Soil microbial activities in a reed-bed used for effluent purification of a small cheese-dairy farm under a Mediterranean climate were described and studied. This work aims to demonstrate (i) whether certain enzyme activities used as bioindicators of dairy waste degradation (P-galactosidase and protease) vary over time, which might influence organic matter degradation and (ii) whether specific microbial communities are selected through contact with the discarded effluent using community level catabolic profiles (CLCPs). P-galactosidase and protease activities were followed in a 14-month monitoring experiment. These enzyme activities were strongly expressed during the whey-discarding period from February to May. CLCPs using Biolog Ecoplate showed great microbial diversity, as described by Shannon-Weaver index, and no difference was observed in microbial diversity between areas at the receiving end of the reed-bed (where effluent was discarded) and those at the opposite end. This may be explained by successive environmental factors which made enzyme activities vary: whey discarded from February to May and Mediterranean climate conditions (drying-rewetting effects on summer). Microbial enumeration using epifluorescence microscopy also showed a pattern linked to Mediterranean conditions with a drastic decrease in biomass during summer drought. These results on functional biodiversity were correlated with high purification yields: the minimum decrease in Biological Demand in Oxygen was 84% and that in suspended solids was 75%. (C) 2008 Published by Elsevier Ltd.