Jiří Kopáček

Chemical composition of the Tatra Mountain lakes: Recovery from acidification

Ninety-one lakes distributed along the Tatra Mountains (most of lakes > 1 ha and 65% of lakes > 0.01 ha) were sampled and analysed for ionic and nutrient composition in September 2004 (15 years after reduction in acid deposition). Eighty-one lakes were in alpine zone and ten lakes in Norway spruce forest. The results were compared to similar lake surveys from 1994 (the beginning of water recovery from acidification) and 1984 (maximum acidification). Atmospheric deposition of SO42− and inorganic N decreased 57% and 35%, respectively, in this region from the late 1980s to 2000. Lake water concentrations of SO42− and NO3− have decreased both by ∼50% on average (to 23 and 19 μmol L−1, respectively, in 2004) since 1984. While the decrease in SO42− concentrations was stable throughout 1984–2004, most of the NO3− decrease occurred from 1994 to 2004. The declines in SO42− and NO3− concentrations depended on catchment coverage with vegetation, being most rapid for SO42− in forest lakes and for NO3− in rocky lakes. Concentrations of the sum of base cations (dominated by Ca2+) significantly decreased between 1984 and 2004, with the highest change in rocky lakes. Most of this decline occurred between 1994 and 2004. Acid neutralising capacity (ANC) did not change in the 1984–1994 period, but increased on average by 29 μmol L−1 between 1994 and 2004, with the highest change in rocky lakes. Over the last decade, the proportion of lakes with ANC > 150 μmol L−1 increased from 15% to 21% and that of ANC < 20 μmol L−1 decreased from 37% to 20%. The highest decline in H+ and Al concentrations occurred in the most acid lakes. On a regional basis, no significant change was observed for total phosphorus, total organic nitrogen, and dissolved organic carbon (DOC) in the 1994–2004 period. However, these parameters increased in forest lakes, which exhibited an increasing trend in DOC concentrations, inversely related (P < 0.001) to their decreasing ionic strength (30% on average in 1994–2004).

Element fluxes in watershed-lake ecosystems recovering from acidification: Plešné Lake, the Bohemian Forest, 2001–2005

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.

Chemical composition of the Tatra Mountain lakes: Response to acidification

Data from two surveys of the Tatra Mountain lakes (Slovakia and Poland) performed in the autumns of 1984 (53 lakes) and 1993 or 1994 (92 lakes) were used to estimate spatial variability in water chemistry in this lake district during the period of maximum European acid deposition. The ionic content of the lakes was generally low, with conductivity (at 20°C) ranging from 1.1 to 4.7 mS m−1 and 23% of the lakes had a depleted carbonate buffering system. Major factors governing differences in lake-water chemistry were bedrock composition and amount of soil and vegetation in their catchment areas. Compared to lakes in the predominantly granitic central part of the Tatra Mountains, lakes in the West Tatra Mountains had higher concentrations of base cations and alkalinity due to the presence of metamorphic rocks in the bedrock. Concentrations of phosphorus, organic carbon, organic nitrogen, and chlorophyll-a were highest in forest lakes and decreased with decreasing density of vegetation and soil cover in the catchment areas. Concentrations of nitrate showed an opposite trend. Several exceptions to these general patterns in chemical and biological composition were due to exceptional geology or hydrology of the lake catchments.

Biomass and element pools of understory vegetation in the catchments of Čertovo Lake and Plešné Lake in the Bohemian Forest

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).

Estimation of tree biomass of Norway spruce forest in the Plešné Lake catchment, the Bohemian Forest

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.

Changes in Soil Dissolved Organic Carbon Affect Reconstructed History and Projected Future Trends in Surface Water Acidification

Preindustrial (1850s) and future (2060) streamwater chemistry of an anthropogenically acidified small catchment was estimated using the MAGIC model for three different scenarios for dissolved organic carbon (DOC) concentrations and sources. The highest modeled pHu2009=u20095.7 for 1850s as well as for 2060 (pHu2009=u20094.4) was simulated given the assumption that streamwater DOC concentration was constant at the 1993 level. A scenario accounting for an increase of DOC as an inverse function of ionic strength (IS) of soilwater and streamwater resulted in much lower preindustrial (pHu2009=u20094.9) and future recovery to (pHu2009=u20094.1) if the stream riparian zone was assumed to be the only DOC source. If upland soilwater (where significant DOC increase was observed at −5 and −15xa0cm) was also included, DOC was partly neutralized within the soil and higher preindustrial pHu2009=u20095.3 and future pHu2009=u20094.2 were estimated. The observed DOC stream flux was 2–4 times higher than the potential carbon production of the riparian zone, implying that this is unlikely to be the sole DOC source. Modeling based on the assumption that stream DOC changes are solely attributable to changes in the riparian zone appears likely to underestimate preindustrial pH.

