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Waitangi River at Waimate North

The Waitangi River originates just east of Lake Omapere, and flows into the Bay of Islands. There are two sites on Waitangi River in the Regional Council's river network; one in the upper to mid reaches at Waimate North and the other in the lower reaches at Watea. At the Waimate North site, the catchment is a mix of beef, sheep and dairy farming, with significant areas of indigenous forest in the headwaters. The underlying geology is predominantly acidic volcanics.

The 2005-2006 results for Waitangi River at Waimate North 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.) 14.9 10.6 - 20
Dissolved oxygen (mg/L) 10.1 9.1 - 12.7 100
Dissolved oxygen (% Sat.) 99 70.7 - 114.2 50
Conductivity (mSm) 9.35 8.7 - 12.9
Water clarity (m) 1.53 0.36 - 2.62 90
Turbidity (NTU) 3.05 1.6 - 55 75
E. coli (n/100mL) 565 166 - 4611 0
Dissolved reactive phosphorus (mg/L) 0.003 0.002 - 0.012 92
Total phosphorus (mg/L) 0.022 0.014 - 0.101 92
Ammoniacal nitrogen (mg/L) 0.01 0.005 - 0.03 92
Total nitrogen (mg/L) 0.551 0.257 - 0.871 75
pH 7.1 6.8 - 7.6 42

In general, water quality in Waitangi River at Waimate North is quite good with nutrient levels elevated above the guidelines on only a few occasions in 2005-2006. Similarly to last financial year, only the median for E. coli and pH were not within accepted guidelines. In fact, the bacteria E. coli exceeded the bathing guideline of 126 per 100mL on all sampling occasions.

A median as high as 565 E. coli per 100 mL and consistently elevated results indicate that intermittent sources of E. coli such as leaking septic tanks, or stock with access to the river may be more of a problem at this site than surface run-off. Restricting stock access and encouraging the maintenance of septic tanks can reasonably easily mitigate these sources.

Like last year, although only significant at a 90% confidence level (not shown on the table in the trends section of this report) there is a long term trend suggesting that bacterial levels are increasing at the Waimate North site. The trend suggests that
E. coli
counts are increasing at a rate of 38/100mL per year.

There was also a long term trend suggesting that pH is increasing at this site by 0.1 pH units/year. Although in general it is not known whether an increase in pH is beneficial or detrimental, it is likely at this site that an increase in pH is beneficial, as pH levels were often below the optimum pH range for the protection of aquatic ecosystem in 2005-2006, never above.