Tadej Dolenec

The Permian–Triassic boundary in Western Slovenia (Idrijca Valley section): magnetostratigraphy, stable isotopes, and elemental variations

Stable isotope analyses of carbonate (δ13Ccarb) and total organic carbon (TOC; δ13Corg), together with geochemical analyses of 54 major, minor, and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed Permian–Triassic (P/Tr) limestone boundary sequence in the Idrijca Valley (W. Slovenia). At the P/Tr boundary, there is a 0.8-cm thick clayey marl layer (PTB) showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major, minor, and trace elements. The P/Tr transition is characterized by (1) an abrupt decrease in sedimentation rate from 32 to 5 cm/100 ka, (2) a well known prominent negative excursion of δ13Ccarb and δ13Corg, reflecting global perturbations in the carbon cycle, and (3) the drastic disappearance of typically Upper Permian marine fauna. Although the shape of the δ13Ccarb curve indicates gradual long-term change across the P/Tr boundary, the sharp negative δ13Corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes. Our observations for selected redox sensitive elements (Mo, U, V and Zn), abundances for organic carbon and sulphur and the rare earth elements (REE) distribution in the boundary sequence, as well as the shape of the Ce/Ce* curve suggest that oceanic anoxia was typical of the Upper Permian, and that the transition to oxygenated conditions occurred at the P/Tr boundary. Oxygenation at the P/Tr transition is coincidental with the terminal phase of the Upper Permian marine regression. The shape of the Ce/Ce* curve indicates that the redox environmental conditions changed again in the earliest Triassic, resulting once more in oxygen deficient conditions.

Major, Minor and Trace Elements in Surficial Sediments from the Open Adriatic Sea: A Regional Geochemical Study

The concentrations and distributions of major (Al, Ca, Fe, K, Mg), minor (Mn, P, Ti), and trace elements (Ag, As, Ba, Be, Co, Cr, Cu, Ag, La, Ni, Pb, Sc, Sr, Th, U, V, Zn, Zr), in the surficial sea bottom sediments were studied in an attempt to establish their distribution in the Adriatic Sea. Results indicate that major, minor and several trace elements are strongly related to the catchment geology, their distribution being essentially controlled by the type of sediments. However, the majority of trace elements are believed to have been introduced into the Adriatic from the riverine inflows that are also affected by the impact of industrial, mining and urban wastes. Other sources of these elements are located along the coast. The highest concentrations for several trace elements were thus recorded from the coastal ecosystems and from the most polluted Albanian and Italian rivers. The concentrations of trace elements generally decrease with distance from the coast. The regional distribution patterns are influenced by the counter-clockwise system of the Adriatic Sea currents which carry these elements away from the riverine inflows. Correlation analysis indicates that the trace elements are largely associated with the clay minerals, Fe and P contents rather than with the Mn concentrations. Magnesian minerals are suggested as the carrier for some trace elements (As, Co, Cr, Ni, Se and V) only in the southern Adriatic, which reflects their ophiolitic origin in the Albanian hinterland. Organic matter concentrations does not considerably influence the abundance and distribution of trace metals.

Effects of fish farm loading on sea grass Posidonia oceanica at Vrgada Island (Central Adriatic): a nitrogen stable isotope study

Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7‰ at p < 0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste.

Decomposition of sedimentary organic matter and methane / formation in the recent sediment of Lake Bled Slovenia

Decomposition of sedimentary organic matter and methane formation in a eutrophic dimictic subalpine lake Lake Bled, . . NW Slovenia were investigated by measurement of in situ concentrations of dissolved inorganic carbon DIC in the pore water and its stable carbon isotopic composition, as well as by incubation experiments. The isotopic composition of carbon in the methane produced during incubation experiments was also studied. The ratio between methane produced by acetate fermentation and CO rH reduction was estimated from d 13 C-DIC vs. DIC concentration profiles in sediment pore water 22 w using a mathematical model developed by LaZerte LaZerte, 1981. The relationship between dissolved carbon dioxide and x its stable isotope ratio in aquatic sediments. Geochim. Cosmochim. Acta 45, 647-656 . It was found that in the spring acetate fermentation is dominant when about 65% of methane is produced by this reaction pathway, whereas in the autumn, over 90% of the methane results from CO reduction. d 13 C of methane released during a 6-week incubation experiment with 2

Potentially toxic contamination of sediments, water and two animal species in Lake Kalimanci, FYR Macedonia: Relevance to human health

