The response of phytoplankton community to the changes in nutrient loading
Date
2010-11-16
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Abstract
Veekogu eutrofeerumine on looduslik protsess, mille kiirus oleneb valgalalt sissekantavate toiteainete hulgast. Üheks eutrofeerumise ilminguks on fütoplanktoni liigne hulk, mis põhjustab hapnikusisalduse ja pH kõikumist, veekogude mudastumist ja stressitingimusi veekogu asukatele. Fütoplankton on toiduahela aluslüliks, mõjutades kogu toiduvõrgustikku. Iga-suvised veeõitsengud on järvedes ja Läänemeres suureks probleemiks, mistõttu nende efektiivseks majandamiseks on vaja eelteadmisi sellest, kuidas toiteainete hulga muutus mõjutab vetikaliike. Mikrovetikad reageerivad toiteainete hulga muutustele suhteliselt kiiresti muutustega nii liigilises koosseisus kui biomassis.
Eksperimentidest selgus, et mõlemad uuritud kooslused (Odense fjordis kevadel ja Tvärminnes suvel) reageerisid biomassitõusuga toiteainete liiaga lisamisele. Tvärminnes domineeriva sinivetikakoosluse vastus toiteainete lisamisele oli liigi-spetsiifiline. Anorgaanilise lämmastiku puudus põhjustas küll üldiselt fütoplanktoni madalama biomassi, aga protsentuaalselt suurema lämmastiku-fikseerijate hulga. Fosforipuudus vähendas osade lämmastiku-sidujate (Anabaena lemmermannii ja Nodularia spumigena) konkurentsivõimet, aga sinivetikaõitsengut see ei välistanud soodsate tingimuste olemasolul. Lisaks toiteainetele kujundasid kooslust liikide-vahelise konkurentsi vähenemine ja zooplanktoni sööm (väikse-rakulised vaguvibur- ja neelvetikad).
Akineetide e. puhkerakkude moodustamine on üks sinivetikate elutsükli oluline osa. A. lemmermannii akineetide produktsioon oli kõrgem fosforipuuduse korral.
Liigse toiteainete lisandumise tõttu oluliselt muutunud fütoplanktoni koosluse näiteks on Verevi järv – algselt mesotroofsest seisundist Planktothrix agardhii domineerimisega hüpertroofseks järveks (80ndail). Praeguses faasis iseloomustab järve suhteliselt suur läbipaistvus ning eutroofsele seisundile vastav vetikakooslus, kuid seisundi paranemine võib olla ajutine hüpolimnionis ja setetes oleva suure toiteainevaru tõttu.
Phytoplankton is the base of a food-chain; its biomass and composition influence the whole functioning of a water body. Extra nutrients cause excess phytoplankton biomass, with fluctuations in O2 content and pH, increased sedimentation and stress to other inhabitants. Cyanobacterial blooms in lakes and in the Baltic Sea are an increasing problem, thus for the successive management the knowledge of species reaction to the changes in nutrient loading is indispensable. From experiments was evident that in both studied communities (Odense Fjord in spring and Tvärminne in summer) the mineral nutrient addition led to a rapid increase of phytoplankton biomass. Moderate, even excessive N additions lowered the competitive ability of some filamentous cyanobacteria (Anabaena spp.), but generally failed to prevent cyanobacterial bloom due to Aphanizomenon sp., when other conditions were favourable. Cutting the nitrogen supply resulted in lower phytoplankton total biomass, but in elevated relative amount of nitrogen-fixing cyanobacteria. Nutrient limitation did not explain the whole dynamics of phytoplankton community, for example Aphanizomenon sp. used internal phosphorus reserves and grew well independently of nutrients. Other factors (temperature, zooplankton grazing and reduced competition with other species) were important in shaping the phytoplankton community composition. Production of akinetes is an important part of the life-cycle of Nodulariaceae. Anabaena lemmermannii produced more akinetes in P-limited conditions. Lake Verevi can be used as an example of cultural eutrophication and intensive changes in phytoplankton community due to nutrient pollution – from initially mesotrophic to a hypertrophic lake with monodominating Planktothrix agardhii in eighties. In the present state water transparency has increased, the phytoplankton biomass has decreased, but this improvement may be temporary, since nutrients are still present in the hypolimnion and in the sediments.
Phytoplankton is the base of a food-chain; its biomass and composition influence the whole functioning of a water body. Extra nutrients cause excess phytoplankton biomass, with fluctuations in O2 content and pH, increased sedimentation and stress to other inhabitants. Cyanobacterial blooms in lakes and in the Baltic Sea are an increasing problem, thus for the successive management the knowledge of species reaction to the changes in nutrient loading is indispensable. From experiments was evident that in both studied communities (Odense Fjord in spring and Tvärminne in summer) the mineral nutrient addition led to a rapid increase of phytoplankton biomass. Moderate, even excessive N additions lowered the competitive ability of some filamentous cyanobacteria (Anabaena spp.), but generally failed to prevent cyanobacterial bloom due to Aphanizomenon sp., when other conditions were favourable. Cutting the nitrogen supply resulted in lower phytoplankton total biomass, but in elevated relative amount of nitrogen-fixing cyanobacteria. Nutrient limitation did not explain the whole dynamics of phytoplankton community, for example Aphanizomenon sp. used internal phosphorus reserves and grew well independently of nutrients. Other factors (temperature, zooplankton grazing and reduced competition with other species) were important in shaping the phytoplankton community composition. Production of akinetes is an important part of the life-cycle of Nodulariaceae. Anabaena lemmermannii produced more akinetes in P-limited conditions. Lake Verevi can be used as an example of cultural eutrophication and intensive changes in phytoplankton community due to nutrient pollution – from initially mesotrophic to a hypertrophic lake with monodominating Planktothrix agardhii in eighties. In the present state water transparency has increased, the phytoplankton biomass has decreased, but this improvement may be temporary, since nutrients are still present in the hypolimnion and in the sediments.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
dissertatsioonid, bioloogia, toiteained, fütoplankton