Seasonal fluctuations of tissue mercury contents in the European shore crab Carcinus maenas from low and high contamination areas (Ria de Aveiro, Portugal)

The main objective was to study the seasonal variation of mercury concentrations in different tissues (muscle, hepatopancreas and gills) of Carcinus maenas from low and high Hg contaminated areas, a valuable resource in temperate estuaries and a possible pathway for human uptake. Individuals of two size classes (around 35 and 55 mm cephalothorax wide) were captured monthly between March 1999 and May 2000 in two areas of Ria de Aveiro: in the main navigation channel that connects the lagoon to the sea, and in the inner lagoon area heavily contaminated by mercury (maximum Hg in sediments of 5.4 microg g(-1)). Pronounced decreases in salinity and temperature and reduced food availability in winter seemed to be the responsible for the decline of the crab condition index (0.75-0.45) in larger individuals. Muscle and hepatopancreas exhibited higher mercury concentrations than gills, with concentrations in the contaminated site ranging from 0.03 to 0.63 microg g(-1) and 0.02 to 0.34 microg g(-1), respectively. Linear regressions between muscle and hepatopancreas (r=0.94, p<0.001) and muscle and gills (r=0.97, p<0.001) suggested a rapid redistribution of mercury inside the organism. During winter, a rapid elimination of mercury was found in the three analysed tissues followed by uptake. Larger crabs presented elimination rates from 18 to 34 ng g(-1) per week, while the smaller crabs showed lower elimination rates (10-24 ng g(-1) per week). The uptake was similar in both size classes (11-15 ng g(-1) and 8.1-15 ng g(-1) per week, respectively for large and small crabs). Our results suggest that C. maenas harvested in the contaminated areas must be considered with caution, since Hg concentrations were found to exceed the threshold concentration allowed for human consumption (0.5 microg g(-1)).     

非航测专业数字摄影测量教材问题研究

随着数字摄影测量的发展,众多行业和相关学科不断向摄影测量与遥感专业渗透,出现了非航测专业数字摄影测量教学问题,其中教材问题已经逐渐成为制约非航测专业数字摄影测量教学发展的障碍。针对非航测专业数字摄影测量教材问题进行研究。     

Remote sensing mapping of macroalgal farms by modifying thresholds in the classification tree

Remote sensing is the main approach to map aquatic vegetation, and classification tree (CT) is superior to various classification methods. Based on previous studies, modified CT can be developed from traditional CT by adjusting the thresholds based on the statistical relationship between spectral features to classify different images without ground-truth data. However, no studies have yet employed this method to resolve marine vegetation. In this study, three Gao-Fen 1 satellite images obtained on 30 January 2014, 5 November 2014 and 21 January 2015 were selected, and two features were then employed to extract macroalgae farms. Results show that the overall accuracies of traditional CTs for three images are 92.0, 94.2 and 93.9%, respectively, whereas those of the two corresponding modified CTs for images obtained on 21 January 2015 and 5 November 2014 are 93.1 and 89.5%, respectively. This indicates modified CTs can map macroalgae with multi-date imagery and monitor their spatiotemporal distribution in coastal environments.     

Spartina maritima (cordgrass) rhizosediment extracellular enzymatic activity and its role in organic matter decomposition processes and metal speciation

Seasonal monitoring was carried out to investigate the influence of extracellular enzymatic activity (EEA) on metal speciation and organic matter cycling in the rhizosediment of Spartina maritima . Heavy metal speciation was achieved by the Tessier scheme, and showed a similar pattern of variation of the organic-bound fraction, indicating a decomposition process in progress. Both humic acid and organic matter showed the same seasonal pattern. The basal respiration of the rhizosediments also presented a similar seasonal pattern, indicating a microbial degradation of organic matter. The high organic-bound fraction found in the summer gradually decreased towards the winter. This decrease was found to be related to the increase of activity of peroxidase, β- N -acetylglucosaminidase and protease. Also the activity of sulphatase was found to be related to the depletion on the exchangeable fraction, probably due to sulphide formation and consequent mobilization. The results show an interaction between several microbial activities, affecting metal speciation.     

