6 research outputs found
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
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”
Recommended from our members
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