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Sirvi Autor "Heinsalu, Atko" järgi

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  • Pisipilt
    Kirje
    Environmental drivers and abrupt changes of phytoplankton community in temperate lake Lielais Svetinu, Eastern Latvia, over the last Post-Glacial period from 14.5 kyr
    (Elsevier, 2021) Tõnno, Ilmar; Talas, Liisi; Freiberg, Rene; Kisand, Anu; Belle, Simon; Stivrins, Normunds; Alliksaar, Tiiu; Heinsalu, Atko; Veski, Siim; Kisand, Veljo; Chair of Hydrobiology and Fishery
    Understanding the long-term dynamics of ecological communities on the centuries-to-millennia scale is important for explaining the emergence of present-day biodiversity patterns and for predicting possible future scenarios. Fossil pigments and ancient DNA present in various sedimentary deposits can be analysed to study long-term changes in ecological communities. We analysed recent compilations of data, including fossil pigments, microfossils, and molecular inventories from the sedimentary archives, to understand the impact of gradual versus abrupt climate changes on the ecosystem status of a regional model lake over the last ~14.5 kyr. Such long and complete paleo-archives are scarce in North-Eastern Europe. The study site lies in a sensitive area, both climatically and in respect to vegetation. Namely the maritime-continentality line runs west to east in the central Baltic area to NE Europe and its south- north transect lies within the gradual decay of the nemoral forest into a boreal environment. Therefore, the selected location is an ideal sampling point to decipher long term environmental changes in the temperate climate zone. The main objective of the present study was to find out external factors influencing phototroph dynamics at temperate Lake Lielais Sv etin ̧ u over the post-glacial period (~14.5 kyr). We were able to model climate change together with vegetation change and the appearance of anthropogenic forcing, either as a gradual change or as abrupt events that influenced the phototrophs, which are keystone groups within the lacustrine ecosystem. Most interestingly, the gradual increase of species richness of phototrophs was linked to similar increase in fungal parasites of the same group e phototrophs. Abrupt climate change in the Late Glacial period caused abrupt events in the ecosystem but equally abrupt events were caused by gradual changes during the stable period of the Holocene Thermal Maximum (HTM). In addition, we highlight the increased frequency and degree of perturbation in pristine lakes due to low impact human activity over a larger region. Both observations demonstrate an impaired relationship between gradual external drivers and ecosystem response and apply to future scenarios of climate warming and increased human impact in north-eastern Europe.
  • Pisipilt
    Kirje
    Late glacial and early Holocene climate and environmental changes in the eastern Baltic area inferred from sediment C/N ratio
    (Springer, 2019) Liiv, Merlin; Alliksaar, Tiiu; Amon, Leeli; Freiberg, Rene; Heinsalu, Atko; Reitalu, Triin; Saarse, Leili; Seppä, Heikki; Stivrins, Normunds; Tõnno, Ilmar; Vassiljev, Jüri; Veski, Siim; Centre for Limnology. Institute of Agricultural and Environmental Science
    We assessed the utility of using the sediment total organic carbon/total nitrogen (C/N) ratio as an indicator of paleoclimate changes in the eastern Baltic area during the late glacial and early Holocene. The C/N ratio in sediments from Lake Lielais Sve ̄tin ̧ u, eastern Latvia, was compared with other sediment variables that are used as proxies of past climate and environment. Analysis revealed that although the organic matter (OM) content in late glacial sediments was extremely low, the C/N ratio captured information about OM origin, and fluctua- tions in the ratio tracked climate oscillations. The C/N ratio was significantly positively correlated with pollen-inferred mean summer temperature. Therefore, C/N ratio was lower under colder conditions, indicat- ing a predominantly phytoplankton origin of OM, and was higher during warmer conditions, when there was more vegetation around the lake. A strong positive correlation between C/N ratio and the paleopigment beta carotene suggested that elevated phytoplankton production resulted from higher nutrient availability that was controlled largely by the input of terrestrial OM to the lake during warmer climate episodes. Thus, C/N ratio was a good indicator of paleoclimate changes, at least for the late glacial period, when generally cold conditions prevailed. This study also demonstrates the power of multi-proxy paleolimno- logical analyses for investigating past environmental changes in lakes and their watersheds.
  • Pisipilt
    Kirje
    Saadjärve seisundi, eutrofeerumise kujunemise ja looduslähedaste foonitingimuste väljaselgitamine põhjasetete paleolimnoloogiliste uuringute abil
    (Tallinna Tehnikaülikool, Geoloogia Instituut, 2025) Heinsalu, Atko; Alliksaar, Tiiu
    TTÜ Geoloogia Instituudi vanemteadurite Atko Heinsalu ja Tiiu Alliksaare poolt koostatud aruanne kajastab EMÜ Limnoloogiakeskuse poolt tellitud uuringu tulemusi. Projekti lähteülesandeks oli setteuuringute põhjal välja selgitada Saadjärve looduslähedased foonitingimused ning taastuletada lähiminevikus asetleidnud võimalikud veekvaliteedi muutused selles veekogus. Järve “hea seisundi” määratlemiseks on vaja teada veekogu foonitingimusi, st looduslähedast intensiivsest inimmõjust veel puutumatu seisundit. Euroopa Parlamendi ja Nõukogu veepoliitika raamdirektiiv (VRD) sätestab liikmesriikidele eesmärgi saavutada veekogude “hea seisund” hiljemalt aastaks 2015 ning VRD nõuete kohaselt on järvede seisundi määratlemise aluseks eri tüüpi veekogude nüüdisolukorra võrdlemine foonitingimustega, st looduslähedase intensiivsest inimmõjust veel puutumatu seisundiga (Directive…, 2000). Et Eesti järvede kohta olemasolevad instrumentaalsed andmeread nii kaugele minevikku, kui veekogud olid veel looduslähedases seisundis, ei ulatu, tuleb VRD kohaselt järvede foonitingimuste väljaselgitamiseks kasutada paleolimnoloogilistele setteuuringutele põhinevaid mudeluuringuid ja rekonstruktsioone (Heinsalu & Alliksaar, 2005). Paleolimnoloogia on teadusharu, mis uurib järvesetteid. Tänu setetes säiluvatele mikroskoopilistele organismidele või nende jäänustele ning sette keemilisele koostisele on järvesetted looduslikuks arhiiviks, kuhu on talletunud informatsioon nii limnoloogiliste, klimaatiliste ja inimtekkeliste protsesside kohta nii järves kui ka selle ümbruses. Paljudes Euroopa Liidu liikmesriikides, näiteks Suurbritannias (Bennion jt, 2004), Saksamaal (Schönfelder jt, 2002), Taanis (Bradshaw jt, 2002), Rootsis (Bradshaw & Anderson, 2001), Soomes (Miettinen jt, 2005; Räsänen jt, 2005) ja Eestis (Heinsalu jt, 2003) on järvede foonitingimuste väljaselgitamisel keskendutud just setete ränivetikate kooslustel põhinevatele rekonstruktsioonidele. Paleolimnoloogiliste uuringute tulemused on aluseks veekogu majandamise või tervendamise projekti edukaks koostamiseks.