Volume 61, Issue 20

The Bohemian Forest (Šumava, Böhmerwald) is situated in Central Europe and is among the most acidified lake districts in the world. Deposition of S and N compounds in the area rapidly increased between 1950 and 1980, and reached a maximum in the 1980s. During the 1990s, acid deposition decreased substantially, and current levels are comparable to the early 20th century for SO42− and NH4+, and to the mid 1960s for NO3−. These changes in acid deposition have led to a partial recovery of the Bohemian Forest lakes. This paper provides an overview of previous research, and details on the organization and aims of current research on the Bohemian Forest lakes. Available historical data and regular monitoring (since 1984) provide a valuable background for long-term ecological research of the catchment-lake ecosystems that currently focuses on (i) chemical reversal and biological recovery of the lakes, (ii) acidification impacts on in-lake nutrient cycling, (iii) climatic effects on water chemistry, and (iv) catchment processes, including soil biogeochemistry and acidification impacts on vegetation.

Pollen analysis has been carried out on a 549 cm thick sediment profile from lake Plešné jezero (Plešné Lake) in the Bohemian Forest (Šumava, Czech Republic; 1090 m a.s.l.; 48°47′ N; 13°52′ E). Analyses of 67 samples characterise the development of the lake biotope and the surrounding landscape during the last ca. 14,000 years. The pollen diagram shows a very distinct transition between the Late Glacial and the Holocene biostratigraphic units at a depth of ca. 312 cm. In the surroundings of Plešné Lake the vegetation was treeless during the entire Late Glacial. The alpine tree limit, formed by Betula and Pinus with undergrowth of shrubs, might have been at ca. 500 m a.s.l. Pollen transported from long distances was significant due to the openness of the landscape, coming from southern Europe and even Africa, and including high numbers of Artemisia, Poaceae, Chenopodiaceae, and some other herbs and shrubs from steppe and forest-steppe areas in southern Europe or Africa (likely Ephedra, certainly Lygeum spartum). The expansion of shrubs, particularly Juniperus, preceded the expansion of trees near the end of the Late Glacial. Afforestation of the region by thin stands of Betula and Pinus occurred during the Preboreal. Significant warming in the Boreal resulted in the expansion of Corylus, Quercetum mixtum (QM) trees, and probably also Picea and Alnus. Picea as well as QM trees were further expanding during the Early Atlantic. Picea was the dominant tree during the Late Atlantic and Fagus started to spread towards its end. Abrupt expansion of Abies marks the Subboreal. A high degree of afforestation (Abies, Fagus, Picea) was characteristic for the Early Subatlantic. During Late Subatlantic, pollen of synanthropic plants appears. Phases of the lake biotope development were defined on the basis of coccal green algae and Isoëtes.

A sediment record of cladoceran remains was analysed in a 543 cm long core from Plešné jezero (Plešné Lake), the Bohemian Forest, Czech Republic. The core covered the time period from the Oldest Dryas to the present. Littoral and benthic Cladocera included 11 species of the family Chydoridae while three species (Bosmina longispina, Daphnia cf. pulicaria and D. cf. longispina) lived in the open water. Remains of Alona quadrangularis and Chydrous sphaericus occurred in the oldest sediment layers from the beginning of the Bølling chronozone. Bosmina longispina and Daphnia cf. pulicaria appeared about 400 years later. Inorganic sediment accumulated at a relatively high rate of ∼ 90 mg cm−2 yr−1 at that time, diluting cladoceran remains and organic matter. Remains of Cladocera accumulated at 0.1 to 0.01 of the Holocene rate, making it difficult to observe effects of climate variation on the species structure of Cladocera in the Late-Glacial. Production of remains increased after warming during the Younger Dryas-Preboreal transition at ∼11.6 kyr BP, and the proportion of littoral species increased. The most important change in cladoceran fauna occurred at ∼10.5 kyr BP and culminated with afforestation of the catchment around 10.3 kyr BP. The domaination of Bosmina longispina lasted for ∼250 years. The afforestation occurred concurrently with a decrease in lake water pH. Bosmina longispina and Daphnia cf. pulicaria disappeared, production of cladoceran remains decreased, but biodiversity increased. Planktonic Cladocera were represented by Daphnia cf. longispina during most of the rest of the Holocene. The production of Cladocera never reached the Preboreal level. Since ∼ 5 cal. kyr BP, the inferred pH continuously decreased. The final decline was likely caused by cooling during the Little Ice Age and by sulphur emissions from ore smelting. The recent acidification of lake water and impoverishment of aquatic fauna was brought about by emissions of sulphur and nitrogen compounds in the 20th century.

