Epiphyte biomass and elemental composition on submersed macrophytes in shallow eutrophic lakes

Abstract

Epiphytes cause a strong light attenuation for submersed macrophytes. Various abiotic and biotic factors determine epiphyte density, among them nutrients, water clarity and possibly allelopathy. We compared epiphyte biomass on the major occurring macrophytes, among them allelopathically active species in four shallow eutrophic lakes in Upper Swabia (Southern Germany). We determined epiphyte chlorophyll a, organic carbon, nitrogen and ashfree dry mass. Mean epiphyte chlorophyll a per macrophyte ranged between 100 and 400 μg g−1 dm in summer and increased up to 1700 μg g−1 dm in autumn. Few differences between species and lakes were observed. No apparent relation was found between epiphyte density and physical or chemical variables of the lakes. Epiphytes had a molar stoichiometry of organic carbon to nitrogen (C:N) slightly below 7:1, a ratio considered to be optimal also for benthic algae. Lakes with higher concentrations of humic compounds exhibited a significant higher ratio of organic carbon to epiphytic chlorophyll a, indicating a higher proportion of heterotrophs in the epiphyte layer. In one lake, one phenotype of Elodea nuttallii exhibited a significant higher C:chl a ratio than other macrophytes. Allelopathy as a factor responsible for this difference is discussed.