Browsing by Subject "limnologia"

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  • Järnefelt, H.; Valle, K. J.; Kontkanen, P.; Tiensuu, L.; Kanervo, E.; Ekman, E,; Suomalainen, E.; Wirtamo, Sirkka (Vanamo, 1934)
    Annales Societatis zoologicae-botanicae Fennicae Vanamo; 14
  • Kenttämies, Kaarle (Vesihallitus. National Board of Waters, 1980)
    Vesientutkimuslaitoksen julkaisuja 39, 13-30
    Tekojärvien ominaisuuksista Suomessa
  • Frisk, Tom (National Board of Waters and the Environment. Vesi- ja ympäristöhallitus, 1989)
    Publications of the Water and Environment Research Institute 5
    Yhteenveto: Järvien ainetasemallien kehittäminen.
  • 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.
  • Seppälä, Jukka (Helsingin yliopisto, 2009)
    To obtain data on phytoplankton dynamics with improved spatial and temporal resolution, and at reduced cost, traditional phytoplankton monitoring methods have been supplemented with optical approaches. In this thesis, I have explored various fluorescence-based techniques for detection of phytoplankton abundance, taxonomy and physiology in the Baltic Sea. In algal cultures used in this thesis, the availability of nitrogen and light conditions caused changes in pigmentation, and consequently in light absorption and fluorescence properties of cells. In the Baltic Sea, physical environmental factors (e.g. mixing depth, irradiance and temperature) and related seasonal succession in the phytoplankton community explained a large part of the seasonal variability in the magnitude and shape of Chlorophyll a (Chla)-specific absorption. The variability in Chla-specific fluorescence was related to the abundance of cyanobacteria, the size structure of the phytoplankton community, and absorption characteristics of phytoplankton. Cyanobacteria show very low Chla-specific fluorescence. In the presence of eukaryotic species, Chla fluorescence describes poorly cyanobacteria. During cyanobacterial bloom in the Baltic Sea, phycocyanin fluorescence explained large part of the variability in Chla concentrations. Thus, both Chla and phycocyanin fluorescence were required to predict Chla concentration. Phycobilins are major light harvesting pigments for cyanobacteria. In the open Baltic Sea, small picoplanktonic cyanobacteria were the main source of phycoerythrin fluorescence and absorption signal. Large filamentous cyanobacteria, forming harmful blooms, were the main source of the phycocyanin fluorescence signal and typically their biomass and phycocyanin fluorescence were linearly related. Using phycocyanin fluorescence, dynamics of cyanobacterial blooms can be detected at high spatial and seasonal resolution not possible with other methods. Various taxonomic phytoplankton pigment groups can be separated by spectral fluorescence. I compared multivariate calibration methods for the retrieval of phytoplankton biomass in different taxonomic groups. Partial least squares regression method gave the closest predictions for all taxonomic groups, and the accuracy was adequate for phytoplankton bloom detection. Variable fluorescence has been proposed as a tool to study the physiological state of phytoplankton. My results from the Baltic Sea emphasize that variable fluorescence alone cannot be used to detect nutrient limitation of phytoplankton. However, when combined with experiments with active nutrient manipulation, and other nutrient limitation indices, variable fluorescence provided valuable information on the physiological responses of the phytoplankton community. This thesis found a severe limitation of a commercial fast repetition rate fluorometer, which couldn t detect the variable fluorescence of phycoerythrin-lacking cyanobacteria. For these species, the Photosystem II absorption of blue light is very low, and fluorometer excitation light did not saturate Photosystem II during a measurement. This thesis encourages the use of various in vivo fluorescence methods for the detection of bulk phytoplankton biomass, biomass of cyanobacteria, chemotaxonomy of phytoplankton community, and phytoplankton physiology. Fluorescence methods can support traditional phytoplankton monitoring by providing continuous measurements of phytoplankton, and thereby strengthen the understanding of the links between biological, chemical and physical processes in aquatic ecosystems.
