Annual report 2006-2007 - Taranaki Regional Council

26
Biological survey
The Council’s standard ‘kick-sampling’ technique was used at seven sites to collect
streambed macroinvertebrates from the Kahouri Stream and an unnamed tributary
on 17 April 2007. Samples were sorted and identified to provide the number of taxa
(richness), MCI and SQMCIS scores for each site.
The MCI is a measure of the overall sensitivity of the macroinvertebrate community
to the effects of organic pollution in stony streams. It is based on the
presence/absence of taxa with varying degrees of sensitivity to environmental
conditions. It may be used in soft-bottomed streams to detect trends over time. The
SQMCIS takes into account taxa abundance as well as sensitivity to pollution, and
may reveal more subtle changes in communities, particularly if non-organic impacts
are occurring.
Significant differences in either MCI or SQMCIS between sites indicate the degree of
adverse effects (if any) of discharges being monitored.
This summer survey of macroinvertebrate communities in the Kahouri Stream
indicated that the communities directly downstream of the tributary that receives the
Taranaki Abattoirs and Ballance Agri-Nutrients discharges were significantly
different than those upstream. Taxa richness and MCI score were slightly healthier
than median community conditions recorded previously at the ‘control’ site. There
was a significant decrease in MCI and SQMCIS scores at the lower site, which may
have been due to additional instream nutrients supplied by the tributary. This is
likely to be due to the impacts from the abattoir, but this is unclear without further
monitoring. Therefore it is recommended that additional sites be included in
subsequent surveys to assess the impact of the abattoir discharge on this unnamed
tributary.
Further downstream at Flint Road, the macroinvertebrate community remained very
similar in community structure and indicated similar stream ‘health’, although there
was a recovery in the SQMCIS score at this site. None of the rest of the Kahouri
Stream sampling sites further downstream showed any significant adverse effects as
a result of industrial discharges to this catchment, consistent with the absence of any
significant heterotrophic growths on the stream substrate.
The macroinvertebrate communities of the Kahouri Stream were generally
characterised by moderate taxonomic richnesses at the time of this April 2007 survey
despite a period of relatively low flows during the latter part of summer. These
communities continued to support abundances of several ‘sensitive’ taxa at all main
stream sites, from upstream of the Taranaki Abattoir, to the confluence with the
Piakau Stream. All sites had relatively similar communities, particularly in terms of
those taxa characteristic to each site. For example, eight taxa dominated the
communities of nearly all of the six Kahouri Stream sites.
Most MCI scores were similar to historical median MCI scores, and higher SQMCIs
scores than historical medians were recorded throughout the stream. There was some
longitudinal deterioration throughout the catchment, a trend which is usually
present in agricultural ringplain catchments due to non-point source discharges and
is demonstrated by decreasing median MCI and SQMCIs scores in a downstream