Pidevmõõtmised - uus lähenemine limnoloogias

A thesis for applying for the degree of Doctor of Philosophy in HydrobiologyUntil recently, time consuming and costly manual measurements have been predominating in lake research and monitoring. Usually, this kind of measurements do not provide sufficient temporal and spatial resolution if any. Using high-frequency measurements (HFM) enabling to study lakes at time scales not achievable by traditional methods, has boosted advancements in a number of fields in limnology. Sensor technologies developing towards higher sensitivity, reliability, and autonomy but with prices going down, makes them widely accessible. The main objective of this thesis was to elucidate the present worldwide use and future perspectives of high-frequency measurements in limnology and offer close insights into two fields of application – using HFM in modelling climate change impacts on thermal stratification of lakes and in describing type specific differences in lakes’ gas regime. The review of literature showed a fast expansion of HFM in lake research since the beginning of the 2000 with a tendency to move from single point measurements towards profiling buoys and sensor networks covering single or multiple lakes to increase spatial resolution. Water temperature modelling based on high-frequency weather data with further applying the model on long-term weather data showed that decreasing wind speeds in 1982-2015 have increased the frequency and duration of stratification events in Lake Võrtsjärv. The analysis of the gas regime in eight lakes of different type revealed trophic state as the main factor determining DO and CO2 distribution and dynamics in those lakes whereas lake morphometry, alkalinity and water colour had significant effects showing the existence of type specific differences in carbon cycling among lakes. Although automated measurements have become an important tool in limnology, they will never fully replace manual field measurements in which the experienced eye and intuition of the researcher have crucial roles.Veel seni kasutab enamus järveuuringuid traditsioonilisi, aga oma olemuselt ajamahukaid ja kulukaid mõõtmismeetodeid, mis tihti ei anna piisavat ettekujutust mõõdetud näitajate ruumilisest jaotusest ja ajalisest muutlikkusest. Suure arenguhüppe mitmes limnoloogilises uurimisvaldkonnas on kaasa toonud pidevmõõtmiste rakendamine, mis annab võimaluse uurida järvi sellistes ajaskaalades, mis traditsiooniliste meetoditega pole võimalikud. Sensortehnoloogiate töökindlus, täpsus ja autonoomsus on kiiresti tõusnud, hinnad aga langenud, mis muudab nad laialdaselt kättesaadavaks. Käesoleva töö peamiseks eesmärgiks on anda ülevaade pidevmõõtmiste praegustest kasutusvaldkondadest, eesmärkidest ja kasutuse ulatusest maailma järvedes ning hinnata võimalikke tulevikuväljavaateid. Elust võetud näidetena on töösse lisatud kaks uuringut, millest ühes kasutasime veetemperatuuri ja ilmastikunäitajate pidevmõõtmisi kliimamuutuse mõju modelleerimiseks järve termilisele kihistumisele ning teises analüüsisime järvede tüübiomaseid gaasirežiimi erinevusi. Kirjandusülevaade näitas pidevmõõtmiste ühe laiemat kasutamist järveuurimisel alates 2000. aastate algusest ja üleminekut üksiksensoritelt ja -sondidelt profileerivatele poidele ning mõõtmisvõrgustikele, mis tagavad andmete ruumilise lahutuse. Järve termilise kihistuse modelleerimine näitas, et perioodil 1982–2015 nõrgenenud tuulte tingimustes on Võrtsjärv suviti üha sagedamini hakanud kihistuma. Gaasirežiimi uuringud kaheksas Eesti eri tüüpi järves näitasid, et lahustunud hapniku ja süsihappegaasi jaotuse ja ööpäevase dünaamika määrab peamiselt järvede toitelisus, kuid olulised on ka järve mõõtmed, vee aluselisus ja värvus, mis viitab tüübiomastele funktsionaalsetele erinevustele järvede süsinikuringes. Hoolimata pidevmõõtmiste üha laialdasemast kasutamisest ei asenda need kunagi täielikult traditsioonilisi mõõtmisi, milles teadlase kogenud silmal ja kaemusel on tähtis roll, ja need kaks mõõtmisviisi jäävad teineteist täiendama.Publication of this thesis is supported by the Estonian University of Life Sciences. This research was supported by European Social Fund’s Doctoral Studies and Internationalisation Programme DoRa and by institutional research funding IUT 21-02, PUT777, ETF8729, ETF8486 of the Estonian Ministry of Education and Research

Kas maksunduslikud siduvad eelotsused võrduvad riigiabi andmisega?

