A mass-balance study on chloride fluxes in a large central European catchment during 1900–2010

Using data on long-term monitoring of water quality, mass budgets, and empirical models, we quantified chloride (Cl) leaching from major diffuse and point sources in a large central European catchment (upper Vltava river, Czech Republic) over a 110-year period (1900–2010), with the major aim to evaluate the influence of historical changes in land use and management practices on Cl leaching from agricultural land. The Cl input to farmland in synthetic fertilizers, livestock feed, and atmospheric deposition tripled in the 1950s–1980s (from 23 to 64 kg ha^?1 year^?1 on average), and then abruptly decreased to ~14 kg ha^?1 year^?1 during 1990–2010. The proportion of drained agricultural land rapidly increased from 4 % in the 1950s to its maximum of 43 % in the 1990s. Until the 1950s, the Cl leaching from agricultural land followed a simple dose–response function. Then, agricultural soils retained on average 16 ± 4 kg ha^?1 year^?1 of Cl during 1959–1985, when the most important changes in land use and management practices occurred, and subsequently became a net Cl source of 11 ± 3 kg ha^?1 year^?1 on average during 1986–2010, when Cl input to soils declined and drainage of new land ceased. Our data suggest that the temporal changes in the Cl storage in agricultural land are associated with changes in Cl concentrations in both permanent soil water and soils. Physico-chemical conditions in freshly drained soils, namely elevated aeration and high concentrations of soil organic matter (SOM), and high Cl inputs probably resulted in a Cl immobilization in soils by formation of organic chlorine (Cl_org) and adsorption that was higher than the Cl production from Cl_org mineralization and desorption. In contrast, Cl_org mineralization and Cl desorption exceeded the Cl retention during the consecutive period of low Cl inputs and decreasing SOM concentrations in agricultural soils. Our study implies that changes in land use and agricultural management can significantly affect dose–response functions even for Cl, which is traditionally considered and modelled as a conservative ion.     

Are Bacteria the Major Producers of Extracellular Glycolytic Enzymes in Aquatic Environments?

In aquatic microbial ecology, it has been considered that most extracellular enzymes except phosphatases are of bacterial origin. We tested this paradigm by evaluating the relationship between bacterial cell number and the activity of three glycolytic enzymes from 17 fresh waters and also from a laboratory experiment. Our large sets of pooled data do not seem to support such a simple explanation, because we found only a weak correlation of bacterial number with activity of α‐glucosidase (r_s = 0.63), β‐glucosidase (r_s = 0.45), and β‐N‐acetylhexosaminidase (r_s = 0.44). We also tested relations of the enzymatic activities to potential sources of natural substrates: dissolved organic carbon (DOC) and phytoplankton (as chlorophyll a). Their correlations with the enzymatic activities tested were very weak or insignificant. On the other hand, we found evidence for distinct producers of extracellular enzymes by analysing enzyme kinetics. The kinetics usually did not follow the simple Michaelis‐Menten model but a more complex one, indicating a mixture of two enzymes with distinct affinity to a substrate. In combination with size fractionation, we could sometimes even distinguish three or more different enzymes. During diatom blooms, the diatom biomass tightly correlated with β‐N‐acetylhexosaminidase activity (>4 μm fraction). We also documented very tight relationships between activity of both glucosidases and dry weight of Daphnia longispina (r_s = 1.0 and 0.60 for α‐ and β‐glucosidases, respectively) in an alpine clear‐water lake. Our data and evidence from other studies indicate that extracellular glycosidic activities in aquatic ecosystems cannot generally be assigned only to bacteria. Also invertebrate animals and other eukaryotes (fungi, diatoms, protozoa etc.) should be considered as potentially very important enzyme producers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effect of Outflow Depth on Phosphorus Retention in a Small,Hypertrophic Temperate Reservoirwith Short Hydraulic Residence Time

Stratification and phosphorus fluxes (input, output, sedimentation, and release from sediments) were studied in České údolí Reservoir (49°43′N, 13°21′E; V – 2.65 × 10⁶ m³; A – 1.04 × 10⁶ m²; z_max – 5.5 m; surface altitude – 314 m a.s.l.) during two summer stratification periods which differed in outlet operation and in hydraulic residence time (1997: surface outlets and 14 days; 1998: bottom outlets and 23 days). Use of bottom outlets resulted in weaker thermal stratification, a less pronounced oxygen deficit in the hypolimnion, and significantly lower P retention (17%) in comparison with surface discharge (42%). Factors apparently contributing to lower retention of P during the use of bottom outlets were: (i) faster flushing of the hypolimnion which intensified longitudinal transport of particles, (ii) more intense P release from sediments due to a lower concentration of nitrate in the water column and to more frequent contact of sediments in the shallows with water of pH >9. During both periods, phytoplankton production was limited only by light, not by nutrients. Phytoplankton biomass was comparable in both years despite some differences in vertical distribution.     

