Global Alteration of Riverine Geochemistry under Human Pressure

Riverine geochemistry and material fluxes have already been much altered at the global scale by agriculture, deforestation, mining, urbanisation, industrialisation, irrigation and damming which have generally appeared in this order. The continental aquatic systems (CAS) are now affected by hypoxia, eutrophication, sali-nisation, and contamination by nitrate, metals and persistent organic pollutants. The historical development of these impacts is now being reconstructed by sedimentary archives or assessed by direct measurements for the last 100, 50 or 30 years. The societal responses to these water quality issues can be described by half a dozen typical strategies and their time scales, which generally spread over more than 20 years are controlled by both environmental and societal inertia. Major differences in environmental control efficiencies are expected between industrialized countries, for which control measures adapted to each occurring issue have been gradually set up over last 50 to 100 years, and fast developing countries which are facing these issues in much shorter periods.