New Zealand Journal of Marine and Freshwater Research abstracts
Physical characterisation of microform bed cluster refugia
in 12 headwater streams, New Zealand
BARRY J. F. BIGGS
MAURICE J. DUNCAN
STEVEN N. FRANCOEUR
WILLIAM D. MEYER
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 8602
Christchurch, New Zealand
Abstract Recent sediment transport research has demonstrated
that microform bed clusters (MBC) are particularly resistant to entrainment
during floods and preliminary biological surveys have shown that such
structures could be providing important refugia for benthos in streams. We
therefore surveyed MBC in a selection of headwater streams, South Island, New
Zealand to determine how common such structures are and then related their
occurrence to flow variability, relative armouring, reach gradient, and
sediment geology/geometry to obtain a greater understanding of hydrological and
hydraulic stream-scale factors affecting their density and composition. MBC
were present in all streams and ranged in density from 0.067 to 0.279
m-2. They occupied up to 4.4% of the surface area of the survey
reaches, generally had 2-3 particles (a maximum of 7), and the average size for
the largest particles ranged from 18.5 to 42.8 cm. MBC density and percentage
site cover was significantly related to the relative armouring, but not to flow
variability. The number of sediment particles per cluster was significantly
correlated with reach gradient, although sediment geology, and associated
geometry of particles, also appeared to be important. Thus, density and
structure of MBC appeared to be primarily controlled by the interaction of
relative armouring and reach gradient with highest densities and the largest
number of cluster particles occurring in steep streams with high bed armouring.
These structures were sufficiently common to be playing a significant role as
flood refugia for benthos in some high gradient, headwater streams.
Keywords sediments; sediment transport; stream geomorphology;
streambed stability; refugia; disturbance; invertebrates; periphyton; stream
ecology
New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31:
413-422
0028-8330/97/3104-0413 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (668K); (scanned from paper original: notes about this process)
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