Attila W. Kovács

Hungarian Academy of Sciences, Budapeŝto, Budapest, Hungary

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Publications (15)25.71 Total impact

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    ABSTRACT: Despite longstanding contributions to oceanography, similar use of fluorescence light detection and ranging (LiDAR) in lake settings is not routine. The potential for ship-mounted, multispectral Ultraviolet Fluorescence LiDAR (UFL) to provide rapid, high-resolution data in variably turbid and productive lake conditions are investigated here through a series of laboratory tank and field measurements carried out on Lake Balaton, Hungary. UFL data, calibrated empirically to a set of coinciding conventionally-analyzed samples, provide simultaneous estimates of three important parameters-chlorophyll a(chla), total suspended matter (TSM) and colored dissolved organic matter (CDOM). Successful UFL retrievals from both laboratory and field measurements were achieved for chla (0.01–378 mg·m −3 ; R = 0.83–0.92), TSM (0.1–130 g·m −3 ; R = 0.90–0.96) and CDOM (0.003–0.125 aCDOM(440); R = 0.80–0.97). Fluorescence emission at 685 nm is shown through tank measurements to display robust but distinct relationships with chla concentration for the two cultured algae species investigated (cyanobacteria, OPEN ACCESS Remote Sens. 2013, 5 4406 Cylindrospermopsis raciborskii, and chlorophyta, Scenedesmus armatus). The ratio between fluorescence emissions measured at 650 nm, related to the phycocyanin fluorescence maximum, to that at 685 nm is demonstrated to effectively distinguish these two species. Validation through both laboratory measurements and field measurements confirmed that site specific calibration is necessary. This study presents the first known assessment and application of ship-mounted fluorescence LiDAR in freshwater lake conditions and demonstrates the use of UFL in measuring important water quality parameters despite the more complicated hydro-optic conditions of inland waters.
    Remote Sensing 09/2013; 5:4405-4422. · 2.10 Impact Factor
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    ABSTRACT: E-Mails: kovacs.attila@okologia.mta.hu (A.W.K.); zlinszky.andras@okologia.mta.hu (A.Z.); presing.matyas@okologia.mta.hu (M.P.); horvath.hajnalka@okologia.mta.hu (H.H.); toth.viktor@okologia.mta.hu (V.R.T.) 2 Centre for Landscape and Climate Research, University of Leicester, Bennett Building, University Road, Leicester LE1 7RH, UK; E-Mails: vnp2@leicester.ac.uk (V.N.-P.); hb91@leicester.ac.uk (H.B.) 3 Shirshov Institute of Oceanology, Russian Academy of Sciences, 36 Nahimovsky Prospect Avenue, Moscow 117997, Russia; E-Mails: vvpelevin@gmail.com (V.V.P.); gosha_stv@mail.ru (I.G.) Abstract: Despite longstanding contributions to oceanography, similar use of fluorescence light detection and ranging (LiDAR) in lake settings is not routine. The potential for ship-mounted, multispectral Ultraviolet Fluorescence LiDAR (UFL) to provide rapid, high-resolution data in variably turbid and productive lake conditions are investigated here through a series of laboratory tank and field measurements carried out on Lake Balaton, Hungary. UFL data, calibrated empirically to a set of coinciding conventionally-analyzed samples, provide simultaneous estimates of three important parameters-chlorophyll a(chla), total suspended matter (TSM) and colored dissolved organic matter (CDOM). Successful UFL retrievals from both laboratory and field measurements were achieved for chla (0.01–378 mg·m −3 ; R = 0.83–0.92), TSM (0.1–130 g·m −3 ; R = 0.90–0.96) and CDOM (0.003–0.125 aCDOM(440); R = 0.80–0.97). Fluorescence emission at 685 nm is shown through tank measurements to display robust but distinct relationships with chla concentration for the two cultured algae species investigated (cyanobacteria, OPEN ACCESS Remote Sens. 2013, 5 4406 Cylindrospermopsis raciborskii, and chlorophyta, Scenedesmus armatus). The ratio between fluorescence emissions measured at 650 nm, related to the phycocyanin fluorescence maximum, to that at 685 nm is demonstrated to effectively distinguish these two species. Validation through both laboratory measurements and field measurements confirmed that site specific calibration is necessary. This study presents the first known assessment and application of ship-mounted fluorescence LiDAR in freshwater lake conditions and demonstrates the use of UFL in measuring important water quality parameters despite the more complicated hydro-optic conditions of inland waters.
