Heterogeneity of soils

Bioavailability is also influenced by certain, albeit poorly understood, characteristics of bacteria. To degrade soil-sorbed molecules, bacteria must either use sorbed molecule directly or facilitate desorption in some manner. Mechanisms underlying the apparent availability of sorbed chemicals are complex due to the divergent properties of chemicals considered, the resultant sorption/desorption mechanisms, the metabolic diversity of microorganisms, and the heterogeneity of soils. Several microbial-based mechanisms have been proposed for the access of soil-sorbed organic chemicals (i) production of bio surfactants (Desai and Banat 1997 Alexander 1999) ... 

Because of the heterogeneity of soils in general and helds in particular, statistics alone cannot provide the best guidance regarding sampling for all situations. Instead some random samples can be taken and the results used in combination with statistical approaches to guide the selection of additional samphng sites. 

The cause of the concentration dependence is not known. Using the data from 62 isotherms from the above references, there is no correlation between 1In for atrazine sorption and organic carbon content, clay content, or pH. It appears the heterogeneity of soils results in a continuum of sorption sites with differing amounts of low- and high-energy sites in different soils. 

Because of the normal heterogeneity of soil and because of possible unnatural alterations introduced at the time of burial, such as grave goods that have since decomposed, elemental analysis of soils and discernment of spatial trends of specific elements are fraught with difficulties. Nonetheless, we believe that we have documented permanent and diagnostic alterations in the soil composition as the result of elemental interchange with the skeleton. Furthermore, these observations correspond in almost every detail to those made in our study of the relative elemental compositions of excavated human ribs and femurs (8). 

Much of soil science is empirical rather than theoretical in practice. This fact is a result of the extreme complexity and heterogeneity of soils, which are impossible to fully describe or quantify by simple chemical or physical models. It is not unusual for working solutions to be found for soil chemical problems with little, or even fallacious, understanding at a fundamental level. The simplicity of the empirical approach becomes the seed of its undoing, because the primary advantage of the scientific method, predictive capability, is curtailed or lost. On the other hand, the universality of chemical principles and laws (i.e., theories) permit processes to be described in such a way that soil chemical behavior can be understood and predicted in many situations not yet studied. 

All the techniques to identify soil minerals have difficulty coping with the heterogeneity of soils and with coatings of organic and weathered materials on soil particles, and have trouble detecting small amounts of a component in a veiy large... 

Often, inherent sample heterogeneity of soils and sludge, related to their chemical composition and climatic events, causes problems of representativeness, which largely exceeds those associated to collection. Therefore, the best choice is to collect a sample as large as practical for sample preparation. An extract will be more homogeneous and provide more reproducible aliquots than a smaller portion of the sample. 

Characterising Spatial Heterogeneity of Soils at Anthropogenic Sites the Testfeld Sud... 

Besides electrokinetic transport, chemical reactions also occur at the electrode surfaces (i.e., water electrolysis reactions with production of at the anode and OH at the cathode). Common mass-transport mechanisms like diffusion or convection and physical and chemical interactions of the species with the medium also occur. In a low-permeable porous medium under an electrical field, the major transport mechanism through the soil matrix during treatment for nonionic chemical species consists mainly of electro-osmosis, electrophoresis, molecular diffusion, hydrodynamic dispersion (molecular diffusion and dispersion varying with the heterogeneity of soils and fluid velocity [8]), sorption/ desorption, and chemical or biochemical reactions. Since related experiments are conducted in a relatively short period of time, the chemical and biochemical reactions that occur in the soil water are neglected [9]. 

Gobrecht, A. et al. (2013) Potential of proximal hyperspectral imaging to estimate the spatial and temporal variability of micro-heterogeneity of soil respiration. 16th International Conference on Near Infrared Spectroscopy, La grande Motte, France. 

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