Carbonaceous materials in size-segregated atmospheric aerosols from urban and coastal-rural areas at the Western European Coast

A high-volume cascade impactor, equipped with a PM10 inlet, was used to collect size-segregated aerosol samples during the summer of 2004 at two Portuguese locations: a coastal-rural area (Moitinhos) and an urban area (Oporto). Concentrations of airborne particulate matter (PM), total carbon (TC), organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were determined for the following particle size ranges: < 0.49, 0.49–0.95, 0.95–3.0, and 3.0–10 µm. The total PM mass concentrations at the urban and coastal-rural sites ranged from 22.8 to 79.6 μg m^− 3 and 19.9 to 28.2 μg m^− 3, respectively, and more than 56% of the total aerosol mass was found in the fractions below 3.0 μm. At both locations the highest concentrations of OC and EC were found in the submicrometer size range. The regional variability for the OC and EC concentrations, with the highest concentrations being found in the urban area, was related to the contribution of local primary sources (mostly traffic emissions). It was also verified an enrichment of the small size particles in WSOC, representing on average 37.3(± 12.4)% and 59.7(± 18.0)% of OC in the very fine aerosol at the coastal-rural and urban areas, respectively. The amount of secondary OC calculated by the minimum OC/EC ratio method indicates that secondary organic aerosol formation was important throughout the study at both sites. The obtained results suggest that long-range transport and favourable summer conditions for photochemical oxidation are key factors determining secondary OC formation in the coastal-rural and urban areas. The ultraviolet absorption properties of the chromophoric constituents of the WSOC fractions were also different among the different particle size ranges and also between the two sampling locations, thus suggesting the strong impact of the diverse emission sources into the composition of the size-segregated organic aerosol.     

An effective Lagrangian description of supernova-core bounce

In standard hydrodynamical supernova computations many variables are needed to describe the time evolution of the stellar core. A numerical grid of points is usually constructed to attain the desirable accuracy. This fact limits the codes to run in the biggest and fastest computers. A new semi-analytical approach for the problem of the dynamical evolution of the collapse, bounce and explosion of a supernova core is proposed. The relevant coordinates of the dynamical problem are chosen to define an effective Lagrangian. The Lagrangian variables are the radii of the shells, seen now as collective coordinates, which describe the global aspects of the process. An effective Lagrangian with these properties for any number of shells is presented. The equations of motion are obtained from this Lagrangian and then integrated numerically. The potentiality of the method is exemplified for the extreme case in which only two shells are used to describe the stellar core. Even in this instance, it is possible to discuss the circumstances for the occurrence of supernova explosion.     

The Juiz De Fora Granulite Complex of the Central Ribeira Belt, SE Brazil: A Paleoproterozoic Crustal Segment Thrust During the Pan-African Orogeny

The granulites of the Juiz de Fora complex occur within thick basement thrust slices associated with the Pan-African shortening process in the central segment of the Ribeira belt. Five lithological units of the Intermediate tectonic domain of the belt can be identified on the basis of detailed geological mapping: a) orthogranulites, b) orthogneisses; c) kinzigite; d) intrusive garnet charnockite and e) amphibolite facies metasediments of probable Meso to Neoproterozoic age, correlated to the cover of the belt. Petrological data indicate high temperatures and intermediate to low lithostatic pressure conditions for the Paleoproterozoic granulite facies metamorphism. Textures and CO₂-rich fluid inclusions are probably related to an IBC path. Geochemical data do not show relevant compositional change as a result of the granulite metamorphism. Two calc-alkaline suites and tholeiitic to alkaline basic rocks can be related to compressional and extensional settings, respectively. The overall composition of the granulites, the lack of substantial LILE depletion as well as the composition of the fluid inclusion points to granulitization process driven by CO₂-rich fluids. Orthogranulites gave rise to banded gneisses as a result of the Pan-African retrograde metamorphism and intense deformation. The U and Th depletion detected in few rocks is possibly related with the hydrated conditions of the retrograde reactions.     

