首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Land/ocean boundaries constitute complex systems with active physical and biogeochemical processes that affect the global carbon cycle. An example of such a system is the mesotidal lagoon named Ria de Aveiro (Portugal, 40°38′N, 08°45′W), which is connected to the Atlantic Ocean by a single channel, 350 m wide. The objective of this study was to estimate the seasonal and inter-tidal variability of organic carbon fluxes between the coastal lagoon and the Ocean, and to assess the contribution of the organic carbon fractions (i.e. dissolved organic carbon (DOC) and particulate organic carbon (POC)) to the export of organic carbon to the Ria de Aveiro plume zone. The organic carbon fractions fluxes were estimated as the product of the appropriate fractional organic carbon concentrations and the water fluxes calculated by a two-dimensional vertically integrated hydrodynamic model (2DH). Results showed that the higher exchanges of DOC and POC fractions at the system cross-section occurred during spring tides but only resulted in a net export of organic carbon in winter, totalling 85 t per tidal cycle. Derived from the winter and summer campaigns, the annual carbon mass balance estimated corresponded to a net export of organic carbon (7957 = 6585 t yr−1 POC + 1372 t yr−1 DOC). On the basis of the spring tidal drainage area, it corresponds to an annual flux of 79 g m−2 of POC and 17 g m−2 of DOC out of the estuary.  相似文献   

2.
Time-series Mark 7 sediment traps were deployed at three stations at 0°N, 13°N and 48°N along 175°E to investigate seasonal and spatial variations of particulate material flux. Chemical analysis of particulate material was performed for four major chemical components, viz. opal, CaCO3, organic material and clay minerals, Cd and P in the particulate material were also determined. We discuss the characteristics of particulate material at each site and the transportation of Cd and P to deep water by the particulate material. The total mass fluxes and variation of fluxes at each site reflect oceanographic conditions, such as biological productivity and kind of major planktonic organisms. At the northern site, large mass fluxes with a spring bloom and high ratios of opal are characteristic. Relatively small mass fluxes with high ratios of CaCO3 are distinct, and dissolution of CaCO3 due to sinking is recognized in the middle latitude and 0°N sites. The larger flux at the lower trap than the upper trap at the equatorial site suggests influence by lateral transport in the deep water. Distinctive decreasing Cd/P ratio and CaCO3 concentrations in the particulate material with increasing depth suggests that the change of Cd/P ratio in the intermediate and deep water occurs through the dissolution of CaCO3. The dissolved Cd/P ratios in the deep water are proportional to the age of the deep water in the Atlantic but not in the Pacific. This is explained by the difference of kinds of particulate material transporting Cd and P in the deep water between the oceans. That is, the major planktonic organisms are planktons of CaCO3 tests in the Atlantic Ocean and diatoms of opal tests in the North Pacific Ocean.  相似文献   

3.
The Mediterranean Basin is rich in mercury from natural and anthropogenic sources. During an extensive research from 2002–2005, measurements of different mercury forms were carried out in the Mediterranean Sea by the Italian research vessel Urania as a part of the Med Oceanor and MERCYMS projects funded by the EU Framework programme. Further on, transport and fate of mercury forms was simulated in water and air compartments by two different models, and an approximate coupling of both models was performed. The new 3-dimensional model PCFLOW3D was completed with the first version of a biogeochemical module which deals with various mercury species in dissolved and particulate forms. Exchange with the bottom and the atmosphere, methylation, demethylation, reduction and oxidation were taken into account. Based on the integrated hydrodynamic-atmospheric model and results of field measurements the mass balance of total mercury in the Mediterranean Sea was determined in order to estimate main sources and sinks and simulate future trends of mercury contamination in the Mediterranean. The following terms were taken into account: sources of mercury from major rivers and from point sources, exchange with the Atlantic Ocean and the Black Sea, estimated natural sources from geotectonic active areas in the sea, exchange with bottom sediments, and evasion to and deposition from the atmosphere.  相似文献   

