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1.
Grid convergence in space and time of variable-density flow in fractured-porous rock is systematically assessed. Convergence of the flow simulation is attained using both uniform and adaptive time-stepping. This contrasts to variable-density flow in unfractured porous media where grid convergence variable-density flow problems is almost never achieved. At high discretization levels, the number of fingers in fractured-porous rock is no longer influenced by spatial-temporal grid discretization, which is not the case in unfractured porous media. However, similar to unfractured porous media, the number of fingers in fractured-porous media varies at low discretization levels. Simulated convective pattern and penetration depth of the dense plume in fractured rock depend more on spatial discretization than on temporal discretization. The appropriate spatial-temporal grid is then used to examine some aspects of mixed convection in fractured-porous rock, characterized by the mixed convection number M. The critical mixed convection number Mc = 46 represents the transition between forced and free convection in fractured porous media, which is much higher than Mc = 1 in unfractured porous media. Thus, for mixed convective flow problems, the value of Mc is not a sufficient indicator to predict the convective mode (free convection-forced convection), and the presence of vertical fractures must be included in the prediction of convective flow modes. 相似文献
2.
Numerical simulations of variable-density flow and solute transport have been conducted to investigate dense plume migration for various configurations of 2D fracture networks. For orthogonal fractures, simulations demonstrate that dispersive mixing in fractures with small aperture does not stabilize vertical plume migration in fractures with large aperture. Simulations in non-orthogonal 2D fracture networks indicate that convection cells form and that they overlap both the porous matrix and fractures. Thus, transport rates in convection cells depend on matrix and fracture flow properties. A series of simulations in statistically equivalent networks of fractures with irregular orientation show that the migration of a dense plume is highly sensitive to the geometry of the network. If fractures in a random network are connected equidistantly to the solute source, few equidistantly distributed fractures favor density-driven transport. On the other hand, numerous fractures have a stabilizing effect, especially if diffusive transport rates are high. A sensitivity analysis for a network with few equidistantly distributed fractures shows that low fracture aperture, low matrix permeability and high matrix porosity impede density-driven transport because these parameters reduce groundwater flow velocities in both the matrix and the fractures. Enhanced molecular diffusion slows down density-driven transport because it favors solute diffusion from the fractures into the low-permeability porous matrix where groundwater velocities are smaller. For the configurations tested, variable-density flow and solute transport are most sensitive to the permeability and porosity of the matrix, which are properties that can be determined more accurately than the geometry and hydraulic properties of the fracture network, which have a smaller impact on density-driven transport. 相似文献
3.
Non-Darcy mixed convective flow of water due to external pressure gradient and buoyancy opposed forces are considered in a vertical channel filled with porous medium, which can be either isotropic or anisotropic. The linear theory of stability analysis has been used to numerically investigate the dependence of the transition behavior of the fully developed basic flow on the permeability of the medium. Numerical experiments indicate that mainly two main instability modes appear: Rayleigh–Taylor (R–T) and buoyant instability. For Darcy numbers (Da) ?10−9, R–T instability dominates within the entire Reynolds number (Re) range considered here. It was also found that for the same Re, the fully developed base flow is highly unstable (stable) for porous media with high (low) permeability. Further, it was seen that the disturbance isotherm cells migrate from the channel walls toward the centerline when permeability is reduced. Reducing the permeability by one order of magnitude (corresponding to a decrease of Darcy number from 10−6 to 10−7) increases base flow stability approximately 20-fold. For higher Reynolds numbers, buoyant, mixed and shear instability of the basic flow were found when Da was increased from 10−7 to 10−3. However, for cases in which permeability and porosity behaved as suggested by Carman–Kozeny relation (CKR), buoyant stability was the only mode of instability. Critical values of the Rayleigh (Ra) and Darcy (Da) numbers in the R–T mode of instability were related to each other by the hyperbolic function RaDa = −2.465. 相似文献
4.
