j 6661 91 0N e H d V I 9 0 N 0 N

MONOGRAPHS OF THE BOREAL ENVIRONMENT RESEARCH

16

Liisa Lepisto assemblages reflecting the ecological status of lakes in Finland

Yhteenveto: Kasviplanktonyhteisot Suomen jarvien ekologisen than kuvaajina

FINNISH ENVIRONMENT INSTITUTE, FINLAND Helsinki 1999 ISSN 1239-1875 ISBN 952-11-0576-3 Tammer-Paino Oy Tampere 1999 Contents

Summarised publications and author’s contribution

Abstract . 7

1 Introduction 8

1.1 Phytoplankton 8 1.2 Terminology 8 1.2.1 8 1.2.2 Classification of phytoplankton 10 1.2.3 Water blooms and 10 1.2.4. Ecological status 10 1.3 Lakes 11 1.4 Aims of the study 12

2 Materials and methods 12

3 Phytoplankton in different types of lakes 13

3.1 Long-term eutrophication of a shallow lake 13 3.2 Effects of forest fertilization on a brown-water lake 15 3.3 Development of the trophic degree in two man-made lakes 16 3.3.1 The Lokka reservoir 16 3.3.2 The Porttipahta reservoir 17 3.4 Problems caused by increased phytoplankton 18 3.5 Phytoplankton as an indicator of the status of lakes in Finland 18 3.5.1 General 18 3.5.2 Oligotrophic lakes 19 3.5.3 Acidic lakes 24 3.5.4 Dystrophic lakes 25 3.5.5 Mesotrophic lakes 26 3.5.6 Eutrophic lakes 26 3.5.7 Hyper-eutrophic lakes 27

4 Problems in the analysis of phytoplankton 28

4.1 Sampling 28 4.2 Analyses 28 4.3 Lake groups 29 4.4 The importance of tradition 29

5 Summary 29

6 Yhteenveto 32 nuaiiuwaeuguiiiwiis 35

References 35

Appendix 1 41

Phytoplankton assemblages reflecting the ecological status of lakes in Finland 5

Summarised publications and the author’s contribution

This thesis is based on the following papers, which are referred to in the text by their Roman numerals I-Vu:

I Lepisto, L., Räike, A. & PietilSinen, 0.-P. 1999. Long-term changes of phytoplankton in a eutrophicated boreal lake during the past one hundred years (1893—1998). Algological Studies 94: 223—244.

II Lepistö, L. & Saura, M. 1998. Effects of forest fertilization on phytoplankton in a boreal brown- water lake. Boreal Environment Research 3: 33—43.

III Lepisto, L. 1995. Phytoplankton succession from 1968 to 1990 in the subarctic Lokka reservoir. Publications of the Water and Environment Research Institute 19: 1—42.

IV Lepisto, L. & Pietiläinen, 0.-P. 1996. Development of water quality and phytoplankton communi ties in two subarctic reservoirs and one regulated lake. In: K. V. Rao (ed.). Proceedings of international conference on aspects of conflicts in reservoir development & management. Dep. Civil Engineering, City University, London, UK. 553—566.

V Lepisto, L., Antikainen, S. & Kivinen, J. 1994. The occurrence of Gonyostomum semen (Ehr.) Diesing in Finnish lakes. Hydrobiologia 273: 1—8.

VI Lepisto, L., Lahti, K., Niemi, J. & Fardig, M. 1994. Removal of and other phytoplankton in four Finnish waterworks. Algological Studies 75: 167—181.

VII Lepisto, L. & Rosenström, U. 1998. The most typical phytoplankton taxa in four types of boreal lakes. Hydrobiologia 369/370: 89—97

• Liisa Lepisto has since 1965 participated in the microscopy work of phytoplankton from the monitored lakes in Finland and is responsible for the phytoplankton data in papers I—Vu. • In paper I L. Lepistö was responsible for planning of the examination, for examination of the unpub lished data, and for processing the phytoplankton data. All authors took part in the physico-chemical data processing, interpretation of results and writing in their own area of expertise. • In paper II the examination was planned and the data processed together with Matti Saura. Phytoplankton was analysed by L. Lepisto. Both authors (L. Lepisto and M. Saura) were responsible for the interpretation and writing of results, L. Lepisto having the main responsibility. • L. Lepistd initiated the treating of data and interpretation of results for paper IV, 0.-P. Pietiläinen participated in the writing. L. Lepiste had the main responsibility. • L. Lepisto and S. Antikainen participated in the planning of the study (V) and in the interpretation and writing of results. S. Antikainen was mainly responsible for data processing. J. Kivinen commented on the manuscript. L. Lepisto had the main responsibility. • In paper VI the examination was planned together with Dr. Kirsti Lahti who was responsible for the toxicity studies and the data from the water works. L. Lepistd examined the phytoplankton samples. All authors took part in data processing, interpretation of results and writing in their own area of expertise. • L. Lepisto planned the examination in paper VII, U. Rosenström treated the data and both authors participated in the interpretation of results and writing, L. Lepisto having the main responsibility.

Phytoplankton assemblages reflecting the ecological status of lakes in Finland 7

Phytoplankton assemblages reflecting the ecological status of lakes in Finland

Liisa Lepisto

Finnish Environment Institute, P.O. Box 140, FIN-0025 1 Helsinki, Finland

Lepistö, L. 1999. Phytoplankton assemblages reflecting the ecological status of lakes in Finland. Monographs of the Boreal Environment Research No. 16, 1999.

ABSTRACT

A review is presented of studies on phytoplankton reflecting the ecological status of natural and man- made lakes in Finland. Attention is paid to phytoplankton quantity and quality in different lake types, and to changes in phytoplankton assemblages caused by human activities, particularly waste water loads and construction of man-made lakes. The response of phytoplankton in Lake Tuusulanjärvi to eutrophication during the twentieth century and to changes in water quality caused by water protection efforts since the late 1970s was investigated as a case study. Reduc tion in the nutrient load in 1979 changed the phytoplankton assemblage, as the non-N2- fixing cyanophytes were replaced by N2- fixing cyanophytes. The total biomass decreased, and some species indicating more oligotrophic conditions reappeared. The possible response of phyto plankton to the fertilization of the catchment area of a humic forest lake with NP-fertilizers was considered. Only in the subsequent spring was an increase in phytoplankton biomass observed. No other biomass maxima were observed in the lake until five years later, when Gonyostomum semen became abundant. After the construction of man-made lakes the phytoplankton develops via several stages; the original river plankton, such as pennate , is succeeded by centric diatoms, especially during periods of strong water level regulation. Phytoplankton quantity re flected the water quality of the reservoirs. In the meso-eutrophic Lokka reservoir, cyanophytes became abundant, especially during warm weather conditions. The feasibility of phytoplankton monitoring as an indicator of the ecological status of lakes, identification problems of phyto plankton and the need for a methodological tradition are considered. The correct identification of phytoplankton is the basis of all phytoplankton assemblage studies. Species diversity, which is an important indicator of water quality, is gravely influenced by methodological problems in phyto plankton analysis.

Key words: Phytoplankton, eutrophication, trophic status, ecological status, lakes, artificial lakes 8 Lepisto Monographs of the Boreal Environment Research No. 16

1 Introduction water body in low densities, it seldom receives at tention. However, when eutrophication manifests 1.1 Phytoplankton itself as an increase in biological productivity, phytoplankton becomes more visible. As a result Studies on phytoplankton assemblages of lakes in of the process of eutrophication several negative Finland were initiated in the late I 890s by Kaarlo impacts, such as an increase of injurious phyto Levander (1900). In the early 1910s, Heikki plankton species, taste and odour problems and Järnefelt (e.g. 1932, 1934, 1956a) started his fun prolonged water blooms are observed (Reynolds damental studies on phytoplankton, covering and Waisby 1975, Paerl 1988). lakes from southern Finland as far north as Lap- The dynamics of seasonal succession of phyto land. He classified the trophic status of lakes ac plankton in oligotrophic lakes generally differ cording to their phytoplankton assemblages from those in eutrophic lakes and the phytoplank (Jarnefelt 1952, 1956a). On the basis of ton is often characterised by typical spring, sum Jarnefelt’ s studies, the monitoring of water bodies mer and autumn assemblages (e.g. Hutchinson in Finland was started by the water authorities in 1967, Ilmavirta 1980, Heinonen 1982, Rott 1984, the early 1960s. The first monitoring network Trifonova 1986, 1993, Willén 1987, l992a, covered 150 lakes (Heinonen 1980). In addition Eloranta 1995). In addition to the seasonal vari to the monitoring data of water authorities, sev ability there are usually also marked interannual eral authors have published phytoplankton data variations in the abundance of phytoplankton. from Finnish lakes. For example, Ilmavirta (1980, The species assemblage from year to year has no 1983), Arvola (1983, 1984) and Salonen et at. exact timing, and hence the occurrence of indi (1984) studied humic lakes and focused on the in vidual species may vary widely so that the dom fluence of water colour on phytoplankton assem inant species at any given successional stage blages. Eloranta (1976, 1986, 1995) examined the will not always be the same. Seasonally the mean phytoplankton of lakes in central and southern population densities may vary within 6-9 orders Finland, including lakes situated in the national of magnitude (Reynolds 1986). parks which could be regarded as reference lakes The composition of a phytoplankton assem for monitoring. Ilmavirta et at. (1984) studied the blage (Fig. 1) does not depend only on nutrients phytoplankton of 151 lakes in eastern Finland but also on physical (e.g. temperature, illumin during the summer stratification. Spatial and sea ation, turbulence and vertical stratification) or sonal variations of phytoplankton of the oligo chemical factors (e.g. vitamins and antibiotics) trophic Lake Paajarvi, Lammi, southern Finland, and on biological factors, such as specific growth was studied by Ilmavirta and Kotimaa (1974). and loss rates among the algae, parasitism, pred The quantity and quality of phytoplankton of ation and competition (OhIe 1955, Hutchinson Lake Pyhajarvi, Sakyla, SW- Finland was briefly 1967, Harris 1986, Reynolds 1986, Sommer discussed by Sarvala and Jumppanen (1988) and 1989). These factors should be taken into account of Lake Ala-Kitka, NE-Finland by Kankaala et at. when considering the reasons for fluctuation of (1990). The horizontal distribution of phyto phytoplankton (Jacobsen and Simonsen 1993), plankton and relationships between phytoplank and due to their complex interactions and rapid ton, and water quality of Lake Sai changes no absolute standards for biological qual maa were examined by Holopainen et at. (1993) ity can be set (Commission of the European Com and Karjalainen et at. (1996). Furthermore, the munities 1999). influence of a sulphite cellulose factory on phyto plankton of Lake Keurusselkä was studied by Eloranta (1972, 1974), and Granberg (1973) stud 1.2 Terminology ied the influence of paper mill waste waters on phytoplankton in Lake Päijanne. 1.2.1 Plankton Lake ecosystems, with their specific chemical compositions and geographical locations are of “Plankton” as a term includes all of ten characterised by their own phytoplankton as microscopical size which float freely and invol semblages, referred to as plankton formations untarily in open water independently of shores (Teiling 1916). When phytoplankton occurs in a and bottom, as demonstrated by Hensen (1887). Phytoplankton assemblages reflecting the ecological status of lakes in Finland 9

10 —1 mg L

8

6 ©

Lu Cu Cu E 0 4 0

2 LI’ --‘,i, ,‘ k-c.

0

A cidic Oligotr. Dystr. Mesotr. E utr.

Lake types

Cyan. Crypt. Dinop. [lChrys. LiDiat. E]Chlor. Liothers

Fig. 1 The composition and quantity (wet weight mg L1) of phytoplankton (June — August) in different lake types (not hyper-eutrophic) with some typical taxa in 1981—1997 (VII, database of FEI). Cyan. = cyanophyta, Crypt. = cryptomonads, Dinop. = , Chrys. = chrysomonads, Diat. = diatoms, Chlor. = green algae. E.g. Gonyosfo mum semen (Raphidophyceae) is included in the group others. Figures according to Tikkanen and Willén (1992).

Many of them are only facultatively planktic The plankton of lakes (limnoplankton) can be (Hutchinson 1967, Round 1981). Plankton could segregated from plankton in ponds (holoplank be regarded as the community of prokaryotic and ton) and rivers (potamoplankton) (e.g. Reynolds eukaryotic organisms, such as bacteria, algae, 1986). The term euplankton () is protozoa and larger zooplankton adapted to sus used to refer to the permanent planktic assem pension in the sea or in fresh waters and liable to blage of organisms which completes their life cy passive movement by wind and currents (Rey cle suspended in water. Species which spend part nolds 1986). According to Hutchinson (1967) and of each season resting on the sediments (mainly Round (1981), the term “community” is used to zooplankton but also several phytoplankton spe denote a collection of species living together and cies) comprise the . Casual species linked to a particular habitat. A collection of derived from other habitats (bottom and littoral) populations is termed an “assemblage” when are referred to as pseudoplankton (tychoplank there is no attempt to define dominance. In this ton), which is also present as epiphytes or as a study the term assemblage is used with this mean loose collection of non-motile organisms, such as ing. In terrestrial environments, the plant commu Tabellaria flocculosa (Roth) KUtzing, and some nities are more fixed entities, whereas plankton desmids e.g. Cosmarium, and Staurastrum communities with short renewal times are less (Round 1981). constant. 10 Lepistä Monographs of the Boreal Environment Research No. 16