A faunal record of chironomid remains was analyzed in the upper 280 cm of a 543 cm long sediment core from Plešné jezero (Plešné Lake), the Bohemian Forest (Šumava, Böhmerwald), Czech Republic. The chronology of the sediment was established by means of 5 AMS-dated plant macroremains. The resolution of individual 3-cm sediment layers is ∼115 years and the analyzed upper 280 cm of the sediment core represent 10.4 cal. ka BP. As the results of DCA show, two marked changes were recorded in the otherwise relatively stable Holocene chironomid composition: (1) at the beginning of the Holocene (ca. 10.4-10.1 cal. ka BP) only oligotrophic and cold-adapted taxa (Diamesa sp., M. insignilobus-type, H. grimshawi-type) were present in the chironomid assemblages, clearly reflecting a cool climate oscillation during the Preboreal period, and (2) during an event dated in the interval 1540–1771 AD, when most taxa vanished entirely and only Zavrelimyia sp. and Procladius sp. were alternately present accompanied by Tanytarsus sp. Although, the age of this event is in agreement with the dating of the Little Ice Age, the most probable reason for the elimination of many chironomid taxa was very low sums recorded in this part of the sediment, rather than cool conditions connected with the LIA. Variations in the chironomid fauna after the Preboreal period were reflected mainly by changes in abundances of dominant taxa rather than by changes in species composition. These variations could be explained by: (1) climatic changes, namely temperature and amount of rainfall resulting in oscillations in lake level, with changes in the occurrence of macrophytes in the littoral and (2) increasingly dense afforestation which led to a considerable input of organic material into the lake and a subsequent increase in the trophic status of the lake water.

Fluxes of major ions and nutrients were measured in the watershed-lake ecosystem of a strongly acidified lake, Čertovo jezero (Čertovo Lake), in the 2001 through 2005 hydrological years. Water balance was estimated from precipitation and throughfall amounts, and measured outflow from the lake. The average water input into and outflow from the watershed-lake ecosystem was 1461 mm and 1271 mm (40 L km−2 s−1), respectively, and the water residence time in the lake averaged 662 days. The ecosystem has been recovering from acidification since the late 1980s. Still, however, Čertovo watershed was an average net source of 23 mmol m−2 yr−1 of SO42−. Nitrogen saturation of the watershed caused low retention of the deposited inorganic N (23% on average). After a dry summer in 2003 and a cold winter in 2004, the watershed became a net source of inorganic N (19 mmol m−2 yr−1). Nitrogen transformations and SO42− release were the dominant terrestrial sources of H+ (81 and 47 mmol m−2 yr−1, respectively) and the watershed was a net source of 42 mmol H+ m−2 yr−1. Ionic composition of tributaries showed seasonal variations with the most pronounced changes in NO3−, base cations, DOC, and ionic Al (Ali) concentrations. The in-lake biogeochemical processes reduced the incoming H+ by ∼50% (i.e., neutralized on average 222 mmol H+ m−2 yr−1, on a lake-area basis). Denitrification, SO42− reduction, and photochemical and microbial decomposition of allochthonous organic matter were the most important in-lake H+ consuming processes (215, 85, and 122 mmol H+ m−2 yr−1, respectively), while hydrolysis of Ali was the dominant H+ generating process (96 mmol H+ m−2 yr−1) in Čertovo Lake. Photochemical liberation from organic complexes was an additional in-lake source of Ali. The net in-lake retention or removal of nutrients (carbon, phosphorus, nitrogen, and silica) varied between 18% and 34% of their inputs.

