Limnologica34,236-248 (2004) ELSEVIER http://www.elsevier.de/limno HMNOLOGICA Type-specific and indicator taxa of phytoplankton as a quality criterion for assessing the ecological status of Finnish boreal lakes Liisa Lepist6 I,*, Anna-Liisa Holopainen 2, Heidi Vuoristo 1 Finnish Environment Institute, Helsinki, Finland 2 Karelian Research Institute, University of Joensuu and North Karelian Environment Centre, Joensuu, Finland Received: June 16, 2004 • Accepted:August 9, 2004 Abstract Key issues in the implementation of the Water Framework Directive are classification of lakes using biological quality parameters and type-specific reference conditions. This work is one of three studies considering different metrics of phytoplankton in the classification of ecological status. Phytoplankton was studied in a total of 55 Finnish boreal lakes, including 32 reference lakes. We tested the suitability of taxonomic composition and abundance of phytoplankton groups for biological classification. We also preliminarily determined the type-specific taxa for the studied lakes. The type-specific taxa for reference conditions are coincidently the indicator species/taxa for high ecological status. Interestingly, some taxa type-specific for impacted oligo-humic lakes proved to be the type-specific taxa for humic reference lakes. The pressure of human impact was observed not only as increase of biomass but also as changes in the species composition. The phytoplankton composition indicated the ecological status of impacted lakes moderately well. There was some variation in the indica- tions given by different algal groups, probably due to the preliminary class boundaries used. However, the preliminary combination of indicative parameters to estimate the ecological status of the studied impacted lakes was in general in accordance with earlier classification of water quality in Finnish lakes. Key words: Phytoplankton composition - type-specific taxa - indicator taxa - indicator pa- rameters - Water Framework Directive - ecological status Introduction structure (taxa, abundances and biomass) and function (response to the environmental conditions) of phyto- Phytoplankton is known to react sensitively to differ- plankton is important when assessing the links between ences in catchment-derived chemical characteristics phytoplankton and the environment. (RosEN 1981; ARVOLAet al. 1999). Indicator species for Diverse phytoplankton assemblages occur in natural different nutritional levels have been presented for olig- waters spatially and temporally (HUTCHINSON 1967; otrophic waters as well as for waters with increased an- HOLOPAINEN et al. 2003). This is based on the abundance thropogenic pollution (J~RNEFELT 1952; BRETTUM of a species as "inoculum" or on the ability of a species 1989). WmLgN (2000) pointed out that knowledge of the to increase at a greater rate than its competitors *Corresponding author: Liisa Lepist6, Finnish Environment Institute, RO. Box 140, FIN-O0251 Helsinki, Finland; Phone: +358 9 40300312, Fax: +358 9 40300390; e-mail address: [email protected] 0075-9511/04/34/03-236 $ 30.00/0 Limnologica (2004) 34,236-248 Type-specific and indicator taxa of phytoplankton 237 (REYNOLDS 1986). Phytoplankton assemblages may be Phytoplankton data designated by the name of one or more dominant species. However, according to HUTCHINSON (1967) Phytoplankton samples were collected from a depth of enumeration of rare, characteristic species can in some 0-2 metres, and preserved using acidic Lugol's solution. cases provide more information about the lake. When Simultaneously, samples for water chemistry were taken looking for type-specific taxa for different lake types, it from a depth of one metre. Phytoplankton biomass was is important to distinguish the indifferent taxa occurring estimated by microscopy using a Nordic variant of the in all lakes from the type-specific taxa, i.e. taxa observed Uterm6hl technique (UTE~MOHL 1958; OLRII~ et al. only in each lake type of reference or impacted condi- 1998), and phase-contrast illumination at x200 and tions. x 800-1200 magnifications by a trained group of investi- The taxonomic composition and abundance of phyto- gators. Cell counts were converted to biovolumes using plankton is one of the biological metrics in the norma- the cell volumes of the phytoplankton database of the tive definitions of ecological status classification in the Finnish Environment Institute. The analysis produced a Water Framework Directive, Annex 1.2 (European list with biovolumes of observed species/taxa, the Union 2000). biomass of different algal groups, and the total phyto- The aim of this study was to consider (i) whether the plankton biomass given as fresh weight, mg 1-1 (Tables 1 type-specific taxa for different ecological status of lakes, and 2). Chemical water quality was analysed according and (ii) the indicator taxa for high ecological status, i.e. to standard methods (NmMI et al. 2000). Of these