排序方式： 共有7条查询结果，搜索用时 15 毫秒
1
1.
Anneli Poska Vivika Väli Pille Tomson Jüri Vassiljev Kersti Kihno Tiiu Alliksaar Miguel Villoslada Leili Saarse Kalev Sepp 《Landscape Ecology》2018,33(4):529-546
Context
Anthropogenic and environmental changes are reshaping landscapes across the globe. In this context, understanding the patterns, drivers, and consequences of these changes is one of the central challenges of humankind.Purpose
We aim to test the possibilities of combining modern multidisciplinary approaches to reconstruct the land-cover and linking the changes in land-cover to socioeconomic shifts in southern Estonia over the last 200 years.Methods
The historical records from five, and maps from six time periods and 79 pollen-based land-cover reconstructions from four lakes are used to determine the land-cover structure and composition and are thereafter combined with the literature based analyses of socioeconomic changes.Results
All information sources recorded similar changes in the land-cover. The anthropogenic deforestation was comparable to today’s (approximately 50%) during the nineteenth century. Major political and socioeconomic changes led to the intensification of agriculture and maximal deforestation (60–85%) at the beginning of the twentieth century. The land nationalisation following the Soviet occupation led to the reforestation of the less productive agricultural lands. This trend continued until the implementation of European Union agrarian subsidies at the beginning of the twenty first century.Conclusions
Pollen-based reconstructions provide a trustworthy alternative to historical records and maps. Accounting for source specific biases is essential when dealing with any data source. The landscape’s response to socioeconomic changes was considerable in Estonia over the last 200 years. Changes in land ownership and the global agricultural market are major drivers in determining the strength and direction of the land-cover change.2.
Punning Jaan-Mati Terasmaa Jaanus Koff Tiiu Alliksaar Tiiu 《Water, air, and soil pollution》2003,149(1-4):77-92
The seasonal fluxes of dry matter, spheroidal fly-ash particles and pollen were studied in a small mesotrophic lake in order to reveal the patterns of their spatial-temporal distribution in regard to seasonal variations. Sediment traps deployed in the lake at different depths and locationswere used to collect samples for calculating sediment fluxes in two years. The results show that resuspension of settled particles in the lake with a small dynamic ratio is moderate and depends on seasonal changes in thermal stratification. The rate of particle deposition during the summer stratification period was low. The weather conditions during early spring, such as air temperature and the thickness of snow-cover, influence the intensity of resuspension. Air temperature and cloudiness during the summer stratification period determine the rate of bioproduction and thermocline parameters, which also have a major effect on the seston composition and fluxes. 相似文献
3.
Fly-ash particles accumulate in sediments and can be used to assess spatial distribution and temporal trends of atmospheric deposition of pollutants derived from high temperature combustion of fossil fuels. Previous work has concerned fly-ash derived from oil and coal. Oil-shale is the main fossil fuel used in Estonia and a major source of atmospheric pollution in the Baltic states. To assess if oil-shale power plants produce specific fly-ash particles, we used scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) to compare fly-ash particles from oil-shale combustion with particles from oil and coal combustion. Two types were analysed, large black (10–30 μm) and small glassy (<5 μm) spheroidal particles. Although particle morphology to some extent is indicative of the fuel burnt, morphological characters are not sufficient to differentiate between particles of different origin. However, our results indicate that with EDX analysis the fly-ash from oil-shale can be distinguished from oil and coal derived particles in environmental samples. Concentrations of large black and small glassy spheroidal fly-ash particles in a sediment core from an Estonian lake showed similar trends to oil-shale combustion statistics from Estonian power plants. 相似文献
4.
Rose N.L. Alliksaar T. Bowman J.J. Boyle J. Coles B. Fott J. Harlock S. Juggins S. Punning J-M. St. Clair-Gribble K. Vukic J. Watt J. 《Water, air, and soil pollution》1998,106(3-4):205-218
The FLAME (FLy-Ash and Metals in Europe: Implications for human and environmental health) research project funded by the EU COPERNICUS programme ran from 1994 to 1996. The main aims of the programme were to further develop an automated chemical characterisation to discriminate between fly-ash particles from the major fossil-fuels used throughout Europe (coal, oil, peat, brown coal and oil shale) and apply this to particles extracted from lake sediments taken from the four participating countries (Estonia, Czech Republic, Ireland and U.K.) in order to determine spatial distributions of deposited particulates from large combustion sources. In combination with trace metal analyses from lake surface sediments and catchment mosses, the fly-ash particle data were able to identify areas of elevated pollutant deposition and suggest potential sources for them. Given the transboundary nature of the pollutants, the techniques and results of FLAME are of relevance throughout Europe. Other papers in this volume describe results and interpretation. This paper describes the background and aims of the FLAME project, outlines the methods employed for sampling sediments and mosses and the analytical techniques for particle enumeration and trace metal analysis for sediments and mosses. Finally brief details of the particle characterisation are given showing how a hierarchical discriminant function was developed, based on energy dispersive spectroscopy (EDS) derived particle chemistry which correctly allocated particles from the five fuel-types with 80% accuracy. 相似文献
5.
