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Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplankton communities largely consisting of the diatom Aulacoseira islandica (O. Muller) Simonsen. To assess the activity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O 2 ) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the activity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O 2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie.

The limnology of offshore Lake Erie during periods of extensive (> 70%) ice cover was examined from ship borne sampling efforts in 2007 to 2010, inclusive. Dense and discrete accumulations of the centric filamentous diatom Aulacoseria islandica (> 10 μg Chl- a /L) were located in the isothermal (

The type material of A. islandica from Botanical Museum of Copenhagen collection was studied with the light microscopy. The seasonal variability of some characteristics (height, diameter of the valves and areolar density in 100 μm2) was analyzed. The type diagnosis of the species (diameter up to 25.5 μm, height of the valve mantle up to 28 μm, the number of areola rows between 9 to 16 in 10 urn, the number of areolae in a row, 9 to 20 in 10 μm) was enlarged and supplemented with data on the number and location of rimoportulae. The latter are located close to the ringleist, in the middle of the mantle and on the spherical valves of auxospores. The total number of them on the valves ranges from 1 to 4. The outer opening of the rimoportulae substitute for areolae in the row.

Reliable identification of the diatoms is of crucial importance to understand the changing environmental signals stored in the sediments of Lake Baikal. Light and scanning electron microscopy combined with mathematical methods, including principal components analysis, were used to estimate morphological diversity in the structure of mantles of the two dominant species of Lake Baikal, Aulacoseira baicalensis (K. Meyer) Simonsen and Aulacoseira islandica (O. Muller) Simonsen. Species-specific features, such as areolar density, ultrastructure and form of linking spines, were found to be widely variable within cells of the same filaments of A. baicalensis. This finding suggests that the diagnosis of this species will have to be broadened. Besides the thin-walled frustules and the ability to form spores, the population of A. islandica in Lake Baikal is characterized by a higher density of areolae on the mantle compared to the published diagnoses, including the diagnosis of the subspecies helvetica. Mo...

The winter phytoplankton of the Russian part of the hyper-trophic Curonian Lagoon (Baltic Sea) was studied in 2010. Diatoms, cyanobacteria and cryptomonads prevailed in phytoplankton. Diatom Aulacoseira islandica was dominant and especially prevailing in the southern area of the lagoon, i. e. the area influenced by the Deyma River. Cyanobacteria Planktothrix agardhii was also a dominant species. The composition of the complex of dominant species and vertical distribution of phytoplankton differed compared to the results obtained 30 years ago in the same area. The study revealed the increase of the abundance of winter phytoplankton compared to the formerly recorded data.

Water level regulation related to hydroelectric power production and flood prevention is an important hydro-morphological pressure on many watercourses around the world. Fouling of fishing nets in autumn during the open water period and in winter under the ice is a common phenomenon in large Finnish lakes where the water level is regulated. This fouling of fishing nets can sometimes be so extensive that fishing has to be stopped. Based on the practical experiences of fishermen, the main cause for the under-ice fouling has been proposed to be the winter draw-down of water causing low water level and stronger currents in lakes, but no conclusive relationship between fouling and water level regulation has yet been demonstrated. Here we show, using long-term winter data from a boreal lake and short-term netting experiments, that fouling of fishing nets results from increased water draw-down during winter (January–March). Our results also show that fouling of fishing nets takes place only if the high water flow rates are accompanied by an intensive lowering of the water level. We also discuss the relevance of our results to other regulated lakes with ice cover. peerReviewed