Josef Hejzlar

The apparent and potential effects of climate change on the inferred concentration of dissolved organic matter in a temperate stream (the Malse River, South Bohemia).

Long-term and seasonal changes in concentration of dissolved organic matter (DOM) and their possible drivers were evaluated for an upland stream in central Europe during 1969-2000. Two periods have been detected within this data set-years with decreased DOM until the middle of 1980s and then years with increased DOM until 2000. Temperature, hydrological regime of runoff from the catchment (namely the amount of interflow), and changes in atmospheric deposition of acidity coincided with the variations in DOM concentrations. The analysis of single runoff events confirmed the relation between the export of increased DOM concentrations from the catchment and interflow. A multiple linear regression model based on monthly averages of temperature and interflow explained 67% of DOM variability. This model suggested a 7% increase in DOM concentration under the scenarios of possible future climate change related to doubled CO(2) concentration in the atmosphere. The scenarios were based on results of several global circulation models.

Hysteresis in Reversal of Central European Mountain Lakes from Atmospheric Acidification

Extremely high emissions of S and N compounds in Central Europe (both ∼280 mmol m-2 yr-1) declined by ∼70and ∼35%, respectively, during the last decade. Decreaseddeposition rates of SO4-2, NO3-, and NH4+ in the region paralleled emission declines. The reduction in atmospheric inputs of S and N to mountain ecosystemshas resulted in a pronounced reversal of acidification in the Tatra Mountains and Bohemian Forest lakes. Between the 1987–1990and 1997–1999 periods, concentrations of SO4-2 and NO3- decreased (average ± standard deviation) by 22±7 and 12±7 μmol L-1, respectively, in theTatra Mountains, and by 19±7 and 15±10 μmol L-1, respectively, in the Bohemian Forest. Their decrease was compensated in part (1) by a decrease in Ca2+ + Mg2+ (17±7 μmol L-1) and H+ (4±6 μmol L-1), and an increase in HCO3-(10±10 μmol L-1) in the Tatra Mountains lakes, and (2) by a decrease in Al (7±4 μmol L-1), Ca2+ + Mg2+ (9±6 μmol L-1), and H+ (6±5 μmol L-1), in Bohemian Forest lakes. Despite the rapid decline in lake water concentrations of SO4-2 and NO3- in response to reduced S and N emissions, their present concentrations in some lakes are higher than predictionsbased on observed concentrations at comparable emission rates during development of acidification. This hysteresis in chemical reversal from acidification has delayed biological recovery of the lakes. The only unequivocal sign of biological recovery hasbeen observed in Černé Lake (Bohemian Forest) where a cladoceran species Ceriodaphnia quadrangular has recentlyreached its pre-acidification abundance.

Natural inactivation of phosphorus by aluminum in atmospherically acidified water bodies

Atmospheric acidification of catchment-lake ecosystems may provide natural conditions for the in-lake control of P cycling. This process is based on the elevated transport of aluminum from acidified soils and its subsequent precipitation in the water body and is described for strongly acidified forest lakes, acidified and circumneutral reservoirs, and a moderately acidified alpine lake. In water bodies with episodically or permanently acidified inflows a pH gradient develops between lake water and tributaries due to: (i) neutralization of acidic inflows after mixing with waters with undepleted carbonate buffering system, and/or (ii) the in-lake alkalinity generation dominated by biochemical removal of NO3- and SO4(2-). With the pH increasing towards neutrality, ionic Al species hydrolyze and form colloidal Al hydroxides (Al(part)) with large specific surfaces and strong ability to bind orthophosphate from the liquid phase. Moreover, Alpart settles and increases the P sorption capacity of the sediment. The presence of Al(part) on the bottom reduces orthophosphate release from sediments after its liberation from ferric oxyhydroxides during anoxia because Al(part) is not sensitive to redox changes. Consequently, the natural in-lake P inactivation may be expected in any water body with elevated Al input and a pH gradient between its inlet and outlet.

