Biogeochemical Processes

Urbanization affects Earth's ecosystems by changing fundamental processes that control the cycling of elements. Biological, hydrological, atmospheric, and geological processes play essential roles in terrestrial biogeochemical cycles by regulating the synchrony between release and uptake of nutrients by microorganisms and plants (NRC 1986, Melillo et al. 2003, Dahlgren 006). Across multiple scales from molecular to the entire ecosystem level, biological processes regulate nutrient cycles by providing fuel and materials to Earth's ecosystems. Humans have altered biogeochemical processes in fundamental ways, by burning fossil fuels, changing land uses, extracting metals, and producing and applying synthetic chemicals (Figure 6.1) (Vitousek et al. 1997).