Füto- ja zooplanktoni dünaamika ja nende omavahelised suhted kui Peipsi järve seisundi indikaatorid

Phyto- and zooplankton, the targets of the study, are the most important links of a water body’s food web. The stability of water body’s ecosystem is largely influenced by the interactions of phyto- and zooplankton. These both are largely influenced by the trophic state of the water body and, at the same time, also by weather conditions. About 20 years ago, the ecosystem of Lake Peipsi was in rather good state, but from the second half of the 1990s, the significant changes took place in the trophic level of the lake: algal blooms in summers became more intense and more frequent. The aims of the study were: to ascertain how phyto- and zooplankton communities and their interactions respond to changes in the trophic level of L. Peipsi; to test in time and space the indicative value of zooplankton to phytoplankton biomass ratio (BZp/BPhyt) in assessing the interrelations between zoo- and phytoplankton and the trophic state of L. Peipsi; to find out how the ice cover duration of L. Peipsi influences the dynamics of nutrients and phyto- and zooplankton in spring. The conclusions of the study were: 1. The continual anthropogenic phosphorus input and decreasing N:P ratio have offered favourable conditions for the development of cyanobacteria. The whole lake, especially L. Pihkva, was characterized by massive cyanobacterial blooms (primarily the genera Microcystis and Aphanizomenon) in summer months. It seems that the ecosystem of the L. Pihkva has lost its resilience to eutrophication. 2. The analyzed data revealed that the biomass of zooplankton decreased. As the pressure of fish on zooplankton has declined, we conclude that cyanobacterial blooms and presence of cyanotoxins are the main reasons for the significant decrease in the amount of zooplankton. 3. The analyzed BZp/BPhyt ratio showed a sharp decrease in parallel with the increasing trophy of the lake and indicated the eutrophic state of L. Peipsi s.s. and the hypertrophic state of L. Pihkva and L. Lämmijärv. Since 1997, the mean ratio for the vegetation period has decreased two times, which indicates a deterioration of the state of L. Peipsi. 4. The ice cover period of L. Peipsi shortened in the last decade. The nutrients’ concentration in lake water depended significantly on the severity of winter: mild winters affected nitrogen and silica concentrations positively and phosphorus concentration negatively. 5. The duration of the ice cover period determines the phytoplankton succession pattern in spring: the growth of all algal groups occurred earlier in springs after warm winters. The development of centric diatoms was most considerable. 6. The short ice duration had a positive impact on the biomass of zooplankton in spring: the biomass was twice as high as after the severe winters. After the warm winters, the densities of thermophobic rotifers were low, while those of more eurythermic rotifers increased. Concurrently, the larger species of copepods and cladocerans benefited from a shorter ice cover period, which raised the mean zooplankter weight and BZp/BPhyt ratio.Doktoritöö käsitleb Peipsi järve avavee planktoni ökoloogiat viimasel aastakümnel. Füto- ja zooplankton on järve