Cell Suspension as a Model System for Electrochemical Analysis

Cell suspensions of marine phytoplankton Dunaliella tertiolecta in 0.1 M NaCl solution are proposed as a suitable model monodispersed system (particle diameter 6-10 μm) for the calibration of electrochemical response in natural aquatic samples containing organic surface-active particles. The electrochemical analysis is performed by direct recording of chronoamperometric curves of oxygen reduction in suspensions using a fast dropping mercury electrode. The electrode acts as adhesion sensor. The adhesion of individual surface-active particles suspended in natural seawater, analogously to Dunaliella tertiolecta cells in model suspensions, results in well resolved attachment signals in amperometric curves. The calibration curve presents dependence of attachment frequency on cell densities in the concentration range 106 to 2.5 x 107 particles L-1 and it can be used for the determination of particle abundance in a seawater sample. The advantage of the electrochemical approach over more conventional methodologies for particle analysis is discussed

Factors favouring phytoplankton blooms in the northern Adriatic: Towards the northern Adriatic empirical ecological model

Influenced by one of the largest Mediterranean rivers, Po, the northern Adriatic (NA) production is highly variable seasonally and interannually. The changes are especially pronounced between winters and seemingly reflect on total Adriatic bioproduction of certain species (anchovy). We analysed the long-term changes in the phytoplankton production in the region, as derived from monthly oceanographic cruises, in relation to concomitant geostrophic currents distribution in the area and to Po River discharge rates in days preceding the cruises. In winter and early spring the phytoplankton abundances depended on existing circulation fields, in summer and autumn they were related to Po River discharge rates 1–15 days earlier and on concomitant circulation fields, while in late spring phytoplankton abundances increased 1-3 days after high Po River discharge rates regardless of the circulation fields. During the entire year the phytoplankton abundances were dependent on forcing of the previous 1-12 months of surface fluxes and/or Po River rates. The role of wind was uncertain but that was partly due to unmatched sampling time frames between meteorological and sea data. Low evaporation rates in November reflected significantly on the next February circulation pattern and, although with somewhat lower significance, on large phytoplankton blooms in the same month. We showed that the role of wind in evaporative flux enhancements is not straightforward as evaporative fluxes are highly dependent on other factors, e.g. air-sea temperature difference. Wind-induced vertical mixing was only sporadically related to phytoplankton abundances. From 1990 to 2004 a shift towards large winter bioproduction induced by circulation changes appeared. The investigations performed represent the preliminary actions in the construction of an empirical ecological model of the NA which can be used in the sustainable economy of the region, as well as for validation of the numerical ecological model of the region, which is currently being developed

Cell Suspension as a Model System for Electrochemical Analysis

Cell suspensions of marine phytoplankton Dunaliella tertiolecta in 0.1 M NaCl solution are proposed as a suitable model monodispersed system (particle diameter 6-10 μm) for the calibration of electrochemical response in natural aquatic samples containing organic surface-active particles. The electrochemical analysis is performed by direct recording of chronoamperometric curves of oxygen reduction in suspensions using a fast dropping mercury electrode. The electrode acts as adhesion sensor. The adhesion of individual surface-active particles suspended in natural seawater, analogously to Dunaliella tertiolecta cells in model suspensions, results in well resolved attachment signals in amperometric curves. The calibration curve presents dependence of attachment frequency on cell densities in the concentration range 106 to 2.5 x 107 particles L-1 and it can be used for the determination of particle abundance in a seawater sample. The advantage of the electrochemical approach over more conventional methodologies for particle analysis is discussed

Ecological Importance of Alkaline Phosphatase Activity in Changing Marine Environmental Conditions

The effects of changing hydrological and climatic conditions on the dynamics of phosphorus (P) were studied in the Northern Adriatic Sea (NA), a coastal system currently affected by these changes. P limitation is one of the key stresses in the NA and it is a globally important phenomenon in aquatic ecosystems. Therefore, the response to P stress by inducing alkaline phosphatase activity (APA) was studied in characteristic water types in the NA, formed by the changing freshwater input in different thermic conditions. APA was important in providing P for microbial growth in upper waters dominated by assimilation during the warmer part of the year in stratified conditions. Contrarily, APA was not important during mixing in the colder part of the year, as well as in waters dominated by regeneration. In waters influenced by freshwater, temperature had no effect on APA, while in high-salinity waters, temperature was an important factor for APA increase. The highest APA occurred during riverine nutrients supply, indicating that the alteration of anthropogenic nutrient loads might strongly change P status in this coastal system. Furthermore, predicted increases in winter sea temperature and summer Po River discharge could delay the water column mixing, prolonging periods of P limitation