Käesoleva magistritöö uurimisprobleemiks on maksumenetluses läbiviidav siduva eelotsuse andmise menetluse hindamine ebaseadusliku riigiabi andmise seisukohast. Käesolevas töös uuritakse kas ja mis määral maksunduslikud siduvad eelotsused täidavad riigiabi kriteeriume. Magistritöö laiem eesmärk on selgitada välja, et millise tähenduse omandab Euroopa Komisjoni tegevus maksunduslike eelotsustusmenetluste uurimisest riigiabi reeglite alusel piiratud pädevuste printsiibi seisukohast. Töö tulemusel on saanud autor uue teadmise komisjoni pädevuse nihkumise määratluste kohta, samuti riigiabi tähenduse laienemise kohta. Ühtlasi on andnud töö laiema teadmise EL institutsioonide pädevuse arengust. Töös püstitatud küsimusele, kas maksunduslikud siduvad eelotsused võrduvad riigiabiga, ühest vastust ei ole võimalik anda, kuid käesolevas töös analüüsitud kaasuste põhjal võib olla seisukohal, et komisjon on riigiabi menetlust Luksemburgi eelotsuste asjades küllaltki laialt tõlgendanud ning tegelikkuses riigiabi menetlus sellistesse raamidesse ei ole ette nähtud.http://www.ester.ee/record=b4578875*es

Summer greenhouse gas fluxes in different types of hemiboreal lakes

Lakes are considered important regulators of atmospheric greenhouse gases (GHG). We estimated late summer open water GHG fluxes in nine hemiboreal lakes in Estonia classified under different lake types according to the European Water Framework Directive (WFD). We also used the WFD typology to provide an improved estimate of the total GHG emission from all Estonian lakes with a gross surface area of 2204 km2 representing 45,227 km2 of hemiboreal landscapes (the territory of Estonia). The results demonstrate largely variable CO2 fluxes among the lake types with most active emissions from Alkalitrophic (Alk), Stratified Alkalitrophic (StratAlk), Dark Soft and with predominant binding in Coastal, Very Large, and Light Soft lakes. The CO2 fluxes correlated strongly with dissolved CO2 saturation (DCO2) values at the surface. Highest CH4 emissions were measured from the Coastal lake type, followed by Light Soft, StratAlk, and Alk types; Coastal, Light Soft, and StratAlk were emitting CH4 partly as bubbles. The only emitter of N2O was the Alk type. We measured weak binding of N2O in Dark Soft and Coastal lakes, while in all other studied lake types, the N2O fluxes were too small to be quantified. Diversely from the common viewpoint of lakes as net sources of both CO2 and CH4, it turns out from our results that at least in late summer, Estonian lakes are net sinks of both CO2 alone and the sum of CO2 and CH4. This is mainly caused by the predominant CO2 sink function of Lake Peipsi forming ¾ of the total lake area and showing negative net emissions even after considering the Global Warming Potential (GWP) of other GHGs. Still, by converting CH4 data into CO2 equivalents, the combined emission of all Estonian lakes (8 T C day−1 ) is turned strongly positive: 2720 T CO2 equivalents per day.This research was inspired by GLEON (Global Lake Ecological Observatory Network) and was funded by Estonian Research Council (PSG32, PUT1598, PSG10, PRG709, PRG1167 and ETF8486), the European Union H2020 WIDESPREAD (TREICLAKE 951963) and the Swiss Program “Enhancing public environmental monitoring capacities”.This research was inspired by GLEON (Global Lake Ecological Observatory Network) and was funded by Estonian Research Council (PSG32, PUT1598, PSG10, PRG709, PRG1167 and ETF8486), the European Union H2020 WIDESPREAD (TREICLAKE 951963) and the Swiss Program “Enhancing public environmental monitoring capacities”

