Geoscience Reference
In-Depth Information
3. Methods
The study has been monthly monitored for 13 months from August 2000 to
August 2001 and during the storm event on August 21-22, 2001. A nested
transect was used to understand the mobility of Ca 2+ across hill slope and
riparian zone. Discharge was continuously recorded at 30 V-notch gauging
weir and rainfall was measured using tipping bucket (recording) rain gauge.
Groundwater, soil water, and stream water samples were collected
prior for Ca 2+ measurement. Groundwater samples were taken from the
piezometer, whereas soil water samples were collected from suction samplers
installed at the same site with piezometer and tensiometer nests. Stream
water was taken at four different sites (Fig. 1).
The water samples were filtered through 0.22 µ m Millipore membrane
filters to separate suspended matter and the filtered solutions were ana-
lyzed for Ca 2+ and SiO 2 .Ca 2+ and SiO 2 concentrations were measured
using Inductive Couple Argon Atomic Emmision Spectro-photometer at
the Chemical Analysis Center of University of Tsukuba.
Ca 2+ flux was quantified to assess Ca 2+ transport using the convection-
dispersion model as follows: 7
D l ∂C l /∂z,
J l = J w C l
D lh ∂C l /∂z
(1)
where J l is the total flux of dissolved Ca 2+ ; J w is the water flux; C l is
dissolved Ca 2+ concentration; D lh is the hydrometric dispersion coecient;
z corresponds to the distance where the Ca 2+ is transported; and D l
is the
soil liquid diffusion coecient.
J w =
Ks ( ∂H ) / ( ∂z ) ,
(2)
D lh = λV,
(3)
V = J w /θ,
(4)
λ =0 . 0169 Ls 1 . 53 ,
(5)
D l
D l
= ξ ( θ )
·
,
(6)
ξ ( θ )= θ 10 / 3 2 ,
(7)
where J l is the total flux of dissolved solute (mg/cm/se); J w is the water
flux (cm/s); C l is dissolved solute concentration (mg/l); D lh is the hydro-
metric dispersion coecient (cm 2 /s); z corresponds to the distance where
thesoluteistransported(cm); D l is the soil liquid diffusion coecient
(cm 2 /s), D l is the diffusion coecient of the solute in water (cm 2 /s), Ks
is saturated hydraulic conductivity (cm/s), ( ∂H ) / ( ∂z ) is hydraulic gradient
(cm/cm), λ is dispersivity (cm) which was adopted from Ref. 8, V is pore
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