The hyporheic refuge hypothesis reconsidered: a review of hydrological aspects

Abstract

The hyporheic zone (HZ) is thought to serve multiple functions for lotic invertebrates, but its role in the persistence of benthic assemblages after disturbances (‘hyporheic refuge hypothesis’, HRH) has never been clearly demonstrated since its initial proposal in 1953. Water exchanges through the HZ appear to be crucial in determining most hyporheic processes and subsequently, in controlling directly or indirectly the distribution of hyporheic assemblages. At present, it seems that the distribution of hyporheic refugia would also be controlled by hyporheic flowpaths, explaining the non-uniform response to the HRH documented in the literature. In light of recent developments in hyporheic hydrology, it is timely to propose research directions for understanding the distribution and patchiness of hyporheic refugia. This review proposes a framework of hypotheses, based on the recognition of hyporheic flowpaths across several scales and predicting the highest refugial capacity in large-scale upwelling zones. Outcomes from this framework include the development of physical indicators measuring the ability of the HZ to protect invertebrates, the identification of river areas demonstrating the highest refuge capacity (hyporheic hotspots) and the promotion in restoration projects of suitable hydrologic exchanges for enhancing the development of hyporheic hotspots.