Veljo Kisand

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The variability and patchiness in composition of bacterial communities were studied in a large eutrophic boreal lake (280 km2) with a mean depth of <3 m. The present study was undertaken to determine the factors that influence species dispersal in the sediment environment of large shallow lakes and to test the hypothesis that species dispersal in the(More)
Humic substances (HS) are the most abundant natural organic compounds in aquatic and terrestrial environments. However, the bacterial degradation of HS in the estuarine salinity gradient and in coastal regions as a sink for HS, entering the open sea, is not well understood. Therefore, we studied the bacterial degradation of humic-rich dissolved organic(More)
Abundance and biomass of the microbial loop members [bacteria, heterotrophic nanoflagellates (HNF), and ciliates] were seasonally measured in the naturally eutrophic and shallow (2.8 mean depth) Lake Võrtsjärv, which has a large open surface area (average 270 km2) and highly turbid water (Secchi depth <1 m). Grazing rates (filter feeding rates) on 0.5-, 3-,(More)
The influence of functional group specific production and respiration patterns on a lake's metabolic balance remains poorly investigated to date compared to whole-system estimates of metabolism. We employed a summed component ecosystem approach for assessing lake-wide and functional group-specific metabolism (gross primary production (GPP) and respiration(More)
Nutrient (P and N) enrichment experiments in small enclosures (20 l) were carried out to determine P and/or N limitation of bacterioplankton in Lake Võrtsjärv. The specific interest of the study was to test if it is possible to detect nutrient `physiological' or growth (rate) limitation of bacterioplankton and competition for nutrients (N and P) with(More)
Lake Võrtsjärv (270 km2, mean depth 2.8 m, Estonia) is an eutrophic and turbid lake (Secchi depth 0.5-1 m) with a high nutrient load (total nitrogen 1-2 mg N l(-1), total phosphorus approximately 50 microg P l(-1)) leading to a highly productive phytoplankton population (average chlorophyll a concentration 24 microg l(-1)). Seasonal dynamics of the main(More)
Bacterioplankton abundance and production were followed during one decade (1991–2001) in the hypertrophic and steeply stratified small Lake Verevi (Estonia). The lake is generally dimictic. However, a partly meromictic status could be formed in specific meteorological conditions as occurred in springs of 2000 and 2001. The abundance of bacteria in Lake(More)
The community composition of bacteria with highly dynamic abundance and activity was observed to be with low variability in a shallow lake sediment with frequent physical disturbance. This suggests that physical disturbance did not create more niches and did not lead to highly variable bacterial community. The major part of the bacterial community was(More)
This study explored the spatiotemporal dynamics of the bacterioplankton community composition in the Gulf of Finland (easternmost sub-basin of the Baltic Sea) based on phylogenetic analysis of 16S rDNA sequences acquired from community samples via pyrosequencing. Investigations of bacterioplankton in hydrographically complex systems provide good insight(More)
The diel dynamics of bacterio- and phytoplankton as main compartments in the pelagic foodweb were followed in order to assess the coupling between algal photosynthesis and bacterial growth during a diel cycle in Lake Võrstjärv, Estonia. Three diurnal studies were carried out, on July 12th–13th, 1994; on June 25th–26th, 1995 and on July 17th–18th, 1995 with(More)