Assessing the disturbance caused by an industrial discharge using field transfer of epipelic biofilm.

A translocation experiment of epipelic biofilm was performed in order to explore the effects on this biological complex when exposed to different water qualities. To carry out such an experiment we employed artificial substrata placed at two sites within a stream that receives a textile effluent: at site 1, located upstream from this influx, and at site 2, downstream. After a 4-week colonization, the substrata at each site were switched in location between sites 1 and 2.The analysis of the epipelon was performed once a week between April and July 2008. In order to evaluate the disturbance on the biofilms we assessed structural (biofilm composition, chlorophyll "a" and ash-free dry weight) and metabolic (net and gross primary production, respiration, and assimilation rate) features. With the metabolic variables that showed significant differences, resistance was calculated. The taxonomic and metabolic variables analyzed responded differently in accordance with the type of environmental challenge presented. In this regard, the biofilm developing at the site upstream from the textile effluent that was later transferred to the downstream site proved to be more resistant to the environmental perturbations with respect to its composition, but not at the level of its metabolic descriptors. Indeed, in the translocated and nontranslocated biofilms growing downstream we observed diatom species with morphological deformations in their frustules, fact that clearly reflects the environmental stress at this site. On the other hand, the biofilm transferred in the opposite direction, in turn, rapidly exhibited tendencies to compensate for its lower biological integrity, but responded more slowly at the metabolic level. Finally, the observation of the changes occurred in the biofilms as a consequence of the worsening and improvement of the water quality could be efficiently evaluated through this experiment.