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Stream Ecology Habitat characteristics determines species richness and community composition in aquatic ecosystems: • Physicochemical parameters of the water • Hydromorphological and structural feature of the physical habitat Geomorphological features of the stream: flow velocity, substrate, river bank, sedimentation, connection with lateral systems and with the hyporheic zone… Climate: temperature, extreme events, flow discharge, sunshine… Connection with the stream vegetation and the riparian zones: flux of energy and organic matter, areas for feeding and reproduction, shadow… Inter-dependent, finely tuned and variable properties Heavily impacted by human activities: water depth, flow regime, river bed morphology… Species-specific preference and tolerance for the different parameters of the physical habitat Morphohydraulic parameters are the major drivers of physical habitat Patchy mosaic of habitats and micro-habitats Swift flow areas: coarse substrate, rheophil, oxyphil or cryophil species (1 to 3) Slow-moving sections: deep water, fine substrate, lentic environment, limnophil species (4) 1 2 3 Thymallus thymallus 4 Stream Ecology Local species richness in rivers depends on habitat heterogeneity Longitudinal: gradients in water depth and velocity Lateral: meanders, river arms, channel dissymmetry (5) spawning area, nurseries, habitats for lentic species… Vertical: substrate permeability exchange of water and organic matter trapping of pollutants Temporal: variable flow rate, flooding Connection with the riparian zone: sharp environmental gradients, buffer zone, ecological corridors, mosaic of landforms… (6 to 10) submersed dead wood as micro-habitats roots as important resting sites and egg-laying sites Troglodytes troglodytes 6 Cinclus cinclus 7 Tinca tinca 8 Open, non-equilibrium ecosystems dynamically linked longitudinally, laterally and vertically by hydrological and geomorphic processes occurring within a temporal hierarchy 9 Squalius cephalus 10 5 5 5 Esox lucius The River Continuum Concept The distribution of organisms - resources - biological processes change along rivers and depend on large-scale and local processes • Stream Zonation Concept (Illies & Botosaneanu 1963) A series of distinct communities along rivers • River Continuum Concept (Vannote et al 1980) River communities and metabolism are influenced by local conditions and by processes occurring upstream Rivers as integrated systems within the landscape • Hyporrheic Corridor Concept (Stanford & Ward 1993) Hydrological and functional connections between the river and the riparian zone extend to the entire alluvial bed • Flood Pulse Concept (Junk et al. 1989) Comprehensive approach focusing on river floodplain dynamics Rivers and their associated floodplains are integrated components of a single dynamic system Dams and hydropower production: Loss of connectivity between compartments All four dimensions of stream ecosystems disrupted Vannote et al. (1980) The River Continuum Concept. Canadian Journal of Fisheries and Aquatic Sciences 7(1): 130-137 Ecological Effects of Water Reservoirs Pike spawning ground 11 Anguilla anguilla 12 Lampetra sp. 13 Salmo trutta 14 Ecological effects upstream and downstream of reservoirs • Upstream: change in river discharge and morphology Complete switch of the community from lotic to lentic Contamination of water and sediment from the stream watershed • Downstream: reduced or no base flow Effects on river bank habitats and connections with lateral compartments (11) Reduced flushing of particles and amplified thermal fluctuations • Along the entire stream: No stream continuity for upstream and downstream migrations Habitat fragmentation and isolated populations (12 to 14) Impaired trophic interactions • Hydro- and thermopeaking: rapid fluctuations in flow discharge and temperature resulting from hydropower plant operation Increase in shear stress Clogging or erosion of the sediment bed and river banks Flooding of spawning and nursery areas Altered lateral connectivity Change in the chemical and physical properties of the water Alteration of five