The added value of bryophytes and macroalgae in ecological assessment of lakes

Bryophytes and macroalgae have frequently been used as indicators of trace elements and organic pollutants, but their potential as indicators of eutrophication has not been accurately evaluated. Here, I used frequency data of aquatic macrophytes (vascular plants, charophytes, bryophytes and macroalgae) from 233 Swedish lakes to assess the additive value of bryophytes and macroalgae for the assessment of ecological status in lakes. Applying an established approach for boundary setting of total phosphorous (Tot-P) concentrations, 18 of the studied 31 macroalgae and bryophyte species (58.1%) were classified as sensitive species, two as indifferent (6.5%) and 11 as tolerant species (35.5%). Several cryptogam species showed sudden drops in their frequency along the Tot-P gradient (e.g. Aegagropila linnaei, Drepanocaldus sordius and Fontinalis antipyretica). The correlation between a macrophyte-based trophic index and Tot-P concentrations was only marginally higher when calculated with compared to without macroalgae and bryophytes. However, the differences between the trophic index calculated with and without these species, respectively, was significantly higher at Tot-P concentrations <35 μg l−1. The here presented results suggest macroalgae and bryophytes as important indicators of eutrophication. Hence, they should be routinely integrated into monitoring and ecological assessment of lakes.