Sedimentin eläinplanktonjäänteet järven ekologisen laadun ja trofiarakenteen ilmentäjinä

To protect and restore lake ecosystems under threats posed by the increasing human population, information on their ecological quality is needed. Lake sediments provide a data rich archive that allows identification of various biological components present prior to anthropogenic alterations as well as a constant record of changes. By providing a longer dimension of time than any ongoing monitoring programme, palaeolimnological methods can help in understanding natural variability and long-term ecological changes in lakes. As zooplankton have a central role in the lake food web, their remains can potentially provide versatile information on past trophic structure. However, various taphonomic processes operating in the lakes still raise questions concerning how subfossil assemblages reflect living communities. This thesis work aimed at improving the use of sedimentary zooplankton remains in the reconstruction of past zooplankton communities and the trophic structure in lakes. To quantify interspecific differences in the accumulation of remains, the subfossils of nine pelagic zooplankton taxa in annually laminated sediments were compared with monitoring results for live zooplankton in Lake Vesijärvi. This lake has a known history of eutrophication and recovery, which resulted from reduced external loading and effective fishing of plankti-benthivorous fish. The response of zooplankton assemblages to these known changes was resolved using annually laminated sediments. The generality of the responses observed in Lake Vesijärvi were further tested with a set of 31 lakes in Southern Finland, relating subfossils in surface sediments to contemporary water quality and fish density, as well as to lake morphometry. The results demonstrated differential preservation and retention of cladoceran species in the sediment. Daphnia, Diaphanosoma and Ceriodaphnia were clearly underrepresented in the sediment samples in comparison to well-preserved Bosmina species, Chydorus, Limnosida and Leptodora. For well-preserved species, the annual net accumulation rate was similar to or above the expected values, reflecting effective sediment focusing and accumulation in the deepest part of the lake. The decreased fish density and improved water quality led to subtle changes in zooplankton community composition. The abundance of Diaphanosoma and Limnosida increased after the reduction in fish density, while Ceriodaphnia and rotifers decreased. The most sensitive indicator of fish density was the mean size of Daphnia ephippia and Bosmina (E.) crassicornis ephippia and carapaces. The concentration of plant-associated species increased, reflecting expanding littoral vegetation along with increasing transparency. Several of the patterns observed in Lake Vesijärvi could also be found within the set of 31 lakes. According to this thesis work, the most useful cladoceran-based indices for nutrient status and planktivorous fish density in Finnish lakes were the relative abundances of certain pelagic taxa, and the mean size of Bosmina spp. carapaces, especially those of Bosmina (E.) cf. coregoni. The abundance of plant-associated species reflected the potential area for aquatic plants. Lake morphometry and sediment organic content, however, explained a relatively high proportion of the variance in the species data, and more studies are needed to quantify lake-specific differences in the accumulation and preservation of remains. Commonly occurring multicollinearity between environmental variables obstructs the cladoceran-based reconstruction of single environmental variables. As taphonomic factors and several direct and indirect structuring forces in lake ecosystems simultaneously affect zooplankton, the subfossil assemblages should be studied in a holistic way before making final conclusions about the trophic structure and the change in lake ecological quality.Järviekosysteemien suojelu, hoito ja kunnostus vaativat tietoa niiden ekologisesta tilasta. Järvien pohjasedimenttiin kerrostuu jatkuvasti jäänteitä järven eliöyhteisöstä, joiden avulla tarkastelu järven tilasta voidaan ulottaa paljon pidemmälle ajanjaksolle, kuin mitä vesinäytteisiin perustuvaa seurantaa on tehty. Eliöjäänteitä analysoimalla voidaan järven tilassa tapahtuneet pitkäaikaiset muutokset suhteuttaa järven luontaiseen tilaan. Eläinplankton on keskeinen osa järven eliöyhteisöä, ja erityisesti vesikirppujen jäänteet voivat antaa monipuolista tietoa järven ravintoverkon rakenteesta. Luotettavat sedimentin eliöjäänteisiin pohjautuvat päätelmät järven historiasta edellyttävät kuitenkin paitsi havaittujen muutosten ekologisen merkityksen ymmärtämistä, myös jäänteiden säilymiseen ja kerrostumiseen vaikuttavien tekijöiden tunnistamista. Väitöskirjatyössäni selvitin eläinplanktonjäänteiden käyttöä järvessä tapahtuneiden muutosten tulkinnassa, erityisesti eläinplanktonia saalistavan kalaston osalta. Selvitin lajien välisiä eroja jäänteiden kerrostumisessa ja säilymisessä Vesijärven Enonselällä vertaamalla vuosilustoisen sedimentin vesikirppujäänteitä yläpuolisen veden eläinplanktonseurannan tuloksiin. Pahoin rehevöityneen Enonselän tila parani 1990-luvulla kuormituksen vähentämisen ja tehokalastuksen seurauksena. Väitöskirjassani selvitin, kuinka nämä tunnetut muutokset Vesijärven tilassa ja kalastossa näkyivät sedimenttiin kerrostuneissa eläinplanktonjäänteissä. Tulosten yleistettävyyttä ja eläinplanktonjäänteiden soveltuvuutta järven ekologisen tilan arviointiin selvitin edelleen 31 eteläsuomalaisella järvellä, joissa vertasin pintasedimentin eläinplanktonjäänteitä järven ravinnepitoisuuksiin, kalastoon ja järven morfometriaan. Tulokset osoittivat, että Daphnia, Diaphanosoma ja Ceriodaphnia -lajien jäänteet olivat sedimenttinäytteissä selvästi aliedustettuina verrattuna hyvin säilyviin Bosmina, Chydorus, Limnosida ja Leptodora -lajeihin. Hyvin säilyvillä lajeilla jäänteiden nettokertymä syvännesedimentissä oli sama tai ylitti eläinplanktonin seurantanäytteisiin perustuvan odotusarvon, mikä kertoi jäänteiden tehokkaasta kerääntymisestä järven syvimpään osaan. Eläinplanktonia syövien kalojen vähentäminen ja veden laadun paraneminen näkyivät lajikoostumuksen suhteellisina muutoksina. Diaphanosoma ja Limnosida lajit runsastuivat ja Ceriodaphnia ja rataseläimet vähenivät. Herkimmin kalastomuutosta osoittivat Daphnia ja Bosmina (E.) crassicornis -vesikirppujen lepomunien tai kuorten keskikoko. Vesikasveja suosivien lajien määrä kasvoi veden kirkastuessa, heijastaen uposkasvien levittäytymistä syvemmälle. Pintasedimenttiaineisto 31 järvestä vahvisti, että pelagiaalisten lajien yhteisökoostumus, kasveja suosivien lajien runsaus, sekä Bosmina -lajien kuoren keskikoko ovat käyttökelpoisia indeksejä arvioitaessa järven ekologista tilaa eteläsuomalaisissa järvissä. Järven morfometria ja sedimentin orgaanisen aineen määrä selittivät kuitenkin huomattavan osan lajiston vaihtelusta, ja ympäristötekijöiden väliset voimakkaat riippuvuussuhteet vaikeuttivat eläinplanktonjäänteisiin perustuvan ennustemallin kehittämistä yksittäiselle ympäristötekijälle. Koska järviekosysteemissä eläinplanktoniin vaikuttavat yhtä aikaa useat suorat ja epäsuorat tekijät, ja jäänteisiin lisäksi niiden sedimentaatioon liittyvät seikat, edellyttää sedimenttiaineistojen tulkinta kokonaisvaltaista tarkastelua

