Assessment of trophic state of four lakes in the Suwałki Landscape Park (NE Poland) based on the...

Assessment of trophic state of four lakesin the Suwałki Landscape Park (NE Poland)based on the summer phyto- and zooplanktonin comparison with some physicochemical parameters

ELŻBIETA JEKATIERYNCZUK-RUDCZYK*, MAGDALENA GRABOWSKA,JOLANTA EJSMONT-KARABIN AND MACIEJ KARPOWICZ

Abstract. The trophic status of lakes determines the development and functioning of aquatic organ-isms. The aim of the present study was to assess the current trophic status of four lakes in the Suwałki Landscape Park (SLP). The analysis included parameters useful to determine trophic state of lakes, i.e. chemical parameters of water and phyto- and zooplankton parameters, both quantitative (abundance, biomass) and qualitative (species composition, dominations) ones.

Lakes situated in the SPK belong to the most pristine aquatic environments in Poland. However, contemporary development of tourism in these areas (in this case agrotourism) affects the water quality. Comprehensive hydrobiological research is necessary to reveal changes in the aquatic environment. The interpretation of background data on hydrology (chemisrty, biology, meteorology, etc) affecting the rate of the water cycle is also very important.

In July 2009, only Lake Hańcza was mesotrophic in terms of physical and chemical parameters. An analysis of the parameters characterizing the specifi c and quantitative structure of phytoplankton community, rotifer and crustacean communities enabled estimation of the trophic state of the studied lakes. The trophic index of the phytoplankton community was calculated on the basis of the abundance of trophic state indicators. The two deepest lakes with the greatest abundance of Bacillariophyceae and fl agellates from Chrysophyceae and Dinophyta were classifi ed as oligo-mesotrophic; two remaining lakes, dominated by Cyanoprokaryota or Cryptophyta, as mesotrophic ones. Among crustacean pa-rameters indicating low trophy, the very important ones were low abundance and high diversity of the community in the epilimnion and domination (73–89%) of large bodied herbivorous zooplankton, mainly from the genus Daphnia. Nevertheless, despite relatively high differences in lake trophy estab-lished from chemical parameters and biological data based on three taxonomic groups (phytoplankton, Rotifera and Crustacea), all these indexes seem to indicate low trophy of Lake Hańcza and Szurpiły and markedly high trophy of Lake Linówek and Lake Okrągłe.

Key words: trophic state of lakes; phytoplankton, rotifer community, zooplankton

Department of Hydrobiology, University of Białystok, Świerkowa 20B, 15-950 Białystok, Poland

* Corresponding author e-mail: [email protected]

Phycological Reports: Current advances in algal taxonomy and its applications: phylogenetic, ecological and applied perspective. Institute of Botany Polish Academy of Sciences, Kraków, 2012: xx–xx.

2 Phycological Reports: Current advances in algal taxonomy

Introduction

Lakes are an important element of the natural environment that defi nes both the land-scape and its ecological functioning. The trophic status of lakes determines the development and functioning of aquatic organisms. Previous studies of water chemistry and plankton of Lake Hańcza were carried out by Spodniewska (1978), Karabin and Ejs-mont-Karabin (1993a), Hilbricht-Ilkowska (1994), Hilbricht-Ilkowska and Wiśniewski (1994), Hutorowicz and Napiórkowska-Krzebietke (2008), Grabowska et al. (2006), Zieliński et al. (2006). Other lakes in the Suwałki Landscape Park (SLP), most of which are mesotrophic lakes (Zieliński at al. 2006), have been rarely studied. Total phosphorus load from the catchment of the SLP lakes is usually below the dangerous level (Hilbricht-Ilkowska 1994), which is the reason why the process of eutrophication of these lakes is slowed down.

The study of lakes in SLP was performed in the summer. In summer the lake eco-systems are vulnerable to major changes due to the development of tourism in natural areas. The changes in the trophic state of aquatic ecosystems in the SLP are small, although marked increase in tourist traffi c are observed. This may be explained by the nature of tourism in the area under consideration. Agrotourism developing in the SLP is thought to be environmentally friendly. At the same time, traditional agriculture is gradually being replaced by organic farming. This could be the reason for the high-class water quality in lakes and rivers of the SLP (Zieliński et al. 2006).

The aim of the present study was to assess the current ecological state of four lakes in the Suwałki Landscape Park. The analysis included parameters useful to determine trophic state of lakes, i.e. chemical parameters of water and phyto- and zooplankton parameters, both quantitative (abundance, biomass) and qualitative (species composi-tion, dominance) ones. Further, we wish to compare the data obtained to previously published reports.

Study Area and Methods

The Suwałki Landscape Park was created in 1976 as the fi rst landscape park in Poland. The Park is located in the north-eastern part of Poland, in the province of Podlasie (the Podlaskie voivodship). The area under investigation represents a typical landscape formed during the last Vistulian glacial nearly 10% of the SLP is covered with post-glacial lakes.

The research covered four SLP lakes: Lake Hańcza, Lake Szurpiły, Lake Okrągłe and Lake Linówek (Fig. 1). These lakes are located in the Lithuanian Lake District, in the Niemen River basin. The catchments of the lakes are mostly unforested with extensive agriculture and population density less than 30 persons per square km. During the sum-mer the SLP lakes are used for recreation. The study was conducted in Lake Hańcza, the deepest lake in Poland, in the Lake Szurpiły, whose maximum depth exceeds 45 m, and in two shallow lakes with maximum depth not exceeding 10 m (Table 1). Three of the lakes (Hańcza, Szurpiły and Okrągłe) have outfl ows and infl ows, whereas Lake Linówek, located in the Szeszupa catchment, has no outfl ow (Bajkiewicz-Grabowska

E. Jekatierynczuk-Rudczyk et al.: Assessment of trophic state of lakes 3

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1994a). Two of the lakes under study were thermally stratifi ed (Lake Hańcza and Lake Szurpiły). Temperature measurements in the lakes allowed all three layers (epi-, meta- and hypolimnion) to be distinguished. The two shallow lakes are polymictic (Fig. 2).