ökosüsteemi toiduvõrgustiku olulised koostisosad. Nende omavahelistest suhetest sõltub suuresti vee ökosüsteemi stabiilsus. Füto- ja zooplankton on mõjutatud ühtaegu nii veekogu troofsustasemest kui ka ilmastikutingimustest. Nende liigiline koostis, dünaamika ning nende omavahelised suhted on keskkonnamõjurite integraalne tulem. Veel 20 aastat tagasi oli Peipsi järve ökosüsteem võrdlemisi heas tasakaalus, kuid alates 1990ndate teisest poolest toimusid järve troofsustasemes olulised muudatused: sagenesid suvised massilised veeõitsengud ning nendega kaasnevad kalade suremised. Töö eesmärkideks olid: välja selgitada, kuidas füto- ja zooplanktoni kooslused on vastanud muutustele Peipsi järve troofsustasemes; hinnata zoo- ja fütoplanktoni biomassi suhte (BZp/BPhyt) indikatiivset väärtust Peipsi järve ökoloogilise seisundi hindamisel; uurida jääkatte kestuse mõju järve kevadisele füto- ja zooplanktonile ning vee biogeenide dünaamikale. Töös jõuti järgmistele tulemustele: 1) Järve jätkuv eutrofeerumine lõi soodsad tingimused sinivetikate arenguks. Kogu järve, eriti kõrgema troofsusega Pihkva järve iseloomustavad suvised massilised sinivetikate (peamiselt perekonnad Microcystis ja Aphanizomenon) õitsengud. Pihkva järv on kaotanud oma ökoloogilise tasakaalu ning vastupanuvõime jätkuvale eutrofeerumisele. 2) Uuritud perioodil vähenes oluliselt zooplanktoni hulk. Kuna kalade surve zooplanktonile on vähenenud, peame peamiseks zooplanktoni hulga kahanemise põhjuseks suviseid massilisi vetikaõitsenguid ning vetikamürke. 3) Analüüsitud zoo- ning fütoplanktoni biomasside suhte (BZp/BPhyt) väärtus langes järve troofsuse tõusuga ning näitas Peipsi Suurjärve eutroofset ning Lämmi- ja Pihkva järve hüpertroofset seisundit. Alates 1997. aastast on vegetatsiooniperioodi keskmine BZp/BPhyt väärtus vähenenud kaks korda, mis viitab järve seisundi halvenemisele. 4) Uuritud perioodi andmed näitavad, et Peipsi järve jääkatte kestus on muutunud lühemaks, mis avaldas mõju vee biogeenide sisaldusele: lühike jääkatte periood mõjutas positiivselt vee lämmastiku ja räni sisaldust ning negatiivselt fosfori sisaldust. 5) Peipsi järve jääkatte kestus avaldas mõju ka füto- ja zooplanktoni koosseisule ning dünaamikale. Kõik fütoplanktoni rühmad ilmusid vette varem kevadel, millele eelnes soe talv lühikese jääkattega (eriti silmatorkav oli väikeste ränivetikate biomassi tõus) 6) Lühike jääkate avaldas positiivset mõju kevadisele zooplanktoni biomassile, mis mais ja juunis oli kuni kaks korda suurem kui pikema jääkattega aastatel. Pärast sooja talve oli külmalembeste keriloomade hulk madal, samal ajal kui eurütermsete keriloomade biomass tõusis. Kalatoiduks sobivate suurte aerjalgsete ja vesikirbuliste arengule mõjus soe talv soodsalt, tõstes zooplankteri keskmist kaalu ning BZp/BPhyt suhet. Perekond Daphnia liikide biomass oli juunis pärast lühikese jääkattega talvesid neli kuni kümme korda suurem kui pikema jääkattega aastatel.The doctoral studies and the publication of the current thesis were supported by the Doctoral School of Ecology and Environmental Sciences created under the auspices of European Union Social Fund. Funding for this research was provided through Estonian target financed project SF0170006s08 and by Estonian Science Foundation grants 6820, 7392 and 7643

