Dissolved nutrient fluxes from the nearshore sediments of Bowling Green Bay,central Great Barrier Reef Lagoon (Australia)

The fluxes of dissolved inorganic N, P, and Si from the nearshore sediments of the Great Barrier Reef Lagoon are significantly lower than those reported from sediments in temperate regions at similar temperatures. The directly measured fluxes range from −23 to +28, −154 to +890, and −990 to +1750 μmol m⁻² day⁻¹ for PO₄³⁻, ΣN(=NH₄⁺ + NO₂⁻ + NO₃⁻) and Si, respectively. Estimates suggest that sediments are the major source of dissolved N to near-shore waters of the Lagoon greatly exceeding the dissolved flux from rivers. Resuspension of up to 1 cm of sediment during storms would have a very small effect on the PO₄³⁻ or Si(OH)₄ concentration of the overlying water, but would significantly raise the ΣN concentration. The productivity of these waters may be controlled at various times by the balance between the steady-state sedimentary flux of nutrients, the fluvial input, and storm resuspension.     

Adsorption–desorption reactions and bioturbation transport of 224Ra in marine sediments: a one-dimensional model with applications

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.     

The Role of Microphytobenthic Primary Production in a Mediterranean Mussel Culture Area

The production and biomass of microphytobenthos in a Mediterranean mussel farm was studied during 1991–92. Gross and net microphytobenthic production and respiration were calculated from oxygen fluxes in transparent and black bell jars at two stations; sediments under a mussel table and reference sediments, both located at 5 m depth. Net oxygen fluxes were mainly negative under the mussel tables (average −19·5 mg O₂ m⁻² h⁻¹, CV=132%), and microphytobenthos production could not meet the sediment oxygen demand; in the reference sediments, microphytobenthos production was responsible for net oxygen production (average +13·0 mg O₂ m⁻² h⁻¹, CV=118%). Benthic respiration rates were, on average, 47·3 mg O₂ m⁻² h⁻¹(CV=82%) under the tables and 27·7 mg O₂ m⁻² h⁻¹(CV=45%) in reference sediments. Aerobic respiration could remineralize less than 2% of the biodeposited carbon under the tables, implying that a large amount of organic material is accumulating under the tables, and that most of the degradation will be anaerobic. Gross microbenthic production showed sharp changes between 1991 and 1992 under the mussel tables and for reference sediments (averages 20·98 mg O₂ m⁻² h⁻¹, CV=135% and 33 mg O₂ m⁻² h⁻¹, CV=48%, respectively). Despite the negative oxygen balance in the sediments under the tables, microphytobenthos was more productive than phytoplankton in bottom waters. Per unit area, phytoplankton was more productive than microphytobenthos at both stations, especially in the area of the mussel tables, where phytoplanktonic production was enhanced by the excretion products of mussels. Microphytobenthos was composed mainly of diatoms in the sediments under the tables, while in reference sediments, the population was more diverse, with algae containing chlorophyllbalso present. Chlorophyllaconcentration in sediments under the tables was 207 mg m⁻²(CV=73%) and 95 mg m⁻²(CV=28%) in reference sediments; the stock of plant pigments was increased under the tables by biodeposition. Microphytobenthos constitutes a compartment with an important contribution in biomass, but also in oxygen production.     

The relationship between seagrass (Posidonia oceanica) decline and sulfide porewater concentration in carbonate sediments

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.     

云贵高原湖泊沉积物─水界面碱度扩散通量研究

于１９９１－１９９５年间５次在云贵高原泸沽湖，洱海湖和贵州阿哈湖，百花湖的湖心采集沉积物柱芯，界面水和湖水样品，通过其ｐＨ值和ＨＣＯ３浓度剖面及界面碱度扩散通量的研究，首次定量评估高原湖泊界面扩散作用上不体碱度的影响程度，研究结果表明，云贵高原某些湖水寄宿时间对较长，湖水深度相对小的湖泊，界面扩散作用是水体碱度的重要来源之一，湖水寄宿时间较短，深度较小的湖泊，界面扩散对上覆水体的影响可以忽略不地。     

中国多金属结核开辟区间隙水中铜、锰、镍的分布规律

通过对东北太平洋海域中国多金属结核开辟区沉积物间隙水中铜、锰、镍等微量元素的详细研究表明,锰主要受沉积环境的影响,其含量的变化范围在0.16～8.61μg/dm3之间;铜和镍则主要与表层海水的初级生产力有关,研究区内间隙水中铜和镍含量的变化范围分别为0.16～20.8和0.80～3.12μg/dm3,且这些元素在沉积物—水界面处均存在最大浓度梯度.利用“Fick扩散定律”计算表明,锰在研究区主要是从上覆海水向沉积物扩散,是沉积物中锰的主要来源之一;而铜和镍则是从沉积物向上覆海水扩散,是底层海水中铜和镍的主要来源。与表层海水中铜和镍向底层海水的输送通量计算结果相比,底层海水中铜和镍的含量主要受沉积物的控制.     

