The development and validation of remote-sensing-based approaches for the retrieval of chromophoric dissolved organic matter (CDOM) concentrations requires a comprehensive understanding of the sources and magnitude of variability in the optical properties of dissolved material within lakes. In this study, spatial and seasonal variability in concentration and composition of CDOM and the origin of its variation was studied in Lake Balaton (Hungary), a large temperate shallow lake in central Europe. In addition, we investigated the effect of photobleaching on the optical properties of CDOM through in-lake incubation experiments. There was marked variability throughout the year in CDOM absorption in Lake Balaton (aCDOM(440) = 0. 06–9.01 m−1). The highest values were consistently observed at the mouth of the main inflow (Zala River), which drains humic-rich material from the adjoining Kis-Balaton wetland, but CDOM absorption decreased rapidly towards the east where it was consistently lower and less variable than in the westernmost lake basins. The spectral slope parameter for the interval of 350–500 nm (SCDOM(350–500)) was more variable with increasing distance from the inflow (observed range 0.0161–0.0181 nm−1 for the mouth of the main inflow and 0.0158–0.0300 nm−1 for waters closer to the outflow). However, spatial variation in SCDOM was more constant exhibiting a negative correlation with aCDOM(440). Dissolved organic carbon (DOC) was strongly positively correlated with aCDOM(440) and followed a similar seasonal trend but it demonstrated more variability than either aCDOM or SCDOM with distance through the system. Photobleaching resulting from a 7-day exposure to natural solar UV radiation resulted in a marked decrease in allochthonous CDOM absorption (7.04 to 3.36 m−1, 42 % decrease). Photodegradation also resulted in an increase in the spectral slope coefficient of dissolved material.

A microalgal biomass offers a potential alternative to the maize silage commonly used in biogas technology. In this study, photoautotrophically grown Scenedesmus obliquus was used as biogas substrate. This microalga has a low C/N ratio of 8.5 relative to the optimum 20-30. A significant increase in the ammonium ion content was not observed. The methane content of the biogas generated from Sc. obliquus proved to be higher than that from maize silage, but the specific biogas yield was lower. Semi-continuous steady biogas production lasted for 2 months. Because of the thick cell wall of Sc. obliquus, the biomass-degrading microorganisms require additional time to digest its biomass. The methane concentration in the biogas was also high, in co-digestion (i.e., 52-56%) as in alga-fed anaerobic digestion (i.e., 55-62%). These results may be related to the relative predominance of the order Clostridiales in co-digestion and to the more balanced C/N ratio of the mixed algal-maize biomass. Predominance of the order Methanosarcinales was observed in the domain Archaea, which supported the diversity of metabolic pathways in the process. (C) 2015 The Authors. Published by Elsevier B.V.

Cylindrospermopsis raciborskii is becoming a major concern among cyanobacteria, due to its potential ability to produce toxic metabolites. We assessed the cytotoxic potential of four C. raciborskii strains (ACT 9502, ACT 9503, ACT 9504 and ACT 9505) isolated from Lake Balaton (Hungary), by lactate dehydrogenase (LDH) leakage measurements and by detecting morphological alterations in CHO-K1 (Chinese Hamster Ovary) cells. The Australian AQS (cylindrospermopsin producer) strain of C rac-iborskii and purified cylindrospermopsin (CYN) were used as positive references in both the biochemical and morphological studies. Chemical analysis for known cyanotoxins was performed on aqueous extracts of ACT and AQS strains by the HPLC-MS technique.Comparing threshold values of LDH leakage data, different toxic potentials of cyanobacterial extracts are suggested in short term (3 h) and long (24 h) exposure regimes. In the acute (3 h) experiments the aqueous extract of the ACT 9505 strain proved to be most toxic (EC50 = 7.4 mg mL(-1)), while after 24 h the ACT 9504 extract was the most effective (EC50 = 0.65 mg mL(-1)). The extract of the AQS strain and the purified CYN exerted most of their toxic effects after 3 h exposure (EC50 0.74 mg mL(-1), and 0.9 pg mL(-1) respectively). The morphological changes of CHO-K1 cells induced by the crude extracts of the ACT strains included fragmentation of the actin filaments then relocation of the depolymerized actin to the perinuclear region, resulting cell rounding and loss of adhesion. Exposure of CHO-K1 cells to the crude extract of the AQS strain, moreover, resulted cell shrinking and formation of filopodia, i.e. distinctly different cytological alterations from that induced by the ACT extracts and the purified CYN.Chemical analysis of the cyanobacterial crude extracts confirmed the presence of cylindrospermopsin in the extract of the AQS strain (8.5 mg CYN g(-1), dry weight), and none of the presently known cyanotoxins have been analytically confirmed in the extracts of the ACT strains isolated from the Lake Balaton.Although significant toxicity of all four ACT C raciborskii strains is confirmed by both biochemical and morphological studies, our results also pointed out the necessity of further studies to identify the toxic, but still unknown metabolic components produced by these cyanobacterial members of the phytoplankton communities. (C) 2011 Published by Elsevier Ltd.

