Rivers are important ecosystems under continuous anthropogenic stresses. The hyporheic
zone is a ubiquitous, reactive interface between the main channel and its surrounding sediments
along the river network. We elaborate on the main physical, biological, and biogeochemical drivers
and processes within the hyporheic zone that have been studied by multiple scientific disciplines for
almost half a century. These previous efforts have shown that the hyporheic zone is a modulator for
most metabolic stream processes and serves as a refuge and habitat for a diverse range of aquatic
organisms. It also exerts a major control on river water quality by increasing the contact time with
reactive environments, which in turn results in retention and transformation of nutrients, trace
organic compounds, fine suspended particles, and microplastics, among others. The paper showcases
the critical importance of hyporheic zones, both from a scientific and an applied perspective, and
their role in ecosystem services to answer the question of the manuscript title. It identifies major
research gaps in our understanding of hyporheic processes. In conclusion, we highlight the potential
of hyporheic restoration to efficiently manage and reactivate ecosystem functions and services in
river corridors.
