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Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/6178

Sirvi

Sirvi Artiklid Autor "Alliksaar, Tiiu" järgi

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  • Pisipilt
    Kirje
    Contrasting responses to long-term climate change of carbon flows to benthic consumers in two different sized lakes in the Baltic area
    (Elsevier, 2018) Belle, Simon; Freiberg, Rene; Poska, Anneli; Agasild, Helen; Alliksaar, Tiiu; Tõnno, Ilmar; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
    The study of lake sediments and archived biological remains is a promising approach to better under- stand the impacts of climate change on aquatic ecosystems. Small lakes have been shown to be strongly sensitive to past climate change, but similar information is lacking for large lakes. By identifying re- sponses to climate change of carbon flows through benthic food web in two different sized lakes, we aimed to understand how lake morphometry can mediate the effects of climate change. We recon- structed the dynamics of phytoplankton community composition and carbon resources sustaining chironomid biomass during the Holocene from the combined analysis of sedimentary pigment quanti- fication and carbon stable isotopic composition of subfossil chironomid head capsules (d13 C HC) in a large lake in the Baltic area (Estonia). Our results showed that chironomid biomass in the large lake was mainly sustained by phytoplankton, with no significant relationship between d13 C HC values and tem- perature fluctuations. We suggest that lake morphometry (including distance of the sampling zone to the shoreline, and lake volume for primary producers) mediates the effects of climate change, making large lakes less sensitive to climate change. Complementary studies are needed to better understand differ- ences in organic matter dynamics in different sized lakes and to characterize the response of the aquatic carbon cycle to past climate change.
  • 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
    Holocene shifts in the primary producer community of large, shallow European Lake Peipsi, inferred from sediment pigment analysis
    (Springer, 2019) Tõnno, Ilmar; Nauts, Kristiina; Belle, Simon; Nõmm, Monika; Freiberg, Rene; Kõiv, Toomas; Alliksaar, Tiiu; Centre for Limnology. Institute of Agricultural and Environmental Sciences
    We used HPLC to identify and quantify pigments in a Holocene sediment record from large, shallow Lake Peipsi, Estonia. The aim of our study was to track the influence of long-term climate change (i.e. temperature fluctuations) on past dynamics of aquatic primary producers. Sedimentary pigments were separated and quantified in 182 samples that span the last ca. 10,000 years. There was an increasing trend in sedimentary pigment concentrations from basal to upper sediment layers, suggesting a gradual increase in lake trophic status through time. Using additive models, our results suggested that primary producer dynamics in Lake Peipsi were closely related to temperature fluctuations. We, however, identified two periods (early Holocene and after ca. 2.5 cal ka BP) when the relationship between primary producer composition and temperature was weak, suggesting the influence of additional drivers on the primary producer community. We postulate that: (a) the increase of primary producer biomass in the early Holocene could have been caused by input of allochthonous organic matter and nutrients from the flooded areas when water level in Lake Peipsi was increasing, and (b) changes in the abundance and structure of primary producer assemblages since ca. 2.5 cal ka BP was related to widespread agricultural activities in the Lake Peipsi catchment. These results suggest that human activities can disrupt the relationship between the primary producer community and temperature in large, shallow lakes.
  • 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.