Termeszetes fitoplankton tomegprodukcio soran gyűjtott mintak es hazai cianobakterium torzsek in vivo toxikologiai elemzese (THAMNOTOX-F, ArTox, DAPHTOX-FTM, ToxAlert 100) ill. in vitro biomarker meresei bizonyitjak, hogy sporadikusan mind a Balatonban mind a Kis-Balaton teruleten megjelenhetnek potencialisan toxikus algatorzsek. A Balatonbol izolalt Cylindrosprmopsis raciborskii torzsek toxikus mechanizmusai a mert biokemiai parameterek (LDH, GST szintek, AchE gatlas) alapjan elternek a cilindrospermopszint termelő ausztral C. raciborskii (AQS) torzs hatasatol, es jobban hasonlitanak az anatoxinokat termelő Oscillatoria (PCC 6505) torzsre. Puhatestű neuronokon kapott elektrofiziologiai eredmenyek (az algakivonatok kolinerg receptorblokkolo, esetenkent AchE gatlo hatasa) is a PCC torzs hatasahoz merhető. In vitro, CHO-K1 sejttenyeszeten vegzett eletkepessegi tesztek es a sejtvaz szerkezeteben kialakulo degenerativ valtozasok rovid-es hosszutavu (feltehetően elterő bioaktiv komponensek vagy mechanizmusok reven) kialakulo citotoxikus hatasokat is kimutattak. Molekularis genetikai vizsgalatok szerint a balatoni C. raciborskii torzsek nem termelnek cilindrospermopszint, es analitikai vizsgalatok sem igazoltak eddig ismert cianotoxinok (anatoxin-a, anatoxin-a(S) vagy szaxitoxinok) jelenletet. Az in vivo es in vitro tesztek szerint okozott toxicitas igy feltehetően egyeb, eddig nem azonositott toxikus metabolitok jelenletenek, illetve ezek szinergista hatasanak koszonhetőek. | Cyanobacterial bloom samples and endogenous cyanobacterial isolates were assessed for environmental risk by a battery of in vivo toxicity tests (THAMNOTOX-F, ArTox, DAPHTOX-FTM, ToxAlert 100) and in vitro biochemical assays of test animals. The results revealed the sporadic appearance of toxic strains of cyanobacteria in the lake Balaton and Kis-Balaton area. Biochemical data (LDH, GST and AchE levels) suggested different toxic mechanisms of the extracts of Cylindrospermopsis raciborskii isolates from the Lake Balaton compared with the cylindrospermopsin producing Australian C. raciborskii strains. The electrophysiological results on identified gastropod neurons showed similar features (cholinegic blocking and AchE inhibiting effects) with the extracts made from the anatoxin-a producing Oscillatoria (PCC 6505) strains. In vitro viability tests and morphological studies on CHO-K1 cell culture separated the short term and long term cytotoxic effects of the C. raciborskii strains, probably due to their different toxic components and target mechanisms. Molecular genetic studies did not prove the presence of cylindrospermopsin, neither analitical analysis showed any of the recently known cyanotoxins (anatoxin-a, anatoxin-a(s), saxitoxin) in the extracts of C. raciborskii strains from Balaton, suggesting that their in vivo and in vitro toxicity is the product of other, recently unidentified toxic substances and their likely synergistic interactions.