Water samples were taken on 23-31 July 2009 in the deepest part of each lake. Samples for chemical and phytoplankton analyses were collected at depths of 0.5, 7.0 and 30 m in Lake Hańcza, 0.5, 7.0 and 22 m in Lake Szurpiły, 0.5 and 6.0 m in Lake Okrągłe and 0.5 and 4.5 m in Lake Linówek. Zooplankton was sampled with a 2–l sampler at each 1 m depth and pooled for the epi-, meta- and hypolimnion layers in stratifi ed lakes, and epi- and a layer below the epilimnion in shallow lakes. The samples were concentrated with a 30 μm mesh size plankton net and fi xed in 4% formalin.

The fi eld measurements included: Secchi disc readings, water temperature, pH, oxygen saturation, and concentration of dissolved oxygen (HachLange Sonde).

Laboratory analyses were conducted according to the methods described by Her-manowicz et al. (1976). Concentration of total phosphorus was determined after acidi-fi cation and mineralization with UV radiation. Total nitrogen content was determined using a Tecator 2300 Kjeldahl analyzer. The dissolved organic carbon (DOC) content was determined using a Shimadzu organic carbon analyzer (TOC) 5050A according to the procedure proposed by Zieliński and Górniak (1999).

Chlorophyll a concentration was determined by the spectrophotometric method. Samples were fi ltered on GF/C fi lters and extracted with boiling 90% ethanol (Lorenzen 1965).

Water samples (500–1500 ml) for phytoplankton studies were immediately fi xed using Utermöhl’s solution. Quantitative analyses were conducted in Fuchs-Rosenthal chambers, with counts including up to 200 individuals. The relationship between the size and the volume of phytoplankton cells was used to determine the biomass of algae. Biomass of rotifers was established following Ejsmont-Karabin (1998).

The trophic state waters was assessed on the basis of presence of indicator phy-toplankton taxa as described by Järnefelt (according to Kawecka & Eloranta 1994), Hutchinson (1967), Hörnström (1981), Rosén (1981) and Szeląg-Wasilewska et al. (1999) with state being expressed on a scale of 1–3 (where 1 = oligotrophic, 2 = mes-otrophic, and 3 = eutrophic). If a taxon was classifi ed differently by those authors, the mean value of the index was used. The trophic index of the phytoplankton community was calculated on the basis of the abundance of trophic state indicators according to the Hörnström formula (1981).

To assess the trophic state of the lakes several indices were used: Carlson’s TSI (Carlson 1997), Crustacean Index (CI) proposed by Karabin (1985) and a number of

Table 1. Description of the studied lakes.

Lake name Area(ha)

Maximum depth (m)

Volume (103· m3)

Catchment area(ha)

Hańcza 311.4 108.5 120364 3924.2Szurpiły 80.9 46.8 8168 1114.0Okrągłe 17.4 8.0 817 55.2Linówek 2.6 5.6 70 25.0


zooplankton indices proposed by Andronikova (1996). The following six rotifer indices of lake trophy (Karabin & Ejsmont-Karabin 1993b) were used to establish the trophic state of the studied lakes: (1) rotifer numbers, (2) rotifer biomass, (3) percentage of bacterivorous species in total numbers of the community, (4) average individual body weight in the rotifer community, (5) percentage of the “tecta” form in the numbers of Keratella cochlearis (Gosse) and (6) contribution of species indicative of high trophy in the numbers of all indicative species.

Results and Discussion

In the epilimnion layer, water temperature exceeded 20°C, whereas in the hypolimnion the temperature dropped below 4oC. Water in the lakes studied was characterized by neutral and slightly alkaline pH. In Lake Hańcza and Lake Linówek oxygen defi cits did not occur. Oxygen saturation in the hypolimnion layer of Lake Szurpiły was below 30%. In Lake Okrągłe in the layer over the bottom oxygen saturation was only 13%. Average concentration of total nitrogen in lake water was 0.83 mg L–1 (from 0.43 mg L–1 in Lake Linówek at a depth of 0.5 m to 1.58 mg L–1 in Lake Okrągłe at a depth

Fig. 2. Vertical changes of water temperature in stratifi ed (a) and polymictic (b) lakes.


of 6.0 m). Average concentration of total phosphorus in the lake waters was 0.13 mg L–1 (from 0.058 mg L–1 in Lake Linówek at a depth of 4.5 m to 0.134 mg L–1 in Lake Szurpiły at a depth of 0.5 m). Water in the studied lakes was rich in dissolved organic carbon compounds. The concentration of biogenic elements changed with the depth of the lakes (Table 2).

The way a lake functions in the natural environment is closely related to its hydro-logical and watershed conditions (Bajkiewicz-Grabowska 1994b). Among the studied lakes, Lake Hańcza is the least susceptible to degradation, with moderate degradation susceptibility of Lake Szurpiły and high susceptibility of Lake Okrągłe and Lake Linówek (Bajkiewicz-Grabowska 1994b).

In July 2009 high water levels were noticed in the SLP lakes. This was a result of high rainfall in May and June 2009 (Fig. 3). The total precipitation in June 2009 was almost 150% of the total precipitation in June from the years 1965–1995 (Górniak 2000).

In July 2009, only Lake Hańcza was mesotrophic (Table 3). Research conducted in 2009 showed a signifi cant increase in the trophic state index (TSI) based on Secchi disc readings (TSISD). At the same time a decrease was noted in the TSI based on the total phosphorus concentration (TSITP) (Table 3). The decrease in TSITP values may be a re-sult of the supply of rainfall directly into the lake (Fig 3) and surface runoff. Extensive

Table 2. Physico-chemical parameters of water in the studied lakes (EC – electrolytic conductivity, SPR – soluble reactive phosphorus, TP – total phosphorus, DOC – dissolved organic carbon).