Observations of non-Fickian transport in sandbox experiments [Levy M, Berkowitz B. Measurement and analysis of non-Fickian dispersion in heterogeneous porous media. J Contam Hydrol 2003;64:203–26] were analyzed previously using a power law tail ψ(t) ∼ t−1−β with 0 < β < 2 for the spectrum of transition times comprising a tracer plume migration. For each sandbox medium a choice of β resulted in an excellent fit to the breakthrough curve (BTC) data, and the value of β decreased slowly with increasing flow velocity. Here, the data are reanalyzed with the full spectrum of ψ(t) gleaned from analytical calculations [Cortis A, Chen Y, Scher H, Berkowitz B. Quantitative characterization of pore-scale disorder effects on transport in “homogeneous” granular media. Phys Rev E 2004;10(70):041108. doi: 10.1103/PhysRevE.70.041108], numerical simulations [Bijeljic B, Blunt MJ. Pore-scale modeling and continuous time random walk analysis of dispersion in porous media. Water Resour Res 2006;42:W01202. doi: 10.1029/2005WR004578] and permeability fields [Di Donato G, Obi E-O, Blunt MJ. Anomalous transport in heterogeneous media demonstrated by streamline-based simulation. Geophys Res Lett 2003;30:1608–12s. doi: 10.1029/2003GL017196]. We represent the main features of the full spectrum of transition times with a truncated power law (TPL), ψ(t) ∼ (t1 + t)−1−βexp(−t/t2), where t1 and t2 are the limits of the power law spectrum. An excellent fit to the entire BTC data set, including the changes in flow velocity, for each sandbox medium is obtained with a single set of values of t1, β, t2. The influence of the cutoff time t2 is apparent even in the regime t < t2. Significantly, we demonstrate that the previous apparent velocity dependence of β is a result of choosing a pure power law tail for ψ(t). The key is the change in the log–log slope of the TPL form of ψ(t) with a shifting observational time window caused by the change in the mean velocity. Hence, the use of the full spectrum of ψ(t) is not only necessary for the transition to Fickian behavior, but also to account for the dynamics of these laboratory observations of non-Fickian transport. 相似文献
5.
This work concludes the investigations into the stability of haline flows in saturated porous media. In the first part [33] a stability criterion for density-driven flow in a saturated homogeneous medium was derived excluding dispersion. In the second part [34], the effects of dispersion were included. The latter criterion made reasonable predictions of the stability regimes (indicated by the number of fingers present) as a function of density and dispersivity variations. We found out that destabilising variables caused an increase in the number of fingers and vice versa. The investigation is extended here for the effects of the medium heterogeneity. The cell problem derived via homogenization theory [20] is solved and its solution used to evaluate the elements of the macrodispersion tensor as functions of time for flow aligned parallel to gravity. The longitudinal coefficient exhibits asymptotic behaviour for favourable and moderately unfavourable density contrasts while it grows indefinitely for higher density contrasts. The range of densities stabilised by medium heterogeneities can thus be estimated from the behaviour of the coefficient. The d3f software program is used for the numerical simulations. The code uses the cell-centred finite volume and the implicit Euler techniques for the spatial and temporal discretisations respectively. 相似文献
6.
The metabolic balance between production and respiration in plankton communities of the Gulf of Papua was investigated in May 2004. Water samples taken at 19 stations were allocated to groups on the basis of physico-chemical characteristics. Oxygen consumption and production in flasks incubated in the dark and in the light was determined by micro-Winkler titration. Dark bottle respiration in samples influenced by the estuarine plume averaged 3.09±1.92 (SD) mmol O2 m−3 d−1 and production within surface light bottles averaged 7.63±3.36 (SD) mmol O2 m−3 d−1. Corresponding values in stations more typical of the central Gulf of Papua were 1.68±1.30 (SD) mmol O2 m−3 d−1 and 1.08±2.25 (SD) mmol O2 m−3 d−1. Despite a shallow (<10 m) euphotic zone within the plume stations, phytoplankton production in the surface layers was sufficiently high to subsidise total water column respiration. Integrating production and respiration over the water column resulted in a calculation of net community production (NCP) of 626±504 (SD) mg C m−2 d−1, and community respiration (CR) of 712±492 mg C m−2 d−1 at the plume stations, with an average P:R ratio of 1.97. In the offshore group NCP was 157±450 (SD) mg C m−2 d−1 and CR was 1620±1576 mg C m−2 d−1. The average P:R ratio was 1.27. Three of the 7 stations allocated to the offshore group were net heterotrophic. In contrast to earlier studies in the area indicating that the Gulf of Papua waters is heterotrophic [Robertson, A.I., Dixon, P., Alongi, D.M., 1998. The influence of fluvial discharge on pelagic production in the Gulf of Papua, Northern Coral Sea. Estuarine, Coastal and Shelf Science 46, 319–331], our data indicate that in May 2004 the Gulf was in positive metabolic balance, but by only ∼120 mg C m−2 d−1. We conclude that waters of the Gulf of Papua under riverine influence are net autotrophic, but that within the central Gulf there is a fine metabolic balance alternating between autotrophy and heterotrophy. 相似文献
7.
