Short-term effects of nutrient enrichment on river biofilm: N–NO3− uptake rate and response of meiofauna

Abstract

Biofilms play a key role in self-depuration processes in rivers. Whilst meiofauna is known to be abundant within river phototrophic biofilms and to perform both grazing and bioturbation within these matrixes, it is still unknown whether the activity of biofilm-associated meiofauna can influence the ability of biofilms to improve river water quality. In this study, we explored the effects of nutrient enrichment on river biofilm N–NO3− uptake rates and associated meiofauna in microcosms for 5 days under nutrient-enriched/non-enriched conditions. Short-time nutrient enrichment stimulated biofilm-associated bacterial and rotifer density, as well as the biofilm uptake rates of N–NO3−, but not algal biomass. Under non-enriched conditions, N–NO3− uptake rate tended to reach a plateau around 104.2 μg g−1 AFDM h−1. At higher N–NO3− concentrations, realised under enrichment, N–NO3− uptake rate seemed to increase linearly, reaching up to 439.2 μg g−1 AFDM h−1. Our results showed a rapid response of rotifers to nitrate enrichment and suggest a possible link between bacteria–meiofauna interactions and the short-term N uptake capacity of biofilms.