Seasonal variations in methane concentrations and diffusive fluxes in the Curonian and Vistula lagoons,Baltic Sea

Expected seasonal variations in methane concentrations and diffusive fluxes from surficial sediments into near-bottom waters were investigated in autumn 2012 and winter 2013 in the Curonian and Vistula lagoons of the Baltic Sea, expanding on earlier findings for summer 2011. Methane concentrations in bottom sediments (upper ca. 2 cm) generally ranged from ca. 1 to 1,000 μmol/dm³, and in near-bottom waters from ca. 0 to 1 μmol/l. Highest concentrations were found in the Curonian Lagoon, plausibly explained by the influence of freshwater conditions and finer-grained, organic-rich sediments. Vistula Lagoon methane concentrations and fluxes are dampened by periodic saline water inflow from the open sea, intensifying sulphate reduction. Calculated diffusive methane fluxes from the upper sediment layer (usually 0–5 cm, i.e. excluding any fluffy layer) into near-bottom waters were highest—2.48 mmol/(m² day)—in clayey silts of the Curonian Lagoon in autumn (September) 2012, contrasting strongly with the minimum value of 0.002 mmol/(m² day) observed there in February 2013 under ice-covered conditions. Seasonal and even weekly variations in methane dynamics can be largely explained by two main drivers, i.e. wind and temperature, operating at various spatiotemporal scales via, for example, wind wave-induced resuspension of bottom sediments, and involving regional weather patterns including autumnal low-pressure zones over the Gulf of Gdansk.     

Fluxes of iron and manganese across the sediment–water interface under various redox conditions

Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m^− 2 day^− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m^− 2 day^− 1) and high fluxes at suboxic conditions (up to 1000 μmole m^− 2 day^− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r² = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes.     

Seasonal survey of copper-complexing ligands and thiol compounds in a heavily utilized, urban estuary: Elizabeth River, Virginia

Concentrations of thiol compounds, copper-complexing ligands, and total dissolved copper were followed over the course of 1 year (October 2002 until September 2003) in the Elizabeth River, Virginia to evaluate seasonality. Copper-complexing ligand concentrations were determined by competitive ligand equilibration-adsorptive cathodic stripping voltammetry (CLE/ACSV). Thiol detection was carried out by high performance liquid chromatography (HPLC) and calibration using a suite of nine thiol compounds (cysteine, glutathione, mercaptoacetic acid, 2-mercaptoethanesulfonic acid, 2-mercaptoethanol, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, and monothioglycerol). Total dissolved copper concentrations reached a January low of 13.1 nM to a June high of 24.7 nM and were found to vary seasonally with higher concentrations occurring from June to September. With a low of 26 nM during April to a high of 56 nM in October, copper-complexing ligand (average log K′_CuL of 12.0 ± 0.2) concentrations displayed a similar seasonal pattern to that of total dissolved copper. Free cupric ion concentrations remained below 1.5 pM for a majority of the year except during March, April, and December when values reached pM levels greater than 1.5. Six of the nine thiol compounds surveyed were detected in the Elizabeth River samples and ranged in concentration from below detectable concentrations (< 5 nM) to individual highs ranging from 25.3 to168.5 nM. The thiol compound concentrations displayed a clear seasonality fluctuating at below detection limits during November to February then increasing with increasing surface water temperatures from March to July. CLE/ACSV was used to assess whether or not the suite of thiol compounds detected by HPLC could contribute to the copper-complexing ligand pool. Conditional stability constants for each one of six thiol standards (average log K′_CuL  12.1 ± 0.5) were found to be statistically equivalent to the naturally occurring copper-complexing ligands (average log K′_CuL  12.0 ± 0.2). This suggests that these thiol compounds could act as copper-complexing ligands in natural samples and could contribute to the copper-complexing ligand pool detected by CLE/ACSV. This study involving seasonality of copper-complexing ligands and thiols in an industrialized, urban estuary underscored several points that have to be substantiated in future research efforts including copper-complexing ligands sources and the role that thiol compounds as well as other unidentified organic compounds play in the copper-complexing ligand pool.     

