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The pollen accumulation rates of four lakes in different regions of Estonia were estimated in order to study the relationship between pollen influx and the character and intensity of disturbances in the pollen catchment area. The pollen influx data obtained are in accordance with model calculations on the size of the pollen source areas. The influx of arboreal pollen and that of the dominant taxa (mainly Pinus) in the lakes investigated shows that, in the case of small lakes (area 3-6ha) in a forested landscapes, the bulk of the pollen originates from an area within 100-200m around the lake. The distribution patterns of influx from two lakes situated close to each other but at different distances from forest fires show that past disturbances can be reliably detected when the disturbance occurred in the immediate vicinity of the lake and at least 25% of the local pollen source area was involved. In the case of a large lake (137ha) only fires embracing thousands of hectares can be detected in the pollen diagrams. 相似文献
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Combining limnological and palaeolimnological approaches in assessing degradation of Lake Pskov 总被引:2,自引:2,他引:0
Mihkel Kangur Külli Kangur Reet Laugaste Jaan-Mati Punning Tõnu Möls 《Hydrobiologia》2007,584(1):121-132
Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies
like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable
fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important
to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged,
migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from
the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of
the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of
substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats
for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics
that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners
migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream
of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during
low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases
from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative
effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were captured.
Electronic supplementary material Supplementary material is available for this article at and accessible for authorized user 相似文献
3.
Diatom analysis of surface sediments and two sediment cores from different sedimentation areas of a small closed lake was
undertaken with the aim of acquiring knowledge on the dependence of the distribution of diatom assemblages on lake bathymetry.
Lake Juusa was selected for the study because we have for this lake a large data set about the lithological composition of
sediments and macrofossil and cladoceran records for the Holocene. A high carbonate content (20–60%) in the sediment sequence
indicates high carbonacity and relatively stable pH values during the Holocene. On the basis of comprehensive analysis, abrupt
water-level fluctuations and changes in the trophic status were established. Results of this study showed that the fluctuations
of the water-level were the leading factor determining the habitats of diatom assemblages in the lake. In the surface sediment
samples planktonic species such as Cyclotella spp., Stephanodiscus spp. and Aulacoseira spp. had a depth optimum at 3–4 m and the most abundant periphytic taxa were distributed mostly at depths shallower than
3.5 m. The same regularity was established in sediment cores where a good correlation between planktonic species and lake
water depth was found in sediments accumulated at water depths >4 m. Lake Juusa appears to be a proper site for detailed environmental
reconstructions over the Holocene, and the results will give us a good opportunity to analyse the history of water-level fluctuations
in other small Estonian lakes.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Handling editor: K. Martens 相似文献
4.
Jaan-Mati Punning Galina Kapanen Tiit Hang Natalia Davydova Mihkel Kangur 《Hydrobiologia》2008,599(1):97-104
A comprehensive study (chronological, lithological and geochemical) of an 8.5 m postglacial sediment sequence from Lake Peipsi was conducted to elucidate the effects of lake-level changes on the sedimentary environment and biogeochemical dynamics in a large lake. Four lithological units were distinguished in the sediment sequence studied: clayey silt, slightly laminated greyish carbonaceous gyttja, brownish-grey gyttja and dark gyttja. These units indicate that large shifts in sedimentation processes occurred in the past. The sediment data show that fluctuations in water depth had a profound impact on the lake environment, recorded as changes in the lithological composition, phosphorus content of sediments and composition of diatom assemblages. The corresponding changes are best reflected in sediments accumulated during phases of regression when the lake area was also smaller. As the water depth and area of the lake increased, wave-induced erosion and resedimentation smoothed or even disturbed the initial information. The increase of phosphorus content in the unconsolidated, high-porosity surface sediments (0.5 m) is most probably connected with active diffusion and matter exchange between the water-sediment pools. 相似文献
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Jaan Mati Punning Tiiu Alliksaar Jaanus Terasmaa Svetlana Jevrejeva 《Hydrobiologia》2004,529(1-3):71-81
A short-core palaeolimnological investigation was undertaken with the aim ofacquiring knowledge of sediment deposition. Analyses of the lithological composition of sediments from the whole-lake basin were performed on the small eutrophic L. Linajärv (northern Estonia) and the concentrations of mineral and organic matter were measured on 647 sub-samples from 14 sediment cores. The accumulation rate of the sediment sequences was established and C/N ratios of organic matter in some cores were recorded. Results indicate that the water depth, basin slopes and distance to the shore have the most important impact on the physical sediment properties. It was shown that variations in the mineral matter concentrations were influenced by the changes in deposition conditions in the areas with steep slopes. The study indicated that more objective information about the sedimentation mechanisms is obtained using analysis of the concentration ratio of mineral and organic matter since it reduces the implied role of diagenetic compaction. 相似文献
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