Christina Schornberg Christian Schmidt Edda Kalbus Jan H. Fleckenstein 《Advances in water resources》2010
Analytical solutions to the one-dimensional heat transport equation for steady-state conditions can provide simple means to quantify groundwater surface water exchange. The errors in exchange flux calculations that are introduced when the underlying assumptions of homogeneous sediments and constant temperature boundary conditions are violated were systematically evaluated in a simulation study. Temperatures in heterogeneous sediments were simulated using a numerical model. Heterogeneity in the sediments was represented by discrete, binary geologic units. High contrasts between the hydraulic conductivities (K) of the geologic units were found to lead to large errors, while the influence of the structural arrangement of the units was smaller. The effects of transient temperature boundary conditions were investigated using an analytical equation. Errors introduced by transient boundary conditions were small for Darcy-velocities > 0.1 m d− 1 in the period near maximum and minimum annual surface water temperatures. For smaller fluxes, however, errors can be large. Assuming steady-state conditions and vertical flow in homogeneous sediments is acceptable at certain times of the year and for medium to high exchange fluxes, but pronounced geologic heterogeneity can lead to large errors. 相似文献
8.
Elastic properties of fluid saturated porous media with aligned fractures can be studied using the model of fractures as linear-slip interfaces in an isotropic porous background. Such a medium represents a particular case of a transversely isotropic (TI) porous medium, and as such can be analyzed with equations of anisotropic poroelasticity. This analysis allows the derivation of explicit analytical expressions for the low-frequency elastic constants and anisotropy parameters of the fractured porous medium saturated with a given fluid. The five elastic constants of the resultant TI medium are derived as a function of the properties of the dry (isotropic) background porous matrix, fracture properties (normal and shear excess compliances), and fluid bulk modulus. For the particular case of penny-shaped cracks, the expression for anisotropy parameter ε has the form similar to that of Thomsen [Geophys. Prospect. 43 (1995) 805]. However, contrary to the existing view, the compliance matrix of a fluid-saturated porous-fractured medium is not equivalent to the compliance matrix of any equivalent solid medium with a single set of parallel fractures. This unexpected result is caused by the wave-induced flow of fluids between pores and fractures. 相似文献
9.
A three-dimensional two-phase flow model is coupled to a non-linear reactive transport model to study the efficacy of potassium permanganate treatment on dense, non-aqueous phase liquid (DNAPL) source removal in porous media. A linear relationship between the soil permeability (k) and concentration of manganese dioxide precipitate ([MnO2(s)]), k = ko + Srind [MnO2(s)], is utilized to simulate nodal permeability reductions due to precipitate formation. Using published experimental column studies, an Srind = −5.5 × 10−16 m2 L/mg was determined for trichloroethylene (TCE) DNAPL. This Srind was then applied to treatment simulations on three-dimensional TCE DNAPL source zones comprising either DNAPL at residual saturations, or DNAPL at pooled saturations. 相似文献
10.
Diffusion in stratified porous media is common in the natural environment. The objective of this study is to develop analytical solutions for describing the diffusion in layered porous media with a position-dependent diffusion coefficient within each layer. The orthogonal expansion technique was used to solve a one-dimensional multi-layer diffusion equation in which the diffusion coefficient is expressed as a segmented linear function of positions in the porous media. The behavior of the solutions is illustrated using several examples of a three-layer system, with constant diffusion coefficient α1 in layer 1 (0 < x < l1), α3 in layer 3(l2 < x < l3), and a linearly position-dependent diffusion coefficient α1(1 + Δ(x − l1)/(l2 − l1)) in the center layer (Δ = α3/α1 − 1). Because of the asymmetry of the layered system, the diffusion and related concentration distributions are also asymmetrical. For a given Δ value, the smaller the value of (l2 − l1)/l3, the more significant the accumulation of concentration in the middle transition zone (l1 < x < l2), the sharper the change in the concentration profile of spatial distribution. Therefore, transition between two layers has significant effects on diffusion. 相似文献
11.
