Jökull - 01.01.2009, Page 23

Chemical and mechanical fluvial denudation in cold environments
terised by a mean annual temperature of -2.0◦C and
a mean annual precipitation of 852 mm yr−1. About
2/3 of the annual precipitation is temporarily stored
as snow during the winter. Snowmelt normally starts
at the end of May/beginning of June. Stable freez-
ing temperatures and autumn snow accumulation usu-
ally occur from September/October onwards. Precip-
itation from June to August accounts for about one
quarter of the mean annual precipitation. Bedrock in
Latnjavagge is mainly composed of Cambro-Silurian
mica-garnet schists and inclusions of marble (Kulling,
1964; Beylich et al., 2004a). The catchment area is
dominated by large and flat plateau areas at 1300 m
a. s. l., steep slopes which bound the glacially sculp-
tured valley, and a rather flat valley floor situated be-
tween 950 and 1200 m a. s. l. (Figure 4). Regolith
thicknesses are shallow and reach locally only a few
meters (Beylich et al., 2004b). Main present soils are
regosols and lithosols. The catchment area belongs to
the mid-Alpine zone with continuous and closed veg-
etation cover up to 1300 m a. s. l. comprising dwarf
shrubs heaths and Alpine meadows and bogs. The
distribution of permafrost is not directly known but
drilling outside the catchment at 1200 m a. s. l. sug-
gests at least sporadic permafrost down to 80 m below
the surface (see Kling, 1996; Beylich et al., 2004b).
There seems to be no ice-rich permafrost on the val-
ley floor around 1000 m a. s. l. and on the lower parts
of the gentle and W-facing valley slope (Beylich et
al., 2004b). The hydrological regime is nival, with
runoff being limited to the period from end ofMay un-
til October/November (Beylich, 2003). Direct human
impact is small and is limited to reindeer husbandry
(extensive grazing), some hiking tourism and field re-
search at the Latnjajaure Field Station (LFS) (Beylich
et al., 2005a).
METHODS
The Hrafndalur catchment lies mostly on a rhyolite
bedrock in the northern part of the Icelandic East-
ern Fjords (Austfirðir). The monitoring programme
in this area was performed from 2001 until 2007. Dis-
charge at the outlet of the Hrafndalur catchment was
measured by continuous monitoring of water level us-
ing a pressure sensor (GLOBAL WATER) and col-
lecting data every hour in combination with numer-
ous propeller measurements with an Ott-propeller C2
during the investigation period. Daily specific runoff
[mm d−1] was calculated by dividing calculated daily
discharge by the contributing catchment area. Fluvial
suspended sediment and solute transport were anal-
ysed by combining continuousmonitoring of turbidity
and electric conductivity (hourly readings, GLOBAL
WATER sensors) with discrete water sampling during
field campaigns. Vertically integrated water samples
were taken with 1000 ml wide-necked polyethylene
bottles. The samples were filtered in the field base
with a pressure filter and ash-free filter papers (Munk-
tell). After the field campaigns the filter papers were
burned to analyse the concentrations of mineralogenic
(inorganic) suspended solids [mg l−1]. The stability
of creeks and channel stone pavements as well as the
range of bedload transport were estimated by using
painted stone tracer lines at selected creeks and chan-
nel stretches (Beylich and Kneisel, 2009).
New accumulations of debris/bed load were anal-
ysed by weighing of debris (portable field balance)
and a detailed measuring of the volumes of fresh
deposits. Surface water electric conductivity, cor-
rected to 25◦C, was measured at different locations
within Hrafndalur using a portable conductivity meter
(WTWWeilheim).
The Kidisjoki catchment can be seen as a repre-
sentative valley for the sub-Arctic Kevo region and the
Latnjavagge catchment is considered as a representa-
tive test site for the Arctic-oceanic Abisko Mountain
region. The Kidisjoki catchment was monitored be-
tween 2001 and 2007 and Latnjavagge between 1999
and 2007. The methods used for quantifying runoff,
solute concentrations, suspended sediment concentra-
tions as well as atmospheric solute inputs into the
catchments are explained in detail in Beylich (2005)
and Beylich et al. (2003; 2006a; 2006b).
The main focus of this paper is to compare rates
and relative importance of chemical and mechanical
fluvial denudation and to quantify the importance of
annual snowmelt- and rainfall-generated runoff peaks
for fluvial transport and budgets in the three different
environments.
JÖKULL No. 59 23