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A limnological survey of eight small, atmospherically acidified, forested glacial lakes in the Bohemian Forest (Šumava, Böhmerwald) was performed in September 2003. Water chemistry of the tributaries and surface layer of each lake was determined, as well as species composition and biomass of the plankton along the water column, and littoral macrozoobenthos to assess the present status of the lakes. The progress in chemical reversal and biological recovery from acid stress was evaluated by comparing the current status of the lakes with results of a survey four years ago (1999) and former acidification data since the early 1990s. Both the current chemical lake status and the pelagic food web structure reflected the acidity of the tributaries and their aluminium (Al) and phosphorus (P) concentrations. One mesotrophic (Plešné jezero) and three oligotrophic lakes (Černé jezero, Čertovo jezero, and Rachelsee) are still chronically acidified, while four other oligotrophic lakes (Kleiner Arbersee, Prášilské jezero, Grosser Arbersee, and Laka) have recovered their carbonate buffering system. Total plankton biomass was very low and largely dominated by filamentous bacteria in the acidified oligotrophic lakes, while the mesotrophic lake had a higher biomass and was dominated by phytoplankton, which apparently profited from the higher P input. In contrast, both phytoplankton and crustacean zooplankton accounted for the majority of plankton biomass in the recovering lakes. This study has shown further progress in the reversal of lake water chemistry as well as further evidence of biological recovery compared to the 1999 survey. While no changes occurred in species composition of phytoplankton, a new ciliate species was found in one lake. In several lakes, this survey documented a return of zooplankton (e.g., Cladocera: Ceriodaphnia quadrangula and Rotifera: three Keratella species) and macrozoobenthos species (e.g., Ephemeroptera and Plecoptera). The beginning of biological recovery has been delayed for ∼20 years after chemical reversal of the lakes.

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Abstract:We studied extracellular acid phosphatase activity (AcPA) of planktonic microorganisms, aluminium (Al) speciation, and phosphorus (P) cycling in three atmospherically acidified (pH of 4.5-5.1) mountain forest lakes: Čertovo jezero (CT), Prášilské jezero (PR), and Plešné jezero (PL) in the Bohemian Forest (Šumava, Böhmerwald). Microorganisms dominated pelagic food webs of the lakes and crustacean zooplankton were important only in PR, with the lowest Al concentrations (193 µg L −1 ) due to 3-4 times lower terrestrial input. The lakes differed substantially in Al speciation, i.e., in the proportion of ionic and particulate forms, with the highest proportion of ionic Al in the most acid CT (pH = 4.5). The P concentration in the inlet of PL (mean: 22.9 µg L −1 ) was about five times higher than in CT and PR (3.9 and 5.1 µg L −1 , respectively). Average total biomass of planktonic microorganisms in PL (593 µg C L −1 ) was, however, only ∼2-times higher than in CT and PR (235 and 272 µg C L −1 , respectively). Enormous AcPA (means: 2.17-6.82 µmol L −1 h −1 ) and high planktonic C : P ratios suggested severe P limitation of the plankton in all lakes. Comparing 1998 and 2003 seasons, we observed changes in water composition (pH and Al speciation) leading to a significant increase in phytoplankton biomass in the lakes. The increase in the seston C : P ratio during the same time, however, indicates a progressive P deficiency of the lakes. The terrestrial Al inputs, together with in-1ake processes controlling the formation of particulate Al, reduced P availability for planktonic microorganisms and were responsible for the differences in AcPA. At pH < 5, moreover, ionic Al forms caused inhibition of extracellular phosphatases. We postulate that both particulate and ionic Al forms affect P availability (i.e., inhibition of extracellular phosphatases and inactivation of P), specifically shape the plankton composition in the lakes and affect plankton recovery from the acid stress.

