Ecological status assessment of European lakes a

Authors: Anne LycheSolheim Christian K Feld Sebastian Birk Geoff Phillips Laurence Carvalho Giuseppe Morabito Ute Mischke Nigel Willby Martin Søndergaard Seppo Hellsten Agnieszka Kolada Marit Mjelde Jürgen Böhmer Oliver Miler Martin T Pusch Christine Argillier Erik Jeppesen Torben L Lauridsen Sandra Poikane

Publish Date: 2013/02/01

Volume: 704, Issue: 1, Pages: 57-74

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Abstract

Data on phytoplankton macrophytes benthic invertebrates and fish from more than 2000 lakes in 22 European countries were used to develop and test metrics for assessing the ecological status of European lakes as required by the Water Framework Directive The strongest and most sensitive of the 11 metrics responding to eutrophication pressure were phytoplankton chlorophyll a a taxonomic composition trophic index and a functional traits index the macrophyte intercalibration taxonomic composition metric and a Nordic lake fish index Intermediate response was found for a cyanobacterial bloom intensity index Cyano the Ellenberg macrophyte index and a multimetric index for benthic invertebrates The latter also responded to hydromorphological pressure The metrics provide information on primary and secondary impacts of eutrophication in the pelagic and the littoral zone of lakes Several of these metrics were used as common metrics in the intercalibration of national assessment systems or have been incorporated directly into the national systems New biological metrics have been developed to assess hydromorphological pressures based on aquatic macrophyte responses to water level fluctuations and on macroinvertebrate responses to morphological modifications of lake shorelines These metrics thus enable the quantification of biological impacts of hydromorphological pressures in lakesThe value of lakes cannot simply be measured in terms of their water volume and chemical quality We also value lakes if they have clear water free of algal blooms suitable for water supply and recreation rich biodiversity worthy of conservation and attractive to tourism and can act as healthy ecosystems for water purification and climate regulation MEA 2005 The most effective methods to determine the health and integrity of our lakes are the plants and animals living there Biological monitoring provides a direct picture of a lake’s status and is much easier understood by the public than chemical data alone Moreover in the scientific literature it is widely recognised that biological monitoring schemes have many advantages compared to chemical monitoring schemes Mason 1981 Karr Chu 1999 Biological metrics respond to intermittent pollution integrating the effect of stressors over longer timescales weeks to years compared to chemical monitoring which provides a single ‘snapshot’ of the quality at the time of sampling These aspects of lake biology are the underlying reasons why phytoplankton macrophytes benthic invertebrates and fish are now required for the assessment of the ecological status of lakes in Europe according to the EC Water Framework Directive WFD EC 2000 Annex V of the WFD outlines the technical requirements for using various characteristics of these four biological quality elements BQEs in the assessment for phytoplankton these are biomass taxonomic composition and bloom metrics for macrophytes taxonomic composition and abundance for benthic invertebrates taxonomic composition abundance and diversity and for fish taxonomic composition abundance and age structure Although some national metrics expressing the responses of several of these characteristics to human pressures were developed and used in lake monitoring programmes prior to the WFD the Directive has stimulated the development and improvement of a large array of different national methods Lyche Solheim et al 2008 Solimini et al 2008 Poikane 2009 Birk et al 2012 Brucet et al 2013The diverse array of national methods has posed great challenges in assessing the comparability of national methods a process known as ‘intercalibration’ required by the WFD WFD CIS 2009 To facilitate the WFD intercalibration process there was an urgent need to develop pressurespecific metrics for all BQEs to be used as robust indicators in national methods or as ‘common metrics’ which allow the comparison of national methods between countriesMost national metrics address eutrophication which is still the most widespread pressure in European lakes EEAETC 2012 However hydromorphological pressure eg altered water level regime shoreline modification is an increasingly important pressure in many lakes in Europe EEAETC 2012 and biological indicators addressing impacts of hydromorphological alteration need to be included in monitoring programmesThere is a need to know which metrics are least affected by natural and methodological variation and thus best reflect the most widespread pressures affecting our lakes and therefore exhibit minimal uncertainties when using them Variation in metric values which may obscure the effects of environmental stress that the evaluator wants to assess is due to i sampling variation and inconsistent sampling method ii sample processing and taxonomic identification bias and iii natural temporal and spatial variation Quantification and subsequent reduction of the various uncertainty components is important to optimise sampling design and reduce uncertainty in the classification of the ecological status of lakesThe objective of this paper is to present an overview of all the metrics and multimetric indices developed for lakes in the WISER EU FP 7 project wwwwisereu Hering et al 2013 for phytoplankton macrophytes benthic invertebrates and fish and assess their strengths and sensitivities to the main pressures as well as their main sources of variability Many of the metrics have been developed to reflect the impact of nutrient pressures eutrophication In addition metrics have been developed to address the impacts of hydromorphological pressures on macrophytes and benthic invertebratesDetails on the development and uncertainty of each of these metrics are given in the other papers in this special issue eg Carvalho et al 2012 Phillips et al 2012 Dudley et al 2012 Mjelde et al 2012 Argillier et al 2012 Clarke 2012 or are published elsewhere eg Kolada et al 2011 Böhmer et al 2011 Sandin Solimini 2012 Pilotto et al 2011 Miler et al 2012 Emmrich et al 2011 2012a b

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