Stefano Guerzoni

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.

The impact of desert dust across the Mediterranean

Preface. Modelling and Climate. Climate Modeling Over the Mediterranean Region: An Overview F. Giorgi. Modeling of Dust Processes for the Saharan and Mediterranean Area S. Nickovic. Quantitative Remote Sensing of African Dust Transport to the Mediterranean F. Dulac, et al. Model Components Necessary to Capture a Dust Plume Pattern Over the Mediterranean Sea M. Schulz, et al. The Preliminary Modeling Results of Saharan Dust Transport to the Mediterranean Sea and Europe S. Grigoryan, L. Erdman. Importance of the Source Term and the Size Distribution to Model the Mineral Dust Cycle Y. Balkanski, et al. The Effects of Desert Particles on Cloud and Rain Formation in the Eastern Mediterranean Z. Levin, E. Ganor. Application of a Lagrangian Model to the Study of the Atmospheric Fluxes to the Western Mediterranean M. Alarcon, et al. Atlantic Perturbations Deeply Penetrating the African Continent: Effects Over Saharan Regions and the Mediterranean Basin M. Conte, et al. Seasonal Distribution of the Boundary Layer Depths over the Mediterranean Basin U. Dayan, et al. Biomass Burning in North Africa and Its Possible Relationship to Climate Change in the Mediterranean Basin D.O. Suman. Modeling the Present and Last Glacial Maximum Transportation of Dust to the Arctic With an Extended Source Scheme K. Andersen, C. Genthon. Geology and Source Regions. Saharan Dust Transport Over the North Atlantic Ocean and Mediterranean: An Overview J.M. Prospero. Mineralogical Characterisation of Saharan Dust with a View to its Final Destination in Mediterranean Sediments E. Molinaroli. The Mineralogical and Chemical Properties and the Behaviour of the Eolian Saharan Dust over Israel E. Ganor, et al. Identification and Quantification of Dust Additions in Peri-Saharan Soils L. Hermann, et al. Sedimentological Characteristics of Saharan and Australian Dusts L. Kiefert, et al. Saharan Dust Input to the Western Mediterranean: An Eleven Years Record in Corsica M.D. Loye-Pilot, J.M. Martin. African Dust Over Northeastern Spain: Mineralogy and Source Regions A. Avila, et al. Saharan Aerosols: From the Soil to the Ocean C. Guieu, A.J. Thomas. Atmosphere-Ocean Mass Fluxes at Two Coastal Sites in Sardinia (39-41 N, 8-10 E) O. Le Bolloch, et al. Mineralogy and Source of High Altitude Glacial Deposits in the Western Alps: Clay Minerals as Saharan Dust Tracers L. Tomadin, et al. Grain Size Analysis of Aerosol and Rain Particles: A Methodological Comparison G. de Falco, et al. Aerobiological Results from the 1994 Cruise of the Urania (CNR) II P. Comtois, P. Mandrioli. Long-Range Transport of Biological Particles of Desert Origin: A Short Review M. Hjelmroos. Chemical Fluxes and Composition of the Atmosphere. The Influence of Saharan and Middle Eastern Desert-Derived Dust on the Trace Metal Composition of Mediterranean Aerosols and Rainwater: An Overview R. Chester, et al. Elemental Composition and Air Trajectories of African Dust Transported in Northern Italy P. Bonelli, et al. The Impact of Saharan Dust on Trace Metal Solubility in Rainwater in Sardinia, Italy F. Frau, et al. Northward Transport of Saharan Dust Recorded in a Deep Alpine Ice Core D. Wagenbach, et al. Estimating Dust Input to the Atlantic Ocean Using Surface Water Aluminium Concentrations C.I. Measures, E.T. Brown. Effect of Saharan Dust Transport on Ozone and Carbon Dioxide Concentration P. Bonasoni, et al. African Dust Influence on Rainwater on the Eastern Coast of Spain A. Carratala, et al. Trace Metal C

Saharan dust inputs to the western Mediterranean Sea: depositional patterns, geochemistry and sedimentological implications

