The Balkan Macrophyte Index (BMI) for Assessment of Eutrophication in Lakes

Abstract

Aquatic plants have long been used as indicators for nutrient enrichment in lakes. In the Mediterranean, however, the process of developing and intercalibrating macrophyte assessment methods for lakes has lagged behind Northern and Central Europe, likely due to the relatively small number and high variability of natural lakes in the Mediterranean but also because of the different monitoring traditions in different parts of Europe. We here present a macrophyte index for assessment of lake eutrophication, tailored to Balkan lakes (Balkan Macrophyte Index, BMI). We analysed submerged aquatic vegetation, water chemistry and sediment total phosphorus content at several sites in lakes Prespa, Ohrid, Lura, Biogradsko, Crno and Sava, located in Albania, North Macedonia, Montenegro and Serbia. Despite the restricted number of lakes in our dataset, the BMI was loosely related to water phosphorus, rather than nitrogen, concentrations. Our results show that macrophyte indices may not be applicable in lakes experiencing annual water level fluctuations of several meters, because the macrophyte vegetation in such lakes may be absent, or alternatively dominated by “oligotrophic” or “eutrophic” species. Once a larger number of lakes has been analysed using the same methods, reference conditions and status class boundaries may be derived from the phosphorus – BMI regression.