The Whakapara River originates from the ranges east of Hikurangi and Whakapara, to eventually mix with the Waiotu River, forming the headwaters of the greater Wairua River. The river cuts through hard sediments formed from faulted greywacke, along a relatively low gradient. The site is located in a beef and sheep farm near State Highway one, with an upstream catchment dominated by forested hills and pastoral farming.
The 2005-2006 results for the Whakapara 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.)||15.8||11.2 - 21.1||-|
|Dissolved oxygen (mg/L)||10.2||8.6 - 12.8||100|
|Dissolved oxygen (% Sat.)||102.5||82.5 - 120||33|
|Conductivity (mSm)||9.2||6.8 - 10.2||-|
|Water clarity (m)||1.62||0.2 - 2.33||90|
|Turbidity (NTU)||4.4||2 - 106||75|
|E. coli (n/100mL)||174||73 - 24192||25|
|Dissolved reactive phosphorus (mg/L)||0.030||0.014 - 0.059||0|
|Total phosphorus (mg/L)||0.056||0.038 - 0.361||0|
|Ammoniacal nitrogen (mg/L)||0.02||0.005 - 0.12||50|
|Total nitrogen (mg/L)||0.47||0.207 - 1.53||75|
|pH||7.2||6.5 - 7.5||50|
Both total phosphorus and dissolved reactive phosphorus in Whakapara River in 2005 –2006 were elevated on all sampling occasions, with no samples meeting the guideline values. Although they were consistently high they did also appear to be related to flow.
Although the medians for dissolved oxygen (% saturation), and E. coli met their respective guidelines, there are several sampling occasions that they did not. Similarly to the phosphorus results these tend to occur in conjunction with elevated flows. The effect of runoff could be minimised with appropriate riparian management such as fencing and planting of a buffer strip of vegetation.
There are long term trends suggesting that both dissolved oxygen (mg/L) and DO percentage saturation are increasing in Whakapara River. This could be related to an increase in the biomass of oxygen weed and other macrophytes in the river. It is unknown whether this is a detrimental or positive trend, as dissolved oxygen levels can be both below and above the optimum range for the protection of aquatic ecosystems.
Other significant long term trends in Whakapara River include an increasing pH, decreasing turbidity with a corresponding increasing trend in water clarity and decreasing trend in nitrite/nitrate nitrogen (NNN) levels, which are all seen as improving trends.