Abstract
Abstract: We investigated the effects of a rare depositional fl ood (return period about 5 years) on the hyporheos of a fl ood-prone river in southern New Zealand. The fl ood deposited 15–40 cm of new sediment across most of the 42-m study site. On four occasions after the fl ood (4 d, 17 d, 35 d, 49 d), pump samples (1 L volume) were col-lected for physicochemical and invertebrate analysis from three depths in the sediment (10, 30, 50 cm). The study site was dominated by downwelling water, therefore, temporal variations in interstitial physicochemistry probably refl ected surface water conditions. Composition of the hyporheos immediately after the fl ood differed from that on subsequent occasions. Densities of most invertebrate taxa were similar across sampling occasions. Nevertheless, the depth distributions of leptophlebiid nymphs (Ephemeroptera), Podonominae larvae (Chironomidae) and the water mite Planaturus setipalpis all changed with time, consistent with post-fl ood recolonisation of recently depos-ited sediments from underlying undisturbed sediments. Invertebrate distributions were not signifi cantly related to measured physicochemical parameters, possibly because any such relationships were obscured by recolonisation patterns. Our results indicate that buried sediments may be an important source of colonists of surface sediments for some epigean (surface-dwelling) taxa during recovery from disturbance associated with sediment deposition.
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