Two decades of macrophyte expansion on the shores of a large shallow northern temperate lake—A retrospective series of satellite images

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.     

Context-Dependency of Agricultural Legacies in Temperate Forest Soils

Ecosystems - Anthropogenic activities have affected forests for centuries, leading to persistent legacies. Observations of agricultural legacies on forest soil properties have been site specific...     

Recent patterns of sediment accumulation in a small closed eutrophic lake revealed by the sediment records

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.     

Emission rate of charged spores in basidiomycetous fungi and the relaxation time of their electric charges

Basidiospores are one of the main components of coarse fraction of atmospheric aerosol. Majority of them, the ballistospores of 20,000 species of Basidiomycotina, carry electrostatic charges when getting airborne. To study the polarity and magnitude of primary charges and the hymenial emission rate of charged spores, 128 spore samples of 31 species of Agaricomycetes were collected in natural conditions. A portable device was placed under the fruiting body and the freely falling charged spores were extracted from the air by a horizontal homogeneous electrostatic field. The charge polarity distribution was the same in all intraspecies spore samples; it was unipolar-positive, unipolar-negative, or bipolar, depending on the species. The mean spore charge magnitude was 21–981 e, and it was not related to the emission rate of charged spores. The hymenial emission rate was fluctuating, and the maximum value was 715 charged spores cm^?2 s^?1. To estimate the territorial emission rate of charged spores, area of the hymenial surface per hectare of forest was calculated for three species and the maximum values were 11 m² ha^?1 and 8.6 × 10⁷ charged spores ha^?1 s^?1. Calculations showed that a spore charge diminished sevenfold within 47 min. Ecologists, health and agricultural scientists could be interested in this information. It could be useful by investigating the role of microorganisms in meteorological phenomena and in atmospheric processes in general.     

The role of MatP,ZapA and ZapB in chromosomal organization and dynamics in Escherichia coli

Despite extensive research over several decades, a comprehensive view of how the Escherichia coli chromosome is organized within the nucleoid, and how two daughter chromosomes segregate has yet to emerge. Here we investigate the role of the MatP, ZapA and ZapB proteins in organizing the replication terminus (Ter) region and in the chromosomal segregation process. Quantitative image analysis of the fluorescently labeled Ter region shows that the replication terminus attaches to the divisome in a single segment along the perimeter of the cell in a MatP, ZapA and ZapB-dependent manner. The attachment does not significantly affect the bulk chromosome segregation in slow growth conditions. With or without the attachment, two chromosomal masses separate from each other at a speed comparable to the cell growth. The separation starts even before the replication terminus region positions itself at the center of the nucleoid. Modeling of the segregation based on conformational entropy correctly predicts the positioning of the replication terminus region within the nucleoid. However, the model produces a distinctly different chromosomal density distribution than the experiment, indicating that the conformational entropy plays a limited role in segregating the chromosomes in the late stages of replication.     

Hybrid aspens responses to alkalisation of soil: growth, leaf structure, photosynthetic rate and carbohydrates

Interactions between photosynthetic rate, transpiration, content of soluble carbohydrates, leaf dimensions and structural parameters and growth of hybrid aspen (Populus tremula?×?P. tremuloides Michx.) were studied in relation to soil pH and chemical composition. The investigations were conducted in two plantations on former agricultural lands in North Estonia. One plantation was established on a territory influenced for a long time by alkaline cement dust pollution before plantation establishment and the other on an unpolluted territory. At pH 7.4 and higher concentrations of Ca, K, Mg, N and P in soil on the polluted area inhibition of height growth and diameter at breast height, leaf area and dry mass was observed compared to the unpolluted plantation with an optimum soil pH of 6.7. Differences in hybrid aspen leaves in the two plantations were related to the lower net photosynthetic and transpiration rates and higher starch and sucrose contents in the polluted plantation. Leaves from alkaline soil had a thicker palisade mesophyll layer and lower number of stomata at abaxial epidermis. The relatively low N concentration in leaves in the polluted area was associated with the low height and diameter at breast height of trees.