4.
Results are presented from particle flux studies using sediment trap and current meter moorings along a transect at the European continental margin at 49°N within the EU-funded Ocean Margin Exchange (OMEX) project. Two moorings were placed, at the mid- and outer slope in water depths of 1500 and 3660 m, with traps at 600 and 1050 m and at 580, 1440 and 3220 m, respectively. Residual currents at the mid-slope follow the slope contour, whereas seasonal off-slope flow was registered at the outer slope. At 600 m on the slope fluxes are similar to those in the abyssal North Atlantic. The flux of all components (bulk dry weight, particulate organic and inorganic carbon, lithogenic matter and opal) increased with water depth. Highest fluxes were recorded at 1440 m at the outer slope, where off-slope residual currents mediate particle export. The injection of biogenic and lithogenic particles below the depth of winter mixing results in the export of particles from shallower waters. Calculated lateral fluxes of particulate organic carbon exceed the primary flux by over a factor of 2 at 1440 m on the outer slope. Estimated lateral fluxes of suspended particulate matter in the water column and intermediate nepheloid layers at the outer slope are potentially large compared to sinking fluxes measured by sediment traps. A comparison is made of particle flux at three continental margin sites and two sites in the adjacent open North Atlantic, from which it is seen that bulk and organic matter flux increases exponentially with proximity to the shelf break. The percentage contribution of particulate organic carbon to biogenic fluxes increases from a mean of 5.7% in the abyssal N. Atlantic to 13.9% at the continental margins.  相似文献   

5.
A 2-yr record of downward particle flux was obtained with moored sediment traps at several depths of the water column in two regions characterized by different primary production levels (mesotrophic and oligotrophic) of the eastern subtropical North Atlantic Ocean. Particle fluxes, of ∼71–78% biogenic origin (i.e. consisting of CaCO3, organic matter and opal) on average, decrease about six-fold from the mesotrophic site (highest fluxes in the North Atlantic) nearer the Mauritanian margin (18°30′N, 21°00′W) to the remote, open-ocean, oligotrophic site (21°00′N, 31°00′W). This decrease largely reflects the difference in total primary production between the two sites, from ∼260 to ∼110 g organic C m−2 yr−1. At both sites, temporal variability of the downward particle flux seems to be linked to westward surface currents, which are likely to transport seaward biomass-rich water masses from regions nearer the coast. The influence of coastal upwelling is marked at the mesotrophic site. The large differences between the 1991 and 1992 records at that site, where carbon export is large, underscore the interest of long-term studies for export budget estimates. The different productivity regimes at the two sites seem to induce contrasting downward modes of transport of the particulate matter, as shown in particular by the faster settling rates and the higher E ratio (particulate organic carbon export versus total primary production) estimated at the mesotrophic site.  相似文献   

6.
1IntroductionThefluxesofcarbon,nutrients,andassoci-atedelementsinvolvedinthebiogeochemicalcyclesoutoftheeuphoticzoneareimportantinthestudyofglobalCO2 change.Someworkershaveproposedthatatthesteadystatethefluxofparticulateorganiccarbonoutoftheeuphoticzoneequalsthenewproduction(EppleyandPe-terson,1979;Eppley,1989).Generallytwometh-odscanbeemployedtoobtainthefluxdata.Oneistousesedimenttrapsintheupperocean(<200m)orfloatingsedimenttraps.Thoughthesedimenttraptechnologyhasshowntobeuse-fulfortimeser…  相似文献   

7.
Surface water was collected from the Jiulong Estuary for determination of activity concentrations of uranium isotopes in different size fractions, namely, greater than 53, 10 -53, 2 - 10, 0.4 -2 μm, 10 000 u -0.4 μm and less than 10 000 u fractions by microfihration and cross-flow uhrafiltration technologies. Results indicated that most of the dissolved uranium （ 〈 0.4 μm） exis- ted in the low molecular mass fraction （ 〈 10 000 u）, and the colloidal uranium-238 （10 000 u -0.4 μm） only contributed less than 1% of the dissolved uranium-238. The fractions of colloidal uranium in the dissolved phases decreased with the increasing sa- linity. A positive linear relationship between uranium-238 activities and salinities was observed for the dissolved, colloidal and low molecular mass fractions, indicating a conservative behavior of uranium in the Jiulong Estuary. In the particulate phases （ 〉 0.4 μm）, the partitioning of uranium isotopes among different size fractions was controlled by the partitioning of particle concentrations. In the regions with salinities below 20, the partitioning of uranium-238 among different size fractions was as follows： 10 - 53 μm 〉 2 - 10 μm 〉 0.4 - 2 μm greater than above 53 μm. However, the order at the offshore station with salinities above 30 changed as follows ： 0.4 - 2 μm 〉 10 - 53 μm 〉 2 - 10 μm greater than above 53 μm. The fraction of the 0.4 - 2 μm particles increased at the offshore station, suggesting the increased contribution of the authigenic uranium. The activity ratio of uranium-234 to uranium-238 in the dissolved phases, including the low molecular mass fraction and the colloidal fraction, was larger than unity, showing the occurrence of excess uranium-234. In contrast, the activity ratio of uranium-234 to uranium-238 in all size fractions of the particulate phase was close to the equilibrium value （1.0）. The observed different values of the activity ratio of uranium-234 to uranium-238 in the dissolved phase and the partic  相似文献   

