Design of our EQAT scheme

The EQAT design is focused on the application of the Utermöhl method using the inverted microscope and consists of three components. Components 1 and 2 are methodological, focussing on the enumeration and biovolume calculation and component 3 is taxonomic in nature.

Components

The 3 components aim to separately test all the skills required for a high quality phytoplankton analysis.

Component 1

This is a plankton counting chamber as used in the work process on the inverted microscope. The EQAT team determines a number and diameter of micro particles (filled circles) for each survey. These micro particles are applied to the bottom glass of a plankton counting chamber. Given a defined sedimentation volume, target values can thus be specified for the particle concentration to be calculated. In addition, the distribution of the microstructures on the bottom glass is simulated by a statistical procedure corresponding to a natural distribution pattern in the sedimentation of algae (Poisson distribution). This approach makes it possible to replicate a natural sedimentation pattern for an algae suspension of defined concentration. The participants are thus able to check the calibration of the respective fields of view at different magnifications as well as the calculation procedures for the cell concentration. This component is free of uncertainties related to the detection and determination of phytoplankton. In this way, systematic errors can be identified. This so-called reference counting chamber remains with the participant of the EQAT scheme and can be used for internal quality assurance when required.

Test parameters and value range:

• Concentration of the reference points in particles/litre (assuming a predefined sedimentation volume) in a range from 1,000 to 50,000,000 particles/L. Decimal places here are 0. The specific measurement uncertainty here is usually between 10-20%.
• Diameter in µm (in a range of 5-100 µm). Decimal places here are 2 or 1. The specific measurement uncertainty here is usually between 5-10%.
• Volume concentration of the reference points in mm³/L (assuming a predefined sedimentation volume) in a range from 0.001 to 100 mm³/L. Decimal places here are 3 or 2. The specific measurement uncertainty here is usually between 20-40%.

Capabilities to be tested:

• Counting of defined partial areas of the reference counting chamber
• Measurement of reference counting points
• Calculation of the particle-, and the volume concentration
• Calibration of the microscopic system

Advantage over component 2:

• Result independent of human action

Component 2

In this component, either a natural phytoplankton sample or a sample prepared from algal cultures is produced. The aim here is to provide a phytoplankton sample that can be processed with comparatively little effort and is free of interfering seston. In addition to the determination of the phytoplankton concentration according to DIN EN 15204: 2006, the calculation of the algal biovolume as a biomass parameter according to DIN EN 16695: 2015 is also required here. The focus here is in particular on the practical processing of the samples including homogenisation and sedimentation but also the selection of suitable counting strategies for the individual species as well as the selection of suitable formulas for calculating the cell volume.

Test parameters and value range:

• Cell concentration of the algae in cells/litre in a range from 1,000 to 50,000,000 cells/L. Decimal places here are 0. The specific measurement uncertainty here is usually between 40-90%.
• Biovolume concentration of different algae taxa in a range from 0.001 to 100 mm³/L. Decimal places here are 3 or 2. The specific measurement uncertainty here is usually between 80-120%.

Capabilities to be tested:

• Counting of defined partial areas of the counting chamber (counting strategy)
• Measurement of different algae taxa and calculation of cell volume (selection of suitable volume formulae)
• Calculation procedure for cell concentration and biovolume concentration

Component 3

This component, on the other hand, focuses exclusively on the taxonomic determination of algae and is thus free of methodological influences. Here, 10 video clips of planktonic algae are produced by the LTV, which are to be taxonomically determined by the participants down to the prescribed determination level. Both the preferred identification and the required identification level are determined in cooperation with taxonomic specialists. In addition to testing species knowledge, the focus is also on the use of taxonomic literature for the identification of unknown species.

Test variables and range of values:

• Taxonomic determination of planktonic algae according to the required level of determination (variety, species, genus, order or class)

Skills to be tested:

• Individual species knowledge (experience)
• Use of the available taxonomic literature for species identification
• Knowledge of systematics and morphological variability of phytoplankton organisms