Abstract.
In
high-energy
beach
aquifers
fresh
groundwater
mixes
with
recirculating
saltwater
and
biogeochemical
reactions
modify
the
composition
of
discharging
to
sea.
Changing
morphology,
hydrodynamic
forces
as
well
hydrogeological
properties
control
density-driven
flow
transport
processes
that
affect
distribution
chemical
reactants.
present
study,
modelling
a
generic
2-D
cross-shore
transect
was
conducted.
Boundary
conditions
aquifer
parameters
were
varied
in
systematic
manner
suite
twenty-four
cases.
The
objective
investigate
their
individual
effects
on
regime,
salt
distribution,
potential
for
mixing
controlled
system
temporally-variable
morphology.
Our
results
show
changing
morphology
causes
migration
infiltration
exfiltration
locations
along
lead
transient
patterns
subsurface,
thereby
enhancing
reactions.
shape
extent
zone
where
potentially
take
place
spatio-temporal
variability
freshwater-saltwater
interfaces
are
most
sensitive
variable
storm
floods,
hydraulic
conductivity
dispersivity.
Environmental Science & Technology,
Год журнала:
2025,
Номер
unknown
Опубликована: Фев. 13, 2025
The
sandy
subterranean
estuary
(STE)
connecting
fresh
groundwater
to
saline
sea
water
is
characterized
by
strong
geochemical
(salinity,
redox,
and
pH)
gradients,
with
evidence
emerging
for
its
role
as
a
hot
spot
consumption
of
labile
substrates.
This
inspired
us
conduct
study
evaluate
whether
this
holds
true
dissolved
organic
matter
(DOM),
especially
given
the
still
mysterious
origin
marine
recalcitrant
DOM.
Here,
characterization
DOM
21
samples
(depth
1-13
m,
salinity
3.9‰
32.4‰)
across
65
m
transect
an
STE
located
in
coastal
Guangdong,
China,
has
found
systematic
biotransformation
toward
"recalcitrant"
carboxyl-rich
alicyclic
molecules
(CRAM).
fraction
CRAM
(%CRAM)
increases
from
33.1%
76.7%
increasing
degree
degradation
salinity.
Further,
processing
DOM,
including
more
"biolabile"
lower
%CRAM
released
aquitard,
active
under
oxic
conditions
than
reducing
conditions.
Given
large
quantities
that
recirculates
through
STEs
globally,
amount
(RDOM)
entering
ocean
after
likely
be
considerable.
While
studies
are
needed,
can
gain
CRAM-like
compounds
way.
Journal of Geophysical Research Biogeosciences,
Год журнала:
2025,
Номер
130(2)
Опубликована: Фев. 1, 2025
Abstract
Seawater
infiltration
into
the
permeable
sands
of
beach
aquifers
creates
a
high
input
biogeochemical
reactants
driven
by
tides
and
waves.
The
upper
sand
layer
acts
as
filter,
retaining
particulate
organic
matter
(POM),
which
is
degraded
bacteria
under
predominantly
oxic
conditions.
seasonal
variation
seawater
POM
oxygen
(O
2
)
entering
zone,
combined
with
filtration
efficiency
highly
morphodynamic
layer,
determines
turnover
subsequent
redox
gradients
along
porewater
flowpaths.
We
investigated
these
effects
quantifying
O
consumption
rates
directly
from
incubations
sediments
taken
transect
in
zone
at
Spiekeroog
Beach,
Germany.
carried
out
two‐monthly
year‐long
sampling
campaign
spatial
resolution
measurements
down
to
1
m
depth.
In
summer,
up
106
μM
hr
−1
were
found
first
decimeters
significant
decline
over
depth,
indicating
efficient
retention
reactive
surface
layer.
Seasonal
carbon
sand's
suspendable
particulates
indicates
rapid
little
storage.
winter,
decreased
significantly
below
11
.
