Water quality


City Forests has worked with the Otago Regional Council to set up an appropriate water and water course monitoring system for key waterways in the company’s forests.  Semi-permanent sample points are established in streams that are adjacent to impending, current or post-harvesting operations, and are intended to monitor for changes in water or water course quality due to harvesting operations.

Attributes assessed are:

  • Water clarity (SHMAK rating)
  • Water temperature
  • Water conductivity
  • Any evidence of substrate sedimentation
  • Invertebrate types and numbers
  • Condition of riparian vegetation.

Evidence of such monitoring consistently shows the benefits of well managed plantation forests to stream water quality, especially when compared to streams which cross farmland.

Some of City Forests’ plantations form part of Dunedin’s water catchment network, including Flagstaff and Ross Creek forests. This demands diligent monitoring and maintenance of the water quality whenever there is harvesting or roading activity taking place in the catchment.

Currently, thirteen active sample points are established in significant waterways, and in 2017/18 these have been installed or remeasured according to our monitoring protocols.  The water quality was consistently good or excellent as usual apart from two points where water clarity was lower than normal and the conductivity measure was high.  We investigated further and drew the following conclusions about these samples:

  • Both locations, while post-harvest, had been consistently excellent at past measurements.  This time they were measured fairly soon after a recent rainfall, and although still at an acceptable level, the water clarity was down a little because of the recent rainfall.
  • There is otherwise no conclusive evidence of any significant deterioration in water quality due to plantation forestry activity, including some nearby harvesting.
  • All water points with rocky streambeds showed high numbers of indicator invertebrates, which designates good stream health.

Water quality from our thousands of hectares of planted forest consistently remains virtually indistinguishable to that coming from natural forests.  In more than twelve years of routine water quality measurements to June 2018 there has been little evidence of any significant deterioration in water quality in monitored waterways.

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