Biogenic processes

Natural biogenic processes of bacteria, fungi, and cyanogenic plants such as sorghum, soybeans, and cassava, also release cyanide into the soil (Knowles 1988 Towill et al. 1978 WHO 1992). Cyanides (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, or copper(I) cyanide) have been detected in soil samples at 187 of the 406 hazardous waste sites, in sediment samples at 97 of the 406 hazardous waste sites, and in soil gas samples at 1 of the 406 hazardous waste sites where cyanides have been detected in some environmental medium (HazDat 1996). The HazDat information used includes data from both NPL and other Superfund sites. 

Natural emissions of sulfur compounds to the atmosphere occur from a variety of sources, including volcanic eruptions, sea spray, and a host of biogenic processes (e.g., Aneja, 1990). Most of the volcanic sulfur is emitted as S02, with smaller and highly variable amounts of hydrogen sulfide and dimethyl sulfide (CH3SCH3). Sea spray contains sulfate, some of which is carried over land masses. 

Biogenic processes, however, emit reduced forms of sulfur, including dimethyl sulfide and hydrogen sulfide, with lesser amounts of carbon disulfide (CS2), dimethyl disulfide (CH3SSCH3), carbonyl sulfide (COS), and methyl mercaptan (Cl I3SH). These reduced sulfur compounds are then oxidized in the atmosphere as described in detail in Chapter 8.E. 

In addition to hydrocarbons, biogenic processes also produce a number of oxygen-containing organics. One of the most important appears to be 2-methyl-3-buten-2-ol (MBO), first identified in a forested area by Goldan et al. (1993) ... 

In short, biogenic processes produce complicated mixtures of organics that are structurally large and have sufficiently small vapor pressures that they are found primarily or exclusively in airborne particles. While the classes of compounds discussed are typical, there are a variety of other compounds found as well, depending on the particular location, time, etc. For... 

Methane formed by biogenic processes ranges in < 13C from about — 60%c to —85%c, while methane from thermogenic processes ranges from —25%c to —55%c (Hunt 1979, p. 25). 

Infiltrating water, passing the soil zone, becomes loaded with C02 formed in biogenic processes. The water turns into a weak acid that dissolves soil components and rocks. The nature of these dissolution processes varies with soil and rock types, climate, and drainage conditions. Dissolution ceases when ionic saturation is reached, but exchange reactions may continue (section 6.8). 

The production of DMS is almost exclusively through biogenic processes and shows strong seasonal and latitudinal variation (Kettle et al. 1999). DMS mainly results from the enzymatic cleavage of DMSP, a compound that is produced in several groups of marine phytoplankton. A complex network of production and consumption pathways of both DMSP and DMS involves most of the microbial food web (Fig. 1) and determines the concentration of... 

The action of termites, organic matter decay, geological activity, and biogenic processes. 

For the past 1.4x10 years or so, U weathered from igneous, metamorphic, or sedimentary rocks generally has been dispersed in the form of the dissolved ion, or one of its complexes. The reaccumulation of U generally has been facilitated by reduction reactions which result indirectly from biogenic processes. The breakup of pre-existing rocks provided the raw materials for the building of new rocks and those built at, or very near the surface of the earth are sedimentary rocks. There are a number of such rocks where U has become enriched. 

Before exploring the intricacies of reef biogenic processes, we should consider some aspects of reef community structure and zonation. Reefs are comprised of large numbers of spectacular animals, particularly the corals themselves, but the far less conspicuous plants (mostly algae) have a standing crop which exceeds that of the animals. The name coral reef therefore is... 

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