Subalpine soil microbial response to compaction of snow pack by snowmobiles Elizabeth GoldenEBIO 4100, Winter Ecology, Spring 2013Mountain 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
0 5 10 15 20 25440
445
450
455
460
465
470
475
(Idealized Data)
CO2 Snow SnowCO2 Trail Snow
Results
0 20 40 60 80 100 120 140455
460
465
470
475
480
485
490
495
500
Trail Snow
0 20 40 60 80 100 120 140435
440
445
450
455
460
465
470
475
Snow Snow
Mean CO2 flux = 0.081 ppm
Mean CO2 flux = 0.037 ppm
Results
0 20 40 60 80 100 120 140455
460
465
470
475
480
485
490
495
500
f(x) = 0.0864910700090095 x + 484.452368474256R² = 0.986831307321853
f(x) = 0.117520801314325 x + 470.602599207401R² = 0.989629279422213f(x) = 0.0372568763580476 x + 478.94933292506R² = 0.829041934527669
Trail Snow CO2 flux from soil surface(Snow depth = 50 cm)
R1Linear (R1)R2Linear (R2)R3Linear (R3)
Time (s)
CO2
(ppm
)
Results
0 20 40 60 80 100 120 140435
440
445
450
455
460
465
470
475
f(x) = 0.0860935926652181 x + 456.180715773275R² = 0.97550868372138
f(x) = 0.0338385712014415 x + 447.827934511437R² = 0.866805420842868
f(x) = − 0.0103609094281626 x + 468.679413421583R² = 0.055522903976201
Snow Snow CO2 flux from soil surface(Snow depth = 62 cm)
R1Linear (R1)R2Linear (R2)R3Linear (R3)
Time (s)
CO2
(ppm
)
Results
TD-TS-R1 TD-TS-R2 TD-TS-R3 TD-SS-R1 TD-SS-R2 TD-SS-R30
2
4
6
8
10
12
14
16
Nitrate content (ppm NO3-) in soil samples
Site ID
NO
3_ p
pm
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 (Marchand 1996)
• 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://192.206.154.93/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.