Harmonisation of H/G and G/M boundaries for phytoplankton composition in Central Baltic Atlantic Lake GIG
Status: draft for CIS Working Group A
1 Introduction
According the Water Framework Directive (WFD) phytoplankton composition is one of the parameters to be assessed for the quality element phytoplankton. The algal community is affected by typology factors (e.g. alkalinity, depth), but also to temperature (seasonal succession), sedimentation characteristics and grazing by zooplankton. Importantly, the composition is also expected to be sensitive for eutrophication i.e. changing nutrient concentrations and light conditions. This is from WFD point of view of interest because these parameters are important indicators for human pressure.
A shift in phytoplankton composition to light competitors (e.g. cyanobacteria) can be expected when eutrophication increases. Especially filamentous cyanobacteria are notorious to dominate in hypertrophic conditions and can be harmful for the environment. In all Member States’ composition metrics representatives of the cyanobacteria are a component in the assessment of the composition. Some cyanobacteria, however, can be characteristic for natural conditions. The EU project ‘REBECCA’ has proposed to use the indicator proportion of cyanobacteria (biovolume basis), but excluding the Chroococcales, except Microcystis sp. This way of selection of taxa improves the description of reference conditions, and focus on the species groups indicating pressure. Other European legislation has also paid attention to cyanobacteria (see DIRECTIVE 2006/7/EC concerning the management of bathing water quality). A clear numerical limit on the density or relative abundance is however not provided. Here we expect a clear synergy for lakes listed as bathing water, because cyanobacterial blooms as mentioned in the Bathing Water Directive are not likely to occur in Good or High Ecological Status.
Tough cyanobacteria play an important role in most assessment methods, several Member States have not focused only on cyanobacteria. Some Member States use also algal groups that indicate low pressure, or have defined blooms of representatives of green algae as indicative for pressure. In this report all Member States methods available are described (see chapter 2), compared, tested and where applicable harmonized (see chapter 3).
2 Classification systems of Member States
2.1 Belgium (BE)
Sampling
Phytoplankton is sampled monthly during the growing season (May-October).
Assessment
The proportion of cyanobacteria in the total phytoplankton biomass is used as an indicator of ecological quality. This proportion is calculated over the growing season, May-October. The average amount of Chlorophyll-a, also calculated over the growing season, determines if all cyanobacteria are taken into account, or with the exclusion of other Chroococcales than Microcystis. The relevant Chlorophyll-a-values are different for the three lake types and equal the G/M boundaries for this parameter (Table 1).
Table 1 Chlorophyll-a-boundaries for the evaluation of cyanobacterial contribution.
Lake type / All cyanobacteria / All cyanobacteria - Chroococcales + MicrocystisL-CB1 / Chla 10 µg/l / Chla < 10 µg/l
L-CB2 / Chla 25 µg/l / Chla < 25 µg/l
L-CB3 / Chla 10 µg/l / Chla < 10 µg/l
Reference and boundary setting
An analyses of Flemish lakes revealed that the proportion of cyanobacteria to total phytoplankton biovolume is less than 2% if macrophyte cover is high (> 75%). Therefore,
the average proportion of cyanobacteria (i.e. –Chroococcales + Microcystis in May-October) in the reference state was set to 2.5%. Class boundaries were chosen more or less arbitrary. The G/M boundary is 10% for all lake types (Table 2).
Table 2 Class boundaries of cyanobacterial relative contribution to phytoplankton biomass.
Reference / H/G / G/M / M/P / P/BBoundary / 2.5% / 5% / 10% / 25% / 50%
EQR / 1.00 / 0.80 / 0.60 / 0.40 / 0.20
2.2 Estonia (EE)
Sampling
In the Estonian lakes the phytoplankton is surveyed each year. The frequency of sampling has increased since 2006, from two times a year to four times a year (Table 3). The abundance of phytoplankton is expressed in terms of biovolume.
Table 3 The Estonian approach of phytoplankton monitoring.
Item / Old program / Program since 2006, since 2007 surveillance monitoringLong term frequency / Each year / Each year
Frequency per year / May, July / May, July, August, September
Sampling / Depending on stratification 2-3 samples (epilimnion 0.5 m, mid metalimnion, hypolimnion) from the deepest point. If lake has curved shoreline, then from different parts from the lake / Depending on stratification 2-3 samples (epilimnion 0.5 m, mid metalimnion, hypolimnion) from the deepest point. If lake has curved shoreline, then from different parts from the lake
Sampling methods / Van Dorn sampler (for counting) and Apstein net (for adjustment of species list) / Van Dorn sampler (for counting) and Apstein net (for adjustment of species list)
Level of identification / Species level if possible, but also large taxa are used (class, order) as indicators / Species level if possible, but also large taxa are used (class, family) as indicators
Calculation of biomass / Utermöhl’s technique, Nordic guidance of calculations / Utermöhl’s technique, Nordic guidance of calculations
Assessment
The Estonian method is a multimetric method that uses four parameters to assess the ecological quality of the phytoplankton:
1. Chla (this one is excluded in the data delivered for the Option 3 intercalibration of taxonomic composition).
2. Evenness. Modified Pielou index is used. The range of values is between 0-1. The scale is divided equally into five classes in each lake type. The basis of that index is the idea that the abundance of species is equally distriubuted in climax communities. A climax community has a high ecological quality. In fact equation is calculated from Shannon’s diversity (H). Another component of the equation is theoretical diversity (Hmax). The latter is calculated if considered that the abundance (or biomass) is equally divided with concrete number of species in smaple. Equation: J = H/Hmax. The higher value, the better ecological quality.
3. Nygaard’s modified compound quotient (PCQ)
The modified Nygaard’s (1949) phytoplankton compound quotient is used to characterize the ecological status of the lake. PCQ gives a quite good estimation of the lakes’ ecological condition, although algal groups in formula may contain species with different preferences. Ott & Laugaste (1996) added to the original formula two extra taxa: Cryptophyta to the numerator and Chrysophyceae to the denominator. This modified index gives a more precise assessment of the Estonian lakes, because the abundance of Desmidiales, the only taxon originally used in the denominator, has dramatically declined during the past decades both in open water as in the littoral zone (Kangro et al. 2005).
PCQ, modified by Ott & Laugaste (1996):
4. Description of the community:
There are four possible categories.
1. Abundance of species is more or less equall it is impossible to determine dominants
2. 3-5 species dominate in abundance (>80%)
3. 1 species dominates in abundance (>80%)
4. Prevailing genera by abundance are Microcystis, Apahnizomenon, Radiocystis, Planktothrix, Limnothrix, Woronichinia, Anabaena or alga from order chlorococcales. The content of Chla is > 20 mg/m3.
Since we did not have data on abundance we use biomass instead.
The final score is summarized using principle of equal weight of used parameters. Each quality class has own score (h –1; g- 2 etc.). Arithmetical avg gives hint to final score which is achieved by rounding off. The national EQR values are therefore discontinuous and are defined as H/G=0.8, G/M=0.6, M/P=0.4, P/B=0.2.
Reference and boundary setting
In Estonia reference sites occur for the L-CB1 type and L-CB3 type of lakes. At the moment Estonia does not have a reference site for the L-CB2 type of lakes, but is still looking for one. In 2007 three potential reference lakes will be surveyed. Reference values are inferred from:
1. Historical data (most of the older data goes back to the 1950s, few data to the 1920s);
2. Paleolimnological investigations (Alliksaar, T. et al. 2005; Nõges, T. et al. 2006; Heinsalu, A. et al.);
3. Principles described in the Water Framework Directive;
4. Expert opinion.
Reference values of the phytoplankton composition parameter were derived as follows:
Evenness: Values range between 0-1. 1 is theoretical maximum and therefore also the reference value in all types.
Compound quotient: Of almost all lakes historical data are avialable. These provide knowledge about the historical background. Reference values are different in lake types (L-CB1 - 2.5; L-CB2: - 2). Frequency diagrams of reference sites are also used to set reference values.
Description of community: The parameter was elaborated during the Ecoframe project in which Estonia participated (Moss et al. 2003). Reference description of the community matches to the description in WFD. This parameter does not give any numerical value.
The four possible categories (see above) are evaluated as follows: Categorie 1 corresponds to H and G classes, categorie 2 to M, 3 to P and 4 to B in all lake types.
References
Alliksaar, T., Heinsalu, A., Saarse, L., Salujõe, J., Veski, S. 2005. A 700-year decadal scale record of lake response to catchment land use from annually laminated lake sediments in southern Estonia. Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie 29(1), 457-460.
Heinsalu, A., Luup, H., Alliksaar, T., Nõges, P. & T. Nõges. Can the ratio of planktonic to periphytic diatoms in the sediment indicate water level changes in a large shallow lake? Hydrobiogia (submitted).