High thresholds for avoidance of sonar by free-ranging long-finned pilot whales (Globicephala melas)
R. Antunes P.H. Kvadsheim F.P.A. Lam P.L. Tyack L. Thomas P.J. Wensveen P.J.O. Miller 《Marine pollution bulletin》2014
The potential effects of exposing marine mammals to military sonar is a current concern. Dose–response relationships are useful for predicting potential environmental impacts of specific operations. To reveal behavioral response thresholds of exposure to sonar, we conducted 18 exposure/control approaches to 6 long-finned pilot whales. Source level and proximity of sonar transmitting one of two frequency bands (1–2 kHz and 6–7 kHz) were increased during exposure sessions. The 2-dimensional movement tracks were analyzed using a changepoint method to identify the avoidance response thresholds which were used to estimate dose–response relationships. No support for an effect of sonar frequency or previous exposures on the probability of response was found. Estimated response thresholds at which 50% of population show avoidance (SPLmax = 170 dB re 1 μPa, SELcum = 173 dB re 1 μPa2 s) were higher than previously found for other cetaceans. The US Navy currently uses a generic dose–response relationship to predict the responses of cetaceans to naval active sonar, which has been found to underestimate behavioural impacts on killer whales and beaked whales. The navy curve appears to match more closely our results with long-finned pilot whales, though it might underestimate the probability of avoidance for pilot-whales at long distances from sonar sources. 相似文献
12.
Phytoplankton growth and microzooplankton grazing in the continental shelf area of northeastern South China Sea after Typhoon Fengshen 总被引：1，自引：0，他引：1
Linbin Zhou Yehui Tan Liangmin HuangJianrong Huang Huaxue LiuXiping Lian 《Continental Shelf Research》2011,31(16):1663-1671
Dilution experiments were used to investigate the phytoplankton growth and microzooplankton grazing in the continental shelf area of northeastern South China Sea during 30 June and 7 July, 2008, occurring about a week after Typhoon Fengshen. We detected negative phytoplankton growth rates (−0.03 to −2.02 d−1) and measured grazing rates of microzooplankton on phytoplankton in size-fractionations of 20-200 μm (1.25±0.44 d−1), 3-20 μm (1.48±0.63 d−1) and <3 μm (1.02±0.42 d−1). Results showed significant correlations between phytoplankton growth and microzooplankton grazing rates, between phytoplankton and ciliate abundance, and between the dominant phytoplankton Thalassionema nitzschioides and the dominant ciliate Helicostomella longa (p<0.05). Phytoplankton decay, due to nutrient-limited conditions occurring with the fading of upwelling and spreading of freshwater plume after Typhoon Fengshen, may account for negative phytoplankton growth rates in this study. Synergism in the specific size-selective grazing of various species, including ciliates and heterotrophic dinoflagellates, may contribute to similar grazing rate on phytoplankton in different size-fractionations, at the integrated level. Interactions between phytoplankton and microzooplankton, including grazing selectivity, top-down and bottom-up control between phytoplankton and microzooplankton may contribute to these findings. Our results indicate that under conditions of negative phytoplankton growth microzooplankton grazing may reduce energy loss from the epipelagic waters by retrieving energy from the decaying phytoplankton community. 相似文献
13.
