Laboratory study of nitrogen and phosphorus remineralization during the decomposition of coastal plankton and seston   总被引：1，自引：0，他引：1  

Jonathan H. Garber 《Estuarine, Coastal and Shelf Science》1984,18(6):685-702

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   

Nitrogen dynamics within a wind-driven eddy     

Claire Mahaffey  Claudia R. Benitez-Nelson  Robert R. Bidigare  Yoshimi Rii  David M. Karl   《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1398

Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO₃⁻), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions (δ¹⁵N-NO₃⁻, δ¹³C-PC and δ¹⁵N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal, a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO₃⁻ concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m⁻²) compared to the surrounding water column (17.8±7.8 mmol N m⁻²). Using N-isotope derived estimates of NO₃⁻ assimilation, we estimated that 213±59 mmol m⁻² of NO₃⁻ was initially injected into the upper 110 m Cyclone Opal formation, implying that NO₃⁻ was assimilated at a rate of 3.75±0.5 mmol N m⁻² d⁻¹. This injected NO₃⁻ supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO₃⁻ remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO₃⁻ assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m⁻²) to the time of sampling (4.0±0.09 mmol N m⁻²), implying that DON accumulated at rate of 0.83±1.3 mmol N m⁻² d⁻¹, and accounted for 22±15% of the injected NO₃⁻. Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO₃⁻ was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO₃⁻ remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO₃⁻ along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ¹⁵N-PN, implying a rapid change in the N source. A change in NO₃⁻ assimilation, or a shift from NO₃⁻ fueled growth to assimilation of a ¹⁵N-deplete N source, may be responsible for such observations.  相似文献   

The behaviour of dissolved Cd, Co, Zn, and Pb in North Atlantic near-surface waters (30°N/60°W–60°N/2°W)     

Klaus Kremling  Peter Streu 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12):28

In September 1993 (M26) and June/July 1996 (M36), a total of 239 surface samples (7 m depth) were collected on two transects across the open Atlantic Ocean (224 samples) and northwest European shelf edge area. We present an overview of the horizontal variability of dissolved Cd, Co, Zn, and Pb in between the northwest and northeast Atlantic Ocean in relation to salinity and the nutrients. Our data show a preferential incorporation of Cd relative to P in the particulate material of the surface ocean when related to previously published parallel measurements on suspended particulate matter from the same cruise. There is a good agreement with results recently estimated from a model by Elderfield and Rickaby (Nature 405 (2000) 305), who predict for the North Atlantic Ocean a best fit for α_Cd/P=[Cd/P]_POM/[Cd/P]_SW of 2.5, whereas the approach of our transect shows a α_Cd/P value of 2.6. The Co concentrations of our transects varied from <5 to 131 pmol kg⁻¹, with the lowest values in the subtropical gyre. There were pronounced elevations in the low-salinity ranges of the northwest Atlantic and towards the European shelf. The Co data are decoupled from the Mn distribution and support the hypothesis of marginal inputs as the dominant source. Zinc varied from a minimum of <0.07 nmol kg⁻¹ to a maximum of 1.2 and 4.8 nmol kg⁻¹ in regions influenced by Labrador shelf or European coastal waters, respectively. In subtropical and northeast Atlantic waters, the average Zn concentration was 0.16 nmol kg⁻¹. Zinc concentrations at nearly three quarters of the stations between 40°N and 60°N were <0.1 nmol kg⁻¹. This suggests that biological factors control Zn concentrations in large areas of the North Atlantic surface waters. The Pb data indicated that significant differences in concentration between the northwest and northeast Atlantic surface waters presently (1996) do not exist for this metal. The transects in 1993 and 1996 exhibited Pb concentrations in the northeast Atlantic surface waters of 30 to 40 pmol kg⁻¹, about a fifth to a quarter of the concentrations observed in 1981. This decline is supported by our particle flux measurements in deep waters of the same region.  相似文献   

N₂O Production, Nitrification and Denitrification in an Estuarine Sediment   总被引：1，自引：0，他引：1  

