Geoscience Reference
In-Depth Information
water velocity (cm/s),
θ
is volumetric water content (cm
3
/cm
3
),
Ls
is the
apparent length scale which is correspond to the distance (m),
ξ
(
θ
)isthe
tortuosity, and
φ
is the porosity.
Assessment of Ca
2+
input from weathering has been made using the
mineralogical data from the X-ray deffragtograms for primary and sec-
ondary minerals in the soil. The trend of its concentration in both soil
and water (groundwater, soil water) was used to synthesize and analyze its
balance.
4. Results and Discussion
4.1.
Weathering and concentration of Ca
2+
As high as 6.07% of CaO has been measured in the top 20 cm of soil in
the riparian zone in which it was much higher than that in 80 cm depth
(1.5%). In contrast, during base flow Ca
2+
concentration in the shallow
(0.2-0.6 m) groundwater was as high as 4.81 mg/l which significantly lower
as that in the deep (1-2 m) groundwater (7.99 mg/l), see Table 1. Stream
Ca
2+
concentration decreased during the rising limb to reach the lowest
concentration at near peak runoff (Fig. 2).
The XRD analysis has shown that quartz (SiO
2
) is the most abun-
dant mineral in the soil, followed by feldspar which is mainly anor-
thite (CaAl
2
Si
3
O
8
), slightly rare gibbsite (Al(OH)
3
), and very rare albite
(NaAlSi
3
O
8
) (Fig. 3). In general, these minerals were distributed homo-
geneously amongst the soil horizons, except for the upper horizon of the
riparian zone.
In the groundwater and soil water, SiO
2
and Ca
2+
concentrations were
dominance suggesting that these solutes are originated from these minerals
through the weathering. However, inconsistency was identified in which
itwasatrendinincreasingCa
2+
concentration in the groundwater with
depth, but not the case in the soil profile. This provides insight into the
process by which Ca
2+
especially in the upper soil solution was leached
out through subsurface runoff. This phenomenon also suggests that the
rate of weathering is inferior to the rate of transport, which leads Ca
2+
concentration to deteriorate.
4.2.
Ca
2+
transport
It has been reported that the near surface riparian/NSR (45%), deep
riparian groundwater/DRG (20%) and hillslope soil water/HSW (35%) are
the major sources area contributing to runoff generation in this catchment.
5
