The main objective was to investigate the importance of the sediment as a nutrient source for blooms of nuiscance filamentous algae. Nutrient fluxes from the sediment were hypothesised to be of greater importance in maintaining algal biomass than were nutrients originating from the overlying water column. We aimed to assess the relative importance of algal mats on sediment geochemistry and nutrient release under stillwater and controlled flow conditions. Using nutrient fluxes as a surrogate for ecosystem function, we wished to investigate the role of species richness in maintaining the integrity of nutrient diagenesis. In this context, it is not necessarily the number of species that is important in maintaining nutrient supply to algal blooms, but the contribution individual species make to mediate nutrient release.