Data are presented for a number of parameters for aerosols and rainwaters collected at a station on Sardinia. The findings are interpreted with special reference to Saharan dusts, and are compared to other data on these dusts obtained from a variety of sites around the Mediterranean Sea. At the Sardinia site the particle size distribution of the Saharan outbreaks exhibits a bimodal structure, the two modes being between 2 and 4 μm and 15 and 30 μm. The presence of giant particles strongly affects the deposition velocities of the Saharan aerosols. Source markers for the Saharan dusts are palygorskite, kaolinite, calcite, dolomite and rounded quartz grains. The input of Saharan dust has important effects on the chemistry of the Mediterranean aerosols. These include: (i) increases in the atmospheric concentrations and sea surface fluxes of crust-controlled trace metals (e.g. Al, Fe); (ii) decreases in the EFcrust values of non-crust-controlled trace metals (e.g. Cu, Zn and Pb) in the aerosols, and (iii) changes in the solid state speciation of Cu, Zn, and Pb, which decrease their solubilities in seawater. The Saharan dusts also affect the composition of rainwater by raising the pH, following the dissolution of calcium, and by decreasing the solubility of trace metals such as Cu, Zn and Pb. Wet deposition controls the flux of Saharan dust to the Mediterranean Sea, but dry deposition can also be important. The dust transport occurs in the form of “pulses”, and the annual dust flux can be controlled by a few episodes of Saharan outbreaks, e.g. sometimes a single outbreak can account for 40–80% of the flux. Saharan dust deposition fluxes range from 2 to 25 g m−2 (average ≅10) in the west Mediterranean between 39° and 42°N, from 6 to 46 g m−2 (average ≅20) in the east Mediterranean, and from 0.4 to 1.0 g m−2 over the Alps on continental Europe. The present day Saharan dust fluxes (≈ 1 mg cm−2 year−1) account for about 10–20% of the recent deep-sea sedimentation in the western Mediterranean (3–15 mg cm−2 year−1).

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].

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.

Total and “Selective” Extraction Methods for Trace Metals in Marine Sediment Reference Samples (Mess-1, NBS 1646)

Abstract Trace metals (Cd, Cr, Cu, Mn, Pb and Zn) and Fe were analyzed in two sediment reference samples (NBS 1646, MESS-1) with AAS fitted with graphite furnace, using five different (three total and two selective) extraction procedures. The comparison of the total digestion methods (hot strong acids) with reference materials gave good results for almost all of them, and the “teflon bomb” was preferred for its rapidity and ease of operation. Some non-referenced data on total and organic carbon, total nitrogen and minerals are given. The two selective leaching extractions (nitric and cold hydrochloric) were also compared with reference values. The use of certified reference materials (CRM) for environmental chemistry is recommended, together with the determination of organic matter and fundamental mineralogical composition.

Hydrological Regime and Renewal Capacity of the Micro-tidal Lesina Lagoon, Italy

A multidisciplinary approach that combines field measurements, artificial neural networks, water balance analyses and hydrodynamic modelling was developed to investigate the water budget and renewal capacity of semi-closed coastal systems. The method was applied to the Lesina Lagoon, a micro-tidal lagoon in the southern Adriatic Sea (Italy). Surface water flux between the lagoon and the sea was determined by neural network prediction and used as input in the analysis. Strong seasonal variations in the water budget equation were predicted. Fresh water inputs estimated by the water balance analysis were used as forcing by a calibrated finite element model to describe the water circulation and transport time scale of the lagoon’s surface waters. The model highlighted the spatial heterogeneity of the renewal behaviour of the system, with a strong east–west water renewal time gradient. Knowledge of spatial distribution of water renewal times is crucial for understanding the lagoon’s renewal capacity and explaining the high spatial variability of the biogeochemistry of the Lesina Lagoon.

Trace Metal Composition and Grain-Size of Particulates in Aerosols and Precipitation Collected in N.W. Mediterranean (39° N, 9° E): A Multivariate Analysis

The chemical characteristics and the grain-size patterns of the mineral fraction in Sardinian aerosols and precipitation were highlighted by means of Q-Mode Factor Analysis (Q-FA) on major elements (Al, Ca, Fe, Mg, Na, K, Si), and trace metal data (Cd, Cr, Pb, Zn). Three factors explained more than 95% of the variability: the first two representing the background aerosols (Mediterranean) and local inputs from different source regions (Sardinian) respectively, and the third one being the Saharan factor. Grain-size modes of background and local aerosols were 1 and 2 μm respectively, whilst Saharan dust mode was in the range 2–8 μm. Mediterranean background aerosols in Sardinia showed a 3 to 25-fold decrease in Efcrust values for Cd, Zn, Pb and Cr compared with coastal stations in the West and in Corsica. Local inputs resulted mainly enriched in Pb and Zn, which could represent Sardinian sources to the Central Mediterranean Sea.

Atmosphere-Ocean Mass Fluxes at Two Coastal Sites in Sardinia (39–41° N, 8–10° E)

At two remote coastal sites in Sardinia, the two major soluble and insoluble components of aerosols and rainwater collected were seasalt (avg. rain = 61 µg g−l; aerosol = 19 µg m−3) and minerals (avg. rain = 13 µg g−1; aerosol = 9 sg m−3). While seasalt content was more or less similar, a three to seven times higher mineral concentration was found in Saharan (SAH) as compared to background (BKG) samples. Mean wet mass flux in Sardinia for the period 1990–1995 was 3 g m−2 yr−1, and wet-to-dry deposition ratio was highly variable (0.8–2.2). Particulate scavenging ratios (SR) were calculated separately for BKG and SAH samples giving values of 600 and 1800, respectively.