Effects of Deadwood on Macroinvertebrate Assemblages in Three Sand-Type Lowland Streams

The objective of the manuscript was to study the effects of dead wood on macroinvertebrates (MI) assemblages occupying different habitat patches. Three streams were studied, with control and wooded sections in each stream from which MI were sampled for all substrate types (wood, fine detritus, gravel, sand). This contribution deals with three German streams Ihle, Nieplitz, and Verlorenwasser, which belong to the stream type 14 (sand-dominated lowland stream) and are located in the landscape unit Flaming. This type of stream, where large wood could be most influential, has been relatively understudied. This study focused on quantifying substrate distribution and macroinvertebrate taxonomy and performing statistical analysis of MI densities with regard to substrate type. The area-specific invertebrate assemblages were differentiated for MI density, dry matter density and taxonomic richness of invertebrates. In addition to macroinvertebrates, a special focus was on aquatic and semi-aquatic insects. There were significant differences between the control and wooden sections. The macroinvertebrate assemblages (individual density, dry matter density and species richness) of the detritus of the wood sections only in the Verlorenwasser was significantly and positively affected (two or three times) by the deadwood. Detritus in the wood sections of the Nieplitz and Verlorenwasser contained more sensitive species like EPT than detritus from the control sections. On the other hand, no significant difference in MI populations were determined for the sand of the wood sections compared to the sand of the control sections. In all water bodies, the wood substrate promoted all investigated indicators of macrozoobenthos as compared to sand of the wood sections. Detritus significantly promoted macrozoobenthos colonization in the wood sections as compared to sand of the Nieplitz and the Verlorenwasser. The MI density and dry matter density in the Ihle was also significantly promoted by detritus, although not significantly with regard species richness. Two significant correlations were also identified. The more sand that was present in the Ihle and the Verlorenwasser, the more the macroinvertebrate assemblages were inhibited. Additionally, the larger the area of detritus in the Ihle and the area of wood in the Nieplitz, the more MI populations were encouraged. The influence of the deadwood position on MI was also investigated, but there was no significant difference. Incline bridges, flow guides and parallel wood position types were settled in similar quality and quantity.