Phosphorus is naturally present in water, primarily as inorganic and organic phosphates. Phosphates can enter aquatic environments in several ways: from the natural weathering of minerals in the drainage basin, from biological decomposition, or as runoff from human activity in urban and agricultural areas.
A comparison of the major watersheds between the two decades showed that northern Europe and North America had lower phosphate concentrations, while the Ganges and Brahmaputra watersheds in south-central Asia had higher concentrations. Nutrient control programmes in municipal and agricultural activities may be key factors in the observed reductions in phosphate concentrations.
Although there are not enough phosphorus data available at the global level to show significant trends, it would seem that some watersheds have improved, while others have declined over the last 20 years as shown in the latest map.