1.2.2 Classification of phytoplankton (<2ltm), nanoplankton (2—20 p.m), Representatives of several groups of planktonic micro- or netplankton (20—200 jim), “algae” and bacteria, as well as the infective stag meso- and macroplankton (>200 jim). es of certain actinomycetes and fungi are sus pended in freshwater. “Algae”, although a much used term, does not have any exact systematic 1.2.3 Water blooms and eutrophication meaning, and should be regarded as a loose blan ket term for “primitive” cryptogamic photoau Naumann (1912) introduced the term “vegetation totrophs, as proposed by Reynolds (1986). Het colouring” for an algal mass occurrence in the erotrophic species, such as Katablepharis ovalis whole water column. “Water bloom” was widely Skuja, have often also been included in the phyto understood as the surface accumulation of plank- plankton. Furthermore, several phytoplankton tic cyanophytes. In this study the term water species are considered to be capable of mixotro bloom is used to refer to such mass occurrences of phy (Ramberg 1979, Salonen and Jokinen 1988, cyanophytes or occasionally of the green alga Tranvik et al. 1989, Jansson et al. 1996, Roberts Botryococcus. and Layborn-Perry 1999). The term eutrophication (nutrient enrichment) A discrete group among algae are the cyano describes a trophic change in the aquatic environ phytes, also referred to as Cyanophyceae, Cyano ment due to the high input of nutrients (Reynolds bacteria, Cyanoprokaryota or simply “blue-green 1986). During the past four decades the enrich algae”. Cyanophytes share affinities with the ment of many of the world’s lakes has been a di prokaryotic organization of bacterial cells; they rect consequence of social or cultural advances lack both the structural organization of chromo made by growing human populations with in somes within a separate nucleus and the discrete creased waste water loads, diffuse loads and run pigment-containing organelles (plastids or chro off from agriculture (Vollenweider 1968, Holtan matophores) characteristic of many plants. The 1980, Kauppi 1984, Willén 1987, 1992a, Re identification of naturally occurring taxa as a bo kolainen 1989, Ekholm 1998). The important tanical approach is proposed to depend on mor roles of nitrogen and phosphorus in increasing eu phological, physiological, genetic, and ecological trophication were recognized at an early stage of data (Anagnostidis and Komárek 1985). As was the study of eutrophication (Pearsall 1932, OhIe noted by Reynolds (1986), there are difficulties in 1955, Vollenweider 1968). matching wild cyanophytes to cultured type- The term natural eutrophication (maturation) strains, because their morphology may alter under describes very gradual changes in the trophic sta laboratory conditions from that of the initial iso tus of a lake over long periods, which are however late. short in a geological time scale (Round 1981). As In addition to cyanophytes, fresh waters also silts derived from the catchment area are in- carry a mixture of cryptomonads (Cryptophy washed and accumulated as lake sediment, the ceae), dinoflagellates (Dinophyceae), chryso lake volume diminishes but no change occurs in monads (Chrysophyceae), diatoms (Diatomo the amount of nutrient reaching the basin. As a phyceae) and green algae (Chlorophyceae). Xan result, the nutrients become more concentrated. thophyceae, Prymnesiophyceae and Prasinophy However, this concept is not accepted by all re ceae are usually less abundant. Euglenids (Eu searchers (Round 1981, Reynolds 1986). Climatic glenophyceae) tend to be abundant in small bod changes directly influence the weathering rate of ies of water (Round 1981, Tikkanen and Willén rocks in the catchment area, throughflow and 1992). Phytoplankton encompasses a great range leaching of the soils, and consequently the load of cell size and cell volume, from the largest ing of nutrients in the recipient lake system forms visible to the naked eye to algae less than 1 (Jhrnefelt 1958a). p.m in diameter. The different sizes are classified, according to Round (1981) and Reynolds (1986) 1.2.4 Ecological status as: Ecological status is an expression of the structure and functioning of aquatic ecosystems associated Phytoplankton assemblages reflecting the ecological status of lakes in Finland 11 with surface waters. Good ecological status is de dense algal surface accumulations, i.e. “water fined in terms of the biological communities, the blooms” (Naumann 1917). Cyanophytes and dia hydrological characteristics and the chemical toms mainly dominate in these lakes (Teiling characteristics. Biological communities with eco 1916). Eutrophic dinoflagellates (Ceratium and logical variability but with minimal anthropogen Peridinium) and green algae, e.g. Pediastrum, are ic impact are the target of protection (Commis also often abundant (Hutchinson 1967). Jarnefelt sion of the European Communities 1999). (1952) also included euglenids in this eutrophic category. When the degree of eutrophication in creases the number of species also first increases 1.3 Lakes (Heinonen 1980, Eloranta 1986), but when the biomass exceeds 10 mg L1 the species number Lakes in Finland have mainly been formed and the diversity may decrease (Brettum 1980, through three events: cracking of the bedrock, Heinonen 1980, økland 1983). transport of boulders and soil by water and ice, Thienemann (1925) added dystrophic lakes to especially during the glacial period, and deglacia the lake category. Jbrnefelt (1956a,b) classified tion, resulting finally in the development of a lake the oligotrophic and eutrophic brown-water lakes (Jbrnefelt 195 8a,b). The lake type depends in gen as dys-oligotrophic and dys-eutrophic or mixo eral on the nature of the weathering bedrock in the trophic lakes. The latter term has not been gener drainage area, on the loose soil particles: clay and ally accepted (Round 1981). Dystrophy charac carbonates in the bedrock cause eutrophy; mo terized by brown or yellow water colour is mainly raine and sand cause oligotrophy. In Finland, nat caused by allochthonous humic compounds origi urally eutrophic lakes are mainly situated in nating from the drainage area. These humic com coastal areas with wide clay plateaus, but are also pounds are of varying composition (Jkrnefelt found elsewhere in areas where clay is abundant 1958a, Wetzel 1983, Pennanen 1988). Dystrophy in the soil or where phosphates occur in the bed is typical in lakes situated in marshy areas and is rock. generally associated with an oligotrophic drain Oligotrophic lakes are situated in the vicinity of age basin. Many of the lakes in forest areas are the Salpausselka formation, in areas where the soil weakly exposed to wind, which leads to mainly consists of sand or crust, and in Lapland meromixis during spring and nutrient depletion in (Maristo 1941, Jarnefelt 1958a). Oligotrophic the productive layers (Arvola 1983). The rapid lakes are more or less rich in humic compounds development of thermal stratification in spring re and are characterized by low phytoplankton bio stricts the availability of nutrients to immobile mass and no occurrences of water blooms (Tei algae. Consequently these lakes are dominated by ling 1916). Dinoflagellates, chrysomonads, some cryptomonads and flagellated green algae (Ilma green algae, especially the genus Botryococcus virta 1983, Smolander and Arvola 1988), able to and desmids are abundant (Järnefelt 1952, 1958a, support their growth by migrating between the Hutchinson 1967, Rosen 1981, Brettum 1989). nutrient-rich hypolimnion and the illuminated A moderate degree of eutrophication is des but nutrient-poor epilimnion (Salonen et al. cribed as mesotrophy (Hutchinson 1967). Meso 1984). Large dystrophic lakes exposed to winds trophic lakes are intermediate between oligo which cause turbulence and with less dark brown trophic and eutrophic waters, with lower concen water colour are dominated by cryptomonads and trations of nutrients and total phytoplankton com diatoms (Jarnefelt 1958a, Ilmavirta and Kotimaa pared to eutrophic lakes (Hutchinson 1967, Hei 1974, Eloranta 1995). nonen 1980, Wetzel 1983). In the 1970s, approxi In Finland most man-made lakes are construct mately 10 % of the monitored 400 lakes in Fin ed by damming a river in its upper catchment land were mesotrophic on the basis of total phyto area, and therefore young man-made lakes can plankton biomass (variation from 1.01 to 2.50 mg be considered as systems intermediate between L’, Heinonen 1980). Usually the species diversi rivers and lakes. During their early stages the de ty is high in mesotrophic lakes (Brettum 1980, composition of organic material causes high nu Økland 1983). trient levels, high biological production and dark Eutrophic lakes in temperate regions are char water colour, especially in drainage areas with acterized by high phytoplankton biomass and by wide peatlands (Vogt 1978, Kinnunen 1982). 12 Lepisto Monographs of the Boreal Environment Research No. 16

Later on, the biota and the nutrient levels of these of long-term or short-term nutrient load, as lakes change towards oligotrophy (Kinnunen well as to the development of trophic degree in 1982, Krzyzanek et al. 1986, Carnier 1992). Wa man-made lakes after their construction and to ter level regulation with strong unidirectional water level regulation flow affects phytoplankton by displacing the wa 3) to evaluate the feasibility of phytoplankton as ter with suspended phytoplankton assemblages, a monitored environmental variable, and the perennating cells and resting spores downstream. significance of single species! taxa as signs of Under these circumstances spring growth may be changes, and finally delayed because the inocula ofphytoplankton is 4) to evaluate the key problems in the analysis of small, although nutrients and light are adequate phytoplankton. (Reynolds 1986). Acidification was recognized as a severe envi ronmental problem in the 1980s both in Europe 2 Materials and methods and in North America. In southern Finland, small clear water lakes with catchment areas mainly of The phytoplankton data included in this study are infertile forest soil or granite bedrock are partic based on the data set of the most intensively mon ularly sensitive to acid deposition (Kauppi et al. itored lakes of the Finnish Environment Institute 1990). However, many lakes in Finland are natur (FEI), with a total of 859 samples from 43 lakes ally acidic and dystrophic or have been so for at and two reservoirs situated between the latitudes least the past 100 years due to dissolved humic 60° and 69° (1—Vu). Phytoplankton records from substances derived from the surrounding soils a brown-water forest lake (II), from two mon (Rask et al. 1986). itored man-made lakes in Lapland (III-IV) and from four lakes examined as raw water sources for water works (VI) are included in the studied 1.4 Aims of the study lakes. Lakes were classified as acidic, oligotro phic, dystrophic, mesotrophic, eutrophic or hy The aims of the present study were: per-eutrophic using average values of some phys 1) to evaluate the typical phytoplankton assem ical and chemical variables in 1991—1997 (Table blages in different lake types 1). The acidic lakes were those examined during

2) to evaluate the response of phytoplankton as the HAPRO project — Acidification in Finland semblages to anthropogenic stresses in terms (Kauppi et al. 1990) (VII).

Table 1. Some water quality variables (mean, maximum and minimum) in the studied lake groups in 1990—1997 (March— October) from the depth of one metre, n = number of the lakes / and the number of samples. Lake types according to Forsberg and Ryding (1980), in which acidic lakes were not included.

Lake types n Total P Total N Water colour pH jig L1 jig L’ mg L-’ Pt

Oligotrophic 9/ 181 6 (3—8) 380 (180—490) 20 (5—30) 7.0 (6.9—7.2) Acidic’ 11 /36 8 (4—16) 280 (170—430) 30 (5—140) 5.5 (4.7—6.0) Dystrophic 10/603 14 (9—23) 460 (320—1100) 70 (50—80) 6.6 (5.8—7.1) Mesotrophic 6/456 18 (13—23) 610 (360—1100) 30 (9—50) 7.0 (6.6—7.5) Eutrophic 5 / 212 57 (37—70) 1300 (800—2200) 90 (50—140) 7.0 (6.5—7.2) Hyper-eutrophic 2 / 276 65 (36—93) 1250 (1200—1300) 75 (50—100) 7.5 (7.4—7.5)

Lokka2 1 / 36 36 (21—60) 610 (440—770) 80 (60—100) 6.8 (5.7—7.6) Porttipahta2 1 / 38 19 (10—38) 370 (310—460) 70 (40—100) 7.0 (6.1—7.7)

1) in 1984—1994 2) man-made lake Phytoplankton assemblages reflecting the ecological status of lakes in Finland 13

Table 2. The sampling time, depth, method and preservatives used in the investigations of phytoplankton (I—Vu). Methods are those used in the monitoring programme of FEI, with the exception of (II).

PubI. Date Sampling depth Sampling method Preservatives No. Year Month >0—2 m 0—2 m’ net Ruttner Form. Lugol21

I 1893—1995 V—IX 0—9m x x x x x II 1988—1994 V—TX x x x lIT 1968—1990 VT—TX 0—lOm x x x x IV 1965—1994 VT—Tx 0—lOm x x x x V 1982, 1986 VTI x x x VI 1991 V—XT 1—12m x x x VTT 1982—1994 VII x x x

1) Since 1971 in general 2) Preserved with acid Lugol’s solution; formaihyde (35 %), as 16 % final solution, added afterwards 3) Sampling from the pipes of raw and treated water

Phytoplankton has been sampled by the Re 3 Phytoplankton in different types of gional Environmental Centres since 1963 (Table lakes 2), and the biomass as fresh weight has been esti mated by microscopy using the Utermöhl (1958) 3.1 Long-term eutrophication of a shallow technique. During the analyses all the observed lake taxa of a permanent area of the chamber bottom are counted and the counting results, including Lake Tuusulanjbrvi is a shallow lake in southern those taxa observed in low numbers, are convert Finland. The naturally eutrophic lake was the raw ed to biomass using coefficients. Phytoplankton water source for the city of Helsinki during the quantity as chlorophyll a concentration (T—V) has 1950s and 1960s. With increasing nutrient con been determined since 1973. The data from the centrations the lake became hyper-eutrophic, study lakes (T—VTI) and additional phytoplankton phytoplankton biomass increased and long-last data from the database of FET were examined to ing water blooms of cyanophytes were frequently find the average biomass of the most important observed. Several water protection procedures taxa during spring, summer and autumn, and the have improved the water quality since the early seasonal succession of phytoplankton in the dif 1980s (I). ferent lake groups. Partly unpublished data from In 1921-1932 the total phytoplankton biomass the database of FET were used when considering was on average 1.4mg L1, but in the l970s it had the long-term changes of cyanophytes, diatoms increased to 22.4 mg L1 (I). Phytoplankton was and total phytoplankton, and the proportion of characterized by strong seasonal and year-to-year different algal groups in lakes in Finland. Acidic fluctuations. The maximum biomass value ever lakes were not included in this treatment as they recorded, 84 mg L1, was caused by Planktothrix were sampled only in July 1987. Qualitative data agardhii (Gom.) Anagnostidis & Komárek in the concerning algal nuisances (water blooms) are in mid 1970s. When the urban waste water load was cluded in the biological database of FEI. This da finished in 1979, the total biomass decreased to tabase was established in 1992, and also contains an average of 14.5 mg L1, although the biomass earlier information (I, IV, VI). The list of valid still varied remarkably in the 1980s. In the 1990s, species names and synonyms is given in Appen the mean biomass decreased further to 8.7 mg L1, dix 1. and peak levels of phytoplankton biomass were clearly lower compared to the maximum values in the 1970s. However, phytoplankton quantity still reflects highly eutrophic conditions (see also Ta ble 3), according to the criteria of Heinonen (1980). During the warm and calm weather condi 14 Lepista Monographs of the Boreal Environment Research No. 16

Table 3. Mean and standard deviation of phytoplankton biomass (wet weight, mg L1 ) and chlorophyll a concentration (tg L1 ) in 1981—1997 (June—August) in the studied lake groups and in man-made lakes. n = number of samples or taxa. SD denotes standard deviation.

Lake types Samples Taxa Biomass mg L’ Samples Chlorophyll a .rg L’ n n Mean SD n Mean SD

Acidic’ 11 77 0.3 0.1 - - - Oligotrophic 165 436 0.3 0.2 181 2.7 1.2 Dystrophic 197 519 0.9 0.7 603 6.2 3.0 Mesotrophic 144 556 2.3 2.0 456 8.7 4.8 Eutrophic 35 313 7.6 7.7 212 36.9 30.1 Hyper-eutrophic 146 486 13.2 12.4 276 52.4 44.0

Lokka2 37 277 3.0 2.4 39 12.3 7.2 Porttipahta2 31 249 1.0 0.9 75 6.7 5.3

1) in 1987 2) man-made lake tions in summer 1997 Aphanizomenon spp. 1959 the water was treated with copper sulphate caused dense water blooms. This emphasizes that (Kangas 1961). According to Kenefick et at. weather is an essential regulating factor in the for (1993) and Lam et at. (1995), such treatment mation of algal blooms (I). probably causes a leakage of toxins from the de Soon after 1910, the cyanophytes Anabaena, caying cyanophytic cells. Water blooms occurred Aphanizomenon and Microcystis were rather each summer in the 1960s and in the early l970s. abundant, although no algal colouring of the Especially in the 1970s, when the waste water water was visible (Jarnefelt 1937, 1956b). At load into the lake was strong, phytoplankton was that time eight species indicating oligotrophy alternatively dominated by cyanophytes, such were included in the phytoplankton assemblage. as Planktothrix agardhii, and diatoms, such as Dinobryon bavaricum Imhof and D. divergens Autacoseira itatica (Ehr.) Simonsen. The Imhof were rather abundant, and the cyanophytes Tabe ltaria flocculosa, favouring oligotrophic Coelosphaerium kuetzingianum Nageli and conditions (Hutchinson 1967), disappeared in Woronichinia naegetiana (Ung.) Elenkin, both 1976 during the highly eutrophic conditions when occurring in oligo-mesotrophic waters (Brettum silicate depletion was also observed. Tabetlaria 1989), were also common, as were the oligotro was absent until 1985. phic diatoms Cyclotella kuetzingiana Thwaites Ptanktothrix agardhii dominated the summer and Tabellaria flocculosa (I). Water blooms phytoplankton until 1979 when the waste water caused by Anabaenaflos-aquae (Lyngb.) Brébis load was stopped. The species was still observed son, A. inacrospora Klebahn and A. spiro ides in 1981, but since then it has occurred only occa Klebahn first developed in 1926 (Jhrnefelt 1937). sionally and in low numbers. Planktothrix was

