8000-year history of palaeoproductivity in a large boreal lake     

Arto Itkonen  Virpi Marttila  Jarno Meriläinen  Veli-Pekka Salonen 《Journal of Paleolimnology》1999,21(3):271-294

An 8000-year record of palaeoproductivity, based on the chemical and chironomid stratigraphies from Lake Päijänne, S. Finland, was assessed with respect to known morphometric, climatic and anthropogenic events. A gradual trend of dystrophication and an associated decrease in aquatic production was detected during the Holocene, with the following exceptions: (1) high diatom and chironomid production around 8000-6000 cal yr BP, (2) eutrophication around 2000 cal yr BP, and (3) an anthropogenic signal during the last few decades.The changes in chironomid assemblages, before the past few decades, have mainly been shifts in concentration, but not in species composition. Variation in chironomid production was mainly explained by the accumulations of biogenic silicon, carbon and organic matter. Nutrient availability seems to be important in controlling biogenic silicon, which we use to infer past diatom production. The high production ca. 8000-6000 cal yr BP and the fluctuation in chironomid influx after ca. 2000 cal yr BP, however, were probably caused by the proposed warm/dry and cold/wet conditions during these times, respectively. These results highlight the sensitivity of boreal shield lake ecosystems to climatic forcing. In contrast, the pronounced change in the morphometry of the basin around 7000 cal yr BP had little effect on the trophic state of the lake. The human-induced trophic change during the past few decades has affected the Lake Päijänne ecosystem to an extent never experienced before during the last 8000-years.  相似文献   

Establishing a high-resolution surface sediment chronology with multiple dating methods – Testing 137Cs determination with Nurmijärvi clastic-biogenic varves     

《Quaternary Geochronology》2017

The uppermost 50 cm of sediments from the 23 m deep lacustrine basin of Nurmijärvi, a lake in south-central Finland, are composed of the clastic-biogenic type of varves. We use multiple dating methods to render a sediment chronology that is as precise and accurate as possible for future paleoenvironmental research on this high-fidelity sedimentary archive. The 250-year-long varve chronology contains a chronological error of ±2%, as estimated based on repeated varve counts. The varve-based chronology was verified with the vertical distribution of ¹³⁷Cs by comparing variations in the paleomagnetic relative declination of the surface sediments with instrumental observations and a calculated representation of declination features in Finland. A comparison of the sediment cesium content using two gamma counters, different sediment pretreatments, and normalization of the ¹³⁷Cs concentration with masses and accumulation rates of different sediment components revealed that the AD 1986 fallout peak from the Chernobyl accident is the dominant feature in the studied sediments, regardless of the sample pretreatment or normalizing procedure. The vertical distribution of the AD 1986 peak in sediments with clastic-biogenic varves is fairly narrow, thus providing an accurate age-depth marker for the recent deposits. However, the Nurmijärvi section also reveals a ca. 10-year-long period of catchment-to-basin ¹³⁷Cs mobilization and redeposition after the AD 1986 fallout, as well as significant downwards diffusion of the Chernobyl-derived cesium in the sediment. This study highlights the ways in which the quality of surface sediment chronology needs to be considered and secured prior to comparisons between paleoproxy records and instrumental observations.  相似文献   

Dating of paleolandslides in western Finnish Lapland          下载免费PDF全文

Antti E.K. Ojala  Mira Markovaara‐Koivisto  Maarit Middleton  Timo Ruskeeniemi  Jussi Mattila  Raimo Sutinen 《地球表面变化过程与地形》2018,43(11):2449-2462

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New radiocarbon dates from Finnish mammoths indicating large ice-free areas in Fennoscandia during the Middle Weichselian     

Pirkko Ukkonen  Juha Pekka Lunkka  Hgne Jungner  Joakim Donner 《第四纪科学杂志》1999,14(7):711-714