Effects of Benthic Flux on Short Term Variations of Nutrients in Aburatsubo Bay

In order to investigate effects of benthic flux on the short-term variations in the distribution of nutrients in coastal waters, the concentrations of nutrients (PO₄ ^3-, NH₄ ⁺ NO₃ ^-, NO₂ ^- and H₄SiO₄) and other oceanographic parameters were measured every three hours over a 24-hour period at four fixed stations in the water column of Aburatsubo Bay, a shallow semi-enclosed inlet. Sediment cores were also taken from a fixed station once in each season over one year to quantitatively determine their benthic flux. Consistent linear negative correlations were found between their concentrations and salinity in the surface layers. This result suggests that fresh water was the main source of these nutrients and a physical mixing was the major process controlling their distribution. Monthly variations of PO₄ ^3- and NH₄ ⁺ monitored for 18 months in the bay also indicate that the high surf concentration of these nutrients was associated with the appearance of low salinity waters. On the other hand, in the bottom layers, a linear correlation between the concentration of the nutrients and salinity became weak, especially for NH₄ ⁺ and PO₄ ^3-. Their concentrations were higher than the predicted value from the conservative mixing between the fresh water and seawater, indicating the possibility of another source in the bottom layers. Benthic flux is suggested as a possible source. Pore water profiles of NH₄ ⁺ and PO₄ ^3- indicate their flux towards the overlying seawater, which is quantitatively consistent with their water column distributions.     

Rates of C,N, P and Si recycling and denitrification at the US Mid-Atlantic continental slope depocenter

Benthic fluxes of O₂, titration alkalinity (TA), total inorganic carbon (TIC), Ca²⁺, NO₃⁻, NH₄⁺, PO₄³⁻, and Si(OH)₄ were measured by in situ benthic flux chamber incubations at 13 locations on the North Carolina continental slope. The majority of measurements were made at water depths of approximately 700–850 m, in the previously identified upper slope depocenter. This region is characterized by extremely high organic matter deposition rates and near saturation bottom water oxygen concentrations. Measured benthic fluxes of TA are reasonably correlated with O₂ benthic fluxes. Because bottom waters are supersaturated with respect to calcite and aragonite at these shallow water depths, these results demonstrate the importance of metabolically driven dissolution in this region. Subtraction of the calcium carbonate dissolution contributions from the TIC benthic fluxes suggests rates of organic matter remineralization ranging from 0.97 to 3.9 mol C m⁻² yr⁻¹ at the depocenter sites, a factor of 3–10 greater than estimated for the adjacent continental rise and upper slope areas. Because biological primary production in the overlying waters does not follow this pattern, these extremely high values are most likely supported by lateral inputs of highly reactive organic matter. Mass balance calculations indicate that despite the oxygenated bottom water conditions, 68% of the organic nitrogen released during organic matter remineralization processes is ultimately denitrified. The release of PO₄³⁻ from the depocenter sediments is equivalent to or larger than that predicted from the remineralization of Redfield organic matter. This implies either that PO₄³⁻ is preferentially released in this setting and that the accumulating sediments must be depleted in PO₄³⁻ relative to organic carbon or that another, non-organic, phase is contributing PO₄³⁻ to the system. The molar ratio of the Si benthic flux and organic carbon remineralization rate ranges from 0.30 to 0.86. This is significantly greater than the ratio reported for most pelagic diatoms. Possible reasons for this high ratio include the deposition of benthic diatoms that may have a larger Si : C ratio than pelagic diatoms, the near-bottom lateral input of partially reworked organic matter that may have an elevated Si : C ratio relative to fresh diatoms, preferential loss of carbon in sinking particulates or the release of Si from non-opaline materials.     