The objectives of the research were: (1) to examine the concentrations of metals in Vimba melanops and Rana temporaria and (2) to evaluate the potential risks of the contaminated organisms to human health in Makedonska Kamenica region. Analyses identified high levels of Cr, Hg, Ni and Pb in studied animals, which also exceeded their permissible levels in food. In sediment and soil samples, levels of Cd, Cu, Cr, Pb, Zn and As were perceived, while Cd, Cu, Ni, Pb, Se and As were increased in water samples. Results of transfer factor revealed that the examined animals had higher bioaccumulation rate from surrounding waters than from sediments or soils. The accomplished Health Risk Index disclosed that studied animals can have considerably high health risks for inhabitants. Conclusively, they could be considered as highly contaminated with metals and can consequently harm human health, especially children in their early development stages.

Benthic foraminifera assemblages as elemental pollution bioindicator in marine sediments around fish farm (Vrgada Island, Central Adriatic, Croatia)

Effects on sediments of fish farming activity near Vrgada Island was analysed through living and total foraminiferal assemblages and concentration of major, minor and trace elements from three sediment cores. Elemental concentrations of sediments are in accordance with carbonate characteristics of the surrounding area and show mostly natural element variations between sampling locations and throughout the cores, with no significant increases due to fish farming activity. Only phosphorus concentration shows elevate values below the fish cage, assigned to fish pellets. Foraminiferal communities are dominated by epifaunal and stress tolerant species, while diversity indices point to normal marine conditions. The type of substrate and phosphorus content in sediments principally influence foraminiferal community composition, while other elemental concentrations have no perceptible effect on the assemblages. Some foraminiferal species Ammoniatepida, Ammoniabeccarii, Elphidiumcrispum, Elphidiummacellum and genus Haynesina are confirmed to be tolerant to elevated nutrient (phosphorus) content, while Ammonia parkinsoniana shows sensitivity to pollution. Postmortem processes cause decrease of foraminiferal density and species richness with core depth. All results point to negligible influence of fish farming and relatively stable environmental conditions at all sampling locations.

Recent Sediments of Makirina Cove (Northern Dalmatia, Croatia): Their Origin Viewed Through a Multidisciplinary Approach

Makirina Cove was formed by the Holocene sea-level rise which caused a marine ingression into the depression formed within Albian– Cenomanian dolomites at approximately 4.5 ka B.P. At present, Makirina Cove represents an restricted, stressed, shallow-marine (<2 m) ecosystem characterized by varying seawater temperatures (0–35°C) as well as fluctuating salinities (up to 41‰) affected by seasonally enhanced evaporation, continuous freshwater supply through on-shore and submarine springs associated with the coastal karst area and surface run-off episodes. These environmental conditions have been conducive to high primary production of organic matter resulting in the formation of organic-rich deposits which contain up to 5 wt.% of organic carbon. Up to the present times, 3.5 m of sediments have been deposited indicating a relatively high sedimentation rate estimated at 0.75 m/1.0 ka in the northern central part of the Cove. The sediments are being deposited mostly as poorly sorted clayey–sandy silts. The distribution and concentration of most of the chemical elements is dependant on the mineralogical composition and granulometric features of the Makirina sediments, which show values more or less similar to those from the Central Adriatic. Accordingly, there is a positive correlation with Al and K concentrations increasing off-shore and with the depth being associated with increasing concentrations of clay minerals within the clay fraction. The same holds true for concentrations of some trace elements, especially Mo and Se which is consistent with the distribution pattern of sulphides. Selenium is preferentially enriched in authigenic pyrite and it is probably the major source of Se in the Makirina Cove sediments. The concentrations of Ca, Mg and Sr decrease off-shore and they are linked to the composition of the surrounding carbonate rocks. The saturation indices show that the water is supersaturated with respect to carbonates enabling the precipitation of authigenic amorphous or crystalline carbonate phases from the pore water in the upper segment of the sediment column. According to the oxygen isotopic (δ18O) composition, molluscs precipitated their carbonate shells mostly during warmer periods (May to November) at or near isotopic equilibrium with their ambient waters. The carbon isotopic δ13C composition of mollusc carbonate shells is environmentally affected due to oxidation and decomposition of organic matter as well as influxes of fresh water into the Cove, indicating their formation out of the predicted isotopic equilibrium with atmospheric CO2. Palynological and organic carbon isotopic (δ13C) composition shows that the sedimentary organic matter (SOM) is 70–90% lipid- and hydrogen-rich and on average 2/3 marine derived (mainly phytoplankton, bacteria and marine macrophytes) and 1/3 terrestrially derived (mainly woody tissue). The variations in composition of SOM have been noted as a function of the distance from the shore. The type and the preservation state of SOM and pyrite as well as the measurements of Eh, pH, total alkalinity, dissolved inorganic carbon (DIC) and the enrichment of redox-sensitive trace elements, indicate oxygen-depleted depositional conditions and that the sediment is highly reductive even in the uppermost segment at the sediment/water interface. According to the results obtained from the applied methods, the features of Makirina sediments strongly reflect the given depositional conditions within this restricted, stressed, shallow- marine environment where these organic-rich sediments originate, and may therefore serve as a calibration standard in further investigations

