Original paper

Effects of a depositional flood event on the hyporheos of a New Zealand stream

Olsen, Dean A.; Matthaei, Christoph D.; Townsend, Colin R.


We investigated the effects of a rare depositional flood (return period about 5 years) on the hyporheos of a flood-prone river in southern New Zealand. The flood deposited 15-40 cm of new sediment across most of the 42-m study site. On four occasions after the flood (4 d, 17 d, 35 d, 49 d), pump samples (1 L volume) were collected 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 reflected surface water conditions. Composition of the hyporheos immediately after the flood 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-flood recolonisation of recently deposited sediments from underlying undisturbed sediments. Invertebrate distributions were not significantly 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.


sediment characteristicsinterstitial physicochemistryinvertebrate distributionrecolonisation patterns