  • Pilla, Rachel M.; Mette, Elizabeth M.; Williamson, Craig E.; Adamovich, Boris V.; Adrian, Rita; Anneville, Orlane; Balseiro, Esteban; Ban, Syuhei; Chandra, Sudeep; Colom-Montero, William; Devlin, Shawn P.; Dix, Margaret A.; Dokulil, Martin T.; Feldsine, Natalie A.; Feuchtmayr, Heidrun; Fogarty, Natalie K.; Gaiser, Evelyn E.; Girdner, Scott F.; González, María J.; Hambright, K. David; Hamilton, David P.; Havens, Karl; Hessen, Dag O.; Hetzenauer, Harald; Higgins, Scott N.; Huttula, Timo H.; Huuskonen, Hannu; Isles, Peter D. F.; Joehnk, Klaus D.; Keller, Wendel Bill; Klug, Jen; Knoll, Lesley B.; Korhonen, Johanna; Korovchinsky, Nikolai M.; Köster, Oliver; Kraemer, Benjamin M.; Leavitt, Peter R.; Leoni, Barbara; Lepori, Fabio; Lepskaya, Ekaterina V.; Lottig, Noah R.; Luger, Martin S.; Maberly, Stephen C.; MacIntyre, Sally; McBride, Chris; McIntyre, Peter; Melles, Stephanie J.; Modenutti, Beatriz; Müller-Navarra, Dörthe C.; Pacholski, Laura; Paterson, Andrew M.; Pierson, Don C.; Pislegina, Helen V.; Plisnier, Pierre-Denis; Richardson, David C.; Rimmer, Alon; Rogora, Michela; Rogozin, Denis Y.; Rusak, James A.; Rusanovskaya, Olga O.; Sadro, Steve; Salmaso, Nico; Saros, Jasmine E.; Sarvala, Jouko; Saulnier-Talbot, Émilie; Schindler, Daniel E.; Shimaraeva, Svetlana V.; Silow, Eugene A.; Sitoki, Lewis M.; Sommaruga, Ruben; Straile, Dietmar; Strock, Kristin E.; Swain, Hilary; Tallant, Jason M.; Thiery, Wim; Timofeyev, Maxim A.; Tolomeev, Alexander P.; Tominaga, Koji; Vanni, Michael J.; Verburg, Piet; Vinebrooke, Rolf D.; Wanzenböck, Josef; Weathers, Kathleen; Weyhenmeyer, Gesa A.; Zadereev, Egor S.; Zhukova, Tatyana V. (Nature, 2021)
    Scientific Data 8 (2021), 200
    Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.
  • Kivinen, Erkki; Laitakari, Erkki (Suomen metsätieteellinen seura, 1958)
  • Liljendahl-Nurminen, Anne (Helsingin yliopisto, 2006)
    In lake ecosystems, both fish and invertebrate predators have dramatic effects on their prey communities. Fish predation selects large cladocerans while invertebrate predators prefer prey of smaller size. Since invertebrate predators are the preferred food items for fish, their occurrence at high densities is often connected with the absence or low number of fish. It is generally believed that invertebrate predators can play a significant role only if the density of planktivorous fish is low. However, in eutrophic clay-turbid Lake Hiidenvesi (southern Finland), a dense population of predatory Chaoborus flavicans larvae coexists with an abundant fish population. The population covers the stratifying area of the lake and attains a maximum population density of 23000 ind. m-2. This thesis aims to clarify the effects of Chaoborus flavicans on the zooplankton community and the environmental factors facilitating the coexistence of fish and invertebrate predators. In the stratifying area of Lake Hiidenvesi, the seasonal succession of cladocerans was exceptional. The spring biomass peak of cladocerans was missing and the highest biomass occurred in midsummer. In early summer, the consumption rate by chaoborids clearly exceeded the production rate of cladocerans and each year the biomass peak of cladocerans coincided with the minimum chaoborid density. In contrast, consumption by fish was very low and each study year cladocerans attained maximum biomass simultaneously with the highest consumption by smelt (Osmerus eperlanus). The results indicated that Chaoborus flavicans was the main predator of cladocerans in the stratifying area of Lake Hiidenvesi. The clay turbidity strongly contributed to the coexistence of chaoborids and smelt at high densities. Turbidity exceeding 30 NTU combined with light intensity below 0.1 μE m-2 s-1provides an efficient daytime refuge for chaoborids, but turbidity alone is not an adequate refuge unless combined with low light intensity. In the non-stratifying shallow basins of Lake Hiidenvesi, light intensity exceeds this level during summer days at the bottom of the lake, preventing Chaoborus forming a dense population in the shallow parts of the lake. Chaoborus can be successful particularly in deep, clay-turbid lakes where they can remain high in the water column close to their epilimnetic prey. Suspended clay alters the trophic interactions by weakening the link between fish and Chaoborus, which in turn strengthens the effect of Chaoborus predation on crustacean zooplankton. Since food web management largely relies on manipulations of fish stocks and the cascading effects of such actions, the validity of the method in deep clay-turbid lakes may be questioned.
