The Awanui River originates from Raetea Forest (Mangamuka's) and meanders north for a significant distance through pasture and the Kaitaia township, eventually flowing into the Rangunu Harbour. There are 3 sites on the Awanui River system in the network; one in the upper reaches on Victoria River, one in the mid reaches at the FNDC water take and the last one in the lower reaches directly above Waihue channel. The FNDC water take from the Awanui River is beside State Highway 1, just south of Kaitaia. The upstream catchment is predominantly pastoral land use, with some semi-forested tributaries such as the Victoria River. Most of the river's bottom is made up of soft sediments, and riparian planting varies from non-existent to quite dense.
The 2005-2006 results for the Awanui River at the location of the FNDC water take 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.)||16.2||11.3 - 21.8|
|Dissolved oxygen (mg/L)||8.3||5.3 - 11||92|
|Dissolved oxygen (% Sat.)||84.7||59.2 - 120.5||0|
|Conductivity (mSm)||19.7||15.5 - 20.8|
|Water clarity (m)||0.60||0.4 - 1.5||55|
|Turbidity (NTU)||6.0||1.5 - 47||50|
|E. coli (n/100mL)||304||104 - 3654||8|
|Dissolved reactive phosphorus (mg/L)||0.019||0.006 - 0.033||8|
|Total phosphorus (mg/L)||0.046||0.02 - 0.118||25|
|Ammoniacal nitrogen (mg/L)||0.005||0.005 - 0.01||100|
|Total nitrogen (mg/L)||0.278||0.101 - 0.636||92|
|pH||7.5||6.9 - 8.1||75|
Similarly to the last two years the nitrogen concentrations were satisfactory, however dissolved oxygen saturation, phosphorus, turbidity, water clarity and E. coli failed to meet the guidelines. Some of these elevated results coincide with elevated flows and therefore are most likely as a result of surface run-off during rainfall events. However some of the spikes in E. coli and phosphorus cannot be as easily linked to rainfall events. This contamination could be as a result of leaking septic tanks or stock with access to the river.
Improved riparian management will assist with mitigating some of these elevated results, by restricting stock access, and reducing excess run-off. Better maintenance of septic tanks within the catchment is also likely to reduce the number and size of contamination events. Another potential source of phosphorus is inefficiently applied fertiliser. Accurate nutrient budgeting and appropriate application can reduce the amount of fertiliser wasted by being washed into streams.
This site was only established in March 2002 and therefore there will not be sufficient data to carry out trend analysis until the end of the 2006-2007 financial year.