Epipelic biofilms respond early to the impacts of urbanization in lowland streams

Abstract

Multiple structural and functional endpoints of stream biofilms are employed by water quality monitoring programs to detect both direct and indirect environmental impacts. Since multiple co-occurring stressors influence biofilm development, active biomonitoring (translocation experiments) could provide a useful monitoring tool that reflects the overall water quality of the urbanized sites. The aim of this research was to study the short-term responses of epipelic biofilms caused by their translocation to more polluted reaches in lowland urban streams. Fluvial sediment was translocated in three streams that run through urban areas following an urbanization gradient. The epipelic biofilms in the sediment were sampled to identify any fast occurring changes in their algal and bacterial biomasses, in their respiration and oxygen consumption. The results show that structural changes in the biofilm, such as an increased bacterial density and chlorophyll-a concentration, were measurable after two days of exposure to sites with impaired water quality. These immediate changes in the structure of the biofilm indicate that they are sensitive endpoints that can be employed in fast and inexpensive biomonitoring programs in urbanized streams.