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Lake Hydromorphological Assessment and Monitoring Methodologies -European survey

Méthodes de suivi et d'évaluation de l'état hydromorphologique des lacs - Enquête européenne

Résumé

The assessment of lake status in Europe has evolved during the last few decades from physico-chemical focused assessment to a more comprehensive ecological approach. The EC Water Framework Directive (WFD) requires the assessment of hydromorphological and physico-chemical conditions of lakes considered as supporting elements of the biological communities. The WFD describes the hydromorphology of lakes using quality elements belonging to the hydrological regime on the one hand and to morphological conditions on the other hand. A lake can achieve good ecological status only if the aforementioned quality elements correspond to natural conditions or deviate from them very slightly. Therefore, hydromorphological assessment is crucial for ecological status assessment. During summer 2020, an inventory of the HYMO assessment and monitoring methods currently implemented or under development in the different European countries for WFD implementation was conducted. This study summarises key information reported through the aforementioned inventory in order to get a comprehensive overview of the hydromorphological methods at the present time and to contribute to more common understanding of how hydromorphological conditions are defined and hydromorphological changes are characterised in different national contexts in Europe. The high response rate of the European survey makes it possible to provide a comprehensive overview of lake hydromorphological assessment and monitoring methods implemented or under development in the different European countries. Currently, 33 methods are applied or in development in 20 countries, 20 are currently assessment methods, 10 are monitoring methods and 3 methods will be replace by new protocols. This report gives also a basis to carry out future relevant good practices suitable with standards such as the water quality guidance standard on assessing the hydromorphological features of lakes – EN 16039:2011 and the water quality guidance standard on determining the degree of modification of lake hydromorphology – EN 16870:2017. Hydrological characteristics are relatively well taken into account by the different countries except the residence time although its evaluation is recommended in the EN 16039:2011 standard. Surface-groundwater interactions and stratification/mixing are also poorly taken into account in the different countries even though the interactions between surface water and groundwater are characterised in a majority of countries but not used to assess lake conditions. Morphological characteristics are also relatively well taken into account by the different countries, in particular lake depth variation, shape of the littoral zone and shore zone aquatic vegetation. Nevertheless, the planform pattern, substrate and aquatic vegetation in the open water are still poorly used to evaluate lake conditions although their evaluation is recommended in the EN 16039:2011 standard. All of the 20 current assessment methods use a scoring system which are mostly quantitative although the degree of confidence is still poorly included in the methods. However, the scoring system and the way in which class thresholds are defined remain to be specified by the different countries. Finally, two main hurdles remain; a methodological hurdle with the determination of reference conditions which is not clearly defined for many countries although this is essential when assessing lake conditions and a scientific hurdle with regard to the link with biology of the different hydromorphological assessment methods. In order to improve best practices and write recommendations further information is needed on how reference conditions and classification are undertaken at Member State level for assessing lake hydromorphology.
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hal-03655122 , version 1 (29-04-2022)

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Christine Argillier, Alexandra Carriere, Sandra Poikane, Wouter van de Bund. Lake Hydromorphological Assessment and Monitoring Methodologies -European survey. 2022, ⟨10.2760/274896⟩. ⟨hal-03655122⟩
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