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1.
This study addresses the influence of calcium as hardening agent, on alginate gel bead stability and suitability for the growth of Phaeodactylum tricornutum Bohlin (Bacillariophyceae) in estuarine waters. Alginate beads produced with 1, 2, 4, 5 and 6% of CaCl2 solutions were investigated for stability and suitability for growth of P. tricornutum cells, under mean salinity 27, at 220 and 440 rpm stirring laboratory conditions, and in devices placed under in situ estuarine conditions. Gel stability and suitability for cell growth were evaluated through bead diameter, bead disruption, dissolution and loss of spherical shape, cell viability and specific growth rates. Beads gelled with 5% CaCl2 were found the most suitable to sustain gel stability and cell growth in the estuarine waters. These beads were surveyed during dredging operations in the Tagus estuary, both in situ and in estuarine water under laboratory conditions, showing significantly lowered growth rates possibly due to Mn, Co and As accumulated in the cells. Results confirmed that the monitoring tool presented is reliable and effective for the assessment of anthropogenic impacts. 相似文献
2.
《Ocean Modelling》2007,16(1-2):1-16
In many global ocean climate models, mesoscale eddies are parameterized as along isopycnal diffusion and eddy-induced advection (or equivalently skew-diffusion). The eddy-induced advection flattens isopycnals and acts as a sink of available potential energy, whereas the isopycnal diffusion mixes tracers along neutral directions. While much effort has gone into estimating diffusivities associated with this closure, less attention has been paid to the details of how this closure (which tries to flatten isopycnals) interacts with the mixed layer (in which vertical mixing tries to drive the isopycnals vertical). In order to maintain numerical stability, models often stipulate a maximum slope Smax which in combination with the thickness diffusivity Agm defines a maximum eddy-induced advective transport Agm1Smax. In this paper, we examine the impact of changing Smax within the GFDL global coupled climate model. We show that this parameter produces significant changes in wintertime mixed layer depth, with implications for wintertime temperatures in key regions, the distribution of precipitation, and the vertical structure of heat uptake. Smaller changes are seen in details of ventilation and currents, and even smaller changes as regards the overall hydrography. The results suggest that not only the value of the coefficient, but the details of the tapering scheme, need to be considered when comparing isopycnal mixing schemes in models. 相似文献
3.
《Coastal Engineering》2006,53(5-6):531-542
The inception of the sheet flow regime as well as the effects of the phase lag when the sheet flow regime is established were investigated for oscillatory flows and combined steady and oscillatory flows. A new criterion for the inception of sheet flow is proposed based on around 300 oscillatory flow cases from experiments. This criterion was introduced in the Camenen and Larson [Camenen, B., Larson, M., 2005. A bedload sediment transport formula for the nearshore. Estuarine, Coastal and Shelf Science 63, 249–260.] bed load formula in order to take into account phase-lag effects in the sheet flow regime. The modification of the Camenen and Larson formula significantly improves the overall agreement with data and yields a correct behavior in relation to some of the main governing parameters, which are the median grain size d50, the orbital wave velocity Uw, and the wave period Tw. The calibration of the new formula was based on more than 200 experimental data values on the net sediment transport rate for a full wave cycle. A conceptual model was also proposed to estimate the ratio between sediment transport rate with and without phase lag, (rpl = qs,net / qs,net,ϕ=0). This simple model provides accurate results and may be used together with any quasi-steady model for bed load transport. 相似文献
4.
Measurements have been made, by amperometric titration using anodic stripping voltammetry, of the zinc binding properties of organic material released by Skeletonema costatum in culture, after the stationary growth phase had been reached. Titration curves showed two inflection points, interpreted as indicating the presence of two analytically distinguishable ligand assemblages (L1 and L2). The complexing capacities of these assemblages increased with time and the associated conditional stability constants K1′ and K2′ decreased with time. This apparent reduction in stability constants could be accounted for by complex dissociation. Several methods for the calculation of complexing capacity and stability constant were employed and although the calculated concentrations of CL varied, each method showed similar trends.Size fractionation of the organic moieties revealed that CL, was composed of organic assemblages with apparent molecular weight greater than 3 × 104. The ligands L2 were of mixed size composition. 相似文献
5.
