The Nature of Organic Matter in the Danube River Particles and North-western Black Sea Sediments (original) (raw)
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Transport and fate of Danube Delta terrestrial organic matter in the Northwest Black Sea mixing zone
Marine Chemistry, 2002
Within the framework of the European project EROS 21, a biogeochemical study of particles transported from the Danube Delta to the Northwestern Black Sea whose carbon cycle is dominated by riverine inputs was carried out in spring off the Sulina branch of the Danube Delta. The distribution of particulate organic carbon (POC), chlorophyll a (Chl a), C/N, and d 13 C evidenced an omnipresent contribution of terrestrial organic matter throughout the study area together with a dilution of these inputs by freshwater and marine organisms. Four lipid series, n-alkanoic acids, n-alkanes, n-alkanols, and sterols were analyzed by gas chromatography and gas chromatography/mass spectrometry. Several signature compounds were selected to delineate dispersion of terrestrial organic carbon: (1) long-chain n-alkanoic acids in the range C 24 -C 34 , long-chain n-alkanes in the range C 25 -C 35 , long-chain n-alkanols in the range C 22 -C 30 , 24-ethylcholesta-5,22-dien-3h-ol (29D 5,22 ) and 24-ethylcholesterol (29D 5 ) for vascular plant-derived material and (2) coprostanol (27D 0,5h ) for faecal contamination associated with sewage effluents. A marked decrease was observed between the concentrations of different vascular plant markers characterizing the two end members: riverine at salinity 0.3 and marine at salinity 15.5. The decrease observed for marine/riverine end members (expressed as a function of organic carbon) varied in a large range, from 4% for n-alkanes to 18.6%, 20.4% and 24% for n-fatty acids, n-alkanols and sterols, respectively. These values reflect a combination of various processes: size-selective particle sedimentation, resuspension of different particle pools of different sizes and ages, and/or selective biological utilization. The multi-marker approach also suggested the liberation in the mixing zone of terrestrial moieties, tightly trapped in macromolecular structures of the riverine material. The greatest decrease for marine/riverine end members was observed for coprostanol (0.9%), underlining the efficiency of the mixing zone as a sink for sewage-derived carbon. D
2000
A positive correlation between the finer grain size fractions (clay and/or silt) and TOC was well established long ago (Buchanan and Longbottom, 1970; Mayer, 1994; Tyson, 1995 etc.). The close association of the two components is probably explained by both the capacity of the finer particles to hinder the diffusion of the oxygen into the sediments, thus favoring the preservation of organic matter and the adsorp-tion of organic particles onto the charged surfaces of the clay minerals. The last process largely depends upon the specific surface of the sediment, so much so that sometimes this parameter is preferred over the percentage of finer fractions as independent variable, determining the TOC concentration in sediments. Of course there is not a unique, generally valid relation. There are important local variations, determined mainly by the local primary production, sedimentary rates and oxygen regime in the water column and sediments. The mathematical relation between the percentag...
The paper presents the distribution of the Total Organic Carbon (TOC) in the surface layer sediments of the Black Sea Romanian shelf, since September 2009 to September 2010. The study is based on the analysis of samples from 21 stations. The results have led to the following conclusions: the TOC content in the surface sediments revealed values in the range „undetectable“ up to 14.94% (mean 3.38%, median 3.28%, standard deviation 2.70%). The values generally highlighted a gradient increasing with distance from the shore and, at the same time, nearby the Danube’s mouths, with the fine sediment fractions increase. Statistically, the TOC content of the stations under the direct influence of the river discharge was significantly higher in 2010 than 2009, due to the historical raised flow of the Danube. The spatial and temporal distribution of TOC content showed also high values in the Constanta area, in late summer, due to the increased river discharge in 2010, algal blooms and the anthropogenic influence of the wastewater treatment plants. Key words: Black Sea, Total Organic Carbon, Surface sediments, Eutrophication
Marine Chemistry, 2007
Sediment cores from the Black Sea were analyzed along two transects across the basin in West-East and North-South direction and ranging from the oxic and suboxic shelf to the anoxic slopes and abyssal plain. On the North-Western shelf, the average concentrations of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in recent sediments showed a decrease with increasing distance to the shore. Compared to the shelf, TP concentration was depleted on the slope and towards the central basin whereas TOC and TN concentrations increased towards the deep central basin. Anthropogenic nutrient loads of the last 50 years have left a clear signature in the sedimentary record. On the shelf, TN and TP were about 40% and 10% higher, respectively, than in the period 1850-1950. Anthropogenic impact on deep-sea sediments is within the natural variability for the last 50 years (+ 5% TN and + 8% TP). Our data and a literature survey were the basis for identifying three major sedimentary areas and for estimating the total annual accumulation of 1.3 × 10 6 t TOC, 1.4 × 10 5 t TN and 4.7 × 10 4 t TP. A mass balance based on river inputs, outflow to the Sea of Marmara and the total accumulation rates indicated that 20% of the TN inputs accumulated in the sediments of the Black Sea whereas denitrification eliminated more than 55% of the inputs. In contrast, a single removal process controls the TP budget with the sedimentary accumulation, mainly on the shelf, representing 80% of the total incoming load.
Estuarine Coastal and Shelf Science, 2002
The mixing zone between the Danube and the Black Sea was investigated at the front of the Chilia and Sulina branches of the Danube delta, in April-May 1997, during two periods corresponding to conditions at the end of winter (Chilia and Sulina branches) and the beginning of spring (Sulina branch). The distribution of the organic matter in the particulate, colloidal and truly dissolved pools along the salinity gradient was characterized at both global and molecular levels using biochemical parameters. The distribution of particulate organic carbon (POC) paralleled that of total suspended matter in winter, whereas decoupling was observed in spring, reflecting active biological mechanisms in the mixing zone off the Sulina branch during this period. This is supported by distribution patterns of polyunsaturated fatty acids (PUFA) and branched fatty acids (BrFA), which are indicators of phytoplankton and bacteria activities, respectively. The 13 C isotopic signature of POC in the Danube-Black Sea mixing zone varied of between 29·1 and 24·6‰, which is consistent with the usual temperate range of estuarine systems. In spring, the observed shift towards lower values in the area of salinity 0-5 suggested a gradual change in the composition of POC, such as that caused by cell lysis of riverine planktonic populations induced by a salinity increase. A subsequent increase of 13 C values towards higher salinities indicated phytoplankton growth in the estuarine/marine zone, as assessed by high concentrations of PUFA. Indirect evidence of sedimentation of terrestrial particles in the upper part of the salinity gradient in the range of 2-3 was suggested by the decrease of the content of particles and POC in fatty acids (C 24 -C 32 ) and n-alkanes (C 25 -C 35 ), both constituents of cuticular waxes of higher plants. A tight coupling was suggested between phytoplankton and bacteria by similar distributions of PUFA and BrFA along the salinity gradient. The distribution of dissolved organic carbon (DOC) varied according to the season. In spring, the DOC concentrations remained constant across the salinity gradient in front of the Sulina branch at about 2·7 mg l 1 , whereas higher concentrations, >4 mg l 1 , were observed in winter at stations located in the low salinity (2-4 and 5-8) area. A few data were obtained for 13 C of the DOC pool, with an average of 26·9‰ in the Danube River end-member and values close to those of POC off the various branches. The low molecular weight (LMW) fraction of DOC isolated from water by sequential cross-filtration was evaluated by summing the pool of the combined and free amino acids and that of the combined and free carbohydrates. The distribution of LMW DOC along the salinity gradient was similar in the three investigated areas. Off the Sulina branch, proportions of LMW DOC fluctuated between 17 and 37‰ in winter and between 23 and 35‰ in spring. Two zones of high LMW DOC were located in two ranges of salinity-between 2 and 4 and between 5 and 8-probably originating from the release of decaying diatoms, assessed by high molecular proportions of serine in the combined amino acids. LMW DOC indicated a high potential for microbal activity, as shown by concomitant distributions of branched fatty acids.
Reprint of Dissolved organic carbon and nitrogen in the Western Black Sea
Marine Chemistry, 2008
Dissolved organic carbon and nitrogen (DOC and DON) concentrations were measured in the Black Sea during May-June 2001. Sampling was conducted along a Shelf-Gyre transect, and was focused at the suboxic-anoxic interface at the deep stations; hypotheses were tested regarding trends in these variables across the transect and between sub-surface water layers. DOC and DON concentrations were higher (272 μM and 15 μM, respectively) on the Shelf compared to the Gyre (200 μM and 11 μM, respectively), as a result of terrigenous inputs and in situ net production. The bulk DOC:DON ratio was constant with distance and depth (approximately 15-19). DOM concentrations decreased with depth (average anoxic layer concentrations of 123 μM and 6.1 μM for DOC and DON, respectively), in contrast to earlier observations of increasing DOC concentration with depth. The deep Basin (2000 m) DOC concentrations were high compared to deep open ocean values (120 vs 45 μM). We suggest that the high deep DOC is a product of mixing of terrigenous (300 μM) and Aegean Sea (60 μM) DOC, with some in situ decomposition over the 600 year residence time for the deep water mass. High surface concentrations of DOC and DON and high DOC:DON ratios throughout the sampling region indicate the pervasive influence of remnant terrigenous DOM with some net production. The timescales for DOM Shelf-Basin exchange and decomposition could not be estimated due to a lack of geochemical tracer data.
2003
On the basis of the analysis of the many-year data on the vertical distributions of particulate organic carbon and nitrogen, we compute their annual average amounts for three typical layers of water in the deep part of the Black Sea: for a layer located above the oxycline and characterized by the formation of new portions of particulate organic matter in the course of photosynthesis, inside the oxycline, where the major part of oxygen is consumed and the major part of the flux of particulate organic matter is oxidized, and for the upper part of the anoxic zone characterized by the most active microbiological processes of oxidation of the organic substances and production of sulfides. The available literature data on sedimentation traps are used to study the downward annual average fluxes of particulate organic matter from the euphotic zone into the oxycline and into the anaerobic zone. The seasonal variability of the amounts and fluxes of particulate carbon and nitrogen is revealed. Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.
Estuarine Coastal and Shelf Science, 2002
Biogeochemical transformations of inorganic nutrients were studied in the mixing zone between the Danube and the north-western Black Sea in July 1995 and in the winter-spring transition period of 1997. Inorganic nutrients, phytoplankton carbon-biomass and biogenic silica were analysed at 10 different locations across the entire salinity gradient in combination with parallel measurements of phytoplankton carbon and inorganic nutrient uptake rates, making use of different tracers ( 14 C, 15 N, 32 Si and 32 P). The quantitative and qualitative nutrient signature of the Danube outflow into the Black Sea varied seasonally, depending on upwards processes of consumption, remineralization, transformation and elimination. Danube DSi (dissolved silicon) and DIN concentrations decreased from winter to summer, although PO 4 remained constant for the whole season. The winter distribution of inorganic nutrients along the salinity gradient was conservative, and phytoplankton biomasses and activities were very low due to strong light limitation. However, significant phytoplankton carbon and inorganic nutrient uptake rates were measured in early spring and during summer at salinities depending on the hydrodynamics of the Danube and Black Sea mixing. Between a salinity of 0 and 10 (using the Practical Salinity Scale), phytoplankton (diatom) growth and mortality processes have been evidenced, which at first strongly lower the inputs of inorganic nutrients to the coastal zone, but also affect the balance among which nutrients are spread over the shelf. These modifications have important consequences for phytoplankton dynamics and species dominance at salinities above 10; diatom growth being apparently P-limited during spring and N-limited during summer. Surprisingly, no DSi limitation of diatom growth has been shown during this study, and a background DSi level of 2-3 M was measured in the entire shelf area. Causes for such an observation appear to be (1) an efficient biotic and abiotic removal of PO 4 during mixing, (2) an important denitrification in the upper estuary and (3) an important recycling of Si, both in the water column and at the sediment-water interface. The negative long-term effect of the quantitative and qualitative (deficiency in DSi) changes of the Danube inputs on the functioning of the Black Sea pelagic and benthic food-webs have been clearly reported in the literature and cannot be questioned by the present data set. Rather, this study simply highlights the complexity of the mechanisms by which propagation of the Danube eutrophication beyond the river plume possibly occurs.
Continental Shelf Research, 2007
The Kara Sea is one of the arctic marginal seas strongly influenced by fresh water and river suspension. The highly seasonal discharge by the two major rivers Yenisei and Ob induces seasonal changes in hydrography, sea surface temperature, ice cover, primary production and sedimentation. In order to obtain a seasonal pattern of sedimentation in the Kara Sea, sediment traps were deployed near the river mouth of the Yenisei (Yen) as well as in the central Kara Sea (Kara) within the framework of the German-Russian project ''Siberian River run-off; SIRRO''. Two and a half years of time-series flux data were obtained between September 2000 and April 2003 and were analyzed for bulk components, amino acids, stable carbon and nitrogen isotopes as well as sterols and fatty acids.