Planktothrix agardhii was observed for the first succeeded by the N2 — fixing Anabaena and time in 1921 and abundantly in 1956 (Järnefelt Aphanizomenon. However, the non-N2 — fixing 1956b). The diatom Acanthoceras zachariasii Microcystis was occasionally abundant although (Brun) Simonsen, typical of eutrophic waters inorganic nitrogen, the important nitrogen source (Lepisto 1990, Rosenström and Lepisto 1996), (Kappers 1980, Blomqvist et al. 1994), remained was common at that time but disappeared in the depleted. Microcystis is capable of vertical migra 1960s (I). This alga seems to be sensitive to hy tions and is able to utilise nutrients present in per-eutrophic conditions (Tables 4—6). deeper strata when the N:P ratio decreases (e.g In the 1950s water blooms of Anabaena result Reynolds 1972, Konopka et al. 1978, Hyenstrand ed in serious taste and odour problems in the tap et at. 1998). Changes in nutrient concentrations, water of the city of Helsinki which used Lake especially the decrease of inorganic nitrogen, af Tuusulanjkrvi as a drinking water reservoir. In fected the phytoplankton assemblage. In 1982 no Phytoplankton assemblages reflecting the ecological status of lakes in Finland 15

significant biomass of cyanophytes was observed. which is considered to reflect the decreased nutri Obviously, this was partly due to the exceptional ent input (Watson and Kalff 1981, Willdn 1987). ly windy and rainy spring and early summer. Dur Large diatoms were succeeded by small-sized ing strong turbulence, diatoms are able to out diatoms, a phenomenon also caused by decreased compete cyanophytes (Reynolds 1980). In the silicate concentration (Stoermer et al. 1985, Sut 1980s diatoms were clearly reduced compared to tle et al. 1987). The increase of small-sized algae the previous decade of vigorous diatom growth, in the material also depends on the development which obviously depleted the silicate. The large- in taxonomy which made possible the identifica sized Aulacoseira granulata (Ehr.) Simonsen was tion of small bacteria-like cyanophytes in the succeeded by the narrow A. granulata v. angus 1990s (I). tissima (0. MUller) Simonsen (I). The high total phosphorus concentration of In the 1990s, more than 10 years after the Lake Tuusulanjhrvi already indicated eutrophy in end of waste water input to the lake, cyanophytes the 1920s. In fact the lake is situated on a clay decreased markedly although they still dominate area and is naturally eutrophic (Järnefelt 1937). the phytoplankton. Aphanizomenon flos-aquae Compared to the median concentrations of phos (L.) Ralfs became abundant (Tables 4—6), but phorus and nitrogen in Finnish lakes (13 jig L1 cryptomonads, dinoflagellates, especially chryso and 400 jig L-1, respectively, Henrikson et al. monads and also green algae increased. As a new 1998), nutrient concentrations in Lake Tuusulan phenomenon the small-sized Rhodomonas lacust järvi are still in the 1990s exceptionally high (to ris Pascher & Ruttner produced a biomass peak in tal median phosphorus 100 jig L-1 and total medi May 1994. There was a shift from Microcystis an nitrogen 1200 jig L-1), indicating eutrophy or dominated, usually hepatotoxic (Watanabe et al. even hyper-eutrophy. Although oxygen availabil 1986, Sivonen et al. 1990), blooms to Aphani ity in the hypolimnion has improved due to water zomenon dominance in the 1990s. Lower phos aeration, the internal loading of the lake is still phorus and nitrogen concentrations not only de operative and the phosphorus concentration re crease the intensity of mass occurrences but fa mains at a high level. After the end of the waste vour less harmful populations of Anabaena and water load to the lake, the decrease or even deple Aphanizomenon (e.g. Ekman-Ekebom et al. 1992, tion of inorganic nitrogen in summer strongly Willén and Mattson 1997, Rapala 1998). suggests that nitrogen may limit algal growth. In In the 1990s, 22 “new” taxa, mainly of cyano fact, the low median DIN:DIP (wlw) ratio, clearly phytes, were identified. Such taxa were Aphano below seven (the optimum ratio for algal growth, thece, Cyanodictyon, Radiocystis, and Snowelia Redfield et ci. 1963), also strongly supports this which form small bacteria-like colonies and are conclusion. typical for naturally eutrophic shallow lakes (Komárkovd-Legnerovd and Cronberg 1994). Furthermore, Anabaena mucosa Kom.-Legnerova 3.2 Effects of forest fertilization on a & Eloranta and the diatom Skeletonema potamus brown-water lake (Weber) Hassle, which earlier was assigned to the green alga Gloeotila according to Turkia and The forests in the catchment area of Lake Kallio Lepisto (1997), were observed. Dinobryon sueci järvi in the Juupajoki municipality, southern Fin cum Lemmermann, Gonyostomum semen (Ehr.) land, were fertilized by NP-fertilizers in mid Diesing (Raphidophyceae) and Botryococcus ter summer 1988 (Frisk et al. 1997). During the ribilis Komkrek & Marvan were also observed in spring flood after fertilization, phosphorus con the 1990s. Some taxa, observed in the late l800s centrations were high when the fertilizers leached and early 1900s, such as Coelosphaerium kuetz into the lake. During the study period nutrient ingianum, Dinobryon bavaricu,’n, D. divergens, concentrations increased in the hypolimnion. D. sociale Ehrenberg, Acanthoceras zachariasii Phytoplankton responded to the increased nu and Rhizosolenia Iongiseta Zacharias were ob trient concentrations by a biomass (3.9 mg L1) served again, indicating a lower trophic status of and chlorophyll a (32 jig L’) peak during the Lake Tuusulanjarvi. first spring. During the subsequent five years total A shift from large to small phytoplankton spe phosphorus concentrations remained relatively cies has been observed since the early 1980s, high, on average 17—18 jig l1 as annual means. In 16 Lepistö Monographs of the Boreal Environment Research No. 16

the hypolimnion nutrient concentrations, organic nella formosa Hassall, typical species of the dys matter, water colour and conductivity increased trophic lake group (Tables 4—6). However, Aula gradually. Five years after the fertilization, in case ira italica, rather common in the dystrophic September 1994, Gonyostomum semen caused a lake group, is rare in Lake Kalliojarvi (II). second maximum, with total biomass 2.9 mg L-1 and chlorophyll a concentration 10 .Lg L-1. Phyto plankton biomass and chlorophyll a concentration 3.3 Development of the trophic degree in were in agreement with the relatively high phos two man-made lakes phorus concentration reflecting meso-eutrophic conditions, according to criteria by Heinonen 3.3.1 The Lokka reservoir (1980) and Wetzel (1983). Except for these two maxima, phytoplankton biomass and chlorophyll The reservoirs Lokka and Porttipahta were con a concentration remained rather low (II). structed by damming the rivers Luiro and Kitinen The fertilization obviously caused an immedi of the Kemijoki watercourse, the second largest ate increase of cryptomonads, accounting for Ca. watercourse in Finland. Due to the northern loca 60 % of the total biomass. Cryptomonas spp. are tion, the reservoirs are ice-covered from the end favoured by N+P addition (Jansson et ai. 1996) of October to the end of May or even into early and are potentially mixotrophic (e.g. Tranvik et June. The filling of the reservoirs takes place dur al. 1989, Roberts and Layborn-Perry 1999). After ing the spring and autumn floods and the water the first spring, cryptomonads contributed less volume is at its minimum in late winter. The regu than 20 % to the total biomass (II). During the lation of the reservoirs was especially strong in study period small , such as the prym 1977—1981. nesiophycean Monochrysis parva Skuja and the The Lokka reservoir is the largest reservoir in green alga Monomastix sp., were typical. Mono terms of surface area in western Europe (Vogt chrysis parva is obviously capable of bacterial 1978). It remains lake-like even during the mini consumption (Holen and Boraas 1996). The chry mum water level, although it is moderately shal somonads Maiiomonas, Pseudopedineila and low (mean depth 5 metres, maximum 10 metres). Synura were also abundant. The large-sized fla The reservoir is constructed on peatland with large gellate Gonyostomum semen is able to maintain swamps, and the abundant organic compounds its growth in brown-water lakes by migrating be make the water colour dark brown (Nenonen and tween the epilimnion and the hypolimnion, where Nenonen 1972, Virtanen et al. 1993). Oxygen de nutrients are concentrated (Cronberg et ai. 1988, pletions release phosphorus from the bottom sedi Arvola et ai. 1990, Eloranta and Raike 1995). ment. However, only a minor part of the nutrients Gonyostomum appears to be able to consume bac are in a bioavailable form as they are bound in hu teria (Holen and Boraas 1996). mic compounds (Boström et al. 1988). One year after the fertilization Merismopedia In May 1968 the phytoplankton biomass was wariningiana Lagerheim, typical for nutrient- rather similar in the recently filled Lokka reser poor, dark and acidic waters (Brettum 1989), was voir to that in September 1965 in the River Luiro abundant. Other cyanophytes, such as Anabaena before any reservoir constructions. The low bio flos-aquae occurred sparsely, as low pH prevents mass of 0.03 mg L-1 reflected oligotrophy. Ten the mass occurrence of cyanophytes (Reynolds years later, after a period of strong water level and Walsby 1975). regulation, phytoplankton biomass was increased, The quantity and quality of phytoplankton in and a record high biomass of 11.3 mg L1 was Lake Kalliojärvi, with average total biomass 0.9 measured in July 1981. The summer chlorophyll mg L1 and chlorophyll a concentration 6.4 sg a concentrations remained high during 1977- L1, is rather similar to that of the dystrophic lake 1983. Due to the increased erosion and nutrient group (Tables 3,4—6) as Cryptomonas spp., Pseu leaching high silicate concentrations were record dopedineiia spp., Mallomonas crassisquoma (As ed, favouring diatoms (III, IV). The average phy mund) Fott and Tabellariafloccuiosa are the gen toplankton biomass remained high in the 1980s, erally dominating taxa and Merismopedia war i.e. 3.6 mg L1, reflecting eutrophy according to mingiana is abundant. Less common in Lake Kal the criteria of Heinonen (1980), although the sili liojärvi are Rhizosolenia iongiseta and Asterio cate and chlorophyll a concentrations slightly de Phytoplankton assemblages reflecting the ecological status of lakes in Finland 17 creased when the extent of water level regulation was diminished in 1981. In the 1990s the average phytoplankton biomass decreased to 1.9 mg reflecting mesotrophy (Table 3). The interannual biomass variations also decreased (III, IV). Small colony-forming cyanophytes, e.g. Eucapsis alpina Clements et Shantz probably de rived from metaphyton in the flooded peaty bogs (Komárek and Anagnostidis 1999), chryso monads and cryptomonads were the main con stituents of the phytoplankton assemblage in the recently filled reservoir. The heterotroph protist Desmarella moniiiformis Kent was also a typical species (III, IV). This species prefers waters with high concentrations of organic compounds and abundant bacteria (Jbrnefelt 1961, Tikkanen and Willén 1992). Furthermore, the commonly ob served Dinobryon bavaricum is closely linked to 4- mixotrophy (Bird and Kalff 1987, Straikrabová ‘:2 and Simek 1993). Many cryptomonads, such as Fig. 2 Aulacoseira italica from the Lokka reservoir Rhodomonas lacustris, are also mixotrophs (5.7.1988). (Haffner et ai. 1980), and are effectively grazed by zooplankton (Porter 1973). The green alga Monoraphidium contortum (Thur.) Kom.-Legne its shape is oblong and labyrinthic. When the water rová was very abundant, obviously as a “relict” level is at its minimum it is river-like (Nenonen from the River Luiro (III, IV). Reynolds (1988) and Nenonen 1972, Virtanen et al. 1993), and classified M. contortum as a true river phyto there is little organic material in the water. Al plankton (potamoplankton) which tolerates high- though the Lokka reservoir drains into the Portti frequency hydraulic disturbances (III, IV). Arvo pahta reservoir, the water quality and also the phy la (1980) described it as a pioneer species able to toplankton composition and quantity of Porttipahta survive in a new labile ecosystem. With the pas differ to some extent from that of the Lokka reser sage of time, diatoms increased and strong water voir. The N:P ratio is high, which is typical for level regulations favoured species, such as Aula lakes in Finland, and phosphorus appears to be the coseira ambigua (Grun.) Simonsen and A. italica limiting nutrient for phytoplankton production. v. tenuissilna (Grun.) Simonsen (III, IV). Silicate In the early history of the Porttipahta reservoir, depletion in summer 1988 obviously caused thin which was constructed some years later than the and bent valves of the cells of Aulacoseira (Fig. Lokka reservoir, phytoplankton biomass reflected 2). Stoermer et al. (1985) and Kling (1993) re oligotrophy but increased simultaneously with ported similar thinly silicified and distorted the strong water level regulation (III, IV). When valves of diatoms during silicate depletion in Ca regulation was diminished the phytoplankton nadian lakes. Diatoms were occasionally replaced quantity began to reflect oligo-mesotrophy. In the by cyanophytes at the end of the very warm sum 1980s the average biomass was 1.1 mg L’, and mer of 1988. Planktothrix mougeotii Skuja be decreased in the 1990s to 1.0 mg L-1, which was came abundant, causing clogging of nets, but was one half of that in the Lokka reservoir. Cyano soon succeeded by Aphanizomenon flos-aquae phytes were moderately rare. which caused water blooms. However, diatoms During the period of intense water level regu still dominate the phytoplankton assemblage. lation (1977-1981) diatoms, e.g. Aulacoseira ital ica and Asterionella formosa, were abundant, al 3.3.2 The Porttipahta reservoir though less so than in the Lokka reservoir. Dia toms are still abundant in the Porttipahta reser The Porttipahta reservoir (mean depth 6m, maxi voir. Typical are Aulacoseira italica, Tabellaria mum 34m) is situated in an area of moraines and flocculosa and Rhizosolenia iongiseta which 18 Lepistd Monographs of the Boreal Environment Research No. 16 seems to be abundant in deep waters with ad ment with almost total reduction of phytoplank equate nitrogen and low phosphorus (database of ton, cells of Microcystis and trichomes of Plank FEI). Cyanophytes are less abundant partly due to tothrix agardhii are also observed in treated water the consistently high mineral nitrogen concentra during the peak occurrence in raw water. Cells of tion. No mass occurrence of cyanophytes was ob the euglenid Trachelomonas spp. are also ineffi served in 1988 (III, IV). ciently removed by the water treatment. How The different morphology and different water ever, the abundant cyanophytes are not necessar quality of the two reservoirs affects the phyto ily toxic (VI). plankton. In the Lokka reservoir, phytoplankton The patchiness of phytoplankton is often sig production seems to be regulated by both nutri nificant during a water bloom. Due to this patchi ents (P and N) alternatively. However, the con ness the species composition of phytoplankton, centrations of phosphorus, which are higher than especially of cyanophytes, may greatly differ in mesotrophic lakes (Table 1), maintain a phyto from that of the bloom formation in the vicinity of plankton assemblage typical for mesotrophic con the water intake. The water bloom may be toxic ditions. In the Porttipahta reservoir, nitrogen con and simultaneously the raw water at the water- centrations are relatively high and consequently works non-toxic or vice versa (VI). It is also phosphorus regulates the growth of phytoplank possible that no water bloom can be observed but ton. Phosphorus concentration is equal to that of Planktothrix is abundant at a depth close to that of mesotrophic lakes on average (Table 1) but phy the raw water intake. Planktothrix seldom forms toplankton biomass reflects oligo-mesotrophy. water blooms but is known to form depth maxima The strong water level regulation promotes the (Lindholm 1992). occurrence of diatoms. Especially in the Lokka A simple water treatment requires raw water reservoir warm weather periods may favour mass of high quality. Sand filtration is not efficient occurrences of cyanophytes. enough if the lake used as raw water source grad ually changes to more eutrophic status. Incipient changes of phytoplankton assemblage in a raw 3.4 Problems caused by increased water body are already evident before eutrophic phytoplankton ation becomes a problem. These changes should be considered as warning signals, as proposed by Oligotrophic lakes are suitable as raw water Davis (1964), who studied the phytoplankton data sources for waterworks using a minimum of only from the incoming raw water of waterworks in sand filtration. The chemical quality is not Lake Erie in 1919—1963. changed during treating of the raw water (VI). Mi croscopical phytoplankton analyses indicate the reduction of total phytoplankton biomass in the 3.5 Phytoplankton as an indicator of the treated water to be on average 76 % and that of status of lakes in Finland cyanophytes 14 %. However, occasionally cells of cyanophytes, such as Snowella spp., are flushed 3.5.1 General from the sand filter with the treated water. Prob ably the filters are overloaded when phytoplank In the 1990s, mass occurrences of cyanophytes ton is abundant. The algal cells in the treated water appeared to increase in lakes in Finland. In gen are in good condition as observed by microscopy. eral, these lakes with water bloom observations In mesotrophic raw waters vernal mass occur are moderately small and shallow, but some of rences of chrysomonads and diatoms cause odour them are fairly large and deep (Lepisto et al. and taste problems in treated water, as the odour- 1998). However, the data set of the monitored causing compounds or the algal cells easily pass phytoplankton in 1963—1996 only partly support intact through the water treatment process (VI). these observations, as cyanophytes decreased in Hyper-eutrophic conditions promote mass occur all lake groups in the 1990s, contrary to the water rences of cyanophytes such as Microcystis wesen bloom observations. Furthermore, in the 1990s bergii Kutzing and M. viridis (A. Br.) Lemmer the total biomass level in oligotrophic and oligo mann in summer, and of Planktothrix agardhii in mesotrophic lakes appears to have decreased autumn (I, VI). Despite the efficient water treat- slightly (Fig. 3) compared to the previous decade. Phytoplankton assemblages reflecting the ecological status of lakes in Finland 19