Fish predation pressure on zooplankton in a large northern temperate lake : impact of adult predators versus juvenile predators

In recent decades, a marked decrease in planktivorous fish (Osmerus eperlanus eperlanus m. spirinchus Pallas and Coregonus albula (L.)) in Lake Peipsi has stimulated research into the potential effect of fish predation on zooplankton. The abundance of planktivorous fish and the abundance and biomass of zooplankton were studied from 1986 to 2014, and the diet of plankton-eating fish was analysed from 2007 to 2013. A linear regression model was used to establish possible trends in the zooplankton assemblages (biomass, abundance, mean weight of individuals) and in the abundance of zooplankton-eating fish. The ANOVA test was used to evaluate differences in the zooplankton assemblages and in fish consumption in the years with large and small fish cohorts. Despite the collapse of the smelt and vendace populations, the abundance of plankton-eating fish remained high due to an increase in the abundance of juvenile fish. Fish juveniles consumed as much as or even more zooplankton than adult planktivores. Since 1986, a significant decrease was observed in the cladoceran and copepod biomass and in the mean body weight of cladocerans. Large cladocerans such as Leptodora kindtii (Focke) and Bythotrephes longimanus Leydig were rare in zooplankton samples and the biomass of Bosmina spp. decreased. Changes in the structure of the zooplankton community were most likely caused by the feeding of juvenile fish as the calculated consumption by fish was high, especially in years with particularly large fish cohorts.The research was supported by the Estonian target financed project SF0170006s08. We gratefully acknow- ledge Ester Jaigma for the linguistic editing of the manuscript, Marina Haldna for assistance in statistical analyses, and Dr Peeter Kangur for data collection. The publication costs of this article were covered by the Estonian Academy of Sciences.The research was supported by the Estonian target financed project SF0170006s08. We gratefully acknow- ledge Ester Jaigma for the linguistic editing of the manuscript, Marina Haldna for assistance in statistical analyses, and Dr Peeter Kangur for data collection. The publication costs of this article were covered by the Estonian Academy of Sciences

Predicting multiple stressor effect on zooplankton abundance, biomass and community composition in two large eutrophic lakes : [presentation]

Presentation at the BIOGEOMON 2022, 10th International Symposium on Ecosystem Behavior, June 26–30, 2022, Tartu, Estonia.We are grateful to Tartu Environmental Research Ltd (Estonia) for water chemistry data and to the Estonian Environment Board for providing long-term air temperature data and supporting lake monitoring. This research was financed by Estonian Research Council Grant PRG709, PRG1167, and institutional research funding P210160PKKH of the Estonian Ministry of Education and Research. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Data collection within the frames of the state monitoring programme were supported by the Estonian Ministry of the Environment

Keystone species Chydorus sphaericus in shallow eutrophic Lake Võrtsjärv (Estonia) – 56 years of continuous zooplankton monitoring and research

Presentation at the 11th International Shallow Lakes Conference, Estonia 11.-16.06.2023.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167

Effects of environmental stressors and their interactions on zooplankton biomass and abundance in a large eutrophic lake

We assessed long-term impacts of multi- ple stressors and their interaction on the zooplankton community of the large, eutrophic, cyanobacteria- dominated Lake Peipsi (Estonia, Russia). Stressor dataset consisted in time series (1997–2018) of temperature, nutrients, pH, water transparency, phy- toplankton biomass and taxonomic richness. The best predictors were selected with random forests machine- learning algorithms and the subsequent models were constructed with generalized linear modeling. We also aimed to identify graphical thresholds representing non-linear, marked responses of abundance or bio- mass to stressors. Temperature was the dominant stressor for explaining zooplankton abundance and biomass, followed by cyanobacteria biomass, total nitrogen concentration and water transparency. The effect of water temperature was positive, whereas the effect of cyanobacteria became negative after their biomass exceeded a threshold of * 2 mg l-1 . How- ever, the two stressors together had antagonistic effects on zooplankton, causing a decrease in biomass and abundance. For zooplankton, critical thresholds of total nitrogen (* 700 lg l-1 ), total phosphorus (* 70 lg l-1 ), and water transparency (* 1.4 m) after which zooplankton metrics changed drastically, were determined. These findings show that although lake warming alone could be positive for zooplankton, the necessity of reducing interacting stressors that influence harmful cyanobacteria growth and biomass, especially nitrogen loads, must be considered.Funding was provided by Estonian Research Council PSG32.Funding was provided by Estonian Research Council PSG32

Narva Reservoir 2018 (Littoral samples)

