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 2016/17 these have been installed or remeasured according to our monitoring protocols.  The water quality was consistently good or excellent as usual apart from three points where water clarity was lower than we normally see.  We investigated further and drew the following conclusions about these samples:

  • Two locations had a significant influence from adjacent wet farmland and the readings were taken during early winter.  We will relocate for future measurements in order to try and exclude this.
  • One location also had an active natural slip further upstream creating some ongoing sedimentation issues.  There had been no harvesting or other site disturbance at this location yet.
  • The third locaiton, while post-harvest, had been consistently excellent at past measurements.  This time it was measured fairly soon after recent rainfall, and although other indicators were good, the water clarity was down a little because of this rain event.
  • 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 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 eleven years of routine water quality measurements to July 2017 there has been little evidence of any significant deterioration in water quality in monitored waterways.

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