    · 2.10 Impact Factor
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    ABSTRACT: Phycocyanin (PC) is one of the water-soluble accessory pigments of cyanobacteria species, and its concentration in aquatic systems is used to estimate the presence and relative abundance of blue-green algae. PC concentration and the PC/Chl-a ratio of four N2-fixing filamentous cyanobacteria strains (Cylindrospermopsis raciborskii, Anabaena spiroides, Aphanizomenon flos-aquae and Aphanizomenon issatschenkoi) common to Lake Balaton (Hungary) were determined using repeated freezing and thawing. A strong linear correlation was found between the extracted PC and Chl-a concentrations for all strains at high Chl-a concentrations (almost stable PC/Chl-a ratio in the range of 20−100 µg l−1 Chl-a). Extraction of PC and Chl-a from samples with low biomass of cyanobacteria (less than 20 µg l−1 Chl-a) proved to be unreliable using the standard protocol of freeze–thaw cycles (coefficients of variation exceeding 10–15%). In order to find an extraction method that is robust in fresh waters characterized by low algae biomass (e.g. Lake Balaton), the effectiveness of four extraction methods (repeated freeze–thaw method and homogenization with mortar and pestle, Ultrasonic, and Polytron homogenizer) were compared using C. raciborskii. It was found that the efficiency of extraction of phycocyanin was highest when a single freeze–thaw cycle was followed by sonication (25% additional yield compared with using the freeze–thaw method alone). Applying this combined method to surface water samples of Lake Balaton, a strong correlation was found between PC concentration and cyanobacterial biomass (R 2 = 0.9436), whilst the repeated freezing–thawing method found no detectable PC content. Here we show that the combined sonication/freeze–thaw method could be suitable for measuring filamentous cyanobacteria PC content, even at low concentrations; as well as for the estimation of cyanobacterial contribution to total biomass in fresh waters.
    European Journal of Phycology 01/2013; 48(3). · 1.91 Impact Factor
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    Kovács AW, Tóth VR, Vörös L
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    ABSTRACT: Cyanobacteria are a worldwide group of photosynthetic prokaryotes that can cause nuisance blooms in eutrophic waters. It is generally accepted that their resting cells, akinetes, play an important role in the dispersal, recruitment, initiation of blooms and survival under unfavourable conditions, therefore information on the germination, distribution and abundance of akinetes in natural sediments is essential for understanding the ecology and bloom dynamics of N2-fixing cyanobacteria. The present study describes the effect of irradiance on the germination and subsequent growth of N2-fixing filamentous cyanobacteria developed from natural akinete stock in sediment of Lake Balaton (Hungary) with varying phosphorous supply. The research focuses on the invasive Cylindrospermopsis raciborskii and Aphanizomenon flos-aquae the most abundant species of this lake. In the experiments, the germination of ten filamentous N2-fixing cyanobacteria species was observed. The species assemblages of the germinated cyanobacteria populations showed strong light and phosphorus dependence. Anabaena and Anabaenopsis species became dominant in phosphorous-rich conditions, while in phosphorus-deficient environments Aphanizomenon species and C. raciborskii dominated. Among the germinated filaments we have detected Anabaenopsis cunningtonii and Anabaena compacta, which have not been observed in Lake Balaton previously. Our results suggest that among the filamentous heterocytic cyanobacteria of this shallow lake the invasive C. raciborskii was the best competitor when phosphorus supply and irradiance were low.
