Spatial pattern in macroinvertebrate communities in headwater streams of New Zealand and a multivariate river classification system : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University, Palmerston North, New Zealand
Macroinvertebrate data collected from 120 headwater streams in New Zealand were used to
test the ability of the Freshwater Environments of New Zealand River Classification
(FWENZ) to explain spatial variation in unimpacted stream invertebrate communities.
FWENZ is a GIS based multivariate river environment classification of the sections of
national river network. The classification performance of the FWENZ was examined to
determine the optimum classification level which could be used for the purpose of
conservation and biomonitoring of New Zealand rivers and streams. The classification
performance of the FWENZ was also compared to those of two other river classification
systems, the ecoregions and the River Environment Classification (REC). Results of the
analysis of similarity (ANOSIM) test showed that discrimination of the study sites based on
interclass differences in macroinvertebrate community composition was optimal at FWENZ
100 class level which classifies the New Zealand rivers and streams into 100 different groups.
The FWENZ 100 class level distinguished the biological variation of the study sites at a finer
spatial scale than the REC Geology level. Although performance of the ecoregions
classification was stronger than both the river environmental classifications, the REC and the
FWENZ, but it was unable to explain the variation in local assemblage structures.
Multivariate analyses of the macroinvertebrate abundance data and the associated
environmental variables at three different spatial scales (upstream catchment, segment, and
reach) were used to identify environmental predictors of assemblage patterns. Catchmentscale
measures of climatic, topographic and landcover factors were more strongly correlated
with macroinvertebrate community structures than segment scale measures, whereas reachscale
measures of instream physicochemical factors and riparian characteristics had the least
association with assemblage patterns. Despite the strong influences of cathment-scale factors
on macroinvertebrate communities, local factors like water temperature, stream velocity,
reach elevation, percent canopy cover and percent moss cover were also involved in
explaining the within-region variation in assemblage patterns, which indicates the importance
of considering regional as well as local factors as surrogates of stream invertebrate
communities to provide a base for stream bioassessment programmes at multiple scales.