Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 4 2008 10.5194/bg-5-1043-2008 http://www.biogeosciences.net/5/1043/2008/ http://www.biogeosciences.net/5/1043/2008/bg-5-1043-2008.html http://www.biogeosciences.net/5/1043/2008/bg-5-1043-2008.pdf 1043 1055 2008-07-28 Surface flow types, near-bed hydraulics and the distribution of stream macroinvertebrates M. A. Reid mike.reid@canberra.edu.au M. C. Thoms Riverine Landscapes Research Lab, Faculty of Applied Sciences, University of Canberra, Australia Spatial variation in hydraulic conditions in streams often results in distinct water surface patterns, or surface flow types. Visual assessments of the distribution of surface flow types have been used to provide rapid assessment of the habitat heterogeneity. The efficacy of this approach is predicated on the notion that surface flow types consistently represent a distinct suite of hydraulic conditions with biological relevance. This study tested this notion, asking three specific questions. First, do surface flow types provide a characterisation of physical habitat that is relevant to macroinvertebrates? Second, how well do near-bed hydraulic conditions explain macroinvertebrate distributions? Third, what components of near-bed hydraulic conditions exert the strongest influence on macroinvertebrate distributions? <br><br> Results show that hydraulic conditions (incorporating direct measurements of near-bed velocity and turbulence in three dimensions) and substratum character (incorporating estimates of particle size distribution, and biofilm and macrophyte cover) within each surface flow type were largely distinct and that macroinvertebrate assemblages differed across flow types in taxon richness and assemblage composition, thus supporting the notion that rapid assessments of surface flow type distributions provide biologically relevant information. <br><br> Macroinvertebrate assemblages were most strongly correlated with water depth, size of a flow type patch, near-bed velocity in the downstream direction, turbulence in the transverse direction, % pebble, % sand, % silt and clay and macrophyte cover. 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