Emanuela Molinaroli

The role of atmospheric deposition in the biogeochemistry of the Mediterranean Sea

Abstract Estimates of atmospheric inputs to the Mediterranean and some coastal areas are reviewed, and uncertainities in these estimates considered. Both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important (50%) or even dominant (>80%) contribution to sediments in the offshore waters of the entire Mediterranean basin. Model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen, one-third of total phosphorus, and 10% of the zinc entering the entire basin. Measured data in sub-basins, such as the north-western Mediterranean and northern Adriatic indicate an even greater proportions of atmospheric versus riverine inputs. When dissolved fluxes are compared (the form most likely to impinge on surface water biogeochemical cycles), the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes. Neglecting co-limitation by other nutrients, new production supported by atmospheric nitrogen deposition ranges from 2–4 g C m−2 yr−1, whereas atmospheric phosphorus deposition appears to support less than 1 g C m−2 yr−1. In spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of N, P or Fe. Future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric/oceanographic forcing functions. A scientific program aimed at elucidating the possible biogeochemical effects of Saharan outbreaks in the Mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended.

Grain size and compositional trends of sediments from Posidonia oceanica meadows to beach shore, Sardinia, western Mediterranean

Abstract Inputs of biogenic carbonate sediment from Posidonia oceanica seagrass meadows to four beaches of the Sinis peninsula (Sardinia, western Mediterranean) were evaluated. Beach and continental shelf sediment samples were analysed for grain size distribution and composition, biogenic vs. siliciclastic, in order to identify the provenance of beach sediments and sediment transport pathways. Seabed mapping was carried out in order to identify the distribution of meadows and sediment deposits offshore. Shelf sediments were collected in unvegetated sites and in P. oceanica meadows. Sediments from unvegetated sites were coarse sands and gravel, mainly siliciclastic (biogenic carbonate content is 3–7%). Sediments from P. oceanica meadows were coarse sand, mainly biogenic (carbonate contents varying between 60 and 90%). Beach sediments showed bimodal grain size distribution (59% of samples) resulting from mixing of coarser siliciclastic with finer biogenic materials in variable proportions. Biogenic carbonate contents in beach sediments range from 0 to 90%, reaching the highest values in offshore samples. Analysis of grain size and compositional trends from shelf to beach sediments highlighted that the latter originate from two different sources: erosion of granitic outcrops, providing the siliciclastic component, and export of sediments from P. oceanica meadows, providing biogenic material. P. oceanica meadows also influence shore by contributing towards maintaining the beach sediment budget.

Mineralogical characterisation of Saharan dust with a view to its final destination in Mediterranean sediments

Saharan dust inputs have a very important influence on the mineralogical composition of particulate matter in the Mediterranean atmosphere. We have characterised Saharan dusts from a mineralogical point of view with regard to their final destination in deep-sea sediments. This work is an attempt to compare mineralogical data of dusts and sediments available from literature together with our mineralogical data of dust collected at Sardinia. The mineralogical source marker for the Saharan dusts is palygorskite in the Western Mediterranean and smectite in the Eastern Mediterranean. Therefore, in Sardinia attention has been focused especially on a morphological study of palygorskite aggregates from where differences in Saharan aerosol collected in both dry and wet deposition were observed. A new question has also arisen about the alteration of calcite grains in Saharan dust collected in Sardinia.