Numerical Prediction of the Boundary-Layer Flow Over the Bolund Hill: Assessment of Turbulence Models and Advection Schemes

Boundary-Layer Meteorology - The WindStation software package is applied to simulate the wind field over the Bolund hill. The standard, ReNormalization Group (RNG), realizable, and limited-length...     

Application of Non-Ionic Solid Sorbents (XAD Resins) for the Isolation and Fractionation of Water-Soluble Organic Compounds from Atmospheric Aerosols

A detailed procedure using non-ionic macropourous XAD-8 and XAD-4 resins is presented for the isolation and fractionation of aerosol water-soluble organic compounds (WSOC) from aerosol samples. The procedure entails adsorption of WSOC fraction onto XAD-8 and XAD-4 resins, desalting of the adsorbed organic material with ultra-pure water, elution of the retained organic matter with 40% MeOH solution and freeze-drying. Due to resin’s different properties and to certain hydrophobic/hydrophilic interactions between the resin polymers and the organic matter, two major fractions were obtained; namely the XAD-8 and the XAD-4 eluates. The XAD-8 eluate, which accounts for 55–60% of total aerosol WSOC, is represented by partially acidic compounds with significant hydrophobic moieties. The XAD-4 fraction holds few conjugated systems and a higher content of hydrophilic structures with low molecular size, and accounts for 9% of total WSOC. The isolated WSOC sub-fractions were nearly free from inorganic species, and successful recoveries of organic matter from the resins were accomplished. With this procedure the XAD-8 eluate yields a mixture representative of those WSOC that are highly conjugated compounds in atmospheric aerosols. It also allows a successful characterisation of the organic material by advanced analytical techniques without the interference of inorganic species present in the original sample of atmospheric particles.     

Mercury distribution in Douro estuary (Portugal)

Determinations of dissolved reactive and total dissolved mercury, particulate and sedimentary mercury, dissolved organic carbon (DOC), particulate organic carbon (POC) and suspended particulate matter (SPM) have been made in the estuary of river Douro, in northern Portugal. The estuary was stratified by salinity along most of its length, it had low concentrations of SPM, typically <20 mg dm(-3), and concentrations of DOC in the range <1.0-1.8 mg dm(-3). The surface waters had a maximum dissolved concentration of reactive mercury of about 10 ng dm(-3), whereas for the more saline bottom waters it was about 65 ng dm(-3). The surface waters had maximum concentrations of total suspended particulate mercury of approximately 7 microg g(-1) and the bottom waters were always <1 microg g(-1). Concentrations of mercury in sediments was low and in the range from 0.06 to 0.18 microg g(-1). The transport of mercury in surface waters was mainly associated with organic-rich particulate matter, while in bottom waters the dissolved phase transport of mercury is more important. Lower particulate organic matter, formation of chlorocomplexes in more saline waters and eventually the presence of colloids appear to explain the difference of mercury partitioning in Douro estuarine waters.     

Recolonization dynamics in a mixed seagrass meadow: The role of clonal versus sexual processes

Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m² gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively, recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors to the overall 450 m² increase in vegetation cover through fast lateral extension (144±6 cm yr⁻¹) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.     

Nekton use of salt marsh creeks in the upper Tejo estuary

The use of the Tejo estuary, Portugal, salt marsh creeks by nekton was examined based on sampling surveys with a fyke net from September 1998 until August 2001. From the 20 taxa (14 fish species, 5 decapod crustacean species, and 1 cephalopod species) identified in the studied creeks, 16 were regularly caught throughout the sampling period. The shrimpPalaemonetes varians was the most numerically abundant species in the creeks, while the biomass was dominated by the mulletLiza ramada. The nekton assemblage was mainly represented by marine-estuarine opportunist species, comprising 85% of the total. A high seasonality was detected on the species abundance patterns: the most abundant species (P. varians, Crangon crangon, L. ramada, Pomatoschistus microps, Syngnathus sp., andAnguilla anguilla) occurred throughout the sampling period,Sardina pilchardus, Dicentrarchus, labrax, andAtherina boyeri were particularly abundant in spring and summer, andEngraulis encrasicholus, Liza aurata, Gambusia holbrooki, Palaemon longirostris, andPalaemon serratus were most abundant in autumn and winter.L. ramada occurred in the tidal creeks in high numbers during neap tides, while the majority of the remaining taxa were most abundant during spring tides, suggesting a differential pattern of habitat use occording to species.     