In fact the 1980s was on average characterised by vented especially in deep lakes (Reynolds 1986). rather heavy precipitation (Finnish Meteorologi However, weather conditions are only one of the cal Institute 1991). Only in mesotrophic lakes did variables affecting phytoplankton (I). diatoms increase the total biomass, obviously as a In the studied lakes, the average total phyto result of slight eutrophication. In eutrophic lakes plankton biomass generally varied from 0.3 mg L’ phytoplankton biomass has clearly decreased due to 4 mg L-1 but in eutrophic lakes it was approxi to water protection procedures (I). According to mately 10 mg L-1, with considerable variation. A the database of the Finnish Meteorological Insti Swedish investigation of 1250 lakes showed equal tute, June was on average colder and more windy phytoplankton quantities in lakes with different in 1990—1996 compared to the previous dec trophic status (Rosen 1981), as did the investiga ade, which might have influenced phytoplankton tion of 40 Tyrolean low- and mid-altitude lakes development. Due to the cold June the summer (Rott 1984). stratification development might be delayed as well as the development of phytoplankton spring 3.5.2 Oligotrophic lakes maxima, or the maxima could be even totally pre 10 In the studied oligotrophic, moderately deep lakes mg Oyanophyta (VI, VII, database of FEI), phytoplankton biomass

0 1963-79 is low, on average 0.3 mg L (SD % = 67) and w 1980-89 varies mainly in May and June (Fig. 4, Table 3). In 5 a keeping with this, chlorophyll a concentrations are S 0 low, on average 2.7 im L’ (SD % = 44). Phyto plankton is composed mainly of similar quantities of chrysomonads (32 %), cryptomonads (21 %) C) and diatoms (21 %). Cyanophytes are of minor im 011g. 011g.- Mes. Eutr. Lo Po mes. portance in oligotrophic lakes as are e.g. members 10 of the classes , Raphidophyceae or mg Diatoms Tribophyceae (group others in Figs. 1, 5, 6).

0 1963-79 The total number of phytoplankton taxa was w 1980-89 436 taxa in 162 samples (Table 3). Chryso a [1990-96 monads, such as the unidentified Ochromonad S 0 ales, Bitrichia chodatii (Rev.) Chodat, Chryso lykos planctonicus Mack, Dinobryon borgei Lem n__LII EL mermann, D. divergens, D. sociale and D. sueci 011g. 011g.- Mes. Eutr. Lo P0 cum, are typical for oligotrophic waters. No single mes. taxon of chrysomonads was dominant, although they were abundant as a group (Tables 4—6). Some mg of the chrysomonads which are considered to indi T 15 cate oligotrophy, such as the genus Dinobryon, (Järnefelt 1952, 1956a, Brettum 1989), are mixo ti 10 a S trophs (Bird and Kalff 1987, Straikrabová and 0 Simek 1993). It seems that mixotrophy is a com petitive advantage in nutrient-poor conditions. The genus Dinobryon is observed in slightly aci Olig. 011g.- Mes. Eutr. Lo Po dic surroundings (Rawson 1956), and according to mes. Eloranta (1989) D. borgei prefers oligotrophic Fig. 3 The long-term changes of cyanophyta, diatoms waters whereas D. divergens may be found in and total phytoplankton biomass (wet weight, mg L’) in more eutrophic waters (I). lakes of different productivity during 1963—1 996 as mean The diatoms Aulacoseira distans biomass of June-August presented in three periods (Ehr.) Si (database of EEl). Olig. = oligotrophic, OIig.-mes. = oligo monsen and especially Rhizosolenia iongiseta, mesotrophic, Mes. = mesotrophic, Eutr. = eutrophic, Lo = reflecting oligotrophic and oligo-mesotro the Lokka reservoir, P0 = the Porttipahta reservoir. Note phic conditions (Jarnefelt 1952, 1956a, Hutchin the different scale in the figure of total biomass. son 1967, Heinonen 1980, Brettum 1989), are 20 Lepisto Monographs of the Boreal Environment Research No. 16

Table 4. The dominant spring taxa in different lake types in 1981—1997 given as average biomass (wet weight, mg L1 ),

+ = observed, - = not observed, n = number of samples. The two dominant taxa shown in bold face. Note the eutrophic lake group with only one sample.

Spring

Taxon Oligotrophic Dystrophic Mesotrophic Eutrophic Hyper-eutrophic 9lakes,n= 3 4lakes,n=21 9lakes,n= 10 llake,n=1 2lakes,n=30

Aphanothece chlathrata - + - - 0.12

Cryptomonas - 0.10 - - - 1,2) Cryptomonas spp. 0.02 - - - -

Cryptomonas spp.2) - - - 0.39 1.57

- Cryptomonas - 0.29 - Rhodomonas lacustris 0.02 0.02 0.06 0.74 1.06

Gymnodinium spp. 0.01 0.02 0.04 - 0.12

Chrysochromulina spp. + - 0.02 0.03 -

Mallomonas akrokomos + 0.02 0.02 - 0.56

Mallomonas allorgei - 0.03 - - - Mallomonas caudata + 0.03 + 0.01 +

Ochromonadales 0.06 0.02 0.01 - 0.07

Mallomonas crassisquama + 0.11 + - +

Pseudopedinella spp. - 0.05 0.03 - 0.08 Synura spp. + 0.03 + 0.18 0.40

Aulacoseira ambigua - + 0.17 - 0.21

Aulacoseira granulata - - - - 0.19

Aulacoseira alpigena - - - (7.19) + Aulacoseira islandica 0.01 0.03 0.12 0.03 +

Aulacoseira italica - 0.01 0.09 0.44 0.80 A. italica v. tenuissima + + 0.04 (7.15) 0.61

Cyclotella spp. - - 0.07 - +

Rhizosolenia longiseta 0.02 0.02 0.02 - +

Stephanodiscus spp. + - + 0.65 0.57 Asterionella formosa + 0.05 0.01 0.01 0.09

Diatoma tenuis 0.01 + + - 0.04 Fragilaria crotonensis + + + 0.06 0.11 Fragilaria (Synedra) Spp. 0.01 + + 0.05 0.05 Tabellaria flocculosa 0.01 0.08 0.02 0.02 +

Gonyostomum semen + + 0.01 0.02 -

Euglena proxima - + - 0.24 +

Lepocinclis steinii - - - 0.74 -

Trachelomonas hispida - - - 0.17 0.02 Chiamydomonas Spp. + 0.01 0.01 0.41 0.10

1) small Cryptomonas Spp. (8x18 lim) 2) medium Cryptomonas spp. (13x26 jim) 3) large Cryptomonas spp. (16x38 jim) Phytoplankton assemblages reflecting the ecological status of lakes in Finland 21

Table 5. The dominant summer taxa in different lake types in 1981-1997 given as average biomass (wet weight, mg L1 ),

+ = observed, - = not observed, n= number of samples. The two dominant taxa shown in bold face.

Summer

Taxon Oligotrophic Dystrophic Mesotrophic Eutrophic Hyper-eutrophic 9 lakes,n= 162 10 lakes,n =197 6 lakes,n= 152 5 lakes,n=35 2 lakes,n= 143

Aphanocapsa reinboldii 0.01 0.02 0.03 0.51 0.34 Microcystis aeruginosa + + + 0.29 0.82

Microcystis flos-aquae - - - 0.11 + Microcystis viridis + + + 0.03 0.73

Microcystis wesenbergii - - + 0.02 0.83

Microcystis sp. - - + - 0.42 Snowella lacustris + + + 0.21 0.07 Anabaenaflos-aquae + + 0.03 0.62 0.52 Anabaena lemmermannii + + 0.01 0.06 0.48 Anabaena solitaria + + + 0.09 0.34 Aphanizomenon spp. + 0.01 0.14 0.39 2.00 Planktothrix agardhii + + 0.04 0.03 0.09

Cryptomonas spp. 2) 0.03 0.13 0.24 0.70 0.89 Rhodomonas lacustris 0.03 0.05 0.07 0.12 0.13 Ceratium hirundinella 0.01 0.01 0.01 0.09 0.35 Gymnodiniumspp. 0.01 0.01 0.03 0.12 0.11

Chrysosphaerella spp. 0.01 + + - - Mallomonas akrokomos + 0.01 0.02 + + Mallomonas caudata + 0.02 0.01 0.02 0.11 Ochromonadales 0.02 0.01 0.02 0.12 0.02 Pseudopedinella spp. 0.02 0.02 0.03 0.02 0.01 Uroglena spp. 0.02 0.01 0.02 0.01 0.03 Synura spp. + 0.01 0.05 0.02 0.01

Acanthoceras zachariasii + 0.03 0.08 0.15 0.09 Aulacoseira ambigua + 0.03 0.07 0.79 0.31 Aulacoseira distans 0.01 0.02 0.06 0.01 0.01

Aulacoseira granulata + - + 0.27 0.37 Aulacoseira italica 0.01 0.06 0.15 0.34 0.59 Rhizosolenia eriensis + 0.01 + + + Rhizosolenia longiseta 0.01 0.10 0.04 0.04 + Stephanodiscus spp. + + + 0.09 2.17 Asterionella formosa 0.01 0.09 0.09 0.04 0.04 Fragilaria crotonensis + + 0.04 0.06 0.23 Tabellaria flocculosa 0.01 0.07 0.25 0.04 0.02

Gonyostomum semen + 0.01 0.09 0.10 +

1) small Cryptomonas spp. (8x18 jim) 2) medium Cryptomonas spp. (13x26 jim) 3) large Cryptomonas spp. (16x38 jim) 22 Lepistö Monographs of the Boreal Environment Research No. 16

Table 6. The dominant autumn taxa in different lake types in 1981-1997 given as average biomass (wet weight, mg L1),

+ = observed, - = not observed, n= number of samples. The two dominant taxa shown in bold face.

Autumn

Taxon Oligotrophic Dystrophic Mesotrophic Eutrophic Hyper-eutrophic 9 lakes, n= 8 4 lakes, n= 21 4 lakes, n=11 1 lake, n=5 2 lakes, n=41

Aphanocapsa reinboldii + + 0.01 0.02 0.17

Microcystis aeruginosa + - + 0.02 0.35

Microcystis viridis - - - - 0.45

Microcystis wesenbergii - - 0.02 - 1.08

Snowella lacustris 0.01 - + - 0.02 Anabaena flos-aquae + + 1.06 0.02 0.47 Aphanizomenon spp. + + 0.01 0.07 0.42

1,2) Cryptomonas spp. - 0.06 - - - 2) Cryptomonas spp. 0.03 - 0.11 0.07 0.41 Rhodomonas lacustris 0.02 0.01 0.03 0.05 0.09

Gymnodinium Spp. 0.03 + 0.01 0.01 -

Peridinium umbonatum + + 0.02 - -

Dinophyceae + 0.01 + - 0.01

Chrysococcus spp. - + + 0.05 + Mallomonas akrokomos + + 0.01 0.05 +

Mallomonas crassisquama - 0.01 - - -

Mallomonas punctifera 0.01 0.01 - - +

Ochromonadales 0.03 0.01 0.01 - 0.02 Pseudopedinella spp. + 0.03 0.01 + 0.01

Uroglena spp. + 0.01 0.02 0.01 -

Synura spp. + 0.01 0.01 - +

Acanthoceras zachariasii + + + 0.46 0.03

Aulacoseira ambigua - + 0.01 0.18 0.60

Aulacoseira distans 0.02 + 0.04 - +

Aulacoseira alpigena + + + 0.21 -

Aulacoseira granulata - - + 0.04 0.26

A. granulata v. angustissima - + - + 0.19 Aulacoseira islandica + 0.03 + 0.04 0.64 Aulacoseira italica + 0.08 0.04 0.08 0.07 A. italica v. tenuissima + 0.02 + 0.01 0.12

Rhizosolenia eriensis - 0.01 + 0.02 - Rhizosolenialongiseta 0.02 0.10 0.03 0.03 + Asterionella formosa + 0.01 0.01 0.07 0.14 Fragilaria crotonensis + + + + 0.14

Tabellaria flocculosa + 0.01 0.03 - -

Gonyostomum semen + 0.12 0.38 + -

Botryococcus spp. + 0.01 0.01 0.01 0.01

Didymocystis bicellularis - + + 0.05 +

1) small Cryptomonas spp. (8x18 jim) 2) medium Cryptomonas Spp. (13x26 jim) 3) large Cryptomonas spp. (16x38 jim) Phytoplankton assemblages reflecting the ecological status of lakes in Finland 23

4yper-eutrophic mg L1 100

C 0. 0 60 a) 40 a) 0. 20 0 V VI VII VIII IX V VI VII VIII IX X Eutrophic 10 80 0 60 0. 0 40 a) Ui 20 0 V VI VII VIII IX X V VI VII VIII IX X Mesotrophic 100 80 % 0 80 60 0 60 ‘a g 40 40 a a) 0 20 20 iL 0 V VI VII VIII IX X V VI VII VIII IX X Dystrophic 10 80 80 o 60 60 C 2.5 g 40 TT 40 >, 20 20 0 0 T ‘F 1’ V S V VI VII VIII IX X V VI VII VIII IX X Oligotrophic 100 80 % 0 80 C 3-60 60 0 2 40 .0’ 40 0 J 20 20 0 0 V • V • • V VI VII VIII IX X V VI VII VIII IX X LcY5n aCrypt. oDinop. aChrys. Diat. ChIor. u0thers Fig. 4 The seasonal succession (May—October) of phyto plankton as mean, minimum and maximum biomass (wet Fig. The weight, mg L1) in 1981—1997 in lakes with different tro 5 proportion of different algal groups in May— phic status (I, IV, VI, VII, database of FEI). October (1 981—1 997) in lakes with different trophic status (I, IV, VI, VII, database of FEI). Explanation of abbrevi ations in Fig. 1, Gonyostomum semen (Raphidophyceae) rather abundant (Tables 4—6). Green algae occur is included in the group others. only sparsely, accounting on average for less than 10 % of the total phytoplankton biomass. Botryo braunii Kutzing (Appendix 1). Furthermore, coccus is a rather common green alga in oligo small-celled colony-forming cyanophytes, such trophic lakes but the ecological requirements of as Aphanocapsa and Merismopedia, are typical the oligotrophic indicator Botryococcus braunii for oligotrophic waters but are not important as Kutzing (Järnefelt 1952, 1956a, Hutchinson biomass (Fig. 1). Occasionally some colonies of 1967, Heinonen 1980, Brettum 1989) are not Microcystis and trichomes of Aphanizornenon, completely understood due to its uncertain identi Anabaena and Planktothrix are also observed fication (Komárek and Marvan 1992). In fact, B. (VI). The tribophycean Isthrnochloron trispina terribilis Komárek & Marvan, and B. neglectus turn (W.&G.S. West) Skuja occurs in low densi Komárek & Marvan were included earlier in B. ties in oligotrophic lakes. 24 Lepisto Monographs of the Boreal Environment Research No. 16

100 3.5.3 Acidic lakes % 0) 80 0 The phytoplankton biomass in the acidic lake 0) C group (VII) is equal to that in oligotrophic lakes, 0 60

C on average 0.3 mg L -‘(Fig. 1, Table 3) but varies Cs 0. 40 less (SD % = 33). A total of 70 phytoplankton taxa 0