    Annales de Limnologie - International Journal of Limnology 01/2012; 48(2):177-185. · 0.74 Impact Factor
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    ABSTRACT: Benthic algal communities can play an important role in matter and energy flux of shallow lakes. Their contribution to total primary production of lakes has been largely unexplored. The aim of this study was to estimate the primary production of the epipsammic algal communities at different water depths in Lake Balaton (Hungary) with photosynthetic measurements performed in laboratory. The photosynthesis of the benthic algae of different origin was studied at nine different irradiance levels, in three replicates. The maximum photosynthetic rate (P max) was always higher in samples from the shallow parts than those from the deeper regions of the lake. Along the west–east longitudinal axis of the lake P max decreased in the southern part and increased in the middle of the lake as a consequence of differences in the chlorophyll-a concentrations. Knowing P max, I k, global radiation and extinction coefficient, the primary production (mgCm−2day−1) of the epipsammic algal community was calculated at different water depths. In the shallow regions at 0.5 and 1m water depth 75–95% and 60–85% of the production was attributable to the epipsammon. The percentage contribution of epipsammon was at 2m water depth 20–65%. In the deeper pelagic region (>3m) more than 85% of the primary production originated from the phytoplankton. KeywordsEpipsammic algal communities-Laboratory measurement-Primary production- P max -Lake Balaton
    Hydrobiologia 01/2011; 660(1):17-27. · 1.99 Impact Factor
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    ABSTRACT: The aim of this research was to test whether NH4 + and NO3 − affect the growth, P demand, cell composition and N2 fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l−1 PO4-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l−1 NH4-N, 4,000 μg l−1 NO3-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH4 + and NO3 − supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N2-grown culture was significantly lower. The maximum specific growth rate of N2-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the P and energy requirement for heterocyte formation, nitrogenase synthesis and N2 fixation. N2 fixation was partially inhibited by NO3 − and completely inhibited by NH4 +. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH4 + or NO3 − is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies.
    Hydrobiologia 01/2009; 623(1):191-202. · 1.99 Impact Factor
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    ABSTRACT: Remote sensing has been used extensively to provide quantitative information on the distribution of phytoplankton in inland waters through the surrogate mapping of chlorophyll a, but as chlorophyll a is common to almost all species of phytoplankton it cannot provide any information on the taxonomic composition of phytoplankton communities. However, the varied optical properties of phytoplankton taxa may present a means to their discrimination via remote sensing data. This paper presents the results of an experimental study in which the spectral dissimilarities of brown, green, blue-green and red algae were examined with a view to establishing a basis upon which broad changes in phytoplankton communities might be monitored through remote sensing. Pseudo phytoplankton communities were simulated in a series of mesocosm experiments from which spectral reflectance measurements were acquired. The results demonstrated that the phytoplankton colour groups examined were indeed spectrally dissimilar. The spectral distinction between colour groups was noted to be greatest at high concentrations of chlorophyll a and between pseudo-communities dominated by a single species; spectral differences were lower in mixed pseudo-communities with co-dominant species. Moreover, it proved possible to quantify the concentration of two potential biomarker pigments, fucoxanthin and C-phycocyanin, through the derivation of simple spectral indices. The coincidental presence of varying concentrations of SPM (SPIM and SPOM) caused significant attenuation of the spectral response of the pseudo-communities and affected the accuracy of biomarker pigment estimation. It is considered that the realisation of a remote sensing technique for the discrimination of phytoplankton taxa in inland waters would be an extremely useful tool for limnological research and water resource management and thus the future application of this research to inland waters is also discussed.
    Remote Sensing of Environment. 01/2008;
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    ABSTRACT: Since the middle of 1990s the trend of Lake Balaton towards an increasingly trophic status has been reversed, but N2-fixing cyanobacteria are occasionally dominant, endangering water quality in summer. The sources of nitrogen and its uptake by growing phytoplankton were therefore studied. Experiments were carried out on samples collected from the middle of the Eastern (Siófok) and Western (Keszthely) basins between February and October 2001. Ammonium, urea and nitrate uptake and ammonium regeneration were measured in the upper 5-cm layer of sediment using the 15N-technique. Ammonium was determined by an improved microdiffusion assay. N2 fixation rates were measured by the acetylene-reduction method. Ammonium regeneration rates in the sediment were similar in the two basins. They were relatively low in winter (0.13 and 0.16 µg N cm−3 day−1 in the Eastern and Western basin, respectively), increased slowly in the spring (0.38 and 0.45 µg N cm−3 day−1) and peaked in late summer (0.82 and 1.29 µg N cm−3 day−1, respectively). Ammonium uptake was predominant in spring in the Eastern basin and in summer in the Western basin, coincident with the cyanobacterial bloom. The amount of N2 fixed was less than one third of the internal load during summer when external N loading was insignificant. Potentially, the phytoplankton N demand could be supported entirely by the internal N load via ammonium regeneration in the water column and sediment. However, the quantity of N from ammonium regeneration in the upper layer of sediment combined with that from the water column would limit the standing phytoplankton crop in spring in both basins and in late summer in the Western basin, especially when the algal biomass increases suddenly.
