The controls on the spatial variability of soil respiration are poorly understood. To address this, we have studied soil respiration across two topographic scales: watershed and plot. The objective of this study is to compare the variability of soil respiration within small, microtopographical sites (25m²) to the more complex terrain of an entire watershed. This experiment was conducted in a high elevation hardwood forest watershed in north central West Virginia. At eighteen locations throughout the watershed, soil respiration measurements were taken during the growing season. Also, three 5 meter diameter plots with homogeneous macrotopography were selected, and 6 sites within each plot were sampled on or about the same day as the watershed plots. At all sites, soil temperature, soil moisture, and soil respiration were measured. We hypothesize that variability in soil respiration in the small plots would be much less than respiration variability across the entire watershed, owing to the much greater topographic variability at the watershed scale.  

Results/Conclusions

Our results show that soil moisture and temperature had the greatest variability through the watershed plots. The two upland microtopographic plots had the least amount of variability of all measurements taken, significantly less than total variability throughout the watershed. However, the third microtopographic site had equal variability in soil respiration to the watershed as a whole. This is due to the considerable microtopographic relief as a result of low wetland hummocks. The tops of the hummocks were dryer than the bottom and the high water table in the wetland had the ability to suppress CO₂ respiration at low spots. Our results indicate that small-scale variability in soil respiration from upland plots is negligible in comparison to larger scale variability induced by watershed topography. The exception to this appears to be in very wet soils, where microtopography can play an important role in determining soil respiration.