排序方式: 共有82条查询结果,搜索用时 15 毫秒
71.
Temporal variation and distribution of chlorophyll a and nutrients concentration was evaluated on the basis of field observations in August 2006 in the Gulf of Finland. Strong
easterly winds in August 2006 generated an upwelling event along the Estonian coast of the Gulf of Finland. It caused a drop
of the water-surface temperature and nutrient enrichment of the upper layer. At first, the chlorophyll a declined in the area affected by the upwelled water due to the strong advective transport of the chlorophyll a rich waters towards the northern coast and due to the intensive water mixing and low seed population in the upwelling waters.
After stabilization of the upwelling, nutrients from the upper mixed layer were consumed fast: there were no nitrites + nitrates
left one week later, and phosphate concentration was under the detection limit 2 weeks later. The smaller phytoplankton size
fraction showed faster response to the upwelled nutrients compared with the bigger size fraction, showing the increase in
chlorophyll a content already during the stabilization of the upwelling. The increase in chlorophyll a concentration in >20-μm size fraction at stations influenced by upwelling was observed only after the relaxation of the upwelling
and formation of stratification. 相似文献
72.
We made use of a 22-year (1985-2007) retrospective archive of moderate resolution Landsat TM and ETM+ satellite images to estimate the changes in cover of emergent macrophytes in the large shallow eutrophic Lake Võrtsjärv (270 km2) in Estonia. An original non-parametric image interpretation methodology was applied on late summer images. The combined GIS and statistical analysis of 217 coastal sections showed that the helophytic macrophyte belt, dominated by common reed (Phragmites australis), has rapidly widened during the last two decades, with an average expansion rate of 2.2 m per year. Statistical model revealed that the vicinity of large inflows had the strongest positive effect on the expansion of macrophytes, on average 1.6 times. In some sub-regions of the lake shore, we found the suppressing effect of the presence of small inflows on the change of helophytic belt width. This effect, however, was probably interconnected with the presence of human activity at the shoreline, which itself had statistically near-marginal suppressing effect on the widening of the reed belt.We showed that medium resolution satellite images can successfully be used for the retrospective monitoring of macrophyte vegetation in the littoral zone of large water bodies by applying very simple image classification methodology. As the lake coastal areas showed a tendency to become overgrown with reed and other macrophytes even in conditions of generally reduced agricultural intensity in the catchment area, we hypothesize that the clonal expansion of reed is probably triggered by the complex of drivers: large seasonal fluctuations in the water level create specific low water conditions in estuaries in combination with nutrients supply resolved from lake bottom or brought by rivers. Estuary areas are characterised by mineral sediments suitable for anchoring and protection-provision against destructive wave- and ice-action.Probably the most efficient biodiversity conservation policy to revealed macrophytic expansion is the reactivation of disrupted management activities along the coastline. 相似文献
73.
74.
75.
Lenzitopsis (Thelephorales, Basidiomycota), typified by Lenzitopsis oxycedri, was monotypic before we described the second species of this genus, Lenzitopsis daii in this study. L. daii resembles L. oxycedri in producing lenzitoid hymenophore as well as brown hyphae and echinulate spores, but it differs from the type species by its annual basidiocarps, amyloid spores and growth exclusively on Juniperus chinensis (Cupressaceae). In the phylogenetic perspective inferred with nuclear large subunit ribosomal DNA sequences, the two species were separated from each other and formed a strongly supported clade in the Thelephorales. The two Lenzitopsis species showed a more than 5% difference in internal transcribed spacer sequences. Lenzitopsis species are wood-decaying fungi, and this is the second genus of the order where mycorrhizal life style is unknown, besides of Amaurodon. 相似文献
76.
77.
Large‐scale migrations of brown bears in Eurasia and to North America during the Late Pleistocene 下载免费PDF全文
Peeter Anijalg Simon Y. W. Ho John Davison Marju Keis Egle Tammeleht Katalina Bobowik Igor L. Tumanov Alexander P. Saveljev Elena A. Lyapunova Alexandr A. Vorobiev Nikolai I. Markov Alexey P. Kryukov Ilpo Kojola Jon E. Swenson Snorre B. Hagen Hans Geir Eiken Ladislav Paule Urmas Saarma 《Journal of Biogeography》2018,45(2):394-405
78.
Magdalena Niedziakowska Karolina Doan Marcin Grny Maciej Sykut Krzysztof Stefaniak Natalia Piotrowska Bogumia Jdrzejewska Bogdan Ridush Sawomira Paweczyk Pawe Mackiewicz Ulrich Schmlcke Pavel Kosintsev Daniel Makowiecki Maxim Charniauski Dariusz Krasnodbski Eve Ranname Urmas Saarma Marine Arakelyan Ninna Manaseryan Vadim V. Titov Pavel Hulva Adrian Blescu Ralph Fyfe Jessie Woodbridge Katerina Trantalidou Vesna Dimitrijevi Oleksandr Kovalchuk Jarosaw Wilczyski Theodor Obad Grzegorz Lipecki Alesia Arabey Ana Stankovi 《Journal of Biogeography》2021,48(1):147-159
79.
Studies on hybridization have proved critical for understanding key evolutionary processes such as speciation and adaptation. However, from the perspective of conservation, hybridization poses a concern, as it can threaten the integrity and fitness of many wild species, including canids. As a result of habitat fragmentation and extensive hunting pressure, gray wolf (Canis lupus) populations have declined dramatically in Europe and elsewhere during recent centuries. Small and fragmented populations have persisted, but often only in the presence of large numbers of dogs, which increase the potential for hybridization and introgression to deleteriously affect wolf populations. Here, we demonstrate hybridization between wolf and dog populations in Estonia and Latvia, and the role of both genders in the hybridization process, using combined analysis of maternal, paternal and biparental genetic markers. Eight animals exhibiting unusual external characteristics for wolves - six from Estonia and two from Latvia - proved to be wolf-dog hybrids. However, one of the hybridization events was extraordinary. Previous field observations and genetic studies have indicated that mating between wolves and dogs is sexually asymmetrical, occurring predominantly between female wolves and male dogs. While this was also the case among the Estonian hybrids, our data revealed the existence of dog mitochondrial genomes in the Latvian hybrids and, together with Y chromosome and autosomal microsatellite data, thus provided the first evidence from Europe of mating between male wolves and female dogs. We discuss patterns of sexual asymmetry in wolf-dog hybridization. 相似文献