Soil micro-climate variation in relation to slope aspect, position, and curvature in a forested catchment

Soil climate (soil moisture and temperature) affects many near-surface earth system processes and ecosystem functions. However, the challenge of acquiring reliable, high-resolution data has impeded the quantitative assessment of the spatial heterogeneity of soil climate at hillslope and catchment scales, namely, soil micro-climate. Here, we examined three years of continuous soil micro-climate data to identify patterns in relation to slope aspect, position, and curvature in a 7.9-ha forested catchment in Pennsylvania, U.S.A. Multi-depth (5 to 162 cm) soil micro-climate data were collected by a sensor network consisting of 33 sites that were distributed throughout the catchment. Results showed a high degree of variability in time and space that alternated between wet-cold seasons (DJFMAM) and dry-warm seasons (JJASON). Compared to dry-warm seasons, soil moisture was spatially more variable but temporally more stable in wet-cold seasons. Slope characteristics substantially mediated soil micro-climate distribution and variability, which were further influenced by the season and soil depth. With increasing soil depth, soil micro-climate became spatially more variable but more stable through time. The north (N)-facing aspect intensified the temporal variability of soil micro-climate more than the south (S)-facing aspect. Swales and the valley floor dampened soil temperature fluctuations relative to planar slopes and the ridges. The N-facing slopes were significantly colder than the S-facing slopes but only in winter. The differences in slope insolation, vegetation cover, soil properties, and hydrology were used to explain soil micro-climate patterns. This study demonstrates the potential of sensor networks to investigate soil micro-climate at scales that are challenging for either point-scale measurements or remote sensing. These findings provide an enhanced understanding of localized soil micro-climate pattern and variability in forested headwater catchments, which can aide modeling water and energy budgets of the Critical Zone in temperate, humid region.