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Organic matter diffusion

Pignatello and Xing [107] used two models, the organic matter diffusion model (OMD) and the sorption-retarded pore diffusion model (SRPD), in order to understand better the meaning of slow sorption/desorption observations and mechanisms and to explore the most likely causes of such slow process in natural solid particles. These authors reported that both OMD and SRPD mechanisms operate in the environment, often probably together in the same particle. OMD may predominate in soils that are high in natural OM and low in aggregation, while SRPD may predominate in soils where the opposite conditions exist. [Pg.215]

PCB biodegradation can be enhanced by increasing the extent and/or rate of the PCB intra-organic matter diffusion, and can therefore lead to an apparent increase in the aqueous PCB concentration available for biodegradation. Treatment methods that have been used to disrupt the sorption of PCBs from the soil matrix include the addition of surfactants, solvents, or caustic. Surfactants have been used... [Pg.236]

After death, cells self-destruct (the process of autolysis) under the influence of hydrolytic enzymes, which, in life, aided the recycling of cellular components. This process makes proteins and other components more readily available to the decomposers. Bacteria and fungi preferentially remove the more labile components from detritus and the residue becomes increasingly refract-ory. Much of the soluble product of the microbial breakdown of organic matter diffuses upward within pore waters to the sediment—water interface and is returned to the water column. Bacteria are important in all environments, but fungi are relatively... [Pg.93]

This removal may also include diffusion of soluble U(VI) from seawater into the sediment via pore water. Uranium-organic matter complexes are also prevalent in the marine environment. Organically bound uranium was found to make up to 20% of the dissolved U concentration in the open ocean." ° Uranium may also be enriched in estuarine colloids and in suspended organic matter within the surface ocean. " Scott" and Maeda and Windom" have suggested the possibility that humic acids can efficiently scavenge uranium in low salinity regions of some estuaries. Finally, sedimentary organic matter can also efficiently complex or adsorb uranium and other radionuclides. [Pg.44]

Explds at 60° after 13 sec in a sealed glass tube (Ref 4). Explds spontaneously when frozen and then thawed. Compd is a violent expl, extremely sensitive to impact or friction. It Jalso explds on exposure to strong light (sunlight or diffused), or when in contact with P, As, ozone, fused alkalies, and organic matter such as turpentine rubber, but not with sugar or resins. Metals strong acids do not cause it to expld,... [Pg.283]

Inputs of organic matter and nutrients, benthic metabolism, and nutrient retention at each stream section depend on diffuse and point sources. Yet, under low flow conditions, water and matter transport downstream becomes impeded or discontinued due to stream contraction and fragmentation during dry periods. Therefore, nutrient export from rivers in semiarid regions will depend, more so than in more humid regions, on the interplay between the spatial configuration of organic matter... [Pg.187]

Upon formation of a metal chelate or complex, the next rate-limiting step in delivering iron to the cell is the diffusion of iron complexes through the. soil in response to diffusion gradients. In the vicinity of plant roots, metal chelates and complexes may also move by bulk flow in the transpiration stream as water moves from the soil into the plant. However, depending on their charge characteristics and hydrophobicity, metal chelators and complexes can become adsorbed to clay and organic matter, which may then decrease their mobility and bioavail-... [Pg.229]

Slow diffusion into very small pores and absorption into organic matter... [Pg.577]

FIGURE 48 A soil profile. Many of the characteristics of soils vary with depth. A convenient way of representing its varying characteristics is by dividing the soil into layers, usually referred to as horizons, identified by letter symbols. The surface layer, which is known as the A horizon, is generally rich in organic matter. Next come the B and C horizons, each of which may have compositional characteristics and modifications. The deepest soil horizon (R) is solid rock. The illustration identifies clearly defined horizons, although in most soils the horizons are not as clear and in some they may be very diffuse. [Pg.245]

I consider a system in which organic matter is oxidized at a steady rate that is a specified function of depth in uniform calcium carbonate sediments. The oxidation of organic matter increases the total dissolved carbon in the pore water of the sediment. The resultant increase in acidity causes the dissolution of calcium carbonate and a consequent increase in alkalinity as well as another increase in total dissolved carbon. The total dissolved carbon and alkalinity are transported by diffusion between different depths in the sediment. [Pg.151]

The elements deposited within the sediment matrix show that mobilization processes may be occurring in the upper layers. At Station SIN 3, figure 4d for example, the element deposited (pg-cm-2) in the topmost layers decreases, often much more than in the concentration (Mg g 1). This may be due to organic matter decomposition and/or to environmental chemical reactions of solubility and precipitation of the given element. The metal must have been removed rapidly from the water column since the sediment concentration is shown to decrease rapidly with distance from the shipyard (Stations SIN 3 and SIN 2). Lead may not be mobilized significantly after deposition since any diffusion in the pore water would tend to "smooth" the concentration profile with time. [Pg.339]

Equation (2.19), which concerns a situation without processes in the biofilm, can be extended to include transformation of a substrate, an electron donor (organic matter) or an electron acceptor, e.g., dissolved oxygen. If the reaction rate is limited by j ust one substrate and under steady state conditions, i.e., a fixed concentration profile, the differential equation for the combined transport and substrate utilization following Monod kinetics is shown in Equation (2.20) and is illustrated in Figure 2.8. Equation (2.20) expresses that under steady state conditions, the molecular diffusion determined by Fick s second law is equal to the bacterial uptake of the substrate. [Pg.31]

Sediment deposition on the seafloor traps interstitial water. After deposition, complex reactions take place in the sediment, most of them fueled by the decay of organic matter, such as sulfate reduction, denitrification,... Because of fast diffusion rates of most cations in seawater, the presence of interstitial water makes exchange between overlying sedimentary layers a much easier process than if sediment deposition was dry. The book by Berner (1980) is entirely dedicated to these processes and only a short example is given here. [Pg.461]

This model requires an excess of sulfate over reducible carbon. Concentrations may be measured in solutions squeezed from sediment cores, diffusion coefficients are known from standard chemical data tables and sedimentation rates determined from 14C, 210Pb, or 230Th dating. Therefore, this model finds its best use in the recovery of the kinetics of organic matter decay. A discussion of this and similar equations and numerical applications may be found in Berner (1980). [Pg.463]


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