Are dead stems suitable substrata for diatom-based monitoring in Mediterranean shallow ponds?

Aquatic macrophytes can play an important role as substrata for benthic diatom assemblages, which constitute the greater part of the epiphytic algae in shallow ponds. This article addresses the question of whether diatom assemblages growing on dead stems differ from diatom assemblages growing on living helophytes. Three lakes in the province of Leon (NW Spain) were selected, in order to analyze the effect of the phenologic status of the host plants, by testing differences between epiphytic diatom assemblages growing on dead and living stems. Diatoms were collected from Schoenoplectus lacustris stems, the dominant helophyte in these lakes. Diatom richness was higher in assemblages that had developed on dead stems, but abundance values showed no differences. Regarding inferred water quality values, SPI scores were slightly higher in samples coming from living stems, but no significant differences were found. In conclusion, there were no ecologically significant differences between the observed diatom assemblages collected from dead and living stems. Therefore, both kinds of substrata can be used in diatom-based shallow lake water quality monitoring programmes.