Browsing by Subject "kasviplankton"

In this study, the goal was to determine which nutrient, phosphorus or nitrogen, limits the phytoplankton growth at the Vanajavesi freshwater site. The aims were to detect spatial and temporal changes and find out if the wastewater treatment plant (hereafter, WWTP) located by the study site affects the nutrient concentrations and the limiting nutrient. The reliability of determining limiting nutrient by bioassays and measuring the phytoplankton response to different treatments as fluorescence was also evaluated. The study was conducted because knowledge of nutrient limitation is essential when allocating resources to reduce nutrient loading and planning other remediation practices in eutrophicated waterbodies. According to the EU Water Framework Directive, all waterbodies in the EU must be in a good ecological status by the year 2027. This goal is yet to be achieved in Vanajavesi; the ecological status of the river Vanajanreitti is poor and that of lake Vanajanselkä is moderate. The samples for bioassays were taken from five different locations. Three sampling sites were in the river and two by the lake. Based on the direction which the water flows, one of the sampling sites was before the outlet from the WWTP and the rest after it. The bioassays were carried out with the water and natural phytoplankton community taken from the study site. The experiment was conducted five times: in November, March, May, July and August. The temperature and light conditions in the incubation room were set to mimic those in Vanajavesi at each given time. Part of the preparations was to filter out the zooplankton using 50 μm plankton net. There were four different treatments: control without nutrient additions, nitrogen addition, phosphorus addition and nitrogen and phosphorus additions. Fluorescence from the 2 litre incubation bottles was measured every 1-3 days during each experiment. Chlorophyll a was determined in laboratory before and after the experiments. Nutrient concentrations were also determined before each experiment. Small seasonal and temporal changes were observed in the nutrient concentrations and the limiting nutrient. These changes were most likely due to changing seasons, effluent from the WWTP and denitrification at lake Vanajanselkä. Phosphorus limited phytoplankton growth year around at all places. At the end of the summer also nitrogen was limiting. In July co-limitation was detected in all sampling sites. In situations of co-limitation there was either no secondary limiting nutrient, or it was phosphorus. Only once, in August at the sampling point before the outlet from the WWTP, was the secondary limiting nutrient nitrogen. On average the nutrient concentrations were higher in the river than in the lake. Chlorophyll a concentrations and some nutrient concentrations were higher after the WWTP. However, no significant negative impact due to WWTP could be detected, especially at lake Vanajanselkä and the WWTP did not result in a change from phosphorus limitation to nitrogen limitation. Bioassays and the phytoplankton yield measured with a fluorometer was a reliable way of determining the limiting nutrient. Chlorophyll a concentrations verified the fluorescence results. The probe used in this study measured only the fluorescence of chlorophyll a. Even more accurate result of the phytoplankton biomass would have been obtained with a probe that measures also the fluorescence of phycocyanin, the photosynthetic pigment in cyanobacteria, because cyanobacteria has less chlorophyll a than other phytoplankton groups. As Vanajavesi is phosphorus limited or co-limited by phosphorus and nitrogen year around, reductions in phosphorus loading will likely improve the water quality. The main source of phosphorus to Vanajavesi is the nutrient loading from agricultural practises on the drainage basin. Efficient management of this diffuse loading will cause the phytoplankton biomass, especially the biomass of harmful cyanobacteria, to decrease. Nitrogen-fixing cyanobacteria is not dependent on the nitrogen concentrations in the water column, but the concentration of phosphorus. Significantly reducing the phosphorus loading is a prerequisite for the Vanajanreitti and Vanajavesi to be in a good ecological status by the year 2027.

