Annual report 2006-2007 - Taranaki Regional Council

45
ecosystems at similar hardness (30 g/m 3 CaCO3) (Figure 16 and Table 12). Elevated
zinc levels have been recorded at this site in the past (Figure 16) but have been below
guideline values since 1999.
Zinc (g/m 3 )
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
Zinc concentrations in tributary of Kahouri Stream
upstream of Kahouri confluence (KHI000369)
Jun-91
Jun-92
Jun-93
Jun-94
Jun-95
Jun-96
Jun-97
Jun-98
Jun-99
Jun-00
Jun-01
Jun-02
Jun-03
Jun-04
Jun-05
Jun-06
Zinc - acid soluble Zinc - dissolved ANZECC USEPA
Figure 16 Zinc concentrations in tributary upstream of confluence with Kahouri Stream
Biological survey
A macroinvertebrate sample was collected from site D (Figure 1) in the tributary 800
m downstream of Taranaki Galvanizers on 17 April 2007. The sample was 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.
The stream at this site had a cloudy flow, with substrate comprising hard clay and
tree roots. Prior to the survey there was a reasonable period of flow recession, being
93 days since a flood in excess of 3 times median flow had occurred.
Site D in the Kahouri Stream tributary would be expected to support ‘poorer’
macroinvertebrate communities than those of the Kahouri Stream due to the clay
substrate, but in this survey the community contained many ‘sensitive’ taxa and had
relatively high MCI and SQMCIs scores, indicating no detrimental effects from
discharges in the Stratford industrial area in the upper part of the tributary which
includes discharges from Taranaki Galvanizers, Egmont Tanneries and Firth
Industries.
A full biological report is given in Appendix II.