Delving deeper: metabolic processes in the metalimnion of stratified lakes

Many lakes exhibit seasonal stratification, during which they develop strong thermal and chemical gradients. An expansion of depth-integrated monitoring programs has provided insight into the importance of organic carbon processing that occurs below the upper mixed layer. However, the chemical and physical drivers of metabolism and metabolic coupling remain unresolved, especially in the metalimnion. In this depth zone, sharp gradients in key resources such as light and temperature co-occur with dynamic physical conditions that influence metabolic processes directly and simultaneously hamper the accurate tracing of biological activity. We evaluated the drivers of metalimnetic metabolism and its associated uncertainty across 10 stratified lakes in Europe and North America. We hypothesized that the metalimnion would contribute highly to whole-lake functioning in clear oligotrophic lakes, and that metabolic rates would be highly variable in unstable polymictic lakes. Depth-integrated rates of gross primary production (GPP) and ecosystem respiration (ER) were modelled from diel dissolved oxygen curves using a Bayesian approach. Metabolic estimates were more uncertain below the epilimnion, but uncertainty was not consistently related to lake morphology or mixing regime. Metalimnetic rates exhibited high day-to-day variability in all trophic states, with the metalimnetic contribution to daily whole-lake GPP and ER ranging from 0% to 87% and<1% to 92%, respectively. Nonetheless, the metalimnion of low-nutrient lakes contributed strongly to whole-lake metabolism on average, driven by a col- linear combination of highlight, low surface-water phosphorous concentration and high metalimnetic volume. Consequently, a single-sensor approach does not necessarily reflect whole-ecosystem carbon dynamics in stratified lakes

Atmospheric stilling leads to prolonged thermal stratification in a large shallow polymictic lake

To quantify the effects of recent and potential future decreases in surface wind speeds on lake thermal stratification, we apply the one-dimensional process-based model MyLake to a large, shallow, polymictic lake, Võrtsjärv. The model is validated for a 3-year period and run separately for 28 years using long-term daily atmospheric forcing data from a nearby meteorological station. Model simulations show exceptionally good agreement with observed surface and bottom water temperatures during the 3-year period. Similarly, simulated surface water temperatures for 28 years show remarkably good agreement with long-term in situ water temperatures. Sensitivity analysis demonstrates that decreasing wind speeds has resulted in substantial changes in stratification dynamics since 1982, while increasing air temperatures during the same period had a negligible effect. Atmospheric stilling is a phenomenon observed globally, and in addition to recent increases in surface air temperature, needs to be considered when evaluating the influence of climate change on lake ecosystems

Phytoplankton as a component of particular organic matter in the inflows and outflow of Lake Võrtsjärv

