Nutrient levels in rivers
Aquatic plants need many types of nutrients for growth, including nitrogen and phosphorus. However, increased levels of these nutrients in water bodies can cause excessive plant growth rates. This can lead to blooms of algae and nuisance weeds. Excessive algal or weed growth can reduce the recreational and aesthetic value of water bodies and affect fish and other aquatic animals.
The level of nutrients in our rivers is influenced by natural factors such as catchment geology, rainfall and river flow patterns. However, land use also has a large influence.
The main source of nutrients in urban waterways is human wastewater (sewage) while in rural environments, agricultural fertilisers and stock manure and urine are the major non-point-sources of nitrogen and phosphorus. Monitoring nutrient levels therefore helps us understand land-use influences on water quality.
The primary indicators of nutrient concentrations are:
Ammoniacal nitrogen is measured as a further indication of overall nutrient levels, and also because this form of nitrogen can be toxic to aquatic animals.
This information has come from the latest state of the environment report Environment New Zealand 2007.
Last updated: March 2009
