sustainability
Article
Ground Water Modelling for the Restoration of Carex
Communities on a Sandy River Terrace
Andrzej Brandyk 1, *, Grzegorz Majewski 2 , Adam Kiczko 2 , Andrzej Boczoń 3 , Michał Wróbel 3
and Paola Porretta-Tomaszewska 4
1
2
3
4
*
Laboratory-Water Center, Warsaw University of Life Sciences, Ciszewskiego Str. 6, 02-776 Warsaw, Poland
Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences,
Nowoursynowska Str. 159, 02-776 Warsaw, Poland; [email protected] (G.M.);
[email protected] (A.K.)
Forest Research Institute, Braci Leśnej Str. 3, S˛ekocin Stary, 05-090 Raszyn, Poland;
[email protected] (A.B.); [email protected] (M.W.)
Faculty of Building Services, Hydro and Environmental Engineering, Warsaw University of Technology,
Nowowiejska Str. 20, 00-653 Warsaw, Poland; [email protected]
Correspondence: [email protected]
Academic Editor: Vincenzo Torretta
Received: 31 August 2016; Accepted: 7 December 2016; Published: 15 December 2016
Abstract: Management for sustainable river valleys requires balancing their natural values against the
need for agricultural and recreational development on surrounding lands. The Southern Całowanie
Peatland near the city of Warsaw sits on a sandy terrace and has well preserved Carex and Molinia
stands existing in part of the area, especially where water tables are less than 1.5 m below the
surface. The existing drainage network in this southern part has been poorly maintained and could
be reestablished to help raise water levels for restoration of the peatland. Modflow was used to look
at influence of drainage channel water levels on the overall water table height in the area. By raising
water levels in the drainage system by 0.5 m it was found that 29% of the area would become suitable
for increasing Carex and Molinia communities.
Keywords: wetlands restoration; wetlands hydrology; modelling; ecosystem protection;
flooding terrace
1. Introduction
Wetland habitats and their unique vegetation have been subject to many threats all over the world,
mainly related with different drainage practices [1]. In western Europe, in particular on large wetland
areas, drainage-irrigation systems were installed to transform them into productive grasslands or
meadows, as well as for other specific goals like flood protection [2–4]. For many decades without
proper water management on those areas, hydrologic conditions have been substantially changed,
leading to gradual loss of valuable ecosystems [1]. It used to be a frequent case, that the parameters
of water management systems (i.e., discharge or drainage rates, water damming heights) were not
properly adjusted and did not maintain water tables necessary for native wetland vegetation [3].
Fortunately, some wetland areas, like the Southern Całowanie Peatland near Warsaw, Poland have
been reported to maintain valuable flora species, most likely as a result of drainage rates decrease
since the hydrologic system has been allowed to revert to more natural state [5,6]. On sandy soils
prevailing there, we found Caricetum gracilis stands (Carex shrubs) which promotes that area to a
high rank from the viewpoint of nature conservation [5,7,8]. Since those stands have still been well
preserved, there arose contemporary management dilemmas—whether (and how) to reintroduce the
control of water levels, striving at the restoration of plant communities, or to leave the system as
Sustainability 2016, 8, 1324; doi:10.3390/su8121324
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will be affected by decisions made by liable authorities, which require evidence for the feasibility of
restoration process [9]. The decision-making ought to be based on hydrological criteria that can be
directly uncontrolled. Undoubtedly, the future of many wetland territories—especially in Poland—will
incorporated into modelling studies and enables one to compare different management scenarios.
be affected by decisions made by liable authorities, which require evidence for the feasibility of
One of the biggest uncertainties in the restoration of wetland hydrology is the form of the criteria,
restoration process [9]. The decision-making ought to be based on hydrological criteria that can be
and the environmental variables that can be easily attributed to target habitat quality—i.e., water
incorporated into modelling studies and enables one to compare different management scenarios.
levels or flooding frequency [6,10]. Since the relevance of criteria is still subject to discussion, we
One of the biggest uncertainties in the restoration of wetland hydrology is the form of the criteria,
considered the adoption of threshold values of ground water levels for sandy soils on the basis of
and the environmental variables that can be easily attributed to target habitat quality—i.e., water levels
Polish experience, summarized by Szuniewicz [11] as: minimum allowable depth (upper limit): 0.35
or flooding frequency [6,10]. Since the relevance of criteria is still subject to discussion, we considered
m, mean depth: 0.40 m, and maximum allowable depth: 0.45 m. Those values are extensively used
the adoption of threshold values of ground water levels for sandy soils on the basis of Polish experience,
over the area of Poland, being justified by research on a wide range of soils. In this way, we attempted
summarized by Szuniewicz [11] as: minimum allowable depth (upper limit): 0.35 m, mean depth:
to ensure the reliability of the analyses herein, basing them on values firmly related to soil physical
0.40 m, and maximum allowable depth: 0.45 m. Those values are extensively used over the area of
properties [7,12].