8.
The likelihood that the carbon fluxes measured as part of the US-JGOFS field program in the equatorial Pacific ocean (EgPac) during 1992 yielded a balanced carbon budget for the surface ocean was determined. The major carbon fluxes incorporated into a surface carbon budget were: new production, particulate organic carbon (POC) and dissolved organic carbon (DOC) export, CaC03 export, C02 gas evasion, dissolved inorganic carbon (DIC) supply, and the time rate of charge. The ratio of the measured concentration gradients of DOC and DIC provided a constraint on the ratio of POC/DOC export. Uncertainties of ±30–50% for individual carbon flux measurements reduce the likelihood that a carbon balance can be measured during a JGOFS process-type study. As a benchmark, carbon fluxes were prescribed to yield a hypothetical surface carbon budget that was, on average, balanced. Given the typical errors in the individual carbon fluxes, however, there was only about a 30% chance that this hypothetical budget could be measured to be balanced to ±50%. Using this benchmark, it was determined that there was a 95 % chance that the carbon flux measurements yielded a surface DIC budget balanced (to ±50%) during El Nino conditions in boreal spring 1992, when the total organic carbon export rate was - 5 mmol C m-2 day- 1 and the POC export was 3 mmol C m−2 day−1. In boreal fall 1992, during cold period conditions, there was a 70% chance that the surface carbon DIC budget was balanced when the total organic carbon export rate was 20 mmol C m−2 day−1 and export was -13 mmol C m-2 day-'. The DOC to DIC concentration gradient ratio of - -0.15, measured in depth profiles down to 100m and in surface waters, was used as an important constraint that most (> 70%) of the organic carbon exported from the euphotic zone was POC rather than DOC. If a balanced surface DIC budget was used to test the compatibility of individual carbon fluxes measured during EgPac, then a three- to four-fold increase in total and particulate organic carbon export between spring and fall is indicated. This increase was not reflected in the POC loss rates measured by drifting sediment trap collections or estimated by234Th deficiencies coupled with the C/Th measured on suspended particles.  相似文献   

9.
Mass, carbon, and nitrogen fluxes and carbon and nitrogen compositions were determined for particulate samples from plankton net tows, shallow floating sediment traps, intermediate and deep moored sediment traps, and sediment cores collected along 140°W in the central equatorial Pacific Ocean during the US JGOFS EqPac program. Mass, particulate organic carbon (POC), and particulate inorganic carbon (PIC) fluxes measured by the floating sediment traps during the Survey I (El Niño) and Survey II (non-El Niño) cruises follow essentially the same pattern as primary production: high near the equator and decreasing poleward. POC fluxes caught in free-floating traps were compared with alternative estimates of export fluxes, including 234Th models, new production, and other sediment trap studies, resulting in widely differing estimates. Applying 234Th corrections to the trap-based fluxes yielded more consistent results relative to primary production and new production. Despite factors of five differences in measured fluxes between different trap types, POC : 234Th ratios of trap material were generally within a factor of two and provided a robust means of converting modeled 234Th export fluxes to POC export fluxes. All measured fluxes decrease with depth. Trap compositional data suggest that mineral “ballasting” may be a prerequisite for POC settling. POC remineralization is most pronounced in the epipelagic zone and at the sediment–water interface, with two orders of magnitude loss at each level. Despite seawater supersaturation with respect to calcium carbonate in the upper ocean, 80% of PIC is dissolved in the epipelagic zone. Given the time-scale differences of processes throughout the water column, the contrasting environments, and the fact that only 0.01% of primary production is buried, sedimentary organic carbon accumulation rates along the transect are remarkably well correlated to primary production in the overlying surface waters. POC to particulate total nitrogen (PTN) ratios for all samples are close to Redfield values, indicating that POC and PTN are non-selectively remineralized. This constancy is somewhat surprising given conventional wisdom and previous equatorial Pacific results suggesting that particulate nitrogen is lost preferentially to organic carbon.  相似文献   