Pattern and annual rates of Scrobicularia plana mercury bioaccumulation in a human induced mercury gradient (Ria de Aveiro, Portugal)

Due to the lack of knowledge regarding annual bioaccumulation rates in estuarine and marine fauna, the main aim of this work was to study the annual mercury bioaccumulation in the well-documented bivalve species Scrobicularia plana along a human induced mercury gradient in the Ria de Aveiro coastal lagoon (Portugal) and in a nearby, non-polluted system (Mondego estuary), parallel to the risks associated with its consumption by humans.Minimum total mercury concentration was as low as 0.019 mg kg⁻¹ (wwt) in 4+ year old organisms in the reference site, where a significant negative correlation (p < 0.05) was found between total mercury concentrations and size, resulting in negative bioaccumulation rates (detoxification). On the other hand, values reached 1.8 mg kg⁻¹ (wwt) in 3+ year old bivalves from the most contaminated area, where a strong positive correlation with size was found (p < 0.01) and annual bioaccumulation rates were as high as 0.25 mg kg⁻¹ yr⁻¹. Annual bioaccumulation rates were highly correlated with suspended particulate matter mercury concentrations. Even though the levels of organic mercury contents increased parallel to the contamination gradient, at each sampling station, no increment was found with age, which corresponded to a decrease in organic mercury percentage with age.In terms of ecological management and public health, the ratio of 0.01 consistently found between Scrobicularia plana annual mercury accumulation rates and SPM mercury levels for most sites may permit to roughly estimate S. plana contamination of commercial sized individuals (>2.5 cm) and, if verified and confirmed in other systems, be used as a simple management tool.     

Sediment deposition and production in SE-Asia seagrass meadows

Seagrass meadows play an important role in the trapping and binding of particles in coastal sediments. Yet seagrass may also contribute to sediment production directly, through the deposition of detritus and also the deposition of the associated mineral particles. This study aims at estimating the contribution of different seagrass species growing across an extensive range of deposition to inorganic (carbonate and non-carbonate) and organic sediment production. Total daily deposition measured with sediment traps varied from 18.8 (±2.0) g DW m⁻² d⁻¹ in Silaqui (Philippines) to 681.1 (±102) g DW m⁻² d⁻¹ in Bay Tien (Vietnam). These measurements correspond to a single sampling event and represent sedimentation conditions during the dry season in SE-Asia coastal areas. Enhalus acoroides was the most common species in the seagrass meadows visited and, together with Thalassia hemprichii, was present at sites from low to very high deposition. Halodule uninervis and Cymodocea species were present in sites from low to medium deposition. The mineral load in seagrass leaves increased with age, and was high in E. acoroides because it had the largest and long-lived leaves (up to 417 mg calcium carbonate per leaf and 507 mg non-carbonate minerals per leaf) and low in H. uninervis with short-lived leaves (4 mg calcium carbonate per leaf and 2 mg non-carbonate minerals per leaf). In SE-Asia seagrass meadows non-carbonate minerals accumulate at slower rates than the production of calcium carbonate by the epiphytic community, consequently the final loads supported by fully grown leaves were, as average, lower than calcium carbonate loads. Our results show that organic and inorganic production of the seagrasses in SE-Asia represents a small contribution (maximum of 15%) of the materials sedimented on a daily base by the water column during the sampling period. The contribution of the carbonate fraction can be locally significant (i.e. 34% in Silaqui) in areas where the depositional flux is low, but is minor (<1%) in sites were siltation is significant (i.e. Umalagan and all the visited sites in Vietnam).