Heirarchical multi-taxa models of urban impacts on lotic macroinvertebrates: catchment-scale stormwater management versus local-scale riparian restoration

The Urban Stream Syndrome is a global phenomenon increasing homogeneity among urban stream systems and constraining ecological function. While there is increasing policy and public support for urban stream restoration, there remains considerable disagreement whether restoration should be undertaken at the reach- or landscape-scale. We evaluated the relative influence of local-scale riparian characteristics and catchment-scale imperviousness on the macroinvertebrate assemblages of streams in the urban metropolis of Perth, Western Australia. Using a hierarchical multi-taxa model we predicted the outcomes of stylized stream restoration strategies to increase the riparian integrity at the local scale or decrease the imperviousness at the catchment scale. In the urban streams of the Perth, we show that local-scale riparian restoration can influence the structure of macroinvertebrate assemblages to a greater degree than repairing catchment-scale imperviousness under certain conditions. We also observed an interaction between the effect of riparian integrity and imperviousness such that the effect of increased riparian integrity was enhanced at lower levels of catchment imperviousness. This study represents one of the first aimed at informing urban stream restoration in Perth and adds to the growing appreciation for heterogeneity of the Urban Stream Syndrome and its importance for urban stream restoration.