Broad Habitat Range of the Phylogenetically Narrow R-BT065 Cluster, Representing a Core Group of the Betaproteobacterial Genus Limnohabitans

ABSTRACT The distribution of the phylogenetically narrow R-BT065 cluster (Betaproteobacteria) in 102 freshwater lakes, reservoirs, and various ponds located in central Europe (a total of 122 samples) was examined by using a cluster-specific fluorescence in situ hybridization probe. These habitats differ markedly in pH, conductivity, trophic status, surface area, altitude, bedrock type, and other limnological characteristics. Despite the broad ecological diversity of the habitats investigated, the cluster was detected in 96.7% of the systems, and its occurrence was not restricted to a certain habitat type. However, the relative proportions of the cluster in the total bacterioplankton were significantly lower in humic and acidified lakes than in pH-neutral or alkaline habitats. On average, the cluster accounted for 9.4% of the total bacterioplankton (range, 0 to 29%). The relative abundance and absolute abundance of these bacteria were significantly and positively related to higher pH, conductivity, and the proportion of low-molecular-weight compounds in dissolved organic carbon (DOC) and negatively related to the total DOC and dissolved aromatic carbon contents. Together, these parameters explained 55.3% of the variability in the occurrence of the cluster. Surprisingly, no clear relationship of the R-BT065 bacteria to factors indicating the trophic status of habitats (i.e., different forms of phosphorus and chlorophyll a content) was found. Based on our results and previously published data, we concluded that the R-BT065 cluster represents a ubiquitous, highly active segment of bacterioplankton in nonacidic lakes and ponds and that alga-derived substrates likely form the main pool of substrates responsible for its high growth potential and broad distribution in freshwater habitats.

Determination of low chemical oxygen demand values in water by the dichromate semi-micro method

A semi-micro modification of the dichromate method for the determination of low concentrations (1–35 mg l–1) of the chemical oxygen demand is described. It is based on the experimentally established dependencies of the oxidation efficiency on the concentrations of H2SO4, K2Cr2O7 and Ag2SO4, and on the temperature and time of heating. The procedure involves increasing the concentration of H2SO4 and heating in closed test-tubes in a heating block at 170 °C for 40 min and the spectrophotometric determination of dichromate at 455 nm. The interfering effect of chloride, up to a concentration of 100 mg l–1, is masked by using a combination of HgSO4 and KCr(SO4)2. The modification has been tested on 30 samples of ground, tap, precipitation and surface waters and on 16 chemical compounds, and gives results comparable to those from a standard reflux method.

Trends and seasonal patterns of bulk deposition of nutrients in the Czech Republic

Abstract Precipitation samples were collected in three-week periods at two sites (site I, Slapy Reservoir and site II, Rimov Reservoir) in the Czech Republic from 1979 to 1994. Chemical composition with an emphasis on concentrations and deposition rates of nutrients were evaluated on seasonal, annual, and long-term basis. Long-range transport dominated the atmospheric deposition at site I, whereas local sources were relatively more important at site II. The average annual bulk deposition rates were 10 and 14 kg ha−1 for total nitrogen (TN), 0.15 and 0.24 kg ha−1 for total phosphorus (TP), and 17 and 20 kg ha−1 fororganic carbon at sites I and II, respectively. NH4N was the major component of TN ( > 40%), NO3N represented ∼ 35%, and organic nitrogen contributed by ∼ 23% to the TN deposition. Concentrations and deposition rates of nutrients showed pronounced annual cycles; concentrations reached the maximum values in late winter and early spring, deposition rates from April to August. These cycles are explained by the seasonality of both precipitation and nutrient sources (agriculture, residential heating sources, pollen, soil dust). The concentrations and/or deposition rates of NH4N and N03N doubled and more than tripled, respectively, in the Czech Republic between 1958 and the mid- 1980s. The concentrations and deposition rates of sulphate decreased at site I already in the 1980s, probably as a result of the general trend of decreasing sulphur emission in Europe, while this trend was surpassed by local sources at site II. However, a sharp decline in both N and S concentrations and deposition rates occurred in the early 1990s, due to the reduced emissions of ammonia NOx and SO2 in Central European post-communist countries after the the 1989 political and economical changes.

