Limnological effects of growth and cessation of agricultural land use in Ladoga Karelia: sedimentary pollen and diatom analyses   总被引：2，自引：0，他引：2  

Juha O.?MiettinenEmail author  Heikki?Simola  Elisabeth?Gr?nlund  Jaana?Lahtinen  Riitta?Niinioja 《Journal of Paleolimnology》2005,34(2):229-243

Reference conditions and changes in limnological conditions during the 20th century have been inferred in a palaeolimnological study of sediments from six lakes of the District of Sortavala, Karelian Republic, Russia. The area is former Finnish territory, which was in intensive use for arable field cultivation until the World War II, when the area was ceded to the Soviet Union. After the war, farming was resumed by cattle sovkhozes, and the fields were mainly used as pasture without regular ploughing. We have studied the history of eutrophication and recovery in some lakes related with the changes of agricultural intensity. The trophic level of the lakes was studied by sedimentary diatom assemblages, including reconstructions of total phosphorus levels in the lakes based on a weighted averaging transfer function. Pollen analyses were used to assess the changes in the land use near the lakes. Valuable background data on all the lakes used in the present study are provided by a doctoral thesis done on their limnology from the 1920s. According to our results, the four lakes situated on the clayey lowlands near the coast of Lake Ladoga were eutrophicating during the first half of the 20th century, and in two of them, a rapid recovery is evident. In two lakes situated in hilly landscape with limited agricultural activities, only minor changes are recorded in the diatom profiles.  相似文献   

Quantitative reconstruction of Holocene precipitation changes in southern Patagonia     

Marcela Sandra Tonello  Maria Virginia Mancini  Heikki Sepp 《Quaternary Research》2009,72(3):410-420

Holocene variations in annual precipitation (P_ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r² = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P_ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P_ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P_ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P_ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.  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   

Age determination of Baltic herring from whole otoliths and from neutral red stained otolith cross sections   总被引：2，自引：1，他引：2  

Peltonen  Heikki; Raitaniemi  Jari; Parmanne  Raimo; Eklund  Jan; Nyberg  Kari; Halling  Folke 《ICES Journal of Marine Science》2002,59(2):323-332

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Predicting oxygen in small estuaries of the Baltic Sea: a comparative approach     

Pirkko Kauppila  Jessica J. Meeuwig  Heikki Pitknen 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1115-1126

Coastal eutrophication, manifested as hypoxia and anoxia, is a global problem. Only a few empirical models, however, exist to predict bottom oxygen concentration and percentage saturation from nutrient load or morphometry in coastal waters, which are successfully used to predict phytoplankton biomass both in lakes and in estuaries. Furthermore, hardly any empirical models exist to predict bottom oxygen from land-use. A data set was compiled for 19 estuaries in the northern Baltic Sea, which included oxygen concentration and percentage saturation, water chemistry, estuary morphometry, and land-use characteristics. In regression analyses, bottom oxygen was predicted both as a function of the percentage of watershed under agriculture and of mean depth. These models accounted for ca. 55% of the variation in oxygen. Additionally, oxygen was linked to fetch (diameter of the area in the direction of the prevailing wind), which accounted for 30% of the variation in oxygen. This suggests that shallow Finnish estuaries are wind-sensitive. In ‘pits’ (sub-thermocline waters of deep basins), near-bottom total nitrogen strongly correlated with oxygen percentage saturation (R²=0.81). Neither chlorophyll a, total phosphorus nor nutrient loading explained oxygen variation in entire estuaries or in ‘pits’, probably mainly due to annual sedimentation/sediment–water flux dynamics. On the basis of the results of cross-validation, the models have general applicability among Finnish estuaries.  相似文献   

Light scattering in cometary dust comae     

Gary Herman  Heikki Salo 《Earth, Moon, and Planets》1987,39(1):51-74

Detailed single and multiple scattering calculations were carried out for a spherically symmetric cometary atmosphere irradiated by a plane parallel source. Using simplifying assumptions in the single scattering approximation, analytical expressions were derived for the total flux impinging the cometary nucleus, which was shown to be a decreasing function of the coma opacity. Moreover, while highly anisotropic phase functions resulted in more light reaching the nucleus than was the case for isotropic phase functions, the net energy flux at the nucleus surface was still found to be smaller in the presence of a coma than in the no coma case. This increased flux due to the anisotropic phase functions was attributed mostly to the effect of directional scattering in the forward Sun-comet axis. The isotropic multiply scattered flux at the surface was found tobe an increasing function of the opacity, , for 2.5. At larger values of , the maximum in the downward directed scattered flux was still seen to increase, but occurred at a height of several radii above the nucleus, resulting in a reduction at the surface. On the other hand, the total flux at the surface was again shown to be a decreasing function of and always less than in the no coma case. Finally, on comparing the multiply scattered flux with that obtained in the plane parallel approximation, it was quite apparent that except in the vicinity of the Sun-comet axis, the plane parallel geometry tends to underestimate the degree of scattering.NRC Resident Research Associate.  相似文献   

Fusing pollen-stratigraphic and dendroclimatic proxy data to reconstruct summer temperature variability during the past 7.5?ka in subarctic Fennoscandia     

Samuli Helama  Heikki Sepp?  Anne E. Bjune  H. John B. Birks 《Journal of Paleolimnology》2012,48(1):275-286

