Human and climate-induced changes in boreal varve characteristics and preservation

Recent variations in varve preservation and characteristics were recorded from Lakes Lehmilampi, Vesijärvi, Kallio-Kourujärvi, Kantele, Kuninkaisenlampi, and Linnanlampi to examine how varve formation, preservation, and characteristics respond to climate and anthropogenic actions. From each lake, long cores and freeze corer samples were recovered for varve, elemental, and diatom analysis. The cores were preserved with epoxy embedding to study varve properties, such as varve thickness and varve microfacies with stereomicroscope, petrographic microscope, and X-ray radiography analysis. In the sediments of Lakes Lehmilampi and Vesijärvi, diatom identification and counting were performed from diatom slides prepared using standard procedures. A diatom-total phosphorous transfer function was applied to reconstruct diatom-inferred total phosphorus for diatom samples. In addition to diatom analysis, μXRF analysis was performed on Lake Vesijärvi sediments. Statistical analyses were conducted on Lake Lehmilampi varve parameters and climate parameters to study the factors controlling variations in the extent of varve preservation. Biogenic lamina thicknesses of Lakes Lehmilampi, Kallio-Kourujärvi, Kantele, Kuninkaisenlampi, and Linnanlampi were compared to climate parameters to evaluate the response of biogenic lamina thicknesses to variations in climate. The results show that the spatial extent of varves and corresponding hypoxia volume varied during the last 200 years in Lake Lehmilampi. The variation seems to be sensitive especially to winter and March temperatures, autumn and October precipitation as well as November temperature and the number of days with snow cover. Varve and diatom analysis suggest that these variations are more likely related to climatic than anthropogenic forcing. The onset of varve preservation in Lake Vesijärvi occurred first at the deepest point of the Enonsaari Deep in the late 1930s due to cultural eutrophication and subsequently proceeded to shallower depths. Varve preservation weakened and varve characteristics changed as a result of rehabilitation actions. Lake aeration had the single most notable impact on varve preservation as it finally terminated it. Moreover, aeration-induced turbulence transformed the accumulation zone in the vicinity of the aerator into a transport or an erosional zone. Biogenic lamina thicknesses in Lakes Lehmilampi, Kallio-Kourujärvi, Kantele, Kuninkaisenlampi, and Linnanlampi were observed to respond to changes in climate during the last 100 years despite anthropogenic influence. Growing season temperature and open water season precipitation control biogenic lamina thickness, which is thus potential for climate reconstructions.Ihmistoiminnan ja ilmaston vaikutus boreaalisten vuosilustojen ominaisuuksiin ja säilymiseen Suomalaisten järvien pohjakerrostumien avulla selvitettiin, miten järvet reagoivat ilmaston ja ihmistoiminnan muutoksiin. Ilmaston ja ihmistoiminnan vaikutusta tutkittiin pohjakerrostumien vuosilustorakenteiden muodostumisen, säilymisen ja ominaisuuksien avulla. Tutkimuksen kohteena olivat Lehmilammen, Vesijärven, Kallio-Kourujärven, Kanteleen, Kuninkaisenlammen ja Linnanlammen pohjakerrostumat. Järvistä kairattiin sekä pitkiä kairanäytteitä että jääsorminäytteitä, joista tehtiin lusto-, alkuaine-, ja piileväanalyysejä. Näytteet imeytettiin epoksiin lustojen ominaisuuksien kuten lustonpaksuuden ja lustojen mikrorakenteiden tutkimusta varten. Näitä ominaisuuksia tutkittiin stereomikroskoopin, petrografisen mikroskoopin ja röntgenkuvien avulla. Lehmilammen ja Vesijärven pohjakerrostumista tunnistettiin piilevät standardimenettelytavan mukaan. Vesijärven pohjakerrostumista mitattiin lisäksi alkuainepitoisuuksia μXRF:llä. Piileväsiirtofunktiota käytettiin piilevien avulla laskettavan kokonaisfosforin laskemiseksi. Lehmilammen lustojen säilyvyyden spatiotemporaaliseen vaihteluun vaikuttavia ilmastoparametrejä tutkittiin tilastollisien menetelmien avulla. Lisäksi Lehmilammen, Kallio-Kourujärven, Kanteleen, Kuninkaisenlammen ja Linnanlammen lustojen biogeenisen lustonosan paksuuden vastetta ilmastoparametrien muutoksiin tutkittiin tilastollisesti. Tulosten perusteella Lehmilammen lustojen säilyvyyden laajuus ja laajuutta vastaava hapettomien vesien tilavuus ovat vaihdelleet viimeisten 200 vuoden aikana. Laajuuteen on vaikuttanut erityisesti talven ja maaliskuun lämpötila, syksyn ja lokakuun sadanta, sekä marraskuun lämpötila ja lumipeitteen kesto. Lusto- ja piileväanalyysit viittaavat siihen, että Lehmilammen lustojen säilyvyyden laajuus on ennemminkin riippuvainen ilmastosta kuin ihmistoiminnasta. Vesijärvessä lustojen säilyminen alkoi ihmistoiminnan seurauksena Enonsaaren syvänteen syvimmässä osassa 1930-luvun lopussa, ja eteni tämän jälkeen syvänteen matalampiin osiin. Kunnostustoimenpiteiden vaikutuksesta lustojen säilyminen heikentyi ja lustojen ominaisuudet muuttuivat. Järven hapettamisella oli suurin yksittäinen vaikutus lustojen säilymiseen, sillä se johti lustojen säilymisen loppumiseen. Hapettimesta aiheutunut turbulenssi muutti hapettimen läheisyydessä sijainneet kerrostumisalueet transportaatio- tai eroosioalueiksi, jolloin lustonmuodostus loppui. Lehmilammen, Kallio-Kourujärven, Kanteleen, Kuninkaisenlammen ja Linnanlammen biogeenisen lustonosan paksuus on ollut riippuvainen ilmastoparametrien muutoksista viimeisten sadan vuoden aikana huolimatta valuma-alueella tapahtuneesta ihmistoiminnasta. Kasvukauden lämpötila ja jäättömän kauden sateisuus ohjaavat biogeenisen lustonosan paksuutta, mikä mahdollistaa biogeenisen lustonosan paksuuden käytön ilmastorekonstruktioissa

