The DOM concept has served its purpose in global carbon cycles on oceanic and geological scales [... more The DOM concept has served its purpose in global carbon cycles on oceanic and geological scales [1] and it has been supported by improvements in opperational DOC measurement techniques [2]. However, the DOM concept is questioned, when it comes to a particular process of a new photosynthetic production and DOM fate in a given marine ecosystem. Therefore it is of importance to reconsider and redefine the traditional DOM concept for costal seas. We have selected the case of a most intensive primary production and DOM transformation in a Mediterranean basen, nothern part of the Adriatic Sea, as a possible excersise in validating the DOM concept in view of new instrumental developments [3 and references therein, 4, 5] understandings of microbiological processes [6] and interactions of biopolymers at micro and nanoscales [5, 7]. Literatura: [1] Hedges J I 1992 Global biogeochemical cycles: progress and problems. Mar Chem 39: 67-93. [2] Hedges J I, Lee C 1993 (eds) Measurement of dissolved organic carbon and nitrogen in natural waters. Mar Chem 41: 1-290. [3] Žutic V, Svetlicic V 2000 Interfacial processes. In: Wangersky P (Ed) Marine Chemistry Vol. 5: The Handbook of Environmental Chemistry, Part D. Springer-Verlag: Berlin-Heidelberg, p 150-165 and references cited therein. [4] Svetlicic V, Žutic V, Durand-Vidal S 2005, Marine ecology at nanoscale: Supramolecular organization of marine gel. Seeing at Nanoscale III Conference, Sante Barbara, 31. [5] Svetlicic V, Žutic V, Durand-Vidal S 2005, AFM as a tool in marine biophysics. Proceedings of 7th Multinational Congress on Microscopy, Portoroz, Slovenia, 213-214. [6] Azam F, Worden A Z 2004, Microbes, molecules and marine ecosystems, Science 303: 1622-1624. [7] Leppard G G 1995 The characterization of algal and microbial mucilages and their aggregates in aquatic ecosystems. Sci Total Environ 165: 103-131.
We demonstrate how spreading and shape of organic droplets at the fluid interface mercury/aqueous... more We demonstrate how spreading and shape of organic droplets at the fluid interface mercury/aqueous electrolyte depend on the interfacial tension that is controlled by the applied potential. We indicate a method to characterize of wetting transients of organic liquids by recording electrical signals of organic microdroplets at the dropping mercury electrode. Electrical signals are fast current transients. The flow of current is caused by double-layer charge displacement due to adhesion and spreading of a single microdroplets. Spike-shaped electrical signals are characterized by maximum current in � ÝA range, duration in ms time scale and displaced charge in nC range. The adhesion and spreading of droplets are enhanced by the hydrodynamic regime of the electrode growing, fluid interface. This technique thus allows precise measurement of area of contact interface assuming validity of the electrical double-layer model. Adhesion of macroscopic hexadecane droplet at stationary mercury electrode leads to immediate formation of an underlying monolayer and to a high over-potential (-700 mV) for droplet detachment. The wetting phenomena identified in these systems apply more generally for the droplets and insoluble films on solid electrodes and the findings can be extrapolated to complex electrochemical systems of technological importance.
Abstract: Despite many advances in research on photosynthetic carbon fixation in marine diatoms, ... more Abstract: Despite many advances in research on photosynthetic carbon fixation in marine diatoms, the biophysical and biochemical mechanisms of extracellular polysaccharide production remain significant challenges to be resolved at the molecular scale in order to proceed toward an understanding of their functions at the cellular level, as well as their interactions and fate in the ocean. This review covers studies of diatom extracellular polysaccharides using atomic force microscopy (AFM) imaging and the quantification of physical forces. Following a brief summary of the basic principle of the AFM experiment and the first AFM studies of diatom extracellular polymeric substance (EPS), we focus on the detection of supramolecular structures in polysaccharide systems produced by marine diatoms. Extracellular polysaccharide fibrils, attached to the diatom cell wall or released into the surrounding seawater, form distinct supramolecular assemblies best described as gel networks. AFM makes ...