Lake depth(m)

Temperature(oC)

Oxygen saturation

(%)

Chlorophyll a

(μg L-1)

Total nitrogen(μg L-1)

TP(μg L-1)

DOC(mg L-1)

Hańcza 0.5 20.9 109 1.17 957 89 20.2Hańcza 7.0 14.4 93 1.76 1419 82 18.2Hańcza 30.0 5.2 66 0.44 729 98 16.0Szurpiły 0.5 22.6 115 1.32 518 134 9.5Szurpiły 7.0 12.6 108 4.39 667 95 10.4Szurpiły 22.0 3.6 27 1.03 759 122 8.8Okrągłe 0.5 21.8 122 5.71 746 116 15.5Okrągłe 6.0 11.0 13 24.73 1575 133 12.9Linówek 0.5 22.5 102 1.61 682 89 19.5Linówek 4.5 18.6 89 3.51 830 58 18.3

Table 3. Carlson’s trophy state index (TSI) for epilimnion in lakes of SLP (SD – Secchi disc, chla – chlorophyll ”a”, TP – total phosphorus; a – Hilbricht-Ilkowska 1994, b – Zieliński et al. 2006, c – own investigation, n.a. – not analyzed).

Lake1983-85(a) 2003(b) 2009(c)

TSI TSISDTSI-Chla

TSITP TSI TSISDTSI-Chla

TSI TP TSI TSISDTSI-Chl.a

TSI TP

Hańcza 31 29 8,0 55 42 34 21 71 46 69 32 38Szurpiły 38 28 32 54 59 50 38 90 55 84 33 46Okrągłe 57 52 n.a. 61 n.a. n.a. n.a. n.a. 57 75 48 50Linówek n.a. n.a. n.a. n.a. 53 45 37 79 54 71 44 45


agriculture in the direct catchment area of the lakes cannot provide signifi cant amounts of phosphorus. Additionally, a part of incoming phosphorus can be stored in the ecotone zone. A lower Secchi disc reading could be associated with the action of waves and a supply of mineral and organic particles with runoff from the catchment. Secchi read-ings in all lakes under study represented almost half that noted at the beginning of the 21st century (Zieliński et. al. 2006). High summer rainfall caused a decrease in nutrient concentrations in the surface layers of both stratifi ed lakes (Table 2). In the metalimnion of Lake Hańcza higher concentrations of organic nitrogen were found. In the metalimnion of Lake Szurpiły concentrations of inorganic nitrogen and DOC were higher than those noted in the epilimnion. The higher concentrations of inorganic nitrogen were recorded in the deeper parts of the lakes. The dominant form of mineral nitrogen was ammonia nitrogen formed in the process of denitrifi cation. This suggestion is supported by the high correlation coeffi cient calculated for the concentration of ammonia nitrogen and oxygen saturation in water (r = –0.46, P=0.0005, n=10).

The study by Hilbricht-Ilkowska and Wiśniewski (1994) showed that the weight ratio of nitrogen to phosphorus in the lakes of the SLP was close to 20, which may suggest a relative defi cit of phosphorus. This may be the reason for low trophy in the lakes. The calculated weight ratio of nitrogen to phosphorus in the lakes surveyed in July 2009 was much lower (av. 7). The lowest ratio of N to P then the average value was found in Lake Szurpiły (3.2), the highest in Lake Hańcza (11.5). A low ratio of N to P suggests that nitrogen may be a limiting factor in phytoplankton growth. In North-eastern Poland, such a situation is observed in the spring (Dunalska 2010). An N to P ratio exceeding 17 was found exclusively in the metalimnion of Lake Hańcza.

Representatives of 7 phytoplankton groups, i.e. Cyanoprokaryota (Cyanobacteria, Cyanophyta), Dinophyta, Cryptophyta, Bacillariophyceae, Chrysophyceae, Chlorophyc-eae and Zygnemathophyceae, were found in all the examined lakes. Two other groups, Xanthophyceae and Euglenophyta, were present only in three of the four studied lakes. Xanthophyceae were not present in Lake Linówek and Euglenophyta were absent in Lake Hańcza. The number of taxa varied from lake to lake, was 63 in Lake Okrągłe

Fig. 3. Precipitation (mm) in the study period compared to the long-term data (Górniak 2000) in Suwałki.


but only 56 in Lake Linówek, 55 in Lake Hańcza and 52 in Lake Szurpiły. The high-est number of taxa was recorded for Chlorophyceae (from 17 to 24), and the lowest for Xanthophyceae (only 1 for lakes Hańcza, Szurpiły and Okrągłe) or Chrysophyceae (3 for Lake Linówek) (Table 4).

Total biomass of phytoplankton (PB) fl uctuated from 0.18 mg L–1 (Lake Hańcza, hypolimnion) to 3.51 mg L–1 (Lake Okrągłe, depth 6 m) (Fig. 4a,b,c,d). In the stratifi ed Lake Hańcza and Lake Szurpiły a vertical differentiation of phytoplankton composi-tion and biomass was observed. The highest biomass of phytoplankton was found in the metalimnion (Fig. 4a, b). The main contributors to phytoplankton biomass in the epilimnion and metalimnion of Lake Hańcza were diatoms (Cyclotella radiosa (Grunow) Lemmerm.), while the community in the hypolimnion was dominated by cryptophytes: Rhodomonas pusilla (Bachm.) Javornický and Cryptomonas spp. In the surface layer, co-dominants were chrysophytes (Dinobryon divergens Imhoff), in the metalimnion dinophytes (Ceratium hirundinella (F.B. Müller) Bergh), while in the hypolimnion dia-toms again co-dominated. In the epilimnion of Lake Szurpiły the highest biomass came from chlorophytes (mainly Phacotus lenticularis (Ehrenb.) F. Stein, Oocystis spp.), in the metalimnion it came from dinophytes (Ceratium hirundinella) and chrysophytes (cf. Ochromonas sp., Dinobryon sertularia Ehrenb., D. sociale Ehrenb. and D. bavaricum Imhoff), while in the hypolimnion dinophytes (Gymnodinium cf. lantzschii Utermöhl and Gymnodinium sp.).

