Transient modeling of physical habitat for stream macrozoobenthos at intermediate spatial and temporal scales – moving towards more dynamic descriptions of hydromorphology

A strategy for modeling the spatiotemporal supply of physical habitat for stream macrozoobenthos is presented and used to explore the limiting role of hydromorphology on species of varying sensitivity. The approach is based on unsteady numerical two‐dimensional shallow water simulations, which are combined with substrate information and tolerance ranges in order to build unsteady physical habitat models for a group of 13 taxa on the upper course of the river Lahn (Germany). The resulting habitat information aims to capture physical habitat gradients on an intermediate scale that is larger than individual organisms but smaller than the stream's geomorphic units, as well as to follow hydrological variations determined by the stream's flow regime. By modeling physical habitat at this spatiotemporal scale, the approach builds on information derived from typical field surveys relating macrozoobenthos and hydromorphology, which are based on quadrat samples placed in different hydraulic zones in the stream (riffles, pools, runs, glides, mid‐channel and shore areas, side arms, cut‐off and slip‐off banks, etc.), and therefore has the advantage of using knowledge thus derived at the same scale it was generated.