A new palaeoclimatic reconstruction of mid-summer (July) temperatures for the last 7.5?ka in northern Fennoscandia is presented. It is based on two botanical proxies: spectra of fossil pollen and tree rings of Scots pine logs recovered from lacustrine sediments in the Arctic tree-line region. A newly developed method of proxy fusion is used to integrate the proxy-specific reconstructions of past summer temperature variability based on the pollen-stratigraphic and dendroclimatic data. The rationale behind the method is that the two proxies are likely to be connected to climate variability in a timescale-dependent fashion and, accordingly, the new reconstruction makes use of the low- and high-frequencies from pollen-stratigraphic and tree-ring data, respectively. The most prominent features of the new reconstruction are: (1) the long-term decline of temperatures by 2.0?°C over the past 7.5?ka, (2) the mid-Holocene warmth culminating between 5 and 4?ka as a deviation from the cooling trend, (3) the Little Ice Age cool phase between 0.7 and 0.1?ka, and (4) the subsequent warming during the past century. These periods are superimposed on year-to-year variations in climate as dated to calendar-year accuracy by dendrochronology. Within the modern period, the years 1934 and 1937 are among the warmest, and the years 1903 and 1910 are among the coldest summers in the context of the past 7.5?ka. On average, the reconstructed Holocene climate was approximately 0.85?°C warmer than the twentieth century.  相似文献   

Comparison of Silver and Gold Inquarting in the Fire Assay Determination of Palladium/Platinum and Rhodium in Geological Samples     

Meeri Suominen  Esko Kontas  Heikki Niskavaara 《Geostandards and Geoanalytical Research》2004,28(1):131-136

The classical lead fire assay is still the most important method for the pre-concentration and separation of Ag, Au and some of the platinum-group elements (PGE) in the analysis of geological materials. The most frequently used fire assay procedure is the determination of Au, Pd and Pt with Ag as collector. When Au is used instead of Ag as a collector, Pd, Pt, Rh and possibly Ir can also be determined. In this study the recoveries by Au and Ag collectors, also called inquarts, were compared in the fire assay analysis of Pd, Pt and Rh in geological reference materials. The amount of gold to be added was optimised. Variable recoveries were obtained with Ag inquart for Rh, but a 2 mg inquart of Au gave good recoveries for all three of these elements in the analysis of reference samples of different geological materials. A procedure, alternative to scorification, to overcome interferences caused by base metals in the cupellation step is presented. The procedure involves cutting the Pb button into pieces and analysing the pieces separately. Prior to this, a homogeneity study of the lead button was made, and it showed that Pd, Pt and Rh were evenly distributed in the Pb button. All determinations were made using inductively coupled plasma-atomic emission spectrometry (ICP-AES).  相似文献   

Holocene annual mean temperature changes in Estonia and their relationship to solar insolation and atmospheric circulation patterns     

Heikki Seppä  Anneli Poska 《Quaternary Research》2004,61(1):22-31

We reconstructed annual mean temperature (T_ann) trends from three radiocarbon-dated Holocene pollen stratigraphies from lake sediments in Estonia, northern Europe. The reconstructions were carried out using a North-European pollen-climate calibration model based on weighted averaging partial least-squares regression. The cross-validated prediction error of the model is 0.89°C and the coefficient of determination between observed modern T_ann values and those predicted by the model is 0.88. In the reconstruction, the Holocene thermal maximum (HTM) is distinguishable at 8000-4500 cal yr B.P., with the expansion of thermophilous tree species and T_ann on average 2.5°C higher than at present. The pollen-stratigraphical data reflect progressively warmer and drier summers during the HTM. Analogously with the modern decadal-scale climatic variability in North Europe, we interpret this as an indication of increasing climatic continentality due to the intensification of anticyclonic circulation and meridional air flow. Post-HTM cooling started abruptly at around 4500 cal yr B.P. All three reconstructions show a transient (ca. 300 years) cooling of 1.5-2.0°C at 8600-8000 cal yr B.P. We tentatively correlate this cold event with the North-Atlantic “8.2 ka event” at 8400-8000 cal yr B.P. Provided that the 8.2 ka event was caused by freshening of the North-Atlantic surface water, our data provide evidence of the climatic and vegetational responsiveness of the boundary of the temperate and boreal zones to the weakening of the North-Atlantic thermohaline circulation and the zonal energy transport over Europe. No other cold events of comparable magnitude are indicated during the last 8000 years.  相似文献   

Gaseous and Particulate Oxidized and Reduced Nitrogen Species in the Atmospheric Boundary Layer in Scandinavia in Spring     

Asgeir Sorteberg  Øystein Hov  Sverre Solberg  Kjetil Tørseth  Hans Areskoug  Martin Ferm  Kit Granby  Heikki Lättilä  Karin Persson  David Simpson 《Journal of Atmospheric Chemistry》1998,30(2):241-271

Observations of the concentration of several nitrogen containing compounds at five rural Scandinavian sites during March–June 1993 are reported. Total nitrate (NO ₃ ^- + HNO₃) and total ammonium (NH ₄ ⁺ + NH₃) were measured by denuder and filter pack. In general the methods agree well. At all sites the particulate fraction dominated, with the largest fraction of NO ₃ ^- and the lowest of NH ₄ ⁺ at the sites which were closest to the emission sources. The fraction of NO ₃ ^- of total nitrate increased with increasing NO₂ concentrations, indicating that the nighttime conversion of NO₂ to NO ₃ ^- is an important route of formation for NO ₃ ^- . A positive correlation was found between HNO₃ and O₃ in June at all sites, while no correlation was found early in the spring. Model calculations were made with a lagrangian boundary layer photooxidant model for the whole period, and compared to the measured concentrations. The calculated ratio between mean observed and modelled daily maximum concentrations of ozone over the measurement period were within +/–10% at all sites. The models ability to describe the daily ozone maximum concentration was satisfactory with an average deviation of 19–22% from the observed concentrations. HNO₃ was underestimated by over 50% at all sites except the one closest to the emission sources. The correlation between modelled and observed concentrations was generally best for the sites with shortest transport distance from the sources of emission.  相似文献