Macrophyte trophic indicator values from a European perspective

Abstract

Ecological optima and ranges of submerged macrophytes are, amongst other factors, assumed to be influenced by ecoregion and flow velocity. In order to test the influence of ecoregion within Europe, species indicator values of three European macrophyte river trophic indices were compared to each other. Species indicator values of the United Kingdom (UK), French and German bioindication methods are significantly correlated with each other. The most obvious difference between the three indicator systems is the number of included indicator taxa. Two species exhibit major differences in indicator values: Callitriche hamulata has a broader ecological amplitude in Germany and France than in the UK, where it is restricted to oligotrophic rivers, while Ranunculus fluitans has a broad ecological amplitude in the UK, whereas the species is restricted to eutrophic rivers in Germany and France. In order to test if current velocity has an influence on macrophyte trophic indicator qualities, species indicator values of a river (Trophic Index of Macrophytes, TIM) and a lake macrophyte trophic index (Macrophyte Index, MI), both of them applicable in Bavaria, Germany, were compared to each other. Species indicator values are significantly correlated. The most important difference is that different species are included in lake and river indicator lists. Only approximately 60% of the total species are used in both TIM and MI. Three species exhibit a major difference in ecological optima between rivers and lakes: Ranunculus circinatus has a broader ecological amplitude in rivers whereas the species is restricted to eutrophic lakes, Myriophyllum spicatum and Nuphar lutea show the opposite reaction.