Poland, being justified by research on a wide range of soils. In this way, we attempted to ensure the
Taking the results of two surveys that discovered vulnerable, river valley habitats on shallow
reliability of the analyses herein, basing them on values firmly related to soil physical properties [7,12].
water table soils into account, we aimed to apply ground water modeling and to determine proper
Taking the results of two surveys that discovered vulnerable, river valley habitats on shallow water
criteria to prove the potential for hydrologic restoration of the Southern Całowanie Peatland. It was
table soils into account, we aimed to apply ground water modeling and to determine proper criteria to
assumed that by increasing water levels in the existing network of channels, ground water table
prove the potential for hydrologic restoration of the Southern Całowanie Peatland. It was assumed
position would meet threshold values for the maintenance of Carex stands within a sandy-valley
that by increasing water levels in the existing network of channels, ground water table position would
terrace.
meet threshold values for the maintenance of Carex stands within a sandy-valley terrace.
2.
2. Material
Material and
and Methods
Methods
2.1. Research Area
The selected
selectedresearch
researcharea
areaofof588.8
588.8
is the
Southern
Całowanie
Peatland,
which
has already
haha
is the
Southern
Całowanie
Peatland,
which
has already
been
been
under
protection
as
a
habitat
for
endangered
wetland
species
of
flora
and
fauna
for
about
10
under protection as a habitat for endangered wetland species of flora and fauna for about 10 years.
years.
It is located
35 kmofsouth
of the city
capital
city of Warsaw,
and constitutes
a large
It is located
35 km south
the capital
of Warsaw,
and constitutes
only partonly
of apart
largeofwetland
wetland
complex
that
covers
a
wide
extent
of
the
Valley
of
the
Vistula
River.
The
whole
Całowanie
complex that covers a wide extent of the Valley of the Vistula River. The whole Całowanie Peatland
Peatland
area
offorms
3500 ha)
forms
vast and interrelated
system
1), containing
valuable
(total
area(total
of 3500
ha)
a vast
andainterrelated
system (Figure
1), (Figure
containing
valuable landscape
landscape
such
astransitional
raised andbogs
transitional
bogs andmeadows—the
single-swath meadows—the
componentscomponents
such as raised
and
and single-swath
biodiversity of
biodiversity
of which
strongly
depends
on human
maintenance
which
have
claimed
be
which
strongly
depends
on human
maintenance
and
which haveand
been
claimed
tobeen
be one
of the to
most
one of the most
vulnerable
habitat
mosaics
vulnerable
habitat
mosaics in
Europe
[5,7]. in Europe [5,7].
Figure 1. Location of Całowanie Peatland Protected Area, Poland. The Southern part was considered
to be the research area.
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The central and northern part of the Całowanie Peatland have already been subject to a wide
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range of research; however, the southern portion lacked sufficient attention until 2011, when urgent
management
issuesand
arose
[5,7]. Itpart
is surrounded
by agricultural
lands,
but been
the development
of new
The central
northern
of the Całowanie
Peatland have
already
subject to a wide
recreational
areas will
most likely
affect existing
conditions.
it is when
crucial
to stress
range of research;
however,
the southern
portionhydrologic
lacked sufficient
attentionHence,
until 2011,
urgent
management
issues
arose
[5,7]. It is consideration
surrounded byto
agricultural
lands,
butstatus,
the development
of new
protection
goals and
give
a thorough
its possible
future
function, and
use.
recreational areas will most likely affect existing hydrologic conditions. Hence, it is crucial to stress
2.2. protection
Geological goals
Setting
and give a thorough consideration to its possible future status, function, and use.
Southern Całowanie Peatland is situated in the glacial valley of the Vistula River (the largest of
the Polish rivers), within the boundaries of its flooding terrace, and partly at the edge of the lower
Southern
Całowanie
Peatland isice-shaped
situated in the
glacial
valley ofby
the
Vistula6River
of the
non-flooding
terrace.