Provenance Characteristics of Detrital Opaque Fe-Ti Oxide Minerals

ABSTRACT We have investigated petrogenetic characteristics of detrital opaque Fe-Ti oxide minerals (DOPQ) in sand samples collected from Holocene streams draining exclusively igneous and metamorphic source rocks in the Rocky Mountain region under a semi-arid climate, and from the Appalachian Mountains under a humid climate. Our sampling strategy allows us to compare and contrast the properties of detrital mineral grains not only from igneous and metamorphic source rocks, but also those from dissected-arc and recycled-orogen provenances. Reflected-light petrography including extensive modal analysis and electron probe microanalysis of polished grain mounts were the two principal methods of data gathering. Between 25% and 50% of all DOPQ show oxidation exsolution and/or other lamellar intergrowth textures, i.e., they are polymineralic grains. Lamellar intergrowth texture is present in about twice as many grains derived from igneous source rocks as from metamorphic source rocks. Lamellae thinner than 2 µm are predominant in grains derived from dissected-arc provenance, whereas lamellae thicker than 10 µm are predominant in grains derived from recycled-orogen provenance. Exsolution lamellae along {111} planes of magnetite (three directions) and presumably along {0001} planes of ilmenite (one direction) characterize dissected-are and recycled-orogen provenance, respectively. Detrital ilmenites derived from the igneous source rocks studied show a wide range of TiO2 co tent with a mode around 47%, whereas those from the metamorphic source rocks show a tight cluster around 52% TiO2 content. DOPQ derived from metamorphic source rocks contain < 0.5% MgO, whereas those from igneous rocks may contain up to 1.2% MgO. Both MgO and MnO are low, 0.3% and 2.5%, respectively, in DOPQ derived from dissected-arc provenance, but may be relatively high, up to 1.2% and 8.0%, respectively, in grains derived from recycled-orogen provenance. Whereas no single character of DOPQ may be diagnostic of provenance, discriminant function analysis of the complete set of data show that collectively they are diagnostic in 95% to 100% of cases. We recommend the use of 1) presence of exsolution texture, 2) minimum lamellae widths and the number of crystallographic orientation of the lamellae, and 3) chemical composition including minor elements of DOPQ as important properties for provenance identification. This should supplement and refine existing criteria for provenance determination.

Role of desert aerosol in metal fluxes in the Mediterranean area.

The chemical composition of aerosols and precipitation collected over Sardinia primarily reflect Saharan and European inputs. European background aerosols in Sardinia show a 3- to 25-fold decrease in EF crust values for Cd, Zn, Pb, and Cr compared with coastal stations in the Western Mediterranean. Partitioning of total atmospheric deposition between soluble and insoluble phases shows that Al, Si, Fe and Pb originating from the atmosphere are mostly in an insoluble form. For Ca, Cd and Cr metals, the dissolved fraction represents 50-90% of the total input. Aerosol dissolution experiments performed at particle concentrations ranging from 3 to 300 mg l -1 show that Cd and Pb have low solubilities at high mass particle concentrations. The solubility of Pb increases with EF crust values and the finest grain-size of the aerosols (<1μm), and is also affected by pH. Dissolution of Al and Fe decreases significantly from 30% (13% for Fe) at aerosol loads lower than 5 mg l -1 to less than 1% for both metals at total aerosol concentrations greater than 100 mg l -1 . The fluxes (dry + wet) of metals in Sardinia show that ∼ 30% of the Cd and Pb to more than 80% of the Fe and Al come from the Sahara.

Measurement of atmospheric deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans in the Lagoon of Venice, Italy

Data on atmospheric fall-out of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were provided by collecting bulk deposition in four stations inside the Lagoon of Venice. A total of 44 monthly samples was collected during the period July 1998-July 1999 in one site near an industrial area (Porto Marghera), one site in the city of Venice, and two sites in the southern- and northernmost ends of the Lagoon. Fluxes of PCDD/Fs were between 0.1 and 470 pg m(-2) d(-1), corresponding to 0-9.2 pg of 2,3,7,8-TCDD equivalents (TEQ) m(-2) d(-1), with a gradient increasing from remote to urban/industrial stations. Thus, annual deposition of PCDD/Fs to the Lagoon (total area=550 km2), calculated with various methods, turned out to be approximately 12 g, corresponding to approximately 400 mg TEQ. Significant differences were found among the stations, with a clear fingerprinting signature (PCDF/PCDD>1) of the deposition collected near Porto Marghera, and a reversed pattern (PCDF/PCDD<1) in the rest of the Lagoon, which pattern was similar to the sediments collected in the same locations. Lastly, the amount of bulk sigmaTEQ of all stations was compared with the guide values for dioxins in depositions proposed by De Fré et al. [Organohalogen Compounds 45 (2000) 324].

