Abstract
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 Cmax 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.
Highlights
The Water Framework Directive (WFD; European Commission 2000) supervises the monitoring and assessment of the ecological status of surface waters within the EU
All the above add to the necessity for the development of a complete lake assessment method based on aquatic macrophytes for the Mediterranean region. We overcome this gap and we present the newly developed ecological assessment method named as Hellenic Lake Macrophyte assessment method (HeLM) for classification of Greek lakes
Based on the environmental data used as pressure indicators, three lakes were selected as potential reference ones: Kourna and Feneos (GR-DNL type) and Paralimni (GRSNL type) (Table 3)
Summary
The Water Framework Directive (WFD; European Commission 2000) supervises the monitoring and assessment of the ecological status of surface waters within the EU. Aquatic macrophytes are commonly used in classification systems in lakes as they play a significant role in determining the structure and functions of lake ecosystems, by altering environmental conditions, nutrient cycling, biotic assemblages, and interactions (Engelhardt and Ritchie 2001; Spoljar et al 2017; Wang et al 2009) Their time of response to changes in nutrient conditions in a water body lies between the fastresponsive phytoplankton and phytobenthos organisms and the slow-responsive invertebrates and fish, which makes them valuable bioindicators, when monitoring the ecological quality of water bodies (Pall and Moser 2009; Penning et al 2008a, b; Schneider and Melzer 2003). Loss of macrophytic vegetation has been experienced in many lakes around the world during the last century due to the increase in the availability of nutrients in the water column that led to a rapid growth of phytoplankton, which in turn caused an increase in water turbidity and a decrease in sunlight penetration and availability (Blindow et al 2006; Hilt et al 2006)
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