.0 with eight common species were identified in 0 20 eleven samples. The low number of taxa is a com mon phenomenon for many acidic lakes (Arvola 0 et ai. 1990). Merisinopedia tenuissima Lemmer <0.25 <0.5 <1 <1.5 <2.5 <5 <10 >10 mann is clearly acidophilic, as observed by Mor Biomass (ww) mg ling and Willén (1990). It is abundant in brown- water oligotrophic lakes (II, VII), as was also re 1CrYpt. m Dinop. 0 Chrys. C Diat. C Chlor. C Others ported by Ilmavirta (1980). Blomqvist (1996) de scribed the dominance of M. tenuissima as acidifi Fig. 6 The proportion of different algal groups in phyto plankton (explanation of abbreviations in Fig. 1) in July cation-induced and as a “dead-end” for energy in 1981-1997 in lakes of different productivity, determined an acidic, clear water lake. Probably the species is as total phytoplankton biomass (wet weight, mg L1)(l, IV, M. warmingiana which has been misinterpreted as VI, VII, database of FEI). The limits, according to the clas M. tenuissima. According to Komhrek and Anag sification < = of Heinonen (1980) are: 0.5 mg L1 oligo nostidis (1999), M. tenuissima is common in fish trophic, < 1 mg L1 = oligo-mesotrophic, >1—2.5 mg L1 = ponds but less common in lakes. mesotrophic, >2.5—10mg L1 = eutrophic and>lomg L1 = hyper-eutrophic. In terms of biomass, dinoflagellates are the most important group of phytoplankton in acidic Spring phytoplankton is dominated by dia lakes (VII). Gienodinium spp. are found in slight toms, e.g. Rhizosolenia iongiseta, Diatoma tenuis ly acidic lakes with very low phosphorus concen Agardh and Fragiiaria spp., and by crypto trations. This genus is rather scarce in other lake monads, mainly Cryptoinonas spp. (small and types (Tables 4—6). Peridinium umbonatum Stein medium), and Rhodomonas iacustris (Table 4, is most abundant in lakes with the lowest pH. Fig. 5), which are typical for oligotrophic waters Algae favouring dystrophy, such as Cryptomonas (Arvola and Rask 1984, Brettum 1989, Willén spp., in agreement with observations of Ilmavirta 1992a). Chrysomonads, especially unidentified (1983) and Brettum (1989), and Maliomonas Ochromonadales, are also abundant. Summer akrokomos Ruttner and Urogiena spp. all show phytoplankton is still dominated by chryso indifference to acidity. The identification of monads, such as Pseudopedinella spp., and Uro cryptomonads, a very heterogeneous group with a giena spp. The cell number of Urogiena, another wide ecological spectrum, is difficult. Interesting mixotrophic genus, can sometimes be very high ly, Dinobryon divergens is found in lakes which in oligotrophic lakes (VII). Although Urogiena is are very acidic and contain only a few other taxa often considered as a typical spring taxa (e.g. (VII). However, Eloranta (1989) classified D. Talling 1993), it appeared to occur in this data set pediforme (Lemm.) Steinecke as the best indica in low densities during spring (Tables 4—6) but to tor of acidic lakes in the genus. increase during summer. According to Tailing Planktic diatoms together with euglenids are (1993), the recent mass occurrences of Urogiena considered to be sensitive to low pH (Kippo-Ed spp. in early summer are connected with increas lund and Heitto 1990) and to have very low bio ing eutrophication. Mixotrophy might be a com mass in acidic lakes or to be totally absent. The petitive advance especially in early summer when studied acidic lakes are small in size, which al nutrients are often depleted due to the effective lows only weak turbulence. This normally ex growth of phytoplankton. Diatoms, e.g. Aulaco cludes the non-motile species such as diatoms. seira itahca, Asterioneilaformosa and Tabeilaria Only some of the green algae, such as Sphaero floccuiosa co-dominate and cryptomonads are cystis schroeteri Chodat, Botryococcus spp. and also abundant in summer. In October the dino Oocystis rhomboidea Fott, appear to prefer acidic genus Gymnodinium dominated the de as well as oligotrophic lakes (VII). Willhn creased biomass (Fig. 5, Table 6). (1992b) classified Eutetramorus nygardii Phytoplankton assemblages reflecting the ecological status of lakes in Finland 25

Komárek, Monoraphidium dybowskii (Wol.) mixotrophic nutrient uptake (Salonen et al. 1984, Hindàk & Kom.-Legnerová and Oocystis subma Salonen and Jokinen 1988, Jansson et ai. 1996, rina v. variabilis Skuja as characteristic algae for Roberts and Layborn-Perry 1999). Flagellated acidic lakes. chrysomonads survive in very low nutrient con centrations in dystrophic waters (Arvola 1983). 3.5.4 Dystrophic lakes The small Chrysococcus biporus Skuja and C. cordiformis Naumann are typical for dystrophic The dystrophic lakes in this study are rather large lakes and the small prymnesiophycean Mono and deep (II, IV, VII, database of FBI). Their aver chrysis parva for dystrophic forest lakes (II). age phytoplankton biomass, 0.9 mg L1, is three Green algae, e.g. Chiamydomonas spp., and fold compared to that in oligotrophic and acidic Botryococcus spp. contribute on average less than lakes, and varies more (SD % = 78). The average 10 % to the total biomass. Several representatives chlorophyll a concentration, 6.2 ig L1 (SD % = of Desmidiales originating from the littoral area, 48), is twofold compared to the oligotrophic lakes such as the large Xanthidium antiiopeum (Brébis (Table 3). The variation of biomass is at greatest son) Kutzing and Hyaiotheca dissiiiens (Smith) in May—June, after which it gradually decreases Brébisson, typical for dystrophic waters (e.g. (Fig. 4). Lakes may became more dystrophic, as Tikkanen and Willén 1992), are occasionally ob did Lake Kemijarvi, the recipient for the two res served. Cyanophytes are sparse in dystrophic ervoirs Lokica and Porttipahta, after their con lakes (Figs. 1, 5, Tables 4—6), contributing only struction. Furthermore, the trophic status of Lake Ca. 5 % to the total biomass. Aphanocapsa rein Kemijärvi changed slightly towards mesotrophy boidii (Richter) Komárek & Anagnostidis and during the period of strong water level regulation Merismopedia warmingiana are abundant, but in the reservoirs. This change was mainly caused these small-sized cyanophytes are of minor im by increase of cryptomonads and diatoms. portance when considering the biomass. In dys A total of 519 taxa were observed in 197 sam trophic lakes cyanophytes, such as Anabaena ples (Table 3). Diatoms clearly dominated the flos-aquae, are only rarely observed to form vis phytoplankton assemblage at Ca. 40 %. Auiaco ible greenish flakes on the water surface (II). seira itaiica, Rhizosolenia iongiseta, Asterioneila Spring phytoplankton is clearly dominated by formosa and Tabeiiariaflocculosa, were the main chrysomonads, especially Mailomonas crassi components (Figs. 1, 5, Tables 4-6). A plausible squoma but M. aiiorgei (Deflandre) Conrad, M. reason for their occurrence is that the monitored caudata Ivanov em. Krieger and Pseudopedinelia lakes do not have very high humus content and spp. are also abundant and may contribute more are rather large in surface area, which enables than 60 % of the total biomass (II). In spring small marked turbulence. In the dystrophic, sheltered Cryptomonas spp. but in summer medium-sized forest lake, Lake Kalliojärvi, diatoms were ob Cryptomonas spp. are abundant. In summer, dia served as abundant only during spring, and flagel toms account for 45 % of the total average bio lated species dominated in the summer months mass, the dominant species being Rhizosoienia (II). Auiacoseira itaiica has been reported to cor iongiseta and Asterioneiiaformosa. The fragile R. relate positively with dystrophy (Pinel-Alloul et eriensis H.L. Smith is common only in dystrophic ai. 1990), due to its low light demands (Talling lakes (Tables 4—6). 1957). According to the present material (data In autumn, diatoms, chrysomonads and cryp base of FBI) it appears to prefer eutrophic lakes. tomonads are almost equally abundant, each con Cryptomonads and chrysomonads occur in tributing approximately 20 % of the total bio equal quantities, each contributing approximately mass. Furthermore, the proportion of Gonyosto 20 % of the total biomass (Figs. 1, 5). It seems mum semen alone is also Ca. 20 % (Fig. 5, Tables that cryptomonads derive benefit from their pig 5—6). Gonyostomum semen is rather rare in large mentation, equal to that of many cyanophytes lakes with relatively high water colour (VII), al (Van den Hoek 1984), in low light conditions in though its occurrence is generally associated with dystrophic waters (Ilmavirta 1980, 1983, Arvola dystrophy. The biomass of G. semen correlates 1984, Rask et ai. 1986, Salonen et ai. 1992). only weakly with pH but more strongly with eu Cryptomonads are also able to respond to occa trophy (V). In the studied forest lake, Lake Kal sional nutrient depletion by their motility, and by liojärvi, G. semen obviously benefitted from the 26 Lepistä Monographs of the Boreal Environment Research No. 16 high concentration of nutrients in the hypolim blooms reported in lakes in Finland (database of nion (II). A deeper sampling depth than 0—2 harmful algae of FBI). Woronichinia naegeliana, metres could be more representative due to the a typical cyanophyte in mesotrophic waters (Bret occurrence of this species in deeper parts of the turn 1989), was only occasionally observed in the water column (Eloranta and Räike 1995). studied lakes (IV, VI). This alga has formed mass occurrences below the ice already in March in the 3.5.5 Mesotrophic lakes mesotrophic Lake Lappajarvi (Lepisto and Stor berg 1995). Uroglena spp. might cause occa In the moderately shallow mesotrophic lakes (IV, sional fish-like odour during mass occurrences in VI, database of FEI), the average total phyto early summer (VI). This phenomenon is liable to plankton biomass, 2.3 mg L-1, is eightfold that in be suppressed with advancing eutrophication oligotrophic lakes, and consists mainly of dia (TaIling 1993). Dinobryon bavaricum and D. di toms (46 %) and cyanophytes (17 %) (Figs. 1, 5). vergens, generally considered to be oligotrophic The variability of biomass is also higher (SD % indicators (Järnefelt 1952, 1956a, Brettum 1989), 87) compared to the less productive lakes. The are frequently observed in mesotrophic lakes (IV, average chlorophyll a concentration, 8.7 ig L-’ VI), which is in agreement with the results of (SD % = 55), is threefold that in oligotrophic Eloranta (1989). Synura spp. is the most abundant lakes (Table 3). The vernal maximum was not ob chrysornonad in this lake group. According to served in mesotrophic lakes in this study (Fig. 4), Jhrnefelt (1952, 1956a), Synura uvella (see Ap due to the late sampling and the varying succes pendix 1) belongs to the eutrophic indicators. Go sion of phytoplankton in the shallow lakes (Tn nyostomum semen (Raphidophyceae) occurs in fonova 1993, Knuuttila et al. 1994). high quantities especially in mesotrophic lakes in Altogether 556 taxa were observed in 152 late summer and in autumn (Tables 4—6). Due to samples (Table 3). Furthermore, the diversity of its high photosynthetic pigment content very high phytoplankton increased from oligotrophic to me chlorophyll a concentrations can be measured sotrophic lakes (Figs. 1, 5, 6), which is in agree during its maximum abundance. G. semen, if ment with previous observations (Brettum 1980, abundant, causes skin irritations in swimmers økland 1983). The phytoplankton assemblage (Cronberg et al. 1988). If abundant in raw water was clearly dominated by diatoms (46 %), e.g. by this alga can clog the filters of waterworks during Acanthoceras zachariasii, Aulacoseira ambigua, water treatment (Manninen 1987). However, it to A. islandica (Muller) Simonsen, all indicators for tally disappears during the water treatment, which eutrophic waters (Järnefelt 1952, 1956a, Brettum destroys the fragile cells (VI). 1989, Lepistd 1990) and by A. italica which Bret The spring phytoplankton is dominated by the tum (1989) classifies as typical for mesotrophic diatoms Aulacoseira ambigua and A. italica (VI) waters. However, the abundance of A. italica ap and medium and large-sized cryptomonads (Fig. peared to increase with increasing trophic degree. 5, Table 4). The biomass maximum observed in Furthermore, Aulacoseira distans is observed July is caused mainly by Aphanizomenon spp. but mainly in mesotrophic lakes, especially in sum diatoms, especially Tabellariaflocculosa, domin mer (Tables 4-6). Asterionella formosa, typical ate the summer phytoplankton (Figs. 4, 5). In au for dystrophic lakes, and Tabellaria flocculosa, tumn more than one half of the phytoplankton is common in the littoral area and favouring oligo composed of cyanophytes, such as Anabaena trophic conditions (Hutchinson 1967), were abun flos-aquae and Microcystis wesenbergii (Fig. 5, dant in mesotrophic lakes. Table 6). Cyanophytes and cryptomonads contribute 17 % and 16 %, respectively, to the phytoplank 3.5.6 Eutrophic lakes ton biomass. Although water blooms are not very frequently observed (IV, VI), cyanophytes may In eutrophic lakes (VI, VII, database of FBI) the become abundant under favourable conditions. In average phytoplankton biomass is 7.6 mg L’ (Ta mesotrophic lakes mainly the N2 — fixing cyano ble 3). However, the variability of biomass is very phytes, such as Anabaenaflos-aquae and Aphani high in these lakes (SD % = 100). The average zomenon spp. are abundant (Tables 5—6). In fact, chlorophyll a concentration is also high, 36.9 jig the genus Anabaena accounts for 60 % of water L1 (SD % 82). A total of 313 taxa were identi Phytoplankton assemblages reflecting the ecological status of lakes in Finland 27 fied in 35 samples. The proportion of cyano nal maximum (Figs. 4, 5) of Aulacoseira caused phytes is on average 40 % and that of diatoms 30 taste and odour in the water (VI), although the % of the total biomass. Cyanophytes belong al number of diatom cells was only half the critical most equally to either N2 — fixing or non-N2 — fix limit (2500 cells! ml) given in the literature (Sep ing taxa. Anabaenaflos-aquae (Lyng.) Brébisson povaara 1971). Diatoms easily pass through fil (earlier also identified as Anabaena circinalis ters in water treatment (VI). In shallow and mod Ktitzing, not Anabaena circinalis Rabenhorst) is erately nutrient-rich waters, diatoms may dom the most abundant cyanophyte in eutrophic lakes, inate throughout the growing season (Willén occurring slightly less in hyper-eutrophic lakes. 1992a), when they benefit from mixing of the wa Aphanocapsa reinboldii and Microcystis aerugi ter column during summer (Lund 1971). In spring nosa are common and several other species of the the proportion of cyanophytes is rather high, 15 genus Microcystis are frequently observed in eu %, with biomass averaging 0.05 mg L’. Summer trophic lakes. The dominating diatoms, e.g. Aula phytoplankton is dominated at maximum of 48 % coseira ambigua and Acanthoceras zachariasii, by cyanophytes, such as Aphanocapsa reinboldii, both indicators of eutrophy (Lepisto 1990, Rosen- Anabaena flos-aquae, and Aphanizomenon spp. strom and Lepistö 1996), clearly prefer eutrophic Diatoms co-dominate, at a maximum of 40 %. lakes but are also common in mesotrophic and Gonyostomum semen and the green alga hyper-eutrophic lakes (Tables 4—6). Pediastrum duplex are typical summer taxa Green algae contribute 10 % to the total aver (Table 5). In autumn, phytoplankton consists age phytoplankton biomass (Tables 4—6). This mainly of diatom (maximum 71 %), Acantho group seldom dominates the biomass, according ceras zachariasii occurs in high quantities and to Mantere and Heinonen (1983). Eutrophic indi Aulacoseira alpigena with slightly lower abun cators (Järnefelt 1952, 1956a, Heinonen 1980, dance. Brettum 1989), small in cell size, such asActinas trum hantzschii Lagerheim, Dichotomococcus 357 Hyper-eutrophic lakes curvatus Korshikov and Tetraedron caudatum (Corda) Hanskirg, are numerous. Pediastrum In hyper-eutrophic lakes (I, VII, database of FEI), duplex Meyen has many modifications, exempli in which 486 taxa were identified in 143 samples, fied by P. duplex v. gracillimum W. & G.S. West the average biomass is 13.1 mg L-1 (SD % = 94) and P. limneticum Thunmark, obviously reflect and the average chlorophyll a concentration 52.4 ing differences in environmental conditions, such jg L1 (SD % = 84) (Table 3). Phytoplankton bio as increased concentrations of nutrients. P. duplex mass, consisting mainly of cyanophytes (Ca. 60 occurred in almost every eutrophic lake sample %), varies strongly due to the high peak values (VII). (Fig. 4, Table 3) and at the same time the diver Euglenids, such as Euglena proxima Dange sity may decrease (Figs. 5, 6). The proportion of ard, Trachelomonas hispida (Perty) Stein and T. the N2 — fixing cyanophytes compared to the non- volvocinopsis Svirenko are abundant in eutrophic N2 — fixing cyanophytes is on average slightly lakes, and T. volvocina Ehrenberg is typical for higher. With increasing eutrophication the aver the Lokka reservoir (IV, VI, VII). The large- age summer biomass of cyanophytes increases sized Euglena oxyuris Schmarda is observed only from 0.4 mg L1 in mesotrophic lakes to 7.5 mg in eutrophic lakes. This species is classified as a L’ in hyper-eutrophic lakes. The proportion of eutrophic indicator (Jarnefelt 1952, 1956a, Hei diatoms is on average only 20 %. nonen 1980) and is often typical in waters receiv The genus Aphanizomenon, including A. fibs ing sewage effluents (Tikkanen and Willén 1992). aquae (L.) Ralfs, A. issatzschenkoi (Usac.) Pro In addition, rather sparsely occurring taxa, mainly shkina-Lavrenko, and A. yezoense Watanabe, pseudoplankton of classes Tribophyceae and dominates. According to Watanabe (1991), A. Conjugatophyceae, are found especially in eu yezoense is abundant in less eutrophic waters. trophic lakes (VII). Furthermore, Microcystis wesenbergii and M. Spring phytoplankton consists mainly of ra aeruginosa occur in high quantities in eutrophic ther small diatoms, such as Aulacoseira alpigena and especially in hyper-eutrophic lakes. Due to (Grun.) Simonsen, A. italica v. tenuissima and taxonomical misinterpretations M. fios-aquae Stephanodiscus cf. hantzschii Grunow. The ver (Wittr.) Kirchner has been included in M. aerugi 28 Lepisto Monographs of the Boreal Environment Research No. 16

