We monitor the river nutrient sources as an indicator of the effects human activities have on our rivers. Nutrient loads from people’s activities can affect how suitable our rivers are for aquatic plants and animals to live in. They can also affect their suitability for swimming.
This indicator is a measure of the annual average input of nutrients to rivers from:
Loads (amounts) of nutrients are expressed per hectare of catchment. This is to allow comparison between point and non-point sources of nutrients and between catchments of different sizes. At this stage, the indicator is restricted to the plant nutrients nitrogen and phosphorus in three of the larger rivers in the Waikato region.
Generally, the background (natural) loads of the plant nutrients nitrogen and phosphorus in our rivers are low.
Most of the nutrients in our water come from human activities, which can be separated into point and non-point sources.
Nitrogen loads from point sources are low in the four major Waikato rivers and are similar to background levels. But the nitrogen loads from non-point sources are high, particularly in the intensively farmed Waihou, Waitoa and Piako River catchments. The loads tend to be highest in areas of intensive dairy farming.
Usually, the phosphorus loads from point sources and non-point sources on developed land are similar to the background loads. But during 2000 - 2009, the point source load of phosphorus to the Waitoa River was particularly high. In 2009, the load fell to about one-quarter of that shown in the graph below because of changes in waste water management at a site on the river.
There are no plans to update this indicator at present.
Water Quality Scientist - Science and Strategy Directorate