New radiocarbon dates from Finnish subfossil mammoth material (Mammuthus sp.), transported by glacial ice, range in age from ca. 32000 to ca. 22500 yr BP. These results suggest that there was a larger ice-free area in Fennoscandia during the Middle Weichselian than previously assumed. In addition, two dates are also presented for bones found in clay with a different transport history. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Radial Basis Functional Link Nets Used as a Prospectivity Mapping Tool for Orogenic Gold Deposits Within the Central Lapland Greenstone Belt, Northern Fennoscandian Shield   总被引：1，自引：0，他引：1  

Vesa Nykänen 《Natural Resources Research》2008,17(1):29-48

Among the more popular spatial modeling techniques, artificial neural networks (ANN) are tools that can deal with non-linear relationships, can classify unknown data into categories by using known examples for training, and can deal with uncertainty; characteristics that provide new possibilities for data exploration. Radial basis functional link nets (RBFLN), a form of ANN, are applied to generate a series of prospectivity maps for orogenic gold deposits within the Paleoproterozoic Central Lapland Greenstone Belt, Northern Fennoscandian Shield, Finland, which is considered highly prospective yet clearly under explored. The supervised RBFLN performs better than previously applied statistical weights-of-evidence or conceptual fuzzy logic methods, and equal to logistic regression method, when applied to the same geophysical and geochemical data layers that are proxies for conceptual geological controls. By weighting the training feature vectors in terms of the size of the gold deposits, the classification of the neural network results provides an improved prediction of the distribution of the more important deposits/occurrences. Thus, ANN, more specifically RBFLN, potentially provide a better tool to other methodologies in the development of prospectivity maps for mineral deposits, hence aiding conceptual exploration.  相似文献   

Modelling ice conditions in the easternmost Gulf of Finland in the Baltic Sea     

Vladimir Ryabchenko  Anton Dvornikov  Jari Haapala  Kai Myrberg 《Continental Shelf Research》2010

To model ice conditions in the eastern Gulf of Finland, a high-resolution three-dimensional hydrodynamic model is coupled with the advanced sea-ice model HELMI (Haapala et al., 2005). To test the model in extreme situations, the ice pattern in the eastern Gulf of Finland was simulated for a mild ice winter (2007–2008) and for a moderate one (2003–2004). The reference runs were performed on the assumption that the ice in the model domain is fast ice if the sea depth is less than 10 m. Using this assumption, the ice thickness averaged over the Neva Bay (the easternmost part of the Gulf of Finland) is overestimated by the model for almost the entire wintertime in the mild winter and during the ice formation and melting periods in the moderate winter, as compared with the thickness reported in ice charts.  相似文献   

Short-code paleolimnological investigation of Lake Pihlajavesi in the Saimaa Lake complex, eastern Finalnd: assessment of habitat quality of an endemic and endangered seal population     

Olavi Sandman  Jarmo Meriläinen  Heikki Simola  Juhani Hynynen  Jaana Lahtinen  Virpi Marttila  Pasi Reinikainen 《Journal of Paleolimnology》2000,24(3):317-329

A short-core paleolimnological investigation was carried out to acquire knowledge of the recent history of Lake Pihlajavesi, Saimaa Lake complex, and define its natural state before cultural disturbances. In the natural state, with negligible human interference, the basin was oligotrophic and oxygen-rich. The bioproductivity in the littoral zone was low and the profundal benthic quality was good according to Wiederholm's Benthic Quality Index.Based on diatom analyses, no significant changes have taken place in the phytoplankton communities during the past decades. Sedimentary chironomid communities reveal, however, slight changes on profundal life in the Pihlajavedenselkä basin, near the main pollution sources, whereas there were no significant changes in the outer basin. Three stages could be distinguished in the pollution history of Pihlajavedenselkä: (1) 'The natural state' up until the 1960s, (2) 'the period of increasing loading' during the 1960s and 1970s, and (3) 'the recovery of the basin' during the past two decades.Untreated municipal waste water from the town of Savonlinna was partly responsible for the commencement of eutrophication in the Pihlajavedenselkä basin in the 1960s. The paper and pulp industry in Varkaus, some 40 kilometres upstream from Lake Pihlajanvesi, has also increased eutrophication, especially during the worst period of water quality in the 1960s and 1970s. More effective waste water purification has markedly reduced effluent loading and led to a general recovery of the area. Neverthless the effects of slight nutrient loading can still be seen, especially in littoral bioproductivity.Our paleolimnological data indicate that the present ecosystem will offer living conditions for the endemic Saimaa ringed seal population that are similar to those that existed prior to human disturbances.  相似文献   

