Inter-annual variation in precipitation affects the spatial heterogeneity of soil CO2 efflux in a West Virginia watershed

Background/Question/Methods

Soil respiration and the hydrologic cycle are tightly coupled, with variation in precipitation affecting soil respiration through the alteration of both soil moisture and soil temperature regimes. Landscape position within heterogeneous terrain can also alter soil moisture and soil temperature regimes through the effects of elevation and the lateral redistribution of soil water. To examine the interactive effect of precipitation with elevation and vegetation cover on carbon and water cycling at the watershed scale, we compared data from the Weimer Run watershed near Davis, West Virginia between a dry year—2010 (precipitation = 1117 mm)—and a wet year—2011 (precipitation = 1828 mm). We have a plot based study where we established three elevation treatments (LOW = 975 m , MID = 1050 m , HIGH = 1130 m) and with three vegetation treatments ( OPEN = forest gap; CANOPY = closed-canopy; SHRUB = shrub layer beneath closed-canopy) at each elevation level with replicates—for a total of 27, 4 m² plots. At each plot, surface soil CO₂ efflux, soil temperature at 5 and 12 cm, PAR, air temperature, and volumetric soil water content from 0-12 cm were measured weekly during the growing season.

Results/Conclusions

For 2010 (dry year), there were statistically significant differences in soil CO₂ efflux across elevation (p = 0.0174; F = 4.94) and vegetation treatments (p = <0.0001; F = 24.35); while for 2011 (wet year), there were only significant differences among vegetation treatments (p = <0.0001; F = 18.21). Peak values of soil CO₂ efflux occurred on average 11 days earlier for 2011 than in 2010, with a differential response across the watershed, with peaks occurring 16 days earlier at high elevations and 3 days earlier at low elevations. A similar effect is seen with vegetation treatments, with peak rates in OPEN sites occurring earlier than in CANOPY and SHRUB sites. The total peak magnitude of growing season soil CO₂ efflux was decreased by 37% from 2010 to 2011—with more severe decreases at HIGH elevations and under SHRUB treatments.