10.
The least known component of the “biological pump” is the active transport of carbon and nutrients by diel vertical migration of zooplankton. We measured CO2 respiration and dissolved organic carbon (DOC) excretion by individual species of common vertically migrating zooplankton at the US JGOFS Bermuda Atlantic Time-series Study (BATS) station. The inclusion of DOC excretion in this study builds on published research on active transport by respiration of inorganic carbon and allows a direct assessment of the role of zooplankton in the production of dissolved organic matter used in midwater microbial processes. On average, excretion of DOC makes up 24% (range=5–42%) of the total C metabolized (excreted+respired) and could represent a significant augmentation to the vertical flux that has already been documented for respiratory CO2 flux by migrant zooplankton. Migratory fluxes were compared to other transport processes at BATS. Estimates of combined active transport of CO2 and DOC by migrators at BATS averaged 7.8% and reached 38.6% of mean sinking POC flux at 150 m, and reached 71.4% of mean sinking POC flux at 300 m. DOC export by migrator excretion averaged 1.9% and reached 13.3% of annual DOC export by physical mixing at this site. During most of the year when deep mixing does not occur, diel migration by zooplankton could provide a supply of DOC to the deeper layers that is available for use by the microbial community. A carbon budget comparing migrant zooplankton transport to the balance of fluxes in the 300–600 m depth strata at BATS shows on average that the total migrant flux supplies 37% of the organic carbon remineralized in this layer, and that migrant DOC flux is more than 3 times the DOC flux gradient by diapycnal mixing. New estimates of active transport of both organic and inorganic carbon by migrants may help resolve observed imbalances in the C budget at BATS, but the magnitude is highly dependent on the biomass of the migrating community.  相似文献   

11.
Particulate fluxes of trace elements (Al, Cd, Co, Cu, Fe, Mn, Ni, P, Ti, V and Zn) in the northeast Atlantic Ocean (three positions at latitudes from 33°N to 54°N along ∼20°W) were measured using time-series sediment traps between March 1992 and September 1994. Significant variabilities of fluxes with season and depth (1000 m to maximum of 4000 m) were observed only for ‘biogenic elements’, such as Cd, Ni, Zn or P. On the other hand, we found a distinct large-scale increase of fluxes into the deep-sea traps to the south for Al, Co, Fe, Mn and V. We attribute this latitudinal gradient to the increasing influence of the Saharan dust plume. The biogenic flux decreased towards the south. This trend was clearly visible for Cd and P only. The fluxes of other ‘nutrient-like’ elements, such as Ni or Zn, exhibited a general decrease between 53°N and 33°N. We compared our sedimentation flux data with published data from the western North Atlantic basins. For this purpose we corrected the deep-sea fluxes of Cu, Mn, Ni and Zn for their lithogenic fractions on the basis of Al, with average crustal material and granitic rocks as references. The comparison indicates that these ‘excess’ fluxes are a factor of at least 2 higher in the western basins for the selected elements. Estimated fluxes are in good agreement with reported atmospheric deposition in the two areas. The noted imbalance between the non-lithogenic atmospheric input of Mn and the determined ‘excess flux’ in the deep northeast Atlantic indicates an additional input in the form of a lateral flux of dissolved Mn(II) species and scavenging onto sinking particles. With respect to the mechanism of sedimentation, a unique behaviour is noticed for the refractory elements Co, Fe, Mn, Ti and V, which were found to correlate with the vertical transport of Al (clay). The ‘excess’ fluxes of Cu, Ni and Zn are linearly related to Corg, whereas the overall relation of Cd to P fluxes exhibits a molar Cd/P ratio of 2.0×10-4, which is close to the ratio in the dissolved fractions in the northeast Atlantic.  相似文献   

