Kuidas fütoplanktoni pigmendid peegeldavad suurte madalate järvede ajaloolist ja tänapäevast seisundit?

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.Fütoplankton on tähtsaim orgaanilise aine esmastootja vee-keskkonnas ning hõlmab umbes pool Maal toimuvast fotosünteesist, pannes aluse enamikele vees olevatele toiduahelatele ning omades olulist rolli atmosfääris olevate kasvuhoonegaaside tasakaaluprotsessides. Euroopa Liidus jõustunud veepoliitika raamdirektiivi kohaselt tuleb kehtestada veekogude hea seisundi kriteeriumid. Loodusliku ja inimtekkelise eutrofeerumise eristamine on tihti võimalik vaid mitmekülgsete paleoökoloogiliste uuringutega, sest seireandmed ulatuvad enamasti vaid mõnede aastakümnete taha, kui veekogud olid juba tugeva inimmõju all. Vetikate valgusenergiat püüdvad ning edasikandvad pigmendid on olulised ajaloolise informatsiooni allikad, kuna säilivad settesse mattununa tuhandeid aastaid ning võimaldavad hinnata järvedes toimunud vetikate biomassi ja taksonite vahelisi muutusi. Erinevalt sügavatest järvedest, on pigmentide kasutamine suurte ja madalate järvede paleolimnoloogilistes uurimustes raskendatud, kuna selget ajaloolist settejälge segab vee intensiivse liikumise poolt põhjustatud setete resuspensioon. Käesoleva töö fookuses on suurtes ja madalates järvedes, Võrtsjärves ja Peipsi järves, toimuvate fütoplanktoni pigmentide voogude ning lähiajaloo uurimine mitmekülgsete paleolimnoloogiliste näitajate kaasabil. Esmalt selgitati Võrtsjärve veesamba ja sette ülemise kihi pigmendivoogude seaduspärasusi ning edasi rekonstrueeriti järvede eutrofeerumise ajalugu 20. sajandil kasutades selleks kromatograafiliselt mõõdetud fütoplanktoni üldist ohtrust näitavaid ja taksonispetsiifilisi pigmente ning teisi eutrofeerumist iseloomustavaid parameetreid, nagu sette poorivee lahustunud orgaanilise aine omadused, karbonaatide ja fosforisisaldus, ränivetikate ohtrus ja taksonoomiline koosseis. Töö tulemusena selgus, et fütoplanktoni pigmentide ja teiste paleoindikaatorite põhjal võib mõlema järve arengus eristada kolme ajaperioodi: 1900 kuni 1950-ndad, 1950-ndad kuni 1990-ndad ning sajandi viimane kümnend. Eutrofeerumine kiirenes mõlemas järves 1950-ndatel, mida toetab ka olemasolev seireandmestik. Kuigi mõned eutrofeerumise indikaatorid saavutasid oma maksimumi 1970-ndatel ei ole märkimisväärset järvede seisundi paranemist sajandi viimasel kümnendil näha. Ajaloolised muutused on paremini talletunud Peipsi järve settes, kuna Võrtsjärve madal veetase ning intensiivne vee liikumine segab settearhiivi moodustumist. Eestis esmakordselt on käesolevas töös kasutatud fütoplanktoni pigmente suurte madalate järvede paleolimnoloogilistes uurimustes ning näidatud nende kasutamisvõimalusi seisundi hindamise kriteeriumite väljatöötamisel

Dynamics of phytoplankton pigments in water and surface sediments of a large shallow lake

Our aim was to find out to which extent fossil phytoplankton pigments in the large shallow and turbid Lake Võrtsjärv carry information on the history of phytoplankton communities. For this purpose we examined how the changes in the pigment composition of surface sediments follow their changes in the water column. Depth-integrated lake water and surface sediment samples were collected weekly in May–October 2007. Considering cyanobacterial and diatom dominance in phytoplankton, we analysed fucoxanthin, diadinoxanthin and diatoxanthin as marker pigments for diatoms, zeaxanthin as a marker pigment for total cyanobacteria and canthaxanthin as a marker pigment for colonial cyanobacteria. Chlorophyll a and its derivative pheophytin a were applied as indicators for total phytoplankton. The dynamics of phytoplankton pigments in surface sediments generally did not follow their dynamics in the water column, possibly due to intensive resuspension and a high sedimentation rate in a large and shallow lake. It was noticed that the surface sediment carries information on pigment degradation intensity and on weight and size characteristics of phytoplankton cells, which affect their sinking and floating velocities. Higher pigment contents of sediment in spring were presumably caused by lower resuspension due to high water level and slower degradation in cold water. Pheophytin a and the marker pigments of cyanobacteria were found to be persistent against degradation in upper sediment layers, which makes them useful indicators for tracking the historical changes in phytoplankton communities also in a shallow lake. Sharp decrease in chemically unstable pigment contents between the sediment surface and deeper layers indicates that only the uppermost sediment surface is resuspended in Lake Võrtsjärv. The transformation of the diatom marker carotenoid diadinoxanthin to diatoxanthin was found to occur mainly in sediments and not in the water column, and the process is not induced by excess light

