Humus stability

The importance of the final settling, or humus, tank can be seen by an examination of what occurs in the trickling filter itself. A new filter is broken in by applying settled sewage as in the normal operation. After a period of time the microbial, or zoogleal, mass forms on the filter medium and stabilizes the waste. Waste material is first adsorbed, and then assimilated by the microorganisms. 

The lysimeter was located next to the landfill Teuftal in Muhlcberg (Canton Berne). It was constructed in the winter of 1990/1991 (AGW 1991 Ochs et aL 1999) and dismantled in December 1997. The lysimeter had two compartments, one containing cement-stabilized APC residues in the form of cubic blocks with an edge length of 0.5 m. This compartment was approximately 1.5 m deep with an area of 15-16 m2. The space around the edge and between the cement blocks (around 1 cm) was filled with sand. The compartment was covered with geotextile, gravel (0.8 m), and humus (0.3 m) layers. The cement-stabilized APC residue blocks were composed of APC residues (41%), Portland cement (22%), water (32%), and NaOH (3%). 

Stott, D. E., Martin, J. P., Focht, D. D. Haider, K. (1983). Biodegradation, stabilization in humus, and incorporation into soil biomass of 2,4-D and chlorocatechol carbons. Soil Science Society of American Journal, 47, 66-70. 

Swaby, R. J., and Ladd, J. N. (1966). Stability and origin of soil humus. In The Use of Isotopes in Soil Organic Matter Studies, Int. Atomic Energy Agency Pergamon Press, Oxford, pp. 153-159. 

Soil and related environments are both an important natural habitat of biota and a natural reservoir of biotic debris consisting of plant remains and dead animals and microorganisms. With time, dead remains are subject to continuous turnover, either mineralized or transformed to diverse organic components which are termed humus. This process is referred to as humification. Humus is composed of humic substances plus nonhumic substances that have become stabilized and are thus an integral part of soil and related environments (Table 2.1). 

Martin, J. R, and Haider, K. (1980). Microbial degradation and stabilization of 14C-labeled lignins, phenols, and phenolic polymers in relation to soil humus formation In Lignin Biodegradation Microbiology Chemistry and Potential Applications, Vol. II. Kent-Kirk, T., Higuchi, T., and Chang, H., eds., CRC Press, Boca Raton, FL, pp. 77-100. 

Stabilization of the soil makes nutrient humus available development of soil organisms nitrogen enrichment (legumes) soil is loosened by the roots deeper-lying nutrients are made available (P) provides shade and thus optimizes soil tilth inhibition of weed growth protection from erosion... 

The second major ecosystem role of decomposition is in the formation and stabilization of humus. The cycling and stabilization of SOM in the litter-soil system is presented in a conceptual model in Figure 2. Parallel with litterfall and most root turnover, detrital processing is concentrated... 

SOM is composed of a continuum of organic resources from fresh plant residues to stabilized organic matter (OM) or humus (Stevenson, 1994). Although this definition of SOM includes intact plant litter, in this review we will often distinguish between decomposition of litter on the soil surface and decomposition/stabilization of OM within the mineral soil. Within the mineral soil, SOM is often divided into four categories the light fraction, microbial biomass (discussed above), dissolved organic matter (DOM), and stable humic substances. 

The unusual thickness of the mollic and umbric horizons is caused by the accumulation of several paleosols formed from the multiple eruptions of two nearby volcanoes and by the stability of the humus-amorphous material complex. 

The MRTs of individual humus fractions also vary, as can be seen from Table 8. The MRT of the original soil (Melfort silt loam) was 870 years whereas the MRTs of individual fractions ranged from 25 to 1410 years. For both humic and fulvic acids, the acid hydrolyzable fractions (6A HCl for 18 hours) had lower MRTs than the nonhydrolyzable fractions. This result is in accord with expectations, because the hydrolyzable material would include the carbon of readily decomposable substrates (e.g., carbohydrates and amino acids). Stability of the major humus fractions followed the order humin = humic acid > fulvic acid (Campbell et al., 1967a). 

Now we are ready to consider the practical application of metal-ligand stability constants to metal adsorption on organic matter. First we will take the case of a metal-humus system that is undersaturated with respect to the metal hydroxide. 

In this case, will be used to exemplify metals strongly predisposed toward precipitation as well as complexation with humus. Like Cu ", AP complexes energetically with catechol-type and other polyphenolic ligands. The stability constant, ATail for the solution reaction ... 

Copper occurs in soil solids and solutions almost exclusively as the divalent cation Cu ". However, reduction of Cu " (cupric) to Cu (cuprous) and Cu (metallic copper) is possible under reducing conditions, especially if halide or sulfide ions ( soft bases) are present to stabilize Cu" (a soft acid). Copper is classified as a chalcophile, owing to its tendency to associate with sulfide in the very insoluble minerals, CU2S and CuS. In reduced soils, then, copper has very low mobility. Most of the colloidal material of soils (oxides of Mn, Al, and Fe, silicate clays, and humus) adsorb strongly, and increasingly so as the pH is raised. For soils with high Cu accumula-... 

Humins (humus coal) are soluble neither in alkalies nor in acids. This group in humic substances have been very little investigated. They are characterized as an insoluble form of humic acids. Humins are considered as the oldest, and ultimate products of the humification process. They are assumed to be strongly carbonized substances, where the high stability is increased by a strong bond to the mineral fraction. Due to their high chemical stability or even inert character, humins do not participate in the soil formation process and they do not fulfil the function of the true humus. 

Conclusions. The processes and the rates of decomposition of OM of marine and fresh phytoplankton in the sea and in fresh water are virtually identical. Temperature changes considerably influence the rate of decomposition. The amount of the dissolved OM in water tends to increase towards the end of the experiment. This is, probably, a refractory OM or water humus of planktonic origin. The remaining non-degradable particulate OM (detritus) also shows a relatively h h stability. 

The analysed data on carbon content and also on content of organic N and P in dissolved and particulate state at the end of all the experiments illustrate the stability of OM. The experiments simulate accumulation of resistant insoluble and soluble organic compounds in reservoirs and soils. These compounds appear as the result of decomposition of dead living matter and its living excretions. The processes are not only responsible for transformation of initial OM (oxidation, polymerisation, condensation), but also for synthetic processes, caused by bacterial activity (Kononova, 1963), and this is the water humus of planktonic origin. 

Buried archaeological wood is the same as ancient wood (often called paleontological wood). Both have been deposited in natural environments and have undergone changes there. Normally these changes would eventually turn the wood to dust, humus, or coal, or would mineralize it, depending on the environment of the burial site. But occasionally the wood appears to be stabilized in a strata, like a buried time capsule. It reaches an equilibrium within the strata s unique environment that allows the wood to apparently survive. 

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