12.
The decomposition of cultured marine phytoplankton (Skeletonema costatum) and natural estuarine seston from Narragansett Bay, RI, was studied at two temperatures (8°C and 18°C) in bottles containing sterile bay-water (30‰) and in bay-water with micro-organisms small enough to pass through a glass fibre filter (nominally < 1μ). About 50% of the particulate organic nitrogen (PON) and particulate phosphorus (PP) was immediately released to the water in dissolved organic forms from both types of organic matter. Comparison of changes in the dissolved organic nitrogen (DON) fraction in the sterile and non-sterile systems indicated that nearly all of the DON initially released was subsequently remineralized. Ammonification proceeded only in non-sterile bay-water. 20–25% of the PP was converted to dissolved inorganic-P (DIP) fraction after only 7 h in both sterile and non-sterile bay-water. Following autolytic releases of DON, DOP and DIP the initial rates of N and P remineralization were temperature dependent: Q10 values for PON and PP decay during first phase of microbially mediated decomposition ranged from 1·3 to 6·4. Rates of remineralization then slowed so that about equal amounts of nutrients were remineralized (45–50% of the N and 57–60% of the P in the phytoplankton and 60–63% of the N and 36–60% of the P in the natural seston) after 30 days storage at either temperature. During 30 days of decomposition in non-sterile seawater the N/P ratios in the dissolved inorganic fractions converged on the ratios of total-N/total-P initially present in the bottles. Kinetic analysis of the decay of total organic-N (TON) and total organic-P (TOP) in the non-sterile systems and analysis of similar sets found in the literature showed that the initial stages of the decomposition of N and P from planktonic POM in vitro could be modelled as the sequential decay, at first-order rates, of two particulate fractions. The first, more labile, fraction comprised about 60% of the particulate N and P. First-order rate constants (−k, base e) for decomposition during the 1st and 2nd phases were 0·02 to 0·2 day−1 and 0·003 to 0·02 day−1, respectively. The decay rates are far too slow to account for the ‘rapid in situ recycling’ of nutrients needed to support phytoplankton production when other means of nutrient resupply (by advection, fixation, rainfall, etc.) are very low.  相似文献   

13.
Data is presented for the concentrations of organic carbon and nitrogen, and C:N ratios, in marine particulate matter, and for POC and PN, from surface waters collected in the northeastern Atlantic, South Atlantic, Indian Ocean and China Sea.The organic carbon content of this particulate matter varies between 4.6% and 29.9%, and has an average of 17.8%. The average organic carbon content of particulate matter from the various oceans decreases in the order: Northeastern Atlantic > South Atlantic > Indian Ocean > China Sea.The nitrogen content of the particulate matter varies between 1.0% and 3.9%, with an average of 2.2%, and in general follows the same trend as that of organic carbon.C:N ratios vary between 5.1 and 10.6, and have an average of 7.9.The POC contents of the oceanic waters vary between 6.6 and 211 μg/l, with an average of 52 μg/l. The concentrations in the surface waters decrease in the following order: Northeastern Atlantic τ China Sea > South Atlantic > Indian Ocean.The concentrations, and compositions, of particulate matter from various coastal localities are given for comparison with the oceanic values.  相似文献   

14.
讨论了1997年冬季在北太平洋西北海域7个站位的表层至200m水深水柱中溶解及颗粒态234Th,颗粒态有机碳(POC)、氮(PON)及叶绿素a浓度的垂直分布剖面.溶解态、颗粒态及总的234Th的放射性在真光层中显著低于母体238U的放射性,总的234Th放射性在水深大于100m时趋于平衡.利用234Th-238U在海洋表层海水中的放射性不平衡推导出了北太平洋西北海域冬季真光层海水中234Th的平均停留时间和输出通量以及颗粒态有机碳和有机氮的输出通量.在亚北极环流区溶解态234Th的停留时间为40~50d,而在黑潮-亲潮共同影响区为20d左右.颗粒态有机碳和有机氮从真光层的输出通量范围分别为3.8~8.2和0.50~0.98mmol/(m2·d),西部海区高于东部海区,南部海区高于北部海区.在黑潮-亲潮共同影响区较高的颗粒态有机碳输出通量表明光照量及陆源营养盐物质的提供是两个决定生产力的主要因素.叶绿素a的水深分布和POC/PON的值同Redfield的比值的一致性表明这个海区的冬季颗粒物主要由浮游植物构成.北太平洋西北海域在冬季的颗粒有机碳输出通量可高于世界大洋一些海区春、夏季的颗粒有机碳输出通量.  相似文献   