T. Usui  I. Koike  N. Ogura 《Estuarine, Coastal and Shelf Science》2001,52(6):769

The mechanisms regulating N₂O production in an estuarine sediment (Tama Estuary, Japan) were studied by comparing the change in N₂O production with those in nitrification and denitrification using an experimental continuous-flow sediment–water system with¹⁵N tracer (¹⁵N-NO−3 addition). From Feburary to May, both nitrification and denitrification in the sediment increased (246 to 716 μmol N m⁻² h⁻¹and 214 to 1260 μmol N m⁻² h⁻¹, respectively), while benthic N₂O evolution decreased slightly (1560 to 1250 nmol N m⁻² h⁻¹). Apparent diffusion coefficients of inorganic nitrogen compounds and O₂at the sediment–water interface, calculated from the respective concentration gradients and benthic fluxes, were close to the molecular diffusion coefficients (0·68–2·0 times) in February. However, they increased to 8·8–52 times in May except for that of NO−2, suggesting that the enhanced NO−3 and O₂supply from the overlying water by benthic irrigation likely stimulated nitrification and denitrification. Since the progress of anoxic condition by the rise of temperature from February to May (9 to 16 °C) presumably accelerated N₂O production through nitrification, the observed decrease in sedimentary N₂O production seems to be attributed to the decrease in N₂O production/occurrence of its consumption by denitrification. In addition to the activities of both nitrification and denitrification, the change in N₂O metabolism during denitrification by the balance between total demand of the electron acceptor and supply of NO−3+NO−2 can be an important factor regulating N₂O production in nearshore sediments.  相似文献   

Seasonality and interannual variability of freshwater inflow to a large oligohaline estuary in the Northern Gulf of Mexico     

Y. Jun Xu  Kangsheng Wu 《Estuarine, Coastal and Shelf Science》2006,68(3-4):619

Quantity, timing, duration, and fluctuation of freshwater inflow are important factors affecting the development and health of aquatic and adjacent wetland ecosystems in coastal estuaries. This study assessed six decades of freshwater inflow from the Amite River, Tickfaw River, and Tangipahoa River watersheds to Lake Pontchartrain, a large oligohaline estuary in the Northern Gulf of Mexico, whose flood waters caused recent damage to the city of New Orleans in the aftermath of Hurricane Katrina. By utilizing the long-term (1940–2002) river discharge and climatic data from the three major tributary watersheds, monthly and annual freshwater inflows have been quantified and their spatial and temporal variations have been analyzed. On average, the three rivers discharged (±standard error) 0.27 ± 0.04 km³ freshwater monthly and 3.29 ± 0.15 km³ freshwater annually into the lake estuarine system, with the highest inflow from the Amite River (0.16 ± 0.03 m³ mon⁻¹, and 1.91 ± 0.09 km³ yr⁻¹) and the lowest inflow from the Tickfaw River (0.03 ± 0.00 km³ mon⁻¹, and 0.34 ± 0.02 km³ yr⁻¹). A distinct seasonality was evident with over 69% of the total annual inflow occurring during December and May (wet months) and with a low flow period from August to November (dry months). The monthly inflow during the wet months was positively correlated with the monthly precipitation (r² = 0.64), while the monthly inflow during the dry months was subject to evapotranspiration. Furthermore, the study found a 20-year low flow period from 1954–1973 (2.76 ± 0.24 km³ yr⁻¹) and a 24-year high flow period from 1975–1998 (3.84 ± 0.24 km³ yr⁻¹), coinciding with both the climate variation and population growth in the watersheds.  相似文献   

The influence of a mature cyclonic eddy on particle export in the lee of Hawaii     

Kanchan Maiti  Claudia R. Benitez-Nelson  Yoshimi Rii  Robert Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1445

