Microclimate stability on the critical zone of a karst hillslope in southwest China: Insights from continuous temperature observations at the air–soil–epikarst interface

Abstract

Temperature is an important near-surface microclimate parameter that plays a key role in hydrological, ecological, and biogeochemical functions. However, the spatio-temporal distribution of temperature on the invisible and inaccessible soil–weathered bedrock continuum, wherein hydrothermal processes are most active, remains poorly understood. Temperature dynamics were monitored at 5 min intervals in the air–soil–epikarst (∼3 m) system at different topographical positions of the karst peak-cluster depression in southwest China. The weathering intensity was characterized based on the physicochemical properties of samples collected through drilling. No significant difference was observed in air temperature across slope positions, which was related to the limited distance and elevation resulting in roughly consistent energy input. The control effect of air temperature on the soil–epikarst was weakened with the decrease in elevation (±0.36 to ±0.25 °C). It is attributed to the enhanced temperature regulation capacity of vegetation cover from the up slope (shrub dominant) to down slope (tree dominant) in a relatively uniform energy environment. Temperature stability is clearly distinguished in two adjacent hillslopes that were differentiated by weathering intensity. For every 1 °C change in the ambient temperature, the amplitude of soil-epikasrt temperature variation on the strongly and weakly weathered hillslopes were ±0.28 and ± 0.32 °C, respectively. The response of soil-epikarst temperature to ambient temperature was more sensitive in the wet season (±0.40 °C) than in the dry season (±0.20 °C), which was related to the cooling effect caused by abundant rainfall. The cooling effect was particularly prominent in the preferential flow development area composed of pipeline cracks, which appear in the hillslope with relatively weak weathering intensity. These demonstrate that soil–epikarst temperature responds more gently to the variability of rainfall and ambient temperature on a relatively strong weathered hillslope. Accordingly, this study highlights that the sensitivity of soil–epikarst temperature to climate change is regulated by vegetation and weathering intensity on karst hillslopes in southwest China.