  • Heinonen, Pertti; Myllymaa, Urpo (Vesihallitus, 1974)
    Vesihallitus. Tiedotus 60
  • Myllymaa, Urpo; Ylitolonen, Anneli (1980)
    Vesihallitus. Tiedotus 191
  • Kuittinen, Salla (Helsingin yliopisto, 2021)
    Auringon säteilyn voimakkuus vaihtelee vuodenaikojen mukaan Suomessa. Tämän seurauksena järvien kerrostuneisuudessa tapahtuu muutoksia. Värriön luonnonpuistossa järvien tutkimus on ollut vähäistä, ja lämpötilaseurantaa ei aikaisemmin alueen järvissä ole tehty ympärivuotisesti. Aineiston avulla selvitettiin Kuutsjärven ja Tippakurulammen lämpötilan muutoksia, eroavaisuuksia, päivittäisiä muutoksia sekä lumen vaikutusta kevään lämpenemiseen tarkastelujakson aikana. Tutkimusaineisto on kerätty Värriön luonnonpuiston Kuutsjärvestä ( 67° 44'N ja 29° 36'E) sekä Tippakurulammesta (67° 46'N ja 29° 37'E) vuosina 2009–2012. Molemmissa järvissä oli yksi termistoriketju järven syvimmässä kohdassa. Termistoreita ketjussa oli viisi kappaletta. Tulosten tarkastelussa apuna käytettiin Ilmatieteen laitoksen sää- ja lumihavaintoja. Auringon säteilyn voimakkuus on merkittävin Kuutsjärven ja Tippakurulammen lämpötiloihin vaikuttava tekijä. Päivittäisissä muutoksissa ei ole eroavaisuuksia järvien välillä. Tippakurulampi lämpenee tummempana ja matalampana järvenä pohjaa myöten kesän aikana. Kesän aikana sedimenttiin varastoitunut lämpö purkautuu talvella veteen. Kevään täyskierto on molemmissa järvissä lyhyt ja tapahtuu toukokuun loppupuolella. Syksyn täyskierto on Tippakurulammessa Kuutsjärveä pidempi, ja Tippakurulampi jäähtyy sekoittuneessa tilassa. Eroavaisuudet järvien välillä johtuvat koko- ja värieroista.
  • Nyroos, Hannele (Vesihallitus, 1973)
    Vesihallitus. Tiedotus 54
    English summary: The development of lake Lohjanjärvi and the factors affecting it
  • Raateoja, Mika (Merentutkimuslaitos, 2006)
    Phytoplankton ecology and productivity is one of the main branches of contemporary oceanographic research. Research groups in this branch have increasingly started to utilise bio-optical applications. My main research objective was to critically investigate the advantages and deficiencies of the fast repetition rate (FRR) fluorometry for studies of productivity of phytoplankton, and the responses of phytoplankton towards varying environmental stress. Second, I aimed to clarify the applicability of the FRR system to the optical environment of the Baltic Sea. The FRR system offers a highly dynamic tool for studies of phytoplankton photophysiology and productivity both in the field and in a controlled environment. The FRR metrics obtain high-frequency in situ determinations of the light-acclimative and photosynthetic parameters of intact phytoplankton communities. The measurement protocol is relatively easy to use without phases requiring analytical determinations. The most notable application of the FRR system lies in its potential for making primary productivity (PP) estimations. However, the realisation of this scheme is not straightforward. The FRR-PP, based on the photosynthetic electron flow (PEF) rate, are linearly related to the photosynthetic gas exchange (fixation of 14C) PP only in environments where the photosynthesis is light-limited. If the light limitation is not present, as is usually the case in the near-surface layers of the water column, the two PP approaches will deviate. The prompt response of the PEF rate to the short-term variability in the natural light field makes the field comparisons between the PEF-PP and the 14C-PP difficult to interpret, because this variability is averaged out in the 14C-incubations. Furthermore, the FRR based PP models are tuned to closely follow the vertical pattern of the underwater irradiance. Due to the photoacclimational plasticity of phytoplankton, this easily leads to overestimates of water column PP, if precautionary measures are not taken. Natural phytoplankton is subject to broad-waveband light. Active non-spectral bio-optical instruments, like the FRR fluorometer, emit light in a relatively narrow waveband, which by its nature does not represent the in situ light field. Thus, the spectrally-dependent parameters provided by the FRR system need to be spectrally scaled to the natural light field of the Baltic Sea. In general, the requirement of spectral scaling in the water bodies under terrestrial impact concerns all light-adaptive parameters provided by any active non-spectral bio-optical technique. The FRR system can be adopted to studies of all phytoplankton that possess efficient light harvesting in the waveband matching the bluish FRR excitation. Although these taxa cover the large bulk of all the phytoplankton taxa, one exception with a pronounced ecological significance is found in the Baltic Sea. The FRR system cannot be used to monitor the photophysiology of the cyanobacterial taxa harvesting light in the yellow-red waveband. These taxa include the ecologically-significant bloom-forming cyanobacterial taxa in the Baltic Sea.