We investigate the sensitivity of numerical-model solutions to regional changes in vertical diffusion. Specifically, we vary the background diffusion coefficient, κb, within spatially distinct subregions of the tropical Pacific, assess the impacts of those changes, and diagnose the processes that account for them.Solutions respond to a diffusion anomaly, δκb, in three ways. Initially, there is a fast response (several months), due to the interaction of rapidly-propagating, barotropic and gravity waves with eddies and other mesoscale features. It is followed by a local response (roughly one year), the initial growth and spatial pattern of which can be explained by one-dimensional (vertical) diffusion. At this stage, temperature and salinity anomalies are generated that are either associated with a change in density (“dynamical” anomalies) or without one (“spiciness” anomalies). In a final adjustment stage, the dynamical and spiciness anomalies spread to remote regions by radiation of Rossby and Kelvin waves and by advection, respectively.In near-equilibrium solutions, dynamical anomalies are generally much larger in the latitude band of the forcing, but the impact of off-equatorial forcing by δκb on the equatorial temperature structure is still significant. Spiciness anomalies spread equatorward within the pycnocline, where they are carried to the equator as part of the subsurface branch of the Pacific Subtropical Cells, and spiciness also extends to the equator via western-boundary currents. Forcing near and at the equator generates strong dynamical anomalies, and sometimes additional spiciness anomalies, at pycnocline depths. The total response of the equatorial temperature structure to δκb in various regions depends on the strength and spatial pattern of the generation of each signal within the forcing region as well as on the processes of its spreading to the equator. 相似文献
6.
《Ocean Modelling》2003,5(1):77-89
Proposed is a method of finding unstable steady solutions based on relaxation to a running mean. It works for moderate supercriticality, when the growth rates of the instabilities do not exceed their frequencies. To calculate the running mean one should use the decaying exponential function as a kernel in the convolution formula, it offers a combination of necessary stabilization properties with the efficiency of numerical implementation. The method requires specification of the relaxation TR and averaging TA time scales, such that in the transformed eigenspectrum frequencies above the cutoff 1/TA experience additional damping with 1/TR rate. All originally decaying modes remain decaying. The zero frequency remains unchanged, which implies that the steady states are invariant under the transformation. The acceptable values for TR and TA can be obtained from an estimate of the frequencies and growth rates of the modes leading to instability. For faster convergence to the steady state TR should be set as large as possible, provided it causes sufficient damping of the instability. The numerical implementation of this method requires only very simple modifications to the program used for time integration of the original system. 相似文献
7.
Estimates of vertical turbulent diffusion coefficient (K t ) in the Black Sea pycnohalocline have been obtained from data of simultaneous observations of seawater temperature, salinity, density, and horizontal current velocity, obtained in the northeastern part of the Black Sea during 2013–2014 with a moored Aqualog profiler. A Munk and Andersson (1948) type parameterization, adapted for the Black Sea environment, is proposed for calculating K t . Strong short-period (several days) variability of turbulent exchange is revealed, induced by vertical shear variations of the current velocity. 相似文献
8.
Calibration of a chalcogenide glass membrane, Fe(III)ISE [Fe2.5(Ge28Sb12Se60)97.5], in buffered saline media has been undertaken in order to assess the suitability of this ISE for seawater analyses. The electrode slopes in saline citrate and salicylate buffers were 26.3 and 28.2 mV/decade, respectively, for Fe3+ concentrations ranging from 10−10 M to less than 10−25 M Fe3+. The calibration lines in the citrate and salicylate buffers were essentially collinear with the response in unbuffered chloride-free standards containing >10−5 M Fe3+, demonstrating that the response of the FeISE is unaffected by chloride ions. A mechanism involving a combination of charge transfer and ion-exchange of Fe(III), at the electrode diffusion layer, can be used to explain the ≈30 mV/decade slope of the FeISE. The response of the FeISE in UV photooxidised seawater containing 8 nM total Fe was measured as the pH was changed from 8.27 to 3.51. The slope of the response was 24.2 mV/decade [Fe3+] calculated as a function of pH using Fe(III) hydrolysis constants for seawater. Moreover, the response was essentially collinear with that in citrate buffers and in unbuffered solutions containing >10−5 M Fe3+ and the slope for the combined data was 26.2 mV/decade. This study was restricted to organic-free seawater because the certainty in Fe(III)–ligand stability constants is insufficient to warrant the selection of an ideal calibration buffer system, and there is evidence that powerful chelating ligands (e.g., EDTA along with humic and fulvic acids) may alter the response of the Fe(III)ISE. The Fe dissolution rate of the FeISE in UV photooxidised seawater was found to be 1.6×10−2 nmol Fe/min, as measured by cathodic stripping voltammetry (CSV). This would contaminate a 100-ml sample by 0.8–1.6 nM Fe over a typical measurement period of 5–10 min obtained using a stability criterion of 0.5 mV/min. Various methods are proposed for reducing the level of contamination in open ocean samples that contain sub-nanomolar concentrations of iron. The FeISE has the potential to detect free Fe3+ at concentrations typically found in natural seawater. 相似文献
9.