Integrated
estimated
mineralization
varies
between
15
(winter)
143
(summer)
mmol
C
−2
d
yearly
average
73
CO
production
35
kg
per
meter
shoreline
characterizes
high‐throughout
system
OM
remineralization
especially
but
Hydrology and earth system sciences,
Год журнала:
2025,
Номер
29(5), С. 1469 - 1482
Опубликована: Март 18, 2025
Abstract.
In
high-energy
beach
aquifers
fresh
groundwater
mixes
with
recirculating
saltwater
and
biogeochemical
reactions
modify
the
composition
of
discharging
to
sea.
Changing
morphology,
hydrodynamic
forces,
hydrogeological
properties
control
density-driven
flow
transport
processes
that
affect
distribution
chemical
reactants.
present
study,
modelling
a
generic
2-D
cross-shore
transect
was
conducted.
Boundary
conditions
aquifer
parameters
were
varied
in
systematic
manner
suite
24
cases.
The
objective
investigate
individual
effects
boundary
on
regime,
salt
distribution,
potential
for
mixing-controlled
system
temporally
variable
morphology.
Our
results
show
changing
morphology
causes
migration
infiltration
exfiltration
locations
along
transect,
leading
transient
patterns
subsurface,
thereby
enhancing
reactions.
shape
extent
zone
where
potentially
take
place,
as
well
spatiotemporal
variability
freshwater–saltwater
interfaces,
are
most
sensitive
storm
floods,
hydraulic
conductivity,
dispersivity.
study
advances
understanding
subsurface
flow,
transport,
mixing
dynamic
beneath
beaches.
These
regulate
nutrient
fluxes
coastal
ecosystems.
Frontiers in Marine Science,
Год журнала:
2023,
Номер
10
Опубликована: Июнь 22, 2023
Subterranean
estuaries
are
connective
zones
between
inland
aquifers
and
the
open
sea
where
terrestrial
freshwater
circulating
seawater
mix
undergo
major
biogeochemical
changes.
They
reactors
that
modify
groundwater
chemistry
prior
to
discharge
into
sea.
We
propose
subterranean
of
high-energy
beaches
particularly
dynamic
environments,
effect
boundary
conditions
propagates
tens
meters
subsurface,
leading
strong
spatio-temporal
variability
geochemical
conditions.
hypothesize
they
form
a
unique
habitat
with
an
adapted
microbial
community
unlike
other
typically
more
stable
subsurface
environments.
So
far,
however,
studies
concerning
have
been
rare
therefore
their
functioning,
importance
for
coastal
ecosystems,
as
well
carbon,
nutrient
trace
element
cycling,
is
little
understood.
addressing
this
knowledge
gap
within
interdisciplinary
research
project
DynaDeep
by
studying
combined
surface
(hydro-
morphodynamics)
on
processes
(groundwater
flow
transport,
reactions,
microbiology).
A
estuary
observatory
was
established
northern
beach
island
Spiekeroog
facing
North
Sea,
serving
exemplary
site
model
system.
It
consists
fixed
permanent
infrastructure
such
pole
measuring
devices,
multi-level
wells
electrode
chain.
This
forms
base
autonomous
measurements,
regular
repeated
sampling,
field
campaigns
experimental
work,
all
which
integrated
via
mathematical
modelling
understand
quantify
functioning
reactor.
First
results
show
collecting
intended
spatially
temporally
resolved
morphological,
sedimentological
data.
Samples
data
further
processed
ex-situ
experiments
modelling.
Ultimately,
aims
at
elucidating
global
relevance
these
common
but
overlooked
Environmental Science & Technology,
Год журнала:
2024,
Номер
58(33), С. 14687 - 14697
Опубликована: Авг. 8, 2024
As
global
change
processes
modify
the
extent
and
functions
of
terrestrial–aquatic
interfaces,
variability
critical
dynamic
transitional
zones
between
wetlands
uplands
increases.
However,
it
is
still
unclear
how
fluctuating
water
levels
at
these
boundaries
alter
groundwater
biogeochemical
cycling.
