State University, Pocatello, ID, Kayla Glossner and Ruth MacNeille, Biological Sciences, Idaho State University, Pocatello, ID, Mark Seyfried, Northwest Watershed Management Research, U.S.D.A. Agricultural Research Services, Boise, ID, Jennifer Pierce, Geosciences, Boise State University, Boise, ID, Jason Williams, USDA ARS, Tucson, AZ, Nicholas Patton, Geosciences, Idaho State University, Pocatello, ID, Gerald Flerchinger and Aaron Fellows, Northwest Watershed Research Center, USDA Agricultural Research Service, Boise, ID, Fred Pierson, USDA-ARS, Boise, ID

Background/Question/Methods
Intermittent streams are ubiquitous in the Western United States (US) and important for processing and delivery of carbon and nutrients to downstream perennial streams. Despite their importance, intermittent streams remain poorly characterized, especially their biogeochemical responses to pulse disturbances. In particular, wildfires are increasing in the Western US and resulting in episodic pulses of C and N to streams but also redistribution of C and N across uplands. Here we synthesize plot-to-watershed scale studies at the Reynolds Creek Critical Zone Observatory (RC CZO) that show how fire mediated disturbances are strongly influencing critical terrestrial and aquatic linkages. Ecosystem carbon fluxes before and after prescribed fire as well as carbon fluxes, soil, and wind and water erosion responses following wildfire are reported.
Results/Conclusions
We find that montane sagebrush ecosystems recover rapidly following a prescribed fire as carbon sinks (high gross primary production relative to ecosystem respiration) as indicated by eddy covariance measurements and modeling. Soil carbon incubations studies on burned soils 2 to 37 months following a wildfire also support lower respiration losses. Surprisingly, significant increases in soil inorganic carbon (SIC) were observed immediately after fire under shrubs (as high as 1.2%) compared to the interplant spaces (0.08%), and these patterns varied significantly with aspect and time. Patterns of hydrologic losses from a burned watershed indicate that of the C was lost as particulate organic carbon (POC), dissolved organic (DOC) and inorganic carbon (DIC) rather than being respired. POC export was the result of redistribution by wind and subsequent flushing of these materials. Our findings indicate that changes in fire regime and vegetation states in dryland ecosystems may lead to short term sequestration of C as SIC where it has not been previously observed. Large hydrologic losses as DIC and DOC indicate possible continued mineralization of materials and alternative hydrologic loss mechanisms after fire.