In shallow Lake Okrągłe the main component of phytoplankton biomass were cyano-prokaryotes, whose composition and biomass, however, changed with depth (Fig. 4d). At the surface layer phytoplankton was dominated by Cuspidothrix issatschenkoi (Usačev) P. Rajan., Komárek, Willame, Hrouzek, Kaštovská, L. Hoffm. et Sivonen. Aphanizomenon skuje Komárek-Legn. et Cronb., Aphanizomenon sp. Anabaena fl os-aquae Bréb., Oscil-latoria sp. and Merismopedia tenuissima Lemm., while in the deeper layer (6 m) mass

Fig. 4. brak


Table 4. List of phytoplankton species in Lake Hańcza, Lake Szurpiły, Lake. Linówek and Lake Okrągłe in July 2009; H – Hańcza, Sz – Szurpiły, L – Linówek, O – Okrągłe.

Taxa H SZ L OCyanoprokaryotaChroococcalesAphanocapsa delicatissima W. West. et G.S. West +Chroococcus turgidus (Kütz.) Nägeli +Chroococcus sp. +Merismopedia tenuissima Lemmerm. + +Woronichinia naegeliana (Unger) Elenkin +OscillatorialesLimnothrix redekei (Goor) Meffert +Oscillatoria sp. +Phormidium sp. +Planktolyngbya (Lemmerm.) Komárek-Legn. et Cronb. +Pseudanabaena limnetica (Lemmerm.) Komárek +Pseudanabaena sp. + +Romeria sp. +Spirulina nordestedti Gomont +NostocalesAnabaena fl os-aquae (Lyngbye) Bréb. ex Bornet et Flahault + + +Anabaena sp. + +Aphanizomenon skuje Komárek-Legn. et Cronb. +Aphanizomenon sp. +Cuspidothrix issatschenkoi (Usačev) P. Rajan., Komárek.,Willame, Hrouzek, Kaštovská, L. Hoffm. et Sivonen

+

Euglenophyta

Astasia sp. +Euglena proxima Dang. +Euglena sp. +Lepocinclis acus (O.F. Müller) +L. oxyuris Schmarda + +Phacus orbicularis Hübner var. orbicularis +Trachelomonas abrupta Svirenko var. abrupta +T. hispida (Perty) F. Stein var. hispida + + +T. nigra Svirenko +T. oblonga Lemmerm. +T. volvocina Ehrenb. +T. volvocinopsis Svirenko +

Cryptophyta

Cryptomonas marssonii Skuja + + +C. rostatiformis Skuja + +C. sp. div. + + + +Rhodomonas pusilla (Bachm.) Javornický +Rhodomonas sp. + +

Dinophyta

Ceratium furcoides (Levander) Langhans +C. hirundinella (O.F. Müller) Dujard. + +Gymnodinium cf lantzschii Utermöhl +Gymnodinium sp. div. + + +Peridiniopsis cunningtonii Lemmerm. +P. elpatiewskyi (Ostenfeld) Bourrelly + +Peridinium cf gatunense Nygaard +


Taxa H SZ L OPeridinium incospicuum Lemmerm. +Peridinium sp. + +

Chrysophyceae

Bitrichia sp. +Chromulina sp. +Dinobryon bavaricum O.F. Imhof +D. divergens O.F. Imhof + +D. serularia Ehrenb. + +D. sociale Ehrenb. + + +Kephyrion rubri-claustri W. Conrad + +Malomonas sp. div. + +cf Ochromonas sp. +Synura echinulata Korshikov + + + +

Xanthophyceae

cf Characiopsis sp. + +Ophrocytium sp. +

Bacillariophyceae

CentralesAulacoseira islandica ??? +Cyclotella radiosa (Grunow) Lemmerm. +C. bodanica Grunow +Cyclotella sp. + +Centricea nd. + + + +PennalesAchnathes sp.div. + + + +Achnathidium minutissimum (Kütz.) Czarn. +Amphora ovalis Kütz. +Asterionella formosa Hassal + + +Cocconeis placentula Ehrenb. + +Cymbella affi nis Kütz. +Cymbella sp. + + +Diatoma vulgaris Bory +Ephitemia sp. +Fragilaria crotonensis Kitton +Hippodonta capitata (Ehrenb.) Lange-Bert. +Navicula sp. +Nitzschia acicularis (Kütz.) W. Smith +N. recta Hantzsch + +N. palea (Kütz.) W. Smith +N. hungarica Grunow + +Fragilaria Desm. var. capucina + + +F. ulna (Nitzsch) Lange-Bert. var. acus +F. ulna var. angustissima Sippen +F. ulna (Nitzsch) Lange-Bert. var. ulna + + +Pinnularia sp. + +

Chlorophyceae

Actinastrum hantzschii Lagerh. +Ankistrodesmus fusciformis Corda +Botryoccocus braunii Kütz. +Characium sp. +

Table 4. (continued)


