Sirvi Autor "Freiberg, Rene" järgi
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Kirje Abrupt rise in the contribution of CH₄-derived carbon to benthic secondary production of a shallow hemiboreal/boreal lake(Wiley, 2018) Belle, Simon; Tõnno, Ilmar; Stivrins, Normunds; Freiberg, Rene; Veski, Siim; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life SciencesUnderstanding long-term carbon flows through aquatic food webs is essential to assess impact of climatic and environmental changes on lake ecosystems. We reconstructed temporal changes in carbon sources fuelling chironomid biomass in a small and shallow hemiboreal/boreal lake over the last 11 000 years. Results were compared with temporal dynamics of known potential controlling factors: summer air temperature, human activities, phytoplankton assemblages and organic matter composition. We report an abrupt rise in the contribution of methane-derived carbon to chironomid biomass. However, this sudden increase was not the consequence of drastic changes in the composition of sedimentary organic matter, mean air temperature, lake trophic state or human activities in the catchment area. Our results suggest that shallowing of the lake caused by sedimentary infilling processes was a possible driver of the expansion of anoxic zones, enhancing CH 4 cycling in lake sediments. However, complementary studies are needed to better understand the mechanisms by which lake shallowing could affect carbon flows to aquatic consumers, and then better assess the natural dynamics of past carbon processing in the benthic food web of shallow lakes.Kirje Boosting the monitoring of phytoplankton in optically complex coastal waters by combining pigment-based chemotaxonomy and in situ radiometry(Elsevier, 2019) Tamm, Marju; Ligi, Martin; Panksep, Kristel; Teeveer, Karolin; Freiberg, Rene; Laas, Peeter; Paavel, Birgot; Kutser, Tiit; Reinart, Anu; Tõnno, Ilmar; Nõges, Tiina; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental SciencesResearch about the occurrence and extent of the cyanobacterial blooms in the Baltic Sea is critical due to their increased magnitude and frequency. Monitoring of the blooms is complicated due to their spatially and tem- porally heterogeneous nature. For adequate assessment of the water quality, phytoplankton dynamics needs to be tracked in large areas with high monitoring frequency. The main objectives of this study were (1) to describe phytoplankton community composition by pigment-based chemotaxonomy and validate the results with mi- croscopy; (2) to improve the retrieval of information about phytoplankton community by combining remote sensing with laboratory based approaches (3) to develop a region-specific algorithm to calculate cyanobacteria biomass from reflectance spectra; (4) to detect and quantify potentially toxic bloom-forming cyanobacteria with molecular methods. In our study the reflectance-based chlorophyll a (Chl a) values overestimated the High- performance Liquid Chromatography (HPLC) values although the correlations with HPLC Chl a measurements were very strong (rp ∼ 0.8, p < 0.001). We found that 709 nm/620 nm reflectance ratio correlated strongly (rp = 0.75, p < 0.01) to cyanobacteria wet biomass in CDOM-rich Väinameri even at low cyanobacterial bio- mass levels. Correlations between pigment-based chemotaxonomy and microscopy were significant in case of cyanobacteria (rp = 0.73, p < 0.01), cryptophytes (rp = 0.71, p < 0.05) and dinoflagellates (rp = 0.64, p < 0.05).Kirje Both climate trends and short-term fluctuations affected algae–zooplankton interactions in a boreal lake during the late Holocene(Wiley, 2021) Belle, Simon; Tõnno, Ilmar; Vrede, Tobias; Freiberg, Rene; Nilsson, Jenny L.; Goedkoop, Willem1. Most studies aiming to explore the response of algae and zooplankton trophic interactions to climate variability have only been focused on unidirectional and very shortterm trends in temperature changes. As a result, the non-stationary aspect of climate change (warming and cooling periods, frequencies) remains completely unstudied. 2. We studied elemental and stable isotope composition of sedimentary organic matter, photosynthetic pigments, and carbon stable isotope composition of Cladocera resting eggs in a sediment record covering the last c. 2,600 years. We examined how past climate change acting at different timescales affected algal biomass and community composition, and carbon assimilation by zooplankton in a boreal lake. 3. Our study revealed major effects of both long-term climate trends and shorter term fluctuations on algae–zooplankton interactions in a boreal lake. We found the main climate trends, in particular the Little Ice Age, induced algal biomass and community composition changes and drastic changes in carbon assimilation by zooplankton. Interestingly, we found that temperature fluctuations could also contribute to regulating algae–zooplankton interactions. Specifically, we observed drastic changes in sedimentary markers and stable isotope composition of zooplankton remains during the most recent period, suggesting a strong influence of ongoing anthropogenic change on algae–zooplankton interactions. 