Human actions were responsible for both initiation and termination of varve preservation in Lake Vesijärvi, southern Finland

The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselkä Basin, Lake Vesijärvi, southern Finland. For the last few decades, the Enonselkä Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijärvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation.</p

Impacts of a deep reactive layer on sedimentary phosphorus dynamics in a boreal lake recovering from eutrophication

Using biogeochemical analyses of sediments and porewaters, we investigate the legacy of a brief, intense period of eutrophication on sedimentary phosphorus (P) cycling in a boreal lake (Enonselka basin, Lake Vesijarvi, Finland). Point-source sewage inputs in the twentieth century caused deoxygenation of the lake and accelerated the focusing of iron (Fe) and manganese (Mn) oxides into deeper areas. Early diagenesis under Fe-Mn-rich conditions now favors rapid burial of P in these areas, likely as a combination of both oxide-bound P phases and authigenic manganous vivianite. A new P budget for Enonselka basin shows that P burial causes an annual drawdown of 1.2% (+/- 0.2%) of the surface sediment P inventory, supporting a long-term trend towards recovery since the construction of a wastewater treatment plant in the mid-1970s. However, remineralization of organic matter and associated dissolution of Fe-Mn oxides continues to regenerate P from a deep reactive layer (20-60 cm depth) deposited at the height of past eutrophication, leading to an upwards diffusive flux of dissolved phosphate towards the surface sediments. The magnitude of this flux is similar to that of external P loading to the lake. The combined incoming fluxes of P are likely to retard the complete recovery from eutrophication by decades, despite ongoing restoration actions.Peer reviewe