Taxa H SZ L OChlamydomonas sp. div. + + +Coelastrum astroideum De Not. +C. microporum Nägeli + +Coenoccoccus planctonicus Korsch. +Crucigenia apiculata (Lemmerm.) Komárek + + +C. tetrapedia (Kirchn.) W. West et G.S. West + +Dictyosphaerium pulchellum H.C. Wood +Didymocystis planctonica Korš. + +Elakatothrix acuta Pascher +E. genevensis (Reverdin) Hindák + +E. spirostoma (Reverdin) Hindák + +Kircheriella lunaris (Kirchn.) Höb. +Koliella spirotaenia (G.S. West) Hindák +K. longiseta (Vischer) Hindák + + +Lagerheimia marssonii Lemmerm. +L. subsalasa Lemmerm. +Monoraphidium arcuatum Hindák +M. griffi thi (Berkeley) Komárek-Leng. +M. minimum (Nägeli) Komárek-Leng. + + +Oocystis borgei Snow +O. lacustris Chodat + + + +Phacotus lenticularis (Ehrenb.) F. Stein + + +Planktosphaeria gelatinosa G.M. Smith + +Pediastrum boryanum var. cornutum (Turpin) Menegh. +P. boryanum var. longicorne Reinsch +P. duplex Meyen +P. duplex var. gracillinum W. West et G.S. West +Pseudodictyosphaerium jurisii (Hindák) Hindák +Pseudotetrastrum punctatum Hindák +Quadrigula closterioides (Bohlin) Printz + +Scenedesmus acuminatus (Lagerh.) Chodat + +S. arcuatus (Lemmerm.) Lemmerm. + +S. ecornis (Ehrenb.) Chodat +S. intermedius Chodat +S. obliquus (Turpin) Kütz. + + + +S. obtusus Meyen + +Schroederia setigera (Schroeder) Lemmerm. + + + +Tetraedron minimum (A.Br.) Hansg. + + +Tetrastrum komarekii Hindák + +Tetrachlorella alternans (G.M. Smith) Korsch. + + +

Zygnematophyceae

Closterium limneticum Lemmerm. +Cosmarium rectangulare Grunow in Rabenh. +Cosmarium sp. 1 +Cosmarium sp. 2 +Desmidium aptogonum Bréb. +Euastrum sp. +Mougeotia sp. +Spondylosium cf papillosum W. West et G.S. West +Staurastrum setigerum Cleve +S. tetracerum (Kütz.) Ralfs + +Staurastrum sp. +Xanthidium sp. +

Table 4. (continued)


development of Spirulina nordestedti Gomont was observed. At the surface predomi-nance of cyanoprokaryotes over other groups (especially dinophytes and chlorophytes) was markedly lower than at a depth of 6m. The highest biomass in two layers of Lake Linówek was reached by cryptophytes (Rhodomonas sp., Cryptomonas spp.), chlorophytes and dinophytes (Peridinium inconspicuum Lemmerm., Peridinium sp.) (Fig. 4c).

Phytoplankton in three of the studied lakes was dominated by nanoplankton (cell size < 20 μm) that represented over 60% of the total phytoplankton biomass, i.e. 70.6% in Lake Szurpiły, 70.1% in Lake Hańcza, and 61.3% in Lake Linówek. The only excep-tion was the eutrophic Lake Okrągłe, where nanoplankton accounted for only 40% of phytoplankton biomass. In Masurian lakes, as well as in lakes of the Suwałki Landscape Park, the contribution of nanophytoplankton was higher in lakes with small summer phytoplankton biomass (Spodniewska 1978).

The concentration of chlorophyll a ranged between 0.44 and 25.0 μg L–1, with the maximum concentrations of chlorophyll a and phytoplankton biomass recorded in the metalimnion. There was a positive correlation between total phytoplankton biomass and chlorophyll a concentration (r = 0.916, p=0.04, n=10).

So far, the phytoplankton of Lake Hańcza has been the most intensively studied. In 1973 the structure of phytoplankton was studied by Spodniewska (1978), in 1994–2007 by Hutorowicz and Napiórkowska-Krzebietke (2008), and in 2003 by Grabowska et al. (2006). The structure and biomass of phytoplankton of Lake Szurpiły in summer 2003 was described by Grabowska et al. (2006). Brief information about the summer value of total phytoplankton biomass for lakes Hańcza, Okrągłe and Szurpiły in 1983–1985 can be found in Hilbricht-Ilkowska and Wiśniewski (1994). Comparison of our data with all the previously published information on phytoplankton of lakes Hańcza (Table 5), Szurpiły (Table 6) and Okrągłe allowed determination of a trends in the changes of trophic state of the lakes. The highest summer phytoplankton biomass for Lake Hańcza was reported by Spodniewska (1978) in 1973 and Hutorowicz and Napiórkowska-Krze-bietke (2008) in 2006–2007. According to Hutorowicz and Napiórkowska-Krzebietke (2008), such a value of phytoplankton biomass indicates the mesotrophic character of a lake system. However, at times the average value of summer biomass of phytoplank-ton was found markedly lower (i.e. < 1 mg L–1) (Table 5), which classifi ed the lake as oligotrophic. In the years 1973–2009, the main components of phytoplankton biomass

Table 5. Long-term changes summer total phytoplankton biomass and dominant groups in Lake Hańcza; data from 1973 for Spodniewska (1978), from 1983-1985 for Hilbricht-Ilkowska and Wiśniewski (1994), from 1999-2001 for Hutorowicz and Napiórkowska-Krzebietke (2008), for 2003 from Grabowska et al. (2006); n.d.a. – no data available.