15.
中国第22次南极科学考察(2005年11月至2006年3月)期间,测定了南极普里兹湾海域5个站位的从表层至150 m水深的不同层位水样中溶解态和颗粒态234Th,238U的放射性比活度以及颗粒有机碳.利用234Th/238U在上层水体中的不平衡,计算了南极普里兹湾上层水体中234Th的平均停留时间和输出通量.结果显示,随着纬度的增加,上层水体中颗粒态和溶解态234Th的平均停留时间总体趋向减小,并在中纬度站位出现了最低值,分别为1~8和29~48 d,而颗粒态和溶解态234Th的输出通量则在中纬度站位出现了最大值,分别为21~38和26~39 dpm/(m3·d).运用箱型清除模式,利用两种不同的方法估算了各水柱中从真光层底部输出的POC通量,平均值分别达到104.7 mmol/(m2·d)(E法)和120.6 mmol/(m2·d)(B法),表明南极普里兹湾夏季存在很高的新生产力,它将会对该海域碳的生物泵过程产生重要作用.  相似文献   

16.
The Amazon River Plume delivers freshwater and nutrients to an otherwise oligotrophic western tropical North Atlantic (WTNA) Ocean. Plume waters create conditions favorable for carbon and nitrogen fixation, and blooms of diatoms and their diazotrophic cyanobacterial symbionts have been credited with significant CO2 uptake from the atmosphere. The fate of the carbon, however, has been measured previously by just a few moored or drifting sediment traps, allowing only speculation about the full extent of the plume's impact on carbon flux to the deep sea. Here, we used surface (0.5 m) sediment cores collected throughout the Demerara Slope and Abyssal Plain, at depths ranging from 1800 to 5000 m, to document benthic diagenetic processes indicative of carbon flux. Pore waters were extracted from sediments using both mm- and cm-scale extraction techniques. Profiles of nitrate (NO3) and silicate (Si(OH)4) were modeled with a diffusion-reaction equation to determine particulate organic carbon (POC) degradation and biogenic silica (bSi) remineralization rates. Model output was used to determine the spatial patterns of POC and bSi arrival at the sea floor. Our estimates of POC and Si remineralization fluxes ranged from 0.16 to 1.92 and 0.14 to 1.35 mmol m−2 d−1, respectively. A distinct axis of POC and bSi deposition on the deep sea floor aligned with the NW axis of the plume during peak springtime flood. POC flux showed a gradient along this axis with highest fluxes closest to the river mouth. bSi had a more diffuse zone of deposition and remineralization. The impact of the Amazon plume on benthic fluxes can be detected northward to 10°N and eastward to 47°W, indicating a footprint of nearly 1 million km2. We estimate that 0.15 Tmol C y−1 is remineralized in abyssal sediments underlying waters influenced by the Amazon River. This constitutes a relatively high fraction (~7%) of the estimated C export from the region.; the plume thus has a demonstrable impact on Corg export in the western Atlantic. Benthic fluxes under the plume were comparable to and in some cases greater than those observed in the eastern equatorial Atlantic, the southeastern Atlantic, and the Southern Ocean.  相似文献   

17.
Produced water undergoes changes in its physical chemistry including precipitation of heavy metals after being discharged and mixed with ambient seawater. Potential impacts of the precipitation of heavy metals on their transport and toxicity were studied using samples from offshore oil production sites on the Scotian Shelf off eastern Canada. Concentrations of aluminum, cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel and zinc were measured in total, particulate and dissolved fractions together with Microtox tests for assessment of toxicity. Heavy metals in produced water were transformed from dissolved to particulate phase in a period of hours under oxygenated conditions, and aggregated to larger particles that settle rapidly (>100 m/day) over a few days. In addition, there was production of buoyant particles comprised of heavy metal precipitates sequestered onto oil droplets that were transported to the surface. The particulate fraction was generally more toxic than the dissolved fraction. This was evident at the mixing interface between produced water and seawater where elevated particulate and toxicity levels were observed. Laboratory studies suggest an increase in the toxicity of discharged produced water over time. Time-series experiments showed a sustained toxic response for more than a week following the oxidation of freshly discharged produced water that initially elicited little or no toxic response in the Microtox test. Chemical processes identified in this study, namely precipitation of heavy metals and consequent settling and rising fluxes of particles, will influence the toxicity, the fate and the transport of potential contaminants in the produced water. Therefore, these processes need to be considered in assessment of the environmental impact associated with offshore oil and gas operations.  相似文献   