Formation of alginate gel microparticles (size range 10-300 m m) induced by calcium addition in a... more Formation of alginate gel microparticles (size range 10-300 m m) induced by calcium addition in an aqueous electrolyte solution was characterized by chronoamperometry at the dropping mercury electrode (DME). The conformational transition of alginate in solution in the presence of divalent cations leads to the formation of physical hydrogel (non-covalently cross linked network). The transformation of alginate free polymers in a solution to gel microparticles, was measured through distinct differentiation of electrochemical response of polymer adsorption from interaction of individual GeP at the DME/solution interface. In this study we present the electrochemical signals of alginate GeP that appear owing to their specific interactions at the DME/aqueous electrolyte interface. Adding calcium (30 mM) to alginate solution (50 mg/L) maximum in GeP concentration was reached (10^7/L) whereas the concentration of free polymers decreased to 15 mg/L. The aim of this work was to validate in sit...
The macroscopic marine gel phase appears episodically in the northern Adriatic Sea. The phenomeno... more The macroscopic marine gel phase appears episodically in the northern Adriatic Sea. The phenomenon manifests itself in rapid production of enormous amounts of gelatinous matter in the water column and on the sea surface. Current views leave no doubt on phytoplankton as a proximal source of polymers constituting the gel network, but the mechanism leading to its rapid formation remains unknown. The mechanism of marine gel formation, its stability and the role of gel state in marine ecosystem is becoming a most challenging exercise in converging disciplines of marine chemistry, microbiology and biophysics. Atomic force microscopy (AFM) imaging of native marine gel demonstrates that an important fraction of specimen consists of entangled fibrils.
• Study of marine bacterial phosphorus regeneration with 64-d mesocosm experiment. • Induction of... more • Study of marine bacterial phosphorus regeneration with 64-d mesocosm experiment. • Induction of phytoplankton bloom by adding phosphorus in phosphorus-limited water. • After the bloom crash, DOC accumulated despite high bacterial carbon-demand. • Bacteria colonized aggregates expressing intense ectohydrolase activities. High carbon and phosphorus turnover due to bacterial activity.
A subsurface bloom of the marine dinoflagellate Gonyaulax polyedra Stein was observed on October ... more A subsurface bloom of the marine dinoflagellate Gonyaulax polyedra Stein was observed on October 19, 1988 in the central part of the Krka Estuary (east Adriatic coast) as a 6-m-thick red-brownish layer, located below the halocline. The bloom might have been initiated by excystment in shallower parts of the estuary, where temperature near the bottom exceeded 20 °C. The autumn of 1988 was exceptionally dry, river inflow was small and the brackish upper layer was 2 m thick and transparent. The exchange rate of water in the marine layer was at its lowest in the year. The supply of nutrients for growth came from sinking and decomposition of freshwater phytoplankton at the halocline and the marine layer.
The occurrence of hypoxia in October 1988 in the Kxka estuary is described, with special referenc... more The occurrence of hypoxia in October 1988 in the Kxka estuary is described, with special reference to the Prokljan Lake. Hypoxia develops near the bottom in autumn in response to the temperature maximum that appears this time of the year. The decomposition rate of naturally present organic matter increases, creating higher biological oxygen demand. As the water column is stratified by salinity and temperature, mixing of seawater near the bottom with oxygen-supersaturated water which resides closer to the surface is very slow. When an extensive marine phytoplankton bloom appears below the halocline in the Prokljan Lake, then, because of the sinking and degradation of phytoplankton near the bottom, the dissolved oxygen concentration decreases further. The hypoxia becomes so severe that it causes massive mortality of benthic macrofauna. The decomposition of the macrofauna further decreases the dissolved oxygen concentration. The hypoxia may persist until an increase in the freshwater inflow occurs, which forces the arrival of colder marine water near the bottom via a compensating flow. In the absence of autumn rains, the hypoxia may be recorded throughout winter.