Changes in bacterial community composition and microbial activities along the longitudinal axis of two canyon-shaped reservoirs with different inflow loading

Changes in microbial activities and bacterial community composition (BCC) were studied using fluorescence in situ hybridization (FISH) along the longitudinal axis of two canyon-shaped reservoirs with contrasting retention times and nutrient and organic matter loads. The reservoirs showed different specific longitudinal changes in plankton communities and BCC shifts that were related mainly to allochthonous input and longitudinal patterns of primary production and nutrient availability. The studied branch of the Orlík reservoir is entered by a large river and so had a short retention time (23 days) and a large allochthonous input. Primary production, bacterial abundance, bacterial production and protozoan bacterivory showed a consistent trend, decreasing gradually from the river inflow downstream. Overall, shifts in BCC were minor and statistically insignificant. The relatively large input of the river-borne allochthonous plankton communities and the short retention time of the reservoir probably limited the effect of the autochthonous in-reservoirs processes. In contrast, the Římov reservoir has a long retention time (∼100 days) and had a limited input of allochthonous organic matter to its lacustrine area. The autochthonous processes of primary and bacterial production were tightly linked and they showed peaks in the middle part of the studied stretch. This together with a trend of downstream decreasing nutrient concentrations and increasing protistan grazing pressure seem to support the development of specific BCC in the lacustrine part of the reservoir that significantly differed from that in river inflow. Apart from the marked differences between the limnological variables of reservoirs we found some commonalties in BCC – in both systems the phylogenetic groups of β-Proteobacteria and Cythophaga/Flavobacterium clearly dominated bacterioplankton assemblages. %

Trophic structure of nine Czech reservoirs regularly stocked with piscivorous fish

For nearly 20 years, most Czech reservoirs supplying drinking water have been under statutory protection which permitted reservoir managers to manipulate fish stocks in order to maintain a sustainable water quality. The most common biomanipulative measure adopted was stocking with piscivorous fish (mostly 5 cm fry) using an annual stocking level of approx. 25 000 fish per reservoir. Nine reservoirs were studied for signs of top-down food web effects, as predicted by the trophic cascade hypothesis based on levels of total phosphorus (TP), chlorophyll a (Chl a), zooplankton biomass (ZB) and zooplankton community structure. In all nine reservoirs, only small Daphnia species were recorded, such as D. galeata and D. cucullata. The proportion of large-bodied daphnids retained on a 0.71 mm sieve was less than 10% of the total crustacean biomass in all reservoirs. The relationship of Chl a level – TP, and of ZB – Chl a, was positive under enhanced piscivory and did not differ statistically from the relationships in other reservoirs with natural fish stocks. This implies that bottom-up forces remained stronger than top-down ones in the studied reservoirs, despite the stocking of piscivorous fish. The failure of this attempt at biomanipulation may be due to an insufficient stocking rate of predatory fish and/or inadequate data on the resident planktivorous fish levels.

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.

Trends in aluminium export from a mountainous area to surface waters, from deglaciation to the recent: Effects of vegetation and soil development, atmospheric acidification, and nitrogen-saturation

We reconstructed the history of terrestrial export of aluminium (Al) to Plesné Lake (Czech Republic) since the lake origin approximately 12,600 year BC, and predicted Al export for 2010-2050 on the basis of previously published and new data on mass budget studies, palaeolimnological data, and MAGIC modelling. We focused on three major Al forms; ionic Al (Al(i)), organically-bound Al (Al(o)), and particulate Al hydroxide [Al(OH)(3)]. In early post-glacial time, Plesné Lake received high terrestrial export of Al, but with a minor proportion of Al(OH)(3) (4-25 microM), and concentrations of Al(i) and Al(o) were negligible. Since the forest and soil development ( approximately 9900-9000 year BC), erosion has declined and soil organic acids increased export of Al(o) from soils. The terrestrial Al(o) leaching ( approximately 7.5 microM) persisted throughout the Holocene until the industrial period. Then, Al(i) concentrations continuously increased (up to 28 microM in the mid-1980s) due to atmospheric acidification; the Al(i) leaching was mostly associated with sulphate. The proportion of Al(i) associated with nitrate has been increasing since the beginning of lake recovery from acidification after approximately 1990 due to reduction in sulphur deposition and nitrogen-saturation of the catchment, leading to persistent nitrate leaching. Currently, nitrate has become the dominant strong acid anion and the major Al(i) carrier. Al(o) (5.5 microM) is predicted to dominate Al concentrations around 2050, but the predicted Al(i) concentrations ( approximately 4 microM) are uncertain because of uncertainty associated with the future nitrate leaching and its effect on soils.