Biochemical weathering

Differences in the hydrologic characteristics for the upper and lower portions of Twelve Mile Creek and for Lake Hartwell are believed to have a significant effect on physiochemical and biochemical weathering processes. The upper portion of Twelve Mile Creek (0-32 km) is characterized by relatively shallow waters and high water velocities. In the lower portion (32-39 km), the creek deepens and widens because of the impoundment of Lake Hartwell. Water velocities are much slower in this portion of the creek, and a significant portion of the solids load is deposited in the sediments. Flow from Twelve Mile Creek eventually enters the top of Lake Hartwell, where it mixes with uncontaminated waters from the Keowee River. The waters then move slowly down this 50-km-long reservoir toward the Hartwell Dam. 

Field Evidence of Biochemical Weathering. PCB congener composition variation with depth in sediment was analyzed for evidence of bio-... 

In situ reductive dechlorination has been cited as an important pathway for biochemical weathering of PCBs in sediments (2, 5). The reductive dechlorination hypothesis is based on the premise that microbial action on PCB congeners is sterically selective for the chlorines in the meta and para positions on the biphenyl rings (i.e., 3, 3, 4, 4, 5, and/or 5 ). Such selectivity would result in the cleaving of the chlorines in these positions (5). If this process occurs, the terminal dechlorination products of the microbially resistant ortho-substituted congeners in the anaerobic environment should be 2,2 -DCB, 2,6-DCB, 2,2, 6-TrCB, and 2,2, 6,6 -TCB. Thus, the weight... 

While chirality is a powerful tool for detecting and understanding biochemical weathering processes in the environment, some caveats and precautions should be kept in mind. First, a compound must be asymmetric in order for chirality to be used. Thus, while extrapolations to structurally similar compounds may be plausible [194], such interpretations must be made cautiously in light of the variability in enantiomer behavior of even structurally similar chemicals. An example of such variability is the observation of enantioselective degradation of PCB 136 by rainbow trout, while structurally similar PCB 95 was not degraded [227,232]. 

Jackson T. A. and Voight G. K. (1971) Biochemical weathering of calcium-bearing ntinerals by rhizosphere microorganisms, and its influence on calcium accumulation in trees. Plant Soil 35, 655-658. 

Among the subcycles shown in Fig. 3.1.1, all involve organisms other than man except the following phosphorites superphosphates, phosphorite igneous and metamorphic rocks, and phosphorites detergents. The path between igneous and metamorphic rocks soil and mantle rock involves biochemical weathering as does phosphorites soil and mantle rock. It has been known for many years that phosphorites are more soluble in humic acids, and phosphatic fertilizers are rated on their citric acid solubilities. 

Methods to estimate the biochemical weathering of minerals in soils... 

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