Mesoscale eddies may enhance primary production (PP) in the open ocean by bringing nutrient-rich deep waters into the euphotic zone, potentially leading to increased transport of particles to depth. This hypothesis remains controversial, however, due to a paucity of direct particle export measurements. In this study, we investigated particle dynamics using ²³⁴Th–²³⁸U disequilibria within a mesoscale cold-core eddy, Cyclone Opal, which formed in the lee of the Hawaiian Islands. ²³⁴Th samples were collected along two transects across Cyclone Opal as well as during a time-series within the eddy core during a decaying diatom bloom. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO₂) fluxes at 150 m varied spatially and temporally within the eddy and strongly depended on the ²³⁴Th model formulation used (e.g., steady state versus non-steady state, inclusion of upwelling, etc.). Particle fluxes estimated from a steady state model assuming an upwelling rate of 2 m day⁻¹ yielded the best fit to sediment-trap data. These ²³⁴Th-derived particle fluxes ranged from 332±14 to 1719±53 μmol C m⁻² day⁻¹, 27±3 to 114±12 μmol N m⁻² day⁻¹, and 33±20 to 309±73 μmol Si m⁻² day⁻¹. Although PP rates within Cyclone Opal were elevated by a factor of 2–3, PC and PN fluxes were the same, within error, inside and outside of Cyclone Opal. The ratio of PC export to PP remained surprisingly low at <0.03 and similar to those measured in surrounding waters. In contrast, bSiO₂ fluxes within the eddy core were three times higher. Detailed analyses of ²³⁴Th depth profiles consistently showed excess ²³⁴Th at 100–175 m, associated with the remineralization and possible accumulation of suspended and dissolved organic matter from the surface. We suggest that strong microzooplankton grazing facilitated particulate organic matter recycling and resulted in the export of empty diatom frustules. Thus, while eddies may increase PP, they do not necessarily increase PC and PN export to deep waters. This may be a general characteristic of wind-driven cyclonic eddies of the North Pacific Subtropical Gyre and suggests that eddies may preferentially act as a silica pump, thereby playing an important role in promoting silicic-acid limitation in the region.  相似文献   

Effects of irradiance on benthic and water column processes in a Gulf of Mexico estuary: Pensacola Bay, Florida, USA   总被引：1，自引：0，他引：1  

Michael C. Murrell  Jed G. Campbell  James D. Hagy III  Jane M. Caffrey 《Estuarine, Coastal and Shelf Science》2009,81(4):501-512

We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH₄⁺, NO₃⁻, PO₄³⁻) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O₂ m⁻² d⁻¹, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O₂ m⁻² d⁻¹ (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O₂ m⁻² d⁻¹, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O₂ m⁻² d⁻¹, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m⁻² d⁻¹ for NH₄⁺, 0.58 ± 1.08 mmol m⁻² d⁻¹ for NO₃⁻, 0.01 ± 0.09 mmol m⁻² d⁻¹ for PO₄³⁻. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems.  相似文献   

Elemental mercury concentrations and formation rates in the Scheldt estuary and the North Sea     

W. Baeyens  M. Leermakers 《Marine Chemistry》1998,60(3-4)

Concentrations of Hg⁰ in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg⁰ concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol·l⁻¹ in the winter and from 0.24 to 0.65 pmol·l⁻¹ in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg⁰ concentrations range from 0.06 to 0.8 pmol·l⁻¹ and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg⁰ were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol·m⁻²·d⁻¹ in winter and 500–701 pmol·m⁻²·d⁻¹ in summer and for the North Sea the fluxes range from 59–1110 pmol·m⁻²·d⁻¹ for an average windspeed of 8.1 m·s⁻¹. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg⁰ formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d⁻¹.  相似文献   

The influence of dissolved petroleum hydrocarbon residues on natural phytoplankton biomass     

M. S. Shailaja 《Marine environmental research》1988,25(4)

The effect of dissolved petroleum hydrocarbons in the environment on phytoplankton biomass measured as chlorophyll a was studied near the oil tanker route in the southern Bay of Bengal. In the transect from 5° N, 77° E to 5° N, 87° E the concentrations of dissolved petroleum hydrocarbons were negatively correlated with phytoplankton biomass, whereas in the 0° N, 87° E to 1° N, 79° E transect they were positively correlated with phytoplankton biomass. The mean petroleum hydrocarbon concentrations in the two transects were 12·12 ± 4·67 μg litre⁻¹ and 11·23 ± 4·5 μg litre⁻¹, respectively.It is surmised that the effect of dissolved petroleum hydrocarbons on phytoplankton biomass varies depending on the nature rather than the quantity of petroleum hydrocarbons present. Culture studies with unialgal Nitzschia sp. in seawater collected from selected stations in the study area as well as in artificial seawater spiked with the water-soluble petroleum hydrocarbon fraction of light Arabian Crude support this.  相似文献   

