Joseph C. Blankinship , Emma P. McCorkle, Matthew W. Meadows, Ryan G. Lucas, and Stephen C. Hart

1. AGU 2012 Fall Meeting B21I. When Winter Changes: Hydrological, Ecological, and Biogeochemical Responses I Consequences of warming and altered snowmelt timing on soil CO2, CH4, and N2O fluxes in the Sierra Nevada rain-snow transition zone Joseph C. Blankinship, Emma P. McCorkle, Matthew W. Meadows, Ryan G. Lucas, and Stephen C. Hart Kearney Foundation of Soil Science 2006-2011 Mission

2. Western North America is facing major climatic and hydrological changes I. Precipitation Type II. Snowmelt Timing Stewart et al. 2005, Journal of Climate Due to 3ºC warming no change more rain What do these changes mean for soil microbial activities and greenhouse gas (GHG) emissions during the warm season? Bales et al. 2006, Water Resources Research

3. Connecting precipitation type & snowmelt timing to soil GHG fluxes Warming in Seasonally Snow-Covered Ecosystems FALL, WINTER, SPRING More Rain Earlier Snowmelt Realistic simulation is difficult Most studies confounded by summer precip and altered water input Timing of Soil Water Availability Soil and plant heterogeneity Timing/Extent of Resources Longer “Microbial Growing Season”? ↑ Microbial Stress? SUMMER ↑ Soil GHG Emission? ↓ Soil GHG Emission?

4. Research Questions Will winter and spring warming exacerbate summer microbial stress in the rain-snow transition zone, thus reducing GHG emissions? If water input stays the same, does snowmelt timing impact soil GHG fluxes for days, weeks, or months?

5. Sierra Nevada climatic gradient “Rain-snow transition zone” Cold & Snowy Warm & Rainy Image from The Mighty Sierra: Portrait of a Mountain World (1972) by Paul Webster and Francis Farquhar

6. Ideal, extreme seasonal and interannual variation in precipitation Little precip after snowmelt Grant Grove, CA; Western Regional Climate Center Water Year 2011: 2nd wettest on record (~170% normal runoff; ~3.5 m max. snow depth) Water Year 2012: 4th driest on record (~50% normal runoff; ~1.5 m max. snow depth)

7. To simulate warming, we moved forest soils across the rain-snow transition zone, twice High elevation site (2,365 m ASL) MAT = 6.8 °C; MAP = ~1000 mm; 75-90% snow Downward Transfer * No difference in mean soil temperature during summer Low elevation site (1,816 m ASL) MAT = 8.2 °C; MAP = ~1000 mm; 40-65% rain

8. Soil GHG fluxes: Carbon Dioxide (CO2) Methane (CH4) Nitrous Oxide (N2O) • Measured weekly or biweekly after snowmelt, and then monthly • Not measured when snow depth > 5 cm

9. Winter warming accelerated summer GHG fluxes CO2 emission CH4 uptake N2O emission

10. “Early Snowmelt”

12. n = 12

13. “Late Snowmelt” 3.1 m 3.1 m n = 12

16. Snowmelt was manipulated by 2 to 3 weeks

17. Earlier snowmelt reduced CO2 emission and increased CH4 uptake Wet Year Dry Year CO2 Complete Snowmelt CH4

18. Research Questions Will winter and spring warming exacerbate summer microbial stress in the rain-snow transition zone, thus reducing GHG emissions? No , warming increased net GHG emission and seemed to relieve stress If water input stays the same, does snowmelt timing impact soil GHG fluxes for days, weeks, or months? CH4: Weeks CO2 (and N2O): Months

19. The warming effect… Warming in Seasonally Snow-Covered Ecosystems More Rain (Less Extreme Winter) More Resources for Microbial Growth? ↑ Soil GHG Emission

20. …is likely constrained by earlier snowmelt. Warming in Seasonally Snow-Covered Ecosystems Earlier Snowmelt ↓ Soil Resources During Summer ↑ Microbial Stress? ↓ Soil GHG Emission

21. Questions?

22. EXTRA SLIDES FOLLOW:

23. Soil Temperature * indicates significant elevation difference (P < 0.05 in one-way ANOVA); # indicates significant effect of snowmelt timing

24. Soil water content outside of experimental cores n.s. n.s.

25. CO2 fluxes