nosa (Kütz.) Kutzing. M. viridis is abundant in the database. However, it seems that in the mainly in hyper-eutrophic lakes (Tables 4—6). studied lakes the vernal maximum was partly However, Planktothrix agardhii is not among the missed due to the late sampling at the end of May most typical taxa although it is observed occa (ca. 20th May). The correct timing of sampling sionally as a very abundant component of phyto depends on the location of the lake, weather con plankton in eutrophic lakes (I, VI, VII). P. agard ditions and the morphology of the lake basin. hii is typical for eutrophic brackish waters (Niemi During more than thirty years of monitoring some 1973, 1979), and can form pronounced deep layer major methodological changes have taken place. maxima during suitable conditions (e.g. Watana The decrease of sampling depth to the two upper be 1979, Lindholm 1992). metres since 1971 (Table 2) has obviously eleva Medium-sized cryptomonads are typical for ted the phytoplankton biomass (Fig. 3), as phyto nutrient-rich lakes, which receive sewage (Rosen plankton is concentrated in the well illuminated 1981), such as Lake Tuusulanjärvi (I). Dinofla upper water layers (Reynolds 1986), especially in gellates produce by far the largest biomass (0.5 humic lakes (Salonen et al. 1984). In clear water mg L1) in hyper- eutrophic lakes, partly due to lakes, phytoplankton may also occur in deeper the rather large cell size of e.g. Ceratium hirundi layers, and in humic lakes flagellated taxa often nella (O.F. Muller) Schrank and Gymnodinium migrate between the epilimnion and hypolimnion spp. (VII) (Tables 4—6). Some dinoflagellates, (Eloranta and Raike 1995), and thus are not al such as Peridinium bibes Stein and P. willei Huit ways covered by sampling. Olrik et al. (1998) feld-Kaas, have been reported as indicators of eu recommended a sampling depth from the surface trophy (Järnefelt 1952, Hutchinson 1967, Brettum to 4—5 metres for lake phytoplankton. However, 1989). In this study P. bibes was observed in eu all changes must be seriously considered. As Har trophic lakes in summer and in hyper-eutrophic ris (1986) noted, data of equal sampling and iden lakes it was moderately abundant in autumn (da tification and adequate enumeration of the small tabase of FEI). er flagellates are needed in order to obtain a cor Spring phytoplankton is dominated by dia rect picture of long-term changes in phytoplank toms, mainly Aulacoseira italica and A. italica v. ton abundance. tenuissima, and by Cryptomonas spp. (medium- sized) and Rhodomonas lacustris. The proportion of cyanophytes is low, less than 10 %, but the av 4.2 Analyses erage cyanophyta biomass in spring is 0.6 mg L-1. In summer the cyanophytes Aphanizomenon, July samples have been studied with comparable Microcystis and Anabaena dominate the biomass methods to those used by Jarnefelt and his co with a maximum proportion of 72 % in August, workers until the end of the 1950s. July samples and diatoms (maximum 43 %), e.g. Aulacoseira are considered to give a common picture of the italica, A. granulata and the small Stephanodis productivity of inland waters during stratified cus spp. co-dominate. In autumn the abundant cy summer conditions (Heinonen 1982), although in anophytes, especially Microcystis wesenbergii, July-August the predation of phytoplankton by M. viridis and Anabaenaflos-aquae, are succeed zooplankton is often very effective and thus may ed by the diatoms Aulacoseira islandica and A. drastically change the community structure of ambigua in October (Fig. 5, Tables 4—6). phytoplankton (Lynch and Shapiro 1981). The qualified identification and counting are to a high degree dependent on the experience and 4 Problems in the analysis of proficiency of the investigator. Intercalibration of phytoplankton phytoplankton counting has demonstrated marked differences between laboratories concerning total 4.1 Sampling numbers of taxa and especially in identification at the species level. This emphasises the need for In Finland the monitoring of lake phytoplankton more exact instructions for phytoplankton count was initiated in the early 1960s. Especially July ing procedures (Niemi et al. 1985). and August phytoplankton data are extensive, This need was recently recognised by Olrik et whereas other months are clearly less represented al. (1998), who proposed Nordic standard meth Phytoplankton assemblages reflecting the ecological status of lakes in Finland 29 ods for phytoplankton analysis in fresh waters. image analysers, cell counting by flow cytometry, The methods include three different levels of pigment analyses using HPLC and the identifi quantitative and qualitative analyses of which cation of species and strains of cyanophytes using level 2, a method without analysis of live samples the highly advanced tools of molecular . and without electron microscopy (SEM and TEM), should be reached in monitoring studies. Unfortunately, the use of living material as an aid 4.3 Lake groups to identification is usually not possible in routine monitoring work. Recommendations for literature The consideration concerning typical phytoplank on identification are also given. However, an iden ton assemblages in different lake groups is based tification procedure only at the genus level as pro on the classification of lakes according to certain posed by Blomqvist and Herlitz (1998) does not variables, such as total phosphoms, water colour provide sufficient information if qualitative or pH. However, each classification approach changes in phytoplankton are considered. The use usually produces slightly different lake catego of the attribute confer (cf.) in front of the species ries. Different physical, chemical and biological name provides more information on the phyto factors influence the phytoplankton assemblages plankton composition together with cell size infor of the lake groups. Furthermore, natural or man mation, photographs and/or illustrations (I—Vu). made lakes, even when situated close to each oth The counting of taxa observed in low numbers er (IV, V), do not necessarily support similar phy causes statistical error (Willén 1976) but yields toplankton assemblages due to their different wa quantitative observations of individual species ter chemistry and morphometry. which might indicate incipient changes in the wa ter body. The simplified method using enumer ation of dominant phytoplankton is complement 4.4 The importance of tradition ed with a list of species occurring sparsely but not included in the biomass (Willén 1976). The processing of the old phytoplankton results, The biomass of phytoplankton estimated as the oldest being from the 1910s from lakes in Fin chlorophyll a does not necessarily have a strong land (I, IV, V), has been possible because the correlation with biomass on a volume basis (I, IV, identification procedures of professor Heikki V). In this study the best correlation of chloro Jbrnefelt have been followed by his students and phyll a with total biomass was obtained in the by his co-workers Toini Tikkanen and Ainikki brown- water forest lake (II). According to Tol Naulapaa, who in turn have trained the phyto stoy (1979), chlorophyll a concentration gener plankton researchers of the Finnish Environment ally provides a good measure for phytoplankton Institute and other limnologists in Finland. Al biomass, although decreasing chlorophyll content though there are no samples deposited in perma does not necessarily signify decreasing phyto nent repositories, as proposed by Stoermer (1984), plankton biomass. The composition of the algal nor photographs of the taxa in the old data, it is assemblage affects the chlorophyll a concentra quite easy due to the continuous tradition to inter tion when the chlorophyll a content of diatoms pret the species list influenced by taxonomical and cyanophytes is low compared to that of cryp changes (Appendix 1) and even to estimate the tomonads and green algae (Tolstoy 1979). This is quantitative values of phytoplankton given by evident when comparing differences between oh Jarnefelt and his co-workers. This tradition in phy gotrophic and eutrophic lakes. The total phospho toplankton identification should be continued. rus concentration increases ninefold and the chlo rophyll a concentration thirteen-fold, but the phy toplankton biomass in eutrophic lakes mainly 5 Summary consisting of large cyanophytes and diatoms is twenty five-fold compared to that in oligotrophic Waters of different status all support their own lakes (Tables 1, 3). typical phytoplankton assemblages. Due to their Several new methods in phytoplankton analy small cell size and therefore high potential growth ses will obviously be useful in the near future, such rate, phytoplankton species react quickly to as automatic identification and cell counting by changes in the surrounding environment, such as 30 Lepisto Monographs of the Boreal Environment Research No. 16

Table 7. The variation of the average (June-August) phytoplankton biomass (wet weight, mg L1) and the chlorophyll a concentration (pg L1) in lake groups with different total phosphorus concentration (pg L1) and water colour number (mg L1 Pt). SD % denotes standard deviation percent.

Lake type Tot. P Water colour Biomass SD % Chlorophyll a SD % pg L’ mg L’ Pt mg L1 pg L1

Oligotrophic 6 20 0.3 67 2.7 44 Dystrophic 14 70 0.9 78 6.2 48 Mesotrophic 18 30 2.3 87 8.7 55 Eutrophic 57 90 7.6 100 36.9 82 Hyper-eutrophic 65 75 13.2 94 52.4 84

Lokka 36 80 3.0 80 12.3 59 Porttipahta 19 70 1.0 90 6.7 79 in water quality. Phytoplankton assemblages are dant in summer, accounting on average for 10 % influenced by several factors, of which nutrient of the total biomass, but may increase in late sum concentrations, water colour and pH are generally mer and under favourable conditions mass occur considered. Furthermore, turbulence, stratifica rences are possible. Most cyanophytes belong to tion conditions, light conditions and catchment the N2 — fixing taxa, such as Anabaenaflos-aquae properties as well as the morphology of the lake and Aphanizomenon Spp. basin may influence the phytoplankton assem In eutrophic lakes the biomass is threefold that blage. In this study the quantity and quality of of mesotrophic lakes and the variation is consid phytoplankton reflecting the ecological status of erable. Cyanophytes contribute on average 20 % lakes of different types are considered. The clas to the total phytoplankton biomass, but increase sification of lakes is based mainly on the average after July approximately to 50 % of the total bio concentrations of total phosphorus (Table 7). mass. The N2 — fixing genera Anabaena and

However, when water colour is used as a factor Aphanizomenon dominate and the non-N2 — fixing for lake classification the abundance of domin genus Microcystis is also abundant. Typical for eu ating taxa changes although the nutrient concen trophic waters are centric diatoms and green trations do not markedly change. algae. In hyper-eutrophic lakes cyanophytes con In oligotrophic, mainly clear-water lakes, phy tribute on average 60 % of the total biomass toplankton biomass is low and varies only slight and they become rather abundant already in May, in ly. Small chrysomonads, some of them capable contrast to the situation in lakes with differ of mixotrophy, cryptomonads, dinoflagellates, ent trophic status. In hyper-eutrophic lakes Micro diatoms, but also small-celled colonies of cyano cystis dominates as the genus biomass but phytes, are the main components of the phyto Aphanizomenon spp. dominates as the individual plankton biomass. In dystrophic lakes and in res taxon. ervoirs phytoplankton biomass is higher than in The importance of individual species (taxon) oligotrophic lakes, and is composed mainly of and algal groups as components of total biomass diatoms, with the exception of brown-water lakes, increases with increasing trophic gradient, and the and cryptomonads. Mixotrophic flagellates are species diversity decreases. The biomass of a abundant. Typical species are Mallomonas single algal group does not necessarily change crassisquoma (Chrysophyceae), Rhizosolenia when the N:P ratio changes but the species com iongiseta (Diatomophyceae) and Gonyostomum position of the group may change quite drastic semen (Raphidophyceae). ally. However, almost all taxa are observed in Mesotrophic lakes in this study can be divided each lake group due to the generally wide ecolo into clear-water lakes and moderately brown-wa gical amplitude of phytoplankton species, but ter lakes. Diatoms dominate the phytoplankton, competition and grazing restrict their occurrence and cryptomonads co-dominate. Gonyostomum in unfavourable conditions. Exceptionally some semen (Raphidophyceae) increases in late sum algae, e.g. Microcystis viridis and Euglena oxyuris mer and autumn. Cyanophytes are not very abun are observed only in eutrophic waters. Phytoplankton assemblages reflecting the ecological status of lakes in Finland 31

