Groundwater arsenic in the Red River delta, Vietnam ... - Fiva

Jessen et al., manuscript to be submitted to Geochim. Cosmochim. Acta
FIGURE CAPTIONS
Figure 1 (a) The location of the field site for the present and related studies. The
transects are located adjacent to tributary channels active in the wet
season. (b) Pumping and selected observation wells in the N transect.
Figure 2 Cross section of the N transect (Fig. 1) and channel bed sediments.
Screened intervals are indicated for the pumping and observation wells.
Three non-screened channel bed drillings are indicated.
Figure 3 Anoxic elution by 10 mM NaHCO3 (pH 7) of a reduced Holocene aquifer
sediment, obtained at a sediment-to-eluent ratio of 106 ± 21 g/L. (a) Total
(cumulated) eluted As and Si as a function of the total amount of eluent
added and (b) as a function of the aqueous As concentration at the end of
each elution step. The arrow in (b) indicates an extrapolation to the y-axis.
Note the different units for As and Si. Model lines indicate CD-MUSIC
and D&M surface complexation models for goethite (full) and ferrihydrite
(dotted), respectively. Model lines in (a) are for As(III) (upper two lines)
and Si (lower two lines). Model lines in (b) are for As(III).
Figure 4 As(III) adsorption isotherm for a reduced Holocene aquifer sediment
calculated using Eq.(1). Dashed lines trace the desorption path between
points obtained by a desorption step following an adsorption step. Model
lines indicate CD-MUSIC and D&M surface complexation models for
goethite (full) and ferrihydrite (dotted), respectively.
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