It is a quaternary
plateau
bounded
uplands
km to(the
thelargest
east and
the Polish rivers), within the boundaries of its flooding terrace, and partly at the edge of the lower
Vistula River 3.5 km to the west [5]. Local altitude differences are negligible, except for the ice-formed
non-flooding terrace. It is a quaternary ice-shaped plateau bounded by uplands 6 km to the east and
upland moraines, having considerable slopes. Mean altitude at the study site equals about 95 m
the Vistula River 3.5 km to the west [5]. Local altitude differences are negligible, except for the iceabove the mean Baltic sea level, with exceptionally few deviations exceeding 0.5 m. Geological survey
formed upland moraines, having considerable slopes. Mean altitude at the study site equals about
showed
sandy
deposits
in with
the valley,
of a mean
thicknessexceeding
equal to 0.5
10 m.
m, Geological
underlain by
95 m prevailing
above the mean
Baltic
sea level,
exceptionally
few deviations
siltysurvey
loamsshowed
(Figureprevailing
2). Regional,
aquifer
of thickness
the sand equal
and silty
stand for
sandyunconfined
deposits in the
valley,isofbuilt
a mean
to 10 loams
m, underlain
its impermeable
base.
Recharge
to
the
aquifer
is
in
the
form
of
lateral
inflow
from
the
uplands
by silty loams (Figure 2). Regional, unconfined aquifer is built of the sand and silty loams stand forand
rainfall
infiltration, base.
enhanced
by atolack
low permeability
(aquitards)
thatthe
would
alsoand
hinder
its impermeable
Recharge
the of
aquifer
is in the form units
of lateral
inflow from
uplands
potential
contaminant
transport.by
Ground
discharges to
the (aquitards)
Vistula River
regional
drainage
rainfall
infiltration, enhanced
a lack ofwater
low permeability
units
that(the
would
also hinder
potential
transport.
GroundPhreatic
water discharges
to theare
Vistula
River
(the regional
drainage
base),
and in contaminant
some local-valley
wetlands.
water tables
found
at depths
ranging
from 1 to
base),
and
in
some
local-valley
wetlands.
Phreatic
water
tables
are
found
at
depths
ranging
from
1 to[5,7].
5 m, and their position close to the surface of the land would contribute to wetlands formation
5
m,
and
their
position
close
to
the
surface
of
the
land
would
contribute
to
wetlands
formation
[5,7].
Estimates of aquifer horizontal and vertical conductivity showed its homogenous character and
Estimates
offrom
aquifer
horizontal
and[5].
vertical
conductivity
showed
its homogenous
values
ranging
16 to
30 m/day
Materials
observed
in 20 soil
borings of a character
depth upand
to 7 m,
values ranging from 16 to 30 m/day [5]. Materials observed in 20 soil borings of a depth up to 7 m,
taken across the site, proved the presence of sandy deposits. Laboratory tests proved that they were
taken across the site, proved the presence of sandy deposits. Laboratory tests proved that they were
very homogenous and contained from 88% to 94% sand fraction, from 0% to 3% loam, and 1% to 6% of
very homogenous and contained from 88% to 94% sand fraction, from 0% to 3% loam, and 1% to 6%
silt, of
and
the hydraulic conductivity derived from granular data reaching from 24 to 30 m/day [10,13].
silt, and the hydraulic conductivity derived from granular data reaching from 24 to 30 m/day
Ground
water
levelswater
were observed
at observed
six double-piezometer
locations, with
one tube
screened
to the
[10,13]. Ground
levels were
at six double-piezometer
locations,
with
one tube
depth
of
2
m
and
the
deeper
one
at
7.5
m
below
ground,
finding
no
head
difference
between
them.
screened to the depth of 2 m and the deeper one at 7.5 m below ground, finding no head difference
A distinctive
feature
was also afeature
relatively
matter
of the soil
at depths
from
between them.
A distinctive
was large
also aorganic
relatively
large content
organic matter
content
of the soil
at 0 to
0.3 m,
amounting
to0.3
15%,
with the minimum
value
3%.
depths
from 0 to
m, amounting
to 15%, with
theof
minimum
value of 3%.
2.2. Geological Setting
Figure
2. Geological
cross-sectionof
ofthe
the Vistula
Vistula Valley
where
1 stands
for sand,
Figure
2. Geological
cross-section
Valley and
andthe
thestudy
studysite,
site,
where
1 stands
for sand,
2—peat and riverine silt, 3—silty loam.
2—peat and riverine silt, 3—silty loam.
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Plant communities were monitored over the study site in years 2003–2004 [5], and also in 2011.
Among
those
dominatingwere
over the
area, Caricetum
gracilis
were found[5],
with
a considerable
Plant
communities
monitored
over the
study(Carex)
site inshrubs
years 2003–2004
and
also in 2011.
share
ofthose
Glyceria
maxima, over
Rorippa
and Iris
pseudacorus.
Particular
conditions
for the
Among
dominating
the amphibia,
area, Caricetum
gracilis
(Carex) shrubs
werehabitat
found with
a considerable
above-mentioned
species Rorippa
involve amphibia,
river valleys
shallow lakeParticular
basins with
the conditions
dominance for
of
share of Glyceria maxima,
and and
Iris pseudacorus.
habitat
mineral-organic
deposits,
and ground
near
land
surfacelake
[14].basins
Nearlywith
permanent
flooding
the above-mentioned
species
involvewater
riverlevels
valleys
and
shallow
the dominance
is
permanent feature;
thus,
they
are often
named
carrs.
