Contribution of the lateral extension of the hyporheic zone in gravel bars in shaping river invertebrate diversity

Gravel bars (GBs) and hyporheic zone (HZ) are two major natural geomorphic features in gravel-bed rivers, having multiple functions ranging from habitat provisioning to nutrient cycling. This study examines whether the lateral extension of HZ in GBs contributes to the total diversity of river aquatic invertebrates. The hyporheic invertebrate community composition was entirely dissimilar from the benthic habitat, with stable GB hyporheic location exhibiting a more distinct community composition compared to wetted channel and active GB across all seasons. The local contribution to beta diversity (LCBD) also showed that stable GB has significantly higher uniqueness across all seasons, indicating a more unique invertebrate community. Species contribution to beta diversity (SCBD) indicates that this uniqueness was mainly driven by hyporheic dwelling species amphipod, Pseudocrangonyx yezonis, and Isopod species. Distance from wetted channel and dissolved oxygen were the factors influencing hyporheic invertebrates distribution. These findings show that the maintenance and restoration of gravel bars are crucial to enhancing and maintaining the overall invertebrate diversity in the river ecosystem.