Dimitrios Zervas

The EU Water Framework Directive foresees the ecological assessment of surface waters against identified pressures. Nutrient loading is the main pressure impairing the ecological quality of lake ecosystems, and aquatic macrophytes are considered good indicators of ecological response. In this study, we statistically assessed different aspects of aquatic plant (macrophyte) diversity in response to different trophic levels in Mediterranean lakes. We used 5690 relevés of aquatic vegetation, distributed over 305 transects, sampled in 18 freshwater lake ecosystems during 2013–2016. Our results show a significant decrease in taxonomic alpha diversity in lakes with a total phosphorus content above 100 μg/L. Syntaxonomic diversity followed the species richness pattern as well. Functional richness decreased along the trophic gradient, while functional dispersion was higher in lakes with high trophic levels. Taxonomic and functional beta partitioning presented changes in assembly processes leading to greater community homogeneity in lakes with higher trophic levels. In summary, we found no redundancy between taxonomic and functional diversity indices. These results provide novel insights into aquatic plant assembly processes of impacted freshwater lakes needed to forward conservation and restoration practices.

The ecological water regime in lake water bodies refers to the water levels that enable the fulfillment of the ecosystem’s multiple functions. Therefore, assessing the ecological water regime necessitates the consideration of hydrological, economic, social, and ecological factors. The present research is focused on the assessment of the ecological water level of four Mediterranean natural lake ecosystems, considering their morphological and biological features. Initially, suggestions on the ecological water regime of the studied lakes were made based on an analysis of the lakes’ morphometry. Further, the ecological and biological requirements of the present fish fauna and aquatic macrophytic vegetation were considered. For the latter, mapping was conducted by extensive sampling according to international standards, in order to assess macrophyte composition, abundance, and chorology, as well as species sensitivity to water level fluctuations. The above guided the proposals on the optimal water level regime that should be met by each lake regarding the macrophytic and fish communities’ sustainability, also taking into account the unique hydromorphological features of each lake. The differences in the outcoming results revealed that hydromorphological and biological approaches should be combined for assessing lakes’ ecological water regimes.

Aims: This study aims to contribute to the knowledge of European freshwater lake ecosystems with updated and new information on aquatic plant communities, by conducting national-scale phytosociological research of freshwater lake vegetation in Greece. Moreover, it investigates the relationship between aquatic plant communities and lake environmental parameters, including eutrophication levels and hydro-morphological conditions.Study area: Lakes in Greece, SE Europe.Methods: 5,690 phytosociological relevés of aquatic vegetation were sampled in 18 freshwater lake ecosystems during 2013–2016. The relevés were subjected to hierarchical cluster and indicator species analyses in order to identify associations and communities of aquatic vegetation, as well as to describe their syntaxonomy. Multiple regression analysis was applied to investigate the relationship between vegetation syntaxa and environmental parameters of lakes, i.e. physico-chemical parameters and water level fluctuation.Results: Ninety-nine plant taxa belonging to 30 different families were recorded. Forty-six vegetation types were identified and described by their ecological characteristics, diagnostic taxa and syntaxonomical status. Thirteen vegetation types, the largest number belonging to the vegetation classCharetea, are considered to be new records for Greece. The distribution of the vegetation types recorded in the 18 freshwater lakes was found to depend on environmental parameters and levels of eutrophication.Conclusions: An updated aquatic vegetation inventory was produced for Greek lakes, and primary results showed that the presence/absence of aquatic plant communities and the community composition in freshwater lakes can be utilized to assess the pressure of eutrophication on lake ecosystems.Taxonomic reference: Euro+Med (2006–).Abbreviations: MNT = Mean number of taxa; WFD = Water Framework Directive.

The Water Framework Directive (WFD) requires Member States to develop appropriate assessment methods for the classification of the ecological status of their surface waters. Mediterranean region has lagged behind in this task, so we propose here the first developed method for Greek lakes, Hellenic Lake Macrophyte (HeLM) assessment method. This method is based on two metrics, a modified trophic index and maximum colonization depth C_max that quantify the degree of changes in lake macrophytic vegetation, as a response to eutrophication and general degradation pressures. The method was developed on the basis of a data set sampled from 272 monitoring transects in 16 Greek lakes. Sites from three lakes were selected as potential reference sites by using a screening process. Ecological quality ratios were calculated for each metric and for each lake, and ecological status class boundaries were defined. For the evaluation of effectiveness of the method, the correlations between individual metrics and final HeLM values and common pressure indicators, such as total phosphorus, chlorophyll a and Secchi depth, were tested and found highly significant and relatively strong. In addition, the ability of HeLM values and its individual metrics to distinguish between different macrophytic communities’ structure was checked using aquatic plant life-forms and found satisfactory. The HeLM method gave a reliable assessment of the macrophytic vegetation’s condition in Greek lakes and may constitute a useful tool for the classification of ecological status of other Mediterranean lakes.

The paper confirms the presence of Elodea canadensis Michx. in Greece and outlines the history of contradictory relevant reports. This is also the first report of the species′ presence in the transboundary lake Great Prespa.