TAILIEUCHUNG - PHOSPHORUS IN THE ENVIRONMENT: Natural Flows and Human Interferences

Poverty-environment linkages take different forms in rural and urban contexts. In rural areas, critical issues relate to access to natural resources such as land, forests, or fisheries and their sustainable use. In urban zones, the poverty-environment agenda centres on questions relating to the use of natural resources such as water or air as sinks for the disposal of human and industrial wastes, and their impact on the poor. For the sake of analytical clarity, this paper attempts to outline the main linkages between poverty and sustainable development by distinguishing between rural and urban contexts, in order to focus on the unique features of each | Annu. Rev. Energy Environ. 2000. 25 53-88 Copyright 2000 by Annual Reviews. All rights reserved Phosphorus in the Environment Natural Flows and Human Interferences Vaclav Smil Department of Geography University of Manitoba Winnipeg Manitoba R3T 2N2 Canada e-mail vsmil@ Key Words biogeochemical cycling phosphates fertilizers eutrophication Abstract Phosphorus has a number of indispensable biochemical roles but it does not have a rapid global cycle akin to the circulations of C or N. Natural mobilization of the element a part of the grand geotectonic denudation-uplift cycle is slow and low solubility of phosphates and their rapid transformation to insoluble forms make the element commonly the growth-limiting nutrient particularly in aquatic ecosystems. Human activities have intensified releases of P By the year 2000 the global mobilization of the nutrient has roughly tripled compared to its natural flows Increased soil erosion and runoff from fields recycling of crop residues and manures discharges of urban and industrial wastes and above all applications of inorganic fertilizers 15 million tonnes P year are the major causes of this increase. Global food production is now highly dependent on the continuing use of phosphates which account for 50-60 of all P supply although crops use the nutrient with relatively high efficiency lost P that reaches water is commonly the main cause of eutrophication. This undesirable process affects fresh and ocean waters in many parts of the world. More efficient fertilization can lower nonpoint P losses. Although P in sewage can be effectively controlled such measures are often not taken and elevated P is common in treated wastewater whose N was lowered by denitrification. Long-term prospects of inorganic P supply and its environmental consequences remain a matter of concern. contents 1. AN ESSENTIAL ELEMENT OF LIFE . 54 2. BIOGEOCHEMICAL CYCLING OF PHOSPHORUS . 55 Natural Reservoirs of Phosphorus. 57 Annual .

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