18.
The present study investigates the differences between nutrient fluxes and particulate organic matter within an artificial reef system (AR) deployed in August 2002 off Faro (Algarve, Southern Portugal) and in a non-reef area (NRA), and how fluxes and suspended material may be affected by the hydrodynamic regime. Surveys to collect sediment cores, suspended/settled particles and overlying water samples were carried out by divers, from March (2006) to October (2007) in AR and NRA. Sediment cores and settled particles were collected to determine grain size, organic and inorganic carbon, nitrogen and phosphorus content. Overlying water and pore water samples were analysed for ammonium, nitrite, nitrate, phosphate, silicate, dissolved organic nitrogen, dissolved organic phosphorus and chlorophyll a. Results from the period studied showed that: (1) the benthic export of dissolved N, P and Si was 2–3 times higher at AR; (2) the particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP) in suspended/settled particles were about 1.5 times higher at AR; (3) at both AR and NRA, the benthic export of dissolved N, P and Si, during a calm weather period, was 2–4 times higher than during or immediately after a storm event; and (4) at both sites, particulate organic compounds (POC, PON and POP) increased about 20 times during a storm event. These findings suggest that both the nutrients transport from sediment to water column and the quantity/quality of suspended/settled particles were highly dependent on the existence of reef structures and on the hydrodynamic regime.  相似文献   

19.
The phase partitioning of 234Th between dissolved (<10-kiloDalton, kD), colloidal (10 kD—0.4 μm), and particulate (⩾0.5 μm) matter across a horizontal transect, from a coastal station to the deep Canada Basin, and a vertical profile in the deep Canada Basin of the western Arctic Ocean was investigated. Concentrations of suspended particulate matter (SPM), dissolved, colloidal and particulate organic carbon, particulate organic nitrogen and nutrients (silicate, phosphate and nitrate) were also measured to assess transport and scavenging processes.Total 234Th (colloidal+particulate+dissolved) indicated deficiencies relative to secular equilibrium with its parent, 238U in the upper 100 m, which suggests active scavenging of 234Th onto particle surfaces. In contrast, at depths >200 m, general equilibrium existed between total 234Th and 238U. The inventory of SPM and the specific activity of particulate 234Th in the Canada Basin was about an order of magnitude higher than the profile reported for the Alpha Ridge ice camp station. This higher concentration of SPM in the southwestern Canada Basin is likely derived from ice-rafted sedimentary particles. Inventories of nutrients, and dissolved organic carbon and nitrogen in the upper 100 m of the Canada Basin are comparable to the other estimates for the central Arctic Ocean. Comparison of the mass concentrations of colloidal and filter-retained particulate matter as well as the activity of 234Th in these phases indicates that only a very small component of the colloidal material is actively involved in Th scavenging. Lower values of the conditional partition coefficient between the colloidal and dissolved phase indicate that the Arctic colloids are less reactive than colloidal material from other regions. The conditional partition coefficient between the filter-retained and dissolved phases (Kf) is generally higher than that for other regions, which is attributed to the higher complexation capacity of glacio-marine sedimentary particles in these waters. The 234Th-derived export of POC for the shelf and deep Canada Basin ranges between 5.6 and 6.5 mmol m−2 d−1, and is in agreement with other estimates reported for the central Arctic Ocean and Beaufort Sea.  相似文献   

20.
1Introduction CarboncyclingintheArcticOceanplaysanim- portantroletoglobalchange.Traditionally,marine productivityintheArcticOceanisthoughttobevery low,andthussomebiogeochemicalprocessessuchas particleexportandcyclingofnutrientsarenotsoac- tivebecauseofthembeingcoveredperenniallybyice, lowtemperatureandshorttimeofphotosynthesis (PlattandRao,1975).Afewpreviousestimatesof particulateorganiccarbon(POC)exportindicateda neglectablemagnitudeinthecentralArcticOcean (Baconetal.,1989).However,recen…  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号