Benthic mucilaginous aggregates in the Mediterranean Sea: Origin, chemical composition and polysaccharide characterization     

Gianfranco Sartoni  Ranieri Urbani  Paola Sist  Daniela Berto  Caterina Nuccio  Michele Giani   《Marine Chemistry》2008,111(3-4):184-198

Benthic mucilaginous aggregates are frequently formed in various parts of the Mediterranean basin, as in the Tyrrhenian and Adriatic Seas. Notwithstanding their wide spatial distribution, the role played by these aggregates in the biogeochemical cycling of organic matter is still largely unknown.The characteristics of the benthic aggregates examined in the present study showed that they are different from other mucilaginous aggregates, such as the “pelagic” ones that can form in the same areas in the water column and subsequently sediment to the seafloor. The aggregates are usually formed of structures of the filamentous macroalgae Acinetospora crinita, Chrysonephos lewisii and Nematochrysopsis marina. The elemental composition of the aggregates showed a marine macrophyte origin on the basis of the bulk organic matter content of the aggregates. Carbohydrates and proteins account for 26.6 to 55.9% of the organic carbon in the mucilage, respectively. Monosaccharide composition of exopolysaccharides in the mucilage aggregates revealed a characteristic pattern, with galactose, xylose or mannose and fucose as the major components. The relatively high content of deoxysugars is another distinctive feature. The abundant sulphate and uronic groups present in the polysaccharides in addition to their macromolecular dimensions and elongation contribute to inter-chain aggregation. Electron microscopic observations suggest that the polysaccharide fraction is the main macromolecular component in the formation of the persistent gel network in the aggregates.  相似文献   

Fractal dimensions of suspended solids in streams: comparison of sampling and analysis techniques     

Dirk H. de Boer  Mike Stone 《水文研究》1999,13(2):239-254

Fluvial suspended sediment typically consists of a variety of complex, composite particles referred to as flocs. Floc characteristics are determined by factors such as the source, size and geochemical properties of the primary particles, chemical and biological coagulation processes in the water column and shear stress and turbulence levels in the stream. Studies of floc morphology have used two contrasting methods of sampling and analysis. In the first method, particles settle on a microscope slide and are observed from below using an inverted microscope. The second method uses filtration at no or low vacuum and particles deposited on the filter are observed with a microscope. Floc morphology can be quantified using fractal dimensions. The aims of the present study were to examine the effect of the two sampling methods on the fractal dimensions of particle populations, and to evaluate for each method how well the fractal dimensions at the various sampling sites reflect basin conditions. Suspended solids were collected in triplicate on inverted microscope slides and on 0·45 μm Millipore HA filters in two southern Ontario streams with contrasting riparian zones during a minor runoff event resulting from the melt of a freshly fallen snowpack. An image analysis system was used to determine area, longest axis and perimeter of particles. The morphology of the particle population of each sample was characterized using four fractal dimensions (D, D₁, D₂ and D_K). Systematic differences in fractal dimensions obtained with the two methods were observed. For the settling method, outlines of larger particles were frequently blurred because of the distance between the focal plane (the top of the inverted microscope slides) and the plane of the particle outline. In this method, the blurring of large particles can cause an increase in the projected area and length of the particle. The effect on the particle perimeter is unpredictable because it depends on the amount of detail lost through blurring and its effect on the apparent increase in particle size. Because of blurring, D and D₁ tend to be systematically lower for the settling method, whereas the net effect on D₂ is unpredictable. Particle size distributions derived from settling are typically coarser because small, low density particles may remain in the water column and all particles may not deposit on the slides. This loss of fines results in systematically lower D_K values for the settling method compared with the filtration method. Fractal dimensions and particle size distributions obtained with the filtration method were sensitive to and clearly indicated differences between drainage basins and between sites within each basin. These differences were explained by basin characteristics and conditions. Fractal dimensions and particle size distributions obtained with the settling method were less sensitive to drainage basin characteristics and conditions, which limits their usefulness as process indicators. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Influence of winds and oceanographic conditions on the mucilage aggregation in the Northern Adriatic Sea in 2003–2006     

Amelia De Lazzari  Daniela Berto  Daniele Cassin  Alfredo Boldrin  Michele Giani 《Marine Ecology》2008,29(4):469-482

