Showing papers by "Jussi Vuorenmaa published in 2010"
TL;DR: In this article, changes in water pH and colour since the late 1980s were studied in 35 small boreal lakes of varying hydrological and landscape settings but similar climate and acid deposition.
Abstract: Changes in water pH and colour since the late 1980s were studied in 35 small boreal lakes of varying hydrological and landscape settings but similar climate and acid deposition. The data was collected during the autumnal overturn on the annual basis except in lake with weekly sampling during the ice-free period. In addition to the deposition data information about catchment soil types as well as local meteorological and hydrological conditions were used for the long-term data interpretation. The lakes are situated in a small area in southern Finland, 130 km north from Helsinki, where sulphate deposition declined by >60% in one decade since the mid-1980s. The results showed that water colour increased in most lakes while pH did not. In lakes dominated by surface runoff there was a distinct upward shift in colour, with an initial increase after the mid-1990s and a second increase in 2004. The first shift appeared when the sulphate deposition reached a level ca. 25% of that in 1988. However, the upward shift in colour also coincided with a change in hydrological conditions after several dry summers. In contrast, the second shift in colour clearly coincided with a switch in hydrology due to the abnormally wet summer of 2004 after severe drought in 2002–2003. Although the hydrological conditions indisputably had a key role in determining the annual variability in colour, a distinct negative relationship between acid deposition and water colour in 90% of the lakes strongly suggested that reduction in sulphate deposition fostered the leaching of coloured organic substances from the catchment soils. Increase in colour, in turn, strongly influenced lake water pH, and the present day higher organic matter concentrations seemingly depress pH values more than in the 1980s, before the reduction in acid deposition.
64 citations
TL;DR: In this article, a paired whole-lake thermocline manipulation experiment of a small shallow dystrophic lake (Halsjarvi) was carried out in southern Finland, where a thermodynamic model was used for both predicting the impacts of climate change scenarios and for determining the manipulation target of the experiment.
Abstract: . Climate change with higher air temperatures and changes in cloud cover, radiation and wind speed alters the heat balance and stratification patterns of lakes. A paired whole-lake thermocline manipulation experiment of a small (0.047 km2) shallow dystrophic lake (Halsjarvi) was carried out in southern Finland. A thermodynamic model (MyLake) was used for both predicting the impacts of climate change scenarios and for determining the manipulation target of the experiment. The model simulations assuming several climate change scenarios indicated large increases in the whole-lake monthly mean temperature (+1.4–4.4 °C in April–October for the A2 scenario), and shortening of the length of the ice covered period by 56–89 days. The thermocline manipulation resulted in large changes in the thermodynamic properties of the lake, and those were rather well consistent with the simulated future increases in the heat content during the summer-autumn season. The manipulation also resulted in changes in the oxygen stratification, and the expansion of the oxic water layer increased the spatial extent of the sediment surface oxic-anoxic interfaces. In addition, the experiment affected several other chemical constituents; concentrations of organic carbon, TotN, and NH4 showed a statistically significant decrease, likely due to both changes in hydrological conditions during the experiment period and increased decomposition and sedimentation. In comparison with the results of a similar whole-lake manipulation experiment in a deep, oligotrophic, clear-watered lake in Norway, it is evident that shallow dystrophic lakes, common in the boreal region, are more sensitive to physical perturbations. This means that projected climate change may modify their physical and chemical conditions in the future.
26 citations
Journal Article•
TL;DR: The observations indicate that the chemical recovery of the study lakes from acidification has been remarkable enough to allow recolonization by aquatic organisms, which means the possibility of a successful re-establishment of populations in previously acidified fishless lakes which, in turn, increases the value of such lakes for fishing.
Abstract: In 2002, we reintroduced perch (Perca fluviatilis) into three small, previously heavily acidified and fishless lakes. Test fishing indicated that released perch had survived in all three study lakes and reproduced successfully in two of them. Growth of introduced individuals had increased sharply after introduction. The increased growth of perch was an apparent consequence of high abundance of macroinvertebrates in the fishless lakes. Activity traps indicated even a 90% decrease in the numbers and size of invertebrates upon the fish releases: a very likely response to the predation by the stocked perch. Our observations indicate that the chemical recovery of the study lakes from acidification has been remarkable enough to allow recolonization by aquatic organisms. For perch, and probably for other acid tolerant fish, this means the possibility of a successful re-establishment of populations in previously acidified fishless lakes which, in turn, increases the value of such lakes for fishing.
15 citations