Sedimented layer maximum concentration

Addition of fuel oil no. 2 to a laboratory marine ecosystem showed that the insoluble, saturated hydrocarbons in the oil were slowly transported to the sediment on suspended particulate material. The particulate material contained 40-50% of the total amount of aliphatics added to the system and only 3-21% of the aromatic fraction (Oviatt et al. 1982). This indicates that most aromatic hydrocarbons are dissolved in the water (Coleman et al. 1984), whereas the aliphatic hydrocarbons are not (Gearing et al. 1980 Oviatt et al. 1982). In a similar experiment, when fuel oil no. 2 was added continuously to a marine ecosystem for 24 weeks, oil concentrations in the sediment remained low until 135 days after the additions began, but then increased dramatically to levels that were 9% of the total fuel oil added (108 g/tank) and 12% of the total fuel oil saturated hydrocarbons. The fuel oil concentrations in the sediment began to decrease quite rapidly after the maximum levels were reached. The highest sediment concentrations of saturated hydrocarbons (106-527 g/g) were found in the surface flocculent layer, with concentrations decreasing with sediment depth from 22 g/g to not detectable at 2-3 cm below the sediment surface. 

If metals, particularly iron, are not available to precipitate the biogenic sulfide, then dissolved sulfide builds up in the pore waters and may even reach toxic levels. When iron is present the dissolved sulfide is significantly lower in concentration. The concentration profiles for dissolved sulfide in sediments often show a depletion in the upper layers and a maximum at a depth of a meter or less. The depletion is interpreted by Goldhaber and Kaplan (1974) to reflect reactions between iron oxide and dissolved sulfide to yield iron sulfides. As a consequence of different reactivities of iron oxides to aqueous sulfide, a depth may be reached where the sulfide production rate exceeds removal as iron sulfide. Volkov et al. (1972) reported that, in sediments off the Japan Depression, the free hydrogen sulfide concentration reaches as high as 150 mg h which is roughly 50% higher than that found in the Black Sea and is comparable to the maximum concentration observed at Saanich Inlet, British Columbia, by Nissenbaum et al. (1972). The... 

In detail, most of the concentration profiles reveal increasing values from the bottom of the core up to a depth of 100 cm, reaching a first maximum there. Subsequently, the values decrease to a fairly constant level at a depth between 80 cm and 30 cm. The averaged values in this zone are Cd 6 pg/g, Ni 50 pg/g, Cr 85 pg/g, Cu 180 pg/g, Pb 240 pg/g and Zn 1100 pg/g. A second concentration maximum was observed at a depth of approx. 25 cm. In the top layers of the sediment core the concentrations decrease down to values similar to those in the 30-80 cm zone. These trends are best developed in the concentration profiles of lead, copper, zinc and cadmium (Fig. 4). 

The pore water samples of the sediment layers close to the surface of both samples, TKWA and TKS, were characterised by DOC values between 16 and 60 mg/L. The maximum values were obtained in the top layer of the TKS sample. The results of the inorganic analyses revealed concentrations of copper and zinc within a range between 1 to 14 mg/L and 0,02 to 0,1 mg/L, respectively. For the TKS samples the highest values were determined in the top layer. The concentrations of lead and cadmium were below the detection limit in all samples investigated. 

Following the occurrence of DDT and its metabolites will be discussed with respect to their vertical distribution in the sediment core investigated. Main contaminant was DDD, the main metabolite of the anaerobic degradation pathway, with maximum values of approx. 24000 ng/g dry weight in the deeper layers. The concentration detected in all sediment layers ranged between 2000 to 24000 ng/g. 

The corresponding upward speed of the discontinuity front from the bottom is obtained from the conditions that p, = and Pi = p, , where p, is the maximum concentration of the particles in the sedimented layer. The boundary condition at the bottom is that = 0, since there is no flux of the sedimented layer, whence... 

The lack of a standard protocol for sediment sampling introduces additional variability in reported concentrations to the natural variability encountered in the Bay. Kroll and Murphy (34) detected atrazine in 93% of their sediment samples taken in 1978 at a Midland site, with a maximum measured concentration of 2.15 ppb. Boynton et ed. (36) measured atrazine concentrations below 1 ppb in the sediment layers in the eastern and western tributaries of the Bay in 1980. More recently, Eskin et al. (37) reported no detectable atrazine concentrations in 40 stations covering the main stem and tributaries of the Bay. The difference between this work and earlier studies rtuQr reflect a removal of atrazine from the sediment layer, or, sittqrly, better accuracy and reliability in the analytical methods. It is reasonable to adopt the most recent results and to consider the atrazine mass resident in the sediment layer insignificant. 

Margin the sediments contain 15-20% (volume) hydrate. This 33% of the total might be taken as a maximum for the hydrate indicated by a BSR. Hyndman and Davis (1992) indicated that the Vp decrease (1) suggested a gradational boundary with the thickest hydrate at the BSR and lesser hydrate concentrations above the BSR and (2) that the BSR did not require a gas layer beneath the hydrate. 

A quantitative comparison of particle expansion determined by the three methods is given in Table I. The particle diamete of the standard acrylic latex was determined by PCS to be 1120 A. This value was used in the calculation of the increase in particle radius at maximum expansion in each case. The sedimentation method yielded the largest increase in radius, 302 A, followed by the viscometric value of 240 K. Possibly the shear involved in the latter method resulted in a partial collapse of the surface layer. The value determined by PCS was found to be approximately half that determined by sedimentation. Since the PCS determination is presumed to be free of particle interactions at a concentration of 5 X 10 4%, we must conclude that the other two methods (at 1% solids) exhibit such interactions. As a result, the charged particles settle slower (19) and yield a higher viscosity than in the absence of these (repulsive) interactions. 

However, the relationship is not simple because minimtin concentrations of methane correlate with the season of maximum productivity. Seasonal and inter-annual production rates of methane suggest that significant quantities are produced in the water column or from surficial layers of bottom sediments. The relative proportions of of methane produced in the water column and bottom sediments could not be determined from these observations, however. 

The measurements showed that major masses of voleanic aerosol in the first period after die volcano cmption were located in layers of 16-18 and 23-25 km (Chen and Lelevkin, 2000). During the period following die sedimentation of particles, the formation of aerosol from sulphur dioxide in the layer of maximum stratospherie ozone concentration (26-28 km) occurred. Therefore, the reduction of total ozone oeeurred (Figure 2), due to the photooxidation reaetion of SO2 (Toktomyshev and Semenov, 2001) ... 

Diffusive Fluxes of Mn(II). If Mn is not transported to the 5-m layer of bottom water by lateral turbulent diffusion or advection, we should observe maximum values of the diffusive fluxes similar to the oxidation rate across the sediment-water interface (up to 3 mmol/m2 per day). Profiles of Mn concentrations in the pore water are shown in Figure 6a. The steep concentration gradients near the sediment-water interface are not at steady state the gradients are at maximum in summer and decrease to a minimum in spring. Sharp peak profiles were observed in June and July 1990. The diffusive flux of Mn(II), Fm in millimoles per square meter per day, was estimated from pore water profiles by using Fick s law with a correction for the porosity, c )... 

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