Long-term antibiotic susceptibility pattern of strains of Neisseria gonorrhoeae isolated in Czechoslovakia in the years 1957-1982

Over the past 25 years a total of 7492 strains of Neisseria gonorrhoeae have been isolated in Czechoslovakia, mainly in Prague (64%). All these strains have been tested for susceptibility to the following antibiotics: penicillin G, ampicillin, tetracycline, spectinomycin, erythromycin, doxycycline, kanamycin, rifampin, chloramphenicol, gentamicin, cephalothin, cephaloridine, lincomycin and clindamycin. In addition, seven derivatives of newer antibiotics of penicillin and cephalosporin series were tested in 1981. The study showed that in 1957 the MIC of 0.03 units of penicillin per ml was effective against 95% of strains, but in 1981 only 37% of isolates were sensitive to this concentration. The first gonococcal strains with the MIC value of 4.0 units/ml to penicillin were detected in 1981. This tendency towards decreased gonococcal susceptibility to benzylpenicillin is alarming. Over the last eight years there have been described sporadic isolations of strains relatively resistant to tetracycline (MIC = 8.0 mg/l). The susceptibility to spectinomycin has been tested in over 4000 gonococcal strains, since 1967. The test showed that this antibiotic remained highly effective against the gonococcal infection with over 95% of gonococci with the MIC value of 16.0 mg/l. No fully spectinomycin resistant strains have been found. Penicillin G as well as spectinomycin and cefotaxim are still considered the antibiotics of the first choice in the treatment of gonorrhoea. The alternative antibiotics may include cefuroxim, chloramphenicol and, in cases of sensitive strains, tetracyclines.     

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.     

Quantifying nitrogen leaching from diffuse agricultural and forest sources in a large heterogeneous catchment

Using mass budget and hydrological models, we quantified the contribution of major diffuse nitrogen (N) sources to surface water loading in a large heterogeneous catchment (upper Vltava river, Czech Republic, about 13,000 km²) over the last 52 years. The catchment reflects the typical development in central and eastern European countries, which witnessed socio-economic shifts from a market to a planned economy in the 1950s and back to a market economy in the 1990s. The former shift was accompanied by increasing N inputs to agricultural and forest areas with ranges for the 1950–1980s of 60–160 and 14–30 kg ha^?1 year^?1, respectively, and with intensive draining of waterlogged farmland. The shift in the 1990s resulted in ~40 and ~50 % reduction of N inputs to agricultural areas and forests, respectively, and farmland draining ceased. The N exports from agricultural land (E _AL ) and from forests (E _FO ) varied within 3–45 and 1.6–7.1 kg ha^?1 year^?1, respectively (with maxima in the 1980s). The E _AL and E _FO fluxes exhibited several similar patterns, being dominated by NO₃-N, increasing with N inputs, and having similar inter-annual variability related to hydrology. The N losses from forests were stable (19 % of N input on average), while those from agricultural land increased from ~10 % in the 1960s up to 32 % in the 2000s, due probably to the previous extensive drainage and tillage of waterlogged fields and pastures. These land use changes reduced the water residence time in agricultural land and induced mineralization of soil organic matter. Continuing mineralization of soil organic N pools thus was the most probable reason for the remaining high E _AL fluxes despite a ~40 % reduction in N inputs to agricultural land, while the E _FO fluxes decreased proportionally to the decreasing N deposition during 1990–2010.     

Phosphorus uptake by suspended and settling seston in a stratified reservoir

Hydrobiologia - Total and abiotic P-uptake rates and P-uptake capacities of seston suspended in the water column and of entrapped settling seston were measured by a radiotracer method in the...     

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

Hydrobiologia - Changes in microbial activities and bacterial community composition (BCC) were studied using fluorescence in situ hybridization (FISH) along the longitudinal axis of two...     

The influence of nutrient loading,climate and water depth on nitrogen and phosphorus loss in shallow lakes: a pan-European mesocosm experiment

Coarse woody debris (CWD) represents a relatively stable habitat in many lakes with forested shorelines providing a living place for a wide range of species. The spatial complexity of CWD is recognized as an important factor promoting the abundance, diversity and productivity of littoral biota, mainly by providing shelters and moderating predator–prey interactions. However, little is as yet known on the response of different species to various levels of CWD complexity and the effects of the spatial arrangement of CWD on the connectivity between littoral populations. It is also unclear how CWD decay, which modifies the surface complexity of wood and the quality of food, affects the diversity of wood-associated species and trophic interactions. Further research is also needed to recognize the contribution of littoral wood to carbon sequestration and nutrient fluxes, considering factors affecting the CWD decay rate, such as wood species and environmental conditions. CWD resources are systematically depleted by shoreline development which leads to disruptions in the functioning of lake ecosystems. Attempts at restoring CWD habitat provided ambiguous effects on littoral species and therefore better understanding of the role of CWD in lake ecosystems is crucial to the development of successful restoration projects and effective management programmes.     

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.