Defining Chlorophyll-a Reference Conditions in European Lakes

Abstract

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets.

Which factors affect phytoplankton biomass in shallow eutrophic lakes?

“…The high percentage of natural land use is one of the most important criteria to be considered in the selection of reference lakes in Europe (Poikāne et al, 2010). Surprisingly, our findings suggest that the type of land use is not an important driver of productivity of shallow lakes' phytoplankton.…”

Comparing aspirations: intercalibration of ecological status concepts across European lakes for littoral diatoms

“…This means not only that we have harmonised status class boundaries between participating countries for lake phytobenthos but that boundaries set for lake phytobenthos should be compatible with those of other BQEs in lakes and comparable with boundaries set for other BQEs in other water body types, all of which have been subject to the same procedures (Bennett et al, 2011;Birk et al, 2012;Poikane et al, 2010). The good/moderate boundary for a lake in the west of Ireland should, in theory at least, represent a similar level of ambition to the good/moderate boundary set for marine invertebrates in benthic habitats off the coast of Cyprus.…”

Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

“…Metrics for phytoplankton biomass are relatively standardised using chlorophyll a or total biovolume (Poikane et al, 2011) and reference conditions and status class boundaries had already been widely agreed for chlorophyll for European lakes (e.g. Carvalho et al,2008;Poikane et al, 2010;Wolfram et al, 2009). The other two features, outlined in the next sections, required further specific developments for the WFD, as highlighted in Birk et al (2012) & Poikane et al (2011).…”

“…More recently, reference-based classification schemes for chl-a have been developed in individual Member States specifically for the WFD (e.g. Carvalho et al, 2008;Søndergaard et al 2005;Wolfram et al, 2009) and chl-a standards have been successfully compared between European member states in an "Intercalibration" (IC) process to ensure that standardised quality classes exist in specific lake types across several geographical regions of Europe (EC, 2008;Poikane et al, 2010). For this reason the WISER project did not re-visit assessment schemes for phytoplankton biovolume or chl-a.…”