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1.
In the Paris Basin, in France, the Callovo-Oxfordian (COx) is currently studied over a 250 km2 surface area by the French national radioactive waste management agency in order to assess the feasibility of long-term underground nuclear waste repository. The COx is a 140 m thick clay-rich layer, which is part of the 2000 m aquitard/aquifer system constituting the sedimentary cover. In such sedimentary context, the transport processes of potential contaminants can be represented by both vertical diffusion and horizontal advection through the most permeable layers.Chloride is used as a natural conservative tracer, and is monitored in term of concentrations and isotopic composition (δ37Cl) for both pore and groundwater. During this study, the samples were collected from three boreholes located in the center of the studied zone, one of them (EST433) going down to 2000 m depth. The main solute transport process is shown to be vertical diffusion from the massive Keuper halite level to the rest of the sedimentary pile. This global diffusive system can be occasionally disturbed by horizontal circulation of groundwater occurring in the Oxfordian and Dogger limestone formations. Therefore, these circulations cut the global diffusive system in a succession of independent diffusive systems. In this study the data set was implemented in a simplified 2D solute transport model and scenarii reproducing known history in term of paleo circulations inside the system, were applied and allowed to obtained a good fit of the data. Model results showed that paleo circulations, occurring between −145 Ma and −110 Ma, still have an impact on current distribution of chloride in the system, especially for δ37Cl. The model highlights the need of the presence of a circulation spatially limited at the base of the Liassic formation to fit the data. The best fit obtained indicated current residence time of 500 ka in the Dogger and Oxfordian, with respective onset of the circulations at −20 Ma and −5 Ma. 相似文献
2.
《Marine Chemistry》2001,74(4):227-243
The distribution of trace metals in sediments and their exchange between sediments and overlying water is governed by multiple processes including molecular diffusion, bioturbation (porewater advection, porewater mixing, and particle mixing), chemical reactions and adsorption–desorption. To understand these processes and their relative contributions, a one-dimensional model was built, which includes bioturbation and adsorption–desorption processes, to describe the transport of 224Ra. Because 224Ra is adsorbed on MnO2, 224Ra may serve as a proxy for trace metal transport. Three sites were sampled and both dissolved and adsorbed 224Ra were analyzed and modeled to understand the transport and exchange processes. It was found that particle transport of adsorbed 224Ra followed by desorption at the sediment/water interface typically represents the dominant flux. We have further been able to define conditions where the porewater transport for adsorption reactive metals like 224Ra (and other metals) may be out of the sediments whereas the active scavenging of 224Ra from the water column at the sediment water interface via adsorption reactions can result in a flux of 224Ra into the sediment. These processes are both predicted by the model and observed in sediment samples. 相似文献
3.
The distribution of trace metals in sediments and their exchange between sediments and overlying water is governed by multiple processes including molecular diffusion, bioturbation (porewater advection, porewater mixing, and particle mixing), chemical reactions and adsorption–desorption. To understand these processes and their relative contributions, a one-dimensional model was built, which includes bioturbation and adsorption–desorption processes, to describe the transport of 224Ra. Because 224Ra is adsorbed on MnO2, 224Ra may serve as a proxy for trace metal transport. Three sites were sampled and both dissolved and adsorbed 224Ra were analyzed and modeled to understand the transport and exchange processes. It was found that particle transport of adsorbed 224Ra followed by desorption at the sediment/water interface typically represents the dominant flux. We have further been able to define conditions where the porewater transport for adsorption reactive metals like 224Ra (and other metals) may be out of the sediments whereas the active scavenging of 224Ra from the water column at the sediment water interface via adsorption reactions can result in a flux of 224Ra into the sediment. These processes are both predicted by the model and observed in sediment samples. 相似文献
4.
《Journal of Sea Research》2004,51(2):93-107
In this study we present in-situ measurements of pore water flow velocities in a coastal sandy sediment (permeability=3.65×10−10 m2). The advective pore water flows were driven by the interaction of oscillating boundary flows with sediment wave ripples, (amplitude=7 cm, wavelength=30 to 50 cm). The measurements were carried out in the Mediterranean Sea at 50 to 70 cm water depth during a phase of very low wave energy (max. wave amplitude=10 cm). An optode technique is introduced that permits direct pore water flow measurements using a fluorescent tracer. Near the sediment surface (0.5 cm depth) pore water reached velocities exceeding 40 cm h−1. Thus, advective transport exceeded transport by molecular diffusion by at least 3 orders of magnitude. Based on the pore water velocity measurements and ripple spacing, we calculate that 140 L m−2 d−1 are filtered through the sediment. Pore water visualisation experiments revealed a flow field with intrusion of water in the ripple troughs and pore water release at the ripple crests. The wave-driven water flow through the sediment, thus, was directly linked to the wave-generated sediment topography, and its spatial dimensions. These results show that surface waves cause water filtration through permeable sediments at water depths smaller than half the wavelength. We conclude that surface gravity waves constitute an important hydromechanical process that may convert large areas of the continental shelves into expansive filter systems. Surface gravity waves thereby could affect suspended particle concentration and cycling of matter in the shelf. 相似文献
5.
Analytical solutions expressed using the hydraulic head for the one-dimensional consolidation of layered structured aquitard soils in a leakage system are deduced by transforming the n-layered structured soils into n + i (i = 1,2,…, n)-layered soils with gradually changing thicknesses, therein considering the behaviors of structured aquitard soils. The solutions are given in the case of instantaneous and linear decreasing confined aquifer water levels. By comparing three different examples, the effects of the structured behaviors on the consolidation characteristics are analyzed for the instantaneous decline of the confined aquifer water level. 相似文献
6.
This contribution presents results from a laboratory study investigating the fluid (gas/water) transport properties in the matrix system of the Scandinavian Alum Shale. The maturity of the organic matter of the shale samples ranged between 0.5 and 2.4% vitrinite reflectance (VRr). Gas (He, Ar, CH4) and water flow properties were determined at effective stresses ranging between 5 and 30 MPa and a temperature of 45 °C. The effects of different controlling factors/parameters on the fluid conductivity including permeating fluid, moisture content, anisotropy, heterogeneity, effective stress, pore pressure, and load cycling were analyzed and discussed. Pore volume measurements by helium expansion were conducted under controlled “in situ” effective stress conditions on a limited number of plugs drilled parallel and perpendicular to bedding.For Alum Shale the intrinsic permeability coefficients measured parallel and perpendicular to bedding (6·10−22–8·10−18 m2) were within the range previously reported for other shales and mudstones. Permeability coefficients were strongly dependent on permeating fluid, moisture content, anisotropy, effective stress and other sample-to-sample variations. The intrinsic/absolute permeabilities measured with helium were consistently, higher (up to five times) than those measured with argon and methane. Permeability coefficients (He, CH4) measured on a dry sample were up to six times higher than those measured on an “as-received” sample, depending on effective stress. The effect of moisture on measured permeability coefficients became more significant as effective stress increased. Permeability coefficients (He, CH4) measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding. Parallel to bedding, all samples showed a nonlinear reduction in permeability with increasing effective stress (5–30 MPa). The stress dependence of permeability could be well described by an exponential relationship. 相似文献
7.
The MITAS (Methane in the Arctic Shelf/Slope) expedition was conducted during September, 2009 onboard the U.S. Coast Guard Cutter (USCGC) Polar Sea (WAGB-11), on the Alaskan Shelf/Slope of the Beaufort Sea. Expedition goals were to investigate spatial variations in methane source(s), vertical methane flux in shallow sediments (<10 mbsf), and methane contributions to shallow sediment carbon cycling. Three nearshore to offshore transects were conducted across the slope at locations approximately 200 km apart in water column depths from 20 to 2100 m. Shallow sediments were collected by piston cores and vibracores and samples were analyzed for sediment headspace methane (CH4), porewater sulfate (SO42−), chloride (Cl−), and dissolved inorganic carbon (DIC) concentrations, and CH4 and DIC stable carbon isotope ratios (δ13C). Downward SO42− diffusion rates estimated from sediment porewater SO42− profiles were between −15.4 and −154.8 mmol m−2 a−1 and imply a large spatial variation in vertical CH4 flux between transects in the study region. Lowest inferred CH4 fluxes were estimated along the easternmost transect. Higher inferred CH4 flux rates were observed in the western transects. Sediment headspace values ranged from −138 to −48‰, suggesting strong differences in shallow sediment CH4 cycling within and among sample locations. Measured porewater DIC concentrations ranged from 2.53 mM to 79.39 mM with δ13CDIC values ranging from −36.4‰ to 5.1‰. Higher down-core DIC concentrations were observed to occur with lower δ13C where an increase in was measured, indicating locations with active anaerobic oxidation of methane. Shallow core CH4 production was inferred at the two western most transects (i.e. Thetis Island and Halkett) through observations of low coupled with elevated DIC concentrations. At the easternmost Hammerhead transect and offshore locations, and DIC concentrations were not coupled suggesting less rapid methane cycling. Results from the MITAS expedition represent one of the most comprehensive studies of methane source(s) and vertical methane flux in shallow sediments of the U.S. Alaskan Beaufort Shelf to date and show geospatially variable sediment methane flux that is highly influenced by the local geophysical environment. 相似文献
8.
《Oceanologica Acta》1999,22(3):291-302
The time-course evolution of ammonium concentration has been examined in the flood water during the first 25 min of tidal inundation. The way this transport fluctuates with the tidal ranges and wind conditions was investigated. Flood water was collected at three sites, located along a transect from the lower to the upper intertidal area of the Tagus estuary. At spring and intermediate tides, the periods of air exposure vary slightly along the transect due to the high tidal amplitude and the flatness of the area, but the upper site remains uncovered at neap tide over the entire tidal cycle. At each site, sampling was performed at different tidal ranges covering the neap-spring tidal cycle and wind conditions. Ammonium was determined in the flood water at short time intervals: 1, 2, 3, 4, 5, 10, 15, 20 and 25 min. A clear pattern was observed along the transect: considerable quantities of ammonium were exported from the sediment to the water column at the beginning of the inundation, ranging from 0.2 to 4.8 mmol m−2 d−1. The highest transport was recorded at the lower intertidal site under spring tide conditions, which corresponds to the higher energetic situation and shorter emersion period. The lowest transport was observed at the upper intertidal site during the first inundation that followed three days of neap tide and continuous exposure of the sediment to the air. The value rates (0.2–4.8 mmol m−2 d−1) were one order of magnitude higher than those calculated from molecular diffusion (0.07 – 0.16 mmol m−2 d−1). This study points to the importance of the tidal flushing of ammonium from the intertidal sediments, and its spatial and tidal fluctuation. 相似文献
9.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(5):957-977
Measurements of gas-, particle- and precipitation-phases of atmospheric mercury (Hg) were made in the South and equatorial Atlantic Ocean as part of the 1996 IOC Trace Metal Baseline Study (Montevideo, Uruguay to Barbados). Total gaseous mercury (TGM) ranged from 1.17 to 1.99 ng m−3, with a weighted mean of 1.61±0.09 ng m−3. These values compare well with Pacific Ocean data and earlier results from the Atlantic. The open-ocean samples recorded a distinctive inter-hemispheric gradient, which is consistent with a long-lived trace gas emitted to a greater extent from the Northern than from the Southern Hemisphere. Correlations with surface 222Rn measurements indicate an influence of regional terrestrial sources on open-ocean TGM concentrations. Total Hg in precipitation ranged from 10 to 99 pM (volume-weighted average: 17.8±2.9 pM). On average, about 72% of the total Hg was “reactive” (i.e., reducible by SnCl2). The data showed an apparent rapid nonlinear decrease in concentration with event size (“washout curve”). The wet depositional flux was estimated at 18–36 nmol m−2 yr−1 (4–7 μg m−2 yr−1), which is slightly lower than that found in mid-continental locations of North America (6–12 μg m−2 yr−1). 210Pb analyses indicate a strong impact of particles on rain Hg concentrations. Particle-phase Hg (range 5–25 fmol m−3; mean 12±1 fmol m−3; 66% “reactive”) was comparable to values over the equatorial Pacific. The dry depositional flux is ca. 0.4 nmol m−2 yr−1, or 0.4–1.0% of the wet flux. Particle-phase Hg concentrations did not change significantly when African dust was present during sampling. However, the Hg/Al ratios were consistent with crustal values during the dust periods. The residence time of TGM was calculated to be 1.3–3.4 yr in this region, based on standing stock estimates. Incubation of rainwater added to surface seawater gave reduction rates [i.e., production of elemental Hg (Hg°); 1.6–4.3% d of total Hg added] comparable to additions of inorganic ionic standards, indicating that Hg+2 from precipitation is reduced in a similar manner in surface waters. Thus, precipitation-phase Hg is generally available for evasion to the atmosphere following deposition to the surface ocean, effectively enhancing the mobility and residence time of Hg at the Earth's surface. 相似文献
10.
June A. Oberdorfer Matthew Charette Matthew Allen Jonathan B. Martin Jaye E. Cable 《Estuarine, Coastal and Shelf Science》2008
Near-shore discharge of fresh groundwater from the fractured granitic rock at Flamengo Bay, Ubatuba, Brazil, is strongly controlled by the local geology. Freshwater flows primarily through a zone of weathered granite to a distance of 24 m offshore. In the nearshore environment this weathered granite is covered by about 0.5 m of well-sorted, coarse sands containing pore water with sea water salinity, with an abrupt transition to much lower salinity once the weathered granite is penetrated. Further offshore, low-permeability marine sediments contain saline porewater, marking the limit of offshore migration of freshwater. Freshwater flux rates based on tidal signal and hydraulic gradient analysis indicate a fresh submarine groundwater discharge of 0.17–1.6 m3/day per m of shoreline. Dissolved inorganic nitrogen and silicate are elevated in the porewater relative to seawater, and appeared to be a net source of nutrients to the overlying water column. The major ion concentrations suggest that the freshwater within the aquifer has a short residence time. Major element concentrations do not reflect in situ alteration of the granitic rocks, possibly because the alteration occurred prior to development of the current discharge zones, or because of large volumes of water discharge in this high rainfall region. 相似文献
11.
《Marine Geology》2005,216(3):127-143
This study was carried out in order to understand the early diagenetic redistribution of phosphorus and relevant mass balance in the sediments of the East Sea. In two cruises during May 1993 and October 1995, 11 box cores were collected in the southwestern part of the East Sea. Dissolved phosphorus and iron were analyzed in the porewater from the cores. Sediment samples were analyzed for solid-phase P species and solid-phase Fe oxyhydroxide by sequential extraction.Phosphorus speciation results show that organic P is the major chemical form of phosphorus in young sediments within the upper 50 cm of sediment. However, the authigenic fraction of total P increases with depth, indicating the precipitation of carbonate fluorapatite (CFA) in the sediments. The authigenic CFA (Ca5(PO4)2.6(CO3)0.4F) was formed and buried at rates of 11–110 μmol cm−2 kyr−1. The main source of dissolved phosphorus for the precipitation of CFA is organic P. Dissolved phosphorus, released from the decomposition of organic P, diffuses upward to return to bottom water, or is sorbed to iron oxides in the oxidized sediments. As sedimentation proceeds, the iron oxide-bound P is released in the reduced layer and enters the dissolved phase, which contributes P to the formation of CFA in addition to that contributed by the organic P.The burial flux of reactive P (iron oxide-bound P+authigenic P+organic P) is 0.09–0.53 g P m−2 yr−1 that accounts for 18–58% of the reactive P arriving at the sediment/water interface. The burial flux of reactive P is high in the upper and lower continental margin sediment. The burial flux of reactive P in the Ulleung Basin sediment is less than those in the continental margin sites by a factor of 6, indicating that the reactive P burial flux is mainly dependent on sedimentation rate. 相似文献
12.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(6):1459-1476
In two recent studies (Tian et al., Deep-Sea Res. I 43 (1996) 723–738; Campos et al., Deep-Sea Res. II 43 (1996) 455–466), in order to explain the observed temporal variations in the distributions of the dissolved iodine species at the time-series stations in the Mediterranean Sea, the North Atlantic and the North Pacific, diverse assumptions were invoked on the relationships between changes in the speciation of dissolved iodine in the surface oceans and biological production such that the surface enrichment of I− was linked to both regenerated production and primary production while the surface depletion of [IO3−+I−] was linked to “new” production. However, while some of the major conclusions in these studies are critically dependent on these assumptions, the validity of the assumptions has yet to be verified with experimental evidence. On the other hand, while there are still significant unknowns in the understanding of the cycling among dissolved iodine species in the surface oceans, presently available data from laboratory cultures and field observations are consistent with an alternative conceptual model in which IO3− and NO3− are taken up at some ratio to each other during NO3− uptake and almost all of the IO3− taken up is exuded as I−. Thus, the depletion of IO3− and the enrichment of I− in the surface water are linked to NO3− uptake. This alternative model is also consistent with the data sets presented by Tian et al. (1996) and Campos et al. (1996). By linking the surface depletion of IO3− to NO3− uptake, significantly different biogeochemical behavior of the marine dissolved iodine system may be inferred. The extent to which I− may be oxidized to IO3− within the euphotic zone during the residence time of the water in the surface ocean is still an open question. 相似文献
13.
Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay 总被引：2，自引：0，他引：2
Tomohiro Kuwae Eiji Kibe Yoshiyuki Nakamura 《Estuarine, Coastal and Shelf Science》2003,57(5-6):929-940
Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l−1 bulk sed. h−1 during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion. 相似文献
14.
Laboratory modeling of the structure of a thermal bar and related circulation in a basin with a sloping bottom 总被引：1，自引：0，他引：1
Development of a thermal bar in a laboratory flume with an inclined bottom (3.7°–12°) under the conditions of cooling/heating of the water with a temperature close to that of the maximal density is studied. The structure of the temperature field and currents during different stages of the circulation is examined: (i) formation of an along-slope gravity current, (ii) generation of a subsurface jet, and (iii) transformation of one type of the circulation into another at passing the temperature of the maximum density. The “fall” and “spring” types of the thermal bar are shown to be dynamically equivalent: the transport of the near-shore waters to the deepwater part, which is driven by the buoyancy flux rather than by the heat flux across the surface, transforms stage (i) into stage (ii), while the opposite (on-shore) flow is generated in the intermediate layers. A comparison of the results with the field and laboratory data published allows us to suggest that the propagation of the thermal bar front in the “fast” stage can be considered as the development of a convective jet with its velocity U ～ h 3/4, which is proportional to the growing thickness of the upper layer h affected by the heating/cooling processes 相似文献
15.
Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels
F. Joel Fodrie Bonnie J. Becker Lisa A. Levin Kristen Gruenthal Pat A. McMillan 《Journal of Sea Research》2011,65(1):141-150
The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78–87% of all cases. Settlement varied between 2 and 27 settlers gram-byssus?1 week?1 at SIO and HI, and both sites were characterized by 2–3 weeks with “high” settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between “high” and “low” settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations. 相似文献
16.
Dongseon Kim Seung Ho Baek Dong-Young Yoon Kyung-Hee Kim Jin-Hyun Jeong Pung-Guk Jang Young-Ok Kim 《Ocean Science Journal》2014,49(3):251-264
A new water quality index for evaluating the water quality of Jinhae Bay and Gwangyang Bay was developed. Four water quality parameters were selected as water quality indicators for the water quality index: dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chlorophyll-a (Chl-a), and dissolved oxygen (DO). Reference levels of DIN, DIP, and Chl-a were determined as 6.22 μmol L?1, 0.38 μmol L?1, and 2.32 μmol L?1, respectively, on the basis of a long-term dataset that was collected monthly in the Korea Strait over a period of seven years (2006–2012). The water quality index established for Jinhae Bay and Gwangyang Bay is (bottom DO grade × 0.33) + (surface Chl-a grade × 0.33) + (surface DIN grade × 0.17) + (surface DIP grade × 0.17). On the basis of a three-year observation, the water quality of Jinhae Bay was classified as “good” in winter and spring, “poor” in summer, and “fair” in autumn and exhibited large spatial variation, with the lowest-quality water observed in Masan Bay. The water quality of Gwangyang Bay was classified as “good” in winter, “fair” in spring, “poor” in summer, and “fair” in autumn. Unlike Jinhae Bay, the water quality of Gwangyang Bay exhibited minimal spatial variation. In both bays, water quality among the four seasons was worse during summer. It is essential that a survey for water quality evaluation be conducted during summer. 相似文献
17.
Coastal groundwater systems can have a considerable impact on sediment transport and foreshore evolution in the surf and swash zones. Process-based modeling of wave motion on a permeable beach taking into account wave-aquifer interactions was conducted to investigate the effects of the unconfined coastal aquifer on beach profile evolution, and wave shoaling on the water table. The simulation first dealt with wave breaking and wave runup/rundown in the surf and swash zones. Nearshore hydrodynamics and wave propagation in the cross-shore direction were simulated by solving numerically the two-dimensional Navier–Stokes equations with a k–ε turbulence closure model and the Volume-Of-Fluid technique. The hydrodynamic model was coupled to a groundwater flow model based on SEAWAT-2000, the latter describing groundwater flow in the unconfined coastal aquifer. The combined model enables the simulation of wave-induced water table fluctuations and the effects of infiltration/exfiltration on nearshore sediment transport. Numerical results of the coupled ocean/aquifer simulations were found to compare well with experimental measurements. Wave breaking and infiltration/exfiltration increase the hydraulic gradient across the beachface and enhance groundwater circulation inside the porous medium. The large hydraulic head gradient in the surf zone leads to infiltration across the beachface before the breaking point, with exfiltration taking place below the breaking point. In the swash zone, infiltration occurs at the upper part of the beach and exfiltration at the lower part. The simulations confirm that beaches with a low water table tend to be accreted while those with a high water table tend to be eroded. 相似文献
18.
19.
Mohammed Rasheed Saber Al-Rousan Riyad Manasrah Fuad Al-Horani 《Journal of Oceanography》2006,62(1):83-89
The role of deep sediment in supporting nutrient budget in the Gulf of Aqaba has been investigated by estimating the flux
of inorganic nitrogen, phosphate and silicate. Fluxes were calculated directly by pore water profiles and indirectly by chamber
incubations carried out onboard the RV Meteor cruise. The results showed that maximum potential fluxes calculated by chamber
incubations were higher than those calculated by porewater profiles for all nutrients (6.4–28.5 fold). This has been attributed
to the additional flux due to bioturbation and flux from advective porewater exchange in the case of chamber incubation, while
porewater fluxes represent diffusive ones. Using a rough estimation considering flux results in addition to the sediment area
and water mass of the Gulf of Aqaba, we estimate that 3.3 × 105, 6.4 × 104 and 6.5 × 106 kg year−1 of inorganic nitrogen, phosphate and silicate respectively are effused from deep sediments to the water column. This quanitity
would certainly support the primary productivity in the oligotrophic water in the Gulf of Aqaba. 相似文献
20.
The relationship between seagrass (Posidonia oceanica) decline and sulfide porewater concentration in carbonate sediments 总被引：2，自引：0，他引：2
Maria Ll. Calleja Núria Marb Carlos M. Duarte 《Estuarine, Coastal and Shelf Science》2007,73(3-4):583-588
In this study we test the hypothesized negative relationship between seagrass status and porewater hydrogen sulfide (H2S) levels, through a comparative analysis within a range of seven Posidonia oceanica meadows growing over carbonate sediments in the NW Mediterranean Sea around Mallorca Island. The studied meadows range from meadows growing on sediments with very low sulfide porewater concentrations (4.6 μM) to those growing over higher sulfide conditions (33.5 μM). Organic matter content, sulfate reduction rates and sulfide porewater concentrations in the sediments were determined concurrently with the assessment of demographic plant dynamics (specific mortality and net population growth rates). Sulfide porewater concentration increased with increasing organic matter content in the sediment, while net population growth decreased significantly with low increases of sulfide concentrations. Our results confirm the previously suspected vulnerability of seagrass meadows growing on carbonate sediments to increased sulfide levels. An excess of 10 μmols H2S L−1 porewater is identified to already conduce P. oceanica meadows to decline, which this study identifies, particularly, as strongly sensitive to sulfides. The results reported here suggest that even moderate increases in organic carbon inputs may lead to enhancement of dissolved sulfides and may be an important factor for seagrass status in these iron-depleted carbonate sediments from the Mediterranean Sea. 相似文献