Lahustunud orgaaniline aine ja selle ökoloogiline tähtsus suurtes madalates veekogudes

About 90% of the organic matter in most aquatic systems is dissolved organic matter (DOM) and the rest forms the pool of particulate organic matter. DOM plays a significant role in the carbon and energy cycle of water bodies and as the main source of energy for microbial metabolism it can have a broad effect on food chains and on the proportions of auto- and heterotrophic processes. The role of DOM in ecological and biogeochemical processes depends on its source and composition. Autochthonous DOM (Au-DOM) is produced in the pelagic and littoral zones of the lake by phytoplankton and other photosynthetic organisms and it consists mainly of non-humic substances. Allochthonous DOM (Al-DOM) is transported from the catchment area, primarily originates from vascular plants and soil organic matter, and consists mainly of humic substances. The composition and sources of DOM in an aquatic ecosystem may vary spatially and temporally. In many lakes, especially within the cool boreal region, net ecosystem production is negative (lakes release carbon), suggesting that appreciable Al-DOM runoff from the catchments increases the respiration within the lake ecosystem to a level that exceeds photosynthetic carbon sequestration. Many studies have considered the origin and the variability of DOM in humic lakes or in rather deep water bodies with relatively clear water while the information from large, shallow and eutrophic water bodies is scarce and the present study aims to fill this gap. The thesis focuses on DOM in eutrophic large and shallow water bodies (coastal areas, large lakes) and the main aims of the study are to estimate: the range of temporal and spatial variability of DOM; the origin and the proportion of allochthonous and autochthonous DOM; the controlling factors of DOM variability and origin; the impact of CDOM on underwater light attenuation; the factors driving long term changes of underwater light field. The conclusions of the study were: the discharges from the main rivers were mainly responsible for CDOM spatial variability and its high values in the coastal/onshore areas in all studied large and shallow water bodies; CDOM values were highest in spring and lowest in autumn with most distinct seasonal pattern in onshore areas close to the river mouths. The impact of the riverine CDOM and share of Al-DOM in lakes and in the bay increased together with the ratio of the catchment area to the lake/bay volume; contrary to our prediction, in Lake Võrtsjärv Au-DOM had lower δ13C values than Al-DOM. This is a consequence of low δ13C values of DIC, phytoplankton and other seston in this lake; with increasing water level the proportion of Al-DOM and the heterotrophy of the ecosystem of Võrtsjärv increased; with increasing water temperature the proportion of Au-DOM increased and the autotrophy of the ecosystem enhanced; according to the DOM δ13C values, the average proportion of Al-DOM in Võrtsjärv was 68% during the active growing season (May-September) and 81% in October- April. The high share of Al-DOM indicates the strong influence of catchment processes and rapid degradation of Au-DOM in the lake ecosystem; the main factor controlling the light attenuation in the Pärnu Bay was CDOM, which overshadowed the impact of organic/inorganic particles. The latter played the main role in Peipsi and Võrtsjärv; the reconstructed time series of diffuse attenuation coefficient (Kd,PAR), based on regressions with optically active substances, enabled the reconstruction of long-term time series of primary production, euphotic depth (z1%) and the mean light intensity in the mixed layer (Emix), which corresponded to the eutrophication history and changes in water levels of studied water bodies; Emix values below the critical threshold showed that in Peipsi phytoplankton was likely light limited in autumn and in Võrtsjärv throughout the year.Umbes 90% veeökosüsteemide orgaanilisest ainest on lahustunud orgaaniline aine (DOM) ja ülejäänu moodustab partikulaarne orgaaniline aine. DOM mängib olulist rolli veekogude süsiniku- ja energiaringes. Olles mikroobse ainevahetuse peamine energiaallikas, on DOM-il suur mõju veekogu toiduahelatele ning auto- ja heterotroofsete protsesside osakaalule. DOM-i roll ökoloogilistes ja biogeokeemilistes protsessides sõltub tema päritolust ja koostisest. Autohtoonset DOM-i (Au-DOM) toodavad veekogude litoraalses ja pelaagilises osas fütoplankton ja muud fotosünteesivad organismid ning see koosneb peamiselt mittehumiinainetest. Allohtoonne DOM (Al-DOM) transporditakse veekokku valgalalt ning ta pärineb peamiselt soontaimedest ja mulla orgaanilisest osast, koosnedes enamjaolt humiinainetest. DOM-i koosseis ja päritolu võivad ühe veekogu piires erineda nii ruumiliselt kui ka ajaliselt. Paljudes järvedes, eriti jahedates boreaalsete piirkondade järvedes on ökosüsteemi koguproduktsioon negatiivne (järved vabastavad süsinikku), kuna Al-DOM-i sissevool valgalalt suurendab järvesisest hingamist sedavõrd, et see ületab süsiniku sidumise fotosünteesi käigus. Paljud uuringud on käsitlenud DOM-i päritolu ja varieeruvust humiinsetes või suhteliselt selgeveelistes ja sügavamates veekogudes, kuid teave suurte madalate eutrofeerunud veekogude kohta on puudulik ja käesolev doktoritöö püüab seda lünka täita. Doktoritöö keskendubki DOM-i uurimisele suurtes madalates eutroofsetes veekogudes, sh hindab: DOM-i ruumilist ja ajalist varieeruvust; DOM-i päritolu; allohtoonse ja autohtoonse DOM-i osakaalusid; millised tegurid mõjutavad DOM-i varieeruvust ja päritolu; CDOM-i mõju valguse nõrgenemisele vees ning millised tegurid mõjutavad veealuse valgusvälja pikaajalisi muutusi. Töö tulemusena leiti: peamiste sissevoolude vooluhulgad mõjutasid enim CDOM-i ruumilist varieeruvust järvedes ja lahes ning põhjustasid CDOM-i kõrgemaid väärtusi ranniku- ning kaldalähedastes piirkondades; CDOM-i väärtused järvedes ja lahes olid kõrgeimad kevadel ja madalaimad sügisel ning taoline muster joonistus eriti selgelt välja kalda- ja rannikulähedastes piirkondades, mis olid sissevoolude lähedal; jõgedest pärineva CDOM-i mõju ning allohtoonse DOM-i osakaal tõusis valgala pindala ja veekogu ruumala suhte suurenemisel; vastupidiselt eeldatule olid Võrtsjärves autohtoonse DOM-i δ13C-väärtused madalamad kui allohtoonsel DOM-il, mis oli tingitud lahustunud anorgaanilise süsiniku (DIC), fütoplanktoni ja muu sestoni madalates δ13C väärtustest järves; kõrgema veetasemega kaasnes Võrtsjärves allohtoonse DOM-i osakaalu suurenemine ja ökosüsteemi muutumine heterotroofsemaks; veetemperatuuri tõusuga suurenes autohtoonse DOM-i osakaal ning ökosüsteem muutus autotroofsemaks; DOM-i δ13C-väärtuste alusel oli allohtoonse DOM-i keskmine osakaal Võrtsjärves vegetatsiooniperioodil (mai-september) 68% ning oktoobrist aprillini 81%; Allohtoonse DOM-i suur osakaal järves näitab valgalaprotsesside tugevat mõju ning autohtoonse DOM-i intensiivset kasutamist järve ökosüsteemis; CDOM oli peamine tegur, mis mõjutas valguse nõrgenemist Pärnu lahes, varjutades orgaaniliste ja anorgaaniliste osakeste mõju , mis omakorda oli oluline Peipsis ja Võrtsjärves; valguse difuusse nõrgenemise koefitsiendi (Kd,PAR) aegread, mis arvutati regressioonidest optiliselt aktiivsete ainetega, võimaldasid taastada primaarproduktsiooni, eufootilise sügavuse (z1%) ning järvevee segunenud kihi keskmise valgustatuse (Emix) aegread, mis muutusid kooskõlas uuritavate veekogude eutrofeerumise ajaloo ning veetaseme muutustega; Emix-väärtused, mis jäid alla fütoplanktonile vajalikku kriitilist piiri, näitasid, et valgus oli fütoplanktoni kasvu limiteerivaks teguriks Peipsi järves sügisel ning Võrtsjärves kogu aasta vältel