Ammonia Nitrogen at the Water–Sediment Interface in Puck Bay (Baltic Sea)     

Jerzy Bola ek  Bo ena Graca 《Estuarine, Coastal and Shelf Science》1996,43(6):767-779

The magnitude of the exchange flux at the water–sediment interface was determined on the basis of the ammonia concentration gradient at the near-bottom water–interstitial interface and Fick's first law. It was established that in Puck Bay, ammonia almost always passes from the sediment to water. Ammonia flux varied from 5 to 1434 μmol NH₄-N m⁻² day⁻¹. In total,c. 138·2 tonneammonia year⁻¹pass from sediments of Internal Puck Bay to near-bottom water, the equivalent value for External Puck Bay being 686·9 tonne year⁻¹. In total, about 825 tonne ammonia year⁻¹passes from the sediment to near-bottom water of Puck Bay. In interstitial waters, ammonia occurred in concentrations varying over a wide range (3–1084 μmol NH₄-N dm⁻³).The basic factors affecting the magnitude of ammonia concentration in interstitial waters included: oxidation of organic matter, type of sediment, and inflow of fresh underground waters to the region examined.This paper involves preliminary studies only and constitutes a continuation of the studies on ionic macrocomponents and phosphorus in interstitial waters of Puck Bay undertaken previously.  相似文献   

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon     

K.R. Muraleedharan  P. Jasmine  C.T. Achuthankutty  C. Revichandran  P.K. Dinesh Kumar  P. Anand  G. Rejomon 《Progress in Oceanography》2007,72(4):364-383

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m⁻³), low surface primary production (2.55 mg C m⁻³ day⁻¹) and low zooplankton biovolume (0.14 ml m⁻³). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO₃–N > 8.2 μM, PO₄–P > 0.8 μM, SiO₄–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m⁻³, PP – 9.23 mg C m⁻³ day⁻¹), and mesozooplankton biovolume (1.12 ml m⁻³) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.  相似文献   

Annual Primary Production in Narragansett Bay with no Bay-Wide Winter–Spring Phytoplankton Bloom     

C. Oviatt  A. Keller  L. Reed 《Estuarine, Coastal and Shelf Science》2002,54(6):1013

Primary production was estimated over the annual cycle from ¹⁴C incubations conducted in 5 m deep enclosures and modeled for 16 stations in Narragansett Bay with data from biweekly surveys in which light, chlorophyll, attenuation coefficients and other parameters were measured. Annual values ranged from 160 g C m⁻² y⁻¹ in the lower West Passage to 619 g C m⁻² y⁻¹ at the mouth of the Providence River. The annual bay-wide, area mean fell near the middle of this range at 323 g C m⁻² y⁻¹ and was not apparently different from previous surveys. In the 1998 warm, El Niño winter, no bay-wide winter–spring phytoplankton flowered. Bloom limitation was correlated with warm temperatures which may have stimulated grazing rates. The lack of a bloom did not change annual levels of primary production but this alteration in carbon flow may impact macrofauna in the benthic infauna community.  相似文献   

Particle export within cyclonic Hawaiian lee eddies derived from Pb–Po disequilibrium     

E. Verdeny  P. Masqu  K. Maiti  J. Garcia-Orellana  J.M. Bruach  C. Mahaffey  C.R. Benitez-Nelson 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1461