4. Our study confirms previous findings showing close long-term linkage between the temporal dynamics of zooplankton diet and planktonic algae, and that both climate trends and short-term fluctuations are key in regulating consumer– resource trophic interactions. 5. Novel approaches that combine high temporal resolution paleolimnological reconstructions and contemporary monitoring studies are needed to better understand climate change effects on algae–zooplankton interactions and lake food webs.Kirje Climate-induced changes in carbon flows across the plant-consumer interface in a small subarctic lake(Nature, 2019) Belle, Simon; Nilsson, Jenny L.; Tõnno, Ilmar; Freiberg, Rene; Vrede, Tobias; Goedkoop, Willem; Centre for Limnology. Institute of Agricultural and Environmental SciencesReconstructions of past food web dynamics are necessary for better understanding long-term impacts of climate change on subarctic lakes. We studied elemental and stable isotopic composition of sedimentary organic matter, photosynthetic pigments and carbon stable isotopic composition of Daphnia (cladocera; crustacea) resting eggs (δ13cclado) in a sediment record from a small subarctic lake. We examined how regional climate and landscape changes over the last 5800 years affected the relative importance of allochthonous and autochthonous carbon transfer to zooplankton. Overall, δ13cclado values were well in line with the range of theoretical values of aquatic primary producers, confirming that zooplankton consumers in subarctic lakes, even in the long-term perspective, are mainly fuelled by autochthonous primary production. Results also revealed greater incorporations of benthic algae into zooplankton biomass in periods that had a warmer and drier climate and clearer water, whereas a colder and wetter climate and lower water transparency induced higher contributions of planktonic algae to Daphnia biomass. This study thus emphasizes long-term influence of terrestrial-aquatic linkages and in- lake processes on the functioning of subarctic lake food webs.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 SciencesThe 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.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 FisheryUnderstanding 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.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 SciencesWe 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.Kirje How phytoplankton pigments reflect historical and contempoarary status of large shallow lakes?(Eesti Maaülikool, 2012) Freiberg, Rene; Tuvikene, Arvo (advisor); Tõnno, Ilmar (advisor)Phytoplankton is the most important primary producer in the aquatic ecosystems and account for half of all photosynthetic activity on earth, thus creating the base for most aquatic food chains. It also plays key role in the oxygen- carbon dioxide balance of the atmosphere and helping to ameliorate green-house gases, by removing nearly a third of the anthropogenic carbon released to the atmosphere. In Europe, the EU has implemented the Water Framework Directive, which is focused on assessing water quality in all waterbodies spanning from ground water to coastal marine waters. The directive requires that undisturbed or reference conditions should be defined for these aquatic environments. Monitoring records rarely go back more than a few decades and in order to define reference conditions other approaches are needed. Phytoplankton pigments that capture and transform light energy are important source of historical information, because if buried in sediments they preserve for centuries and can give information about algal communities in the past. As opposed to deep lakes, the use of phytoplankton pigments in palaeolimnological studies is complicated, because constant resuspension of sediments disturbs the formation of clear sediment archives. This dissertation is focused on phytoplankton pigment analysis of two interconnected large shallow lakes Võrtsjärv and Peipsi. The first issue that is covered is how the pigments in the upper sediment layer of the lake Võrtsjärv follow