Impact of climate and hydrology on juvenile fish recruitment towards estuarine nursery grounds in the context of climate change

Larvae of various coastal fish undergo immigration from spawning grounds towards estuarine nurseries. Several environmental factors can have an important impact on survival at this stage making it crucial for recruitment. Generalized linear models were applied in order to investigate the relation between river drainage, sea surface temperature (SST), NAO index and the North-South wind component intensity, over the two months prior to the estuarine colonization peak, and the densities of Platichthys flesus, Dicentrarchus labrax, Diplodus vulgaris and Diplodus bellottii in the nursery grounds based on a discontinuous historical dataset (from 1978 to 2006), for the Tagus estuary. The relation between SST over the 12 months prior to the estuarine colonization peak and fish densities in the nurseries was also investigated, as it integrates the periods of spawning stock maturation, spawning and larval immigration. While SST over the prior 12 months was negatively correlated with the abundance of P. flesus, it was positively correlated with the abundance of D. bellottii. Abundance of D. vulgaris was positively correlated with SST in the two months prior to the estuarine colonization peak, while the abundance of D. labrax was positively correlated with river drainage. The relations between SST and the abundance of P. flesus, a cold-water species with declining densities, and the subtropical species D. bellottii and D. vulgaris, which are increasing in abundance, are indicative of species abundance alterations related to climate warming. Dicentrarchus labrax will probably also be affected by climate change because of lowered precipitation and consequently river drainage.     

Testing the predictive power of seagrass depth limit models

The power of equations predicting seagrass depth limit (Z_c) from light extinction (K _z) was tested on data on seagrass depth limits collected from the literature. The test data set comprised 424 reports of seagrass colonization depth and water transparency, including data for 10 seagrass species. This data set confirmed the strong negative relationship betweenZ _c andK _z. The regression equation in Duarte (1991) overestimated the realized seagrass colonization depths at colonization depths < 5 m, while there was no prediction bias above this threshold. These results indicated that seagrass colonizing turbid waters (K _z 0.27 m^-1) have higher apparent light requirements than those growing in clearer waters. The relationship between seagrass colonization depth and light attenuation shifts at a threshold of light attenuation of 0.27 m^-1, requiring separate equations to predictZ _c for seagrass growing in more turbid waters and clearer waters, and to set targets for seagrass restoration and conservation efforts.     

An epigenetic origin for the Passagem de Mariana gold deposit, Quadrilátero Ferrífero, Minas Gerais, Brazil

The gold–tourmaline quartz–vein deposit of Passagem de Mariana, in the southeastern part of the Quadrilátero Ferrífero, produced more than 60 tonne of gold, from the end of the 17th Century until 1954. The mine has not operated since 1985. Orebodies are veins composed of white quartz (> 60 vol.%), carbonate (ankerite), tourmaline, sericite and sulfides. Tourmaline (dravite), up to 10 vol.% of the vein, occurs as subhedral, coarse, commonly zoned crystals, and is concentrated along vein boundaries and on the edges of host rock inclusions in the veins. Tourmaline is present in all rock types in the mine, but the chemical composition of the host rocks determinates the intensity of tourmalinization, with the alteration being greater in sericitic phyllites, graphite–sericite phyllites, and calcareous rocks. The most abundant sulfide is arsenopyrite, which is normally associated with pyrite and pyrrhotite. Minor amounts of chalcopyrite, galena, löllingite, berthierite, and maldonite are present throughout the deposit. Sulfides are concentrated at veins boundary or are dispersed in the veins. Arsenopyrite is associated, most commonly, with calcareous rocks, and graphite–sericite phyllite. Pyrrhotite is usually found at the base of itabirites. Gold abundance is directly proportional to sulfide concentration. Hydrothermal alteration associated with the veins includes silicification, tourmalinization, and sulfidation. The mineralized zone is a shear zone associated with a bedding-parallel thrust fault that juxtaposes the itabirite (Lower Proterozoic Minas Supergroup) over other units. This shear zone/thrust fault extends for tens of km beyond the Passagem mine and hosts numerous gold deposits. The richest orebodies are along the itabirite footwall contact and within the graphite–sericite phyllite (Main orebody). Although many lithologic units were mineralized the graphite–sericite phyllite appears to have been most favorable for gold deposition.The area underwent three phases of deformation, D₁, D₂ and D₃. Mineral assemblages indicate upper-greenschist to lower-amphibolite conditions of regional metamorphism. Retrograde metamorphism, characterized by chloritization of biotite and chloritization and biotitization of garnet, developed locally. The gold-bearing veins crosscut the main foliation and lithologic contacts at low angle and occur within, or are in contact with, all lithotypes. Field and laboratory data indicate that gold mineralization at Passagem de Mariana is epigenetic. Gold deposition occurred after the peak of metamorphism, within the late- to post-D₂ period of deformation, which is correlated with second set of structures of Trasamazonian age of Alkmim and Marshak [Alkmim, F.F., Marshak, S., 1998. Transamazonian Orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research 90, 29-58.], indicating that the gold mineralization occurred between 2.124 and 2.04 Ga. We choose to regard Passagem de Marina as an orogenic gold deposit as defined by Groves et al. [Groves, D. I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic gold deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews 13, 7-27.], i.e., an epigenetic, structurally-hosted lode–gold vein system in a deformed metamorphic terrane.