  • Lepistö, Liisa (National Board of waters and the Environment. Vesi- ja ympäristöhallitus, 1995)
    Publications of the Water and Environment Research Institute. 19
    Tiivistelmä: Kasviplanktonin kehitys vuosina 1968-1990 subarktisessa Lokan tekoaltaassa
  • Kyröläinen, Helena (Vesihallitus, 1978)
    Vesihallitus. Tiedotus 139
  • Vuorenmaa, Jussi (Helsingin yliopisto, 2007)
    The present work provides a regional-scale assessment of the changes in acidifying deposition in Finland over the past 30 years and the current pattern in the recovery of acid-sensitive lakes from acidification in relation to changes in sulphate deposition. This information is needed for documenting the ecosystem benefits of costly emission reduction policies and further actions in air pollution policy. The development of sulphate deposition in Finland reflects that of European SO2 emissions. Before the 1990s, reductions in sulphur emissions in Europe had been relatively small and sulphate deposition showed no consistent trends. Due to emission reduction measures that were then taken, sulphate deposition started to clearly decline from the late 1980s. The bulk deposition of sulphate has declined 40-60% in most parts of the country during 1990-2003. The decline in sulphate deposition exceeded the decline of base cation deposition, which resulted in a decrease in acidity and acidifying potential of deposition over the 1990s. Nitrogen deposition also decreased since the late 1980s, but less than that of sulphate, and levelling off during the 1990s. Sulphate concentrations in all types of small lakes throughout Finland have declined from the early 1990s. The relative decrease in lake sulphate concentrations (average 40-50%) during 1990-2003 was rather similar to the decline in sulphate deposition, indicating a direct response to the reduction in deposition. There are presently no indications of elevated nitrate concentrations in forested headwater lakes. Base cation concentrations are still declining in many lakes, especially in south Finland, but to a lesser extent than sulphate allowing buffering capacity (alkalinity) to increase, being significant in 60% of the study lakes. Chemical recovery is resulting in biological recovery with populations of acid-sensitive fish species increasing. The recovery has been strongest in lakes in which sulphate has been the major acidifying agent, and recovery has been the strongest and most consistent in lakes in south Finland. The recovery of lakes in central Finland and north Finland is not as widespread and strong as observed in south. Many catchments, particularly in central Finland, have a high proportion of peatlands and therefore high TOC concentrations in lakes, and runoff-induced surges of organic acids have been an important confounding factor suppressing the recovery of pH and alkalinity in these lakes. Chemical recovery is progressing even in the most acidified lakes, but the buffering capacity of many lakes is still low and still sensitive to acidic input. Further reduction in sulphur emissions are needed for the alkalinity to increase in the acidified lakes. Increasing total organic carbon (TOC) concentrations are indicated in small forest lakes in Finland. The trends appear to be related to decreasing sulphate deposition and improved acid-base status of the soil, and the rise in TOC is integral to recovery from acidification. A new challenge is climate change with potential trends in temperature, precipitation and runoff, which are expected to affect future chemical and biological recovery from acidification. The potential impact on the mobilization and leaching of organic acids may become particularly important in Finnish conditions. Long-term environmental monitoring has evidently shown the success of international emission abatement strategies. The importance and value of integrated monitoring approach including physical, chemical and biological variables is clearly indicated, and continuous environmental monitoring is needed as a scientific basis for further actions in air pollution policy.