Changes in phytoplankton communities along a north–south gradient in the Baltic Sea between 1990 and 2008

Evaluation of changes in Baltic Sea phytoplankton communities has been hampered by a lack of quantitative long-term data. We investigated changes in biomass of summer (June–September) phytoplankton over the last two decades (1990–2008) along a north–south gradient in the Baltic Sea. The areas were characterized by different temperature, salinity and nutrient conditions. Thirty taxonomic groups were selected for the statistical analysis. Increases in total phytoplankton, particularly cyanobacterial, biomass were observed in the Gulfs of Bothnia and Finland. In these two areas over the study period cyanobacteria also became abundant earlier in the season, and in the Curonian Lagoon Planktothrix agardhii replaced Aphanizomenon flos-aquae as the most abundant cyanobacterium. In general, water temperature was the most influential factor affecting the summer phytoplankton communities. Our data suggest that temperature increases resulting from climate change are likely to cause basin-specific changes in the phytoplankton communities, which in turn may affect overall ecosystem functioning in the Baltic Sea

Report on the checklist for maintaining contact with individuals taking family breaks

The report compiles a checklist that will help to maintain contacts with the individuals taking family breaks and for employees returning to regular working conditions afterwards. Binding procedures will be recommended to guarantee a successful career continuation with continuous institutional support

