Biogeochemical and exposure peculiarities of tropical soils

The Seasonal Tropical Forest and Woody Savanna ecosystems are common in tropical regions with a short dry period. The characteristic features of soils from these ecosystems are the neutral reaction of soil solution and periodic leaching during wet season. The herbaceous species favor the formation of both sward and humus horizons. 

Different conditions are typical for Dry Tropical Wood, Dry Savanna and Dry Woody Shrub ecosystems in areas with precipitation rates of 400-600 mm and a prolonged dry season. The microbial activity is suppressed during a dry season. The soils of these ecosystems have no even periodic leaching, the formation by transpiration of a biogeochemical barrier in the upper soil layer favors the alkaline reaction and accumulation of soluble salts. This decreases also the intensity of exposure to different pollutants for living organisms. 

Heavy metals Content in Clark content humus horizon Clark content Content in humus horizon 

The example of these relationships with the ancient geological rocks is shown in Table 3. 

Both of the soils are enriched in various elements, like zirconium, titanium, beryllium, niobium, and strontium, due to their enlarged content in the alkali basalts and phonolites of the East-African Rift. We can see that soils of Tanzanian Dry Savanna ecosystems contain niobium 11 times, beryllium and molybdenum 6 times, and titanium and zirconium 4 times as high as compared to the respective crust concentrations (darks) of these metals. In the Ugandan soils, the chromium content is 7 times higher 

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