Vadose Zone Journal,
Год журнала:
2022,
Номер
22(1)
Опубликована: Ноя. 17, 2022
Abstract
Biogeochemical
gas
production
resulting
in
free
phase
formation
can
severely
affect
groundwater
and
solute
transport
aquifers.
Such
gas–water
interactions
are
important
aquifers
affected
by
geogenic
As,
which
commonly
associated
with
biogeochemical
CH
4
production.
Additionally,
the
influence
of
aquitards
on
As
concentrations
contaminated
has
recently
been
challenged.
These
observations
prompted
analysis
through
a
heterogeneous
aquitard
overlying
high
−gas‐producing
zone
an
As‐contaminated
aquifer.
A
sediment
core
taken
was
analyzed
for
noble
gases
to
assess
how
physically
contributes
underlying
Results
reveal
that
pore
space
is
unsaturated
two
separate
layers
hanging
water
constrained
air‐like
phase.
This
interlayering
saturated
zones
identifies
aquitard's
stratigraphy
as
key
determining
hydrostatic
pressure—a
main
control
(i.e.,
)
The
partly
conditions
reduce
pressure
30%
compared
fully
conditions.
To
our
knowledge,
this
first
study
applying
examine
physical
state
Further,
such
low
conductivity
might
provide
preferential
pathways
periodic
flow,
fostering
aquitard–aquifer
transport.
Groundwater
samples
additionally
collected
throughout
site
confirm
more
widespread
degassing
than
previously
reported.
Up
90%
expected
atmospheric
lost
from
immediately
below
investigated
core.
Environmental Science & Technology,
Год журнала:
2024,
Номер
58(11), С. 5079 - 5092
Опубликована: Март 7, 2024
Redox
conditions
in
groundwater
may
markedly
affect
the
fate
and
transport
of
nutrients,
volatile
organic
compounds,
trace
metals,
with
significant
implications
for
human
health.
While
many
local
assessments
redox
have
been
made,
spatial
variability
reaction
rates
makes
determination
at
regional
or
national
scales
problematic.
In
this
study,
were
predicted
contiguous
United
States
using
random
forest
classification
by
relating
measured
water
quality
data
from
over
30,000
wells
to
natural
anthropogenic
factors.
The
model
correctly
oxic/suboxic
78
79%
samples
out-of-bag
hold-out
sets,
respectively.
Variables
describing
geology,
hydrology,
soil
properties,
hydrologic
position
among
most
important
factors
affecting
likelihood
oxic
groundwater.
Important
variables
tended
relate
aquifer
recharge,
travel
time,
prevalence
electron
donors,
which
are
key
drivers
Partial
dependence
plots
suggested
that
decreased
sharply
as
streams
approached
gradually
depth
below
table
increased.
probability
increased
base
flow
index
values
increased,
likely
due
well-drained
soils
geologic
materials
high
areas.
topographic
wetness
(TWI)
decreased.
High
occur
areas
a
propensity
standing
overland
flow,
limit
delivery
dissolved
oxygen
recharge;
higher
TWI
also
tend
discharge
areas,
contain
long
times.
A
second
was
developed
predict
elevated
manganese
(Mn)
concentrations
(i.e.,
≥50
μg/L).
Mn
relied
on
same
be
used
identify
where
Mn-reducing
there
is
an
risk
domestic
supplies
concentrations.
Model
predictions
produced
study
help
regions
country
vulnerability
stream
groundwater-derived
contaminants.
Water Research,
Год журнала:
2021,
Номер
200, С. 117300 - 117300
Опубликована: Май 27, 2021
Geogenic
arsenic
(As)
contamination
of
groundwater
is
a
health
threat
to
millions
people
worldwide,
particularly
in
alluvial
regions
South
and
Southeast
Asia.
Mitigation
measures
are
often
hindered
by
high
heterogeneities
As
concentrations,
the
cause(s)
which
elusive.
Here
we
used
comprehensive
suite
stable
isotope
analyses
hydrogeochemical
parameters
shed
light
on
mechanisms
typical
high-As
Holocene
aquifer
near
Hanoi
where
advected
low-As
Pleistocene
aquifer.
Carbon
signatures
(δ13C-CH4,
δ13C-DOC,
δ13C-DIC)
provided
evidence
that
fermentation,
methanogenesis
methanotrophy
actively
contributing
heterogeneity.
Methanogenesis
occurred
concurrently
levels
(>200
µg/L)
DOC-enriched
aquitard
pore
water
infiltrates
into
Along
flowpath
Holocene/Pleistocene
transition,
methane
oxidation
causes
strong
shift
δ13C-CH4
from
-87‰
+47‰,
indicating
reactivity.
These
findings
demonstrate
previously
overlooked
role
cycling
DOC
infiltration
aquifers.
Environmental Science & Technology,
Год журнала:
2021,
Номер
56(2), С. 928 - 937
Опубликована: Дек. 24, 2021
Chronic
exposure
to
groundwater
contaminated
with
geogenic
arsenic
(As)
poses
a
significant
threat
human
health
worldwide,
especially
for
those
living
on
floodplains
in
South
and
Southeast
(S–SE)
Asia.
In
the
alluvial
deltaic
aquifers
of
S–SE
Asia,
aqueous
As
concentrations
vary
sharply
over
small
spatial
scales
(10–100
m),
making
it
challenging
identify
where
contamination
is
present
mitigate
exposure.
Improved
mechanistic
understanding
factors
that
control
levels
essential
develop
models
accurately
predict
spatially
variable
concentrations.
Here
we
demonstrate
surface
flooding
duration
interannual
frequency
are
master
variables
integrate
key
hydrologic
biogeochemical
processes
affect
A
machine-learning
model
based
high-resolution,
satellite-derived,
long-term
measures
effectively
predicts
heterogeneous
at
fine
Cambodia,
Vietnam,
Bangladesh.
Our
approach
can
be
reliably
applied
locations
safe
unsafe
sources
sufficient
accuracy
management
decisions
by
solely
using
remotely
sensed
information.
This
work
important
evaluate
exposure,
impacts
public
health,
shed
light
underlying
hydrogeochemical
drive
mobilization
into
groundwater.