phos- reference conditions, assumed by the Water Framework phorus and nitrogen concentrations, water colour, pH Directive can be determined. We also discuss (iii) how and chlorophyll a concentrations were used in this study anthropogenic impact manifested as eutrophication is (Tables 1 and 2). reflected as changes in phytoplankton assemblages and in type-specific taxa composition and (iv) how the per- Statistical analysis centage and the biomass of some algal groups determine the ecological status of the studied impacted lakes. To discriminate the reference lakes the correlations be- tween phytoplankton assemblages using the algal taxa biomass and water quality were examined by dedrended correspondence analysis (DCA) using the CANOCO Material and Methods computer program (TEe BRAAK 1987, 1990). Cumula- tive distribution function was used when setting the Characteristics of the study lakes class boundary between high and good ecological status We selected a total of 55 lakes for our study. These lakes for the type-specific indicator species in the studied lake belong to the national water-quality monitoring net- groups. work, and were sampled for phytoplankton and water chemistry in July 2002. The study lakes were mostly lo- Determination of type-specific and indicator taxa, cated in southern Finland, with some lakes in eastern and ecological status of impacted lakes and northern parts of the country (Fig. 1). The estimated mean depth of the lakes varied from 0.5 to 21 metres. The Water Framework Directive (European Union The area of the lakes (or main basins) varied from 0.04 2000) assumes nomination of type-specific taxa. Phyto- to 1040 km 2. plankton species/taxa were discriminated with the DCA- The complete set of lakes was divided in two parts: analysis. Taxa, which were observed only in a particular reference lakes with no or only very minor anthro- reference lake type, were nominated as type-specific pogenic alterations, and impacted lakes. In this study the taxa. Furthermore, cumulative distribution function was term "impacted" is used to refer to non-reference lakes used to select the 90 th percentile as a class boundary for reaching at best the ecological status of good. The divi- indicator species/taxa between high and good ecological sion was based mainly on expert judgment in the Finnish status. Furthermore, taxa, which were observed only in Environment Institute. A total of 32 reference lakes were impacted lakes of a particular type were nominated type- selected and phytoplankton assemblages in lake groups specific for impacted lakes. (Fig. 2) were compared to those of 23 impacted lakes The ecological quality ratio EQR (median value in the with typology characteristics corresponding rather reference lake group/observed value in impacted lakes) closely to those of the reference lake groups. of the biomass and the percentage of cyanobacteria and In this paper we use the appellations: diatoms were applied for preliminary determination of - "oligo-humic" for lakes with water colour < 60 mg 1-1 Pt; the ecological status of 23 impacted oligo-humic and - "humic" for lakes with water colour 60-120 mg 1-1 Pt; humic lakes. The ecological status was assessed on the - "dystrophic" for lakes with water colour > 120 mg 1-1 Pt. basis of the scale presented in the Refcond Guidance Limnologica (2004) 34,236-248 238 L. Lepist6 et al. ®47 I "° ) 0 O Impacted lakes @l ® Reference fakes ~ ~-~ 44 @ O 9 2O 0 o o-f @39 @46 55@ 03 15~737 @14 0 7 038 322~716 @40 34~ 50. ~,11 45 52~D "~28 ~9 24 51 ~29 ~ 025 @42 / ~2I 0 27 . Fig. 1. The observation sites in July 2002. Reference lakes (grey dots): 1 = Haukkajhrvi; 2 = Hormajhrvi; 3 = Pihlajavesi; 4 = An~tti; 5 = Unarinj~rvi; 6 = Valkea-Kotinen; 7 = Karjalan Pyh~j~rvi; 8 = Iso-Hietaj~irvi; 9 = Lika-Py6ree; 10 = Inarij~rvi; 11 = Iso-L6yt~ne; 12 -- Iso-Araj~rvi; 13 = Iso-Hanhij~rvi; 14 = Iso-Haukivesi; 15 = Iso-Helvetinj~rvi; 16 = Kallioj~rvi; 17 = Kattilaj~rvi; 18 = Kukkia; 19 = Kuolimo; 20 = Pielinen; 21 = Punelia; 22 = Puuj~rvi; 23 = P~ij~nne 78; 24 = Saimaa, Ilkonselk~; 25 = Saimaa, Riutanselk~; 26 = Siikaj~rvi; 27 = Sh~iksj~rvi; 28 = Vehkaj~rvi; 29 = Vuohij~rvi; 30 = Mallasvesi, 31 = Yli-Kitka; 32 = N~sij~rvi. Impacted lakes (black dots): 33 = Iso-Roine; 34 = Roine; 35 = Katumaj~rvi; 36 = Kernaalanj~rvi; 37 = Tarjannevesi; 38 = Kyr6sj~rvi; 39 = Lappaj~irvi; 40 = P~ij~nne 71; 41 = L~ngelm~ivesi; 42 = Haukk@irvi; 43 = M~yh~j~rvi; 44 = Ouluj~rvi; 45 = Houhaj~rvi; 46 = P-Kallavesi; 47 = Porttipahta; 48 = Vanajanselkh; 49 = Vanaja; 50 = Vesij~irvi; 51 = Pyh~ij~rvi 93; 52 = Pyh~j~rvi, Sorvanselk~; 53 = P~j~irvi; 54 = Rehtij~rvi; 55 = Toisvesi. Limnologica (2004) 34,236-248 Type-specific and indicator taxa of phytoplankt0n 239 nO r"h v ro 0 0 OOh m _C O_ .'.J 0 g o c.D 000 r0 "~ O0 pq 00 ~o~ ~:~.~, E ddddddddodddddd odddddoddd do~ d~5 do o 0 0 ~P'xl Or Pq ~0 O0 ~d f'q ~0 Pq 0 0 ~.~ ~- 0 p,4 ~_e'~ ,,D o~ 0 O0 "~" f'~ 00 ¢q ~ O0 ~O 0 0 U .~ E o = o U pq 0~~~0~0 oqq~oo~oqq .