The DOM concept has served its purpose in global carbon cycles on oceanic and geological scales [... more The DOM concept has served its purpose in global carbon cycles on oceanic and geological scales [1] and it has been supported by improvements in opperational DOC measurement techniques [2]. However, the DOM concept is questioned, when it comes to a particular process of a new photosynthetic production and DOM fate in a given marine ecosystem. Therefore it is of importance to reconsider and redefine the traditional DOM concept for costal seas. We have selected the case of a most intensive primary production and DOM transformation in a Mediterranean basen, nothern part of the Adriatic Sea, as a possible excersise in validating the DOM concept in view of new instrumental developments [3 and references therein, 4, 5] understandings of microbiological processes [6] and interactions of biopolymers at micro and nanoscales [5, 7]. Literatura: [1] Hedges J I 1992 Global biogeochemical cycles: progress and problems. Mar Chem 39: 67-93. [2] Hedges J I, Lee C 1993 (eds) Measurement of dissolved organic carbon and nitrogen in natural waters. Mar Chem 41: 1-290. [3] Žutic V, Svetlicic V 2000 Interfacial processes. In: Wangersky P (Ed) Marine Chemistry Vol. 5: The Handbook of Environmental Chemistry, Part D. Springer-Verlag: Berlin-Heidelberg, p 150-165 and references cited therein. [4] Svetlicic V, Žutic V, Durand-Vidal S 2005, Marine ecology at nanoscale: Supramolecular organization of marine gel. Seeing at Nanoscale III Conference, Sante Barbara, 31. [5] Svetlicic V, Žutic V, Durand-Vidal S 2005, AFM as a tool in marine biophysics. Proceedings of 7th Multinational Congress on Microscopy, Portoroz, Slovenia, 213-214. [6] Azam F, Worden A Z 2004, Microbes, molecules and marine ecosystems, Science 303: 1622-1624. [7] Leppard G G 1995 The characterization of algal and microbial mucilages and their aggregates in aquatic ecosystems. Sci Total Environ 165: 103-131.
We demonstrate how spreading and shape of organic droplets at the fluid interface mercury/aqueous... more We demonstrate how spreading and shape of organic droplets at the fluid interface mercury/aqueous electrolyte depend on the interfacial tension that is controlled by the applied potential. We indicate a method to characterize of wetting transients of organic liquids by recording electrical signals of organic microdroplets at the dropping mercury electrode. Electrical signals are fast current transients. The flow of current is caused by double-layer charge displacement due to adhesion and spreading of a single microdroplets. Spike-shaped electrical signals are characterized by maximum current in � ÝA range, duration in ms time scale and displaced charge in nC range. The adhesion and spreading of droplets are enhanced by the hydrodynamic regime of the electrode growing, fluid interface. This technique thus allows precise measurement of area of contact interface assuming validity of the electrical double-layer model. Adhesion of macroscopic hexadecane droplet at stationary mercury electrode leads to immediate formation of an underlying monolayer and to a high over-potential (-700 mV) for droplet detachment. The wetting phenomena identified in these systems apply more generally for the droplets and insoluble films on solid electrodes and the findings can be extrapolated to complex electrochemical systems of technological importance.
Abstract: Despite many advances in research on photosynthetic carbon fixation in marine diatoms, ... more Abstract: Despite many advances in research on photosynthetic carbon fixation in marine diatoms, the biophysical and biochemical mechanisms of extracellular polysaccharide production remain significant challenges to be resolved at the molecular scale in order to proceed toward an understanding of their functions at the cellular level, as well as their interactions and fate in the ocean. This review covers studies of diatom extracellular polysaccharides using atomic force microscopy (AFM) imaging and the quantification of physical forces. Following a brief summary of the basic principle of the AFM experiment and the first AFM studies of diatom extracellular polymeric substance (EPS), we focus on the detection of supramolecular structures in polysaccharide systems produced by marine diatoms. Extracellular polysaccharide fibrils, attached to the diatom cell wall or released into the surrounding seawater, form distinct supramolecular assemblies best described as gel networks. AFM makes ...
