Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe

Carvalho, Laurence; Solimini, Angelo G.; Phillips, Geoff; Pietilainen, Olli-Pekka; Moe, Jannicke; Cardoso, Ana Cristina; Solheim, Anne Lyche; Ott, Ingmar; Sondergaard, Martin; Tartari, Gianni; Rekolainen, Seppo. 2009 Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe. Hydrobiologia, 633 (1). 59-66.

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The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline, or ‘reference condition’. This paper describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area, and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity, and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Water > WA Topic 3 - Science for Water Management > WA - 3.4 - Develop novel and improved methods to enable the sustainable management of freshwaters and wetlands
CEH Topics & Objectives 2009 - 2012 > Water > WA Topic 2 - Ecohydrological Processes > WA - 2.3 - Assess the responses of river, lake and wetland ecosystems to ecohydrological drivers
UKCEH and CEH Sections/Science Areas: Watt
ISSN: 0018-8158
Additional Information. Not used in RCUK Gateway to Research.: The original publication is available at
Additional Keywords: lake, chlorophyll, WFD, Water Framework Directive, phytoplankton
NORA Subject Terms: Ecology and Environment
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Date made live: 20 Oct 2009 09:47 +0 (UTC)

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