Here,
we
used
high-temporal
resolution
data
along
gradients
from
to
during
freshwater
coastal
areas
capture
spatiotemporal
patterns
redox
potential
(Eh).
We
observed
that
topography
influences
Eh
higher
in
than
wetlands;
however,
high
within
TAI
challenged
establishment
distinct
zonation.
Declining
generally
decreased
Eh,
but
most
locations
exhibited
significant
variability,
which
associated
with
rare
instances
short-term
level
fluctuations,
introducing
oxygen.
The
Eh-oxygen
relationship
showed
hysteresis
patterns,
reflecting
poising
capacity
maintaining
more
oxidizing
states
longer
dissolved
oxygen
presence.
Surprisingly,
frequent
uplands.
infer
occasional
entering
specific
wetland–upland
acts
as
control
points.
High-resolution
can
such
yet
instances,
supporting
redox-informed
models
advancing
predictability
climate
feedback.
Advances in Water Resources,
Год журнала:
2024,
Номер
191, С. 104763 - 104763
Опубликована: Июнь 28, 2024
Subterranean
estuaries
(STE)
are
hotspots
of
biogeochemical
reactions.
Here,
dissolved
constituents
in
waters
terrestrial
and
marine
origin
transformed
before
they
discharge
to
the
coastal
oceans.
The
involved
reactions
complex
non-linear,
calling
for
application
numerical
reactive
transport
modeling
(RTM)
improve
process
understanding.
aim
this
study
was
assess
roles
organic
matter
degradation
coupled
secondary
mineral
fate
species
STEs
sandy
beaches.
A
comprehensive
RTM
approach
applied
purpose,
accounting
effects
ion
activities,
pH,
pe,
redox
reactions,
equilibria
(calcite,
goethite,
siderite,
iron
sulfide,
hydroxyapatite
vivianite)
as
well
surface
complexation.
Results
show
that
STE
biogeochemistry
associated
fluxes
very
sensitive
assumed
reaction
network.
For
example,
inorganic
carbon
pH
were
largely
controlled
by
calcite
siderite
dynamics,
Fe2+
HS-
precipitated
and/or
sulfides.
Moreover,
PO43-
concentrations
affected
both
formation
vivianite
or
This
work
helped
establish
relative
importance
some
major
processes
STE.
However,
further
field
studies
needed
understand
which
play
a
role
real-world
STEs,
including
an
exploration
deep
subsurface
STEs.
Such
field-based
observations
will
our
conceptual
understanding,
is
key
developing
well-constrained
RTMs.
Water Resources Research,
Год журнала:
2025,
Номер
61(1)
Опубликована: Янв. 1, 2025
Abstract
Coastal
aquifers
experience
water
table
fluctuations
that
push
and
pull
air
through
organic‐rich
soils.
This
exchange
affects
the
supply
of
oxygen,
dissolved
organic
carbon
(DOC),
nitrogen
(N)
to
shallow
influences
groundwater
quality.
To
investigate
fate
N
species,
we
used
a
meter‐long
column
containing
sequence
natural
topsoil
aquifer
sediments.
A
fluctuating
head
was
imposed
at
bottom
with
local,
nitrate‐rich
(16.5
mg/L
NO
3
‐N).
We
monitored
in‐situ
redox
potential
collected
pore
samples
for
analysis
inorganic
species
DOC
over
16
days.
Reactive
processes
were
more
complex
than
anticipated.
The
remained
anaerobic,
while
mineral
sediments
beneath
alternated
between
aerobic,
when
dropped
sucked
across
preferential
flow
paths,
anaerobic
conditions,
high.
fluid
reactive
transport
model
shows
rises
into
soils,
it
limits
soils
release
DOC,
which
stimulates
removal
nitrate
from
by
denitrification.
At
end
experiment,
introduced
seawater
mimic
storm
surge.
Seawater
mobilized
soil
horizons,
could
reach
if
surge
is
long
enough.
These
are
relevant
quality
in
developed
coastal
areas
anthropogenic
sources,
as
climate
change
rising
seas
will
drive
changes
flood
dynamics.
