Clorofila

Freshwater Biology (2011)

doi:10.1111/j.1365-2427.2011.02588.x

APPLIED ISSUES

Determining algal assemblages in oligotrophic lakes and streams: comparing information from newly developed pigment/chlorophyll a ratios with direct microscopy
¨ T. L. LAURIDSEN*, L. SCHLUTER† AND L. S. JOHANSSON* *National Environmental Research institute, Aarhus University, Silkeborg, Denmark † Centre forEnvironment and Toxicology, DHI, Hørsholm, Denmark

SUMMARY 1. Pigment analyses by high performance liquid chromatography (HPLC) are commonly used for determining algal groups in marine and estuarine areas but are underdeveloped in freshwaters. In this study, 15 characteristic pelagic algal species (representing five algal groups) of oligo- ⁄ mesotrophic lakes were cultured and pigment ⁄ Chl aratios determined at three light intensities. 2. With the exception of cyanophytes, light treatment had little effect on pigment ⁄ Chl a ratios. This justifies the use of the same pigment ⁄ Chl a ratios during seasonal studies where light conditions may change. 3. The determined pigment ⁄ Chl a ratios were tested on seasonal samples from five oligo- ⁄ mesotrophic lakes and three streams using CHEMTAXsoftware. Pigment ratios of both pelagic and benthic algal communities from the lakes and streams were analysed to determine whether the pelagic algae-based ratios can be used for benthic algal communities. 4. HPLC combined with CHEMTAX was useful for identifying freshwater phytoplankton classes and for quantifying the abundance of phytoplankton groups. However, although correlations weresignificant for six of seven phytoplankton classes studied, they were weak and varied with season. 5. HPLC was valid for quantifying benthic diatom groups in stream samples, whereas for lakes more benthic algal groups were recorded with HPLC than with microscopy and correlations between the two methods were not significant. 6. The use of both HPLC and microscopy is recommended as a cost-efficient methodfor analysing many samples. It is crucial, however, that the CHEMTAX software is calibrated with the correct information, and the user is aware of the limitations.
Keywords: benthic algae, CHEMTAX, microscopy, phytoplankton, Water Framework Directive

Introduction
The composition and biomass of algae in marine and freshwaters are traditionally determined by microscopy. During the last twodecades, efforts have been
Correspondence: T. L. Lauridsen, National Environmental Research institute, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark. E-mail: tll@dmu.dk Ó 2011 Blackwell Publishing Ltd

made to develop more cost-efficient measures. One of the most promising is a chemotaxonomic method involving analysis of the pigment content of phytoplankton, using high performance liquidchromatography (HPLC), to determine the phytoplankton group composition (Jeffrey, Mantoura & Wright, 1997). This method, used in marine and coastal areas (e.g. Andersen et al., 1996; Schluter et al., 2000; Havskum ¨ et al., 2004), allows determination of even picosized
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T. L. Lauridsen et al.
freshwater pigment ⁄ Chl a ratios are also suitable for quantifying benthic groups in streams.The primary aims of this project were to: (i) develop pigment ⁄ Chl a ratios for phytoplankton species typical of oligo- ⁄ mesotrophic lakes, (ii) document the use of such ratios to classify lakes and (iii) validate pigment ratios with microscopy. A secondary aim was to investigate whether the pigment ⁄ Chl a ratios developed here could be used for identifying and quantifying benthic algal groupsof both streams and lakes. Consequently, this study included two stages: (i) cultures of specific freshwater algae were grown in the laboratory to determine the pigment ⁄ Chl a ratios and to estimate the role of light conditions for the pigment ⁄ Chl a ratios, and (ii) the pigment ratios were tested using the CHEMTAX program to calculate the biomass as Chl a of phytoplankton groups from five...