Impacts of a deep reactive layer on sedimentary phosphorus dynamics in a boreal lake recovering from eutrophication

Using biogeochemical analyses of sediments and porewaters, we investigate the legacy of a brief, intense period of eutrophication on sedimentary phosphorus (P) cycling in a boreal lake (Enonselka basin, Lake Vesijarvi, Finland). Point-source sewage inputs in the twentieth century caused deoxygenation of the lake and accelerated the focusing of iron (Fe) and manganese (Mn) oxides into deeper areas. Early diagenesis under Fe-Mn-rich conditions now favors rapid burial of P in these areas, likely as a combination of both oxide-bound P phases and authigenic manganous vivianite. A new P budget for Enonselka basin shows that P burial causes an annual drawdown of 1.2% (+/- 0.2%) of the surface sediment P inventory, supporting a long-term trend towards recovery since the construction of a wastewater treatment plant in the mid-1970s. However, remineralization of organic matter and associated dissolution of Fe-Mn oxides continues to regenerate P from a deep reactive layer (20-60 cm depth) deposited at the height of past eutrophication, leading to an upwards diffusive flux of dissolved phosphate towards the surface sediments. The magnitude of this flux is similar to that of external P loading to the lake. The combined incoming fluxes of P are likely to retard the complete recovery from eutrophication by decades, despite ongoing restoration actions

Routakallio - Puistosuunnitelma muuttuvaan louhosmaisemaan

This diploma work is a concept plan for Routakallio quarry located in Seinäjoki. Routakallio quarry was established for mining bedrock aggregates in 1965 and these mining activities will continue until year 2019. The plan area is included in a new master plan devised for the district of southern Seinäjoki and a new highway called Itäväylä. The reference year for the master plan is set to 2025. The master plan defines Routakallio area as a new recreational area, which will be landscaped after soil extraction and redeveloped as a part of a larger network of holiday, sport and recreational services. This diploma work focuses on the opportunities of using old quarries from the perspective of landscape architecture. The work consists of two parts. The first part describes the stages of soil extraction with an emphasis on the closure and reclamation of a quarry. This background information is followed by references to special sites and activities established in old quarries around Europe and the Nordic countries. The first part of the thesis ends in presenting the starting point and facts of the planning area as well as the special characteristics created in the landscape by soil extraction. The second part of the diploma work is a concept plan. The plan area covers an area of approximately 25 hectares. The basis for the concept plan is an aesthetically dramatic, natural transformation of the landscape that will overtake the area as the soil extraction ends. The two quarries of rugged rock walls will fill up with water as decades pass. The concept plan includes the estimated final stages of quarrying and the time duration required for the quarries to fill up with water. These estimations are based on planning materials and interviews. The concept plan is divided into three study areas: two quarries formed by soil extraction, the edges and other areas close to the quarries and finally by broader areas surrounding the quarries. The concept plan introduces Routakallio as a recreational and nature area where the traces of quarrying remain and create a new aesthetic look to the area. This means accepting the history of the site and understanding the regenerative processes of time, for example in the form of rising water levels. The concept plan brings past and upcoming changes together and creates a new, natural starting point for the area.Diplomityö on ideatasoinen puistosuunnitelma Routakallion maa-ainestenottoalueelle. Suunnittelualue sijaitsee Seinäjoella. Maa-ainesten otto ja louhostoiminta alkoi Routakallion alueella vuonna 1965 ja jatkuu vuoteen 2019 asti. Suunnittelualue liittyy vuonna 2009 laadittuun Eteläisen Seinäjoen ja Itäväylän osayleiskaavaan, jonka ohjevuosi on 2025. Siinä Routakallio on esitetty erityisalueena, joka maa-ainesten oton päätyttyä maisemoidaan ja asemakaavoitetaan osaksi laajempaa matkailu-, urheilu- ja virkistyspalveluiden kokonaisuutta. Diplomityössä perehdytään louhosalueiden jälkikäytön mahdollisuuksiin maisema-arkkitehtuurin näkökulmasta. Työ jakautuu kahteen kokonaisuuteen. Ensimmäisessä kuvataan maa-ainesten oton eri vaiheet painottuen toiminnan päättymiseen ja jälkihoitoon. Taustatietojen jälkeen esitellään referenssikohteita louhosalueiden jälkikäytöstä Pohjoismaissa sekä Keski-Euroopassa. Ensimmäisen osan lopuksi esitetään suunnittelualueen lähtötiedot sekä esitellään maa-ainesten oton aikaansaamia maisemallisia erityispiirteitä. Työn toinen osa on ideasuunnitelma. Suunnittelualueen pinta-ala on noin 25 hehtaaria. Suunnitelman laht6kohtana on louhosymparist6ssa tapahtuva, esteettisesti voimakas muutos maa-ainesten oton päätyttyä. Louhosaltaisiin kertyvä vesi peittää jylhien kallioseinämien hallitseman maiseman alleen vuosikymmenten kuluessa. Työ perustuu lähtöaineiston ja haastattelujen avulla tehtyyn arvioon louhinnan lopputilanteesta ja louhosaltaiden täyttymiseen kuluvasta ajasta. Ideasuunnitelma jaetaan kolmeen tarkastelualueeseen, jotka ovat maa-ainesten otossa syntyneet louhosaltaat. niitä ympäröivät reuna-alueet sekä laajemmat lähialueet. Ideasuunnitelma esittää Routakallion virkistys- ja luontoalueena, jossa louhostoiminnan jäljet ovat osa alueen uutta estetiikkaa. Tämä tarkoittaa alueen historian hyväksymistä, mutta myös uusiutumisprosessien ajallisuuden ymmärtämistä esimerkiksi nousevan vedenpinnan muodossa. Suunnitelma nostaa ympäristössä tapahtuneet ja tulevat muutokset alueen uudeksi, luontevaksi lähtökohdaksi

