Biogeochemical cycle and exposure pathways in arid ecosystems

Ecosystem Nitrogen Ash species Nitrogen Ash species Nitrogen Ash species 

The biomass of arid ecosystems is significantly less than that of Forest ecosystems and changes from 10 to 25 ton/ha, by dry weight, in Steppe, from 4.0 to 4.5 ton/ha in Desert and from 2 to 3 ton/ha in Extra-Desert Ecosystems of the Central Asia. The overall biomass of Arid Steppe and Desert ecosystems is an order of magnitude less than that of Forest ecosystems (Rodin et al., 1975). 

The ash content of Arid Steppe and Desert ecosystem vegetation is about 2 times higher than that of forest species. Accordingly, the biogeochemical fluxes of elements are similar to those in the forest ecosystems, in spite the smaller biomass (see above). The compartments of biogeochemical turnover in Steppe and Desert ecosystems are shown in Table 1. 

The characteristic biogeochemical feature inherent in all Steppe and Desert ecosystems is the most intensive cycling of different chemical species in comparison with forest ecosystems. For a Steppe ecosystem the biogeochemical cycle is 2-3 years and this means that the complete renewal of all ecosystems biomass takes place over this period. Remember that in Forest ecosystems the biogeochemical cycling is about 3- 25 years and even about 50 years in Forest Swamp ecosystems. The turnover is the highest in Ephemeral Desert and gradually decreases to the north. 

The annual biogeochemical turnover of trace ash elements is calculated in Table 2. 

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