76 research outputs found
Indices of zooplankton community as valuable tools in assessing the trophic state and water quality of eutrophic lakes: long term study of Lake Võrtsjärv
No full textOn the basis of long-term (1964-2011) research, we tested the hypothesis that the zooplankton community has a highly indicative value in assessing the ecosystem and trophic state of water bodies. Basing on the results of our study and taking into account relevant data from numerous zooplankton studies, we can conclude that the zooplankton measures deserving to be used as indicators in the monitoring of Lake Võrtsjärv (and other similar eutrophic water bodies) could be the following: i) indicatory species of eutrophic waters [Anuraeopsis fissa (Gosse), Keratella tecta (Gosse), Trichocerca rousseleti (Voigt), Chydorus sphaericus (O. F. Müller), Bosmina longirostris (O. F. Müller)]; ii) indicatory species of oligo-mesotrophic waters [Conochilus unicornis Rousselet, Kellicottia longispina (Kellicott), Ploesoma hudsoni (Imhof), Bosmina berolinensis Imhof, Eudiaptomus gracilis (Sars)]; iii) number and diversity of species; iv) mean zooplankter weight, mean cladoceran weight, mean rotifer weight and mean copepod weight; v) rotifer abundance; vi) the share (%) of rotifers in total zooplankton abundance; vii) the ratio of abundance of large cladocerans to abundance of all cladocerans (NLargeClad/NClad); viii) the ratio of calanoid copepod abundance to cyclopoid copepod abundance (NCal/NCycl); ix) the ratio of crustacean abundance to rotifer abundance (NCrust/NRot ). The results of our study show that several zooplankton parameters are among the biological quality elements (BQE) deserving to be included in the Water Frame Directive system.</p
A comparison of zooplankton densities and biomass in Lakes Peipsi and Võrtsjärv (Estonia): rotifers and crustaceans versus ciliates
No full textFüto- ja zooplanktoni dünaamika ja nende omavahelised suhted kui Peipsi järve seisundi indikaatorid
No full textPhyto- 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
The status of the southernmost part (Lake Pihkva) of large Lake Peipsi: A purification pond or polluter?
No full textLarge Lake Peipsi (3555 km2) is divided between two countries, Estonia (44%) and Russia (56%). The southernmost part of the lake, Lake Pihkva, is almost entirely (99%) in Russia, and is continuously being polluted by the greatest inflow to Lake Peipsi, the insufficiently purified River Velikaya. Research on this lake (Lake Peipsi) in the growing season has been possible as a result of Estonian–Russian joint expeditions (2003–2010) in the month of August. Our study has demonstrated statistically significant variances in the hydrochemistry and zoo- and phytoplankton data between the lake parts. Several parameters used for characterizing the lake's ecosystem were considerably higher for Lake Pihkva than for the larger Lake Peipsi s.s. These include increases in TP concentration (3×); TN (2×); Chlorophyll a (3×); biomass of cyanobacteria (4×); Microcystis (4×); Aphanizomenon (5×); abundance of Chydorus sphaericus (5×); Keratella tecta (8×). However, several values were lower in Lake Pihkva than in Lake Peipsi: water transparency (3×); ratio between zoo- and phytoplankton biomasses (2×); cladoceran mean weight (3×); abundance of Eudiaptomus gracilis (1.5×); abundance of Kellicottia longispina (1.8×). Different natural conditions (topography, catchment area, relative depth) and different pollution loads in the lake parts have resulted in apparently different resistances in their ecosystems and different responses to human activity. At present, on the basis of TP data (up to 200 mg m−3), Lake Pihkva appears to act a polluter of adjacent lake part rather than a purification pond.</jats:p
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