Minhan Dai Weidong Zhai Wei-Jun Cai Julie Callahan Bangqin Huang Shaoling Shang Tao Huang Xiaolin Li Zhongming Lu Weifang Chen Zhaozhang Chen 《Continental Shelf Research》2008
We observed a phytoplankton bloom downstream of a large estuarine plume induced by heavy precipitation during a cruise conducted in the Pearl River estuary and the northern South China Sea in May–June 2001. The plume delivered a significant amount of nutrients into the estuary and the adjacent coastal region, and enhanced stratification stimulating a phytoplankton bloom in the region near and offshore of Hong Kong. A several fold increase (0.2–1.8 μg Chl L−1) in biomass (Chl a) was observed during the bloom. During the bloom event, the surface water phytoplankton community structure significantly shifted from a pico-phytoplankton dominated community to one dominated by micro-phytoplankton (>20 μm). In addition to increased Chl a, we observed a significant drawdown of pCO2, biological uptake of dissolved inorganic carbon (DIC) and an associated enhancement of dissolved oxygen and pH, demonstrating enhanced photosynthesis during the bloom. During the bloom, we estimated a net DIC drawdown of 100–150 μmol kg−1 and a TAlk increase of 0–50 μmol kg−1. The mean sea–air CO2 flux at the peak of the bloom was estimated to be as high as ∼−18 mmol m−2 d−1. For an average surface water depth of 5 m, a very high apparent biological CO2 consumption rate of 70–110 mmol m−2 d−1 was estimated. This value is 2–6 times higher than the estimated air–sea exchange rate. 相似文献
14.
D.G. Redalje S.E. Lohrenz M.J. Natter M.D. Tuel G.J. Kirkpatrick D.F. Millie G.L. Fahnenstiel F.M. Van Dolah 《Continental Shelf Research》2008
As part of the ECOHAB: Florida Program, we studied three large blooms of the harmful bloom forming dinoflagellate Karenia brevis. These blooms formed on the West Florida Shelf during Fall of 2000 off Panama City, and during Fall 2001 and Fall 2002 off the coastline between Tampa Bay and Charlotte Harbor. We suggest that these blooms represent two different stages of development, with the 2000 and 2001 blooms in an active growth or maintenance phase and the 2002 bloom in the early bloom initiation phase. Each bloom was highly productive with vertically integrated primary production values of 0.47–0.61, 0.39–1.33 and 0.65 g C m−2 d−1 for the 2000, 2001 and 2002 K. brevis blooms, respectively. Carbon specific growth rates were low during each of these blooms with values remaining fairly uniform with depth corresponding to generation times of 3–5 days. Nitrogen assimilation by K. brevis was highest during 2001 with values ranging from 0.15 to 2.14 μmol N L−1 d−1 and lower generally for 2000 and 2002 (0.01–0.64 and 0.66–0.76 μmol N L−1 d−1 for 2000 and 2002, respectively). The highest K. brevis cell densities occurred during the 2001 bloom and ranged from 400 to 800 cells mL−1. Cell densities were lower for each of the 2000 and 2002 blooms relative to those for 2001 with densities ranging from 100 to 500 cells mL−1. The 2000 and 2001 blooms were dominated by K. brevis in terms of its contribution to the total chlorophyll a (chl a) pool with K. brevis accounting generally for >70% of the observed chl a. For those populations that were dominated by K. brevis (e.g. 2000 and 2001), phytoplankton C biomass (Cp,0) constituted <30% of the total particulate organic carbon (POC). However, in 2002 when diatoms and K. brevis each contributed about the same to the total chl a, Cp,0 was >72% of the POC. The fraction of the total chl a that could be attributed to K. brevis was most highly correlated with POC, chl a and salinity. Nitrogen assimilation rate and primary production were highly correlated with a greater correlation coefficient than all other comparisons. 相似文献
15.