Fluxes of major ions and nutrients were measured in the watershed-lake ecosystem of a strongly acidified lake, Plešné jezero (Plešné Lake), in the Czech Republic in hydrological years from 2001 through 2005. The lake is situated in a Norway spruce forest and has a steep watershed between elevations of 1090 and 1378 m. The average water input and output from the ecosystem was 1372 mm and 1157 mm (37 L km−2 s−1), respectively, and the water residence time averaged 306 days. Despite ecosystem recovery from acidification occurring since the late 1980s, the Plešné watershed was an average net source of 25 mmol SO42− m−2 yr−1. Nitrogen saturation of the watershed caused low retention of the deposited inorganic N (< 44% on average) before 2004. Then, the watershed became a net source of 28–32 mmol m−2 yr−1 of inorganic N in the form of NO3− due to climatic effects (a dry summer in 2003 and a cold winter in 2004) and forest dieback caused by a bark beetle attack in 2004. Nitrogen transformations and SO42− release were the dominant terrestrial sources of H+ (72 and 49 mmol m−2 yr−1, respectively) and the watershed was a net source of 24 mmol H+ m−2 yr−1. Ionic composition of surface inlets showed seasonal variations, with the most pronounced changes in NO3−, ionic Al (Ali), and DOC concentrations, while the composition of subsurface inlets was more stable. The in-lake biogeochemical processes reduced on average 59% of the incoming H+ (251 mmol H+ m−2 yr−1 on a lake-area basis). NO3− assimilation and denitrification, photochemical and microbial decomposition of allochthonous organic acids, and SO42− reduction in the sediments were the most important aquatic H+ consuming processes (358, 121, and 59 mmol H+ m−2 yr−1, respectively), while hydrolysis of Ali was the dominant in-lake H+ generating process (233 mmol H+ m−2 yr−1). Photochemical liberation from organic complexes was an additional in-lake source of Ali. The net in-lake retention or removal of total phosphorus, total nitrogen, and silica were on average 50%, 27%, and 23%, respectively. The lake was a net source of NH4+ due to a cease in nitrification (pH < 5) and from NH4+ production by dissimilation exceeding its removal by assimilation.

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-lake 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.

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.

Eight glacial lakes of the Bohemian Forest (Czech Republic and Germany) were characterised by the distribution of chironomids collected as pupal exuviae. Twenty-eight taxa were identified, including some faunistically interesting species of the region. Two-way indicator species analysis (TWINSPAN) was used to classify lakes according to their taxonomic composition. Canonical correspondence analysis (CCA) and multiple regression were used to relate the chironomid assemblages to two sets of explanatory variables: (i) local environmental variables, and (ii) broad-scale spatial variables. The TWINSPAN classified the lakes into four groups, whereas presence/absence of three taxa was indicative for this classification. The CCA of assemblage composition on environmental variables showed that chironomids respond significantly to altitude and alkalinity. The ordination of composition data on geographical variables revealed strong longitudinal gradient in chironomid distributions. Altitude and alkalinity accounted for 36.2% of the total variation, while the geographic gradient explained 20.5%. As revealed by the variation partitioning procedure, the significant effect of these variables was, in large part, independent of each other. Overall taxonomic richness appeared to be governed by altitude only. Causal ecological and historical factors underlying these results are discussed. This paper may provide a basis for hypothesis testing in future research of the Bohemian Forest lakes.

