Restoration of Streams with Large Wood: Effects of Accumulated and Built-in Wood on Channel Morphology, Habitat Diversity and Aquatic Fauna

Abstract

Large wood was added to regulated and straightened reaches of two third-order streams in Central Germany; the Jossklein and the Lüder. In the Jossklein, the wood was a by-product of the forest management in the floodplain and accumulated in the channel during peak floods. In the Lüder, logs were builtin as deflectors in regular intervals and fixed within the stream bank. In the Jossklein, the addition of large wood improved the channel morphology within four years. The variation in channel width and depth was considerably larger than in a regulated section. The extension of the riparian zone, especially of the semi-aquatic gravel and sand bars was strongly correlated with the amount of large wood that accumulated in the single sections. The number of microhabitats and their patchiness on the stream bottom was higher in restored sections, as well as the density of macroinvertebrates and the species number. In the Lüder, some of the observed trends were similar, but not that clear. This differences can be explained by higher amounts of LWD in the Jossklein, organised in dynamic debris dams situated above the water level at low flow, in contrast to the single stacks of logs at the Lüder, situated as stable deflectors within the low flow water level.