Freshwater alkalinity: 1976-2008

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Toward a world of thirst?ForewordExecutive summary Water and population

1. State of the world’s water

2. Freshwater resources3. Coastal and marine water4. Water and climate change

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Alkalinity is commonly used to indicate a water body’s capacity to buffer against acidity; that is, the ability to resist, or dampen, changes in pH. Thus, alkaline compounds in water, such as bicarbonates, carbonates, and hydroxides, lower the acidity of the water and increase the pH.

Alkalinity (as CaCO3) was analysed for all sampling stations available at the continental level. Concentrations remained reasonably steady between the two decades for Africa, Asia, South America and Australasia, but significant increases were noted for European and North American rivers, which may indicate a shift towards reduced acidic impacts at the continental scale. Overall, during the last 30 years , alkalinity has decreased in North America and Europe, but has significantly increased in Asia.

Examination of the outflow stations in 82 monitored river basins indicate a decrease in bicarbonate concentrations between the two decades , in the northern latitudes, including North America, Europe and Asia. For the period 1976-1990, European rivers displayed the highest concentrations of calcium at a continental level, with concentrations varying between 2 mg and 50 mg per litre for major rivers. Comparing the two decades, observations of surface water showed an increase in calcium concentrations in the Laurentian shield region of North America, and in the rivers of the north central European region.

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