Käesolev magistritöö põhineb aastatel 2008-2009 Võrtsjärve viie suurema sissevoolu (Tänassilma, Tarvastu, Õhne, Väike Emajõgi, Konguta) alamjooksult ja väljavoolu (Emajõgi) ülemjooksult kogutud materjalil. Töö eesmärk oli kirjeldada jõgedega Võrtsjärve kantavat ja järvest väljuvat fütoplanktonit, samuti analüüsida partikulaarse orgaanilise aine dünaamikat ning fütoplanktoni osakaalu selles dünaamikas. Töös kasutati minu enda poolt arvutatud ja analüüsitud fütoplanktoni tulemusi, Limnoloogiakeskuse töötajate poolt määratud hüdrokeemiliste analüüside tulemusi ning Eesti Meteoroloogia ja Hüdroloogia Instituudi andmebaase. Töö hinnangulised tulemused põhinevad programmi „Statistica 10“ mitteparameetrilistel andmeanalüüsidel. Töö tulemused kokkuvõtlikult: 1) Võrtsjärve sissevooludes oli fütoplanktoni funktsionaalsete gruppide arv suur ja aastati erinev. Sissevooludes domineerisid seisuveekogude väga erinevatele ökoniššidele (Y ja X2) või vooluveekogudele (D ja Tb) iseloomulikud grupid. Väljavoolus oli fütoplanktoni liigiline koosseis suhteliselt ühtlane, mis peegeldus funktsionaalsete gruppide väikeses ja stabiilses arvus nii erinevatel aastaaegadel kui erinevatel aastatel; domineerisid madalatele kihistumata toiteaineterikastele järvedele iseloomulikud grupid S1 ja MP. 2) Võrtsjärve väljavoolu fütoplanktoni biomass, samuti domineeriv grupp S1 olid positiivses seoses hüdroloogiliste ja hüdrofüüsikaliste näitajatega ning negatiivses seoses hüdrokeemiliste näitajatega (Nüld ja räni). Sissevoolude fütoplanktoni biomassil ja domineerivatel gruppidel (X2 ja Y) leiti seoseid keskkonnanäitajatega vähem: kõik kolm fütoplanktoni näitajat olid positiivselt seotud veetemperatuuriga ja negatiivselt seotud räni hulgaga. Üksikutel sissevooludel eraldi leiti seoseid fütoplanktoni ja keskkonnanäitajate vahel rohkem. 3) Võrtsjärve sissevooludes oli fütoplanktoni biomass, klorofülli sisaldus ja liigirikkus suure aastaajalise varieeruvusega, kuid üldiselt madalal tasemel. Võrtsjärve väljavoolus olid eelpoolnimetatud näitajad kõrgemad, eriti vegetatsiooniperioodi lõpuperioodil, mis peegeldas Võrtsjärve küllaltki suurt mõju väljavoolule. 4) Võrtsjärve sissevooludes ja väljavoolus tõusid partikulaarse orgaanilise süsiniku (POC) maksimaalsed kontsentratsioonid kuni 20 mg/L, kuid moodustasid kogu orgaanilisest süsinikust (TOC) ligikaudu 10%. Veidi kõrgemad POC väärtused esinesid sissevooludes, kus märgalade protsent valgalal oli suurem. Leiti statistiliselt usaldusvääne POC erinevus ühelt poolt sissevoolude ja teiselt poolt väljavoolu vahel, samuti POC erinevus kahe uurimisaasta vahel. 5) Võrtsjärve väljavoolus oli fütoplanktoni osakaal POC-s tunduvalt suurem kui sissevooludes. Kõrvutades fütoplanktoni süsinikusisalduse ja POC kontsentratsiooni sesoonseid dünaamikaid, leiti, et fütoplankton moodustab vegetatsiooniperioodil suurema ja enam-vähem kindla proportsiooni POC-st. Sügis-talvisel perioodil ja varakevadel vähenes POC-s fütoplanktoni osakaal, seega pidi sellel perioodil ülekaalus olema teistlaadi orgaanika (valgalalt leostunud osakesed, bakterid, taimede lagunenud osakesed).The present master’s thesis is based on the material collected in 2008-2009 from the lower course of five largest inflows (Tänassilma, Tarvastu, Õhne, Väike Emajõgi, Konguta) and from the upper course of the outflow (Emajõgi) of Lake Võrtsjärv. The aim of the study was to describe the phytoplankton carried into Lake Võrtsjärv by the rivers and the phytoplankton and the phytoplankton discharged from the lake, as well as to analyze the dynamics of particular organic matter and the share of phytoplankton in this dynamics. In the study use was made of the phytoplankton related results calculated and analyzed by myself, the results of hydrochemical analyzes performed by researchers of the Center for Limnology, and databases of the Estonian Meteorological and Hydrological Institute. The estimated results of the study are based on nonparametric data analysis using the program Statistica 10. Summarized results of the study: 1) In the inflows of Lake Võrtsjärv, the number of functional groups was large and varied in different years. In the inflows dominating were groups characteristic of very different ecological niches of standing water bodies (Y and X2), or typical of running water bodies (D and Tb). In the outflow, the species was reflected by the small and stable number of functional groups both in different seasons and different years; dominating were groups S1 and MP which are characteristics of shallow uncertified eutrophic lakes. 2) Phytoplankton biomass in the outflow of Lake Võrtsjärv, as well as the dominating group S1 correlated positively with hydrological and hydrophysical indicators and negatively with hydrochemical indicators (TN and Si). Less correlations were found of phytoplankton biomass and dominating groups in the inflows (X2 and Y) with environmental indicators: all three phytoplankton indicators were positively correlated with water temperature and negatively correlated with Si amount. Single inflows in isolation showed more correlations between phytoplankton and environmental indicators. 3) In the inflows of Lake Võrtsjärv, phytoplankton biomass, chlorophyll content and species richness showed high seasonal variation but were generally at a low level. In the outflow, Lake Võrtsjärv, the above indicators were higher, particularly towards the end of the growth period, which demonstrated a relatively high impact of the lake on the outflow. 4) In the inflows and in the outflow of Lake Võrtsjärv, maximum concentrations of particular organic carbon (POC) increased up to 20 mg/L, accounting for about 10% of total organic carbon (TOC). The concentrations of POC were somewhat higher in the inflows where the percentage of wetlands in the catchment area was higher. A significant difference in POC was found between the inflows and the outflow, as well as between the two study years. 5) In the outflow of Lake Võrtsjärv, the share of phytoplankton in POC was significantly larger than in the inflows. Comparison of the seasonal dynamics of carbon content in phytoplankton and POC concentration revealed that phytoplankton makes up a large and relatively stable share in POC in the growth period. As the share of phytoplankton in POC decreased in late autumn and early spring, there periods must have been dominated by different organic matter (particles leached from the catchment, bacteria, decayed plant particles)