  • Niemistö, Juha (Helsingin yliopisto, 2008)
    Sediment resuspension, the return of the bottom material into the water column, is an important process that can have various effects on a lake ecosystem. Resuspension caused by wind-induced wave disturbance, currents, turbulent fluctuations and bioturbation affects water quality characteristics such as turbidity, light conditions, and concentrations of suspended solids (SS) and nutrients. Resuspension-mediated increase in turbidity may favour the dominance of phytoplankton over macrophytes. The predator-prey interactions contributing to the trophic state of a lake may also be influenced by increasing turbidity. Directly, the trophic state of a lake can be influenced by the effect of sediment resuspension on nutrient cycling. Resuspension enhances especially the cycling of phosphorus by bringing the sedimentary nutrients back into the water column and may thereby induce switches between phosphorus and nitrogen limitation. The contribution of sediment resuspension to gross sedimentation, turbidity, and concentration of SS and nutrients was studied in a small, deep lake as well as in a multibasin lake with deep and shallow areas. The effect of ice cover on sediment resuspension and thereby on phosphorus concentrations was also studied. The rates of gross sedimentation and resuspen¬sion were estimated with sediment traps and the associations between SS and nutrients were considered. Sediment resuspension, caused by wind activity, comprised most of the gross sedimenta¬tion and strongly contributed to the concentration of SS and turbidity in the lakes studied. Additionally, via the influence on SS, resuspension affected the concentration of total phosphorus (TP) and soluble reactive phosphorus (SRP), as well as the total nitrogen to total phosphorus (TN:TP) ratio. Although contrasting results concerning the dependence between the SS and SRP concentrations were observed, it could be concluded that sediment resuspension during strong algal blooms (pH > 9) led to aerobic release of P. The main findings of this thesis were that in the course of the growing season, sediment resuspension coupled with phytoplankton succession led to liberation of P from resuspended particles, which in turn resulted in high TP concentrations and low TN:TP ratios. This development was likely a cause of strong cyanobacterial blooms in midsummer.
  • Lehikoinen, Annukka (2006)
    Työssä tutkittiin Suomenlahdella uuden tulokaslajin, valekirjosimpukan (Mytilopsis leucophaeata Condrad) soveltuvuutta indikaattorilajiksi radioekologisiin tutkimuksiin ja ydinvoimalaitoksen ympäristötarkkailuun. Samassa yhteydessä tehtiin kartoitusta lajin levinneisyydestä ja kannan tilasta Loviisan ydinvoimalaitoksen jäähdytysvesien vaikutusalueella ja sen ulkopuolella. Työhön sisältyi myös vaihtoehtoisten aineistonkeruumenetelmien testausta lajin populaatiokartoitusten ja indikaattorilajitutkimusten tarpeisiin. Valekirjosimpukkanäytteitä kerättiin sukeltamalla ja keinotekoisilla alustoilla. Näytteistä tehtiin gammaspektrometriset- ja strontiumanalyysit radionuklidikoostumuksen ja aktiivisuuspitoisuuksien selvittämiseksi. Havaituille radionuklideille laskettiin rikastumiskertoimet. Tuloksia verrattiin Säteilyturvakeskuksen (STUK) ydinvoimaloiden ympäristötarkkailuohjelman tuloksiin eri trofiatasojen indikaattorilajeista. Olkiluodosta Tarkastelussa oli mukana kaksi muuta simpukkalajia, sinisimpukka (Mytilus edulis L.) ja itämerensimpukka (Macoma baltica L.). Valekirjosimpukka ei radionuklidien rikastajana vaikuttaisi poikkeavan merkittävästi muista tutkituista simpukkalajeista. Juveniilien ja aikuisten välillä ei havaittu suuria eroja näytteistä löytyneiden radionuklidien tai niiden rikastumisen suhteen. Simpukat eivät rikastaneet 137Cs:ia erityisen tehokkaasti. Valekirjosimpukka osoittautui kuitenkin kohtalaisen hyväksi 90Sr:n kerääjäksi. Näytteistä löydettiin myös pieniä määriä täysin voimalaitosperäisiä 60Co:ia ja 110Ag:aa. Radionuklidien rikastumiseen valekirjosimpukoissa vaikuttivat vuodenaika ja etäisyys voimalaitoksen jäädytysvesien purkupaikasta. Elinvoimainen valekirjosimpukkapopulaatio on tällä hetkellä keskittynyt ydinvoimalan jäähdytysvesien läheisyyteen. Planktiset toukkavaiheet leviävät virtauksien mukana jopa 20 km:n päähän voimalasta ja asettuneita poikasia havaitaan loppukesällä ainakin Pernajanlahdella asti. Poikaset selviävät ilmeisesti varsin heikosti talvesta normaaleissa itäisen Suomenlahden veden lämpötiloissa.
  • Laaksonen, Reino; Malin, Väinö (Vesihallitus. National Board of Waters, 1980)
    Vesientutkimuslaitoksen julkaisuja 36
    Changes in water quality in Finnish lakes and rivers 1962-1977