Browsing by Author "Ojaranta, Arja"

The subarctic ponds of northern Fennoscandia are often clear-water, fish-free and oligotrophic (relatively low primary production). The ponds in the area are useful physical geography research sites, as the human impact in these areas is relatively small. These ponds are often phosphorus-limited and serve as good indicators of air pollution. Understanding and anticipating changes in water chemistry is particularly important for both the people and the ecosystems in the region. Changes in these ecosystems due to the climate change, for example, can be harmful. The effects of the climate change are and will continue to be strongest in arctic and subarctic areas. The current relatively short growing season is lengthening, so habitats and vegetation zones will either relocate or, alternatively, organisms and plants will have to adapt to the changing conditions. Yet many of the cold-water endemic species worldwide will become extinct. The aim of this thesis was to focus on the biomass of benthic algae growing on the rocks of subarctic ponds. These cyanobacteria, green algae, and diatoms are important primary producers in subarctic ponds and an important part of the food web in these waters. The biomass in this thesis refers to the actual amount of benthic biomass expressed by the amount of dissolved nutrients (not their theoretical, potential amount). The aim of the thesis was to find out how well the physical variables (pond area, average water temperature of the last month of measurement and median solar radiation) and chemical variables (water metal and nutrient concentrations, pH, and conductivity) explain the benthic biomass of subarctic ponds. The Kilpisjärvi area is the only area in Finland that belongs to the old Caledonian orogeny range in the northern part of Fennoscandia. All these 39 ponds were studied, and they are located in Kilpisjärvi in Finnish Lapland, in the areas of about 30 km² of Malla Strict Nature Reserve and about 40 km² of Ailakkavaara, at altitudes of 486–882 m a.s.l. Some of the ponds are located above and some below the tree line. Water samples were collected in August 2020, when data from continuous temperature and radiation meters installed in the late summer of 2019 were also read. During the sampling of the ponds, the biomasses of epilithic, rock-bearing benthic algae groups were measured with a BethoTorch field device and a water pH with a YSI PRO field meter. Water samples were analyzed for metal concentrations by ICP-MS and nutrient concentrations by IC. The results obtained after this spectrometric and chromatographic laboratory analyzes were analyzed statistically, including by means of a generalized linear model (GLM). The water chemistry of the ponds and the biomass of benthic algae are affected by many biotic and abiotic factors. Among other things, geographical location, topography, and climate (in the polar region or the equator) affect both water chemistry and pond biomass. The total metal concentrations in the studied ponds ranged from about 20 to 220 μg/l and the nutrient concentrations from about 2 to 17 mg/l. Based on the results, the chemical variables explained the occurrence of 57 % diatoms, 56 % green algae, and 27 % cyanobacteria, and the physical variables explained 28 % diatoms, 8 % green algae, and 4 % cyanobacteria. According to the F-test, of the chemical variables, the metal concentrations in the water played the largest role in the biomass of benthic algae. The pond area had the largest impact from the physical variables. Surprisingly, nutrients did not appear to play much role in the benthic biomass, although the literature suggests that. The warmer the water, the more likely cyanobacteria are the dominant species and the colder the water more likely are diatoms. This is because the growth peak of cyanobacteria coincides with the warmest time of the year, late summer, and diatoms in springtime immediately after the break-up of ice. The advantage of the BenthoTorch instrument was it is ease of use and speed of measurement, but more specific results could have been obtained, for example, by microscopy of the abundance of the benthic species. In the future, special attention should be paid to the stabilization of chlorophyll-a concentrations in the measurement of benthic algae biomasses. This could produce results that are more consistent and comparable.