Lake Hańcza Total biomass(mg L–1)

Main dominants (% of total biomass)

1973 2.0 dinofl agellates (45.0), cyanoprokaryotes (30.0)1983–1985 0.1 n.d.a.1999–2001 0.60 cyanoprokaryotes (37.8), diatoms (28.1), chlorophytes (14.2)

2003 av. 0.20 diatoms (68.6)2006–2007 1.70-1.73 diatoms (59.7), cyanoprokaryotes (19.9)

2009 av. 0.82 diatoms (56.4), chrysophyces (22.3)


were dinofl agellates, cyanoprokaryotes or diatoms (Table 5). Diatoms of the genus Cy-clotella replaced a cyanophyte Aphanocapsa incerta that dominated earlier (Hutorowicz & Napiórkowska-Krzebietke 2008). The dominant species in 2009, Cyclotella radiosa (Grunow) Lemmerm. has been reported from many alkaline and well oxyganeted inland European waters (Van Dam et al. 1994). This species was also found in numerous lakes of different trophic status in the Wielkopolska National Park (Burchardt & Marshall 2001) indicating that the factors affecting its distribution are not yet fully understood.

Total biomass of phytoplankton in the epilimnion and metalimnion of Lake Szurpiły was in 2009 about 6.0 and 2.5 times (respectively) lower than in 2003. There has also been a complete change of the phytoplankton community composition (Table 6). In 2003 the diatoms dominated the epilimnion and metalimnion, while in our study they did not dominate in any of the lake strata. In our samples they were replaced in the epilimnion by chlorophytes and in the metalimnion by dinophytes and chrysophytes. In our study, cyanoprokaryotes were recorded exclusively in the surface layer (2.8% of phytoplankton biomass), while in 2003 they were an important component in both layers (Table 6). The average phytoplankton biomass (0.4 mg L–1) in our study was very similar to that (0.3 mg L–1) reported by Hilbricht-Ilkowska and Wiśniewski (1994). In the case of Lake Okrągłe the differences were much greater. In 1983–1985 the biomass reached a value of 2.1 mg L–1 and in 2009 only 0.73 mg l–1.

The trophic index indicates that lakes Hańcza and Szurpiły are in transition between the oligo- and mesotrophic states (Table 7). Lake Linówek and Okrągłe can be classifi ed as mesotrophic (Table 7). Species present in large populations had a greater infl uence on the trophic index. On the other hand many species noted in lakes, such as those from the genera Rhodomonas and Cryptomonas were found in various other types of water bodies, thus they had little value as indicators of lakes water trophic status (Hörnström 1981; Szeląg-Wasilewska et al. 1999; Gołdyn & Szeląg-Wasilewska 2004). Species from the genera Dinobryon, Kephyrion, Peridinium, Gymnodinium and Oocystis are good indicators of low trophy while the presence of Trachelomonas, Scenedesmus and Anabaena strongly increases trophic index values (Szeląg-Wasilewska et al. 1999).

Table 6. Annual changes of total phytoplankton biomass and dominant groups in Lake Szurpiły; data from 2003 after Grabowska et al. (2006).

year layer Total biomass(mg L-1)

Main dominants (% of total biomass)

2003 epilimnion 1.998 diatoms (31.1), cyanoprokaryotes (17.0)2003 metalimnion 1.760 diatoms (44.0), cyanoprokaryotes (32.4)2009 epilimnion 0.335 chlorophytes (48.0), dinofl agellates (22.3)2009 metalimnion 0.724 dinofl agellates (32.6), chrysophyces (28.8)

Table 7. Trophic state index based on abundance of phytoplankton indicators species.

Lake Hańcza Szurpiły Linówek OkrągłeValues of index 1.403 1.587 2.065 2.176


Rotifer fauna in the studied lakes was composed of the same dominant species in all the lakes (Fig. 5). These included Keratella cochlearis Gosse and two species of the genus Polyarthra (P. remata Skorikov and P. vulgaris Carlin). In two lakes there were observed differences in terms of dominants. The rotifer community in Lake Hańcza was strongly dominated by Conochilus hippocrepis (Schrank), a colonial species typi-cal of very low trophy (mesotrophic lakes). Another species indicative of low trophy (mesotrophic and meso-eutrophic lakes) – Gastropus stylifer Imhoff, was found among the dominants in Lake Linówek.

Rotifer numbers were relatively low in all the studied lakes and the lowest in Lake Szurpiły (Fig. 5). The density of 117 ind. L–1 in the epilimnion of the lake seems to indicate its mesotrophy. All the remaining lakes had higher densities of their epilimnetic Rotifer community, with 255 ind. L–1 in Lake Hańcza, 417 in Lake Linówek and 501 in Lake Okrągłe. Rotifer communities were more abundant in the metalimnion comparing to the epilimnion in Lake Szurpiły and Lake Hańcza, whereas the opposite (i.e. rotifer densities lower in deeper layers) was observed in Lake Okrągłe and Lake Linówek.

Concentration of rotifers in the metalimnion is a phenomenon often observed in lakes of low trophic status and may indicate migration of zooplankton into water layers with higher food concentration. From among rotifer species indicative of (meso- and meso-eutrophic lakes) low trophy, four were present in the studied lakes. They played a relatively important role in lakes Szurpiły, Hańcza and Linówek. All fi ve species in-dicative of high trophy were found in Lake Okrągłe, the only lake where the percentage of high trophy species is higher than the low trophy ones (Table 8).

The above mentioned differences in trophic state of the studied lakes are confi rmed by the results of rotifer estimation indices of lake trophy (Fig. 6). Lake Szurpiły and Lake Hańcza are the least eutrophic among the studied lakes, and also Lake Linówek seems to be inhabited by rotifer communities typical of meso-eutrophic lakes. The

Fig. 5. Density of Rotifera (ind. L-1) with marked dominant species in particular layers. Abbreviations: E – epil-imnion; M – metalimnion; BL – benthic layer.


TSIROT value for Lake Okrągłe is markedly higher than for the other lakes and indicates eutrophy of the lake. This level of trophy has been maintained in the lake since 1983 (Karabin & Ejsmont-Karabin 1993a).