海洋沉积物孔隙水中痕量金属元素的测试分析方法

孔隙水是沉积物-海水界面链接沉积物颗粒和上覆水体的一个重要过渡相态,针对其研究可更好地了解痕量金属在固-液界面的早期成岩过程。近年来,针对孔隙水中痕量元素研究的方法较为匮乏,为此建立了一种分析测定海洋沉积物孔隙水中7种痕量金属元素(Mn、Cu、Zn、Ni、Cd、Co、Pb)的方法,该方法使用Nobias PA1树脂进行富集分离,再使用电感耦合等离子体质谱(ICP-MS)进行测试,可针对孔隙水中的痕量金属元素进行准确分析。通过实验结果发现该方法最优实验条件为: Nobias PA1树脂富集时的pH值为5.5~6.0,洗脱酸浓度为1.3 mol/L硝酸,体积为1 mL。同时,样品需进行紫外消解4 h以上以分解有机络合物,该消解步骤对Cu和Co这两种元素尤其重要。该方法通过加标回收获得Mn、Cu、Ni、Co和Pb的回收率在92%~100%, Zn和Cd的回收率分别为72%和82%; Mn、Cu、Zn、Ni的方法检出限范围为0.03~0.53 nmol/L, Cd、Co、Pb的方法检出限范围为2.66×10^-3~8.60×10^-3 nmol/L,满足孔隙水中痕量金属浓度的测试需求。同时,根据检出限计算的结果显示,孔隙水样品只需1 mL,即可应用该方法进行测试。应用该方法测试了一根采集于北黄海中部沉积物短柱的孔隙水样品,测试结果显示其垂相分布合理、较符合早期成岩过程规律。此研究为分析海洋沉积物孔隙水中痕量金属元素提供了一种准确而简便的方法。     

Nutrient dynamics at the sediment-water interface in a Mediterranean lagoon (Thau, France): influence of biodeposition by shellfish farming activities

The Thau Lagoon, a French Mediterranean shallow lagoon, is a site where extensive shellfish farming occurs. The aim of the present work is to evaluate the role of this activity on nutrient exchange at the sediment-water interface in relation to organic matter (OM) sedimentation and degradation. Two stations inside (C5) and outside (C4) of the shellfish farming areas were sampled at three seasons. Porewater chemistry surveys and calculated diffusive fluxes were used to evaluate the trophic status of the Thau lagoon. Quantitative (Particulate Organic Carbon) as well as qualitative OM (Hydrogen Index, Carbohydrates) analyses were performed on sediments to assess OM characteristics. Results emphasized that surficial sediments at C5 are always more enriched in OM. Porewater nutrient concentrations are 10-20 times higher at C5 than at C4. In June 2003, the porewater profiles exhibit a sharp gradient at the bottom waters, indicating a hypereutrophic status, leading to an anoxic crisis.     

Manganese and Iron Oxidation During Benthic Oxygenic Photosynthesis

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.     

Pore-water distribution and quantification of diffusive benthic fluxes of nutrients in the Huanghai and East China Seas sediments

1 Indroduction The coastal zone and continental shelf area is an important region in the global biogeochemical cycle of nutrients in the ocean. This portion of the global ocean interacts closely with the continents, atmosphere and the open ocean in a comp…     

Annual Variation of Benthic Nutrient Fluxes in Shallow Coastal Waters (Gulf of Trieste, Northern Adriatic Sea)

Abstract. Benthic fluxes of dissolved N. Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O₂ from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly for 16 months, using laboratory incubated flux chambers at in siru temperatures in the dark. The annual average fluxes were: 02 = -19.3 ± 8.2, DIC = 13.7 ± 9.6, NO3 = -0.04 ± 0.16, NH4 = 0.3 ± 0.4. PO₄= 4.001 ± 0.01, Si = 0.9 ± 0.1 mmol m-² d^-1, with strong temporal fluctuations. The highest effluxes of all nutrients and DIC were observed in the summer. Small effluxes of DIC and NH4 and influxes of Si and PO4 were observed in late winter. Only NH₄ (ca. 50%) and Si (ca. 70%) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality of sedimented organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIC, NH₄ and Si effluxes observed in May 1993 during low temperature were due to the degradation of sedimentary organic matter produced by an early spring bloom of benthic microalgae which occurred about 6 weeks earlies while the autumn phytoplankton bloom was simultaneously reflected in enhanced benthic fluxes due to higher temperature. The role of benthic biological advection in this transport across the sediment-water interface, evaluated by comparison between measured benthic and calculated diffusive fluxes from nutrient pore water concentrations, was of minor importance. This is probably due to low infaunal activity throughout the year it was localized mostly in the narrow surficial layer. The annual average diffusive fluxes of NH4 and PO4 were higher than those measured, probably due to the presence of nitrificationdenitrifi-cation processes and redox-dependent chemical reactions at the oxic sediment-water interface, respectively. Only during bottom-water hypoxia in September 1993 did strong PO₄ effluxes prevail. Calculations based on the Redfield stoichiometry of oxic decomposition of organic N to NH4 and NO3, and differences between diffusive and measured NH₄ fluxes showed that denitrifkation averaged 0.8 mmol m^-2 d^-1. Significant correlations between NH₄ and PO₄ DIC and Si, and NH4 and Si fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes observed were not significantly linked to O₂ consumption, suggesting also that anaerobic oxidation processes were important at the sediment-water interface in the gulf. The N, P and Si nutriqnts released from sediment pore waters are probably utilized in benthic microalgal and bottorn-hater primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other.     