Formation of alginate gel microparticles (size range 10-300 m m) induced by calcium addition in a... more Formation of alginate gel microparticles (size range 10-300 m m) induced by calcium addition in an aqueous electrolyte solution was characterized by chronoamperometry at the dropping mercury electrode (DME). The conformational transition of alginate in solution in the presence of divalent cations leads to the formation of physical hydrogel (non-covalently cross linked network). The transformation of alginate free polymers in a solution to gel microparticles, was measured through distinct differentiation of electrochemical response of polymer adsorption from interaction of individual GeP at the DME/solution interface. In this study we present the electrochemical signals of alginate GeP that appear owing to their specific interactions at the DME/aqueous electrolyte interface. Adding calcium (30 mM) to alginate solution (50 mg/L) maximum in GeP concentration was reached (10^7/L) whereas the concentration of free polymers decreased to 15 mg/L. The aim of this work was to validate in sit...
The macroscopic marine gel phase appears episodically in the northern Adriatic Sea. The phenomeno... more The macroscopic marine gel phase appears episodically in the northern Adriatic Sea. The phenomenon manifests itself in rapid production of enormous amounts of gelatinous matter in the water column and on the sea surface. Current views leave no doubt on phytoplankton as a proximal source of polymers constituting the gel network, but the mechanism leading to its rapid formation remains unknown. The mechanism of marine gel formation, its stability and the role of gel state in marine ecosystem is becoming a most challenging exercise in converging disciplines of marine chemistry, microbiology and biophysics. Atomic force microscopy (AFM) imaging of native marine gel demonstrates that an important fraction of specimen consists of entangled fibrils.
• Study of marine bacterial phosphorus regeneration with 64-d mesocosm experiment. • Induction of... more • Study of marine bacterial phosphorus regeneration with 64-d mesocosm experiment. • Induction of phytoplankton bloom by adding phosphorus in phosphorus-limited water. • After the bloom crash, DOC accumulated despite high bacterial carbon-demand. • Bacteria colonized aggregates expressing intense ectohydrolase activities. High carbon and phosphorus turnover due to bacterial activity.
A subsurface bloom of the marine dinoflagellate Gonyaulax polyedra Stein was observed on October ... more A subsurface bloom of the marine dinoflagellate Gonyaulax polyedra Stein was observed on October 19, 1988 in the central part of the Krka Estuary (east Adriatic coast) as a 6-m-thick red-brownish layer, located below the halocline. The bloom might have been initiated by excystment in shallower parts of the estuary, where temperature near the bottom exceeded 20 °C. The autumn of 1988 was exceptionally dry, river inflow was small and the brackish upper layer was 2 m thick and transparent. The exchange rate of water in the marine layer was at its lowest in the year. The supply of nutrients for growth came from sinking and decomposition of freshwater phytoplankton at the halocline and the marine layer.
The occurrence of hypoxia in October 1988 in the Kxka estuary is described, with special referenc... more The occurrence of hypoxia in October 1988 in the Kxka estuary is described, with special reference to the Prokljan Lake. Hypoxia develops near the bottom in autumn in response to the temperature maximum that appears this time of the year. The decomposition rate of naturally present organic matter increases, creating higher biological oxygen demand. As the water column is stratified by salinity and temperature, mixing of seawater near the bottom with oxygen-supersaturated water which resides closer to the surface is very slow. When an extensive marine phytoplankton bloom appears below the halocline in the Prokljan Lake, then, because of the sinking and degradation of phytoplankton near the bottom, the dissolved oxygen concentration decreases further. The hypoxia becomes so severe that it causes massive mortality of benthic macrofauna. The decomposition of the macrofauna further decreases the dissolved oxygen concentration. The hypoxia may persist until an increase in the freshwater inflow occurs, which forces the arrival of colder marine water near the bottom via a compensating flow. In the absence of autumn rains, the hypoxia may be recorded throughout winter.
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