ABSTRACT
Humans make an increasingly material impact on the stores and fluxes in the biogeochemical cycles at local, regional and global scales. In doing so, they have themselves become a potent driver of global change, largely through activities related to food production, urbanization, industrialization and water management. Humans affect global biogeochemical cycles, including the carbon, nitrogen and sulphur cycles; they mobilize such metals as arsenic and mercury. The chief human-induced drivers that affect element interactions are agricultural intensification and extent, urbanization and industrialization, atmospheric chemistry, and species introductions, species harvesting and species losses. Dams have impacts on ecosystems upstream and downstream as a result of flooding, flow manipulation, and the fragmenting of river habitats. Land clearance, most land-use change and land disturbance cause an increase of sediment loads. The water cycle involves stores and fluxes of water as ice, liquid and vapour. Modification of the water cycle can lead to areas drying up, as in the case of the Aral Sea.