Particle export from the upper waters of the oligotrophic ocean may play a crucial role in the global carbon cycle. Mesoscale eddies have been hypothesized to inject new nutrients into oligotrophic surface waters, thereby increasing new production and particle export in otherwise nutrient deficient regimes. The E-Flux Program was a large multidisciplinary project designed to investigate the physical, biological and biogeochemical characteristics of cold-core cyclonic eddies that form in the lee of the Hawaiian Islands. There, we investigated particle dynamics using ²¹⁰Pb–²¹⁰Po disequilibrium. Seawater samples for ²¹⁰Pb and ²¹⁰Po were collected both within (IN) and outside (OUT) of two cyclones, Noah and Opal, at different stages of their evolution as well as from the eddy generation region. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO₂) export fluxes were determined using water-column PC, PN, and bSiO₂ inventories and the residence times of ²¹⁰Po. PC and PN fluxes at 150 m ranged from 1.58±0.10 to 1.71±0.16 mmol C m⁻² d⁻¹ and 0.22±0.02 to 0.30±0.02 mmol N m⁻² d⁻¹ within Cyclones Opal and Noah. PC and PN fluxes at OUT stations sampled during both cruises were of similar magnitudes, 1.69±0.16 to 1.67±0.16 mmol C m⁻² d⁻¹ and 0.30±0.03 to 0.26±0.03 mmol N m⁻² d⁻¹. The bSiO₂ fluxes within Cyclone Opal were 0.157±0.010 mmol Si m⁻² d⁻¹ versus 0.025±0.002 mmol Si m⁻² d⁻¹ at OUT stations. These results of minimal PC and PN export, but significant eddy-induced bSiO₂ fluxes, agree very well with other studies that used a variety of direct and indirect methods. Thus, our results suggest that using elemental inventories and residence times of ²¹⁰Po is another independent and robust method for determining particle export and should be investigated more fully.  相似文献   

The impact of groundwater discharges on mercury partitioning, speciation and bioavailability to mussels in a coastal zone     

F.J.G. Laurier  D. Cossa  C. Beucher  E. Brvire 《Marine Chemistry》2007,104(3-4):143-155

The Mussel Watch program conducted along the French coasts for the last 20 years indicates that the highest mercury concentrations in the soft tissue of the blue mussel (Mytilus edulis) occur in animals from the eastern part of Seine Bay on the south coast of the English Channel, the “Pays de Caux”. This region is characterized by the presence of intertidal and submarine groundwater discharges, and no particular mercury effluent has been reported in its vicinity. Two groundwater emergence systems in the karstic coastal zone of the Pays de Caux (Etretat and Yport with slow and fast water percolation pathways respectively) were seasonally sampled to study mercury distribution, partitioning and speciation in water. Samples were also collected in the freshwater–seawater mixing zones in order to compare mercury concentrations and speciation between these “subterranean” or “groundwater” estuaries and the adjacent macrotidal Seine estuary, characterized by a high turbidity zone (HTZ). The mercury concentrations in the soft tissue of mussels from the same areas were monitored at the same time.The means of the “dissolved” (< 0.45 μm) mercury concentrations (HgT_D) in the groundwater springs were 0.99 ± 0.15 ng l^− 1 (n = 18) and 0.44 ± 0.17 ng l^− 1 (n = 17) at Etretat and Yport respectively. High HgT_D concentrations were associated with strong runoff over short water pathways during storm periods, while low concentrations were associated with long groundwater pathways. Mean particulate mercury concentrations were 0.22 ± 0.05 ng mg^− 1 (n = 16) and 0.16 ± 0.10 ng mg^− 1 (n = 17) at Etretat and Yport respectively, and decreased with increasing particle concentration probably as a result of dilution by particles from soil erosion. Groundwater mercury speciation was characterized by high reactive-to-total mercury ratios in the dissolved phase (HgR_D/HgT_D: 44–95%), and very low total monomethylmercury concentrations (MMHg < 8 pg l^− 1). The HgT_D distributions in the Yport and Etretat mixing zones were similar (overall mean concentration of 0.73 ± 0.21 ng l^− 1, n = 43), but higher than those measured in the adjacent industrialized Seine estuary (mean: 0.31 ± 0.11 ng l^− 1, n = 67). In the coastal waters along the Pays de Caux dissolved monomethylmercury (MMHg_D) concentrations varied from 9.5 to 13.5 pg l^− 1 (2 to 8% of the HgT_D). Comparable levels were measured in the Seine estuary (range: 12.2– 21.1 pg l⁻¹; 6–12% of the HgT_D). These groundwater karstic estuaries seem to be mostly characterized by the higher HgT_D and HgR_D concentrations than in the adjacent HTZ Seine estuary. While the HTZ of the Seine estuary acts as a dissolved mercury removal system, the low turbid mixing zone of the Pays de Caux receives the dissolved mercury inputs from the groundwater seepage with an apparent Hg transfer from the particulate phase to the “dissolved” phase (< 0.45 μm). In parallel, the soft tissue of mussels collected near the groundwater discharges, at Etretat and Yport, exhibited significantly higher values than those found in the mussel from the mouth of the Seine estuary. We observe that this difference mimics the differences found in the mercury distribution in the water, and argue that the dissolved phase of the groundwater estuaries and coastal particles are significant sources of bioavailable mercury for mussels.  相似文献   