Optical investigations of CDOM-rich coastal waters in Pärnu Bay

Pärnu Bay in the Eastern Baltic Sea was chosen for studying the spatial-temporal variability of water parameters as an optically complex and semi-enclosed coastal area. The water properties of Pärnu Bay are influenced by the town of Pärnu with its 70 000 inhabitants and by the high inflow from the Pärnu River. The in situ database was collected during the ice-free period of 2006–2007 (11 sampling stations, 10 series of field trips). According to the results, the main factor influencing the light attenuation in the water was coloured dissolved organic matter (CDOM) which overshadows the relationships between the radiation characteristics and organic/inorganic particles. In April and May, when the freshwater discharge of the Pärnu River was highest, the values of aCDOM(380) were between 4.6 and 31.8 m–1, while in September they varied only within 2.52–10.2 m–1. The concentrations of chlorophyll a (including its metabolite phaeophytin a) generally ranged from 4 to 12 mg m–3 but during algal blooms they rapidly increased to 31.8 mg m–3. The temporal and spatial irregularity of suspended matter concentrations was caused by the loading of unpacked peat at the Pärnu River mouth as well as by undulation and ship traffic in Pärnu Bay. MODIS level 1 data with 250 m resolution were used for illustrative comparison of spatial and temporal variations in the water properties in Pärnu Bay and the Gulf of Riga. An attempt to perform the quantitative analysis with the purpose of estimating the concentrations of different optically significant substances separately gave statistically incorrect results

Mapping Water Quality Parameters with Sentinel-3 Ocean and Land Colour Instrument imagery in the Baltic Sea

The launch of Ocean and Land Colour Instrument (OLCI) on board Sentinel-3A in 2016 is the beginning of a new era in long time, continuous, high frequency water quality monitoring of coastal waters. Therefore, there is a strong need to validate the OLCI products to be sure that the technical capabilities provided will be used in the best possible way in water quality monitoring and research. The Baltic Sea is an optically complex waterbody where many ocean colour products, performing well in other waterbodies, fail. We tested the performance of standard Case-2 Regional/Coast Colour (C2RCC) processing chain in retrieving water reflectance, inherent optical properties (IOPs), and water quality parameters such as chlorophyll a, total suspended matter (TSM) and coloured dissolved organic matter (CDOM) in the Baltic Sea. The reflectance spectra produced by the C2RCC are realistic in both shape and magnitude. However, the IOPs, and consequently the water quality parameters estimated by the C2RCC, did not have correlation with in situ data. On the other hand, some tested empirical remote sensing algorithms performed well in retrieving chlorophyll a, TSM, CDOM and Secchi depth from the reflectance produced by the C2RCC. This suggests that the atmospheric correction part of the processor performs relatively well while IOP retrieval part of the neural network needs extensive training with actual IOP data before it can produce reasonable estimates for the Baltic Sea

Changes in phytoplankton communities along a north-south gradient in the Baltic Sea between 1990 and 2008

Evaluation of changes in Baltic Sea phytoplankton communities has been hampered by a lack of quantitative long-term data. We investigated changes in biomass of summer (June–September) phytoplankton over the last two decades (1990–2008) along a north–south gradient in the Baltic Sea. The areas were characterized by different temperature, salinity and nutrient conditions. Thirty taxonomic groups were selected for the statistical analysis. Increases in total phytoplankton, particularly cyanobacterial, biomass were observed in the Gulfs of Bothnia and Finland. In these two areas over the study period cyanobacteria also became abundant earlier in the season, and in the Curonian Lagoon Planktothrix agardhii replaced Aphanizomenon flos-aquae as the most abundant cyanobacterium. In general, water temperature was the most influential factor affecting the summer phytoplankton communities. Our data suggest that temperature increases resulting from climate change are likely to cause basin-specific changes in the phytoplankton communities, which in turn may affect overall ecosystem functioning in the Baltic Sea

First Experiences in Mapping Lake Water Quality Parameters with Sentinel-2 MSI Imagery

The importance of lakes and reservoirs leads to the high need for monitoring lake water quality both at local and global scales. The aim of the study was to test suitability of Sentinel-2 Multispectral Imager’s (MSI) data for mapping different lake water quality parameters. In situ data of chlorophyll a (Chl a), water color, colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) from nine small and two large lakes were compared with band ratio algorithms derived from Sentinel-2 Level-1C and atmospherically corrected (Sen2cor) Level-2A images. The height of the 705 nm peak was used for estimating Chl a. The suitability of the commonly used green to red band ratio was tested for estimating the CDOM, DOC and water color. Concurrent reflectance measurements were not available. Therefore, we were not able to validate the performance of Sen2cor atmospheric correction available in the Sentinel-2 Toolbox. The shape and magnitude of water reflectance were consistent with our field measurements from previous years. However, the atmospheric correction reduced the correlation between the band ratio algorithms and water quality parameters indicating the need in better atmospheric correction. We were able to show that there is good correlation between band ratio algorithms calculated from Sentinel-2 MSI data and lake water parameters like Chl a (R2 = 0.83), CDOM (R2 = 0.72) and DOC (R2 = 0.92) concentrations as well as water color (R2 = 0.52). The in situ dataset was limited in number, but covered a reasonably wide range of optical water properties. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for lake monitoring and research, especially taking into account that the data will be available routinely for many years, the imagery will be frequent, and free of charge