Analyse des Larventransportes aus dem Ballastwasser im Hafengebiet Ploče

Za akvatorij Luka Ploče uspostavljen je 3D numerički model cirkulacije mora i pronosa ličinki unesenih na fiksnoj poziciji lučkog terminala uslijed ispuštanja balastnih voda iz brodskih tankova. Modelske čestice ličinki nisu pasivne, već imaju senzoričku sposobnost prepoznavanja okolišnih uvjeta i kognitivne reakcije u vidu promjene smjera i intenziteta svoga kretanja (ABM, eng: agent based model) u smjeru optimalnog intenziteta svjetlosti i temperature mora. Modelske simulacije su provedene za razdoblje 12.3.2008.-10.5.2008., uz primjenu izmjerenog protoka i temperature rijeke Neretve na postaji Žitomislići (polusatna rezolucija), modelskih rezultata brzine i smjera vjetra iz numeričkog modela Aladin-Hr (trosatna rezolucija), satne dinamike morskih razina i izmjerene vertikalne raspodjele temperature i saliniteta mora na otvorenoj granici modela (CTD sonda). Čestice ličinki unose se u 4 termina (14.3., 22.3., 7.4. i 20.4.2008.), na početku situacija sa registriranom karakterističnom kombinacijom okolišnih uvjeta („mali“ ili „veliki“ protok Neretve sa „malom“ ili „velikom“ brzinom vjetra iz smjerova ENE, SW, S i E). Rezultati provedenih simulacija pokazuju da u situaciji većeg protoka Neretve i manjih brzina vjetra (prosječno za 7 dana nakon termina unosa ličinki QSR-7dana = 490 m3/s i WSR-7dana = 2.9 m/s) dolazi do najizraženije sedimentacije ličinki u zatvorenom dijelu lučkog bazena. S druge strane, u slučaju manjeg protoka Neretve i većih brzina vjetra (QSR-7dana = 114 m3/s i WSR-7dana = 3.7 m/s u rasponu smjerova S-SW) ličinke se intenzivno pronose u SE smjeru pružanja neretvanskog kanalaA 3D numerical model of sea circulation and transport of larvae introduced at a fixed position of the port terminal due to discharges of ballast water from ship tanks for the Port of Ploče waters was established. The model larvae particles are not passive but have sensory capacity to recognize environmental conditions and cognitive reaction regarding direction change and their movement intensity (ABM, agent based model) in view of optimal light intensity and sea temperature. The model simulations were conducted for a period from 12.3.2008 to 10.5.2008, using the measured discharges and temperatures of the Neretva River at the station Žitomislići (half-hour resolution), model results of wind speed and direction from the numerical model Aladin-Hr (three-hour resolution), hourly dynamics of sea levels and measured vertical distribution of sea temperatures and salinity at the open boundary of the model (CTD probe). The larvae particles were introduced at 4 dates (14.3., 22.3., 7.4. and 20.4.2008), at the start of situations with a registered characteristic combination of environmental conditions (“low“ or “high“ discharges of the Neretva with “low“ or “high“ wind speeds from the ENE, SW, S and E directions). The results of conducted simulations indicate that in a situation of higher Neretva discharges and lower wind speeds (on average in 7 dana after the larvae introduction QSR-7days = 490 m3/s and WSR-7days = 2.9 m/s), the most pronounced larvae sedimentation occurs in the closed part of the port basin. On the other hand, in case of lower Neretva discharges and higher wind speeds (QSR-7days = 114 m3/s and WSR-7days = 3.7 m/s in the S-SW direction range), the larvae are intensely transported in the SE direction of the Neretva channel.Für das Wassergebiet des Hafens Ploče wurde ein dreidimensionales numerisches Modell der Meereszirkulation und des Transportes von Larven erstellt, die an einem bestimmten Ort am Hafenterminal nach der Entleerung von Ballastwassertanks ins Meer eingeleitet werden. Die Modellpartikeln von Larven sind nicht passiv, sondern sie haben eine Sensorfähigkeit zur Wahrnehmung von Umweltbedingungen und eine kognitive Reaktion im Sinne der Änderung von Bewegungsrichtung und Bewegungsintensität (agentenbasiertes Modell; Engl. ABM – agent-based model) in der Richtung der optimalen Lichtintensität und Meerestemperatur. Die Modellsimulationen wurden für den Zeitraum zwischen 12. März 2008 und 10. Mai 2008 durchgeführt unter Anwendung des gemessenen Durchflusses und Temperatur des Flusses Neretva auf der Station Žitomislići (halbstündige Auflösung), der Modellergebnisse für Windgeschwindigkeit und Windrichtung aus dem numerischen Modell Aladin-Hr (dreistündige Auflösung), der einstündigen Dynamik von Meeresebenen sowie der gemessenen vertikalen Temperaturverteilung und Salinität an den offenen Modellrändern (die CTD-Rosette). Die Larvenpartikeln wurden an vier Terminen (14. März, 22. März, 7. April und 20. April 2008) eingeleitet, am Anfang von Situationen mit der registrierten charakteristischen Kombination von Umweltbedingungen (Kombinationen vom kleinen oder großen Durchfluss vom Fluss Neretva mit niedriger oder erhöhter Windgeschwindigkeit aus den Richtungen ONO, SW, S und O). Die Ergebnisse der durchgeführten Simulationen zeigen, dass in der Situation eines größeren Durchflusses von Neretva (Q = 490 m3/s) und niedrigerer Windgeschwindigkeit (W = 2.9 m/s) durchschnittlich sieben Tage nach der Einleitung von Larven zur ausgeprägtesten Bildung vom Larvensediment im geschlossenen Teil des Hafengebietes kommt. Andererseits werden in der Situation eines kleineren Durchflusses von Neretva (QSR = 114 m3/s) und erhöhter Windgeschwindigkeit (W = 3.7 m/s) im Windrichtungsbereich S-SW die Larven intensiv entlang des Neretva-Kanals in der südöstlichen Richtung transportiert