Braided river ecology: a literature review of physical habitats and aquatic invertebrate communities / Duncan Gray and Jon S. Harding.

Keywords: Braided rivers, benthic invertebrates, geomorphology, springs, diversity, groundwater.

Includes bibliographical references (p. 38-48)

1. Introduction -- 2. The habitat template: physical conditions within a braided river -- 3. Floodplain habitats of braided rivers -- 4. Invertebrate communities -- 5. A holistic perspective on braided rivers -- 6. Threats and pressures -- 7. Recreation and landscape values -- 8. Management implications and future research -- 9. Conclusion -- 10. Acknowledgements -- 11. References -- Appendix 1 Studies included in the meta analysis of braided river main channel invertebrate communities -- Appendix 2 Studies included in the analysis of braided river spring invertebrate communities.

A braided river is one that, over some part of its length, flows in multiple, mobile channels across a gravel floodplain. In New Zealand, many braided rivers remain in a relatively unmodified condition, but increasing demands for hydro-electricity generation, irrigation, gravel extraction and flood protection works are placing pressure on these systems. However, apart from a limited number of studies on the ecology of individual species or reaches, there has been little coordinated ecological research to assess the overall values and function of braided river ecosystems in New Zealand. This review summarises the international and New Zealand literature on braided rivers, with particular emphasis on benthic invertebrate ecology. Braided rivers typically experience short-term channel migration within the active bed and greater lateral channel migration across the entire floodplain in the longer term. Channel migration occurs because steep headwater tributaries supply highly variable discharges and mobile erodable substrates to the mainstem. Braided rivers typically possess extended floodplains, which may contain a mosaic of floodplain habitats ranging from highly unstable main-stem channels to stable spring complexes. Main channel aquatic invertebrate communities are frequently low in diversity and dominated by the leptophlebiid mayfly Deleatidium spp., but also chironomids and elmid beetles. In contrast, floodplain springs can have highly diverse communities rich in amphipods, mayflies, caddis, snails and chironomids. Groundwater and floodplain pond habitats also occur frequently and can contain several specialist taxa. Braided rivers and their floodplains are spatially complex, temporally dynamic habitats with high landscape- and reach-scale biodiversity values. The challenge facing managers is to protect this biodiversity within the context of increasing human demands on the rivers. This report highlights the particular threats and management issues associated with braided rivers in New Zealand and identifies areas where future research is required.

ELECTRONIC