Annual report 2006-2007 - Taranaki Regional Council

MCI value
Number of taxa and MCI values in the Kahouri Stream 20 u/s Piakau
Stream confluence (KHI000480)
140
120
100
80
60
40
20
0
Jan-88
Jan-89
Jan-90
Jan-91
Jan-92
Jan-93
Jan-94
Jan-95
Jan-96
Jan-97
Jan-98
Jan-99
Jan-00
Jan-01
Jan-02
Jan-03
Jan-04
Jan-05
Jan-06
Jan-07
MCI value M edian M CI to date
No. of taxa M edian no. of taxa to date
Figure 10 Number of taxa and MCI values in the Kahouri Stream at site N (KHI000480)
Very few significant differences in individual taxon abundances were found between
adjacent sites G and N. However, subtle decreases in abundances of certain ‘sensitive’
mayfly and cranefly taxa and increases in ‘tolerant’ midges resulted in a decrease in SQMCIS
score of 0.6 units between sites. The MCI score was similar to the score recorded at site G
upstream. The MCI and SQMCIS scores were also similar to their respective medians (Table
2).
Summary and Conclusions
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,
where taxa richness and MCI score were slightly healthier than median community
conditions recorded previously at this ‘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.
13
70
60
50
40
30
20
10
0
No. of taxa