Atmospheric acidification brought about the extinction of several species of planktonic Crustacea in lakes of the Bohemian Forest (Šumava, Böhmerwald). The recent reversal in chemical parameters of lake water towards pre-acidification values raises the question whether the return of missing species is possible. We have designed a bioassay to test water from different lakes for the survival of Daphnia longispina, which inhabited the lakes under study but disappeared from those most affected by acidification. The bioassay showed the best survival in water from Plešné Lake, one of those where Daphnia and Cyclops became extinct. A large-scale experiment was conducted by transplanting Daphnia longispina (Crustacea, Cladocera) and Cyclops abyssorum (Crustacea, Copepoda) from Prášilské Lake, where they have survived until the present, to Plešné Lake. One year later, a successful reintroduction was confirmed for Cyclops abyssorum.

Coelastrum pascheri sp. n. is described. It is similar to Coelastrum morus W. et G. S. West sensu Skuja (1930) in the morphology of the free processes, but differs from it in cell size (it is significantly smaller, 13–16 µm) and in the number of cells in a cenobium (usually 4). The new alga was found in the littoral of some lakes: Černé jezero (Černé Lake), Grosser Arbersee and Kleiner Arbersee in the Bohemian Forest (Šumava, Böhmerwald) and also in Sphagnum within a small puddle in the Upolínová meadow in the Slavkovský les Mts.

Using image analysis, chlorophyll autofluorescence was measured in single cells of green alga Monoraphidium dybowskii and in filaments of cyanobacteria (Pseudanabaena sp. and Limnothrix sp.) in the vertical profile of small acidified mountain lake Plešné jezero (Plešné Lake) from May to November of 2003. Cell chlorophyll autofluorescence was converted to cell chlorophyll content using a conversion factor determined by comparing the total autofluorescence of phytoplankton in a microscope field with spectrophotometrically determined total chlorophyll concentration; the conversion factor did not differ between epilimnion (0.5 m depth) and hypolimnion (9 m depth). Vertical patterns of chlorophyll concentration and of cellular chlorophyll content depended on water column mixing: during the period of stable thermal stratification, a metalimnetic peak in total chlorophyll concentration was present and cellular chlorophyll contents in the metalimnion and hypolimnion were notably elevated compared to the surface. Monotonous vertical profiles of both total chlorophyll concentration and cell chlorophyll content were typical for the period of water column overturn. During the stratification period, hypolimnetic Monoraphidium cell chlorophyll content was on average twice as high (maximum difference 2.7-fold) compared to surface values (of 3.2–12.9 fg µm−3), while in filamentous cyanobacteria (surface cell chlorophyll content of 2.2–13.3 fg µm−3), the difference was much higher — six-fold on average, with an 11.6-fold maximum value. The values measured with image analysis in 2003 were compared to unpublished values of total phytoplankton biomass-specific chlorophyll concentrations obtained using manual phytoplankton biomass determination and spectrophotometric chlorophyll measurement in 1998 at the same locality. Good agreement was found in seasonal patterns and vertical profiles of chlorophyll between both seasons.

The role of litter composition and quality on the nutrient release was studied in three month laboratory experiment. Spruce needles and leaves of four species dominant in understorey vegetation of the Norway spruce forest were collected in early autumn and incubated at 5°C, 10°C and 15°C. C mineralization was measured every two weeks, concentration of NH4, NO3, dissolved organic N, dissolved organic C and oxalate extractable P at the beginning and end of incubation and decay rate and nutrient release was calculated. Freshly senescent leaves contained less N and P indicating nutrient reallocation. Effect of temperature on a decay rate and nutrient transformation was not significant while the effect of litter quality expressed by C/N ratio at the end of incubation was. The decay rate was the fastest for the fern (Athyrium alpestre) and decreased in order: Callamagrostis villosa > Vaccinium myrtillus > Avenella flexuosa > spruce needles. The critical C/N ratio bellow which mineral N was released in high amount was around a value of 32. The results indicte that an increase of coverage of understorey vegetation can increase a risk of nutrient release.

