Concentration in pore water from

De Groot et al. (1998) also gave regression parameters for calculating the total metal concentration in pore water from the total concentration in the soil. If site-specific physicochemical pore water characteristics are also available, the predicted total metal concentration in pore water can be extrapolated to the bioavailable ion concentration in pore water by site-specific application of the MINTEQ model. 

The concentration of Fe in pore water from core 1 was 50 mg/L, and the concentration in pore water from core 2 was 32 mg/L (Table 2). Chemical analyses measured only Fe(II) Fe(III) was below the detection limit. The concentration of Fe(II) in leachate from the contaminated cores rapidly decreased as Fe-free uncontaminated ground water displaced the contaminated pore water (Figs. 8a-8b). Within a few pore volumes, Fe(II) concentrations were less than 5 mg/L. For the remainder of the experiments, Fe(II) concentrations deaeased at a much slower rate. The low concentrations (<5 mg/L) measured in the first 25 pore volumes of leachate coincided with higher flow velocities and measurable O2 concentrations. Based on the mass of Fe(II) in leachate from core 1, the concentration of reactive organic carbon necessary to reduce Fe(III) to Fe(II) was about 2% of the total organic carbon. 

Fig. 14.17 A. Diagram illustrating the double BSR observed in seismic data in the vicinity of Site 1247. B. Chloride concentration in pore waters from site 1247, compared with expected values derived from a diffusive attenuation model following gas hydrate dissociation. The assumed hydrate content at time zero has a width of 10 m and a magnitude comparable to the anomaly observed just above the present BSR (BSRp). The data suggest that the hydrate dissociation occurred 5000 yrs ago. The authors postulate that pressure and temperature changes in the period of 8000 to 4000 years ago, led to a shift in the depth of the hydrate stability zone, creating the double BSR (modified from Bangs et al. 2005).

Table 8.5. Sulfate concentrations Cs°4 (mmol l 1) at depth z (cm) in pore waters from the Saanich Inlet, British Columbia (Murray et al., 1978).

Hg Concentrations in Pore Waters. Profundal sediment pore-water concentrations varied from 10 to 30 ng/L throughout the profile (Figure 3). 

Preliminary work (10) on the transition from oxidized surface sediment to reduced subsurface sediment in Milltown Reservoir showed that the redox transition occurs in the upper few tens of centimeters. Strong chemical gradients occur across this boundary. Ferrous iron in sediment pore water (groundwater and vadose water) is commonly below detection in the oxidizing surface zone and increases with depth. Arsenic is also low in pore water of the oxidized zone, but increases across the redox boundary, with As(III) as the dominant oxidation state in the reduced zone. Copper and zinc show the opposite trend, with relatively high concentrations in pore water of the oxidized surface sediment decreasing across the redox boundary. 

Figure 17 The relationship between the asymptotic H4Si04 concentration in pore waters and the relative detrital and opal content of the sediments (Van Cappellen, personal communication). (Data from ( ) Rickert (2000) ( ) King et al (2000) ( ) Koning et al (1997) (ffl) Van Cappellen and Qiu (1997a)).

Much higher concentrations of arsenic frequently occur in pore waters extracted from unconsolidated sediments than in overlying surface waters. Widerlund and Ingri (1995) reported concentrations in the range 1.3-166 p.g in pore waters from the Kalix River estuary, northern Sweden. Yan et al. (2000) found concentrations in the range 3.2-99 p.g in pore waters from clay sediments in Saskatchewan, Canada. 

Figure 15.13. The sediment-water interface, (a) Direction of fluxes expected for dissolved constituents between sediment pore waters and the overlying waters (oceans and lakes), (b) For sediments and pore water, the one-dimensional distribution of concentrations is time and depth dependent. Arrows indicate fluxes at the sediment-water interface depending on the concentration gradient in pore water. The overlying water (ocean or lakes) is assumed to be well mixed, (c) Sulfate, phosphate, and ammonia versus depth in pore waters from Santa Barbara Basin, California. (From Sholkovitz, 1973.)...

Figure 6. Dissolved organic carbon concentrations in leachate from cores I and 2. Initial DOC concentration in pore water of core I was 45 mg/L C, and in pore water from core 2 was 31 mg/L C. Dissolved organic carbon in uncontaminated ground water eluent was below detection.