critical components: magnitude of discharge, frequency of occurrence of flow, duration of specific high or low flow conditions, timing or predictability of flows and rate of flow change Flow Alteration Effects on abiotic parameters in watercourses • Rapid and significant changes in hydraulics: Discharge Flow velocity Bed shear stress • Chemical and physical water quality: Diurnal cycle of turbidity and temperature Conductivity Concentration of nutrients and contaminants • Morphology: Movement of an overlying fine gravel layer Suspension or deposition of fine sediments Grain distribution Meile et al. (2005) 15 Synthesebericht Schwall/Sunk. Publikation des Rhone-Thur-Projekts Changes in abiotic factors influence biotic communities • Rapidity of change: cannot be sensed by organisms • Change in composition (15-16) (e.g. Pof and Alan 1995 Ecology 76) • Decline in abundance or biomass Fish, benthic macro-invertebrates and algae Riparian fauna • Stranding of organisms and increased drift density 16 Reduced exchanges with the hyporheic zone • Water table lowering • Riverbed clogging Berry and Hill (2003) The biological effects of suspended and bedded sediment in aquatic systems: a review. USEPA Internal Report Thermal Alteration 17 The ecological integrity of lotic systems depends on the natural dynamics of the thermal regime Ecological consequences of modified regimes • Altered spawning opportunities and success of native fish species • Reduced growth rates 17 turnover • Decline of native species and species • Effects on invertebrate communities Reduced developmental cues Asynchrony of life cycle and resources Changes in assemblage structure (17) Olden and Naiman (2010) Incorporating thermal regimes into environmental flows assessments: modifying dam operations to restore freshwater ecosystem integrity. Freshwater Biology 55:86-107 Drift Responses Of Benthic Invertebrates Sudden releases of hypolimnetic water also cause thermopeaking • Large dams: highly variable and frequently depressed summer water temperatures • Smaller dams: increases in downstream temperatures Drift response to hydropeaking • Flow is a major determinant of physical • Species-specific differences driftisabundance habitat in streams, which ininturn a major (18) (e.g. Mochizuki et al. 2006 Limnology) • Use of refugia of during disturbance (19-20) (e.g. Lancaster 1999 Freshwater Biology) determinant bioticflow composition • • Importance of thehave rateevolved of increase in flow (e.g. Imbert and Perry 2000 Hydrobiologia) Aquatic species life history • Sediment mass driftto(e.g. Gibbins et al. 2007 Can. J. Fish. Aquat. Sci.) strategiesmovement primarily intriggers direct response • Changes in taxa diversity and abundance (e.g. Bruno et al. 2009 Ann. Limnol.) their natural flow regimes • Maintenance of Interactive effectsof ofnatural hydro- patterns and thermopeaking longitudinal drift and lateral connectivity is drift (e.g. Bruno et al. 2012 Ecohydrology) • Catastrophic followed by behavioral essentialeffects to the viability of populations of • Synergic many riverinedifferences species in response to hydro- and thermopeaking • Taxon-specific • The invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes 18 19 20 Bunn and Arthington (2002) Basic Principles and Ecological Consequences of Altered Flow Regimes for Aquatic Biodiversity. Environmental Management 30(4):492-507 Bruno et al. (2013) Multiple drift responses of benthic invertebrates to interacting hydropeaking and thermopeaking waves. Ecohydrology 6(4):511-522 Photo Credits (1) www.maxisciences.com (2) www.plymouth.edu (3) www.luontoportti.com (4) www.louisbourdon.com (5) Biodiversité et caractéristiques physiques des cours d’eau (Jean-Claude Philippart) (6) www.wise-photographie.e-monsite.com (7) www.geowi.skynetblogs.be (8) www.zoomalia.com (9) www.droidcorps.com (10) www.pnr-scarpe-escaut.fr (11) Guide technique pour la restauration des frayères à brochet UFBAG (Laurent Rougerie) (12) www.naturfoto.cz (13) www.infohightech.com (14) www.calvados-littoral.f (15) www.imgkid.com (16) www.desman-pyrenees.com (17-18) www.wikipedia.org (19) www.discoverlife.org (20) www.biopix.com