Aquatic-terrestrial linkages
Connectivity in braided river landscapes
As part of his PhD research, Duncan Gray investigated connectivity in braided river landscapes at multiple spatial scales. At the broadest spatial scale Duncan has considered patterns in invertebrate diversity and abundance between multiple habitats, within reaches, within eleven rivers across New Zealand (Fig. 1).
Figure 1. Eleven braided river catchments included in the survey, three in the North Island and 8 in the South Island.
Additive partitioning of beta diversity indicated that diversity values at the broad spatial scales of reach and river contribute disproportionately to overall diversity. This result indicates that river managers concerned with maintaining diversity need to focus their efforts at the whole river scale rather than attempting management of smaller units representing local-scales. However, at finer scales, lateral floodplain habitats (particularly springs and floodplain ponds) are hotspots of diversity and protection, and remediation of these habitats is particularly important (Gray & Harding 2009, pdf, 850kb). Any national scale survey stands a good chance of turning up something rare or unusual. In this case we described a new species of alpine stonefly, Zelandobius edensis from the upper Rangitata River, Canterbury (Gray 2009, pdf, 2.3mb), and also extended the known range of a rare freshwater polychaete Namanereis tiriteae (Gray et al. 2009, pdf, 700kb).
An analysis of relationships between invertebrate communities and the environment has revealed that braided river assemblages are overwhelmingly influenced by physical disturbance due to flooding. However, whilst main channels are regulated by the magnitude and seasonal timing of antecedent flooding, lateral habitats respond more to successional processes post flood (Fig. 2). The later components of this project have focused on the biogeochemical cycling of carbon within floodplains with a particular emphasis on the groundwater-surface water ecotone (Fig. 3).
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Figure 2. Braided river showing main channel and later habitats. |
Figure 3. Spring-fed stream at the groundwater-surface ecotone. |
To date we have shown extreme depletion of δ13C at the spring source. This carbon signature is distinct from that of any carbon fixed either by terrestrial or aquatic plants using atmospheric CO2. This deplete carbon signature in the groundwater is derived from the respiration of terrestrial organics by soil micro-organisms and ultimately terrestrial vegetation itself. The deplete carbon in the groundwater is incorporated into the algal food chain within the spring and the isotopic signature can be observed in invertebrates and fish. From this we can infer the importance of linkages or cycling of materials between terrestrial, subterranean and aquatic units of the floodplain.
People involved in this project
University of Canterbury
Duncan Gray
Jon Harding
Mike Winterbourn
Travis Horton
National Institute of Water & Atmospheric Research (NIWA)
Graham Fenwick
Publications
Gray 2005. Braided river springs: distribution, benthic ecology, and role in the
landscape. MSc thesis, University of Canterbury (pdf, 4.8mb).
Gray 2009. A new species of Zelandobius (Plecoptera: Gripopterygidae: Antarctoperlinae) from the upper Rangitata River, Canterbury, New Zealand. New Zealand Journal of Marine and Freshwater Research 43: 605-611 (pdf, 2.3mb).
Gray & Harding 2007. Braided river ecology: a literature review of physical habitats and
aquatic invertebrate communities. Science for Conservation publication 279 (pdf, 1.2mb).
Gray & Harding 2009. Braided river benthic diversity at multiple spatial scales:
a hierarchical analysis of beta diversity in complex floodplain systems. Journal of the North American Benthological Society 28: 537-551 (pdf, 850kb).
Gray, Harding & Winterbourn 2009. Namanereis tiriteae, New Zealand’s freshwater polychaete: new distribution records and review of biology. New Zealand Natural Sciences 34: 29-38 (pdf, 700kb).
Gray, Scarsbrook & Harding 2006. Spatial biodiversity patterns in a large New Zealand braided river. New Zealand Journal of Marine and Freshwater Research 40: 631-642 (pdf, 1.7mb).
Scarsbrook, Barquin & Gray 2007. New Zealand coldwater springs and their biodiversity. Science for Conservation publication 278 (pdf, 2.2mb).