Epilithic ectoenzyme activity in a nutrient-rich Mediterranean river

The epilithic biofilms of a fourth-order river, the Ter, was characterized by high algal biomass and activity and bacterial density. The epilithon was the most important site for the cycling of organic matter, while the water column had rather low activities. In spite of being a nutrient-rich system, the ectoenzymatic activities were not significantly higher in the River Ter than in other streams of lower nutrient content. Biomass and activities followed a markedly seasonal pattern, mainly showing a peak in spring and autumn. Discharge and nutrients were the most important factors for the regulation of the biofilm metabolism. Drastic decrease in mid-summer were related to the extremely dry conditions during that period. The activity of epilithic ectoenzymes was higher during high discharge periods, which were coupled with higher DOC content in the stream water.