《Ocean Modelling》2001,3(1-2):67-94
The effect of variable vertical diffusivity is investigated in dynamically reduced models of the thermohaline circulation (THC) in a rectangular basin. In a simple box model, sufficiently strong variation of the diffusivity κv with stability G can lead to the existence of two stable equilibria. Related behaviour is found in well-resolved frictional geostrophic (FG) models. A hierarchy of under-resolved FG models is constructed, the simplest of which is an 8-cell cube, to connect the two extremes of resolution. Multiple solutions in low-order models are found to correspond to the formation of high-gradient layers which are unlikely to be resolved by current ocean models. Physical arguments show that layering and multiple solutions require κv to decrease more rapidly than 1/G and sensitivity experiments suggest that, in addition, κv must vary by a factor of 10–100. In two-hemisphere runs with salinity forcing included, the dependence of diffusivity on stratification is found to marginally favour equatorially symmetric states. Finally, such variation is shown to have a profound effect on the periodic, flush-collapse cycle under strong saline forcing; specifically, if diffusivity is taken to be a function of stratification rather than depth, regime transitions can occur much more easily. It will therefore be important for climate modelling to determine which is more realistic. 相似文献
10.
Measurements have been made, by amperometric titration using anodic stripping voltammetry, of the zinc-binding properties of organic material released by Thalassiosira fluviatilis in culture over a period from the beginning of growth to senescence. After the onset of the stationary phase, titration curves showed two inflection points, interpreted as indicating the presence of two analytically distinguishable ligand assemblages (L1 and L2). The complexing capacities (CL) of these assemblages changed with time, CL1 increasing linearly from <0.5 × 10?8 M to 2.0 × 10?6 M into the stationary phase and then more rapidly during senescence, and CL2 increasing after its initial appearance to a final value of 4.4 × 10?6 M. These changes were accompanied by systematic decreases in the corresponding conditional stability constants (K′) calculated for 1 : 1 associations of the ligands with zinc. Values of log K′1 decreased from 6.6 to 5.8, and those of log K′2 from 7.2 to 6.2. The presence of the second ligand assemblage may be related to the release of intracellular material during senescence. 相似文献
11.
The relationships between the linear dimensions and body weight and the ratio between the masses, growth, and production were studied for the bivalve Astarte borealis inhabiting the southeastern Baltic Sea. The maximal shell length was 21.09 mm, while the maximum age was 8+. The linear growth was described by the Bertalanffy equation L τ = (1 - e -0.0894(τ-(-0.7354))). The annual production was 7.60 kJ/m2 at a P s/B coefficient of 0.41. It was found that the A. borealis inhabiting the southeastern Baltic Sea was characterized by a lower linear growth rate compared to the mollusks of other parts of the geographical range due to the low salinity of the Baltic Sea. 相似文献
12.
《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(2):363-375
Phytoplankton growth and microzooplankton grazing rates were measured by the dilution technique in the subarctic North Pacific Ocean along a west–east transect during summer 1999. Average phytoplankton growth rates without added nutrients (μ0) were 0.33, 0.41, 0.20 and 0.49 d−1 for the four regions sampled: the Western Gyre, the Bering Sea, the Gulf of Alaska gyre and stations along the Aleutian Trench. Average grazing mortality rates (m) were 0.34, 0.27, 0.20 and 0.49 d−1. Limitation of phytoplankton growth by macronutrients, such as NO3 and SiO2, was identified only at a few stations, with overall μ0/μn (μn is nutrient-enhanced growth rate) averaging 0.9. Phytoplankton growth and microzooplankton grazing were approximately balanced, as indicated by high m/μ0 ratio, except in the Bering Sea, where the m/μ0 ratio was 0.65, indicating the relative importance of the diatom-macrozooplankton grazing food chain and possible higher export flux to the deep layer. Flow cytometric analysis revealed that the growth rates of picoplankton (Synechococcus and picoeukaryotes) were usually much lower than the total phytoplankton community growth rates estimated from chlorophyll a, except for stations in the Gulf of Alaska Gyre, where the growth rates for different populations were about the same. Lower than community-average growth rate for picoplankton indicates larger phytoplankters, presumably diatoms, were growing at a much faster rate. Suppressed phytoplankton growth in the Gulf of Alaska was probably a result of iron limitation. 相似文献
13.
