River and stream water quality and ecology - Greater Wellington ...

River and stream water quality and ecology in the Wellington region: State and trends
MCI scores at RSoE sites showed a strong positive correlation with both
habitat quality and water quality, and a strong negative correlation with
periphyton biomass. Multivariate analysis of macroinvertebrate community
composition and environmental data suggested that TKN and substrate size
were the environmental variables most strongly correlated with changes in
macroinvertebrate community composition across the 55 RSoE sites.
Significant trends in one or more macroinvertebrate metrics were exhibited at
16 RSoE sites between 2004 and 2011. Most of these sites (13) exhibited
trends of deteriorating macroinvertebrate health. In most cases the reasons for
these trends were unclear although at some sites deteriorating trends coincided
with deteriorating water quality (Whangaehu River 250 m from confluence),
increasing periphyton biomass (Ruamahanga River at Gladstone) or a potential
increase in streambed sedimentation (Whareroa Stream at Waterfall Road).
Similar to the trends in periphyton growth reported in Section 5.2.2, high river
flows, short accrual periods and corresponding high macroinvertebrate metric
scores at the start of the trend analysis period (2004 and 2005) may have
influenced some of the deteriorating trends.
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