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The Effects of Water Supply Intakes on Macroinvertebrate Communities in the Waikato Region during Summer 2008

TR 2008/41
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Report: TR 2008/41

Author:Alex James, Zoë Dewson (F.I.S.H Aquatic Ecology)

Abstract

As an extension of a previous study in summer 2006-2007, we sampled macroinvertebrates from small, stony streams above and below water intakes in predominantly native forest catchments in mid-February 2008.

The previous study had found that with a few exceptions, water takes at these sites had little impact on stream macroinvertebrate communities over the summer low flow period. However, there was a rainfall event prior to the second sampling that may have influenced this finding. This study compares the new data (February 2008) to that collected in December the previous summer (2006).

Sites downstream of water takes generally had lower water velocity, depth and wetted width than upstream sites at the time of sampling, but this varied considerably among streams.

Decreases in flow had little or no effect on spot measurements of water temperature, conductivity, pH or dissolved oxygen. There was no overall consistent response of chlorophyll a concentrations to water abstraction in either December 2006 or February 2008, but variable differences between upstream and downstream sites in individual streams.

There was no consistent relationship between the volume of water removed and upstream-downstream changes to invertebrate density, number of taxa, percentages of Ephemeroptera, Plecoptera and Trichoptera taxa and individuals, MCI or QMCI relative to December 2006. The greatest changes to invertebrate metrics were seen in two streams that had some of the largest abstractions. However, another stream with an equally large abstraction showed minimal change to the invertebrate community between upstream and downstream, and significant changes to the invertebrate community were observed in a stream with a small take.

Despite minimal changes to invertebrate density downstream of water takes, declining wetted widths suggest that the overall abundance of benthic invertebrates would have decreased at the reach scale.

The impact of water removal on small, stony streams in forested catchments appears to be site specific, making it difficult to predict its effect on benthic macroinvertebrates based solely on abstraction volume.

The Effects of Water Supply Intakes on Macroinvertebrate Communities in the Waikato Region during Summer 2008 [PDF, 1.3 MB]

Table of contents

  Acknowledgements i
  Executive summary vi
1 Introduction 1
2 Methods 2
2.1 Study sites 2
2.2  Survey design 10
2.3 Sampling protocols 10
2.4  Data analysis 11
3 Results 11
3.1 Physicochemical characteristics 11
3.2 Periphyton biomass 14
3.3 Invertebrate community diversity 16
3.4 Invertebrate community composition 23
3.5 Invertebrate metrics and abstraction volume  25
4 Conclusions  27
  References 30
  Appendix 1. 32
  Appendix 2. 33
  Appendix 3. 34
  Appendix 4. 39
  Appendix 5. 41