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Waipoua River

The Waipoua River originates in and flows through Waipoua Forest, the home of the legendary giant Kauri Tree, Tane Mahuta on the West Coast of Northland. The river cuts through volcanic soils, and has a predominantly indigenous forest catchment. The Waipoua River site is the only site in the network that is classified as "hill elevation" by the ‘River Environment Classification' (NIWA & MfE 2004) and therefore the results have been compared to the trigger values for an upland river. The Waipoua River is one of the nearest to pristine condition of all the rivers in the network.

The 2005-2006 results for the Waipoua River site are summarised in the table below including the median, range and percentage of sampling occasions that comply with relevant guidelines for the 12 sampling occasions. Medians shown in red are outside the recommended guidelines.

Parameter Median Range % comply with guideline
Temperature (deg. cel.) 13.6 9.3 - 17.9
Dissolved oxygen (mg/L) 10.8 9.2 - 11.9 100
Dissolved oxygen (% Sat.) 101.8 96.3 - 106 75
Conductivity (mSm) 9.9 7.2 - 11
Water clarity (m) 2.44 1.02 - 3.85 100
Turbidity (NTU) 1.8 0.9 - 4.4 100
E. coli (n/100mL) 25 10 - 359 92
Dissolved reactive phosphorus (mg/L) 0.018 0.002 - 0.24 33
Total phosphorus (mg/L) 0.025 0.008 - 0.375 75
Ammoniacal nitrogen (mg/L) 0.005 0.005 - 0.03 92
Total nitrogen (mg/L) 0.076 0.054 - 0.524 100
pH 7.5 6.8 - 7.9 75

The results confirm that Waipoua River remains in a relatively pristine condition. The medians of all parameters, except for dissolved reactive phosphorus, were within their relevant guideline for an upland river. Also the majority of parameters met the guidelines on either 11 or all of the 12 sampling occasions. The median dissolved reactive phosphorus of 0.018 mg/L slightly exceeds the trigger value for the protection of aquatic ecosystems for an upland site of 0.009 mg/L.

The slightly elevated dissolved reactive phosphorus levels at this site are a concern, as this is the first year that elevated levels have been detected and the guideline was exceeded on eight of the 12 sampling occasions in 2005-2006. This will be investigated further, to identify potential sources of contamination.

The Waipoua River site was only added to the network in 2002, meaning there will not be adequate data available for long-term trend analysis until the end of 2006-2007. However it is clear from the four years data currently available that water quality in Waipoua River is excellent, with consistently good water clarity and dissolved oxygen, and low nutrient levels.