Rose N.L. Alliksaar T. Bowman J.J. Fott J. Harlock S. Punning J-M. St. Clair-Gribble K. Vukic J. Watt J. 《Water, air, and soil pollution》1998,106(3-4):329-351
Detailed discussion of the FLAME data at individual country level is included in other papers in this volume but some aspects of the analyses and data interpretation are best discussed on a broader level and that is the aim of this paper. The spatial distribution of fly-ash particles in the participating countries shows good agreement with expected sources and this implies that the majority of particulates travel less than 100 km from their source although lower concentrations of particles were detected at all sample sites. Areas of elevated concentration mostly coincide with population centres and imply possible impacts on human health by fine particulates (e.g. PM10) from fossil-fuel sources in these areas. Problems with the particle characterisation, developed within the FLAME project, include difficulties in allocation due to the overlap between coal-series fuels and the presence of a 'mineral coal' background at lake sites thought to be due to persistent sediment minerals surviving the chemical pre-treatment and becoming allocated to coal. This leads to implications for the inclusion of further fuels into the classification and the application of the technique to the same fuels beyond Europe. The combination of lake sediment SCP data and sediment and moss metals data can also provide an indication of the impact from anthropogenic contamination at a site and probable source types. Comparison with previous moss analyses from 1990 show that metal concentrations in central Europe may have decreased but levels in the UK have shown little change. Finally, comparisons of FLAME data with the EMEP model for pollutant budgets across Europe generally show good agreement for pathways, although further work is needed in receptor countries for additional confirmation. 相似文献
6.
The concentrations of fly-ash particles were studied in the surface sediments of 42 lakes in Estonia. Concentrations of both spheroidal carbonaceous particles (SCPs) and inorganic ash spheres (IASs) were determined and the particles chemically characterised to different fuel types. This was accompanied by trace metal analyses from lake surface sediments and catchment mosses in order to determine the distribution of atmospheric pollutants. The obtained spatial distribution data for fly-ash particles varied to a great extent, partly due to differences in sedimentation rates but mainly due to higher deposition in industrial areas. The distribution patterns of the different particle types in lake sediments, as well as the trace metals in mosses, show that the deposition of airborne particulates is of local origin around pollution sources and that the share of long-range transported atmospheric impurities is high along the main cyclonic routes in Estonia. 相似文献
7.
Aina Leeben Annika Mikomägi Viia Lepane Tiiu Alliksaar 《Journal of Soils and Sediments》2014,14(2):269-279
Purpose
The feasibility of applying the method of single-scan fluorescence emission spectra of humic substances (HSs) without chemical pretreatments of sediment pore-water samples was tested to ascertain the past productivity and sources of organic matter of lakes.Materials and methods
Sediment samples were collected from ten Estonian lakes (located between 57°36′ and 59°25′N and 22°12′ and 26°59′E) covering all levels of the trophic scale. The height (fluorescence intensity), location (fluorescence maximum) and shape (fluorescence index, the ratio of intensities at the emission wavelengths 450 and 500 nm) of the fluorescence emission spectrum at an excitation of 340 nm were under consideration.Results and discussion
Pore-water humic substances (pwHSs) from sediments of eutrophic lakes had generally a high fluorescence intensity and fluorescence index and their fluorescence maximum was located at shorter wavelengths. Characteristic features of pwHSs from oligotrophic lakes were low fluorescence intensity, emission of maximum fluorescence at shorter wavelengths and high fluorescence index values. Pore-water humic substances from sediments of dystrophic lakes were characterized by a low fluorescence intensity and fluorescence index and their spectral peak was shifted to longer wavelengths. The study also demonstrated that a shift in the peak location of pwHSs fluorescence was accompanied with a change in the C/N ratios of sedimentary organic matter, and the alteration in the fluorescence index of pwHSs was synchronous with the changes in their molecular weight.Conclusions
The obtained results suggest that fluorescence spectroscopy of pwHSs without using chemical pretreatments has a great potential in the reconstruction of past lake conditions. 相似文献
1