The Victoria River begins in the native forest of the Mangamuka Ranges, and runs north through pasture before joining with the Awanui River near Kaitaia. Approximately two kilometres from the native forest, the site is somewhat affected by pastoral land use, however the catchment is still dominated by indigenous forest. The geology of this site is classified as volcanic acidic in the ‘River Environment Classification' (NIWA & MfE 2004).
The 2005-2006 results for the Victoria 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.)||14.3||10.1 - 19.3|
|Dissolved oxygen (mg/L)||10.1||7.2 – 13.6||100|
|Dissolved oxygen (% Sat.)||97.7||76.8 - 137||33|
|Conductivity (mSm)||16.5||13 - 17.4|
|Water clarity (m)||2.00||0.5 - 2.3||91|
|Turbidity (NTU)||1.1||0.2 – 13.5||83|
|E. coli (n/100mL)||181||19 - 1658||25|
|Dissolved reactive phosphorus (mg/L)||0.017||0.00 - 0.03||25|
|Total phosphorus (mg/L)||0.022||0.01 - 0.036||92|
|Ammoniacal nitrogen (mg/L)||0.005||0.005 – 0.01||100|
|Total nitrogen (mg/L)||0.066||0.051 - 0.203||100|
|pH||7.4||6.7 - 7.9||67|
For the most part, the water quality of the Victoria River is excellent. The median for the majority of parameters are within relevant guidelines and five parameters are within guidelines on at least 11 sampling occasions; dissolved oxygen, water clarity, total nitrogen, total phosphorus and ammoniacal nitrogen.
The parameters of the most concern are dissolved oxygen saturation and dissolved reactive phosphorus. Dissolved oxygen saturation was outside the trigger value range of 98 to 105% on 8 of the 12 sampling occasions, however raw dissolved oxygen levels are consistently above the commonly used guideline of 6 mg/L. The elevated dissolved reactive phosphorus tend to occur during slightly increased flows and are associated with elevated turbidity and bacterial results, and therefore is most likely as a result of land use within the farming catchment.
A positive result at the Victoria River site are long-term trends indicate that nitrate/nitrite nitrogen (NNN) and turbidity levels are declining. However, there is also long term trends indicating that pH is increasing (becoming more alkaline) and dissolved oxygen (% saturation) is increasing. It is unknown at this stage whether these are positive or detrimental trends.