Spatial variability in organic material sinking export in the Hudson Bay system,Canada, during fall 总被引：1，自引：0，他引：1
Amandine Lapoussière Christine Michel Michel Gosselin Michel Poulin 《Continental Shelf Research》2009
Spatial variations in the sinking export of organic material were assessed within the Hudson Bay system (i.e., Hudson Bay, Hudson Strait and Foxe Basin) during the second oceanographic expedition of ArcticNet, on board the CCGS Amundsen in early fall 2005. Sinking fluxes of particulate organic material were measured using short-term free-drifting particle interceptor traps deployed at 50, 100 and 150 m for 8–20 h at eight stations. Measurements of chlorophyll a (chl a), pheopigments (pheo), particulate organic carbon (POC), biogenic silica (BioSi), protists, fecal pellets and bacteria were performed on the collected material. In parallel, sea surface salinity and temperature were determined at 121 stations in the Hudson Bay system. Three hydrographic regions presenting different sedimentation patterns were identified based on average surface salinity and temperature. Hudson Strait was characterized by a marine signature, with high salinity (average=32.3) and low temperature (average=2.1 °C). Eastern Hudson Bay was strongly influenced by river runoff and showed the lowest average salinity (26.6) and highest average temperature (7.6 °C) of the three regions. Western Hudson Bay showed intermediate salinity (average=29.4) and temperature (average=4.4 °C). Sinking fluxes of total pigments (chl a+pheo: 3.37 mg m−2 d−1), diatom-associated carbon (19.8 mg m−2 d−1) and BioSi (50.2 mg m−2 d−1) at 50 m were highest in Hudson Strait. Eastern Hudson Bay showed higher sinking fluxes of total pigments (0.52 mg m−2 d−1), diatom-associated carbon (3.29 mg m−2 d−1) and BioSi (36.6 mg m−2 d−1) compared to western Hudson Bay (0.19, 0.05 and 7.76 mg m−2 d−1, respectively). POC sinking fluxes at 50 m were low and relatively uniform throughout the Hudson Bay system (50.0–76.8 mg C m−2 d−1), but spatial variations in the composition of the sinking organic material were observed. A large part (37–78%) of the total sinking POC was unidentifiable by microscopic observation and was qualified as amorphous detritus. Considering only the identifiable material, the major contributors to the POC sinking flux were intact protist cells in Hudson Strait (28%), fecal pellets in eastern Hudson Bay (52%) and bacteria in western Hudson Bay (17%). A significant depth-related attenuation of the POC sinking fluxes (average loss between 50 and 150 m=32%) and a significant increase in the BioSi:POC ratio (average increase between 50 and 150 m=76%) were observed in Hudson Strait and eastern Hudson Bay. For all other sinking fluxes and composition ratios, we found no statistically significant difference with depth. These results show that during fall, the sinking export of total POC from the euphotic zone remained fairly constant throughout the Hudson Bay system, whereas other components of the organic sinking material (e.g., chl a, BioSi, fecal pellets, protist cells) showed strong spatial variations. 相似文献
16.
We investigate the origin of diversity of eruption styles in silicic volcanoes on the basis of a 1-dimensional steady conduit flow model that considers vertical relative motion between gas and liquid (i.e., vertical gas escape). The relationship between the assemblage of steady-state solutions in the conduit flow model and magma properties or geological conditions is expressed by a regime map in the parameter space of the ratio of liquid-wall friction force to liquid–gas interaction force (non-dimensional number ε), and a normalized conduit length Λ. The regime map developed in the companion paper shows that when ε is smaller than a critical value εcr, a solution of explosive eruption exists for a wide range of Λ, whereas an effusive solution exists only when Λ ~ 1. On the other hand, when ε > εcr, an effusive solution exists for a wide range of Λ. Diversity of eruption styles observed in nature is explained by the change in ε accompanied by the change in magma viscosity during magma ascent. As magma ascends, the magma viscosity increases because of gas exsolution and crystallization, leading to the increase in ε. For the viscosity of hydrous silicic magma at magma chamber, ε is estimated to be smaller than εcr, indicating that an explosive solution exists for wide ranges of geological parameters. When magma flow rate is small, the viscosity of silicic magma drastically increases because of extensive crystallization at a shallow level in the conduit. In this case, ε can be greater than εcr; as a result, a stable effusive solution co-exists with an explosive solution. 相似文献
17.