Nitrogen and Phosphorus Diffusive Fluxes Across the Sediment-Water Interface in Estuarine and Coastal Tidal Flats

Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082～2.56, 0.03～0.58, 0.69～5.38 and 0.035～0.53 mg/L, respectively, while 0.0025 ～ 1.35 mg/L for NH4+-N, 0. 0055 ～ 0.20mg/L for NO2--N, 0.61～1.14 mg/L for NO3--N and 0.11～0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusion fluxes across the sediment-water interface are between -0.024～0.99, -0.39～ -0.0019, -3.09～the source of phosphorus and an important sink for nitrogen in the waters.     

Significance of vertical flux as a sink for surface water DMSP and as a source for the sediment surface in coastal zones of northern Europe

In April 1997 and 1998 the significance of sedimentation as a sink for epipelagic dimethylsulphoniopropionate (DMSP) production and as a source for marine sediments was reassessed using a newly designed sediment trap. The behaviour of the traps in immersion was monitored continuously and the collection efficiency was evaluated with ²³⁴Th measurements. Net DMS(P) fluxes were corrected for some physical and biological losses during the whole sedimentation process providing reliable estimates of gross DMSP fluxes. It is shown that daily losses by sedimentation account for between 0.1% and 16% of seawater particulate DMSP (DMSPp) standing stocks, and between 3% and 75% of daily DMSPp production. In the Malangen fjord we observed temporal increases of DMSP production and standing stocks which resulted also in increases of DMSP vertical fluxes and DMS(P) concentrations at the sediment surface. This result illustrates how tight the coupling can be between pelagos and benthos, and confirms that DMS(P) concentration in the sediment was a reliable diagnostic indicator of vertical export from overlying waters in Malangen fjord. In Ullsfjord, however, DMS(P) concentrations in the sediment were poorly indicators of Phaeocystis pouchetii export during the early stage of growth of a bloom. The high load of DMS(P) in Balsfjord's sediments could neither be attributed to local vertical sedimentation nor to short-term lateral advection of fresh DMSP-containing phytoplanktonic material, and provides indication that this tracer sometimes also can be misleading. The highest loads of DMS(P) in sediments and the fastest rates of sedimentation occurred in the Southern Bight of the North Sea.     

Seasonal variations of dissolved organic matter and nutrients in sediment pore water in the inner part of Tokyo Bay

At four stations in Tokyo Bay, pore water profiles of dissolved organic carbon (DOC), nitrogen (DON), phosphorus (DOP), and inorganic nutrients were determined at 3-month intervals over 6 years. Concentrations of dissolved organic matter (DOM) and nutrients were significantly higher in pore waters than in the overlying waters. Pore water DOC, DON, and DOP concentrations in the upper most sediment layer (0–1 cm) ranged from 246 to 888 μM, from 14.6 to 75.9 μM, and from 0.02 to 9.83 μM, respectively. Concentrations of DOM and nutrients in pore waters occasionally showed clear seasonal trends and were highest in the summer and lowest in the winter. The seasonal trends in the pore water DOM concentrations were coupled with trends in the overlying water temperature and dissolved oxygen concentration. Benthic effluxes of DON and DOP were low compared with those of inorganic nutrients, accounting for only 1.0 and 1.5 % of the total benthic effluxes of nitrogen and phosphorus, respectively; thus benthic DOM fluxes were quantitatively insignificant to the inorganic nutrient fluxes in Tokyo Bay. The DOM fluxes represented about 7, 3, and 10 % of the riverine discharge of DOC, DON, and DOP to Tokyo Bay, respectively.     

云贵高原湖泊沉积物─水界面碱度扩散通量研究

于1991-1995年间5次在云贵高原泸沽湖、洱海湖和贵州阿哈湖、百花湖的湖心采集沉积物柱芯、界面水和湖水样品，通过其pH值和HCO-3浓度剖面及界面碱度扩散通量的研究，首次定量评估高原湖泊界面扩散作用上覆水体碱度的影响程度。研究结果表明，云贵高原某些湖水寄宿时间相对较长、湖水深度相对小的湖泊，界面扩散作用是水体碱度的重要来源之一;湖水寄宿时间较短、深度较小的湖泊，界面扩散对上覆水体的影响可以忽略不计。