Human actions were responsible for both initiation and termination of varve preservation in Lake Vesijarvi, southern Finland

The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselka Basin, Lake Vesijarvi, southern Finland. For the last few decades, the Enonselka Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijarvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation.Peer reviewe

Varve Distribution Reveals Spatiotemporal Hypolimnetic Hypoxia Oscillations During the Past 200 Years in Lake Lehmilampi, Eastern Finland

We investigated 34 sediment cores to reconstruct spatiotemporal variations in hypolimnetic hypoxia for the past 200 years in Lehmilampi, a small lake in Eastern Finland. As hypoxia is essential for varve preservation, spatiotemporal changes in varve distribution were used as an indicator for hypolimnetic hypoxia oscillations. The hypoxic water volume was used as a variable reflecting hypolimnetic hypoxia and determined for each year by estimating the water volume beneath the water depth where shallowest varves were preserved. As a result, seven hypoxia periods, highlighting the variations in hypolimnetic hypoxia, are established. These periods may be influenced by bioturbation, lake infill, and lake level changes. Furthermore, we evaluated the relationship between hypolimnetic hypoxia oscillations and climatic factors. Diatom assemblage changes were also analyzed to estimate whether the hypoxia periods could be related to anthropogenic eutrophication. The diatom analyses suggest relatively stable nutrient conditions for the past 200 years in Lake Lehmilampi. Climate, on the other hand, seems to be an important driver of hypoxia oscillations based on correlation analysis. The role of individual forcing factors and their interaction with hypolimnetic hypoxia would benefit from further investigations. Understanding climatic and anthropogenic forcing behind hypolimnetic hypoxia oscillations is essential when assessing the fate of boreal lakes in a multi-stressor world