In total, 26 species of Crustacea, including 8 species of Cyclopoida, 3 species of Calanoida and 15 species of Cladocera were found in the open water zone of the stud-ied lakes. It is worth noting that there is a relatively high species richness of the genus Bosmina (5 species) and the occurrence of species which are rare in Polish waters: Hete-rocope appendiculata ??? in Lake Szurpiły and Bythotrephes longimanus Leydig in Lake Hańcza. The latter species has not been found in the last year in this lake (Table 9).

In deep lakes with a relatively low trophic status (such as Lake Szurpiły and Lake Hańcza), the epilimnion was inhabited by a less numerous but more diversifi ed group of pelagic crustaceans. However, in Lake Szurpiły the abundance of zooplankton in the metalimnion was over four times higher than in the epilimnion. This may be explained as a result of zooplankton foraging for food since abundance of algae in the metalimnion is

Table 8. Contribution of species indicative of low and high trophy in the total numbers of Rotifera.

Taxa Szurpiły Hańcza Okrągłe Linówek

Indicative for low trophyAscomorpha ovalis 2.6 0.2 0.7Conochilus hippocrepis 28.2 Gastropus stylifer 7.0 0.4 12.5Polyarthra major 2.6 0.2

Total 11.6 28.6 0.4 13.2

Indicative for high trophyKeratella cochlearis “tecta” 1.7 21.9 Filinia longiseta 3.0 1.9Keratella quadrata 0.2 Pompholyx sulcata 2.2 Trichocerca pusilla 0.6

Total 1.7 27.9 1.9

Fig. 6. Mean values of rotifer indices of lake trophy.


three times higher (if expressed as chlorophyll a concentration) than in the upper layer. In Lake Szurpiły and Lake Hańcza the total biomass of Crustacea was higher than the biomass of phytoplankton. Zooplankton was clearly dominated by herbivorous Crustacea and the species from the fi rst ecological group, i.e. characteristic for low trophy, mainly due to the dominance of Daphnia cucullata G.O. Sars. The participation of species characteristic for high trophy in these lakes did not exceed 10%. In the more eutrophic lakes, Lake Okrągłe and Lake Linówek, crustacean zooplankton was more abundant yet characterized by a smaller average weight of single individuals (Table 9). The commu-nity was characterized by a higher share of species from the second ecological group, mainly due to higher abundance of Cyclopoida (Thermocyclops oithonoides G.O. Sars and Mesocyclops leuckarti Claus) and Cladocera (Diaphanosoma brachyurum Liévin and Chydorus sphaericus O.G. Müller). The biomass of zooplankton in the lakes was lower than the biomass of phytoplankton, thus the situation was reversed when compared to the lakes of lower trophy.

Table 9. Species composition of Crustacea in the studied lakes.

Taxa Szurpiły Hańcza Okrągłe Linówek

Cyclopoida

Cyclops abbysorum G.O. Sars 1863 +C. scutifer G.O. Sars 1863 + +C. vicinus Uljanin1875 + +Acantocyclops sp. + +Megacyclops sp. +Mesocyclops leuckarti Claus 1857 + + + +Thermocyclops oithonoides G.O. Sars 1863 + + + +Ectocyclops phaleratus Koch 1838 +

Calanoida

Eudiaptomus gracilis G.O. Sars 1863 + + +E. graciloides Lilljeborg 1888 + + +Heterocope appendiculata G.O. Sars 1863 +

Cladocera

Daphnia cristata G.O. Sars 1861 + + +D. cucullata G.O. Sars 1862 + + + +D. longispina O.F. Müller 1776 +Bythotrephes longimanus Leydig 1860 +Eubosmina coregoni Baird 1857 +E. crassicornis Lilljeborg 1887 +E . thersites Poppe 1887 +E. gibbera Schoedler 1863 +Bosmina longirostris O.F. Müller 1785 + + +Diaphanosama brachyurum Liévin 1848 + + + +Chydorus sphaericus O.F. Müller 1776 +Ceriodaphnia quadrangula O.F. Müller 1785 + +Alonella nana Baird 1843 +Leptodora kindtii Focke 1844 + + + +Acroperus harpae Baird 1835 +


To determine the impact of eutrophication on the pelagic zooplankton structure, the following two ecological groups of crustaceans (Karabin & Ejsmont-Karabin 1994) were distinguished: typical of low trophy (group I) and typical of high trophy (group II). The fi rst ecological group was represented in Lake Wigry by Daphnia species Eubosmina coregoni, Heterocope appendiculata ... and Eurytemora lacustris .... The second ecologi-cal group characteristic for high trophy was represented by: Mesocyclops leuckarti Claus, Thermocyclops oithonoides G.O. Sars, Bosmina longirostris O.F. Müller, Diaphanosoma brachyurum Liévin and Chydorus sphaericus O.F. Müller.

The trophic structure of pelagic Crustacea was compared for lakes with differ-ent environmental conditions. The lakes of low trophic state, Lake Hańcza and Lake Szurpiły, were dominated by the “medium mesh fi lter-feeders” feeding mainly on nano-phytoplankton. This fact, along with the dominance of zooplankton over phytoplankton biomass in the lakes (Fig. 7, Table 10) confi rms the presumption on good environmental conditions in both lakes. More eutrophic lakes were characterized by a higher share of

Fig. 7. Percentage of trophic groups in the biomass of pelagic Crustacea in the studied lakes.

Table 10. Numbers (N), biomass (B) and Crustacea trophic state indices for the epilimnion of the studied lakes, w - mean individual weight of zooplankton.