Changes in particulate organic matter passing through a large shallow lowland lake

Different sources of particulate organic matter (POM) as well as its composition affect the biological food web and hence the self-purification potential and water quality of rivers. We studied the effect of a large shallow lake on the POM pool of the water passing through it. Over four years, we analysed monthly the amount and composition of POM and a set of environmental variables in the inflows and in the outflow of Lake Võrtsjärv (Estonia). In the inflows, the live pool of POM consisted of phytoplankton – small crypto-, dino-, and chlorophytes. The concentration of chlorophyll a (Chl a), as a proxy of phytoplankton biomass, was positively correlated with temperature and total phosphorus and negatively with dissolved silica, total nitrogen, and discharge. In the outflow, the share of the live component of POM was much larger than in the inflows but was also dominated by phytoplankton represented by grazing resistant filamentous cyanobacteria. Chl a was positively correlated with total phosphorus, temperature, pH, and precipitation, and negatively with dissolved silica, total nitrogen, and discharge in the outflow. The different amounts, composition, and seasonal dynamics of POM in the inflows and in the outflow have potentially substantial impacts on the food web with a predominating classical pathway in the inflows versus a detrital pathway in the outflow.This study was supported by the institutional research funding (IUT 21-2) of the Estonian Ministry of Education and Research and by the MARS project ‘Managing Aquatic Ecosystems and Water Resources under Multiple Stress’ funded under the 7th EU Framework Programme, Theme 6 ‘Environment including climate change’ (Contract No. 603378). We are grateful to Dr. Jonne Kotta and to the two anonymous reviewers for valuable comments on the manuscript. Mrs Ester Jaigma kindly revised the English text of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences.This study was supported by the institutional research funding (IUT 21-2) of the Estonian Ministry of Education and Research and by the MARS project ‘Managing Aquatic Ecosystems and Water Resources under Multiple Stress’ funded under the 7th EU Framework Programme, Theme 6 ‘Environment including climate change’ (Contract No. 603378). We are grateful to Dr. Jonne Kotta and to the two anonymous reviewers for valuable comments on the manuscript. Mrs Ester Jaigma kindly revised the English text of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences