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1.
The influence of bioturbation on certain aspects of the biogeochemistry of sulfur and iron was examined in shallow-water sediments of Great Bay Estuary, New Hampshire. A bioturbated (JEL) and non-bioturbated (SQUAM) site were compared. Annual sulfate reduction measured with 35S, was 4·5 times more rapid at JEL. A significant portion of this difference was attributed to rapid rates which occurred throughout the upper 12 cm of sediment at JEL due to infaunal reworking activities. Sulfate reduction decreased rapidly with depth at SQUAM. FeS in the upper 2 cm at JEL increased in concentration from 3 to 45 μmol ml−1 from early May to late July while only increasing from 3 to 8 μmol ml−1 at SQUAM. Infaunal irrigation and reworking activities caused rapid and continous subsurface cycling of iron and sulfur at JEL. This maintained dissolved iron concentrations at 160–170 μM throughout the summer despite rapid sulfide production. Therefore, dissolved sulfide never accumulated in JEL pore waters. Although dissolved organic carbon (DOC) was generated during sulfate reduction, bioturbation during summer caused a net removal of DOC from JEL pore waters. Sulfate reduction rates, decomposition stoichiometry and nutrient concentrations were used to calculate turnover times of nutrients in pore waters. Nutrient turnover varied temporally and increased three-to five-fold during bioturbation. A secondary maximum in the abundance of recoverable sulfate-reducing bacteria occurred at 10 cm in JEL sediments only during periods of active bioturbation, demonstrating the influence of macrofaunal activities on bacterial distributions.  相似文献   

2.
In July 2002, a combination of underway mapping and discrete profiles revealed significant along-shore variability in the concentrations of manganese and iron in the vicinity of Monterey Bay, California. Both metals had lower concentrations in surface waters south of Monterey Bay, where the shelf is about 2.5 km wide, than north of Monterey Bay, where the shelf is about 10 km wide. During non-upwelling conditions over the northern broad shelf, dissolvable iron concentrations measured underway in surface waters reached 3.5 nmol L−1 and dissolved manganese reached 25 nmol L−1. In contrast, during non-upwelling conditions over the southern narrow shelf, dissolvable iron concentrations in surface waters were less than 1 nmol L−1 and dissolved manganese concentrations were less than 5 nmol L−1. A pair of vertical profiles at 1000 m water depth collected during an upwelling event showed dissolved manganese concentrations of 10 decreasing to 2 nmol L−1, and dissolvable iron concentrations of 12–20 nmol L−1 in the upper 100 m in the north, compared to 3.5–2 nmol L−1 Mn and 0.6 nmol L−1 Fe in the upper 100 m in the south, suggesting the effect of shelf width influences the chemistry of waters beyond the shelf.These observations are consistent with current understanding of the mechanism of iron supply to coastal upwelling systems: Iron from shelf sediments, predominantly associated with particles greater than 20 μm, is brought to the surface during upwelling conditions. We hypothesize that manganese oxides are brought to the surface with upwelling and are then reduced to dissolved manganese, perhaps by photoreduction, following a lag after upwelling.Greater phytoplankton biomass, primary productivity, and nutrient drawdown were observed over the broad shelf, consistent with the greater supply of iron. Incubation experiments conducted 20 km offshore in both regions, during a period of wind relaxation, confirm the potential of these sites to become limited by iron. There was no additional growth response when copper, manganese or cobalt was added in addition to iron. The growth response of surface water incubated with bottom sediment (4 nmol L−1 dissolvable Fe) was slightly greater than in control incubations, but less than in the presence of 4 nmol L−1 dissolved iron. This may indicate that dissolvable iron is not as bioavailable as dissolved iron, although the influence of additional inhibitory elements in the sediment cannot be ruled out.  相似文献   

3.
This one-year survey conducted in the macrotidal estuary of Penzé (Brittany, Western part of the Channel, France) was aimed at examining the variations of the various dissolved and particulate copper species. Ten field stations along the whole freshwater–seawater mixing zone were sampled each month. Different biogeochemical parameters (SPM, chl-a, pH and DOC) were also measured. The levels in total dissolved and total particulate copper ranged from 1.8 to 9.5 nM and from 5 to 98 μg g−1, respectively; such amounts are indicative of a pollution-free system. Extractable C18 copper (non-polar hydrophobic organic copper species), in winter and spring, accounted for 30–40% of the total dissolved copper. In summer, this contribution rapidly rose to 60% in the salinity range 20–30; over the same period of time, total particulate copper decreased. The change in dissolved copper speciation and the lowering of particulate copper concentrations were attributed to the release of strong organic ligands by phytoplankton. Our field data evidenced a highly variable behaviour for the various copper species over the seasonal cycle, and then led us to identify the following mechanisms: (i) metal desorption from organic river-flown particles (winter and spring), (ii) metal desorption from resuspended sediment in the upstream section (summer), (iii) competition between particles, non-extractable C18 organic ligands and phytoplankton-released extractable C18 organic ligands to complex copper in the downstream section (summer), and (iv) removal of non-extractable C18 organic copper by adsorption (autumn). Dissolved copper species fluxes were assessed: most of metal inputs to the estuary (60–74%) corresponded to non-extractable C18 organic copper. Winter and spring metal output fluxes were mainly constituted of non-extractable C18 organic complexes; on the other hand, extractable C18 organic complexes were predominant in summer and autumn output fluxes.  相似文献   

4.
The objectives of this study were to investigate the seasonality, abundance, sources and bioreactivity of organic matter in the water column of the western Arctic Ocean. The concentrations of particulate and dissolved amino acids and amino sugars, as well as bulk properties of particulate and dissolved organic matter (DOM), were measured in shelf, slope and basin waters collected during the spring and summer of 2002. Particulate organic matter concentrations in shelf waters increased by a factor of 10 between spring and summer. Dissolved organic carbon (DOC) and nitrogen (DON) concentrations exhibited only minor seasonal variations, whereas dissolved amino acid concentrations doubled between spring and summer, and dissolved amino sugars increased by 31% in shelf waters of the Chukchi and Beaufort Seas. Concentrations of DOC did not exhibit a significant seasonal change in surface waters of the Canada Basin, but dissolved amino acid concentrations increased by 45% between spring and summer. No significant seasonal differences were detected in the concentration or composition of DOM in waters below 100 m in depth. Concentrations of particulate and dissolved amino acids and amino sugars were strongly correlated with chlorophyll-a, indicating a plankton source of freshly produced organic matter. The amino acid and amino sugar compositions of freshly produced DOM indicated that a large portion of this material is bioavailable. While freshly produced DOM was found to be relatively bioreactive, preformed DOM in the Arctic appears to be less bioreactive but similar in degradation state to average DOM in the Atlantic and Pacific. These data demonstrate substantial summer production of POM and DOM on the Chukchi and Beaufort shelves that is available for utilization in shelf waters and export to the Canada Basin.  相似文献   

5.
Concentrations of zinc, cadmium, copper, manganese, iron, cobalt, nickel and molybdenum are examined in brown algae, Fucus serratus and F. vesiculosus, from Cardigan Bay, Irish Sea, Great Britain. In both species a seasonal variation in metal content was observed. Zinc, cadmium, copper, iron nickel and cobalt concentrations were highest in the spring and lowest in the autumn, probably reflecting levels of metabolic activity and climatic factors. All the studied elements, except nickel, reached highest concentrations in harbour specimens from Aberystwyth and Aberaeron where rivers draining mineralized areas enter the sea. Outside harbours, marked regional variations were observed in most of the studied elements. Zinc values were highest in the Aberystwyth area while copper and manganese were highest in the northeast part of the bay.Trace-element concentrations varied among different species from the same locality and also varied according to position on the shore.Marine algae may be used to monitor coastal-water trace-metal concentrations, provided a careful sampling procedure is adopted.  相似文献   

6.
Concentrations of dissolved oxygen and sulfide, and of dissolved and particulate iron, manganese, and phosphate were measured as functions of salinity at a station in the Chesapeake Bay during stratification and deep water anoxia in spring and summer, 1981. The observed concentration/salinity profiles showed that oxygen was transported in a direction opposite to that of salt, while dissolved sulfide was transported in the same direction as salt through the anoxic water to be oxidized in oxygen consumption zones located below the steepest parts of the halocline. Both oxygen and sulfide were transported conservatively on 18 June. Their fluxes were 1·2 and 2 mol m−2 d−1, respectively. The oxygen flux was 30% of that stoichiometrically needed to oxidize the sulfide transported, suggesting that the oxygen consumption zone was advancing to shallower, less saline water, thus increasing the volume of anoxic water. Although oxygen was transported conservatively, sulfide was produced as it was transported through the anoxic water on 8 July.The anoxic water was supersaturated with respect to ferrous sulfide on 18 June, but most of the anoxic water was saturated on 8 July. Precipitation of ferrous sulfide had little effect on the sulfide flux on 18 June. The manganese(II) concentration/salinity profile exhibited a maximum in the oxygen consumption zone on 18 June. On 8 July the profile was independent of salinity at high salinities. Iron(II) and manganese(II) consumed little if any oxygen in the oxygen consumption zone.Soluble reactive phosphate was transported conservatively through the anoxic water on 18 June. It was produced as it was transported on 8 July. All of the phosphate was consumed in the oxygen consumption zones by sulfide oxidizing bacteria. On 18 June its flux, estimated to be 2·8 mmol m−2 d−1, was less than 10% of that required for bacterial oxidation of the sulfide reaching the oxygen consumption zone. The rest was oxidized chemically. The growth and activity of the bacteria were limited by the rate at which soluble reactive phosphate was transported to the oxygen consumption zone.Little or none of the sulfide, iron(II), or phosphate originated in the bottom sediment at the station. The results indicate that they were transported into the water sampled from deeper more saline water downstream, suggesting that they originated in the deep trough that extends along the spine of the Bay. Manganese(II), however, resulted from the reduction and dissolution of oxidized manganese particles as they sank into the anoxic water.  相似文献   

7.
《Marine Chemistry》2001,73(1):21-36
As part of the ANTARES 3/F-JGOFS cruise, the distributions of dissolved iron and manganese were measured in October 1995 in the north–east wake of the Kerguelen archipelago (48°40′–49°40′S, 68°70′–70°50′E), an area that shows high phytoplankton biomass (CZCS and SeaWiFS data) in the middle of the High Nutrient Low Chlorophyll (HNLC) Southern Ocean. The study area (about 25,000 km2) comprised a branch of the Polar Front with Antarctic surface water (AASW) intruding northward, shouldering the shelf break of the Kerguelen Plateau. The coastal zone was clearly affected by material of lithogenic origin (riverine discharges, soil leaching by rain waters, aeolian inputs), as well as by inputs from the sediments (effluxes from the sediment–water interface, resuspension from the sediments), its near surface waters showing considerable enrichment in dissolved iron (5.3–12.6 nM) and in dissolved manganese (2.9–8.6 nM). The offshore waters, although less enriched in trace-metals, were also affected by trace-metal inputs from coastal and continental shelf origin. Dissolved iron and manganese concentrations in these waters were 0.46–0.71 and 0.68–1.3 nM, i.e. far over typical antarctic open ocean surface water concentrations of 0.16 nM for iron [Martin, J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antarctic waters. Nature, 345: 156–158.] and around 0.1 nM for manganese [Martin, J.H., Gordon, R.M., Fitzwater, S.E., 1990. Iron in Antarctic waters. Nature, 345: 156–158; Sedwick, P.N., Edwards, P.R., Mackey, D.J., Griffiths, F.B., Parslow, J.S., 1997. Iron and manganese in surface waters of the Australian subantarctic region. Deep-Sea Res., 44: 1239–1253.]. The dissolved iron enrichment in coastal waters of the Kerguelen Islands is much more important (about 10 times for dissolved iron) than for the Galapagos Islands, another oasis in the HNLC Equatorial oceanic system, where the concentration increase in dissolved iron in the surface waters around the islands is mostly driven by upwelling of the Equatorial Under Current (EUC) as it reaches the Galapagos Platform.  相似文献   

8.
The relationship between changes in lipid classes and phytoplankton composition and abundance in the northern Adriatic was studied during spring and summer 2008 at two stations with different nutrient levels, i.e. at the western mesotrophic and eastern oligotrophic areas. Changes in the phytoplankton community depended on temporal surface nutrient depletion and bottom accumulation; that is, microphytoplankton, mainly diatoms Pseudo-nitzschia sp., developed at nutrient richer surface layers of the mesotrophic area in spring and at deeper layers of the oligotrophic site in late summer. In other periods nanophytoplankton dominated. Dissolved organic carbon (DOC) and lipid content were comparable for the two stations, while particulate organic carbon (POC) was richer at the mesotrophic side. Total lipid concentrations varied in the range from 8.0 to 92.2 μg l−1 and from 16.9 to 76.9 μg l−1 in the dissolved and particulate fractions, respectively. DOC and POC contents were in the ranges from 0.77 to 1.58 mg l−1 and from 0.06 to 0.56 mg l−1, respectively. Lipid and organic carbon distribution did not follow phytoplankton progression, indicating decoupling between organic matter production and decomposition throughout the investigation period. The main sources of lipids were marine phytoplankton and bacteria. Low nutrient conditions caused increased biosynthesis of lipids. Also, increasing oligotrophy led to an increasing number of phytoplankton taxa. The synthesis and accumulation of glycolipids by the developed taxa were enhanced during nutrient exhaustion, contributing in late summer, on average, 20.2 and 22.0% at the mesotrophic and oligotrophic stations, respectively, in the particulate fraction. The distribution of bacterial lipids and lipid breakdown products implies that bacterial lipid degradation was significant in spring, while very probably lipid abiotic degradation took place during summer.  相似文献   

9.
To assess the magnitude, distribution and fate of net community production (NCP) in the Chukchi Sea, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), and particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured during the spring and summer of 2004 and compared to similar observations taken in 2002. Distinctive differences in hydrographic conditions were observed between these two years, allowing us to consider several factors that could impact NCP and carbon cycling in both the Chukchi Shelf and the adjacent Canada Basin. Between the spring and summer cruises high rates of phytoplankton production over the Chukchi shelf resulted in a significant drawdown of DIC in the mixed layer and the associated production of DOC/N and POC/N. As in 2002, the highest rates of NCP occurred over the northeastern part of the Chukchi shelf near the head of Barrow Canyon, which has historically been a hotspot for biological activity in the region. However, in 2004, rates of NCP over most of the northeastern shelf were similar and in some cases higher than rates observed in 2002. This was unexpected due to a greater influence of low-nutrient waters from the Alaskan Coastal Current in 2004, which should have suppressed rates of NCP compared to 2002. Between spring and summer of 2004, normalized concentrations of DIC in the mixed layer decreased by as much as 280 μmol kg−1, while DOC and DON increased by ∼16 and 9 μmol kg−1, respectively. Given the decreased availability of inorganic nutrients in 2004, rates of NCP could be attributed to increased light penetration, which may have allowed phytoplankton to increase utilization of nutrients deeper in the water column. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004 with warmer temperatures in the mixed layer that could have enhanced NCP. Estimates of NCP near the head of Barrow Canyon in 2004 were ∼1500 mg carbon (C) m−2 d−1 which was ∼400 mg C m−2 d−1 higher than the same location in 2002. Estimates of NCP over the shelf-break and deep Canada Basin were low in both years, confirming that there is little primary production in the interior of the western Arctic Ocean due to near-zero concentrations of inorganic nitrate in the mixed layer.  相似文献   

10.
Abstract

The surface distribution of salinity, temperature, nitrate‐nitrogen (N03‐N), and chlorophyll a in the southern New Zealand, Foveaux Strait region in February 1977, 1978, 1979, and 1980 was highly variable. The source of new nitrogen appears to be incursions of high‐salinity water west and east of Stewart Island. Although it seems likely that the source of this high‐nutrient, high‐salinity water is vertical, a horizontal advective source cannot be ruled out The chlorophyll a content of surface waters was not related directly to the NO3‐N concentrations. This lower food chain variability may be linked to variability in economically important species. Oysters grew twice as fast in the summer of 1978/79 as they did in 1979/80. But the mean chlorophyll a values were very similar for February of both years (2.5 and 2.2 μg 1?1, respectively). The elevated NO3‐N levels in 1979 may have resulted in much higher phytoplankton levels later that summer and resulted in the higher oyster growth rate that year. The mechanisms driving this variability have yet to be determined.  相似文献   

11.
The organic speciation of copper, iron and zinc in estuarine waters is studied using electrochemical techniques. Complexing capacities for copper and zinc were determined by cathodic stripping voltammetry (CSV) of their complexes with respectively catechol and amino pyrrolidine dithiocarbamate (APDC). Iron speciation was studied by CSV measurements of dissolved iron before (‘free iron’) and after acidification and UV-irradiation (‘total iron’) of the filtered samples. Complexing capacities of copper were found to vary between 1·4 and 5 × 10−7m with conditional stability constants, logK′CuL, between 9·2 and 10·3 in the Tamar estuary. Complexing capacities of zinc were less at between 0·4 and 1·6 × 10−7m with values for logK′ZnL between 8·1 and 9·4. Copper complexing capacities generally decreased with increasing salinity, and variations in the results were related to high concentrations of suspended material. Similar variations in the dissolved vanadium concentrations suggested that part of this element was associated with colloidal material. The total dissolved iron concentration in samples from the River Ribble decreased from 10−6m at low salinity to 10−7m at high salinity, but the free iron concentration was found to decrease from 8 to 3 × 10−8m over the same salinity range, which may be compared with the calculated solubility of iron in seawater of 2 × 10−8m. Comparative experiments showed that on average about 24% of the non-labile iron fraction was stabilized by organic material, the rest being composed of inorganic colloidal material.  相似文献   

12.
Water samples collected during a spring plankton bloom in the northern North Sea were investigated for dissolved organic carbon (DOC), total dissolved sugars (TDS) and dissolved amino acids (TDAA). Their concentrations varied in the range of 0.6 to >4 mg 1?1 for DOC, 40—400 γg 1?1 for TDS and 100—850γg 1?1 for TDAA. TDS and TDAA contributed to less than 20% of the DOC, but showed variations independent of each other. Changes in the efficiency of heterotrophic utilization and its selectivity seem to have caused these variations. These, together with differences in the sources of dissolved organic matter — phytoplankton and detrital materials — were also reflected in the qualitative composition of TDS and TDAA in the water column. In the TDS fraction glucose and mannose showed maxima during the phytoplankton bloom and galactose, rhamnose, xylose, arabinose and fucose after it. Glutamic acid registered maximum in the early stages of the phytoplankton bloom, histidine towards its end and aspartic acid, glycine, alanine and lysine after it. Serine was present in large amounts throughout the investigated time interval. The results of the present study are discussed in the light of previously published data on the formation and utilization of dissolved organic matter in the sea.  相似文献   

13.
Summer porewater and spring and summer surficial sediment samples were collected from 26 locations in the intertidal region of the Fraser River estuary. Porewaters were analysed for dissolved iron and manganese (as defined by species <0·2μm in diameter) to assess the contribution of diagenesis to concentrations of iron and manganese oxides at the sediment–water interface. Surficial sediment samples were geochemically characterized as: % organic matter (% LOI); reducible iron (RED Fe, iron oxides) and easily reducible manganese (ER Mn, manganese oxides). Grain size at each site was also determined. The sediment geochemical matrix, as defined by the above four parameters, was highly heterogeneous throughout the intertidal region (three-way ANOVA;P<0·0001). For RED Fe and ER Mn, this heterogeneity could be explained by either diagenetic processes (RED Fe) or by a combination of the proximity of the sample sites to the mouth of the Fraser River estuary plus diagenetic processes (ER Mn). Correlation (Spearman Rank Correlation Test (rs), of dissolved iron within the subsurface sediments with amounts of RED Fe recovered from the associated surface sediments was highly significant (rs=0·80, P<0·0001); high concentrations of RED Fe at the sediment–water interface co-occurred with high concentrations of dissolved iron, regardless of the proximity of the sample locations to riverine input. Compared with iron, the relationship between dissolved manganese and ER Mn from surface sediments was lower (rs=0·58;P<0·0008). Locations most strongly influenced by the Fraser River contained greater concentrations of ER Mn at the sediment–water interface than that which would be expected based on the contribution from diagenesis alone. Sediment grain size and organic matter were also influenced by the proximity to riverine input. Surficial sediment of sites close to the river mouth were comprised primarily of percent silt (2·0μm–50μm) whereas sites not influenced by riverine input were primarily percent sand (grain size >50μm). Concentrations of organic matter declined from the mouth to the foreslope of the estuary. With the exception of RED Fe, temporal variation (May vs July) was insignificant (P>0·05, three-way ANOVA). Concentrations of RED Fe recovered from the surficial sediments were in general greater in the summer vs spring months, although spring and summer values were highly correlated (Pearson Product Moment Correlation Coefficient; PPCC; R=0·89;P<0·0001). As the bioavailability of metals is dependent on sediment geochemistry, availability throughout the intertidal region will also be spatially dependent. This heterogeneity needs to be taken into account in studies addressing the impact of metals on estuarine systems.  相似文献   

14.
长江每年有上千万吨有机物质注入河口邻近海域，影响着这一海域独特的生态环境。 本文根据1985年8月至1986年5月专业调查资料,论述了长江口邻近海域溶解有机碳(DOC)和颗粒有机碳(POC)的分布及变化，并从有机物质的变化推测三峡工程对河口海生态系的影响。  相似文献   

15.
The presence of a strongly developed oxygen minimum zone (OMZ; [O2]<2 μM) in the northeastern Arabian Sea affords the opportunity to investigate whether oxygen deficiency in bottom waters enhances the preservation of organic matter in the underlying sediments. We explored if the observed patterns of organic matter accumulation could be explained by differences in productivity, sedimentation rate, water depth, and mineral texture. The differences in the burial rates of organic matter in sediments deposited within or below the OMZ could not be explained on the basis of these factors. All collected evidence points to a coupling of low oxygen concentrations and enhanced organic matter preservation. Under more oxygenated conditions bioturbation as well as the presence of labile manganese and iron oxides are probably important factors for a more efficient microbially mediated degradation of organic matter. Pore water profiles of dissolved Mn2+ and Fe2+ show that reduction of manganese and iron oxides plays a minor role in sediments lying within the OMZ and a larger role in sediments lying below the OMZ.  相似文献   

16.
Cathodic stripping voltammetry (CSV) is used to determine total (after UV-irradiation) and labile dissolved metal concentrations as well as complexing ligand concentrations in samples from the river Scheldt estuary. It was found that even at high added concentrations of catechol (1 m for copper and 0·4 m for iron) and of APDC (1 m for zinc) only part of the dissolved metal was labile (5–58% for copper, 34–69% for zinc, 10–38% for iron); this discrepancy could be explained by the low solubility of iron which is largely present as colloidal material, and by competition for dissolved copper and zinc by organic complexing ligands. Ligand concentrations varied between 28 and 206 n for copper and between 22 and 220 n for zinc; part of the copper complexing ligands could be sub-divided into strong complexing sites with concentrations between 23 and 121 n and weaker sites with concentrations between 44 and 131 n . Values for conditional stability constants varied between (logK′ values) 13·0 and 14·8 for strong and between 11·5 and 12·1 for weaker copper complexing ligands, whereas for zinc the values were between 8·6 and 10·6. The average products of ligand concentrations and conditional stability constants (a-coefficients) were 6 × 102 for zinc and 6 × 106 for copper.The dissolved zinc concentration was found to co-vary with the zinc complexing ligand concentration throughout the estuary. It is argued that the zinc concentration is regulated, in this estuary at least, by interactions with dissolved organic complexing ligands. A similar relationship was apparent between the dissolved copper and the strong copper complexing ligand concentration. The total copper complexing ligand concentrations were much greater than the dissolved copper concentrations, suggesting that only strongly complexed copper is kept in solution.These results provide evidence for the first time that interactions of copper and zinc with dissolved organic complexing ligands determine the geochemical pathway of these metals.  相似文献   

17.
Vertical distributions of dissolved species across the sediment–water interface (SWI), including major cations (sodium, potassium, magnesium, calcium), minor cations (lithium, strontium, barium), redox sensitive species (dissolved manganese, iron, sulfate, sulfide, ammonium) and other chemical parameters (pH, alkalinity, soluble reactive phosphorous, dissolved silica) were studied in a Mediterranean lagoon used for intensive shellfish farming. In order to quantify the impact of this activity on diagenetic processes and the influence of seasonal changes, two stations contrasted with respect to organic carbon fluxes were sampled in Thau lagoon from March 2001 to August 2002 during four field campaigns in winter, spring, summer and fall. Well-defined layers enriched with redox sensitive species were observed following the conventional sequence of early diagenetic reactions. However, differences were observed between both stations in depths and thickness layers. Concentration gradients extended down to more than 92 cm depth at the central position of the lagoon (station C4 – 8 m depth) and down to 40 cm depth inside shellfish farming zones (station C5 – 9 m depth). Station C4 showed an unusual diagenetic signature: sharp dissolved oxygen, iron, nitrate and manganese gradients existed at the SWI but gradients of dissolved sulfide and alkalinity as well as other parameters (dissolved silica, Ba, etc.) were recorded only from 25 to 30 cm depth downward. Seasonal changes were observed in pore water composition as deep as 30–50 cm in station C4 (only 15 cm in station C5). The center of the lagoon is not directly subjected to biodeposits deriving from shellfish activity. Isotopic and bioturbation data allowed to rule out a reworking of the sediment deeper than a few centimeters. In addition to organic content of the sediment, physical parameters were likely to induce the 10–20 cm gap between dissolved iron and sulfide profile as well as the higher vertical extent of diagenetic sequence observed at station C4. Conversely to station C5, station C4 underwent stronger currents and wave effect probably generating advective transport of water through the sediment, but no permeability data were available to confirm this hypothesis. During summer, climatic conditions generated vertical stratification of the water column and transient suboxic conditions at the bottom. Such conditions drove the upward shift of redox fronts, compacting the diagenetic sequence. These effects were reinforced at station C5 by shellfish and its farm structures (mainly attenuation of current and increased heat absorption).  相似文献   

18.
The behavior of dissolved and particulate iron and manganese and dissolved silicon has been studied as a function of chlorinity in the Peconic River estuary, New York. This study sought to identify important geochemical processes in a relatively pristine estuary facing increasing anthropogenic impact.Dissolved iron behaved in the classical non-conservative manner exhibiting removal of nearly 80% at very low chlorinities, while particulate iron increased by a corresponding amount over the same chlorinity range. Dissolved manganese was enriched by up to 200% over its predicted concentration at low and intermediate chlorinities by desorption from suspended particulates and by a probable benthic flux. Dissolved silicon was enriched by up to 100% at low and intermediate chlorinities also from a probable benthic flux. These fluxes were estimated to be 5 μg cm?2 day?1 for dissolved manganese and 70 μg cm?2 day?1 for dissolved silicon.The quantity of both particulate iron and manganese increased at high chlorinities due to an influx of suspended inorganic particulates. In the intermediate to high chlorinity region, oxidation of sediment-derived manganese is believed to contribute to the observed increase in particulate manganese.Total iron was essentially conservative throughout most of the estuary, while total manganese was non-conservative presumably due to extensive remobilization of dissolved manganese from the sediments.  相似文献   

19.
The effect of benthic oxygenic photosynthesis on sediment-water fluxes of manganese and iron was studied for an intertidal sediment. Undisturbed sediments were incubated at an incident surface irradiance of 250 μE m−2 s−1at 26 °C. Oxygenic photosynthesis was selectively inhibited by adding [3-(3,4-dichloro)-1,1-dimethyl-urea] (DCMU). Benthic fluxes were determined experimentally from the change in manganese and iron concentrations in the overlying water, and were predicted from the pore water concentration gradients at the sediment-water interface assuming molecular diffusion as the transport mechanism. The experimental fluxes of manganese and iron in DCMU-treated cores amounted to −0·84 and −0·59 mmol m−2day−1, respectively, and were directed from the sediment towards the overlying water. In the control cores, showing high rates of benthic oxygenic photosynthesis, the fluxes of manganese and iron were directed towards the sediment, 0·06 and 0·01 mmol m−2day−1, respectively. Mass balances for the 0·1–0·14 cm thick oxic zone, calculated from the experimental fluxes and the predicted fluxes, suggest a minimum areal reoxidation of 0·6 mmol m−2day−1for manganese and of 0·48 mmol m−2day−1for iron in cores showing benthic photosynthesis. The estimated turnover times for dissolved Mn2+and dissolved Fe2+in the oxic surface layer during benthic photosynthesis were 0·8 and 0·25 h, respectively. Sediment oxygen microprofiles and the sediment pH profiles suggest that chemical precipitation and reoxidation dominates the retention of manganese and iron during benthic oxygenic photosynthesis in shallow intertidal sediments.  相似文献   

20.
To unravel the factors that regulate DOC dynamics in the freshwater tidal reaches of the Schelde estuary, DOC concentration and biodegradability were monitored in the upper Schelde estuary and its major tributaries. Although the Schelde estuary possesses a densely populated and industrialized catchment, our data suggest that the bulk of DOC in the freshwater tidal reaches is not derived from waste water. This was concluded from the low biodegradability of DOC (on average 9%), DOC concentrations that are close to the mean for European rivers (4.61 mg l−1) and the absence of an inverse relationship between DOC and discharge. Most DOC originating from waste water being discharged in tributaries of the estuary appears to be remineralised before these tributaries reach the main estuary. Although dense phytoplankton blooms were observed in the upper estuary during summer (up to 700 μg chl a l−1), these blooms did not appear to produce large quantities of DOC in the freshwater tidal reaches as DOC concentrations were low when phytoplankton biomass was high. The fact that DOC concentrations were high in winter and decreased in summer suggests a predominantly terrestrial source of DOC in the freshwater tidal reaches of the Schelde estuary.  相似文献   

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