Browsing by Subject "murtovesi"

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  • Bergström, Irina (Finnish Environment Institute, 2011)
    Monographs of the Boreal Environment Research 38
    The carbon dioxide (CO2) and methane (CH4) fluxes from aquatic sediments have recently received considerable interest because of the role of these gases in enhancing climate warming. CO2 is the main end product of aerobic respiration and CH4 is produced in large amounts under anaerobic conditions. Shallow, vegetated sediments are an important source of both gases. CH4 may be transported via rhizomes and aerenchymal tissues of aquatic plants from the sediment to the atmosphere, thus avoiding oxidation in the aerated sediment surface and water column. Temperature is known to be a key factor affecting benthic CO2 and CH4 flux rates, but the interplay between other factors that may affect the fluxes from sediments is still poorly known. In order to study the spatial and temporal variability of carbon gas fluxes in boreal aquatic sediments, the area-based CO2 production rates in lake and brackish water sediments and CH4 emissions in vegetated lake littorals were measured in this work. The effects of temperature, sediment quality, plant species, zoobenthos and seasonal variation on flux rates were also estimated. The range of CO2 production rates measured in the field was 0.1–12.0 mg C m–2 h–1 and that of CH4 emission rates 0–14.3 mg C m–2 h–1. When incubated at elevated temperatures (up to 30 °C) in the laboratory, the CO2 production rates increased up to 70 mg C m–2 h–1. Temperature explained 70–94% of the temporal variation in the CO2 production in lake sites and 51% in a brackish water site. In the lake mesocosm, temperature explained 50–90% of the variation of CH4 emission. By contrast, CH4 oxidation rate was not dependent on temperature. The CH4 fluxes through the plants of six emergent and floating-leaved plant species were studied in the field (temperature range 20.4–24.9 °C). Stands of the emergent macrophyte Phragmites australis emitted the largest amounts of CH4 (mean emission 13.9 ± 4.0 (SD) mg C m-2 h–1), the mean emission rate being correlated with mean net primary production (NPP) and mean solar radiation. In the stands of floating-leaved Nuphar lutea the mean CH4 efflux (0.5 ± 0.1 (SD) mg C m–2 h–1) was negatively correlated with mean fetch and positively with percentage cover of leaves on the water surface. On a regional level, stands of the emergents P. australis and Equisetum fluviatile emitted 32% more CH4 than natural open peatland during the growing season, although their areal coverage in the study region was only 41% of that of peatland area. Climate warming will presumably increase the carbon gas emission from vegetated littorals. The model-based estimated increase of CO2 production rate in June was 29% and for CH4 emissions as much as 65% for the time interval of 110 years from 1961–1990 to 2071–2100. The results indicate that carbon gas fluxes from aquatic sediments, especially from vegetated littorals, are significant at the landscape level. They are linked to temperature but also to several other interacting factors such as e.g. water and bottom quality and ecosystem composition. Detailed investigation of the overall links between the causes and effects is urgently needed in order to understand and predict the changes caused by warming climate.
  • Lehtoranta, Jouni (Finnish Environment Institute, 2003)
    Monographs of the Boreal Environment Research 24
    One of the main threats facing the Baltic Sea is eutrophication due to an excess supply of nutrients. In the Gulf of Finland, primary productivity and biomasses of autotrophic and heterotrophic organisms are among the highest in the Baltic. The high biomasses are attributed mainly to the eutrophying effects of the large land-derived nutrient inflow from St. Petersburg and via the River Neva. The role of sediment phosphorus (P) in eutrophication is, however, poorly understood in the Gulf. The aim of this study was to obtain information on the regional levels of sediment P and to specify the pools of P. Efforts were also made to define the sediment retention ability of P along the estuarine gradient, to establish the factors that affect the benthic fl ux of P and to assess whether sulphur (S) is a significant factor in sediment P cycling. On the basis of the results it was possible to quantify and consider the ecological implications of the benthic flux of P.The sediments of the Gulf are rich in organic matter, nitrogen (N) and P. A large portion of the mobile pool of P in these sediments consists of iron (Fe)-bound P, which is released when Fe(III) oxides are reduced under anoxic conditions. The increase in the sediment organic matter concentration along the estuarine gradient seems to impair the sediments’ ability to retain P. The highest benthic P efflux was measured in summer and the lowest in winter. The decrease in the near-bottom oxygen concentration in summer may favour anaerobic sulphate reduction followed by iron sulphide (FeS) formation close to the sediment- water interface. In the sediment, the key role in preventing P from entering the water is played by the binding ability of P related to diffusing Fe. In the brackish Baltic Sea, in contrast to most lake systems, the diffusion of Fe may be inactivated by FeS formation. Thus, high effluxes of P to oxic water were measured on bottoms where black sediment indicating the presence of FeS extended to the surface of the sediment.The P released from the sediments of the Gulf itself may largely explain the high P concentrations and low N:P ratios in near-bottom waters in summer and, after autumn mixing, in the entire water column. However, the input of P from the main Baltic basin may also lead to an increase in P concentrations in the Gulf. The high release rates of P measured – rather than denitrification – largely explain the N limitation of the primary production. A relationship seems to exist between the increase in near-bottom salinity and the weakening of the sediment oxidation state of the Gulf since 1996. The inflow of saline water to the Gulf strengthens density stratification, thus favouring the release of P to water. Therefore, the variations in hydrological factors may produce a marked between-year variation in the benthic P efflux and counteract the reduction in the external P load. The ability of sediment to retain P could most likely be promoted by decreasing the sedimentation of labile organic matter on the bottom. Organic matter sedimentation could be lowered by cutting the amount of bioavailable N and P from an anthropogenic sources.
  • Kurki, Outi (University of Helsinki, 1994)
  • Luotamo, Ilkka (University of Helsinki, 1971)
  • Koli, Lauri A. (University of Helsinki, 1953)
  • Myrberg, Kai; Kuosa, Harri; Leppäranta, Matti (Yliopistopaino, 2006)
    Palmenia-sarja ; 17
    Itämeren fysiikka, tila ja tulevaisuus on ensimmäinen Itämeren fysiikan oppikirja, jossa tuodaan esille myös fysiikan kytkennät Itämeren tilaan ja ekologiaan. Alalta on olemassa runsaasti eritasoista tietoa. Tämä tieto on kuitenkin melko hajallaan, eikä kokonaisvaltaista kirjallisuutta ole vielä paljon. Kirja sisältää yksityiskohtaisen kuvauksen Itämeren altaista ja niiden topografiasta sekä hydrografiasta, Itämeren lämpötaloudesta ja kiertoliikkeestä sekä jääoloista. Lisäksi käydään läpi Itämeren kriittisiä prosesseja kuten suolapulssien esiintyminen, kumpuaminen ja vedenkorkeuden muutokset. Itämeren fysiikan ymmärtäminen on tärkeää, sillä se määrää ne ulkoiset olosuhteet, joissa meren kemialliset ja biologiset prosessit tapahtuvat. Meren fysikaalisten ominaisuuksien tuntemus luo perustan koko Itämeri-systeemin toiminnan ymmärtämiseen. Teoksen loppuosassa esitellään Itämeren pitkäaikaisia muutoksia ja tarkastellaan Itämeren tulevaisuutta erilaisten ilmastoskenaarioiden avulla.
  • Leskinen, Elina (University of Helsinki, 1984)
  • Salminen, Jani (Suomen ympäristökeskus, 2010)
    Suomen ympäristökeskuksen raportteja 3/2010
  • Ullvén, Johanna (University of Helsinki, 1992)