Development of phytoplankton of Lake Vesijarvi during recovery from eutrophication

Wastewaters discharged to Lake Vesijarvi ruined its recreational value and demanded mitigation measures. In the mid-1970s, the diversion of wastewaters elsewhere reduced epilimnetic total phosphorus concentration by similar to 40% from > 100 mg P m(-3) in 5 years, but this was not enough to eliminate cyanobacterial blooms. In 1979-1984, hypolimnetic oxygenation was applied to decrease internal nutrient loading, but pumping warm surface water to the hypolimnion probably intensified gas ebullition from the sediment, carrying nutrients to the epilimnion and intensifying cyanobacterial blooms. Intensive fish removal in 1989-1994 was more successful. Five years of summer trawling removed over three-quarters of roach and smelt stock, and after the two most intensive fishing years, TP and chlorophyll concentrations abruptly decreased by similar to 35%. During subsequent years fish removal continued at similar to 30% intensity and maintained chlorophyll and total nutrient concentrations at a lower level until the end of the study. At the same time, the frequency of cyanobacterial blooms decreased from annual to twice per decade. Larger-scale oxygenation after 2010 no longer resulted in ebullition, and its effect on phytoplankton was indistinguishable from natural variability. Consequently, it was abandoned. The intensity of fish removal needed to maintain the present status of the lake is still awaiting evaluation.Peer reviewe