Robust optimal output tracking control of a midwater trawl system based on T-S fuzzy nonlinear model
A robust optimal output tracking control method for a midwater trawl system is investigated based on T-S fuzzy nonlinear model.A simplified nonlinear mathematical model is first employed to represent a midwater trawl system,and then a T-S fuzzy model is adopted to approximate the nonlinear system.Since the strong nonlinearities and the external disturbance of the trawling system,a mixed H 2 /H ∞ fuzzy output tracking control strategy via T-S fuzzy system is proposed to regulate the trawl depth to follow a desired trajectory.The trawl depth can be regulated by adjusting the winch velocity automatically and the tracking error can be minimized according to the robust optimal criterion.In order to validate the proposed control method,a computer simulation is conducted.The simulation results indicate that the proposed fuzzy robust optimal controller make the trawl net rapidly follow the desired trajectory under the model uncertainties and the external disturbance caused by wave and current. 相似文献
14.
The stability of the ion pair NaSO4 was determined by measuring the change in sodium activity with medium composition at constant ionic strength, using a sodium-sensitive glass electrode. The stability constants of MgSO4 and MgCl+ were determined indirectly from measurements of the stability of MgF+ in different media. All measurements were performed at 1 atm pressure, 25 ± 0.1 °C and 0.7 M formal ionic strength. The stability constants for NaSO4?, MgSO4, MgF+ and MgCl+ are 1.8 ± 0.1, 6.3 ± 0.1, 22.9 ± 0.1 and 0.34 ± 0.02 M?1, respectively. 相似文献
15.
16.
This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of −5 °C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus ES of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E0 was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr–Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M–C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region. 相似文献
17.
Severe red tides due toChattonella antiqua occur sporadically during summer in the Seto Inland Sea, Japan, and cause significant damage to the fishing industry. In order to assess the chemical environment with respect to the outbreak ofC. antiqua, environmental factors that affect the growth ofC. antiqua were monitored around the Ie-shima Islands, the Seto Inland Sea, in the summer of 1986. In addition, a growth bioassay of the seawater usingC. antiqua was conducted under a semicontinuous culture system. Although temperature, salinity and light intensity were optimum for the growth ofC. antiqua, red tides by this species did not occur. Concentrations of NH 4 + , NO 3 ? and PO 4 3? were low (<0.4, <0.2, <0.06 µM, respectively) above the thermocline (8–12 m) and high below it (0.6–2, 4–8, 0.4–0.8 µM, respectively). Vitamin B12 concentrations did not change significantly between the surface (0 m) and below the thermocline (25 m) in the level of 2–4 ng·l?1. The growth bioassay revealed that in the surface waters, concentrations of N- as well as P- nutrients were too low to support a rapid growth ofC. antiqua. At the depth of 25 m, neither N, P nor B12 limited the growth rate. In order to obtain more quantitative information on the growth rate as a function of the concentrations of N- and P- nutrients,C. antiqua was grown in a semicontinuous culture system by changing nutrient concentrations systematically. The observed growth rate (μ) can be approximated as follows: $$\mu = \mu _{\max } .\frac{{S_N }}{{K_g ^N + S_N }}.\frac{{S_{PO4} }}{{K_g ^P + S_{PO4} }},$$ whereS N is the concentration of NO 3 ? plus NH 4 + (0–6 µM),S PO, the concentration of PO 4 3? (0–0.6 µM), μmax (0.97 d?1) the maximal growth rate,K 0 N (1.0 µM) andK 0 P (0.11 µM) the half saturation constants for NO 3 ? and PO 4 3? , respectively. Using the above equation with nutrient concentrations measured, the rate at which seawater supports the growth ofC. antiqua can be estimated and this can be used for the assessment of chemical environments with respect to the outbreak ofC. antiqua. 相似文献
18.
