VARIABILITY OF MESOHABITAT CHARACTERISTICS IN RIFFLE-POOL REACHES: TESTING AN INTEGRATIVE EVALUATION CONCEPT (FGC) FOR MEM-APPLICATION

This paper investigates the variability of mesohabitat characteristics in various riffle-pool reaches. The tested river sections (n = 13) feature clear variation in slope (0.0004-0.0132) and low flow discharge (0.05-915 m(3)s(-1)) in different river types (straight to meandering). Mesohabitat characteristics (water depth, flow velocity, bottom shear stress) were calibrated according to the MEM-concept (MEM-Mesohabitat Evaluation Model). Statistical analysis clearly revealed significant differences (p < 0.001) for the same mesohabitats (e. g. riffles) in different rivers concerning the tested abiotic habitat parameters. A comparative analysis of hydro-morphological parameters (width-depth variance, Froude number) showed no correlation to mesohabitat variability based on 2D/3D numerical modelling related to a range of flows (n = 10) (low flow to annual flood). Only an increasing hydraulic radius (R-hy) was correlated to an increase in fast run and a decrease in run habitats. In a case study, a Fish Guild Concept (FGC) is presented which links mesohabitats to the rheophilic fish guild (12 fish species grouped) at the Sulm River. Mesohabitat suitability (preferred, useable and avoided) for the FGC was determined for spawning, juveniles (0+, 1+), sub-adult and adult stages based on meso-unit and point abundance electro-fishing. Copyright (C) 2010 John Wiley & Sons, Ltd.