Stable Isotope Event Markers Near the Permo-Triassic Boundary in the Karavanke Mountains (Slovenia)

Permo-Triassic (P/Tr) boundary events, which took place approximately 250 Ma ago, led to the most extensive mass extinction in the history of life. A number of possible explanations for this profound break in the evolution of life have been proposed, such as volcanic activity, sea-level fluctuation, changes in sea-water chemistry, an extra-terrestrial impact event and various related factors (YOICHI, 1994). The most recently proposed cause of the mass extinction at the end of the Permian is a combination of these more or less co-occurring events operating in three phases (ERVIN, 1996). The first began with the marine regression during the Late Permian and resulted in the destruction of many marine basins, reduction in the habitat area of many organisms and increased climatic instability. The second phase involved the eruption of the Siberian Traps and further environmental degradation. The final phase may have started immediately prior to the boundary when the Late Permian regression ended and the earliest Triassic transgression begun. The global events outlined above coincide with isotope and elemental anomalies recorded in several P/ Tr boundary sections all

The role of sedimentary biogeochemistry in the formation of hypoxia in shallow coastal waters (Gulf of Trieste, northern Adriatic)

Abstract Pore water measurements of dissolved organic matter (DOM) and inorganic nutrients in the surficial sediment of the Gulf of Trieste showed the highest concentrations to be in late summer due to the higher microbial activity and restricted upward fluxes to the overlying water because of density stratification in the water column. The benthic fluxes of DOM, in terms of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP), and the inorganic nutrients NH+4 and PO3−4, measured in parallel with sediment oxygen consumption (SOC) and production, showed in general a net influx indicating benthic consumption. Only strong DOC fluxes out of the sediment prevail in late summer. The bulk of DOC in pore water was found to be refractory, with a significant proportion consisting of a high molecular weight fraction. DON and DOP were more reactive in aerobic and anaerobic pathways of decomposition and not directly temperature dependent, probably because of a randomly fluctuating supply of degradable sedimentary organic matter and oxidants. In constructing the mass balance of C, N, and P it emerged that the sediment is primarily anoxic because the SOC is higher than benthic oxygen production. Oxygen must be therefore introducted to the sediment-water interface by physical factors and water column photosynthesis to prevent bottom layer hypoxia and anoxia in the period of strong density stratification in the water column. The role of particulate organic matter (POM) sedimentation is not of primary importance to SOC, and a fraction of summer POM is probably refractory and of allochtonous origin.

Seasonal differences of stable isotope composition and lipid content in four bivalve species from the Adriatic Sea

Abstract The feeding ecology of four bivalve species co-occurring in the Mali Ston Bay, the most important bivalve aquaculture area of the Eastern Adriatic, were investigated by analysing the stable isotope composition and lipid content in two tissue types. Analyses included two cultured species: Mytilus galloprovincialis and Ostrea edulis, and two naturally occurring species: Modiolus barbatus and Arca noae. Total lipid concentrations were higher in the digestive gland than in the adductor muscle in all species studied. The study confirmed seasonal variability of stable isotope signatures. Observed seasonal changes were more pronounced in the digestive gland than in the adductor muscle, suggesting that the former better reflects seasonal trophic patterns. The results obtained indicate isotopic niche overlap in the investigated species with the highest degree of overlap (~60%) among two cultured species during the spring–summer period, and between two naturally occurring species during the autumn–winter period (~60%). A lower degree of overlap between other species might suggest utilization of different additional food sources during certain times of the year. This study contributes to our understanding of trophic interactions between different bivalve species and is important for future modelling of food webs and sustainable management of wild and cultured populations.