Exploring the potential of circular economy to mitigate pressures on biodiversity     

《Global Environmental Change》2023

The effects of circular economy on biodiversity are poorly understood. This study provides observations on approaches for assessing circular economy and illustrates, with a Finnish case study, the potential of circular economy to mitigate pressures on biodiversity. The case study focuses on the construction and real estate sectors, as well as the forest industry. The findings imply that circular economy actions that reduce the extraction of virgin raw materials and relieve land use pressures are effective. Improving material efficiency, increasing the cascading use of wood, and optimizing the use and reuse of materials and products, as well as extending the lifetime of buildings and optimizing space use, have good potential for mitigating pressures on biodiversity in Finland. However, as forest utilization has a major impact on Finnish biodiversity, certain actions that possibly increase the use of forest resources (e.g., replacing fossil-based, concrete, or steel materials with wood-based solutions) may impair biodiversity if biodiversity-enhancing forest management practices are not utilized. Assessing the biodiversity impacts of circular economy is challenging, and the need for further research and the development of indicators and assessment methods is clear.  相似文献   

Absolute pollen productivity and pollen–vegetation relationships in northern Finland     

Shinya Sugita  Sheila Hicks  Henna Sormunen 《第四纪科学杂志》2010,25(5):724-736

Pollen productivity is one of the most critical parameters for pollen–vegetation relationships, and thus for vegetation reconstruction, in either pollen percentages or pollen accumulation rates. We obtain absolute pollen productivity of three major tree types in northern Finland: pine (Pinus sylvestris), spruce (Picea abies) and birch (Betula pubescens ssp. pubescens and B. pubescens ssp. czerepanovii treated as one taxon). Long‐term monitoring records of pollen traps from 15 sites (duration: 5–23 years) and tree volume estimates within a 14 km radius of each trap were compared to estimate pollen productivity (grains m^?3 a^?1) of these trees using a regression method. The slope of the linear relationship between pollen loading and distance‐weighted plant abundance represents pollen productivity. Estimated productivities of pollen (×10⁸ grains m^?3 a^?1) for pine, spruce and birch are 128.7 (SE 31.5), 341.9 (SE 81.3) and 411.4 (SE 307.7), respectively. The birch estimate (P > 0.05) is not as good as the others and should be used with caution. Pollen productivities of pine, spruce and birch in northern Finland are, in general, comparable to those of congeneric species in other regions of Europe and Japan. Although the year‐to‐year variations are significant, our volume‐based estimates of pollen productivity for pine and spruce will be essential for quantitative reconstruction of vegetation in the region. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Gypsum treatment as a restoration method for sediments of eutrophied lakes – experiments from southern Finland     

V.-P. Salonen  E. Varjo 《Environmental Geology》2000,39(3-4):353-359

The internal load of phosphorus can be treated with chemicals improving a sediment's phosphorus binding capacity. Gypsum (CaSO₄?2H₂O) is a novel material to be applied for this purpose. In the hypereutrophic Lake Enäjärvi, southern Finland, sediments were treated with gypsum in test basins. The basins were isolated from open water to create artificial anoxia, which allowed the effects of the treatment on the internal load to be measured. The results indicate that gypsum treatment decreases the sediment's release of nutrients under anoxic conditions. This was demonstrated as less increased total-P and total-N concentrations and decreased chlorophyll-a concentrations in the water column of treated basins as compared with the control basins. Because the gypsum treatment prevents internal load, it has potential in lake restoration in cases where the internal load of phosphorus is accelerated by anoxic conditions at the sediment/water interface.  相似文献