Plankton dynamics and carbon flux in an area of upwelling off the coast of Morocco     

E. J. H. Head  W. G. Harrison  B. I. Irwin  E. P. W. Horne  W. K. W. Li 《Deep Sea Research Part I: Oceanographic Research Papers》1996,43(11-12)

A carbon flux study was carried out off the coast of Morocco, at 31°N, in a region characterized by the presence of a persistent cyclonic eddy. Two short-term (4 and 3 day) deployments of free-floating sediment traps were combined with water column sampling and rate process measurements as the ship followed the traps. For a period of 36 h between trap deployments, a hydrographic section was run along 31°30'N as part of a larger scale survey being carried out simultaneously on the R.V. A. von Humboldt. The first trap deployment was near the eastern margin of the eddy and the traps moved to the north and west in a frontal jet associated with its northern boundary. After the second deployment, which was at the recovery point of the first, the traps moved to the west and then to the southwest. Throughout the study, chlorophyll concentrations varied between 27 and 125 mg m⁻² (0–100 m), with highest concentrations in the upwelled water nearest the coast and in upwelled water generated within the cyclonic eddy. Particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations were relatively uniform (13.6±1.8 and 1.63±28 g m⁻² with phytoplankton carbon accounting for 16–85% of total POC. Bacterial carbon was 5% of total POC and mesozooplankton carbon concentrations were equivalent to 9% of total POC. Microzooplankton biomass was not assessed but POC:PON ratios in the water column were often high, suggesting there was sometimes a large detrital component in the POC. Primary production rates varied between 1.0 and 2.5 g C m⁻² day⁻¹. Bacterial consumption accounted for 50% of primary production. Metabolic rates suggested that copepods were ingesting more than 0.4 g C m⁻² day⁻¹. while filtration rates suggested that ingestion of phytoplankton carbon was only 0.2 g C m⁻²day⁻¹, even when phytoplankton constituted 85% of the POC. f-ratios (based on uptake rates for ¹⁵N-nitrate and ammonia) were between 0.1 and 0.4, and excretion by mesozooplankton could account for 40% of the daily ammonium uptake by phytoplankton. HPLC pigment analysis showed that when chlorophyll biomass was high, diatoms were dominant, whereas when it was low, small prymnesiophytes, chlorophytes and diatoms were all important. The composition of the fluoresecent pigments in material in the sediment traps indicated that intact phytoplankton and copepod faecal pellets were the main sources but the relative rates of sedimentation of pigment, POC and PON for the two trapping periods did not reflect differences that were observed in the overlying water column. This was likely to be the result of spatial heterogeneity and strong horizontal currents heterogeneity and strong horizontal currents within the euphotic zone. Thus, material collected at 100 m probably did not originate in the water column immediately overlying the traps and trapping efficiencies might also have been variable.  相似文献   

Scleractinian coral population size structures and growth rates indicate coral resilience on the fringing reefs of North Jamaica   总被引：1，自引：1，他引：0  

M.J.C. Crabbe   《Marine environmental research》2009,67(4-5):189-198

Coral reefs throughout the world are under severe challenges from many environmental factors. This paper quantifies the size structure of populations and the growth rates of corals from 2000 to 2008 to test whether the Discovery Bay coral colonies showed resilience in the face of multiple acute stressors of hurricanes and bleaching. There was a reduction in numbers of colonies in the smallest size class for all the species at all the sites in 2006, after the mass bleaching of 2005, with subsequent increases for all species at all sites in 2007 and 2008. Radial growth rates (mm yr⁻¹) of non-branching corals and linear extension rates (mm yr⁻¹) of branching corals calculated on an annual basis from 2000–2008 showed few significant differences either spatially or temporally. At Dairy Bull reef, live coral cover increased from 13 ± 5% in 2006 to 20 ± 9% in 2007 and 31 ± 7% in 2008, while live Acropora species increased from 2 ± 2% in 2006 to 10 ± 4% in 2007 and 22 ± 7% in 2008. These studies indicate good levels of coral resilience on the fringing reefs around Discovery Bay in Jamaica.  相似文献   

