Macrophyte assessment in European lakes: Diverse approaches but convergent views of ʽgoodʼ ecological status

• Published in: Ecological Indicators
• Main Authors: POIKANE Sandra, PORTIELJE Rob, DENYS Luc, ELFERTS Didzis, KELLY Martyn, KOLADA Agniezska, MAEMETS Helle, PHILLIPS Geoff, SONDERGAARD Martin, WILLBY Nigel, VAN DEN BERG Marcel
• Language: English
• Published: ELSEVIER SCIENCE BV 2018
• Subjects: Zannichellia palustris
• Online Access: https://publications.jrc.ec.europa.eu/repository/handle/JRC111950; https://www.sciencedirect.com/science/article/pii/S1470160X1830503X; https://doi.org/10.1016/j.ecolind.2018.06.056

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on ʽgoodʼ ecological status. In this study, nine national macrophyte-based approaches for assessing ecological status were compared and harmonized, using a large dataset of 539 European lakes. A macrophyte common metric, representing the average standardized view of each lake by all countries, was used to compare national methods. This was also shown to reflect the total phosphorus (r2=0.32), total nitrogen (r2=0.22) as well as chlorophyll-a (r2=0.35-0.38) gradients, providing a link between ecological data, stressors and management decisions. Despite differing assessment approaches and initial differences in classification, a consensus was reached on how type-specific macrophyte assemblages change across the ecological status gradient and where ecological status boundaries should lie. A marked decline in submerged vegetation, especially Charophyta (characterizing ʽgoodʼ status), and an increase in abundance of free-floating plants (characterizing ʽless than goodʼ status) were the most significant changes along the ecological status gradient. Macrophyte communities of ʽgoodʼ status lakes were diverse with many charophytes and several Potamogeton species. A large number of taxa occurred across the entire gradient, but only a minority dominated at ʽless than goodʼ status, including filamentous algae, lemnids, nymphaeids, and several elodeids (e.g., Zannichellia palustris and Elodea nuttallii). Our findings establish a ʽguiding imageʼ of the macrophyte community at ʽgoodʼ ecological status in hard-water lakes of the Central-Baltic region of Europe. JRC.D.2 - Water and Marine Resources