Identification and quantification of phytoplankton groups in lakes using new pigment ratios – a comparison between pigment analysis by HPLC and microscopy

Abstract

1. Pigment analysis by high-performance liquid chromatography (HPLC) combined with data analysis using the CHEMTAX program has proven to be a fast and precise method for determining the abundance of phytoplankton groups in marine environments. To determine whether CHEMTAX is applicable also to freshwater phytoplankton, 20 different species of freshwater algae were cultured and their pigment/chlorophyll a (Chl a) ratios determined for exponential growth at three different light intensities and for stationary growth at one light intensity. 2. The different treatments had a relatively insignificant impact on the absolute values of the diagnostic pigment/Chl a ratios, with the exception of cyanobacteria and cryptophytes for which the zeaxanthin/Chl a and alloxanthin/Chl a ratios varied considerably. 3. The pigment ratios were tested on samples collected in six different eutrophic Danish lakes during two summer periods using the CHEMTAX program to calculate the biomass of the phytoplankton groups as Chl a. The CHEMTAX-derived seasonal changes in Chl a biomass corresponded well with the volume of the microscopically determined phytoplankton groups. More phytoplankton groups were detected by the pigment method than by the microscopic method. 4. Applying the pigment ratios developed in this study, the pigment method can be used to determine the abundance of the individual phytoplankton groups, which are useful as biological water quality indicators when determining the ecological status of freshwater lakes.

Variability of phytoplankton pigment ratios across aquatic environments

“…Woitke et al (1996) found a range of 0.35-0.63 and Schlu¨ter et al (2006) 0.39-0.72 in the FUCO:chl a ratio in diatom cultures, thus corresponding rather well to the ratio we calculated from our freshwater data (0.49-0.9). Apart from a light-induced 'fucoxanthin cycle', which seems to operate in some specific haptophyte species (Stolte et al, 2000;Rodrıguez et al, 2006), fucoxanthin is generally considered as a light-harvesting pigment.…”

“…Although the calculation procedure allows for adjustment of the ratios within a userdefined interval, these initial values can influence the final biomass estimates and may be critical in providing correct quantitative phytoplankton assessment. Typical ratios have been given in the literature from cultures of marine (Jeffrey et al, 1997) and, to a lesser extent, for freshwater algae (Nicklisch & Woitke, 1999;Schlu¨ter et al, 2006). A recent paper by Latasa (2007) described a method to reduce processing errors which may be related to wrong estimates of initial ratios: repeating CHEMTAX processing in successive runs, using the output from each run as the input for the next one, the pigment ratios generally adjust automatically towards the true value, improving initial pigment ratio values and, therefore, biomass estimates.…”

“…Fewer studies have demonstrated intra-class variations of pigment composition and cell content (Nicklisch & Woitke, 1999;Zapata et al, 2004;Muylaert et al, 2006 and references therein), which are potentially a problem for the assessment of phytoplankton biomass based on pigments, but can also help increase the discriminative power of the pigment method. The recent study by Schlu¨ter et al (2006), however, represents significant progress in defining adequate pigment ratios for the main freshwater phytoplankton classes by taking into account the light conditions. That study also considered intra-class variation of pigment content: for instance, large variation in pigment composition occurred among cyanobacteria species, as well in their in response to environmental factors.…”

Late-summer phytoplankton in western Lake Erie (Laurentian Great Lakes): bloom distributions, toxicity, and environmental influences

“…Because carotenoid:Chl a ratios within phytoplankton communities might be expected to vary depending upon species composition, cell physiological state, irradiance, etc., the data set was divided into annual and transect subsets, prior to independent CHEMTAX calculations (Mackey et al 1998;Schlüter et al 2000). CHEMTAX calculations are sensitive to the initial carotenoid:Chl a ratios identified for each group; as such, initial ratios were chosen from those previously derived for and/or applicable to Great Lakes phytoplankton Schlüter et al 2006). To further minimize error arising from ratio variation, data subsets were assessed independently using the initial ratio matrix and an additional 59 matrices generated randomly as the product of the initial values and a randomly determined factor (F):…”

Water Quality of Four Major Lakes in Mississippi, USA: Impacts on Human and Aquatic Ecosystem Health

“…ChemTax, a matrix factorization program, was used to calculate the relative abundances of major algal groups in the water samples from the HPLC photopigment data [52,53]. For ChemTax, an iterative scheme [54] was followed using the initial pigment ratios from published ratios [55,56]. The ChemTax analysis revealed the relative abundance of seven major algal groups including cyanobacteria, euglenophytes, chlorophytes, dinoflagellates, cryptophytes, diatoms and chrysophytes.…”