Avoin ympäristötieto – yhteistyön kehittäminen vesistöjen seurannassa. Järvien vedenlaatupalvelu -hankkeen loppuraportti

Julkisten tietovarantojen mahdollisimman tehokkaan käytön on katsottu tuottavan uutta tietoa ja palveluita sekä lisäävän hyvinvointia. Kerätyn ympäristötiedon heikko hyödyntäminen yritystoiminnassa on kuitenkin jo pitkään tiedossa ollut ongelma. Syitä tähän voi etsiä ympäristötiedon epäkaupallisesta luonteesta, sen keräämistavoista ja saatavuudesta tai esimerkiksi julkisen sektorin vahvasta roolista toimialalla. Järvien vedenlaatupalvelu -hankkeessa (Tekes, 2009-2012) haluttiin edistää julkisen tiedon hyödyntämistä yksityisellä sektorilla sekä kehittää yhteistyötä eri toimijoiden välillä. Lähtökohtana oli paikallisen tutkimusinfrastruktuurin kehittäminen niin, että eri lähteistä kerätty vedenlaadun mittaustieto olisi tietokannan kautta helposti yritysten käytettävissä. Lisäksi hankkeessa tutkittiin eri käyttäjien tarpeita vedenlaatutiedolle, kehitettiin menetelmiä tiedon tarkkuuden parantamiseksi sekä luotiin muun muassa lyhyen aikavälin ennustemalleja. Konkreettinen tulos oli myös uuden “jokamiehen” vedenlaadun mittalaitteen kehittäminen. Tämä esimerkiksi matkapuhelimen kameran käyttöön perustuva mittalaite tuo uusia mahdollisuuksia edullisen vedenlaatutiedon keräämiseen, kansalaishavainnointiin ja samalla myös erilaiseen liiketoimintaan. Julkiseen ympäristötietoon perustuvaa liiketoimintaa pohdittiin kahdessa työpajassa. Työpajoissa keskusteltiin siihen liittyvistä haasteista ja mahdollisuuksista sekä myös ideoitiin uusia julkiseen ympäristötietoon perustuvia liiketoimintamahdollisuuksia. Tässä julkaisussa pohditaan julkisen ja yksityisen sektorin yhteistyön mahdollisuuksia Järvien vedenlaatupalvelu -hankkeen tulosten pohjalta

Effect of Temperature on the Size of Sedimentary Remains of Littoral Chydorids

The body size of aquatic invertebrates is, to a great extent, dependent on ambient temperature, but size distributions are also determined by other factors like food supply and predation. The effect of temperature on organisms is formulated in the temperature–size hypothesis, which predicts a smaller body size with increasing temperature. In this study, the effect of temperature on the subfossil remains of three littoral Cladocera (Alona affnis, A. quadrangularis, and Chydorus cf. sphaericus) was investigated. Exoskeletal remains of these species can be found in large numbers in lacustrine sediments and over a wide north–south range in Europe. The total length of both headshield and postabdomen for A. affinis and A. quadrangularis and carapace length for C. cf. sphaericus were measured to observe their response to changes in latitude and temperature. A different response to ambient temperature in the growth of body parts was observed. The size of the headshields of both Alona species and of the carapace of Chydorus was significantly larger in colder regions as opposed to warm ones. It turned out that the postabdomen was not a good predictor of ambient temperature. While the sizes of all remains increased with latitude, the sizes of the Alona remains was smaller in the mountain lakes of the Southern Carpathians than in other cold lakes, in this case in Finland, a fact indicative of the importance of other factors on size distribution. This study demonstrates that a morphological response to climate is present in littoral cladocerans, and, therefore, changes in the length of headshield and carapace may be used as a proxy for climate changes in paleolimnological records