Moss, B.; Steohen, D.; Alvarez, C.; Becares, E.; VandeBund, W.; Collings, S. E.; VanDonk, E.; DeEyto, E.; Feldmann, T.; FernindezAliez, C.; FernindezAliez, M.; Frankeng, R. J. M.; GarckaCriado, F.; Gross, E.; Gyllström, M.; Hansson, L.–A.; Irvine, K.; Järvalt, A.; Jenssen, J.–P.; Jeppesen, E.; Kairesalo, T.; Kornijow, R.; Krause, T.; Künnap, H.; Laas, A.; Lill, E.; Lorents, B.; Luup, H.; Miracle, M. R.; Nõges, P.; Nõges, T.; Nykänen, M.; Ott, I.; Peczula, W.; Peeters, E. T. H. M.; Phillips, G.; Romo, S.; Russell, V.; Salujõe, J.; Scheffer, M.; Siewertsen, K.; Smal, H.; Tesch, C.; Timm, H.; Tuvikene, L.; Tõnno, I.; Virro, T.; Wilson, D. (2003). The determination of ecological quality in shallow lakes – a tested system (ECOFRAME) for implementation of the European Water Framework Directive. Aquatic Conservation. Aquatic Conservation-Marine and Freshwater Ecosystems, 13, 507 - 549.
Nõges, T., Heinsalu, A., Alliksaar, T. and P. Nõges. 2006. Paleolimnological assessment of eutrophication history of large transboundary Lake Peipsi, Estonia/Russia. Verh. Internat. Verein. Limnol. 29: 1135-1138.
Nygaard, G. 1949. Hydrobiological studies on some Danish ponds and lakes II. The
quotient hypothesis on some new or little known phytoplankton organisms. Det Kongelige Danske Videnskabernes Selskab 7: 293 pp.
2.3 France (FR)
Sampling and analyses
In each annual cycle sampling is carried out three times during the following periods:
- a first period in spring when the thermocline is setting up;
- a second period when the thermocline is well established during summer,
- a third period at the end of the summer stratification, before the temperature drops and stratification disappears.
Phytoplankton is sampled using a Nansen type net with a mesh size of 10 µm and an opening of 30 to 40 cm. Two kinds of samples are taken:
- one sample taken from the bottom to the surface;
- one sample taken horizontally by pulling the net 1 to 2 m below the water surface on a 100 m length.
Each sample is stored in a 100 to 250ml bottle and preserved with lugol.
Samples are analysed microscopically. Of each sample around 100 individuals are identified at magnifications of 200× and 600×.
Assessment
The French phytoplankton index (Ipl) is calculated for each sampling period by the following formula:
Index = ∑Qi*Aj
In this formula, Qi is a weighting factor for the different algae groups (table 4) and Aj indicates the relative abundance of the groups (Table 5). For each lake year a final index is calculated as the arithmetic mean of the three indices of each sampling period.
Table 4 Group specific weighing factors (Qi). Table 5 Classification of relative abundances (Aj).
Relative abundance (%) / Aj / Algae groups / Qi0 to ≤ 10 / 0 / Desmidiaceae / 1
10 to ≤ 30 / 1 / Diatomeae / 3
30 to ≤ 50 / 2 / Chrysophyceae / 5
50 to ≤ 70 / 3 / Dinophyceae and Cryptophyceae / 9
70 to ≤ 90 / 4 / Chlorophyceae (except Desmidieae) / 12
90 to ≤ 100 / 5 / Cyanophyceae / 16
Euglenophyceae / 20
Reference and boundary setting
No information available.
2.4 Germany (DE)
Sampling and analyses
The German assessment procedure includes and requires a fixing of standardized methods for sampling, preservation and storage, and microscopic analysis.
For the assessment six samples per year are needed from epilimnion or euphotic zone (clear water lakes, of which four samples must be taken in the period May-September. To determine indicator species additional diatom preparation is recommended.
Assessment
The German assessment method is a multi-metric tool using total biovolume, biovolume contribution of algal classes and the biovolume contribution of indicator taxa. There are separate metrics for the L-CB types. The method is based on Nixdorf et al. 2005a and b, modified after actual tests and intercalibration exercises.
The multi-metric consists of the following components:
1. Total biomass: this is composed of
a) The total biovolume of phytoplankton in the epilimnic or euphotic zone of the lake (arithmetic mean in the vegetation period from April to October of at least four samples; six samples per year are recommended for future investigations;
b) Chlorophyll-a concentration (arithmetic mean in the vegetation period from April to October;
c) Maximum Chlorophyll-a value if the number of covered months is greater than 2 and the deviation from the mean is more than 25%.
2. Algal classes: the biovolume or its percentage of total biovolume in specific annual periods (e.g. mean values of cyanophytes, dinophytes and of chlorophytes from July to October; mean value from chrysophytes from April to October);
3. PTSI (Phytoplankton Taxa Lake Index): this index evaluates the species composition based on lake-type specific lists of indicator species (332 different species) and their special trophic scores and weighting factors. The method works in two steps: 1) trophic assignment results in a PTSI index per sample or lake year; 2) assessment by comparing current trophic state with the lake type specific trophic reference status