ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

lic roughness [i.e., bedforms, large woody debris (Lwd) ,
etc.]. Empirically determined ranges of textural response
to sediment supply and hydraulic roughness allow examination
of the geomorphic controls on salmonid spawning
grounds.
We find that the availability of preferred spawning gravel
sizes can be significantly enhanced by textural response to
sediment supply and hydraulic roughness. For example, in
fully armored plane-bed channels (i.e., channels not exhibiting
textural fining), spawning gravels only occur for
bankfull shear stresses ranging from about 5-20 Pa. However,
as a result of textural fining caused by bedform and
Lwd roughness, spawning gravels have the potential to occur
in a variety of different channel types and over a greater
range of bankfull shear stresses (5-300 Pa). Although
the extent of salmonid spawning habitat can expand through
increases in either hydraulic roughness or sediment
supply, the latter may induce higher embryo mortality, offsetting
any potential gains in spawning habitat extent. Increased
sediment supply can cause bed mobility at stages
less than bankfull, and thus more frequent scour and a higher
probability of egg excavation. Furthermore, increased
sediment loading may lead to greater interstitial filling of
bed material, resulting in reduced intra-gravel oxygen flow
to buried salmonid embryos.
Geomorphic controls on spawning grounds can be rapidly
assessed using empirical findings of the bankfull-threshold
model coupled with predictions of shear stress and channel
type determined from digital elevation models (Derns),
For example, we examined the effect of bedform and Lwd
roughness on salmonid spawning habitat using a Dem of
the Finney Creek watershed of western Washington, USA.
We restricted our analysis to channels with slopes 20.04, typical
of plane-bed and pool-riffle streams used by salmonids.
These channels were further divided into three types
of potential spawning channels based on bankfull shear
stress ranges associated with spawning gravels in plane-bed
(5-20 Pa), self-formed pool-riffle (>20-80 Pa), and Lwdforced
pool-riffle channels (>80-300 Pa); a fourth shear
stress category (>300 Pa) was designated unusable for
spawning. Our analysis indicates that plane-bed channels
with suitable spawning gravels comprise, at most, only 20/0
of the stream length with slopes 0.04. However, an additional
42 % of this stream length can be opened to spawning
if characterized by a self-formed pool-riffle morphology
and consequent textural fining caused by bedform
roughness. Another 52 % can be opened if characterized
by a Lwd-forced pool-riffle morphology and textural fining
resulting from the combined effects of bedform and
Lwd roughness.
Land management practices of splash damming, riparian
clearcutting and «stream cleaning» have decreased the
amount of Lwd in many channels throughout North America.
Our results suggest that consequent textural coarsening
in response to Lwd loss may have decreased salmonid
spawning habitat availability and may be a factor in historic
declines of fish populations and shifts in species type.
Wood loss can further compound impacts on fish populations
by decreasing pool frequency and area, and thus the
availability of potential rearing habitat.
ELZBIETA BUKOWSKA-IANIA 1, MARIAN PULINA 2
& JACEK JANIA 2
Calcium carbonate in deposits of the last scandinavian
glaciation and contemporary chemical denudation
in Western Pomerania (NW Poland)
1 Department of Physical Geography, University of Silesia,
UI. Bedzinska 60, 41-200 Sosnowiec, Poland
2 Department of Geomorphology, University of Silesia,
UI. Bedzinska 60, 41-200 Sosnowiec, Poland
The studied area is located in the marginal zone of the Pomeranian
Phase of the Vistulian (Weischel) Glaciation
(16,500 yr BP). Relatively high content of CaC0 3 has been
noted in moranic and fluvioglacial· deposits (5-15 % by volume).
Exposed on the surface youngest deposits are separated
from the bedrock by more than 100 m thick older
Quaternary glacial sediments. Moreover, exposures of carbonate
rock are not watched below the Quaternary series
beneath the studied area and hundreds kilometres
upstream of the last ice sheet. Problem of origin of CaC0 3
in glacial and fluvioglacial sediment is considered basing
upon results of studies of the actually glaciarized areas in
Spitsbergen. A model cryochemical enrichment in these
deposits in the calcium carbonate is applied.
Quaternary deposits are a source of calcium carbonate for
contemporary dissolution by waters from precipitation,
ground waters and flowing waters. The majority of river
and lake waters in the area has got relatively high mineralisation
(up to 300 mg/ 1) and there hydrochemical type is
HCO- 3 - Ca 2 + - Mg 2 + (S042-). Some of springs has even higher
minaralisation (more than 350 rng/l). Hydrochemical
'studies combined with the hydrological data of two medium
size catchments (Pilawa - 342 sq km and Plytnica 170
sq km) indicate intensive, chemical denudation of the area
built by last glacial deposits. The dissolved denudation ratio
varies between 7.4 up to 21.5 m 3/km2/yr in particular
subcatchments. Calcium carbonates are deposited in lakes
as qythia and lake-marl. Discussion in the paper concerns
modern balance of chemical denudation and attempt to
estimate amount of CaC0 3 which has been being removed
since the ice sheet left this area. Results show importance
of CaC0 3 content and its active migration in the post glacial
environment of the northern Poland.
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