Subalpine soil microbial response to compaction of snow pack by snowmobiles Elizabeth Golden EBIO 4100, Winter Ecology, Spring 2013 Mountain Research Station, University of Colorado, Boulder
Introduction • Snow pack • Provides insulation (Halfpenny and Ozanne 1989). • Lower thermal conductivity • Allows plants, animals, and microbes to remain active throughout winter (Marchand 1996). • Depends on depth and density • Compacted snow has less insulative value
Introduction • Soil Microbes in Winter • Active (Schmidt and Lipson, STURM et al. 2005). • Steady soil temperature • Moist conditions • More microbial activity = more plant available N?
Introduction • Snowmobiles • Transportation • Recreation
Introduction • Snowmobiles • Snow compaction • Compress snow pack • Less insulative effect • Press snow pack to soil surface • Removes insulating layer of air • Result in slower snowmelt and increases time it takes the soil to thaw
Hypothesis snow compaction = microbial activity Snowmobile tracks = lower soil CO2 flux
Methods • Snowmobile track • Need avoid hiking trails, confounding factors • Trail to watershed, low usage • Snow pits (3 random sites, 2 pits/site) • Under track • Adjacent to track • Take CO2 measurements • 3 replications • Collect soil samples • Collect from where measured CO2
What went wrong • First snow pits over creek bed -> large, frozen rocks • Couldn’t use CO2 analyzer • Couldn’t get to soil to collect samples • Issues • Ran out of time, weather concerns • Frozen water tube • Data collected • CO2 measurements and soil samples (3 replications) from 1 pit
Results Mean CO2 flux = 0.081 ppm Mean CO2 flux = 0.037 ppm
Discussion • CO2 flux measurements for snow adjacent to snowmobile tracks inaccurate due to user error with CO2 equipment • Snowmobile track used for experiment was much less compacted than expected due to low snowmobile traffic • Snowmobile track snow depth = 50 cm • Adjacent snow depth = 62 cm • Marschand : >40cm snow depth, soil temp unaffected by fluctuations in air temp (Marchand1996) • NO3- same between samples, indicates no difference in microbial activity
Conclusions • Reject hypothesis • Experiment supports snow pack as insulation theory • Under 50 cm of snow and under 62 cm of snow, soil temperatures and microbial activity similar • Snow acts as insulative layer against air fluctuations because snow has low thermal conductivity • In the future? Same hypothesis, better experiment design
Literature Cited • Fahey, Barry D., and Kate Wardle. 1998. Likely Impacts of Snow Grooming and Related Activities in the West Otago Ski Fields. Department of Conservation. http://220.127.116.11/upload/documents/science-and-technical/sfc085.pdf. • Halfpenny, James C., and Roy Douglas Ozanne. 1989. Winter: An Ecological Handbook. 1st ed. Johnson Books. • Marchand, Peter J. 1996. Life in the Cold: An Introduction to Winter Ecology. 3rd ed. UPNE. • Monson, R. K., D. L. Lipson, S. P. Burns, A. A. Turnipseed, A. C. Delany, M. W. Williams, and S. K. Schmidt. 2006. “Winter Forest Soil Respiration Controlled by Climate and Microbial Community Composition.” Nature 439 (7077): 711–714. • Schimel, J. P., C. Bilbrough, and J. M. Welker. 2004. “Increased Snow Depth Affects Microbial Activity and Nitrogen Mineralization in Two Arctic Tundra Communities.” Soil Biology and Biochemistry 36 (2): 217–227. http://dx.doi.org/10.1016/j.soilbio.2003.09.008 • STURM, MATTHEW, JOSH SCHIMEL, GARY MICHAELSON, JEFFREY M. WELKER, STEVEN F. OBERBAUER, GLEN E. LISTON, JACE FAHNESTOCK, and VLADIMIR E. ROMANOVSKY. 2005. “Winter Biological Processes Could Help Convert Arctic Tundra to Shrubland.” BioScience 55 (1) (January 1): 17–26. doi:10.1641/0006-3568(2005)055[0017:WBPCHC]2.0.CO;2.