Effective water protection efforts during the The increase of biological productivity in wa past two decades appear to have improved the ters as a consequence of eutrophication often pro state of the lakes. Phytoplankton reacts immedi motes nuisance in the form of mass occurrences ately to decreasing waste water load and de of algae. Even in moderately eutrophic lakes the creased nutrient concentrations in the water, but spring maxima of chrysomonads and diatoms the reaction also continues over a long period. may cause taste and odour problems which are in Due to the decrease of nitrogen compounds the convenient, especially in surface waters used as non-N2 — fixing Planktothrix are soon out-com raw water for water works. Cyanophytes increase peted, and cyanophytes may totally disappear af in late summer in moderately nutrient-rich waters ter some years. The internal loading sustains ad but may increase in early summer in very eu equate phosphorus concentration for the N2 — trophic lakes, and the possibility of abundant fixation in water, and the N2 — fixing Anabaena toxic Microcystis — species increases. Gonyosto and Aphanizomenon occur alternatively with the mum semen increases in late summer even in non-N2 — fixing genus Microcystis, which is an slightly eutrophic lakes. The slight eutrophication effective competitor for nutrients. Over longer of dystrophic lakes does not increase markedly periods of time, taxa typical for less eutrophic the quantity of cyanophytes in these lakes. conditions, such as the diatoms Rhizosolenia and In general the state of Finnish lakes seems to Tabeilaria and the chrysomonad Dinobryon are have improved in the 1 990s according to the data observed. Simultaneously the species diversity of of phytoplankton monitoring, although the the phytoplankton assemblage may increase, and number of observations of algal blooms has in it may change towards smaller species accom creased. Only in mesotrophic lakes does phyto panied by decrease in the biomass. plankton biomass appear to have increased in the The construction, water level regulation, and 1990s, mainly due to increase of diatoms. A slow later the ageing process have all affected the water eutrophication process might be the reason for quality and phytoplankton assemblages in the res this phenomenon. In highly eutrophic lakes the ervoirs Lokka and Porttipahta. In the young res total biomass, including cyanophytes and dia ervoirs river phytoplankton with small cyano toms, has strongly decreased in the 1990s, and Ca. phyta colonies, the green alga Monoraphidium 50 % of cyanophytes are those which only seldom contortum and flagellated and heterotrophic taxa produce toxic strains. The state of the hyper-eu were abundant. The period of strong water level trophic Lake Tuusulanjärvi has clearly improved regulation increased nutrients in the water and wa due to the effective restoration efforts. ter colour also increased due to the organic matter. The estimation of phytoplankton quantity by The high quantity of available silicate benefitted analysing the chlorophyll a concentration is an ef diatoms regardless of the turbidity of water, and fective method and provides much data, but rou especially Aulacoseira italica was abundant. Nu tine chlorophyll analyses do not provide informa trient and organic matter concentrations decreased tion about the composition of phytoplankton. In during the ageing process of the reservoirs. formation about water quality is provided by However, total phosphorus concentration in the monitoring of the occurrence of cyanophytes by Lokka reservoir is still twofold that in mesotrophic microscopy, even at a qualitative level, which is lakes, close to the concentrations of eutrophic recommended in surface water used as a raw wa lakes. Due to the humic compounds, phosphorus is ter source for waterworks. The reason for unpre only partly bioavailable for phytoplankton, and dicted increase of chlorophyll a might be e.g. Go perhaps for this reason the phytoplankton biomass nyostomum semen, an alga with many chloro is equal to that in mesotrophic lakes. In the Portti plasts. pahta reservoir nutrient concentrations are lower, Phytoplankton volume and chlorophyll a val typical for mesotrophic waters, but the biomasses ues show relatively good correlation if plotted are only one half of those recorded in mesotrophic against each other in oligotrophic and dystrophic lakes. Auiacoseira italica is typical for both res lakes, because the phytoplankton composition ervoirs but Rhizosolenia iongiseta is typical for the consists of small cryptomonads and other algae Porttipahta reservoir. However, during very warm with high chlorophyll a contents. Eutrophic lakes, weather conditions cyanophytes may still form wa however, are dominated by large cyanophytes and ter blooms in the Lokka reservoir. diatoms, often with rather low chlorophyll a con- 32 Lepisto Monographs of the Boreal Environment Research No. 16

tents. Thus the chlorophyll a concentrations in slightly in hyper-eutrophic lakes. In oligotrophic these lakes are rather low compared to the total lakes different algal groups are almost equally phytoplankton volume. Total phytoplankton vol abundant as biomass but chrysomonads are abun ume may be overestimated due to difficulties in dant as cell numbers. Typical for dystrophic lakes estimating the volume of large cyanophyta colo are diatoms and cryptomonads but in small nies and also due to errors in microscopic analyses. brown-water forest lakes diatoms are rare. Meso In long-term monitoring the seasonal and in trophic lakes are also clearly dominated by dia terannual variability of phytoplankton, e.g. due to toms, and the average biomass of cyanophytes

weather conditions, is often remarkable. The vari consisting mainly of N2 — fixing Nostocales is ability appears to increase with increasing trophic moderately low until late summer. In eutrophic degree. The distinction between changes caused lakes and especially in hyper-eutrophic lakes by eutrophication and the natural variability is cyanophytes become abundant already in the ear one of the basic challenges for monitoring. ly summer. Finally, diatoms appear to be the most “New” members in the phytoplankton assem important group in the studied lakes, and crypto blage might at an early phase predict changes in monads co-dominate. Only in eutrophic lakes, cy ecological status of a water body. However, anophytes dominate the phytoplankton assem progress in the taxonomy of phytoplankton also blage. Furthermore, in lakes in Finland the quan causes the appearance of “new” species and the tity of cyanophytes seems not to have increased in disappearance of some other species during long- the 1990s. term monitoring. Furthermore, in an ideal situa tion the long-term monitoring based on micro scopical analyses should be performed by one 6 Yhteenveto person or by one group with close cooperation and unbroken tradition. Regularly repeated inter- En tyyppisissh vesissh on niille ominainen kas calibrations between different phytoplankton re viplanktonyhteiso. Pienikokoiset, nopeasti lisään searchers are therefore important, because other tyvät kasviplanktonsolut heijastavat herkästi ym wise the changes observed in the phytoplankton paristossaan, kuten veden laadussa tapahtuvia assemblage may only reflect changes beside the muutoksia. Kasviplanktonin koostumukseen vai microscope, not in the environment. kuttavista tekijdistä tarkastellaan etenkin ravinne In conclusion, the results show that phyto suhteita, veden varib ja happamuutta. Myos veden plankton reflects the ecological status of lakes virtaus- ja kerrostuneisuusolosuhteet, valaistus and also responds both qualitatively and quantita olosuhteet, valuma-alueen ominaisuudet ja altaan tively to changes therein. The average phyto morfologia vaikuttavat kasviplanktonin koostu plankton biomass increases with increasing eutro mukseen. Tässh tydssä tarkastellaan kasviplank phy, as does the variation of biomass. This vari tonyhteisojen lajikoostumusta ja määrää erityyp ation is highest in eutrophic lakes but decreases pisten jbrvien ekologisen tilan ilmenthjinh. Jar-

Taulukko. Erityyppisten jarvien keskimaaräisen (kesa—heinäkuu) kasviplanktonbiomassan (mg L1) ja a.klorofyllin pitoi suuksien (tg L1) vaihtelu kokonaisfosforin (ig L1) ja veden väriluvun (mg L1 Pt) muuttuessa. SD % kuvaa standardi. poikkeaman prosentuaalista vaihtelua.

Jarvityyppi Kok. P Veden van Biomassa SD % a-klorofylli SD % jig L1 mg L-1 Pt mg L-1 jig L-1

Oligotrofinen 6 20 0.3 67 2.7 44 Dystrofinen 14 70 0.9 78 6.2 48 Mesotrofinen 18 30 2.3 87 8.7 55 Eutrofinen 57 90 7.6 100 36.9 82 Hyper-eutrofinen 65 75 13.2 94 52.4 84

Lokantekoallas 36 80 3.0 80 12.3 59 Porttipahdan tekoallas 19 70 1.0 90 6.7 79 Phytoplankton assemblages reflecting the ecological status of lakes in Finland 33

vien luokittelussa on ensisijaisesti kaytetty koko lajikoosturnus saattaa rnuuttua rnerkittavästi. Kas naisfosforin keskimääräisiä pitoisuuksia. Kun ye- viplanktonlajit ovat yleensa ymparistovaatirnuk den varilukua kaytetaan luokittelevana tekijäna, siltaan joustavia, ja niitä tavataan kaikissa tarkas valtalajit ja niiden runsausjarjestys muuttuvat, telluissa jarviryhmissa. Kasviplanktonlajien kes vaikka ravinnepitoisuudet eivät juurikaan muutu. kinainen kilpailu ja niihin kohdistuva saalistus ra Vahäravinteisten, oligotrofisten, paaosin kir joittavat kuitenkin niiden esiintymista suhteessa kasvetisten jarvien ryhmassa kasviplanktonbio toisiinsa, ja niiden mhärk saattaa olla alhainen massa on aihainen ja sen vaihtelu vähäistä. Pieni epasuotuisissa olosuhteissa. On kuitenkin poik kokoiset kultalevät, joista nsa on miksotrofisia, keuksia, kuten Microcystis viridis ja muutamat nielulevät, panssarisiimalevät, piilevat mutta silmalevat, kuten Euglena oxyuris, joita tavataan myös pienisoluiset sinilevayhdyskunnat muodos pelkästäan rehevissä vesissä. tavat pääosan kasviplanktonista. Tummavetisissa, Tehokkaiden vesiensuojelutoimenpiteiden an eli dystrofisissa jarvissa ja molemmissa tutkituis siosta järvet näyttaisivät karuuntuneet viimeisten sa tekoaltaissa kasviplanktonin mkärä on suurem parin vuosikymmenen aikana. Kasviplanktonyh pi kuin oligotrofisissa vesissä ja lajisto koostuu teisö reagoi jätevesipäastojen loppumiseen ja alen lahinnä piilevista, poikkeuksena kuitenkin turn tuneisiin ravinnepitoisuuksiin sekä välittömästi mavetiset pienet metsajarvet, ja nielulevistä. Mik että pitkan ajan kuluessa. Typpiyhdisteiden vahe sotrofisia lajeja on runsaasti. Tyypillisia lajeja nemisen takia Planktothrix -suku ei kykene kilpai ovat Mallomonas crassisquoma (Chrysophyce lemaan ravinteista typpeäsitovien sinilevien kans ae), Rhizosolenia Iongiseta (Diatomophyceae) ja sa. Sinilevayhteiso saattaa jopa romahtaa täydelli Gonyostomum semen (Raphidophyceae). sesti muutaman vuoden kuluttua jatevesipäästojen Mesotrofisista, lievästi rehevoityneista jarvista lopettamisesta. Sisäinen kuormitus tuottaa veteen osa on suhteellisen kirkasvetisiä ja osa melko rus edelleen typensidontaa varten riittävasti fosforiyh keavetisiä. Piilevät ovat vallitsevina ja nielulevat disteita ja typensitojat Anabaena ja Aphanizome muodostavat rnerkittavän osan näiden jarvien kas non vuorottelevat ei-typpea sitovan Microcystis viplanktonista. Sinilevien osuus on keskimäarin -suvun kanssa, joka puolestaan kilpailee tehok 10 % kesän kasviplanktonbiomassasta, inutta nii kaasti ravinteista. Ajan myotä vaharavinteisem den osuus saattaa kasvaa loppukesalla ja suotui mille vesille tyypilliset piilevat kuten Rhizosolenia sissa olosuhteissa saattaa muodostua massaesiin ja Tabellaria, seka Dinobryon-kultalevat yleisty tymia. Phaosa sinilevisth on typensitojia, joista vat, sarnalla kuin lajisto rnonipuolistuu ja muuttuu yleisimpia ovat Anabaena flos—aquae ja Aphani pienikokoisemmaksi ja biomassa laskee. zomenon spp. Reheviksi, eli eutrofisiksi luokitel Rakentaminen, vedenpinnan saännostely ja luissa vesissä sinilevien osuus biomassasta on ikaantyminen ovat nähtävissä Lokan ja Porttipah keskimäärin 20 %, mutta saattaa heinakuussa dan tekoaltaiden veden laadussa j a kasviplankton nousta liki 50 %:iin. Typensitojasuvut Anabaena yhteisoissa. Nuorissa tekoaltaissa vallitsi ns. jo ja Aphanizonenon ovat valtalajeina, mutta Micro kiplankton, jossa pienisoluiset sinilevayhdyskun cystis -sukuun kuuluvia lajeja on myos runsaasti. nat, ja esimerkiksi Monoraphidiu,n con tortuin Sentristen piilevien ja viherlevien osuus biomas -viherleva sekä siimalliset ja heterotrofiset lajit sasta on suurimmillaan eutrofisissa järvissa. Erit olivat runsaina. Voimakas saannostelyjakso lisäsi tam rehevissä, eli hyper-eutrofisissa jarvissä sini rayinteiden ja silikaattipiin pitoisuuksia vedessä, levien osuus on keskimäärin 60 % biomassasta ja ja runsas orgaaninen aine tummensi vettk entises ne runsastuvat jo toukokuusta lahtien toisin kuin tään. Vaikka vesi oh sarneaa, runsas sihikaattipii muissa jarviryhmissa. Hyper-eutrofisissa jarvissa edesauttoi piilevien kasvua. Aulacoseira italica Microcystis -suvun lajien osuus kesän sinilevabio muodosti paäosan kasviplanktonista. massasta on suurin mutta runsaimmin tavattu yk Altaiden ikaantyessa veden ravinnepitoisuus sittäinen taksoni on Aphanizonenon spp. ja orgaanisen aineen määrh laskivat. Lokan teko Mitä rehevimmistä vesistä on kyse sita suu altaassa kokonaisfosforia on kuitenkin edehleen rempi on yksittaisten lajien (taksonien) ja levä keskirnäbrin kaksinkertainen määrä mesotrofisiin ryhrnien merkitys biomassasta, milcä alentaa laji järviin verrattuna, hiki eutrofisten jarvien tasolla. diversiteettiä. Yksittaisen levaryhman biomassa Vedessä oleva runsas humus sitoo osan fosforista, ei välttamättä rnuutu ravinnesuhteiden (lähinnä eikä se ole kasviplanktonin kaytettavissa. Ehka N:P-suhteen) muuttuessa, mutta ryhman sisälla sen vuoksi Lokan kasviplanktonbiornassa vastaa 34 Lepistö Monographs of the Boreal Environment Research No. 16 kin mesotrofisen jarven keskimaäräista biomas pitoisuuden kanssa sekd karuissa että tummaveti saa. Porttipahdan tekoaltaassa ravinteiden pitoi sissdjdrvissd, koska niissd on pienikokoisia nielu suudet ovat aihaisempia, mesotrofisille vesille ja muita levia, joiden a-klorofyllin pitoisuus on tyypillisiä, mutta kasviplanktonin biomassa on suuri. Rehevissd jarvissa sen sijaan dominoivat alle puolet mesotrofisten j ärvien keskimääräisesta suurikokoiset sinilevat ja piilevat, joiden a-ldoro biomassasta. Aulacoseira italica on edelleen tyy fyllin pitoisuus on suhteellisen aihainen, jolloin piffinen molemmille tekoaltaille mutta Porttipah kasviplanktonbiomassa on suhteellisesti suurem dan lajistolle tyypillinen on Rhizosolenia ion pi. Biomassa-arvoja saattaa lisaksi nostaa etenkin giseta. Poikkeuksellisen lämmin kesa saattaa yha suurten sinilevayhdyskuntien tilavuuden arvioin edesauttaa sinilevien massaesiintymien muodos tivirheet, samoin kuin muut mikroskooppisen tumista Lokan tekoaltaassa. analysoinnin virheet. Biologisen tuotannon lisaäntyminen järvien Pitkaaikaisessa seurannassa kasviplanktonin vahitellen rehevoityessa ilmenee haitallisina levä kasvukauden aikainenja vuosittainen vaihtelu, la esiintyminä. Alkavan rehevoitymisen myötä ke hinna saaolosuhteista johtuen, saattaa olla huo väiset kultalevien ja piilevien maksimit runsastu mattava. Vaihtelu on sitä suurempaa, mitä rehe vat ja aiheuttavat haju-ja makuhaittoja, jotka ovat vammista vesistä on kysymys. Luonnollisen vaih kiusallisia etenkin raakavesilähteenä kaytetyissa telun erottaminen rehevoitymisen aiheuttamasta pintavesissä. Sinilevät runsastuvat loppukesalla vaihtelusta on seurannan perushaaste. Kasvi mesotrofisissa järvissä mutta erittain rehevissh planktonyhteison “uudet lajit” saattavat jo var järvissäjo alkukesälla. Pahimmillaan levaesiinty ham ennustaa jdrven ekologisen tilan muutoksia, mat ovat myrkyllisten Microcystis-lajien muo mutta “uusien” lajien ilmaantuminen taijoidenkin dostamia. Gonyostomum semen-limalevä runsas lajien hdvidminen pitkan seurannan aikana johtuu tuu loppukesalla jo lievästi rehevdityneissä jar myds taksonomisista muutoksista. Mahdollisuuk vissh. Tummavetisten jarvien lievh rehevöitymi sien mukaan tulisi kasviplanktonanalyysien teki nen ei usda merkittdvdsti sinilevien maärdd. jdiden ja tutkimusmenetelmien olla samoja mah Suomalaisten jdrvien tila kasviplanktonseu dollisimman pitkaan. Myos sddnnöllisesti toiste rannan tulosten perusteella arvioituna ndyttaisi tut interkalibroinnit takaavat vertailukelpoiset tu 1990-luvulla kohentuneen, vaikka ilmoitukset si uokset. Pahimmillaan kasviplanktonyhteisossd nilevaesiintymista ovatkin lisaantyneet. Ainoas havaitut rnuutokset eivdt kuvasta muutoksia ym taan mesotrofisissa jdrvissd kasviplanktonin indä paristdssa, vaan pelkastaan tutkijan vaihtumista. rä on 1990-luvulla kasvanut, lahinna piilevien ii Yhteenvetona voidaan todeta, ettd tulokset saantymisen takia. Kyseessa saattaa olla hidas re osoittavat kasvipuanktonin kuvastavan jarvien hevoityminen eli ns. “nuhraantuminen”. Erittdin ekologista tiuaa ja reagoivan seka madrallisesti rehevissa jarvissd kasviplanktonin kokonaisbio ettd laadullisesti niiden tilassa tapahtuviin muu massa samoin kuin sinilevien ja piilevien määrä toksiin. Kasvipuanktonin keskimddrdinen biomas on selvdsti laskenut 1990-luvulla. Noin 50 % sini saja sen vaihtelu kasvavat rehevoitymisen myota. levistä on niitä, jotka harvemmin muodostavat Vaihtelu on suurinta rehevissd jdrvissd mutta las myrkyllisia kantoja. Erittain rehevan Tuusulan kee jonkin verran erittdin rehevissd jarvissa. Va jarven tila on selvästi parantunut tehokkaiden haravinteisissa järvissd en levaryhmien osuus on kunnostustoimenpiteiden ansiosta. biomassana Idhes yhtd suuri mutta solumddrdltddn Kasviplanktonin mddrdn mittaaminen a-kloro kultalevät ovat rnerkittavin ryhma. Tummavetisil fyllin pitoisuuksina on menetelmänd nopea ja te le jdrville on tyypiulista piilevien ja nielulevien hokas mutta ei rutiinimenetelmana kerro kas suuri mddrd, mutta pienissa erittäin tummavetisis viplanktonin koostumusta. Sinilevien esiintymis sajarvissa piilevia on vdhdn. Myos lievdsti rehe tä pintavetta kayttavdn vesilaitoksen raakavedes voityneissa jarvissa piilevat dominoivat ja smile sd seurataan yhd useammin mikroskopoimalla, vien mddrd on verraten aihainen lisddntyen loppu jopa kvalitatiivisesti, jolloin veden laadusta saa kesdlld. Sinilevayhteiso koostuu padasiassa typ daan ama lisatietoa. Syyna normaalista poikkea peasitovista siniuevista. Rehevissaja erittdin rehe vaan a klorofyllipitoisuuteen saattaa esimerkiksi vissd vesissd sinilevat ovat vallitsevina, ja niitd on olla runsaasti kioroplasteja sisaltävd Gonyosto usein runsaasti jo aukukesaula. Lopuksi voidaan mum semen. todeta, ettd paaosassa tutkituista jdrvistd piilevat Kasviplanktonbiomassa korreloi a-klorofyllin ovat merkittavin ryhma, nielulevid on jonkin ver Phytoplankton assemblages reflecting the ecological status of lakes in Finland 35 ran vähemman, ja vain rehevissä jarvissa sinilevät Arvola, L. 1980. On the species composition and bio dominoivat kasviplanktonyhteisoa. Tutkimuksen mass of the phytoplankton in the Lokka reservoir, perusteella sinilevien mhärä ei nayttaisi lisaanty northern Finland, Ann. Bot. Fennici 17: 325—335. neen Suomenjhrvissh 1990-luvulla. Arvola, L. 1983. Primary production and phytoplank ton production in two small, polyhumic forest lakes in southern Finland. Hydrobiologia 101: Acknowledgements 105—110. Arvola, L. 1984. Vertical distribution of primary pro duction and phytoplankton in two small lakes with I started phytoplankton studies on 7 January, different humus concentration in southern Fin 1965. Since then my colleagues, Pirkko Kokko land. Holarctic Ecology 7: 390—398. nen, Reija Jokipii and Maija Niemela and I have Arvola, L. & Rask, M. 1984. Relations between phyto identified and counted more than 11 000 phyto plankton and environmental factors in a small plankton samples, both for monitoring and study spring—meromictic lake in southern Finland. Aqua purposes. We have had good intercalibration con Fennica 14: 129—138. tacts with several phytoplankton researchers both Arvola, L., Metsala, T.R., Similh, A. & Rask, M. in Finland and in Nordic Countries. I particularly 1990. Phyto— and zooplankton in relation to water thank Mrs Ainikki Naulapaa, Phil. Lic. Toini pH and humic content in small lakes in Southern Tikkanen, Dr. Gertrud Cronberg, Professor Pertti Finland. Verh. Internat. Verein. Limnol. 24: 688— Eloranta and Dr. Guy Hällfors for the teaching of 692. species identification. Special thanks go to Pro Bird, D.F. & Kalff, J. 1987. Algal phagotrophy: Regu lating fessor Reino Laaksonen, Professor Ake Niemi factors and importance relative to photo synthesis in Dinobryon and Dr. Pertti Heinonen, who have encouraged (Chrysophyceae). Limnol. Oseanogr. 32: 277—284. me to bring this work to its conclusion. The sum Blomqvist, P. 1996. Late summer phytoplankton re mary paper was greatly improved due to the com sponse to experimental manipulations of nutrients ments of Dr. Lauri Arvola. I wish to thank Sirkka and grazing in unlimed and limed Lake Njupfatet, Vuoristo, who drew the figures in this work and central Sweden. Arch. Hydrobiol. 137 (4): 425— Päivi Laaksonen who helped in the typeing of ta 455. bles. The English language of the summary paper Blomqvist, P. & Herlitz, E. 1998. Methods for quanti and the articles was revised by Michael Bailey. tative assessment ofphytoplankton in freshwaters, The summary paper was partly written with sup part 2. Naturvhrdsverket, A6—Gl. Stockholm. port from the Academy of Finland. In addition, I 78 pp. thank numerous persons in the Finnish Environ Blomqvist, P., Petterson, A. & Hyenstrand, P. 1994. ment Institute and elsewhere not mentioned Ammonium—nitrogen: A key regulatory factor above who have helped me in scientific and per causing dominance of non—nitrogen—fixing cyano sonal issues. bacteria in aquatic systems. Arch. Hydrobiol. 132, (2): 141—164. I dedicate this thesis to my family, especially Bostrom, B., Persson, G. & Broberg, B. 1988. Bio to my three grandchildren Pauli, Heikki and Mik availability of different phosphorus forms ko. in fresh water systems. Hydrobiologia 170: 133—156. Brettum, P. 1980. Planteplankton som indikator ph Helsinki, September 1999 Liisa Lepisto vannkvalitet i norske innsjøer. 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Vollenweider, R.A. 1968. Scientific fundamentals of Økland, 3. 1983. Planter og dyr — økologisk oversikt. the eutrophication of lakes and flowing waters, Ferskvannets verden 2. Universitetsforlaget, Oslo. with particular reference to nitrogen and phos 209 pp. Appendix 1. Some valid names and their synonyms of the species in the studied material (, not synonym).

