Response of epilithic diatom assemblages to urbanization influences
Urbanization has long been recognized to alter the hydrology, water quality and channel form of waterways. Recently, consideration of urban impacts on waterways has expanded to include assessment of the aquatic biota, generally focusing upon the macroinvertebrate fauna. This study compares the impacts of urbanization on the structure of stream benthic diatom communities in 16 first- and second-order streams in the east of Melbourne, Australia. Relationships between the physical elements of urbanization, water quality and diatom communities were examined using multivariate analyses with compositional similarity, and univariate analyses with selected diatom species and indices,. There was a strong negative correlation between urban density and the diatom indices of water quality. The element of urbanization most strongly related to the measured decline in the diatom community was drainage connection. Electrical conductivity was the most influential water quality variable. It is hypothesized that, in addition to increasing electrical conductivity, drainage connection may be impacting the diatom community by increasing the delivery of phosphorus during small storm events. The study suggests that reducing directly piped drainage connection using infiltration and retention is a logical step in the mitigation of urban impacts upon receiving streams. A corollary part of the project indicated strong potential for using overseas diatom indices in studies on water quality in southeastern Australia.