Phytoplankton samples were picked with bottle from among reed stands or from above thick beds of submerged plants from the depth 20-30 cm, were preserved in Lugol’s (acidified iodine) solution and counted under an inverted microscope (Utermöhl, 1958). 3 ml of preserved sample was settled overnight and counted in random fields or transects. Biovolumes of algal cells, colonies and/or filaments were calculated using assigned geometric shapes dimensions, and converted to biomass assuming the specific density of 1 g cm-3 in accordance with Edler (1979). Macroscopic colonies of Gloeotrichia echinulata were enumerated visually in 500 ml measuring cylinder. Counting units are independent (single) algal cells, colonies or filaments/trichomes. One species or taxon may be present in the sample as different counting units and may be counted at different magnifications. References of methods accepted Approved by CEN on 14 July 2006 “Water quality - Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)” (CEN 15204, 2006) European Standard EN 15204:2006 Utermöhl, H., 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen der Internationale Vereinigung für Theoretische und Angewandte Limnologie 9, 1-38. Edler, L. (ed.), 1979. Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll. Baltic Marine Biologists WG 9. (13) Biovolume calculation for pelagic and benthic microalgae | Request PDF. Available from: https://www.researchgate.net/publication/220031275_Biovolume_calculation_for_pelagic_and_benthic_microalgae [accessed Oct 29 2018]. The most commonly used traditional biomass estimate for microalgae is cell biovolume, which is calculated from microscopically measured linear dimensions (Steinman et al. 1991, Snoeijs 1994, Sommer 1994, 1995, Hillebrand and Sommer 1997). Hand-books, most representative Huber-Pestalozzi, G., Komarek, J., Fott, B. 1983. Das Phytoplankton des Süsswassers. 7(1). Chlorophyceae. Chlorococcales. Stuttgart. 1044. S. Komarek, J., Anagnostidis, K. 1999. Süsswasserflora von Mitteleuropa. 19/1. Cyanoprocaryota. 1. Chroococcales. Elsevier Spectrum Academischer Verlag. Heidelberg. Berlin. 548 S. Komarek, J., Anagnostidis, K. 2005. Süsswasserflora von Mitteleuropa. 19/2. Cyanoprocaryota. 2. Oscillatoriales. Elsevier Spectrum Academischer Verlag. 759 S. Komárek, J., 2013. Cyanoprokaryota 3. Teil: Heterocystous Genera. Süsswasserflora von Mitteleuropa. B. 19/3. Springer Spektrum. 1130 S. Krammer, K., Lange-Bertalot, H. 1997-1991. Süsswasserflora von Mitteleuropa. Bacillariophyceae. B. 2, 1-4. Spectrum Academischer Verlag.Heidelberg. Berlin.. Popovský, J., Pfiester, L.A. 20008. Dinophyceae (Dinoflagellida). Süsswasserflora von Mitteleuropa. B. 6. Springer Spektrum. 272 S. Косинская Е.К. 1960. Флора споровых растений СССР. Том 5. Конъюгаты и Сцеплянки. (2). Изд. АН СССР. Москва-Ленинград. 706 стр. In Russian. Korshikov, A.A. (1953). Viznachnik prisnovodnikh vodorosley Ukrainsykoi RSR [Vyp] V. Pidklas Protokokovi (Protococcineae). Bakuol'ni (Vacuolales) ta Protokokovi (Protococcales) [The Freshwater Algae of the Ukrainian SSR. V. Sub-Class Protococcineae. Vacuolales and Protococcales]. pp. 1-439. Kyjv [Kiev]: Akad. NAUK URSR. In Ukrainian. Матвiенко О.М. 1965. Визначник прiсноводных водоростей Украǐнской РСР. 3. Частина 1. Золотисти водорости – Chrysophyta. Изд. Наукова Думка. Киǐв. 367 стр. In Ukrainian. Попова Т.Г. 1955. Определитель пресноводных водорослей. Вып. 7. Эвгленовые водоросли. Изд. Советская Наука, Москва. 282 стр. In Russian

