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Zic V.,Ruder Boskovic Institute | Zic V.,Central Water Management Laboratory | Truesdale V.W.,Oxford Brookes University | Cuculic V.,Ruder Boskovic Institute | Cukrov N.,Ruder Boskovic Institute
Hydrobiologia | Year: 2011

Despite iodine being one of the most abundant of the minor elements in oxic seawater, the principal processes controlling its interconversion from iodate to iodide and vice versa, are still either elusive or largely unknown. The two major hypotheses for iodate reduction involve either phytoplankton growth in primary production, or bacteria during regeneration. An earlier study intended to exploit the unusual nature of anchialine environments revealed that iodide is oxidised to iodate in the bottom of such caves, whereas reduction of iodate occurs in the shallower parts of the water column. This investigation was made on the hypothesis that study of the nitrogen and phosphorus nutrient systems within the caves might offer a bridge between the iodine chemistry and the marine bacteria which are assumed to be the agent of change of the iodine in the caves. Accordingly, the hydrography, the nutrient chemistry, and some further iodine studies were made of two anchialine caves on the east coast of the Adriatic Sea in Croatia. Iodate and iodide were determined by differential pulse voltammetry and cathodic stripping square-wave voltammetry, respectively. Total iodine was determined indirectly, as iodate, after oxidation of reduced iodine species with UV irradiation and strong chemical oxidants. Nutrient concentrations were measured by spectrophotometry. Nutrient profiles within the well stratified water columns indicate a relatively short-lived surface source of nitrate and phosphate to the caves, with a more conventional, mid-water, nutrient regeneration system. The latter involves nitrite and ammonium at the bottom of the halocline, suggestive of both autotrophic and heterotrophic microbial activity. High iodate/low iodide deep water, and conservative behaviour of total inorganic iodine were confirmed in both systems. Iodate is reduced to iodide in the hypoxic region where nutrient regeneration occurs. The concentrations of organic iodine were surprisingly high in both systems, generally increasing toward the surface, where it comprised almost 80% of total iodine. As with alkalinity and silica, the results suggest that this refractive iodine component is liberated during dissolution of the surrounding karst rock. A major, natural flushing of one of the caves with fresh water was confirmed, showing that the cave systems offer the opportunity to re-start investigations periodically. © 2011 Springer Science+Business Media B.V.

Stankovic I.,Central Water Management Laboratory | Vlahovic T.,Croatian Natural History Museum | Gligora Udovic M.,University of Zagreb | Varbiro G.,Balaton Limnological Research Institute | Borics G.,Balaton Limnological Research Institute
Hydrobiologia | Year: 2012

Influence of hydrological characteristics and nutrient concentrations on phytoplankton was investigated in four large rivers (Mura, Drava, Danube and Sava) in the Pannonian ecoregion in Croatia to understand how phytoplankton of rivers can be explained by the "different functional group approach". To gain a clearer understanding of the factors that affect river phytoplankton, the present study examined phytoplankton biomass and composition in relationship with physical and chemical parameters assessed in detail by preparing self-organising maps using functional groups and morpho-functional groups. Total nitrogen along with water residence time showed to be the best predictor to determine phytoplankton biomass and chlorophyll a. Phytoplankton diversity increased with higher water discharge, but it had the consequence of diluting algae and decreasing biomass. Bacillariophyceae and Chlorophyceae species dominated the phytoplankton assemblages in all rivers. Diatoms predominated in rivers with shorter residence time. Dominant diatom codons of functional groups were C, D and TB while morpho-functional groups were represented by only diatom group VI. As residence time increased, the proportion of chlorococcalean green algae, represented by functional group codon T and morpho-functional group IV grew in summer. Since potamoplankton is dominated by diatoms, functional groups with its fine partition of diatom codons proved to be excellent descriptor of the potamoplankton. Application of morpho-functional groups originally developed from the lake data, showed to be limiting because of the predominating presence of only one diatom group. © 2012 Springer Science+Business Media B.V.

Truesdale V.W.,Oxford Brookes University | Zic V.,Ruder Boskovic Institute | Zic V.,Central Water Management Laboratory | Garnier C.,University of Toulon | Cukrov N.,Ruder Boskovic Institute
Estuarine, Coastal and Shelf Science | Year: 2012

A study of foams formed on the marine Lake Mir, Croatia, and elsewhere on the same coast demonstrates, for the first time, that they are fractionated (enrichened) in org-I by up to 630 times relative to the water from which they form. The results are consistent with an I/C mole ratio for in-situ organic matter. Foams created artificially in the laboratory from natural samples of water from Lake Mir were similarly fractionated, although to a lesser degree. These differences were effectively removed when enrichments were expressed as molar ratios, e.g., Ptot/Itot, rather than straightforward concentrations. This similarity in the behaviour to enrichment for organic forms of I, N and P suggests that the time over which foams age is a major determinant of the enrichment they display. It is argued that this period allows time for the seawater occluded in the interstitial spaces between bubbles, to drain away. Since foam production is ubiquitous over the oceans it seems likely that this process local to coastal environments is much more common than at first might appear to be the case. The paper explains how this work provides circumstantial evidence that the bubble-bursting mechanism current since the 1960s may well provide the iodine which appears to be missing in many modelling calculations based upon an atmospheric system dependant upon sorption of the species IO upon the marine aerosol. © 2012 Elsevier Ltd.

Zic V.,Ruder Boskovic Institute | Zic V.,Central Water Management Laboratory | Truesdale V.W.,Oxford Brookes University | Garnier C.,University of Toulon | Cukrov N.,Ruder Boskovic Institute
Estuarine, Coastal and Shelf Science | Year: 2012

The marine chemistry of iodine has been studied in the marine lake, Mir, regarded as a natural reactor situated in the karstificated carbonate rocks of the Croatian Adriatic coast. The investigation covered the major variables: salinity, temperature, dissolved oxygen, pH and alkalinity, some nutrients, organic carbon, and iodide, iodate and organic-I. Lake Mir was found to be meso-trophic, with dynamic nutrient cycling of a magnitude usually associated with the temperate zone but within a Mediterranean clime. An essentially U-shaped pattern exists in the plot of nutrient concentration versus time for the June-November period studied. Together, the major variables and the nutrient chemistry confirm that Lake Mir is essentially isolated from the nearby (90 m) Adriatic seawater, and this also may explain the meso-trophic nature of the lake, with dry and wet deposition as the source of the extra nutrient. It is of note that iodate was essentially absent from Mir during the sampling period. This appears to be consistent with iodine's behaviour in the oceans in general, where iodate is reduced generally as a result of the presence of the biota. The chemistry of iodine in Lake Mir is consequently dominated by changes in iodide and organic-I concentrations, with the latter at higher concentrations than those found in seawater. Even so, the total iodine concentration in Mir is only about one-quarter of that in the adjacent Adriatic seawater, and again it is argued that this is probably a function of Lake Mir's isolation. © 2012 Elsevier Ltd.

Vuckovic I.,Central Water Management Laboratory | Previsic A.,University of Zagreb | Graf W.,University of Natural Resources and Life Sciences, Vienna | Kucinic M.,University of Zagreb
Aquatic Insects | Year: 2011

Annitella apfelbecki is one of three Annitella species with distribution ranges restricted to the Balkan Peninsula. In this paper, we describe the hitherto unknown female of A. apfelbecki and give the most important morphological features to enable its identification and separation from the other Annitella females. Additionally, we provide new data on distribution and discuss zoogeography, life cycle and ecology of this species. © 2011 Copyright Taylor and Francis Group, LLC.

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