《Coastal Engineering》2006,53(9):711-722
In this paper it will be shown that the wave height parameter H50, defined as the average wave height of the 50 highest waves reaching a rubble-mound breakwater in its useful life, can describe the effect of the wave height on the history of the armor damage caused by the wave climate during the structure's usable life.Using Thompson and Shuttler (Thompson, D.M., Shuttler, R.M., 1975. Riprap design for wind wave attack: A laboratory study on random waves. HRS Wallingford, Report 61, UK) data it will be shown that H50 is the wave parameter that best represents the damage evolution with the number of waves in a sea state. Using this H50 parameter, formulae as van der Meer (van der Meer, J.W., 1988. Rock slopes and gravel beaches under wave attack. PhD Thesis. Technical University of Delft) and Losada and Giménez-Curto (Losada, M.A., Gimenez–Curto, L.A., 1979. The joint effect of the wave height and period on the stability of rubble mound breakwaters using Iribarren's number. Coastal Engineering, 3, 77–96) are transformed into sea-state damage evolution formulae. Using these H50-transformed formulae for regular and irregular sea states it will be shown how damage predictions are independent of the sea state wave height distribution.To check the capability of these H50-formulae to predict damage evolution of succession of sea states with different wave height distributions, some stability tests with regular and irregular waves have been carried out. After analysing the experimental results, it will be shown how H50-formulae can predict the observed damage independently of the sea state wave height distribution or the succession of sea states. 相似文献
19.
《Coastal Engineering》1999,37(1):1-36
Seasonally open tidal inlets usually occur in microtidal, wave-dominated coastal environments where strong seasonal variations of streamflow and wave climate are experienced. These inlets are closed to the ocean for a number of months every year due to the formation of sand bars across their entrances. The annual closure of these inlets inhibits ocean access for boats and could also cause deterioration of water quality in the estuary/lagoon connected to the inlet. As these estuaries/lagoons are commonly used as harbours or recreational facilities there is increased interest in keeping the inlets permanently open. A process-based numerical model capable of simulating inlet closure is invaluable in terms of identifying the natural processes governing inlet closure. As a further step, this type of model could also be used to determine the effect of any proposed engineering solutions to keep the inlet open on the adjacent beaches. A morphodynamic model capable of simulating the seasonal closure of inlets, which includes both longshore (LST) and cross-shore transport (CST) processes, was developed in this study. Application of the model to two idealised scenarios indicated that cross-shore processes govern inlet behaviour when LST rates were low. The Dean's criterion [Dean, R.G., 1973. Heuristic models of sand transport in the surf zone. Proc. Conf. on Eng. Dynamics in the Surf Zone, Sydney, pp. 208–214.] for on–offshore transport was employed to show that, for small offshore wave incidence angles, onshore transport aided inlet closure when the offshore wave steepness (Ho/Lo) was less than the critical wave steepness (Ho/Lo)crit, while offshore transport helped to keep the inlet open when (Ho/Lo) was greater than (Ho/Lo)crit. LST was found to be the dominant process leading to inlet closure when (Ho/Lo) was much larger than (Ho/Lo)crit or when the offshore wave incidence angle was large. 相似文献
20.
An ultraviolet spectroscopic study at 25°C is used to determine the stoichiometric stability constant of CuCO30 (βCuCO30) over a range of ionic strengths; extrapolation to zero ionic strength provides a thermodynamic constant (log β0CuCO30 = 6.89). At 0.69 m ionic strength, log βCuCO30) is 6.33.This study provides the first experimental evidence for the existence of CuHCO3+. At 0.69 m ionic strength, log βCuHCO3+ is 2.77.The ultraviolet molal absorptivity spectra for the two complexes are also determined. The spectrum for CuCO30 consists of a single band centered at 276.5 nm and was described well by a Gaussian function. The spectrum of CuHCO3+ consists of at least two overlapping bands.Side reactions which might affect the data interpretation were included in the analysis of the results. The effects of the Cu(II) hydrolysis reactions were accounted for by using data from previous work, and possible effects due to copper-organic species were eliminated by a subtraction procedure. 相似文献