The zooplankton of oligotrophic lakes in North Patagonia is often dominated by mixotrophic ciliates, particularly Stentor amethystinus and Stentor araucanus. Therefore, we tested whether Stentor spp. (i) is an important food for juvenile endemic (Cheirodon australe, Galaxias maculatus, Odontesthes mauleanum, Percichthys trucha) and introduced (Oncorhynchus mykiss) fish species, and (ii) represents a remarkable grazer of bacteria. Ingestion rates of fish estimated by disappearance of Stentor in feeding experiments ranged between 8 (G. maculatus) and 53 (C. australe) ciliates per fish and day, and assimilation rates measured by using radioactively labelled Stentor ranged between 3 (P. trucha) and 52 (C. australe) ciliates per fish and day. However, although we detected the consumption of Stentor by fish, the daily consumption amounted to at most 0.2% of the fish biomass which can not cover the energy requirement of the fish. Furthermore, the daily consumption was equivalent to a maximum of 1.6% of the Stentor standing stock so that fish predation does not seem to be an important mortality factor for the ciliates. The clearance rate of Stentor sp. on natural bacteria was on average 3.8 μl cil−1 h−1. The daily ingestion (mean 3.9 ng C cil−1 d−1) was about 3.5% of the individual biomass of Stentor sp. Therefore, bacteria ingestion might explain a ciliate growth rate of appr. 1% d−1, which was about 17% of the photosynthesis of endosymbiotic algae. The maximum density of Stentor sp. in the lake could ingest about 1 μg C L−1 d−1 bacteria which is only 3% of average bacterial production. Thus, grazing by Stentor sp. does not seem to be a main loss factor for the bacteria. 相似文献
18.
D. Zúñiga F. Alonso-PérezC.G. Castro B. ArbonesF.G. Figueiras 《Continental Shelf Research》2011,31(5):414-424
The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m−2 d−1 and 22 mg chl a m−2 d−1, respectively) and minimum values during winter (22 mg m−2 d−1 and 0.1 mg chl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension. 相似文献
19.
Phytoplankton viability in ballast water from international commercial ships berthed at ports in Korea 总被引：1，自引：0，他引：1
We investigated the viability of phytoplankton from ballast water of international commercial ships berthed at the ports of Ulsan and Onsan, Korea. The incubation conditions used were temperatures of 13 °C to represent ambient water and 20 °C to represent the thermal optimum, as well as nutrients in ballast water, shipside water, and F/2 medium. Phytoplankton in new (∼7 days) and old (20 and 23 days) ballast water survived when incubated under the nutrients typical of shipside water and F/2 medium at 13 °C and 20 °C. Colonization process was mostly dominated by Skeletonema costatum, Cylindrotheca closterium and pennate diatoms (<10 μm in diameter). S. costatum and C. closterium were persistent during incubation time, whereas pennate diatoms dominated in the three types of media from doubling to last phase of growth. This study showed that bloom-forming and pennate diatoms appear to be the species most likely to become successfully established in the two ports. 相似文献
20.
Catherine Lalande Jacqueline M. Grebmeier Paul Wassmann Lee W. Cooper Mikhail V. Flint Valentina M. Sergeeva 《Continental Shelf Research》2007
Drifting sediment traps were deployed at 9 stations in May-June (ice-covered conditions) and July-August (ice-free conditions) 2004 in the Chukchi Sea to investigate the variability in export fluxes of biogenic matter in the presence and absence of sea ice cover. Measurements of chlorophyll-a (Chl-a), particulate organic carbon (POC), particulate nitrogen (PN), phytoplankton, zooplankton fecal pellets, and the stable carbon isotope composition (δ13C) of the sinking material were performed along Barrow Canyon (BC) and a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. POC export fluxes were similarly high in the presence (378±106 mg C m−2 d−1) and in the absence of ice cover (442±203 mg C m−2 d−1) at the BC stations, while fluxes were significantly higher in the absence (129±98 mg C m−2 d−1) than in the presence of ice cover (44±29 mg C m−2 d−1) at the EHS stations. The C/N ratios and δ13C values of sinking organic particles indicated that POC export fluxes on the Chukchi continental shelf were mostly composed of freshly produced labile material, except at the EHS stations under ice cover where the exported matter was mostly composed of refractory material probably advected into the EHS region. Chl-a fluxes were higher under ice cover than in ice-free water, however, relatively low daily loss rates of Chl-a and similar phytoplankton carbon fluxes in ice-covered and ice-free water suggest the retention of phytoplankton in the upper water column. An increase in fecal pellet carbon fluxes in ice-free water reflected higher grazing pressure in the absence of ice cover. Elevated daily loss rates of POC at the BC stations confirmed other indications that Barrow Canyon is an important area of carbon export to the basin and/or benthos. These results support the conclusion that there are large spatial and temporal variations in export fluxes of biogenic matter on the Chukchi continental shelf, although export fluxes may be similar in the presence and in the absence of ice cover in highly productive regions. 相似文献