LIMITATIONS OF FST HEMISPHERES IN LOTIC BENTHOS RESEARCH

1. FST hemispheres have been proposed as a method for assessing flow characteristics near the river bottom. We suspected that the hemispheres were too big for this goal and that the ground plate would significantly affect near-bottom microhydraulics. 2. The results we present have confirmed our assumption about the limitations of this method: the correlation between FST results and current velocity (measured by an anemometer, phi = 1.2 cm) was best at 40% of depth ('mean current velocity', coefficient of determination r(2) = 0.58) and decreased to r(2) = 0.24 at 0.6 cm above the bottom; the correlation with (calculated) shear stress was only r(2) = 0.23. A correlation between FST results and macroinvertebrate abundance was found for only four of eight investigated taxa and was similar to the correlation between abundance and 'mean current velocity'. 3. We conclude that for fieldwork the FST hemispheres have about the same limitations as has a conventional (i.e. propeller-type) anemometer. With the hemispheres we could not obtain better data than with other methods.