the annual dynamics of phytoplankton pigments in the water column. Thereafter eutrophication history and palaeolimnological aspects of these two lakes on the 20th century are compared in a multi-proxy studies. As a result of contemporary pigment flux and multi-proxy palaeolimnological studies of lakes Peipsi and Võrtsjärv we can conclude that according to fossil pigments and other palaeoindicators three periods in the evolution of lakes Peipsi and Võrtsjärv can be distinguished on the 20th century: from 1900 to 1950s, from 1950s to 1990s and from 1990s to 2000. Palaeoindicators show that eutrophication of both lakes started to increase rapidly in 1950s. This is also supported by the monitoring data that is available. Although some palaeoindicators peaked in 1970s no significant recovery to more natural state was observed. Results do show, that phytoplankton pigments can be used in multi-proxy palaeolimnological studies to track changes in phytoplankton communities and work out reference conditions even in large shallow lakes.Kirje The immediate response of freshwater autotrophic picoplankton to increased nitrogen loading differs among climate warming scenarios - a mesocosms experiment : [poster](Estonian University of Life Sciences, 2023) Seller, Siim; Lauringson, Velda; Tamm, Marju; Freiberg, Rene; Nõges, TiinaPhotoautotrophic picoplankton (PPP) being the smallest phytoplankton fraction, ranging from 0,2 to 2 μm. Picoplankton dominate oceans and oligotrophic waters, consisting anywhere between 50% to 90% of the whole phytoplankton abundance in those conditions [1]. Because of climate change and eutrophication, picoplankton importance in lakes may also increase. For that, mesocosms provide an excellent opportunity to test PPP reaction at different temperatures and nutrient levels.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 ScienceWe 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.Kirje Parallel assessment of marine autotrophic picoplankton using flow cytometry and chemotaxonomy(Elsevier, 2018) Tamm, Marju; Laas, Peeter; Freiberg, Rene; Nõges, Peeter; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental SciencesAutotrophic picoplankton (0.2–2 μm) can be a significant contributor to primary production and hence play an important role in carbon flow. The phytoplankton community structure in the Baltic Sea is very region specific and the understanding of the composition and dynamics of pico-size phytoplankton is generally poor. The main objective of this study was to determine the contribution of picoeukaryotic algae and their taxonomic com- position in late summer phytoplankton community of the West-Estonian Archipelago Sea. We found that about 20% of total chlorophyll a (Chl a) in this area belongs to autotrophic picoplankton. With increasing total Chl a, the Chl a of autotrophic picoplankton increased while its contribution in total Chl a decreased. Picoeukaryotes play an important role in the coastal area of the Baltic Sea where they constituted around 50% of the total autotrophic picoplankton biomass. The most abundant groups of picoeukaryotic algae were cryptophytes (16%), chlorophytes (13%) and diatoms (9%). Picocyanobacteria were clearly dominated by phycoerythrin containing Synechococcus. The parallel use of different assessment methods (CHEMTAX and flow cytometry) revealed the share of eukaryotic and prokaryotic part of autotrophic picoplankton.Kirje Towards understanding the abundance of non-pollen palynomorphs : A comparison of fossil algae, algal pigments and sedaDNA from temperate lake sediments(Elsevier, 2018) Stivrins, Normunds; Soininen, Janne; Tõnno, Ilmar; Freiberg, Rene; Veski, Siim; Kisand, Veljo; Centre for Limnology. Institute of Agricultural and Environmental SciencesGiven the increased interest in non-pollen palynomorphs (microscopic objects other than pollen identified from pollen slides) in palaeoecological studies, it is necessary to seek a deeper understanding of the reliability of these results. We combined quantitative information of algal pigments and sedimentary ancient DNA (sedaDNA) of phylotaxonomical resolution to validate the richness and abundance of fossil algae in the sediment of a small temperate lake. For the first time, fossil and sedaDNA algae data were combined in a composite data-set and used to reconstruct algae turnover rates over the last 14,500 years. This comparison serves as both an example of howfossil algae can be used to answer various research questions and as a method of revealing towhat extent we can rely on palaeoecological interpretations based solely on the fossil algae record from pollen slides.