New Zealand Journal of Marine and Freshwater Research abstracts
M00019Received 19 April 2000; accepted 17 July 2000
Influence of reach geomorphology on hyporheic communities in a gravel-bed
stream
D. A. OLSEN
C. R. TOWNSEND
Department of Zoology
University of Otago
P. O. Box 56
Dunedin, New Zealand
email: dean.olsen@stonebow.otago.ac.nz
C. D. MATTHAEI
Department of Zoology
University of Munich (LMU)
Karlstr. 23-25, 80333 Munich
Germany
Abstract The surface sediment, subsurface sediment, and
hyporheos were sampled by freeze-coring at three sites of contrasting
geomorphology in a New Zealand gravel-bed stream. No differences in size class
composition were detected among the subsurface sediments of the three sites but
the forced pool-riffle (a stretch of stream where the sequence of pool and
riffles is controlled by in-channel bedrock outcrops) had significantly finer
surface sediments than the other sites. The hyporheos of all sites was
dominated numerically by insects, including nymphs of
Deleatidium and
Oniscigaster, and chironomid larvae. Of the non-insect taxa, Isopoda,
Oligochaeta, and Acari were most common. No significant differences existed
between total invertebrate density or taxon richness at the sites.
Aoteapsyche was found only in the plane bed site, whereas
Nesameletus was found only in the forced pool-riffle.
Psilochorema
and Nematoda occurred at significantly lower densities in the forced
pool-riffle than in the plane bed or floodplain sites. For most taxa, local
variation within a site was greater than that between sites. Total invertebrate
density was highest near the sediment surface but no significant differences
were found between the three sites in this or any other depth layer.
Significant site-depth interactions were obtained for three taxa
(
Zelandobius, Ostracoda, and Oligochaeta) indicating that local
geomorphology may result in differential depth distributions of hyporheic
species.
Keywords stream ecology; hyporheos; freshwater
macroinvertebrates; geomorphology; patchiness; New Zealand
New Zealand Journal of Marine and Freshwater Research, 2001, Vol. 35: 181-190
0028-8330/01/3501-0181 $7.00 (c) The Royal Society of New Zealand 2001
PDF file of entire paper: medium quality (760K); (scanned from paper original: notes about this process)
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