This paper presents data on species composition, biomass, and element pools (C, N, P, Ca, Mg, Na, K, Al, Fe, Mn) of the understory vegetation of spruce forests in the catchments of lakes Čertovo jezero (CT) and Plešné jezero (PL) in the Bohemian Forest (Šumava, Czech Republic). Calamagrostis villosa was the most abundant species in the CT catchment, while Vaccinium myrtillus was the most abundant species in the PL catchment. The catchments weighted mean (CWM) of above-ground biomass of the understory vegetation was 288 and 723 g m−2 in the CT and PL catchments, respectively. The significant difference in the biomass between the catchments was caused by the much higher abundance of V. myrtillus in the PL catchment. The CWM of below-ground biomass of the fine roots was 491 and 483 g m−2 in the CT and PL catchments, respectively. The respective CWM element pools of biomass in the CT and PL catchments were: C (33 and 51 mol m−2), N (0.8 and 1.0 mol m−2), P (24 and 34 mmol m−2), Ca (53 and 113 mmol m−2), Mg (24 and 41mmol m−2), Na (3.7 and 6.5 mmol m−2), K (83 and 109 mmol m−2), Al (50 and 42 mmol m−2), Fe (13.3 and 7.3 mmol m−2), and Mn (4.2 and 8.8 mmol m−2).

This paper evaluates the total biomass and pools of major nutrients and ecologically important metals of the tree layer in the catchment of Plešné jezero (PL) in the Bohemian Forest (Šumava, Czech Republic), and compares them to analogous data on understory vegetation and soils. The results are based on field measurements and semi-automatic image analyses of aerial orthophotographs. The tree layer was relatively sparse with open canopy in some parts of the catchment. Stand density varied between 44 and 328 individuals per hectare. The catchment weighted mean total biomass of trees was 134 t ha−1 dry weight, of which needles, branches, roots, and stems represented 5%, 10%, 14%, and 71%, respectively. The stem wood and bark represented 67% and 4%, respectively, of the total tree biomass. The catchment weighted mean element pools were 568 and 3.0 mol m−2 (i.e., 68 and 0.42 t ha−1) for C and N, respectively. The other pools were 76 mmol P m−2, 602 mmol Ca m−2, 133 mmol Mg m−2, 39 mmol Na m−2, 347 mmol K m−2, 19 mmol Al m−2, 6.2 mmol Fe m−2, and 35 mmol Mn m−2. The element pools accumulated in the tree biomass represented from < 1% (Al, Fe) to 37% (C) of their total pools (soil + tree layer + understory vegetation) in the catchment. Pools of Ca and Mg in the tree biomass were similar to their exchangeable pools in the catchment soils, while those of K were 3 times higher. Nutrient (N, P, Ca, Mg, and K) and C pools in the tree biomass were 2–11 times higher than those in the understory vegetation, with the minimum for P and maximum for C.

We studied water chemistry and phytobenthos in streams of the Bohemian Forest (Šumava, Böhmerwald) in order to determine the influence of sewage originating from recreational usage on the diversity and structure of periphytic assemblages. Sites both above and below the outflow of sewage from touristically exploited villages and small recreational centres were compared. All together, we identified 113 species of algae and cyanobacteria in the samples, including very rare species such as Clastidium setigerum (Cyanobacteria). In some streams, waste discharge increased the concentration of nutrients to a marked degree. Species richness of phytobenthos was correlated neither to nutrient concentration nor to algal growth potential. However, an increase in chlorophyll-a, and a shift in the structure of phytobenthos assemblages were observed at sites below the source of pollution. At the most polluted sites Chlorophyta (e.g., Pseudodendoclonium basiliense, Chlorosarcina sp.) dominated, and Bacillariophyceae species sensitive to pollution were replaced by tolerant ones (Cymbella minuta, C. caespitosa, Diploneis oblongella and Nitzschia spp.).