Towards understanding the abundance of non-pollen palynomorphs : A comparison of fossil algae, algal pigments and sedaDNA from temperate lake sediments

Given 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 how fossil algae can be used to answer various research questions and as a method of revealing to what extent we can rely on palaeoecological interpretations based solely on the fossil algae record from pollen slides. (C) 2017 Elsevier B.V. All rights reserved.Peer reviewe

Use of sedimentary algal pigment analyses to infer past lake-water total phosphorus concentrations

AbstractWe tested the feasibility of using sedimentary algal pigment analyses by spectral deconvolution to infer past lake-water total phosphorus concentrations. We established equations that link lake-water nutrient concentrations and sediment pigment concentrations, using a combination of calibration in both space and time, with a training set of 31 Swedish lakes. The calibration dataset yielded a significant positive relationship between total carotenoid concentrations and lake-water total phosphorus concentrations. We also compared sediment-pigment-based nutrient inferences with time series of water column monitoring data to evaluate whether temporal changes in total phosphorus concentrations are well captured by analysis of sedimentary pigments. We found that changes in pigment preservation through time can alter the relationship between concentrations of lake-water nutrients and sedimentary pigments, thus limiting the reliability of historical ecological conditions inferred from pigments in the sediment. Our data suggested that ratios of Chlorophyll derivatives to total carotenoids (CD/TC ratio) and Chlorophyll a to Chlorophyll derivatives (CPI) can be used as proxies for pigment preservation. Using our approach, inferred temporal changes in water-column total phosphorus concentrations in lakes are promising, but require further development, specifically with respect to the influence of pigment degradation in both the water column and sediments, as well as the factors that control such degradation.</jats:p

Both climate trends and short-term fluctuations affected algae-zooplankton interactions in a boreal lake during the late Holocene

Most studies aiming to explore the response of algae and zooplankton trophic interactions to climate variability have only been focused on unidirectional and very short-term trends in temperature changes. As a result, the non-stationary aspect of climate change (warming and cooling periods, frequencies) remains completely unstudied. 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. 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. 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. 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

Parallel assessment of marine autotrophic picoplankton using flow cytometry and chemotaxonomy

Autotrophic 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.We gratefully thank Dr. Tiit Kutser (Estonian Marine Institute, Uni- versity of Tartu) for organizing the cruises and helping with the sample collection and Karolin Teeveer for providing microscopy counts. This work was supported by Estonian Ministry of Education and Research (IUT 21-02); Estonian Science Foundation (ETF9102, ETF8576); Swiss Grant for Programme “Enhancing public environmental monitoring ca- pacities” and Estonian Doctoral School of Earth Sciences and Ecology. We are thankful for the two reviewers who provided excellent advice to improve this manscript.We gratefully thank Dr. Tiit Kutser (Estonian Marine Institute, Uni- versity of Tartu) for organizing the cruises and helping with the sample collection and Karolin Teeveer for providing microscopy counts. This work was supported by Estonian Ministry of Education and Research (IUT 21-02); Estonian Science Foundation (ETF9102, ETF8576); Swiss Grant for Programme “Enhancing public environmental monitoring ca- pacities” and Estonian Doctoral School of Earth Sciences and Ecology. We are thankful for the two reviewers who provided excellent advice to improve this manscript

Abrupt rise in the contribution of CH₄-derived carbon to benthic secondary production of a shallow hemiboreal/boreal lake

Understanding 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.Financial support was provided by institutional research grant IUT21-2, IUT1-8 from the Estonian Science Agency and by Estonian University of Life Sciences, project No. 8M160101PKLJ, and ‘Estophilus Grant’ from the Ministry of Culture of Estonia. We are grateful to Christian Hossann (INRA, Nancy, Champenoux) for assistance with the stable isotope analysis of carbon. The PTEF facility is supported by the French National Research Agency through the Laboratory of Excellence ARBRE (ANR-11-LABX-0002-01).Financial support was provided by institutional research grant IUT21-2, IUT1-8 from the Estonian Science Agency and by Estonian University of Life Sciences, project No. 8M160101PKLJ, and ‘Estophilus Grant’ from the Ministry of Culture of Estonia. We are grateful to Christian Hossann (INRA, Nancy, Champenoux) for assistance with the stable isotope analysis of carbon. The PTEF facility is supported by the French National Research Agency through the Laboratory of Excellence ARBRE (ANR-11-LABX-0002-01)

Climate-induced changes in carbon flows across the plant-consumer interface in a small subarctic lake

International audienceAbstract Reconstructions 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 (δ 13 C Clado ) 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, δ 13 C Clado 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

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

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 similar to 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 Svetinu over the post-glacial period (similar to 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 - 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. (C) 2021 The Authors. Published by Elsevier Ltd