HYDROLOGY RELATED DISTRIBUTION OF MACRO-INVERTEBRATES IN SOFT-BOTTOMED LOWLAND STREAMS (THE NETHERLANDS)

P.F.M. Verdonschot. Institute for Forestry and Nature Research, PO Box 23, 6700 AA Wageningen, The Netherlands. </authors><abstract>Ten low-gradient, soft-bottomed streams are studied. They range from rain-fed streams, which show strong fluctuations in discharge, to spring fed streams with a fairly constant discharge pattern throughout the year. The differences in discharge patterns cause the streams to differ in hydrologic dynamics and thus also to differ in hydraulic and substrate characteristics. The main substrate in these streams is quite homogeneous fine sand. Changes in substrate patterns are recorded and can be related to changes in discharge. The substrate stability is directly related to the hydrology of the respective stream. The macrofauna distribution and abundances depend, besides on season, on stream hydrology (discharge fluctuation), hydraulics and substrate type. Determining factors for these habitats are particle size and horizontal distribution of both the mineral and organic component of the substrate. Both related to fine scaled hydraulics which in their turn are due to hydrology. The differences in the latter cause major differences in macroinvertebrate assemblage composition in between streams