Kasvi- ja eläinplanktonia esiintyy käytännössä kaikissa boreaalisissa järvissä ja lammissa. Kasviplankton on koko järviekosysteemille tärkeä perustuottajaryhmä, kun taas eläinplankton on tärkeä kasviplanktonin kuluttajaryhmä. Ne siirtävät energiaa korkeammille trofiatasoille. Lisäksi ne toimivat ympäristöntilan indikaattoreina, sillä erityisesti kasviplankton reagoi herkästi elinympäristönsä muutoksiin. Tämän vuoksi kasvi- ja eläinplanktonin esiintymiseen ja levinneisyyteen vaikuttavien tekijöiden tunteminen on tärkeää. Tässä maisterintutkielmassa selvitettiin kasvi- ja eläinplanktonin levinneisyyttä boreaalisissa järvissä viidellä eri valuma-alueella Suomessa. Levinneisyyttä tarkasteltiin kolmen selittävän tekijän avulla, jotka olivat runsaus, ekolokeron koko ja lajipiirteet. Nämä selittävät muuttujat valittiin, koska kirjallisuuden perustella ne vaikuttavat merkittävästi lajin levinneisyyteen. Runsaus kuvaa lajin paikallista esiintymistä, ekolokeron koko puolestaan vuorovaikutusta muiden lajien kanssa ja lajipiirteet vaikuttavat pääasiassa leviämiskyvyn lisäksi saalistuspaineeseen. Tutkimuksen aineisto sisälsi yhteensä 100 järven kasvi- ja eläinplanktonlajien yksilöiden määrän kussakin järvessä sekä fysikaalis-kemiallisten ominaisuuksien mittaustulokset. Lajipiirteistä valittiin tutkittavaksi solukoko, jonka arvot pohjautuivat kirjallisuuteen. Levinneisyyden yhteyttä selittäviin muuttujiin tutkittiin regressioanalyysin avulla sekä tärkeimmille järvien fysikaalis-kemiallisille muuttujille tehtiin pääkomponenttianalyysi (PCA). Runsaus sekä ekolokeron koko korreloivat merkitsevästi levinneisyyden kanssa. Solukoolla ei havaittu lainkaan yhteyttä kasviplanktonin levinneisyyden kanssa. Eläinplanktonilla yhteys näiden muuttujien välillä havaittiin, mutta tulos ei ollut merkitsevä. Tulokset levinneisyyden ja solukoon välillä eivät kuitenkaan olleet luotettavia tai vertailukelpoisia, koska aineiston lajeilla oli liian pieni otanta. Aiempien tutkimusten perusteella voidaan kuitenkin sanoa, että solukoolla olisi käänteinen suhde levinneisyyden kanssa. Lajisto ja järvien fysikaalis-kemialliset olosuhteet olivat samankaltaisempia mitä lähempänä valuma-alueet olivat toisiaan.

In many Fennoscandian lakes, diatoms account for majority of phytoplankton biomass during the spring and autumn maximum. Autumnal blooms of filament-forming diatoms are known to cause fishing net fouling in several boreal lakes. Observations of such net sliming diatom blooms in the northern part of Lake Vesijärvi have increased during 2010’s. This thesis was done in collaboration with Lake Vesijärvi Foundation. The goal was to determine the starting time of the autumnal diatom bloom of 2018 and reveal the species that causes net sliming. Additionally, differences in water quality and phytoplankton composition between Enonselkä and Kajaanselkä basins were examined. Fishing net sliming was studied with netting experiments. Their results were complemented with water quality sampling and observing water column mixing conditions. Local fishermen reported net sliming to begin at week 40 (starting 1.10.2018) in Kajaanselkä basin during autumnal turnover. Results of netting experiments and water quality sampling revealed simultaneous increase in diatom abundance in the area, although no visible sliming occurred during sampling. Based on fishers’ reports and sampling results, fishing net sliming was caused by filament-forming diatom Aulacoseira islandica, that increased in abundance as water temperature reached ca. 11 °C. In Enonselkä, no similar net sliming was observed, and phytoplankton was dominated by cyanobacteria Planktothrix agardhii. Both basins of the lake are affected by eutrophication, but Enonselkä basin more so than Kajaanselkä. Although no clear explanation for differing phytoplankton composition between the two basins was discovered, it’s possible that Aulacoseira islandica receives competitive edge over cyanobacteria in mildly eutrophic waters of Kajaanselkä basin. The fact that Planktothrix agardhii seems to thrive in higher nutrient concentrations might explain its domination over diatoms in phytoplankton community of Enonselkä basin. Future research on net sliming would ideally be conducted as a combination of sliming accounting done by local fishermen and spatially and temporally more comprehensive netting experiments. Furthermore, studying the effects of wind and currents to diatom distribution in lakes could provide useful information for sampling setup.