The response of hyporheic invertebrate communities to a large flood in the Hunter River, New South Wales |
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Authors: | Peter J Hancock |
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Institution: | (1) Ecosystem Management, University of New England, 2351 Armidale, Australia |
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Abstract: | Previous studies on recovery in hyporheic communities have found that communities rapidly return to pre-disturbance levels.
However, most of these studies have concentrated on small floods or ones with short return periods. I studied the impact of
a large 1 in 6 year flood on the hyporheic community at 2 sites in the Hunter River, a large coastal river in New South Wales
with a mean daily flow of 15 m3 s−1. The flood peaked at 1270 m3 s−1 and afterwards invertebrate densities at the 2 sites were 83 and 67% less than they were before. Recovery to pre-flood densities
was slow but was aided by increases in the oligochaete and cyclopoid populations. At Site 1, there was a boom in oligochaete
and cyclopoid numbers 61 d after the flood, but the communities resumed their pre-flood densities by Day 139. Recovery at
Site 2 took 139 d. Most groundwater taxa (stygobites) living in the hyporheic zone did not recover from the disturbance when
compared to non-stygobites. Apart from Microturbellaria and the harpacticoid Parastenocaris sp., numbers of all stygobite taxa continued to decline after the flood, becoming absent after 61 d. The poor recovery of
stygobites is probably due to their adaptations for survival in the relatively stable groundwater environment. This study
shows that hyporheic communities are sensitive to large bed-moving floods and supports the hypothesis that ecotonal species
with a strong affinity to one ecosystem can be poor at recovering from disturbances that occur in an adjacent ecosystem. |
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Keywords: | hyporheic zone disturbance flood ecotone stygobites groundwater-surface water interactions |
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