Habitat characteristics of the hyporheic zone in a mountain streambed: a case study of the upper mountainous river in China

Abstract The physicochemical characteristics of the hyporheic zone in streambed have a critical impact on the river ecosystem health. This study investigated eleven physicochemical parameters of the hyporheic habitat of a mountainous river in southwestern China. The results showed that all sections exhibited negative vertical hydraulic gradients, indicating downwelling conditions where surface water recharges groundwater. A highly significant positive correlation was observed between interstitial water temperature (T i ) in the hyporheic zone and surface water temperature (T s ). The pH, dissolved oxygen (DO), and electrical conductivity (EC) of hyporheic water were consistently lower than those in the surface stream. A significant negative correlation was identified between dissolved oxygen in the hyporheic zone and surface water flow velocity. The five parameters, which include heterogeneity(H), percentage of fine sediment (PFS), median grain size (D 50 ), vertical hydraulic conductivity (K v ), and interstitial water temperature (T i ), collectively provide a representative characterization of hyporheic habitat attributes in the studied river reach. Among these, K v , D 50 , and T i are the key factors that characterize the differences of the hyporheic zone among various river segment in the studied river. Future research should focus on identifying key habitat parameters specific to different river types, as well as elucidating the effects of heterogeneous habitat characteristics on the formation and dynamics of biogeochemical hot spots and hot moments. Furthermore, watershed water environment management should account for the heterogeneous habitat characteristics of the hyporheic zone.