After a snap-shot survey of water quality of streams draining various coal
measures carried out in 2000 - 2001, West Coast Regional Council expanded its
monitoring programme to better establish the condition of streams draining coal
mining areas and to characterise the variability of water quality with respect
to stream flow. Samples were collected for water quality indicators such as pH,
sulphate, turbidity, conductivity, temperature and dissolved oxygen as well as
macro-invertebrates, fish and assessments of stream habitat. Water quality
sampling was carried out at 27 sites on 21 streams located from Page Stream near
Seddonville in the north, to Seven Mile Creek near Dunollie in the South, and to
Garvey Creek east of Reefton.
There was relatively low variability of pH, conductivity and sulphate
concentrations at most of the sites sampled. Conductivity and sulphate
concentrations reduced with increasing flow and pH generally increased.
Significant effects on macro-invertebrate and fish populations were identified
at several of the sites where water quality sampling was undertaken. Of the
water quality parameters tested, macro-invertebrates were mostly affected by pH.
Although not sampled directly (conductivity was used as a surrogate) heavy metal
concentration may explain some of the variation in macro-invertebrate
communities. Three creeks affected by mine drainage were sampled for fish and no
fish were present. Fish appear to be more sensitive to acid rock drainage that
invertebrates. Using data from this survey and other studies conducted in the
region, the total length of stream that is actually or highly likely to be
adversely affected by acid rock drainage was estimated at 125 km. This figure is
useful as a gauge as to the magnitude of the issue in this region and for
setting of priorities for remediation. However, as it is only an estimate based
on limited sampling sites, it should be used with caution.