Progresses of weathered bedrock ecohydrology in the Earth’s critical zone

Abstract

<p indent="0mm">Weathered bedrock is crucial in the Earth’s critical zone, which connects soil moisture dynamics and shallow groundwater recharge, and therefore plays an essential role in the ecohydrological cycle on the terrene surface. The exchangeable water stored in weathered bedrock is an essential source of water that is different but parallel to soil water or groundwater. This water in the weathered bedrock, namely, rock moisture, is much greater than that in the soil, which is a pivotal and stable water source for plants, especially in dry years or arid and semiarid areas. When rainfall occurs, the infiltration and lateral flow of water are not limited to the soil layer. The rainwater that infiltrates by piston flow and preferential flow can pass through the fractured or weathered bedrock layer and collect at the fresh bedrock interface to form groundwater. Then, it flows laterally to adjacent river channels, where it also plays an important role in the distribution of evapotranspiration and runoff. Moreover, after weathered bedrock water storage accumulates to its maximum in the rainy season, the additional rainwater becomes base flow in the form of runoff or fissure flow. However, research on the ecohydrological cycle of the terrestrial surface layer has long focused on vegetation water absorption, surface soil moisture, and groundwater replenishment. Little attention has been given to the ecohydrological changes in the weathered bedrock layer and their external effects, and review articles are relatively scarce. Therefore, to clarify the latest research progress on weathered bedrock ecohydrology, the relevant documents collected in the Web of Science core collection database and the China National Knowledge Infrastructure (CNKI) journal database in the past 30 years were retrieved. The developments of the current focuses of research and potential research directions were quantitatively visualized using VOSviewer and bibliometrics, and the potential influential pathways of weathered bedrock ecohydrology were then drawn. The results show that weathered bedrock ecohydrological research is interdisciplinary and has a rich theoretical foundation of geology, water resources, environmental science ecology, and engineering. The number of published articles has gradually increased annually, and major mainstream Earth science journals wish to report these new findings; however, there is room for expansion and discussion in the international arena. The research area in this field mainly uses a shallow overlying soil layer, such as karst, as the platform and focuses on the karst hydrological model, the distribution of hydrological resources, the ecological risk, the lithologic characteristics of vegetation, and the interaction between bedrock and groundwater. Unfortunately, less attention has been given to areas with relatively thick soil layers, such as the hilly valley region. Moreover, ecohydrological effects of weathered bedrock include not only differences in the characteristics but also external disturbances, such as soil water redistribution, groundwater recharge, excretion regulation, and plant growth regulation. Future research might focus on the following: Water storage and its dynamic changes in the bedrock weathered layer, outflow characteristics, the process and mechanism of organism interactions, the process and mechanism of exchange with groundwater recharge, the process of water exchange with the soil-bedrock interface, the action of the vegetation root system and plant growth, and the framework and application of the ecological hydrological model of the atmosphere-vegetation-soil-weathered bedrock-groundwater continuum in the Earth’s critical zone. Furthermore, potential influential pathways of weathered bedrock ecohydrology might be regulating seasonal water shortage by inhibiting soil water infiltration, groundwater runoff, and replenishment; expanding bedrock fissure water storage by increasing animal activity; and transporting water and nutrients by participating in mycorrhizal hyphae. This study might provide a reference for deepening critical zone science, expanding ecohydrology research, and providing rational management for vegetation restoration.