Jökull - 01.01.2009, Blaðsíða 24

A. A. Beylich
CHEMICAL AND MECHANICAL
FLUVIAL DENUDATION RATES
Annual runoff, mean discharge-weighted solute and
suspended sediment concentrations, chemical and
mechanical fluvial denudation rates as well as mean
annual runoff and chemical andmechanical fluvial de-
nudation (yields of suspended sediments) rates for the
Hrafndalur (period 2002–2007), the Kidisjoki (period
2002–2007) and the Latnjavagge catchment (period
2000–2007) are presented in Tables 1–3. The mean
annual atmospheric solute inputs are 26 t km−2 yr−1
in Hrafndalur (Beylich andKneisel, 2009), 5.1 t km−2
yr−1 in Kidisjoki (Beylich et al., 2006b) and 4.1 t
km−2 yr−1 in Latnjavagge (Beylich, 2008).
Hrafndalur
Based on our data (2002–2007) about 78% of the
annual precipitation contributes to runoff in Hrafn-
dalur. The mean annual discharge-weighted TDS (To-
tal Dissolved Solids) value for the Hrafndalur catch-
ment is 41.3 mg l−1 and the mean chemical denuda-
tion rate is 29.3 t km−2yr−1 (Table 1). The mean
annual discharge-weighted suspended sediment con-
centration at the outlet of the catchment is 13.4 mg
l−1 and the mean annual yield of suspended sedi-
ments is 18.5 t km−2yr−1. Denudation rates in this
very steep catchment are relatively high which is con-
nected to the steepness of this high-energy system
with the related high frequency of denudative slope
processes events and to the existing rhyolites causing
limited vegetation cover. Chemical denudation dom-
inates over the yield of suspended sediments, which
makes this rhyolite area different from the extended
basalt basement of Austfirðir where yields of sus-
pended sediments are generally higher than chemical
denudation rates (Beylich, 2000; Beylich and Kneisel,
2009). Due to high bedload transport rates total me-
chanical denudation anyway dominates over chemi-
cal denudation in Hrafndalur (Beylich and Kneisel,
2009).
Kidisjoki
Based on the measurements carried out from 2002 to
2007 approximately 78% of annual precipitation con-
tributes to runoff in Kidisjoki (see also Vakkilainen,
1986; Dankers, 2002; Harding et al., 2002). Themean
annual discharge-weighted TDS value at the outlet
of the Kidisjoki catchment is 25.2 mg l−1 (Table 2).
The calculated mean chemical denudation rate (2002–
2007) is 3.1 t km−2yr−1. The mean annual discharge-
weighted suspended sediment concentration is 0.8 mg
l−1 and the mean annual yield of suspended sedi-
ments is 0.25 t km−2yr−1 (Table 2). Denudation rates
in this low-relief environment with limited sediment
availability are altogether very low, with chemical de-
nudation being clearly more important than mechan-
ical fluvial denudation. Bedload transport appears to
be of very little importance (Beylich et al., 2006b).
Altogether, chemical denudation is about twelve times
higher than mechanical fluvial denudation.
Latnjavagge
Based on the measurements carried out in Latn-
javagge approximately 87% of annual precipitation
contributes to runoff (Beylich, 2008). Mean an-
nual discharge-weighted TDS values for the Latn-
javagge catchment are 12.0 mg l−1 for the entire
catchment (Table 3). The mean chemical denudation
rate (2000–2007) is 4.6 t km−2yr−1. The mean an-
nual discharge-weighted suspended sediment concen-
tration is 3.2 mg l−1 (measured at the inlet of lake Lat-
njajaure) and the mean annual yield of suspended sed-
iments is 2.3 t km−2yr−1. Denudation rates are low in
this Arctic-Alpine environment, which is mainly due
to a closed and stable vegetation cover in this area.
Altogether, chemical denudation dominates over me-
chanical fluvial denudation and is about two times
higher than the yield of suspended sediments (Table
3).
Comparison of denudation rates in the three catch-
ments
Chemical denudation in Latnjavagge is altogether 1.5
times higher than in the Kidisjoki catchment, and
the mean annual yield of suspended sediment is 9.4
times higher than in the Kidisjoki catchment. The
mean chemical denudation rate in Hrafndalur is about
10 times higher than in Kidisjoki and about 6 times
higher than in Latnjavagge. The mean annual yield of
suspended sediments in the Hrafndalur catchment is
74 times higher than in Kidisjoki and about 8 times
higher than in Latnjavagge. Due to high bedload
24 JÖKULL No. 59