Pools and composition of soils in the alpine zone of the Tatra Mountains

The basic physical, chemical, and biochemical properties of mountain soils were determined in alpine-zone meadow and moraine areas of the Tatra Mountains (Slovakia, Poland) in 2000–2001. The amount of soil (dry weight soil < 2 mm) varied from 38 to 255 kg m−2 (average of 121 kg m−2) in alpine meadows and averaged 13 kg m−2 in moraine areas. Concentration of organic C was the parameter that most strongly and positively correlated with N, P, S, effective cation exchange capacity (CEC), exchangeable base cations, exchangeable acidity, and all biochemical parameters (C, N, and P in microbial biomass and C mineralisation rates). The relationship between C and P was less straightforward due to inorganic P forms associated with Fe and Al oxides. The average pools of C, N, P, and S, were respectively 696, 41, 2.9, and 1.9 mol m−2 (i.e., 84, 5.7, 0.91 and 0.61 t ha−1) in meadow soils, and 38, 2.1, 0.45 and 0.12 mol m−2 (i.e., 4.5, 0.30, 0.14 and 0.04 t ha−1) in moraine areas. Soil pH was generally low, with the lowest pHH2O values (3.8–4.9) in the A-horizons. Average pools of CEC were 12 and 0.7 eq m−2 in meadows and moraine areas, respectively. The base saturation (BS) was 4–45% (12% on average) of CEC, and was primarily based on Ca2+ and K+ (∼40% and ∼22% of BS, respectively). C:N molar ratios (14–20) were only slightly lower than those observed in the alpine Tatra Mountain zone ∼40 years ago. Concentrations of C, N, and P in soil microbial biomass were high (on average 1.6, 3.4, and 25% of total C, N, and P concentrations), suggesting high microbial activity in alpine soils.

Chemical composition of modern and pre-acidification sediments in the Tatra Mountain lakes

Concentrations of major nutrients (C, N, P) and acid soluble metals (Ca, Mg, K, Al, Fe, Mn, Pb, and Zn) were determined in modern (0–1 cm) and pre-acidification (5–10 cm) sediment layers collected from 37 alpine and 3 forest lakes in the Tatra Mountains (Slovakia, Poland) in 1996–1998. Sediment composition reflected catchment characteristics and productivity of lakes. In the sediments of alpine lakes, C and N concentrations decreased and Mg increased with a decreasing proportion of vegetation and soil in the catchment. Decreasing Ca:Mg ratios in sediments along the vegetation gradient was inverse to that in water, and could be associated with different ratios of cations in water leachate from catchments and in solids which enter the lake due to soil erosion. Phosphorus concentrations increased with the proportion of moraine areas, with till soils rich in P. Concentrations of C, N, P, and Ca in sediments positively correlated to their concentrations in water. Sediment concentrations of Al and Al:Ca ratios increased with decreasing sediment and water pH. A negative correlation between water pH and concentrations of organic C in water and sediments indicated the important impact of organic acids on the acid status of the lakes exposed to higher terrestrial export of organic matter. Compared to the pre-acidification period, the modern sediments had significantly higher Fe, Mn, Zn, Pb, and K, but lower Mg concentrations. The Zn and Pb enrichment was more evident in oligotrophic alpine lakes than in more productive forest lakes and was independent of lake water or sediment pH. Fe and Mn concentrations in the modern sediments were higher than in ambient soils and bedrock, while those in pre-acidification sediments were similar to contemporary soils and to the rock layer. The enrichment of the modern sediments with Fe and Mn thus probably resulted from both their redox recycling and ecosystem acidification.

Seasonal photochemical transformations of nitrogen species in a forest stream and lake.

The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40–58 µmol L−1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4 +) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3 −) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4 + production in winter and spring, and the maximum NO3 − reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4 + concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3 − fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form.

Integrated ecological research of catchment-lake ecosystems in the Bohemian Forest (Central Europe): A preface

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.