Meteorological and oceanographic conditions in the Northern Adriatic Sea in a year notable for massive mucilage formation (2004) were compared with those in years where this phenomenon did not occur (2003, 2005 and 2006) to suggest possible links. The months preceding the mucilage event in 2004 were considered the ‘incubation period’ and were characterized by a strong freshet in May which increased the water column stability. Winter cooling and scarcity of freshwater inputs from the Po River triggered the dense water formation and intrusion in the northern basin. Weak southeasterly winds and an increase in surface seawater temperatures contributed to maintain and reinforce the water column stability, and at the same time an intense diatom spring bloom created the conditions for accumulation of organic matter. The interplay of climatological forcings and biological processes caused temporal variations of dissolved organic carbon (DOC) and particulate organic carbon (POC) in the basin, with POC playing an important role in the aggregation process, as suggested by its increase relative to DOC before massive mucilage formation. We therefore suggest that high POC/total particulate nitrogen ratios in the suspended particulate organic fraction, a steep increase of POC/Chlorphyll a, and the decreased DOC/POC ratios represent ‘early warning’ signals of the main processes that lead to mucilage events in the Northern Adriatic Sea.  相似文献   

Probabilistic seasonal streamflow forecasts of the Citarum River,Indonesia, based on general circulation models     

Netrananda?SahuEmail authorView author&#;s OrcID profile  Andrew?W.?Robertson  Rizaldi?Boer  Swadhin?Behera  David?G.?DeWitt  Kaoru?Takara  Manish?Kumar  R.?B.?Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(7):1747-1758

In this study we discuss probabilistic forecasts of Citarum River streamflow, which supplies 80 % of the water demands in Jakarta, Indonesia, based on general circulation model (GCM) output, for the September–November (SON) season. Retrospective forecasts of precipitation made over the period 1982–2010 with two coupled-ocean atmosphere GCMs, initialized in August, are used in conjunction historical streamflow records, with a cross-validated regression model. Pearson’s product moment correlation skill values of 0.58–0.67 are obtained, with relative operating characteristic scores of 0.67–0.84 and 0.74–0.92 for the lower and upper tercile categories of flows respectively. Both GCMs thus demonstrate promising ability to forecast below/above normal streamflow for the Citarum River flow during the SON season.  相似文献   

Origin of sedimentary organic matter in the north-western Adriatic Sea   总被引：1，自引：0，他引：1  

M. Giani  D. Berto  F. Rampazzo  F. Savelli  F. Alvisi  P. Giordano  M. Ravaioli  F. Frascari 《Estuarine, Coastal and Shelf Science》2009,84(4):573-583

In order to evaluate the origin and the transformation of organic matter on the shallow shelf of the NW Adriatic Sea, organic carbon, total nitrogen and stable isotope ratios of organic carbon were analysed in riverine suspended matter and sediments as well as in marine suspended and sedimentary organic matter, in marine phytoplankton and zooplankton.The deposition of organic matter is influenced by fine sediment concentration. Surface sediments were characterised by highly variable biogeochemical conditions on the sea floor, whereas sub-surface sediments showed a more homogeneous hypoxic/anoxic environment.Low C_org/N ratio and high organic carbon and nitrogen concentrations in riverine suspended organic matter indicate an important contribution of freshwater phytoplankton within rivers, particularly during low flow regimes, which adds to the marine phyto- and zooplankton at shelf locations.In order to evaluate the importance of terrestrial, riverine and marine sources of OM in shelf sediments, a three end-member mixing model was applied to shelf surface sediments using ¹³C/¹²C values for organic matter and N/C ratios. The model showed an elevated contribution of terrestrial organic substances at intermediate depths (10–15 m), mostly corresponding to an area of coarser grain-size, whereas the riverine and marine organic fractions were mainly accumulating near the coast and offshore, respectively.  相似文献   

Spatial and temporal variability in bio-optical properties of the Wadden Sea     

Annelies Hommersom  Steef Peters  Marcel R. Wernand  Jacob de Boer 《Estuarine, Coastal and Shelf Science》2009

The Wadden Sea, a shallow coastal area bordering the North Sea, is optically a complex area due to its shallowness, high turbidity and fast changes in concentrations of optically active substances. This study gathers information from the area on concentrations of suspended particulate matter (SPM), Chlorophyll-a (Chl-a), and Coloured Dissolved Organic Matter (CDOM), on total absorption and beam attenuation, and on reflectances from the whole area. It examines the processes responsible for variations in these. Sampling took place at 156 stations in 2006 and 2007. At 37 locations also the specific inherent optical properties (SIOPs) were determined. Results showed large concentration ranges of 2–450 (g m^-3) for SPM, 2–67 (mg m^-3) for Chl-a, and 0–2.5 m⁻¹ for CDOM(440) absorption. Tides had a large influence on the SPM concentration, while Chl-a had a mainly seasonal pattern. Resuspension lead to a correlation between SPM and Chl-a. The absorption of CDOM had a spatial variability with extremely high values in the Dollard, although the slope of CDOM absorption spectra was comparable with that of the North Sea. The Chl-a specific pigment absorption proved to be influenced by phytoplankton species and specific absorption of non-algal particles at 440 nm was correlated with the mud content of the soil at the sample locations. SPM specific absorption was not found to correlate with any measured factor. As the concentrations of optically active substances changed, we also found spatial and temporal variability in the absorption, beam attenuation and reflectances. Reflectance spectra categorized in groups with decreasing station water depths and with extreme CDOM and SPM concentrations showed distinguishable shapes.  相似文献   

