The pigments were extracted from the concentrated algal sample in an aqueous solution
of acetone. The resulting absorbance measurements were then applied to a standard equation (SCOR-UNESCO 1966). To estimate N and B of phytoplankton, 1 L (dm3) samples of water were taken using a Ruthner bathometer from the lake surface (0.5 m) and subsequently preserved with a few drops of 40% formaldehyde up to a 2% concentration in the sample. After a 3-day sedimentation, the phytoplankton samples were processed using a Nageotte chamber (0.02 cm3) under an optical microscope at 420 × and 600 × magnifications. N of basic taxa (individual cells and colonies of algae size > 4 μm) were re-calculated KU-60019 order as the total number of algae
per 1 dm3. All the organisms identified belonged to a number of taxonomic groups: Cyanobacteria, Euglenophyceae, Dinophyceae, Cryptophyceae, Chrysophyceae, Bacillariophyceae and Chlorophyceae. The benthos was sampled with an Ekman grab (two grabs per site) with a 0.025 m2 sampling area. The samples were sieved (mesh Ceritinib purchase net size 0.33 mm) and rinsed with pure water and preserved with 4% formaldehyde. In the laboratory, invertebrates with body sizes > 2 mm were hand-picked from the sample. Three taxa – Oligochaeta, Amphipoda and Chironomidae – were found to be the predominant ones in all the samples. The animals were counted and weighed on an electro-balance to the nearest 0.001 g. Prior to weighing the animals were blotted with filter paper to remove water. N and B were re-calculated as the total number of organisms per 1 m2. The relationships between the climatic variables and the biological characteristics were analysed using Spearman’s rank correlation and multiple regression analysis (Statistica 6.0). The annual
AT over the catchment area of Lake Onega for the long-term period of 1951–2010 was calculated as 2.4°C (Figure 2). This value exceeded the current climatic norm (2.1°C), obtained for the period of 1961–1990. The annual AT over the past 15 years made the most important contribution to this increase. Analysis of changes in annual AT using a linear trend showed a 0.2°C per ten years increase in average temperature in the study area. 5-FU chemical structure This temperature increase was accompanied by a reduction in the ice cover of Lake Onega. ICE-FREE in Petrozavodsk Bay during the study period averaged 233 days (Figure 3), exceeding the average value for 1960–2010 by 6 days. During June–October (ice-free period) of 1950–2010, WT in the study area averaged 12.1°C with a July maximum (Figure 4). July WT averaged 15.0°C for 1950–2010 and 17.8 for 2000–2011. The trend of the increase in summer WT was notable especially in recent years, when maximum July WTs were recorded (20.1°C in 2010 and 21.4°C in 2011). For 1999–2010 WT averaged from 14.6 to 19.7°C at the water surface and from 5.6 to 14°C at 15 m depth (Figure 4).