    12/2007: pages 87-95; · 1.99 Impact Factor
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    ABSTRACT: Ammonium and nitrate uptake and N2-fixation of the heterocystous cyanoprokaryote Cylindrospermopsis raciborskii was examined in continuous cultures under different nitrogen concentrations and dilution rates using the 15N technique. It was found that at luxury phosphorus supply (5 mg PO4-P l–1) the biomass was similar in all cultures irrespective of the amount and portioning (continuous or pulsed) of available nitrogen forms. The added ammonium and nitrate was fully taken up by C. raciborskii and the remaining nitrogen demand was met by N2-fixation. Different ammonium concentrations (300, 750, 1500 and 3000 g 15N l–1) added at the same dilution rate did not affect the growth of C. raciborskii. In the culture supplied with pulsed ammonium, N2-fixation was detected prior to ammonium addition only. After the ammonium pulse, the N2-fixation continued for a while then decreased and stopped. In addition, the inflowing ammonium was fully taken up by the organism. The rate of nitrogen fixation reached its original level after 8–24 hours, depending on the dilution rate. It can be suggested that the nitrogen fixation system stopped and was then activated again depending on the nitrogen content of the cells.
    Hydrobiologia 10/2003; 506-509(1):169-174. · 1.99 Impact Factor
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    ABSTRACT: Morphological characteristics of Cylindrospermopsis raciborskii were investigated in batch culture under P-starvation and in continuous cultures at two growth rates with different N forms. The species displayed an enormous morphological variability under controlled condition. In the P-starved batch culture very short and extreme morphology trichomes with conical or drop-shape heterocytes were formed. In continuous culture extremely long, twisted filaments were found near the maximum growth rate. Rarely, C. raciborskii formed intercalary heterocytes.
    Hydrobiologia 10/2003; 506-509(1):163-167. · 1.99 Impact Factor
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    ABSTRACT: Between 1996 and 1998 phytoplanktonic primary production and bacterioplankton production were measured monthly at five sampling stations in the lower Kis-Balaton reservoir. The open water area of the reservoir was rich in phytoplankton and had hypertrophic characteristics, but inside the reed stand (80% of the surface area) phytoplankton biomass and production were substantially (30–50 times) lower. The algal removal efficiency of the lower Kis-Balaton reservoir was 96%. The reservoir had a considerably smaller effect on bacterioplankton removal than on the phytoplankton. The decrease of biomass and production of bacterioplankton in the through-flowing water was approximately 60%. Inside the reed stand the biomass and the production of planktonic bacteria exceeded that of the phytoplankton by several times, suggesting that the release of biodegradable dissolved organic (humic) substances from macrophytes stimulated the metabolism of bacterioplankton. The significant reduction of phytoplankton inside the dense reed stand was primarily the result of the shading effect of the reeds. In the open water area a shading experiment demonstrated that a 1-week residence period for planktonic algae in the reed-covered area was sufficient for their complete elimination. The decomposition of planktonic algae, reed material and the lack of primary production inside the reed stand created oxygen-deficient and phosphorus-rich conditions during the vegetative period. These results suggest that reed-covered water bodies can effectively retain suspended solids and planktonic algae, but because of decomposition processes they cannot retain biologically-available phosphorus.
