Waiarohia Stream is a small stream originating from Pukenui Forest and the Western Hills in Whangarei. The upper catchment is mainly indigenous forest with some exotic forestry. The stream flows through a small area of low intensity farm land with mostly lifestyles blocks, before it reaches residential housing and the central business area of Whangarei. This site is located in the central business area and was added to the RWQMN in 2005-2006 to look at urban influences on water quality. Results for this site can be compared to the upstream site in Whau Valley.
The first year of results for the Waiarohia Stream site at Second Ave 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.)||17.5||12.7 - 24.4|
|Dissolved oxygen (mg/L)||10.8||8.8 - 13.6||100|
|Dissolved oxygen (% Sat.)||111.2||95.6 - 142.6||25|
|Conductivity (mSm)||24.6||14.3 - 37.1|
|Water clarity (m)||1.60||0.21 – 2.60||92|
|Turbidity (NTU)||2.8||1.8 - 63||83|
|E. coli (n/100mL)||507||299 - 9804||0|
|Dissolved reactive phosphorus (mg/L)||0.022||0.006 - 0.042||33|
|Total phosphorus (mg/L)||0.051||0.018 - 0.216||17|
|Ammoniacal nitrogen (mg/L)||0.005||0.005 - 0.03||92|
|Total nitrogen (mg/L)||0.648||0.235 - 1.28||33|
|pH||7.4||7 - 7.7||83|
This is the first year of results so limited conclusions can be drawn at this stage; however the 2005-2006 results highlight several areas of concern in the Waiarohia Stream. The highest temperature of all the RWQMN sites was recorded at this Second Ave site on 18 January 2006 of 24.4°C. It is commonly accepted that water temperatures of greater then 25°C are potentially harmful or even lethal for aquatic biota. It is likely that this site exceeds 25°C on occasion at certain times of the time in the hottest summer days.
Bacterial levels are consistently elevated, with none of the samples meeting the recreational bathing guideline of 126 E. coli/100 mL. Dissolved reactive phosphorus, total phosphorus and total nitrogen are also often elevated with none of their medians for 2005-06 meeting their respective guidelines. The source of the nutrient and bacterial contamination is likely to be surrounding small scale pastoral farming and related to the direct access that stock have to the stream in many places.
Commencing in 2006-2007 sediment samples will be collected and analysed for several indicator heavy metals at this site to better understand the effects of urban land use on water quality.