??? Szurpiły Hańcza Okrągłe LinówekNumbers (ind. L–3) 35 62 117 101Biomass (mg L–3) 1.46 3.19 3.46 2.12

CRUSTACEAN TROPHIC STATE INDICES

Crustacea TSI (Karabin) 38.65 44.75 45.65 58.00% of herbivorous Crustacea 89 73 67 35I group (low trophy index %) 76.8 68.0 52.0 4.3II group (high trophy index %) 8.7 6.7 26.0 32.9B Cycl / B Cal 0.74 7.40 1.84 2.16N Cla / N Cop 1.50 1.00 0.68 0.16B predators / B fi lter-feeders 0.10 0.36 0.18 1.64w = B /N 0.041 0.051 0.029 0.021B zoo / B phyto 1.10 2.72 0.61 0.82


“fi ne mesh fi lter-feeders” for which the optimum food size is 2–5 μm, and that feed mostly on bacteria-detritus suspension. During the summer phytoplankton blooms in eutrophic lakes, “fi ne mesh fi lter-feeders” are most abundant. This is due to high abun-dance of suspended bacteria which are available as food only for fi lter feeding species with fi ne-meshe fi ltering apparatus (Geller & Muller 1981). The zooplankton of Lake Okrągłe was dominated by herbivores, nevertheless fi ne mesh fi lter-feeder zooplank-ton was also abundant. A completely different structure was found in Lake Linówek, where medium mesh fi lter-feeders had a very small share in Crustacea. The zooplankton community of Lake Linówek was strongly dominated by Thermocyclops oithonoides (Table 9), with a high proportion of juvenile forms which are macrofi ltrators and feed on nanophytoplankton. Moreover, in the studied lakes the dominance of T. oithonoides over Mesocyclops leuckarti was observed in order Cyclopoida. This phenomenon was earlier reported by Karabin and Ejsmont-Karabin (1994) as distinctive just for lakes in the Suwałki district.

Conclusions

An analysis of Carlson’s trophy state index in four lakes SLP indicates that, the only Lake Hańcza was mesotrophic in July 2009. Other lakes (Lake Szurpiły, Lake Okrągłe and Lake Linówek) were eutrophic. Research conducted in July 2009 showed a signifi -cant increase in the trophy state index based on the Secchi disc readings (TSISD) in all lakes. The lower readings were associated with the action of waves and the supply of mineral and organic particles with runoff from the catchment. At the same time, there was a decrease in the trophy state index based on the total phosphorus concentration (TSITP) in all lakes. The lower values of TSITP in all lakes were the result of the sup-ply of rainfall and surface runoff directly into the lakes. Since the beginning of the 21st century, TSIchl in Lake Hańcza has been increasing. In Lake Szurpiły this index has remained at the same level.

An analysis of the parameters characterizing the specifi c and quantitative structure of phytoplankton, rotifer and crustacean communities enabled estimation of the trophic state of the studied lakes. According to phytoplankton biomass and trophic index the deepest and stratifi ed lakes (Hańcza and Szurpiły) can be classifi ed as oligo-mesotrophic. All the considered crustacean parameters indicated mesotrophy of Lake Szurpiły and Lake Hańcza. At the same time rotifer indices seem to indicate low meso-eutrophy of both stratifi ed lakes. Among the identifi ed phytoplankton species those from genera Cyclotella (Hańcza), Gymnodinium, Oocystis (Szurpiły) and Dinobryon (Hańcza and Szurpiły) were most responsible for the trophic determination. Among crustacean pa-rameters indicating low trophy, very important were low abundance and high diversity of the community in the epilimnion and domination (73–89%) of large bodied herbivorous zooplankton, mainly from the genus Daphnia. Low trophy of the lakes is also confi rmed by the presence in the lower limnetic strata of species typical for mesotrophic waters and, among them, rare species such as Heterocope appendiculata in Lake Szurpiły, and Bythotrephes longimanus in Lake Hańcza. The latter has not been recorded in this lake for many years. Lake Okrągłe is a remnant of a large ribbon lake of the transitional


meso-eutrophic type. In this lake, higher abundance was observed among phytoplankton, rotifer and crustacean communities.

Phytoplankton trophic index was strongly affected by the dominant species of cy-anoprokaryotes (Anabaena, Aphanizomenon and Oscillatoria), chlorophytes (Tetrastrum, Scenedesmus and Lagerheimia) and euglenoids (Trachelomonas). According to the value of the index (2.176), Lake Okrągłe can be classifi ed as mesotrophic. Rotifer community of the lake was typical of eutrophic lakes. Although Crustacea were dominated here by herbivores (mainly Daphnia cucullata and less abundant D. cristata), which constituted 44–67%, signifi cant contribution was noted for species like Thermocyclops oithonoides, Mesocyclops leuckarti and Diaphanosoma brachyurum. Such changes in zooplankton might result from a growing abundance and diversity of the food base. According to phytoplankton, the trophic index is only slightly lower in Lake Linówek (2.065) than in Lake Okrągłe (2.176). In Lake Linówek most abundances reached cryptophytes, but they are not trophic indicators. In Lake Linówek the value of the index was determined primarily by dinofl agellates (Gymnodinium and Peridinium), chlorophytes (Scenedesmus, Tetrastrum and Crucigenia), chrysophytes (Dinobryon) and diatoms (Cyclotella). The structure of zooplankton community in Lake Linówek was characterized by the dominance of small zooplankton that feeds on detritus and bacteria, and relatively high numbers of predatory Cyclopoida. Daphnia cucullata, although present, was small-bodied. Hence, the crustacean structure indicates the eutrophic character of Lake Linówek, whereas the rotifer community is rather characteristic for high meso-eutrophy. Nevertheless, despite relatively great differences in lake trophic status indicated by chemical parameters and biological data (based on three taxonomic groups: phytoplankton, Rotifera and Crus-tacea), all these indexes seem to indicate low trophy of Lake Hańcza and Szurpiły and markedly high trophy of Lake Linówek and Lake Okrągłe.

ACKNOWLEDGEMENTS. The study was supported by the Ministry of Science and Higher Education (MNiSW ) under project number N N306 275135.

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