Microclimate carbonation

Fragmentation of the Pedemontana Jungle generates microclimate changes at its edge, which could affect the sequestration of the carbon stock. 

An exhaustive field study by Moulton et al. (2000) (see also Moulton and Berner, 1998) quantified plant effects on weathering in western Iceland. The study area includes several adjacent basaltic areas one of which was barren (covered only by sporadic moss and hchens) and the others populated by birches and conifers. All of the areas have similar slopes and microclimate and do not have either acid rain (a problem in the northeastern USA, Europe, and elsewhere) or hydro-thermal activity. Also, calcium carbonate is absent which, because it weathers rapidly, could confuse the results. 

The bulk luminal pH is heavily affected by the fermentation of carbohydrates to short-chain fatty acids however, near the colonic mucosa, the pH rises and changes in the bulk pH have little effect on the epithelial microclimate. Bicarbonate/chloride exchange is partly responsible for raising the pH against the challenge posed by the high colonic pCOi and the acid production by fermentation. The mucus has been shown to contain a distinct carbonic anhydrase, produced by epithelial tissues that help to carefully regulate the thick unstirred layer of the colonic epithelium. 

Figure 5.2 Example of penetration of carbonation in concrete in relation to the microclimate (average of 27 concretes) [5]...

Variability. The examples of Figures 19.1 and 19.2 summarise the process of evaluation of the depth of concrete removal when a single rebar is considered and measurement of carbonation, chloride and cover thickness are available locally. In a real structure carbonation and chloride penetration may vary due to spatial variation of exposure conditions (microclimate) and of concrete properties (e. g. cracking or had compaction), etc. The cover depth may also be very variable. 

Some of the factors affecting film formation and subsequent changes have been analyzed in experiments in recent years in relation to atmospheric exposure and are, therefore, discussed in Chapter 2. In dry air, a film of zinc oxide is initially formed by the influence of the atmospheric oxygen (e.g., at a speed of approximately 40 nm/24 h when a part leaves the galvanizing bath). The subsequent reactions with the atmosphere are complicated and more often than not depend on the local climate or microclimate. Therefore, the formation of an insoluble zinc patina is irregular both in place and in time. But when the zinc surface becomes wet with rain, mist, or dew, the atmospheric carbon... 

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