    Aquatic Botany 01/2003; 77(2):99-110. · 1.59 Impact Factor
  • Attila W. Kovács, Eszter Koncz, Lajos Vörös
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    ABSTRACT: The progressive eutrophication of Lake Balaton was perceived in the early 1970s. From 1975 to 1994, the development of summer blooms of N&2inf;-fixing cyanobacteria, especially Cylindrospermopsis raciborskii, became a regular phenomenon in the western part and sometimes in the eastern part of the lake. Since 1995, the biomass of phytoplankton, particularly N&2inf;-fixing cyanobacteria, has decreased dramatically. This paper investigates the change in the akinete abundance of N&2inf;-fixing cyanobacteria in the lake sediment in the 1980s and 1990s. A direct counting method was developed for determination of the abundance of akinetes in the sediment. It was found that in parallel with the reduction in biomass of N&2inf;-fixing cyanobacteria, the abundance of akinetes decreased approximately two orders of magnitude after 1994. However, the results also suggest that the decreasing number of akinetes in the sediment could not cause a `disappearance' of cyanobacteria from the phytoplankton assemblage.
    Hydrobiologia 01/2003; · 1.99 Impact Factor
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    ABSTRACT: The effect of anatoxin (ANTX), the crude extract (AlgTX) and purified fraction (F1) isolated from cyanobacterium C. raciborskii was studied on the neurones of two snail species. ANTX and AlgTX exerted excitatory, inhibitory and biphasic effects on the spontaneous activity of identified neurones. Both ANTX and AlgTX elicited an inward current, which could be decreased by curare or amiloride. On the contrary, F1 had no direct effect on the spontaneous activity; it was not able to induce conductance changes of the neuronal membrane, but it did antagonise the acetylcholine (ACh)-induced inward current. We concluded that ANTX affects the neuronal membrane of neurones acting on ACh receptors. The AlgTX had similar effects, and therefore the extract of C. raciborskii may contain an ANTX-like component. The purified fraction prolonged and decreased the ACh-elicited response, but had no direct membrane effect. We suggest, therefore, that both AlgTX and the purified fraction F1 interact with the ACh receptor, but they have different binding sites on the neuronal ACh receptor-ion channel complex. The possible neurotoxic effects of the C. raciborskii extract and F1 are demonstrated for the first time; the molecular mechanism of their action, however, remains to be elucidated.
    Comparative Biochemistry and Physiology Part C Toxicology & Pharmacology 03/2002; 131(2):167-76. · 2.71 Impact Factor
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    ABSTRACT: An insect test was developed to investigate the toxicity of cyanobacteria. The African locust, Locusta migratoria migratorioides R.F. was used as a test animal instead of mouse. The cyanobacteria tested were Aphanizomenon flos-aque, Anabaena aphanizomenoides, Cylindrospermopsis raciborskii, Microcystis aeruginosa. The toxicity of authentic microcystin-LR was also tested. Cyanobacteria producing toxins killed the animals when the homogenized cell suspension was injected into the animals. The locust test proved to be more sensitive than the mouse test. The LD50 values of the different cyanobacteria for locusts and for mice, respectively were the following: 90 microg/animal (60 mg/kg) and 8000 microg/animal (320 mg/kg), for Aphanizomenon flos-aquae; 255 microg/animal (170.2 mg/kg) and 3750 microg/animal (150 mg/kg), for Anabaena aphanizomenoides; 195 microg/animal (131.4 mg/kg) and 5750 microg/animal (230 mg/kg), for Cylindrospermopsis raciborskii; 22.5 microg/animal (15 mg/kg) and 6000 microg/ animal (240 mg/kg), for Microcystis aeruginosa. In locusts the LD50 value for authentic microcystin-LR was 0.2 microg/animal (130 mg/kg). Since the weight of the mice is 15 to 20 times larger than that of the locusts, hence less toxic cells are needed to kill the locusts. The locust test is cheaper than the mouse test, large number of animals can be used in the experiments and the LD50 values can be estimated more precisely. The toxicity of C. raciborskii was significantly lower when the lyophilized cells were extracted in methanol (LD50 = 767 mg/kg), instead of NaCl solution (LD50 = 131.4 mg/kg).
    NeuroToxicology 01/1998; 19(4-5):605-8. · 2.65 Impact Factor
  • Hidrológiai Közlöny. 87:144-147.