Valid names Synonyms

Aphanocapsa planctonica (G.M. Smith) Kom. & Anagnostidis Aphanocapsa elachista f. planctonica G.M. Smith 0 Aphanocapsa reinboldii (Forti) Kom. & Anagnostidis Microcystis reinboldii (Richter) Forti 5) Merismopedia tenuissima Lemmermann (In fertilized fish ponds, less common in lakes) 5) C) Merismopedia warmingiana Lagerheim Merismopedia minima Beck CD Snowella lacustris (Chod.) Kom. & Hindák Gomphosphaeria lacustris Chodat 0- Woronichinia naegeliana (Unger) Elenkin Coelosphaerium naegelianum Unger CD Gomphosphaeria naegeliana (Unger) Lemmermann CO Anabaena flos-aquae Brébisson Anabaena circinalis Kutzing Aphanizomenon yezoense Watanabe Aphanizomenon flos-aquae (L.) Ralfs CD Leptolyngbya mucicola (Lemm.) Kom. & Anagnostidis Lyngbya mucicola Lemmermann Limnothrix planctonica (Wolosz.) Meffert Oscillatoria planctonica Woloszynska Phormidium tenue (Ag. ex Gom.) Anagn. & Komárek Oscillatoria tenuis Ag. ex Gomont (5 Planktolyngbya limnetica (W.West) Anagn. & 0CD Komárek Lyngbya subtilis W.West, Lyngbya limnetica Lemmermann 0 Planktothrix agardhii (Gom.) Anagn. & Komárek Oscillatoria agardhii Gomont Pseudanabaena limnetica (Lemm.) Anagn. & Komárek Oscillatoria limnetica Lemmermann 5) Pseudanabaena mucicola (Naum. & Hub-Pest.) Anagn. & Komárek Phormidium mucicola Naum. & Hub.-Pestalozzi CO Pseudanabaena sp. (Cyanodictyon sp.) “Phormidium dictyothallum” Skuja

Trichodesmium lacustre (Klebahn) Anagn. & Komárek Oscillatoria lacustris (Klebahn) Geitler CO 0 Ceratium spp. Ceratium hirundinella (OF. Muller) Schrank iii Ceratium furcoides (Lev.) Langhaus 5) Peridinium umbonatum Stein Peridinium inconspicuum Lemmermann

Bicosoeca lacustris J. Clark Bicoeca lacustris J. Clark 5) Bicosoeca planctonica v. multiannulata (Skuja) Bourrelly Bicoeca multiannulata Skuja 0 Mallomonas punctifera Korshikov Mallomonas reginae Teiling Ochromonadales mainly Uroglena cells, Flagellata cetera Uroglena spp. Uroglena americana Calcins Uroglena volvox Ehrenberg Synura spp. Synura uvella Stein em. Korshikov

Acanthoceras zachariasii (Brun) Simonsen Attheya zachariasii Brun Cyclotella radiosa (Grun.) Lemmermann Cyclotella comta (Ehrenb.) KUtzing Aulacoseira alpigena (Grun.) Simonsen Melosira distans v. alpigena Grunow Aulacoseira ambigua (Grun.) Simonsen Melosira ambigua (Grun.) 0. MUller Aulacoseira italica (Ehrenb.) Simonsen Melosira crenulata (Ehrenb.) Kütz., M. italica (Ehrenb.) KUtzing Aulacoseira distans (Ehrenb.) Simonsen Melosira distans (Ehrenb.) Kutzing Aulacoseira granulata (Ehrenb.) Simonsen Melosira granulata (Ehrenb.) Ralfs Aulacoseira granulata v. angustissima (0. MUll.) Simonsen Melosira g. v. angustissima 0. Muller Aulacoseira lirata (Ehrenb.) R. Ross Melosira distans v. lirata (Ehrenb.) Hustedt Aulacoseira islandica (0. Mull.) Simonsen Melosira islandica 0. MUller Diatoma tenuis Agardh Diatoma elongatum (Lyngb.) Agardh Fragilaria berolinensis (Lemm.) Lange-Bertalot Synedra berolinensis Lemmermann Fragilaria nanana Lange-Bertalot Synedra nana Meister Fragilaria ulna (Nitzsch) Lange-Bertalot Synedra acus KUtz, S. acus var. angustissima (Grun.) van Heurck Fragilaria ulna (Nitzsch) Lange-Bertalot Synedra ulna (Nitzsch) Ehrenberg Tabellaria flocculosa (Roth) Kutzing Tabellaria fenestrata (Lyng.) KUtzing Bacillariales Diatomaceae cetera

Goniochioris fallax Fott Tetraedron trigonum Auctor Istmochloron trispinatum (W.&G.S .West) Skuja Tetraedron trispinatum (W.&G.S .West) Hub.-Pestalozzi Pseudostaurastrum enorme (Ralfs) Chodat Tetraedron enorme (Reinsch) Hansgirg Pseudostaurastrum planctonicum (G. M. Sm.) Chodat Tetraedron planctonicum G. M. Smith 0 0 Chiamydocapsa ampla (Kutz.) Fott Gloeocystis gigas (Kütz.) Lag. sensu Bachmann Nephrocytium limneticum (G. M. Smith) G. M. Smith Gloeocystopsis limnetica G. M. Smith Pseudosphaerocystis lacustris (Lemm.) Novákova Gemellicystis neglecta Teiling em. Skuja Pseudosphaerocystis neglecta (Teil.) Bourrelly Gemellicystis neglecta Teiling em. Skuja Sphaerocystis planctonica (KorL) Bourrelly Gloeococcus schroeteri (Chod.) Lemm. sensu Skuja Sphaerocystis schroeteri Chodat Gloeococcus schroeteri (Chod.) Lemm., Eutetramorus fottii (Hind.) Komárek Thorakochioris cf. nygardii Komárek Gloeocystis planctonica (W. et G.S.West) Lemm. sensu Bourrelly Ankistrodesmus fusiformis Corda Ankistrodesmus falcatus (Corda) Ralfs Koliella spiculiformis (Visk.) Hindák Ankistrodesmus falcatus (Corda) Ralfs Monoraphidium mirabile (W. & G. S. West) Pankow Ankistrodesmus mirabilis (W. & G. S. West) Lemmermann Chiorolobion?; Ankistrodesmus falcatus v. mirabile sensu Hortobogay Chiorolobion braunii (Nag.) Komárek Monoraphidium braunii (Nag.) Kom.-Legnerová Koliella setiformis (Nyg.) Nygaard Ankistrodesmus falcatus v. setiforme Nygaard Monoraphidium contortum (Thuret) Kom.-Legnerova Ankistrodesmus falcatus v. spirilliformis G.S. West Closteriopsis longissima v. longissima Lemmermann Ankistrodesmus longissimus (Lemm.) Wille Keratococcus suecicus Hindák Ankistrodesmus setigerus (SchrUder) G. S. West sensu Skuja Botryococcus spp. Botryococcus braunii KUtzing Botryococcus neglectus Komárek & Marvan Botryococcus terribilis Komárek & Marvan Korschikoviella limnetica (Lemm.) Silva Characium limneticum Lemmermann a) Crucigeniella rectangularis (Nag.) Komárek Crucigenia rectangularis (Nag.) Gay Crucigeniella truncata (G. M. Sm.) Komárek Crucigenia truncata G. M. Smith 0 Crucigenia lauterbornii (Schm.) Schmidle Hofmania lauterbornii (Schmidle) Wille a) a) Fusola viridis Snow Elakatothrix viridis Printz a) CD Kirchneriella contorta v. elongata (G. M. Smith) Komárek Kirchneriella elongata G. M. Smith Nephrochlamus willeana (Printz) Korshikov Nephrocytium willeana Printz 0- 0 Pediastrum angulosum (Ehr.) ex Meneghini Pediastrum araneosum (Racib.) Raciborski CD Cl) Pediastrum duplex v. gracillimum W. & G. S. West Pediastrum gracile A. Br., P. gracillimum Thunmark Pediastrum duplex Meyen Pediastrum limneticum Thunmark CD Pediastrum tetras (Ehr.) Ralfs Pediastrum tetras v. tetraodon (Corda) Hansgirg C) Teilingia granulata (Roy & Biss.) Bourrelly Sphaerozosma granulatum Roy & Bisset CQ Scenedesmus subspicatus Chodat Scenedesmus abundans (Kirchn.) Chod. sensu G.M. Smith CD

Scenedesmus obtusus f. alternans (Reinsch) Compère Scenedesmus alternans Reinsch CD 0 Didymocystis bicellularis (Chod.) Komárek Scenedesmus bicellularis Chodat 0 0 Didymocystis fina Komárek Scenedesmus bicellularis Chodat 0 Scenedesmus ecornis (Ehr.) Chodat Scenedesmus bicellularis Chod. sensu Uherkovich Scenedesmus linearis Komárek. Scenedesmus bijugatus (Turbin) Kütz. (sensu auct. post) a) Scenedesmus bijuga sensu auct. post Fott & Komárek Scenedesmus a) denticulatus Lagerheim Scenedesmus fenestratus (Teil.) Uherkovich 0 Scenedesmus quadricauda (Turp.) Bréb. sensu Chodat Scenedesmus longus Meyen

CD Staurodesmus convergens (Ehr.) Teiling Arthrodesmus convergens Ehrenberg a) Staurodesmus dejectus (Br.) Teiling Staurastrum dejectum Brébisson

a) 0. Anagnostidis & Komárek 1988 EttI & Gartner 1988 Haworth 1988 Komárek & Fott 1983 Komárek & Marvan 1992 Komárek & Anagnostidis 1999 Koppen 1975 Tikkanen & Willén 1992 Williams et at. 1988

Ca

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