Some dynamical consequences of Greenhouse gas warming     

G.J. Boer 《大气与海洋》2013,51(4):731-751

Abstract

The change in December‐February climate simulated by the CCC GCM for a doubling of CO₂ is viewed from a Northern Hemisphere middle‐latitude persepctive. The simulated change in temperature is such as to reduce equator‐to‐pole and ocean‐to‐land temperature gradients in the body of the troposphere and this is expected to result in less baroclinicity and baroclinic instability, weaker eddies and transports and generally to a decrease in synoptic activity or, in other words, to more “summer‐like” conditions.

The overall “rate of working” of the atmosphere, as measured by the generation of available potential energy, its conversion to kinetic energy and subsequent dissipation, decreases by some 12%. However, while the amount of available potential energy in the atmosphere decreases by about the same amount, the amount of kinetic energy is unchanged. Differences to the mean zonal, standing and transient eddy components of available potential and kinetic energies and to their rates of generation and conversion show that the energy cycle has changed in ways that might not be immediately expected.

Despite the general decrease in activity, the net poleward transport of energy by the atmosphere is remarkably unchanged. This is accomplished with the expected decrease in the transport of dry static energy being off‐set by an increase in latent energy transport. This is true both for mean zonal and eddy transports. That the same amount of energy is transported by a generally less active atmosphere shows that, in a sense, the flow structures are more “efficient” in the warmer climate and calculations are made to quantify this. The transport of energy in latent form is much more efficient due to the strong increase in moisture content that accompanies the temperature increase.  相似文献   

A comparative study on a complex URM building: part II—issues on modelling and seismic analysis through continuum and discrete-macroelement models     

Castellazzi  G.  Pant&#;  B.  Occhipinti  G.  Talledo  D. A.  Berto  L.  Camata  G. 《Bulletin of Earthquake Engineering》2022,20(4):2159-2185

Bulletin of Earthquake Engineering - The paper presents the comparison of the results obtained on a masonry building by nonlinear static analysis using different software operating in the field of...  相似文献   

Spectra of a shallow sea—unmixing for class identification and monitoring of coastal waters     

Annelies Hommersom  Marcel R. Wernand  Steef Peters  Marieke A. Eleveld  Hendrik Jan van der Woerd  Jacob de Boer 《Ocean Dynamics》2011,61(4):463-480

Ocean colour-based monitoring of water masses is a promising alternative to monitoring concentrations in heterogeneous coastal seas. Fuzzy methods, such as spectral unmixing, are especially well suited for recognition of water masses from their remote sensing reflectances. However, such models have not yet been applied for water classification and monitoring. In this study, a fully constrained endmember model with simulated endmembers was developed for water class identification in the shallow Wadden Sea and adjacent German Bight. Its performance was examined on in situ measured reflectances and on MERIS satellite data. Water classification by means of unmixing reflectance spectra proved to be successful. When the endmember model was applied to MERIS data, it was able to visualise well-known spatial, tidal, seasonal, and wind-related variations in optical properties in the heterogeneous Wadden Sea. Analyses show that the method is insensitive to small changes in endmembers. Therefore, it can be applied in similar coastal areas. For use in open ocean situations or coastal or inland waters with other specific inherent optical properties, re-simulation of the endmember spectra with local optical properties is required. However, such an adaptation requires only a limited number of local in situ measurements.  相似文献   

Dating of coal fires in Xinjiang, north-west China     

Xiangmin Zhang  Salomon B. Kroonenberg  Cor B. de Boer 《地学学报》2004,16(2):68-74

Coal fires in China consume vast amounts of fuel and cause serious environmental problems. Most of these coal fires are related to mining activity. However, naturally produced palaeo coal fires in Xinjiang, north‐west China, have been recognized via burnt rocks. The burnt rocks in the study area are found at different river terraces underlying unburnt alluvial and river terrace deposits. Several age groups of coal fires have been identified based on the positions of burnt rocks at river terraces and the relationship between the burnt rocks and the terrace deposits. These palaeo coal fires are: (1) Pliocene – Early Quaternary in age at 200 m above present river terrace deposits; (2) Middle Pleistocene in age, at > 90 m; (3) Late Pleistocene, at 90–70 m; (4) Holocene; (5) burnt rocks relating to active coal fires. Palaeomagnetic data of the burnt rocks from different terraces give normal remanent magnetization and help further to constrain the ages of the coal fires.  相似文献