Mercury levels in the dissolved and particulate fractions of the Tyrrhenian sea     

Romano Ferrara  Alfredo Seritti  Corrado Barghigiani  Antonio Petrosino 《Marine Chemistry》1986,18(2-4)

Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l⁻¹ for ·total dissolved mercury’, 0.5–5.9 ng l⁻¹ for ·reactive dissolved mercury’ and 0.3–8.0 ng l⁻¹ for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.  相似文献   

Flux of Reduced Sulfur Gases Along a Salinity Gradient in Louisiana Coastal Marshes   总被引：3，自引：0，他引：3  

R. D. Delaune  I. Devai  C. W. Lindau 《Estuarine, Coastal and Shelf Science》2002,54(6):1003

Seasonal and diurnal reduced sulfur gas emissions were measured along a salinity gradient in Louisiana Gulf Coast salt, brackish and freshwater marshes. Reduced sulfur gas emission was strongly associated with habitat and salinity gradient. The dominant emission component was dimethyl sulfide (average: 57·3 μg S m⁻² h⁻¹) in saltmarsh with considerable seasonal (max: 144·03 μg S m⁻² h⁻¹; min: 1·47 μg S m⁻² h⁻¹) and diurnal (max: 83·58 μg S m⁻² h⁻¹; min: 69·59 μg S m⁻² h⁻¹) changes in flux rates. Hydrogen sulfide was dominant (average: 21·2 μg S m⁻² h⁻¹, max: 79·2 μg S m⁻² h⁻¹; min: 5·29 μg S m⁻² h⁻¹) form in brackishmarsh and carbonyl sulfide (average: 1·09 μg S m⁻² h⁻¹; max: 3·42 μg S m⁻² h⁻¹; min: 0·32 μg S m⁻² h⁻¹) was dominant form in freshwater marsh. A greater amount of H₂S was evolved from brackishmarsh (21·22 μg S m⁻² h⁻¹) as compared to the saltmarsh (2·46 μg S m⁻² h⁻¹) and freshwater marsh (0·30 μg S m⁻² h⁻¹). Emission of total reduced sulfur gases decreased with decrease in salinity and distance inland from the coast. Emission of total reduced sulfur gases over the study averaged 73·3 μg S m⁻² h⁻¹ for the saltmarsh, 32·1 μg S m⁻² h⁻¹ for brackishmarsh and 2·76 μg S m⁻² h⁻¹ for the freshwater marsh.  相似文献   

Comparison of β-dimethylsulfoniopropionate (DMSP) levels in two mediterranean ecosystems with different trophic levels     

Natacha Jean  Grard Boge  Jean-Louis Jamet  Dominique Jamet 《Marine Chemistry》2006,101(3-4):190-202

β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO₃⁻]_max. = 30.3 μM; [PO₄³⁻]_max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a]_mean = 2.4 μg/L) compared to Niel Bay ([NO₃⁻]_max. = 19.7 μM; [PO₄³⁻]_max. = 0.17 μM; [chl a]_mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSP_d < 0.2 μm) and particulate DMSP (DMSP_p > 0.2 μm) concentrations. The DMSP_p was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSP_d concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSP_p concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSP_p concentrations were much lower (6–9 nM in March–April), whereas DMSP_d concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSP_p. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSP_p to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSP_p to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.  相似文献   

Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland     

Sren Rysgaard  Torkel Gissel Nielsen 《Progress in Oceanography》2006,71(2-4):426

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m⁻²) is similar to phytoplankton production (6–10 g C m⁻²). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m⁻² yr⁻¹. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m⁻² yr⁻¹ is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m⁻² yr⁻¹ of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m⁻² yr⁻¹ was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.  相似文献