Quantitative sampling of the benthic fauna in a large, fast flowing river (Austrian Danube)
Bretschko, G.; Schönbauer, B.
The free flowing Austrian Danube is a 9th order gravel stream, deep and fast flowing and under these conditions obtaining quantitative samples is still problematic. Four methods (Slurp Gun, Petersen Grab, Deep Water Freeze Corer and Air Lift) have been tested against each other and against a freeze corer with in situ electro positioning. The evaluation has to be a relative one, because the absolute population descriptors are unknown. Test criteria were therefore: the qualitative composition and the relative and absolute abundances of the stream fauna, in addition to the purely technical performance of the equipment. A multivariate discriminant analysis revealed constant performance traits for all four methods, regardless of variations in sediments and fauna, at least to the extent that there are variations in the stretch of the Danube that was sampled. All test criteria proved the 'Air Lift' sampler to be the best method. Second was the 'Deep Water Freeze Corer', which is the only available method for studying the vertical distribution of the stream fauna within the sediment, although with certain limitations. The 'Slurp Gun' and 'Petersen Grab' are very poor methods for quantitative sampling in these circumstances.