Reliability and application of detrital opaque Fe-Ti oxide minerals in provenance determination

Abstract A survey of detrital opaque Fe-Ti oxide minerals in Holocene sands derived exclusively from known source rocks in the Rocky Mountains, USA (semi-arid climate, high relief) and the Appalachian Mountains, USA (humid climate, low relief) shows that, despite obvious differences in weathering rates, the abundance of detrital ilmenite relative to parent rocks is similar in these two regions. Because ilmenite is very common in many crystalline rocks, ilmenite is considered to be a useful Fe-Ti oxide mineral for varietal studies. About 30% to 50% of detrital Fe-Ti oxide minerals are polymineralic grains with intergrowths of two or more phases. Discriminant function analysis indicates that morphological varieties of detrital Fe-Ti oxide minerals in combination with their chemical compositions are useful guides to provenance. An igneous or metamorphic source of 96% of the Holocene samples is correctly identified by this method. The method is used to determine the relative contribution of igneous and metamorphic source rocks to the sandstones of the part of the Tertiary Renova Formation, which was deposited within a dissected magmatic arc in southwestern Montana, USA. A separate discriminant function is calculated using the chemical compositions of detrital ilmenite and morphological properties of detrital Fe-Ti oxide minerals in Rocky Mountain Holocene sands. Classification of detrital Fe-Ti oxide minerals in Renova sandstones using this function suggests that igneous and metamorphic rocks contributed 77% and 23% respectively to the Renova sandstones in this area.

STREAM-SCANNING LASER SYSTEM, ELECTRIC SENSING COUNTER AND SETTLING GRAIN SIZE ANALYSIS: A COMPARISON USING REFERENCE MATERIALS AND MARINE SEDIMENTS

Abstract Surface and deep-sea core sediments and two sets of standards were measured by three different techniques — Galai Cis-1 laser system, Coulter Counter TA II, and Micromeritics SediGraph 5000D — in order to compare the Galai results with the other two. The differences between the three types of measuring device turned out to be greater in sediments than in standards, and were attributed to the physical properties, shape, density and composition of the particles (complexity of the matrix). Comparison of moment statistics showed that the Galai determines coarser grain sizes than the Coulter and finer than the SediGraph, particularly as regards analysis of surface sediments. The relationships between Galai and SediGraph were estimated using analysis of variation/residuals within individual intervals. The analysis showed a higher variability of residuals for the coarser fractions (8–16 μm and 16–32 μm) with respect to the finer (2–4 μm and 4–8 μm) fractions. The

Toxic metals in Venice lagoon sediments: model, observation, and possible removal

We have modeled the distribution of nine toxic metals in the surface sediments from 163 stations in the Venice lagoon using published data. Three entrances from the Adriatic Sea control the circulation in the lagoon and divide it into three basins. We assume, for purposes of modeling, that Porto Marghera at the head of the Industrial Zone area is the single source of toxic metals in the Venice lagoon. In a standing body of lagoon water, concentration of pollutants at distancex from the source (C0) may be given byC=C0e−kx wherek is the rate constant of dispersal. We calculatedk empirically using concentrations at the source, and those farthest from it, that is the end points of the lagoon. Averagek values (ppm/km) in the lagoon are: Zn 0.165, Cd 0.116, Hg 0.110, Cu 0.105, Co 0.072, Pb 0.058, Ni 0.008, Cr (0.011) and Fe (0.018 percent/km), and they have complex distributions. Given thek values, concentration at source (C0), and the distancex of any point in the lagoon from the source, we have calculated the model concentrations of the nine metals at each sampling station. Tides, currents, floor morphology, additional sources, and continued dumping perturb model distributions causing anomalies (observed minus model concentrations). Positive anomalies are found near the source, where continued dumping perturbs initial boundary conditions, and in areas of sluggish circulation. Negative anomalies are found in areas with strong currents that may flush sediments out of the lagoon. We have thus identified areas in the lagoon where higher rate of sediment removal and exchange may lessen pollution.

Integrated coastal management in the Venice lagoon and its watershed

The Venice Lagoon (VL) is a complex ecosystem in which public participation and area-based management has often been neglected by administrative bodies involved in the planning of coastal projects and public works. In this area, the analysis of the local situation highlighted a substantial absence of coordination among the various administrative bodies in charge of planning and management at various governmental levels and in different regulated economic sectors. This paper analyses public participation and collaboration with reference to the Integrated Coastal Management context (ICM). The paper examines specific requirements, constraints, and opportunities for the complex case of the VL where participatory management and institutional coordination need enhancement.