Abstract

Environment Waikato has been carrying out annual assessments of invertebrate community composition in streams and rivers since 1994 as part of the regional ecological monitoring of streams programme. Sampling has now been of sufficient duration and frequency with consistent collection protocols and invertebrate numbers to enable assessment of temporal trends in ecological condition at 49 sites.

Analysis across all monitoring samples indicated that values for invertebrate metrics were mostly well below/below the average for all samples in Hauraki, as well as upper/middle Waikato and lower Waikato. Several invertebrate-based measures of condition were mostly well above/above average in Taupo, West Coast, Waipa and Coromandel. Habitat quality scores were also below/well below the average in most assessments from lower Waikato, upper/middle Waikato and Hauraki, and above/well above the average in most assessments from Taupo and Coromandel.

Analysis of invertebrate metric values and habitat quality scores in 2005 in relation to landcover indicated highly significant statistical differences, with lower values for sites with adjacent reaches and upstream catchments dominated by pasture compared to indigenous vegetation.

Analysis of trends indicated that ecological condition appears to have been "stable" (inconclusive evidence of change) over the monitoring period at around three-quarters of sites, with the remainder of sites showing statistically and/or ecologically significant evidence of change.

Of the apparently changing sites, around two-thirds showed signs of net declines and one-third showed signs of net increases in overall ecological condition. Relationships between landscape variables and the magnitude of change in invertebrate indicators for sites where declines were deemed probable/clear suggested that the magnitude of decline over time may partly reflect upstream landcover, as well as stream size and landscape position, such that declines appear greater in smaller, lowland streams with higher proportions of upstream catchment development.

Some of the previously-reported trends in water quality among sites within the region are consistent with the patterns observed in invertebrate-based measures of ecological condition at the same sites. Declines in water quality have been largely attributed to changes in landuse, particularly pastoral intensification and land drainage. The effects of these impacts on water and habitat quality are also likely to have contributed to observed patterns and trends in ecological condition based on the invertebrate measures assessed.

Patterns and Trends in the Ecological Condition of Waikato Streams Based on the Monitoring of Aquatic Invertebrates from 1994 to 2005 [PDF, 587 KB]

Contents
Acknowledgements	i
Summary	v
1 Introduction	1
2 Sites	1
3 Methods	6
3.1 Sample collection	6
3.2 Sample processing	7
3.3 Data compilation	7
3.4 Data analysis	7
4 Results	8
4.1 Spatial patterns	8
4.2 Temporal trends	11
4.2.1 Magnitude of change	13
4.2.2 Relationships with environmental factors	13
5 Discussion	15
6 Conclusions	15
References	17
Appendix 1: Spearman rank correlation coefficients between 17 invertebrate community metrics and sampling year in summer	18
Appendix 2: Spearman rank probability values for EPT* richness, %EPT, MCI and ECS (Ecological Condition Score), with probabilities deemed significant using the False Discovery Rate highlighted with **	20
Appendix 3: Plots of selected invertebrate community metrics over time (summer)	21
Appendix 4: Summary of trend classes for four invertebrate metrics at long-term monitoring sites. Probable-clear trends are indicated in bold	26

Patterns and Trends in the Ecological Condition of Waikato Streams Based on the Monitoring of Aquatic Invertebrates from 1994 to 2005

Abstract

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