Some factors (such as global population growth) will begin to decline in importance and others (distribution of people, climate change, and changes to nutrient cycles) will gain more importance in the near future.

Nutrient loading is projected to become an increasingly severe problem, particularly in developing countries. Nutrient loading already has major adverse effects on freshwater ecosystems and coastal regions in both industrial and developing countries.

Unsustainable practices in irrigation and production may lead to increased salinization of soil, nutrient depletion and erosion. An estimated 950 million ha of salt-affected lands occur in arid and semi-arid regions, nearly 33% of the potentially arable land area of the world. Globally, some 20% of irrigated land (450,000 km2) is salt-affected, with 2,500–5,000 km2 of lost production every year as a result of salinity (UNEP, 2008).

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...

Nutrients are essential to life. In aquatic systems, nitrogen and phosphorus are the two nutrients that most commonly control the growth of aquatic plants, algae and bacteria. Nitrogen and phosphorus are considered to be the primary drivers of eutrophication of aquatic ecosystems, where increased nutrient concentrations lead to increased primary productivity. Some systems are naturally eutrophic, whereas others have become eutrophic as a result o...

This graphic illustrates the strong link between areas with high densities of industrial activity and zones of seasonally oxygen-depleted waters. There is a strong link between areas with high densities of industrial activity and zones of seasonal oxygen-depleted waters. In recent years there has been an increasing focus on treating and reducing municipal and industrial waste, and on reducing nitrogen levels in agricultural runoff. However, less...