Response of boreal lakes to episodic weather-induced events

Weather-induced episodic mixing events in lake ecosystems are often unpredictable, and their impacts are therefore poorly known. The impacts can be short-lived, including changes in water temperature and stratification, but long-lasting effects on the lake’s biology may also occur. In this study we used automated water quality monitoring (AWQM) data from 8 boreal lakes to examine how the episodic weather-induced mixing events influenced thermal structure, hypolimnetic dissolved oxygen (DO), fluorometric chlorophyll estimates (Chl-a), and lake metabolism and how these events varied in frequency and magnitude in lakes with different characteristics. Rise in wind speed alone had an effect on the lakes with the weakest thermal stability, but a decrease in air temperature together with strong wind induced mixing events in all lakes. The return period of these mixing events varied widely (from 20 to 92 d) and was dependent on the magnitude of change in weather. In lakes with strong stability, thermal structure and hypolimnetic DO concentration were only slightly affected. Weather-induced mixing in the upper water column diluted the surface water Chl-a repeatedly, whereas seasonal maximum occurred in late summer on each lake. Although Finnish lakes have been characterized with stable stratification during summer, we observed many substantial mixing events of relatively short return periods relevant to both chemical and biological properties of the lakes

Distribution patterns of epiphytic reed-associated macroinvertebrate communities across European shallow lakes

So far, research on plant-associated macroinvertebrates, even if conducted on a large number of water bodies, has mostly focused on a relatively small area, permitting limited conclusions to be drawn regarding potentially broader geographic effects, including climate. Some recent studies have shown that the composition of epiphytic communities may differ considerably among climatic zones. To assess this phenomenon, we studied macroinvertebrates associated with the common reed Phragmites australis (Cav.) Trin. ex Steud in 46 shallow lakes using a common protocol. The lakes, located in nine countries, covered almost the entire European latitudinal range (from <48°N to 61°N) and captured much of the variability in lake size and nutrient content in the region. A Poisson Generalized Linear Mixed Model (GLMM) showed the number of macroinvertebrate epiphytic taxa to be negatively associated with water conductivity and positively associated with medium ice cover duration (approximately 1 month). A Gamma GLMM showed a positive effect of chlorophyll a on the density of macroinvertebrates, and a significantly greater density in lakes located at the lowest and highest latitudes. Individual taxa responded differently to lake environmental conditions across climate zones. Chironomidae dominated in all climate zones, but their contribution to total density decreased with increasing latitude, with progressively greater proportions of Naidinae, Asellidae, Ephemeroptera and Trichoptera. Our study demonstrates that epiphytic macroinvertebrate fauna, even when analyzed at low taxonomic resolution, exhibits clear differences in diversity, relative abundance of individual taxa and total density, shaped both by geographic and anthropogenic variables. The results were discussed in the context of climate change. To our best knowledge this is the first study to examine epiphytic fauna carried out on a European scale

Distribution patterns of epiphytic reed-associated macroinvertebrate communities across European shallow lakes

So far, research on plant-associated macroinvertebrates, even if conducted on a large number of water bodies, has mostly focused on a relatively small geographical area, permitting limited conclusions to be drawn regarding potentially broader geographic effects, including climate. Some recent studies have shown that the composition of epiphytic communities may differ considerably among climatic zones. To assess this phenomenon, we studied macroinvertebrates associated with the common reed Phragmites australis (Cav.) Trin. ex Steud in 46 European shallow lakes using a common protocol. The lakes, located in nine countries, covered almost the entire European latitudinal range (from < 48°N to 61°N) and captured much of the variability in lake size and nutrient content in the region. A Poisson Generalised Linear Mixed Model (GLMM) showed the number of macroinvertebrate epiphytic taxa to be negatively associated with water conductivity and positively associated with medium ice cover duration (approximately 1 month). A Gamma GLMM showed a positive effect of chlorophyll a on the density of macroinvertebrates, and a significantly greater density in lakes located at the lowest and highest latitudes. Individual taxa responded differently to lake environmental conditions across climate zones. Chironomidae dominated in all climate zones, but their contribution to total density decreased with increasing latitude, with progressively greater proportions of Naidinae, Asellidae, Ephemeroptera and Trichoptera. Our study demonstrates that epiphytic macroinvertebrate fauna, even when analyzed at low taxonomic resolution, exhibits clear differences in diversity, relative abundance of individual taxa and total density, shaped both by geographic and anthropogenic variables. The results were discussed in the context of climate change. To our best knowledge this is the first study to examine epiphytic fauna carried out on a European scale