Introduction
In Chapter 22, we reviewed the cycling of nutrients within ecosystems associated with biological uptake and decomposition. The movements of these biologically important elements are linked at a global scale that transcends ecological boundaries at the ecosystem and biome scales.
Ecological processes at the ecosystem scale (e.g., net primary production, decomposition) influence global phenomena (e.g., climate via greenhouse gas emissions and uptake). In addition, the realization that humans are increasingly changing the physical and chemical environment at a global scale has fostered a greater awareness of ecology at these larger spatial scales. Emissions of pollutants, dust, and greenhouse gases into the atmosphere have caused widespread environmental problems, including climate change, acid precipitation, eutrophication, and loss of stratospheric ozone. A major focus of global ecology is therefore the study of the extensive environmental effects of human activities.The first part of this chapter will cover the global-scale cycles of chemical elements, which are influenced by, but distinct from, the ecosystem-scale cycles covered in Chapter 22. Knowledge of these cycles is important for understanding global environmental change. Humans have had profound effects on these element cycles; for example, human activities now dominate the global nitrogen cycle (Fowler et al. 2015). We will review the environmental changes associated with anthropogenic effects in the remaining sections.