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, Ple?né jezero (Ple?né 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 Ple?né watershed was an average net source of 25 mmol SO ₄ ^2? 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 NO ₃ ^? 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 SO ₄ ^2? 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 NO ₃ ^? , ionic Al (Al_i), 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). NO ₃ ^? assimilation and denitrification, photochemical and microbial decomposition of allochthonous organic acids, and SO ₄ ^2? 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 Al_i 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 Al_i. 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 NH ₄ ⁺ due to a cease in nitrification (pH < 5) and from NH ₄ ⁺ production by dissimilation exceeding its removal by assimilation.     

Antimicrobial profile of ceftazidime: the situation in three larger hospitals in Prague between 1981 and 1983

As a part of preclinical trials of 2,996 clinical isolates from three larger hospitals in Prague were qualitatively and quantitatively assayed for in vitro sensitivity to ceftazidime. In gramnegative bacteria the incidence of resistance to ceftazidime in strain of Enterobacter, Serratia Proteus and Pseudomonas species ranged from 4% to 6% of strains. In grampositive bacteria only strains of enterococci, listeriae and anaerobic bacteria are excluded from the action of this broad-spectrum antibiotic. According to present experiences the antipseudomonal activity of ceftazidime is approximately the same as that of cefsulodine and cefoperazone. Alarmingly, one of the Pseudomonas aeruginosa isolates was found to show a distinct multiresistance to all available lactam, aminoglycoside and broad-spectrum antimicrobials, including ceftazidime.     

Evaluation of the long term monitoring of phytoplankton assemblages in a canyon-shape reservoir using multivariate statistical methods

Hydrobiologia - Long term monitoring of the Římov Reservoir provided a data set for the analysis of phytoplankton composition and biomass in coincidence with physical, chemical,...     

Distribution of the bathypelagic perch fry layer along the longitudinal profile of two large canyon-shaped reservoirs

The distribution of the bathypelagic perch Perca fluviatilis fry (BPF) layer and its qualitative and quantitative changes were studied along the longitudinal profiles of the large canyon-shaped Slapy and Orlík Reservoirs (Czech Republic), using acoustic methods (SIMRAD EY500 echosounder, split-beam transducer, Sonar5 post-processing software). In Slapy Reservoir (sampled in late May), the BPF layer created by the mass of non-shoaling perch larvae and juveniles (average total length, L _T, 10·4 mm) was recorded from the dam for 29 km upstream. The BPF layer only vanished in the upper third of the reservoir due to the extremely cold hypolimnetic water discharged from Orlík Reservoir, which is situated upstream in the cascade. Both abundance and size of BPF increased significantly upstream following, in Slapy Reservoir, the trophic gradient. In Orlík Reservoir (sampled in late June), the BPF layer was created predominantly by shoaling perch fry individuals (average L _T 31·8 mm), recorded along the whole longitudinal profile of the reservoir (>50 km, filled with relatively warm water). Both the sizes of BPF and their shoaling activity again increased significantly from the dam towards the inflow following, in Orlík Reservoir, the trophic gradient. Pooling the data from both reservoirs, it was evident that the tendency to flock in a dense layer and, much later, to create distinct shoals, increased continuously with the size of BPF. A number of variables describing the BPF layer in Slapy and Orlík Reservoir are given.     

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.     

Seasonal strengths of the abiotic and biotic drivers of a zooplankton community

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

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.Heterotrophic bacterioplankton assemblages found in a broad variety of freshwater ecosystems are frequently dominated by representatives of a few phylogenetic clusters of Betaproteobacteria and Actinobacteria (1, 7, 9, 17, 21, 23, 34, 40). One of these clusters is the phylogenetically defined R-BT065 group (34), which is currently represented by >700 environmental ribosomal sequences deposited in the GenBank database. These sequences were obtained in several nonquantitative diversity studies of many European and North American freshwater habitats (5, 10, 18, 27, 30, 42). The R-BT065 cluster is characterized by a minimum level of intragroup 16S rRNA sequence similarity of 97.3%, and investigations of recently cultivated strains demonstrated that members of the group are heterotrophic bacteria (V. Kasalický, J. Jezbera, K. Šimek, and M. W. Hahn, submitted for publication). This cluster forms a phylogenetically distinct subgroup of the so-called “Rhodoferax sp. BAL47” cluster (42). The new genus Limnohabitans was recently established for some strains affiliated with the “Rhodoferax sp. BAL47” cluster (11), and it has to be assumed that bacteria belonging to the R-BT065 cluster are also affiliated with this genus (Kasalický and coworkers, submitted for publication).Bacteria belonging to the R-BT065 cluster in natural systems can be quantified using a homonymous fluorescence in situ hybridization (FISH) probe (34). This probe enabled intensive investigations of the ecology of R-BT065 bacteria; however, only a few freshwater systems (mainly representing larger pH-neutral lakes and reservoirs) have been quantitatively investigated to determine the presence of this bacterial group so far (2, 13, 24, 27, 30, 30). In the few habitats investigated, R-BT065 bacteria comprised 3 to 50% of the total bacteria. Importantly, these bacteria consistently had the highest net growth rates and showed high levels of substrate uptake in a freshwater reservoir (12, 13, 31, 32), as well as in an alpine lake (27). These investigations indicated that the ecology of the R-BT065 group is rather uniform and is characterized by (i) the potential for a rapid response to environmental changes, (ii) a high level of vulnerability to flagellate predation (14, 35), and (iii) a strong link with phytoplankton-derived organic material as the key growth substrate for the bacteria (24, 25, 33). However, these findings were based on quantitative investigations of only a few freshwater systems, and we can only speculate that the findings could be generalized for populations of this bacterial group in systems with different limnological characteristics. In particular, investigations of the habitat range, as well as investigations of environmental factors modulating the abundance of R-BT065 bacteria, have not been performed. Therefore, we set out to conduct a comprehensive survey of a broad variety of freshwater habitats that could support our hypothesis concerning the potential general importance of the cluster.The specific aims of this study were (i) to quantify the R-BT065 bacteria in the surface waters of a large variety of central European freshwater ecosystems (102 habitats) spanning broad ranges of system type and size (from large and deep alpine lakes to small and shallow ponds or various fishponds), type of bedrock, altitude, trophic status, pH, and humic substance content; (ii) to determine the proportion of R-BT065 bacteria in the total bacteria and in the total Betaproteobacteria in these habitats using FISH probes; and (iii) to suggest major physical, chemical, and biological factors that influence the occurrence of the R-BT065 phylotypes in the bacterioplankton.     

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

Fluxes of major ions and nutrients were measured in the watershed-lake ecosystem of a strongly acidified lake, ?ertovo jezero (?ertovo 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, ?ertovo watershed was an average net source of 23 mmol m^?2 yr^?1 of SO ₄ ^2? . 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 SO ₄ ^2? 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 NO ₃ ^? , base cations, DOC, and ionic Al (Al_i) 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, SO ₄ ^2? 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 Al_i was the dominant H⁺ generating process (96 mmol H⁺ m^?2 yr^?1) in ?ertovo Lake. Photochemical liberation from organic complexes was an additional in-lake source of Al_i. The net in-lake retention or removal of nutrients (carbon, phosphorus, nitrogen, and silica) varied between 18% and 34% of their inputs.