Abstract-The reversal of water acidification has been recently indicated by both empirical data and experiments. The world's largest whole-ecosystem "experiment" involving -30% and -40% reduction in nitrogen and sulfur emissions, respectively, has occurred in Central Europe due to the political and economic changes in the postcommunist countries since 1989. Parallel decreases in deposition rates of SO,*-, NO,-, and NH,+ have resulted in ,a rapid reversal in hydrochemistry of acidified lakes in the Sumava Mountains and the High Tatra Mountains. Concentrations of SO,>-and NO,-in lakes were reduced by 11-14 and 13-32 mmol m-', respectively, between the late 1980s and middle 1990s. Leaching of calcium, magnesium, and aluminum from the watersheds decreased while lake water pH and alkalinity increased. The immediate decline in NO,-concentrations after reduced nitrogen emissions has suggested a rapid reversibility of nitrogen saturation of the mountainous ecosystems in response to decreased amounts of nitrogen deposition.In the last two decades, studies have focused on the level of freshwater acidification in response to two opposing processes: reduction of acid deposition, and nitrogen saturation of terrestrial ecosystems. Reversibility of soil and water acidification has been indicated by both empirical data and experiments. Decreases in sulfur emission in North America and Europe, as well as experimentally reduced acid deposition, have initiated reversal of acidification and the recovery of affected ecosystems (Schindler 1988;Wright and Hauhs 1991). In contrast to the reported decreasing trends in SOd2-concentrations in acidified lakes, levels of NO,-have largely increased in the last two decades (e.g. Henriksen and Brakke 1988;Murdoch and Stoddard 1992). The reason for this is increased leaching of NO,-from N-saturated watersheds exposed to chronically high atmospheric deposition of N (Stoddard 1994;Dise and Wright 1995). NO,-outputs from the N-saturated watersheds have been thus far decreased only in large-scale experiments with drastically reduced loads of SO, 2-, NO,-, and NH, ' (Wright et al. 1988). Because the level of N emissions over the Northern Hemisphere was relatively stable in the last decade, no empirical evidence exists on the response of NO,-leaching from N-saturated terrestrial ecosystems to reduced N deposition.We herein integrate results from published and original data in order to evaluate (1) historical changes in acidifica-$on of lakes in two Central European mountain ranges (the Sumava Mountains and the High Tatra Mountains) in response to the trends in Central European emissions of S and N pollutants, and (2) empirical data on reversibility of acidification of the lakes after economically derived reduction in S and N emissions in former East Germany, Poland; Czech Republic, and Slovakia in the early 1990s. Our data represent the first observations of an immediate response of the N-saturated sites to the nonexperimental reduction in the atmospheric deposition of NO,-and NH,'.The mountain lakes...

Acidification of lakes takes place when pH of rainwater is less than 4.5 and the catchments lie on sensitive geology. Both conditions are met for most lakes in Bohemia and Slovakia. Since 1978 we have studied mountain lakes in the Sumava and in the High Tatra Mountains.In Sumava the three lakes under study are of glacial origin. The catchments are small, with steep sides covered by spruce. The bedrocks are biotite-rich paragneiss, together with gneiss, quartzite and granite. In summer 1936 surface pH was 5.7-6.9 in the Lake Certovo and 6.9-7.0 in the Lake Cern6. Now the pH values are 4.3-4.8 in the two lakes and in the Lake PrdSilsk6 as well. Old reports on zooplankton are from the years 1871, 1892-96, 1935-37, 1947 and 1960. Since 1979 we have not found any planktonic Crustacea in the lakes Cern6 and Certovo. Lake PrdSilsk6 is inhabited by Daphnia longispina and Cyclops abyssorum. In July 1989 the pH values were 4.4, 4.7 and 4.7, concentrations of labile monomeric Al were 0.83, 0.68 and 0.24 mg -' in the lakes Certovo, Cern6 and PrdSilsk6, respectively. High levels of toxic Al compounds might be responsible for the extinction of planktonic Crustacea in the lakes Certovo and Cern6. All the three lakes are void of fish at present.In the High Tatra Mts. we examined more than 40 lakes above timberline in altitudes 1612-2145 m. They are all clearwater, naturally fishless lakes. The bedrock is granite. Owing to different levels of calcium the lakes are now in different stages of acidification. According to recent changes in the zooplankton they can be divided into three groups:(1) Species composition of planktonic Crustacea has not changed.(2) Planktonic Crustacea were present until 1973 but are absent now.(3) From the original species of Crustacea only Chydorus sphaericus is present.The three groups are well separated along the gradients of calcium, ANC and pH. They can be identified with the Henriksen's bicarbonate (our group 1), intermediate (our group 2) and acid (our group 3) lakes. We suppose that in the process of acidification the lakes of the group (2) have been shifted from oligotrophy to ultraoligotrophy.

phytoplankton, mountain lakes, lake acidificatio