Composition and abundance of oligochaetes in large Scandinavian lakes in a morpho-edaphic index framework—in the 1970s and 50+ years later

Abstract

Bottom-living oligochaetes and chironomid larvae, thanks to their supposedly integrative power, could provide more robust measures of the water quality of lakes than separate chemical data. The oligochaete fauna of the large lakes of southern Scandinavia has been studied in detail over many years—often 100 years or more (Milbrink, 2020). Characteristic species associations and the ecological preferences of each oligochaete species are thus relatively well-known. In Milbrink (2020) it was shown that the precision could be greatly improved if the relationship between oligochaete species and chemical data could be instead demonstrated within a morpho-edaphic index framework (Ryder et al. 1974). The percentage composition and total abundance of oligochaetes per sample in a number of large lakes or selected basins of large lakes in southern Sweden and Norway were thus tested against this index in the 1970s (Milbrink, 1978). The trophic change which had taken place in the oligotrophic Lake Vättern—first with eutrophication and later with oligotrophication—was illustrated graphically and discussed in this work (Milbrink, 2020).

A very similar trophic change could also be seen in the oligotrophic Lake Vänern (the basin of Värmlandssjön), as well as in the more eutrophic Lakes Mälaren and Hjälmaren. All these large lakes, once eutrophied in the 1950s and 1960s, are today undergoing oligotrophication. We simply have a melioration thanks to advanced sewage treatment since the 1960s. With our new knowledge, it is informative studying changes in species composition after trophic change. In a time when efforts to save the environment often fail, this new development is a real success story.