Influences of catchment and corridor imperviousness on urban stream macroinvertebrate communities at multiple spatial scales |
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Authors: | Kevin J Collier Bryan L Clements |
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Institution: | (1) Environment Waikato, PO Box 4010, Hamilton, New Zealand;(2) The University of Waikato, Private Bag, 3105 Hamilton, New Zealand |
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Abstract: | Resolving land cover hierarchy relationships in urban settings is important for defining the scale and type of management
required to enhance stream health. We investigated associations between macroinvertebrate assemblages in urban streams of
Hamilton, New Zealand, and environmental variables measured at multiple spatial scales comprising (i) local-scale physicochemical
conditions, (ii) impervious area in multiple stream corridor widths (30, 50 and 100 m) along segments (sections of stream
between tributary nodes) and for entire upstream networks, and (iii) total impervious area in stream segment sub-catchments
and upstream catchments. Imperviousness was higher for stream segment sub-catchments than for entire catchments because of
the agricultural headwaters of some urban streams. Imperviousness declined as corridor width declined at both segment and
catchment scales reflecting the vegetated cover along most urban stream gullies. Upstream catchment imperviousness was strongly
and inversely correlated with dissolved organic carbon concentration, whereas segment and upstream corridor scales were correlated
with water temperature and pH. Corridor imperviousness appeared to be a stronger predictor than catchment imperviousness of
Ephemeroptera, Plecoptera and Trichoptera taxa richness and the Quantitative Urban Community Index specifically developed
to assess impacts of urbanisation. In contrast, imperviousness at all measured scales added only marginal improvement in assemblage-based
models over that provided by the local-scale physicochemical variables of reach width, habitat quality, macrophyte cover,
pH and dissolved oxygen concentration. These findings infer variable scales of influence affecting macroinvertebrate communities
in urban streams and suggest that it may be important to consider local and corridor factors when determining mechanisms of
urbanisation impacts and potential management options. |
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