Cool winters versus mild winters: effects on spring plankton in Lake Peipsi

Abstract. The influence of two winter periods with a different duration of the ice cover on Lake Peipsi (Estonia) on plankton and nutrient content was analysed. The winters of 2005 and 2006 were cold with ice duration of 140 days, whereas the winters of 2007 and 2008 were mild with about 50 and 15 days of ice duration, respectively. Total phosphorus (TP) concentration was lower, while silicon content and the nitrogen-phosphorus ratio (TN : TP) were markedly higher in the springs after the short winters of 2007 and 2008. The high Si concentration and TN : TP ratio persisted throughout the growing season of those years. Unicellular centric diatoms showed a sharp increase in April 2008, while the large filiform diatom Aulacoseira islandica dominated in the cool winters and after ice break-up. The high spring peak of diatoms was followed by their low biomass in summer. In May 2008, total zooplankton biomass, cladoceran biomass, and rotifer biomass were two times and that of copepods three times as high as in the Mays after the long-lasting ice cover. In the Junes after the mild winters the biomasses of total zooplankton and both crustacean groups (Cladocera, Copepoda) were about two times as high as the corresponding indicators for the Junes after the cool winters. The biomass of rotifers, on the contrary, was two times lower in the Junes after the warm winters because the numerous cold stenotherms Polyarthra dolichoptera and Synchaeta verrucosa had totally disappeared from zooplankton. The influence of ice duration on phytoplankton is most likely indirect, acting through nutrients, and on zooplankton direct, acting through water temperatures. The springs after warm winters related positively to zooplankters' mean weight, zooplankton-phytoplankton biomass ratio, and the timing of the clear water period

Lake Peipsi 2022 (Phytoplankton samples)

Method: Phytoplankton samples were preserved in Lugol’s (acidified iodine) solution and counted under an inverted microscope (Utermöhl, 1958). 3-10 ml of preserved sample was settled overnight and counted in random fields or transects. Biovolumes of algal cells, colonies and/or filaments were calculated using assigned geometric shapes dimensions, and converted to biomass assuming the specific density of 1 g cm-3 in accordance with Edler (1979). Approved by CEN on 14 July 2006 “Water quality - Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)” (CEN 15204, 2006) European Standard EN 15204:2006 Utermöhl, H., 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen der Internationale Vereinigung für Theoretische und Angewandte Limnologie 9, 1- 38. Edler, L. (ed.), 1979. Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll. Baltic Marine Biologists WG 9. Leg: K. Blank, K. Palmik-Das, L. Tuvikene, A. Tuvikene; det: K. Maileht

Lake Peipsi 2021 (Phytoplankton samples)

Method: Phytoplankton samples were preserved in Lugol’s (acidified iodine) solution and counted under an inverted microscope (Utermöhl, 1958). 3-10 ml of preserved sample was settled overnight and counted in random fields or transects. Biovolumes of algal cells, colonies and/or filaments were calculated using assigned geometric shapes dimensions, and converted to biomass assuming the specific density of 1 g cm-3 in accordance with Edler (1979). Approved by CEN on 14 July 2006 “Water quality - Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)” (CEN 15204, 2006) European Standard EN 15204:2006 Utermöhl, H., 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen der Internationale Vereinigung für Theoretische und Angewandte Limnologie 9, 1- 38. Edler, L. (ed.), 1979. Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll. Baltic Marine Biologists WG 9. Leg: K. Blank, K. Palmik-Das, L. Tuvikene, A. Tuvikene; det: K. Maileht

Lake Peipsi 2013 (Phytoplankton samples)

DatasetMethod: Phytoplankton samples were preserved in Lugol’s (acidified iodine) solution and counted under an inverted microscope (Utermöhl, 1958). 3 ml of preserved sample was settled overnight and counted in random fields or transects. Biovolumes of algal cells, colonies and/or filaments were calculated using assigned geometric shapes dimensions, and converted to biomass assuming the specific density of 1 g cm-3 in accordance with Edler (1979). Approved by CEN on 14 July 2006 “Water quality - Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)” (CEN 15204, 2006) European Standard EN 15204:2006 Utermöhl, H., 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen der Internationale Vereinigung für Theoretische und Angewandte Limnologie 9, 1- 38. Edler, L. (ed.), 1979. Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll. Baltic Marine Biologists WG 9