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the average CÜ2-concentration in the atmosphere outside the forests. It is seen in Fig. 3.31B,C that there are also vertical gradients of 813C of the air and of the leaf biomass (Buchmann et al. 2004; see also Sect. 2.5).

3.4.4 Mineral Nutrients 3.4.4.1 Inorganic Nutrient Cycling

When we consider inorganic nutrient cycling in tropical forests we must include, of course, the soil. It is frequently assumed that the major portion of minerals in wet tropical forests is bound in the living biomass. This is not always true and the soil may contain a considerable fraction of the minerals in the ecosystem. It is often the soil which is the most vulnerable part in tropical forests. Exposed by unbalanced logging systems or methods of shifting agriculture it may rapidly become oxidized and eroded. With vegetation and soil we obtain a conspicuous vertical structure (Figs. 3.32 and 3.33). Mineral nutrients show variability over the horizontal strata of forests, because interaction with leaves and stems causes precipitation to become enriched in nutrients and the throughfall of rain and the stemflow in the forests show much higher concentrations of most mineral ions than the rain water itself (Table 3.2).

An example of inorganic nutrient cycling in a wet tropical forest is given in Fig. 3.32. Input of minerals to the soil is via rain, canopy leaching with throughfall and stemflow (see also Table 3.2) and via litter fall (see also tables on page 232 and Fig. 10.2, page 277 in Richards 1996).

Table 3.2 Mineral nutrients in rainwater, throughfall and stemflow. (A) Average nutrient concentration in rainwater and annual input in several tropical locations throughout the world. (Data from Medina and Cuevas 1994) (B) Values measured in a forest in Central-America. (Data from Junk and Furch 1985)

Table 3.2 Mineral nutrients in rainwater, throughfall and stemflow. (A) Average nutrient concentration in rainwater and annual input in several tropical locations throughout the world. (Data from Medina and Cuevas 1994) (B) Values measured in a forest in Central-America. (Data from Junk and Furch 1985)

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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