Biotic processes

Biogeochemical cycling in forests includes elemental inputs, exports, and a complex set of physical, chemical and biotic processes which comprise internal nutrient cycles (Fig. 1). Any disturbance, whether anthropogenic (i.e. 

This chemistry has been investigated and implemented for wastewater minerahza-tion by oxidizing the organic pollutants. The process is very efficient, not selective and, as a consequence, almost all carbon matter can be removed. Topical areas also include soil and aquifer treatments, sometimes in combination with a secondary biotic process [145]. 

Table 20.5 also indicates whether a process is biotic (mediated or initiated by organisms in the environment), abiotic (not involving biological mediation), or both. Biotic processes are limited to environmental conditions that favor growth of mediating organisms. Abiotic processes occur under a wide range of conditions. Adsorption, precipitation, complexation, and neutralization are abiotic all other processes in Table 20.5 may be either. 

The ammonium dynamics showed that the initial concentrations of N were reduced after the first 3 days, and after that, a release of the mineral occurred from day 3 up to day 14. Later still, the concentration of ammonium decreased by up to < 14 mg N kg 1 dry soil for all the treatments in both the Otumba and Texcoco soils, and the ammonium concentration decreased by up to < 2 mg N kg 1 dry soil for all treatments, except for the soil treated with sterilized sludge, < 31 mg N kg 1 dry soil. The contour of the ammonium dynamics was similar in both the Otumba and Texcoco soils. Many abiotic and biotic processes might affect the concentration of NH4+ in soil, such as NH4+ fixation in the soil matrix, volatilisation of NH3, and immobilization or oxidation of NH4+. Some soil processes were occurring at too low a level to be detectable, such as NH4+ fixation and the volatilisation of NH3. The nitrate dynamics were similar in both soils. The concentration of N03 was 120 mg N kg 1 dry soil in the control treatment in both soils. The ammonium concentration was similar in both soils, > 200 mg N kg 1 dry soil, treatments with sludge reached > 255 mg N kg 1 dry soil and > 300 mg N kg 1 dry soil in the Texcoco and Otumba soils respectively, and soils treated with sterilized sludge increased the concentration... 

The sampling points must be on groundwater flow lines from the source of contamination or above the observation point. The down-gradient observations must accurately reflect the abiotic and biotic processes occurring between the two points. 

For air, the major degradation process involves reactions with free radicals such as hydroxyl groups (Atkinson 1985). For other media, it is clear that chloroform can be mineralized through both abiotic and biotic processes. Information in the available literature (Bouer and McCarty 1983 Rhee and Speece 1992) documents the disappearance of chloroform in water and soil media under both aerobic and anaerobic conditions as well as identification of the end products. 

The atmospheric carbon reservoir is largely controlled by biotic processes. To obtain a better sense of this, it is helpful to consider the turnover time of carbon in the... 

Abiontic, involving free extracellular enzymes or solubilizing agents, enzymes bound to soil surfaces, enzymes within dead or non-proliferating cells, or enzymes associated with dead cell fragments. Extracellular enzymes are important in the initial stages of organic matter oxidation, in which polysaccharides and proteins are hydrolysed to soluble compounds that can be absorbed by microbial cells and further oxidized in biotic processes. 

A focus on compounds found only in cellular macromolecules would overlook labile LMW compounds produced by photochemical reactions. Although many organic compounds produced by photochemistry can also be produced by biotic processes, the contribution of photochemically-derived organic compounds to the DOM flux may be much larger than indicated by the occurrence of these compounds in cellular macromolecules or metabolic processes. Technically, most organic compounds produced by photochemical... 

A biofilm is commonly visualized as a two-dimensional matrix layered on a solid surface. However, aggregates of exopolymer, detritus, and cells also form in the water column through a variety of physical, chemical, and biotic processes (Ward et al., 1994 Grossart et al., 1997 Chapter 12). These aggregates are variously described as floes or snow . A type of aggregate... 

Any improvement of the global model of the biosphere can only be achieved by extending our knowledge of the biogeochemical cycles involved in it. The need to parameterize a unit describing sulfur fluxes in natural systems is dictated by the dependence of biotic processes on the content of sulfur in biospheric compartments. The available data on the supplies and fluxes of sulfur compounds in the atmosphere, soils, vegetation cover, and hydrosphere, enable formulation of mathematical relationships to describe the global sulfur cycle. 

Life on Earth makes use of only a limited number of diastereomers of all those that are possible. Moreover, biotic processes display an enantiomeric excess e.g., left-handed amino acids and right-handed sugars almost exclusively predominate in living systems. 

Photochemical degradation has been recognized as an abiotic mechanism that contributes to the loss of waste constituents in soils [71,72], It does not often result in complete degradation but allows further action of biotic processes. Phototransformation of soil-adsorbed pollutants takes place through two main pathways. 

An understanding of the chemistry involved in the abiotic and metabolic processes, and of the biochemistry in the biotic processing of xenobiotic compounds and natural compounds, may lead to important considerations. For example, this understanding can help to determine which chemicals can be employed that are not only safe for the environment and human health, but also beneficial for human use, and which ones, if used, are dangerous and carry a high risk for humanity. 

Nutrient recycling and supply is tightly regulated by largely biotic processes, such as retranslocation or resorption prior to leaf abscission (Medina and Cuevas 1989, Cuevas and Medina 1990). Nutrients are also reutilized from decomposing residues through rapid mineralization and uptake by a dense... 

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