Fig. 3.6 Sulfate profile in pore water from sediments of the Amazon deep sea fan at a water depth of about 3500 m. A linear concentration gradient can be distinctly derived from the sediment surface down to a depth of about 5.4 m. The gradient change, and thus a change in the diffusive flux, is strongly limited to a depth interval of at the most 10 to 20 cm (after Schulz et al. 1994).

Fig. 14.18 Upper panel illustrates dissolved chloride concentration in pore waters collected from the summit of Hydrate Ridge during ODP leg 204 (Sites 1249, 1250, from Torres et al. 2004) and from a gravity core recovered from this area during RV SONNE expedition SO-143 (Haeckel et al. 2004). These data (panels A-C) indicate that hydrate is forming at very fast rates, so as to maintain the extremely high chloride values. Furthermore, to sustain the rapid formation rates, Torres et al. (2004) and Haeckel et al. (2004) show that methane must be supplied in the gas phase, as illustrated by the cartoon in panel. Methane solubility in seawater is too low for aqueous transport to deliver sufficient methane to form the observed hydrate deposits. D. Mass balance calculations based on a simple box model (E) indicate that the massive deposits recovered from the Hydrate Ridge summit probably formed in a period of the order of lOO s to lOOO s of years, highlighting the dynamic nature of these near-surface deposits (modified from Torres et al. 2004 and Haeckel et al. 2004).

The concentration-dependent boundary conditions assigned to the model s upper-boundary limits (unspecified but constant concentrations in the cells Fll and 111) are relatively unproblematic since they represent a constant concentration in the bottom water zone. This is an imperative prerequisite for assuming a steady state in pore waters from superficial sediments. The condition for the lower boundary of the profile is somewhat more problematical. In the above example, the concentrations of both oxygen and nitrate were set to zero. In the model, this is tolerable as long as the value 0.0, constituting the lower boundary... 

The concentrations in pore water at a depth of only one centimeter below the sediment surface are considered as stationary. What release rates applying to phosphate must we postulate for the bacteria if it is known from experiments that the precipitation kinetics of phosphate minerals are in a certain range, and if the measured concentration profile in pore water is to be simulated correctly ... 

Silica concentrations in pore waters particularly and also in other subsurface and surface waters were determined in dozens of samples as part of this study, using atomic absorption spectrophotometry as well as inductive coupled plasma. This was essential for silica budget estimations. Present-day and paleothermal profiles were obtained from measured temperatures in boreholes, vitrinite reflectance (Rq) in interlayered-with-sandstones shales and from basins thermal modeling. 

Carbon dioxide is produced as a result of metabolism of all heterotrophic organisms. The concentrations of CO2 in pore water of reduced sediments are therefore high. Autotrophic microorganisms consume CO2 in the oxidized part of the sediment, which can vary in depth from a meter in deep sea sediments to a few mm... 

When a recovery well is located within a contaminant plume and the pump is started, the initial concentration of contaminant removed is close to the maximum level during preliminary testing. As the pump continues to operate, cleaner water is drawn from the plume perimeter through the aquifer pores toward the recovery well. Some of the contaminant is released from the soil into the water in proportion to the equilibrium coefficient. For example, if the Kd is 1000, at equilibrium, 1 part is in the water and 1000 parts are retained in the soil. If the water-soil contact time is sufficient, complete equilibrium will be established. After the first pore volume flush (theoretically), the concentration in the water will be 0.9 and that on the soil will be 999. With each succeeding flush, the 1000 1 ratio will remain the same. If the time of water-soil contact is not sufficient to establish equilibrium, the recovered water will contain a lesser concentration. A typical decline curve is shown on Figure 9.2. Note the asymptotic shape of the curve where the decline rate is significantly reduced. 

Most commonly observed pore-water concentration profiles, (a) A nonreactive substance, such as chloride (b) a chemical, such as O2, which undergoes removal in the surface sediment as a result of aerobic respiration (c) a chemical that is consumed by a reaction that occurs in a subsurface layer, such as Fe2+(aq) precipitating with S2-(aq) to form FeS2(s) (d) a chemical released in surface sediments, such as silica via dissolution of siliceous hard parts (e) a chemical released into pore waters from a subsurface layer, such as Mn +(aq) by the reduction of Mn02(s) and (f) a chemical released at one depth (reactive layer 1), such as Fe2+(aq) by reduction of FeOOFI(s), and removal at another depth (reactive layer 2), such as Fe +(aq) precipitating as FeS2(s). Source From Schulz,... 

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