Effects of large dams on the aquatic food web along a coastal stream with high sediment loads

• DOI: 10.3389/fevo.2023.1250892
• Publication Date: 2024-01-03T04:39:50Z
• Authors: Jean-Marc Roussel; Stéphane Fraisse; Olivier Dézerald; Ophélie Fovet; Alexandrine Pannard; Hector Rodriguez-...; Alain Crave; Caroline Gorzerino; Maxime Poupelin; Guillaume Forget; Dominique Huteau; Alban Thomas; Manuel Chevé; Laura Soissons; Christophe Piscart
• Keywords: Primary producers; Detritus

The contribution of two basal energy sources – detrital organic matter and primary producers as part aquatic food webs varies typically along river continua. A host barriers to flow increase the water residence time sediment nutrient retention in reservoirs worldwide, potentially alter balance between detritus-based algae-based pathways downstream webs. We explored this issue on Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high runoff. Seasonal measurements following parameters were compared upstream large dams (16 m 36 high): fluxes, chlorophyll concentrations, algal communities epilithic biofilm (taxonomic composition, biomass growth), benthic invertebrate (abundance trophic guild structure). As anticipated, annual fluxes much lower reservoirs, where significant decreases turbidity, phosphate silicate concentrations recorded. higher concentration pelagic algae taxa photosynthetic suggested drifting deposition reservoir-borne phytoplankton downriver. Photosynthetic growth was spring fall, so abundance herbivores community, notably scrapers eaters. Energy within riverine traced using stable isotope analyses carbon (C) nitrogen tissues consumers (invertebrates fish). Mixing models revealed discontinuity origin C entering continuum, confirming greater reservoirs. These results illustrate mechanisms whereby can modulate loads, make it possible anticipate effects dam removal future ecosystem.