Poster Presentation Society for Freshwater Science 2026 Annual Meeting

Hyporheic resilience: Invertebrate communities minimally affected by variable channel stability along a gravel-bed river. (135840)

Connor Bruemmer 1 , Korinna Brandt 1 , Marc Owen 2 , Deb S Finn 1
  1. Missouri State University , Springfield, Missouri, United States
  2. Ozarks Environmental and Water Resources Institute , Springfield , Missouri, United States

The major ongoing effect of climate change in central North American rivers is increasing frequency and magnitude of floods, driving increased streambed sediment mobilization, lateral migration, and bank erosion. The hyporheic zone is a physical habitat within these shifting sediments, but little is known of how hyporheic invertebrates might respond to increasing habitat instability. Given previously observed patterns of alternating stable and unstable channels along the Gasconade River (Missouri, USA), we asked if invertebrate communities in hyporheic gravels varied between stable and unstable locations. We chose 3 sites along a ~55-km length of the Gasconade, each with paired stable and unstable reaches. During baseflow in July 2025, we collected 4 Bou-Rouch style samples within each ~100-m reach, all located at the downstream end of glides. All samples were collected from ~45 cm hyporheic depth at points of shallow surface-water depth (~0-0.3 m) and with minimal evidence of upwelling or downwelling. We also measured dissolved oxygen and temperature of hyporheic water prior to invertebrate sample collection. Invertebrate communities were diverse, with 29 unique taxa overall (25 from stable and 22 from unstable reaches), with a blend of benthic- and groundwater-associated taxa indicating the ecotonal nature of functional hyporheic zones. Samples also included an amphipod (Allocrangonyx hubrichti), previously known only from true groundwater. Unstable reaches tended to have greater invertebrate densities (individuals L⁻¹), but overall community structure varied just as much within individual reaches as among reaches, suggesting high heterogeneity at fine spatial scales and that broader-scale patterns of channel stability have not fundamentally affected hyporheic communities. Furthermore, local-scale variables such as dissolved oxygen and water temperature did not help explain differences in community structure among samples. These results imply resilience of hyporheic communities to the increasing movement of gravel beds associated with climate change. Future studies directly following bed-moving floods will increase understanding of how hyporheic communities respond to variably shifting channels. Hyporheic invertebrates are a major source of secondary production in gravel-bed rivers, so it is important to understand their response to ongoing changes in disturbance regime.