Influence of degradation on soil water availability in an alpine swamp meadow on the eastern edge of the Tibetan Plateau

Abstract

Degraded ecosystems refer to systems that deviate from their natural state as a result of natural or anthropogenic disturbances. Alpine swamp meadows on the eastern edge of the Tibetan Plateau have dramatically degraded owing to climate change, overgrazing, and rodents. Understanding the influence of meadow degradation on soil water availability is essential for the development of hydrological models and alpine swamp meadows restoration, which has been poorly explored in the eastern Tibetan Plateau. In this study, we analyzed how degradation affects variation in soil water availability with a series of parameters derived from soil moisture content and soil water retention curves. Our results showed that (1) soil moisture content consistently decreased with degradation and increased with soil depth; (2) soil water retention curves decreased with increasing degradation due to coarser soils and organic matter loss. Field water capacity and the permanent wilting point decreased, whereas the air entry value increased with the severity of degradation; and (3) soil water availability, as represented by soil water potential, available soil water content and fraction was less responsive to degradation than individual soil moisture content or soil water retention curves, which showed similar decreasing trends. However, soil water potential, available soil water content and fraction under moderate and severe degradation were relatively lower than those under light degradation, especially in deep soil layers (>20 cm). Thus, swamp meadow degradation negatively influences soil water availability, which might impede water absorption by deeply rooted species, thereby inducing soil-water stress and possibly increasing drought vulnerability.