On the
other
hand,permanent
numerous
oftheir
mineral-organic
deposits,
and
ground
water
levelsriverside
near land
surface
[14].
Nearly
Molinia
appearedfeature;
within thus,
the study
site,
attributable
to peat-mineral
soils,
floodingmeadows
is their permanent
they are
often
named riverside
carrs. Onor
themarsh
other hand,
characterized
by variable
water
contentwithin
and ground
water
depth
of 0 to 1.5
m, which makes
them
numerous Molinia
meadows
appeared
the study
site,
attributable
to peat-mineral
or marsh
permanently
or periodically
wetwater
or moist
[8,14,15].
soils, characterized
by variable
content
and ground water depth of 0 to 1.5 m, which makes
them permanently or periodically wet or moist [8,14,15].
2.3. Channel Network
2.3. Channel Network
The study site is part of a large drainage-irrigation system constructed in the valley of the Vistula
studyto
site
is part proper
of a large
system constructed
in the
valley
of the
Vistula
RiverThe
in order
develop
soildrainage-irrigation
water content of existing
peatlands and
arable
lands
(Figure
3)
River
in orderimportant
to developgoal
proper
content
of existing
peatlands
andinarable
3) [7].
[7].
Another
wassoil
to water
provide
for flood
hazard
mitigation
that lands
valley.(Figure
Like many
Anothersystems
important
goal wasEurope,
to provide
floodwas
hazard
that valley.
Like many
similar
similar
in Western
thatfor
system
not mitigation
sufficientlyinmanaged
throughout
decades,
systems
Western
Europe,
that system
was not[3,7].
sufficiently
managed
throughout
decades,
thus
and
thusin
failed
to realize
its designed
functions
However,
the presence
of wetland
plantand
species
failed
to
realize
its
designed
functions
[3,7].
However,
the
presence
of
wetland
plant
species
suggests
suggests that the current function of the system should be to increase ground water levels in areas
that the current
function of the system should be to increase ground water levels in areas targeted
targeted
for restoration.
for restoration.
Figure 3. Hydrographic network of the Southern Całowanie Peatland.
Figure 3. Hydrographic network of the Southern Całowanie Peatland.
The study site is bounded from the north, south, and west by main drainage irrigation channels,
which
served
theispast
to supply
to secondary
ditches
thedrainage
area [7]. irrigation
Those ditches
have
The
studyinsite
bounded
fromwater
the north,
south, and
westwithin
by main
channels,
had
limited
maintenance,
and
were
finally
overgrown
with
vegetation.
The
present
physical
condition
which served in the past to supply water to secondary ditches within the area [7]. Those ditches have
of the
system
enables the and
surface
water
levels
to be adjusted
only in the
main
surrounding
had
limited
maintenance,
were
finally
overgrown
with vegetation.
The
present
physical channels.
condition
of
the system enables the surface water levels to be adjusted only in the main surrounding channels.
2.4. Ground Water Model
In order
to conduct
2.4. Ground
Water
Model analysis of ground water table changes versus the assumed canal water
levels, we utilized the common and recognized Modflow code, which can simulate ground water flow
In order to conduct analysis of ground water table changes versus the assumed canal water
response to changing boundary conditions. The governing partial-differential equation of this model
levels, we utilized the common and recognized Modflow code, which can simulate ground water
can be written in the following form [16]:
flow response to changing boundary conditions. The governing partial-differential equation of this
model can be written indthe
following
form
[16]:
dH
d
dH
d
dH
dH
Tx
+
Ty
+
Ty
−W = S
(1)
dx
dx
dy
dy
dz
dz
dt
d  dH  d  dH  d  dH 
dH
T

T

T

W

S
(1)




dx  x dx  dy  y dy  dz  y dz 
dt
where Tx , Ty , Tz —aquifer transmissivities in three directions: x, y, z (m2 /s); H—hydraulic head (m);
where
Tx, Tor
y, T
z—aquifer
x, y, (e.g.,
z (m2rainfall,
/s); H—hydraulic
head
(m);
W—inflow
outflow
fromtransmissivities
internal sourcesinorthree
sinksdirections:
of water (m/s)
evaporation,
channel
W—inflow
or outflowyield
from(dimensionless);
internal sources or
sinks of
water
(m/s)etc.).
(e.g., rainfall, evaporation, channel
seepage); S—specific
t—time
(days,
years,
seepage); S—specific yield (dimensionless); t—time (days, years, etc.).
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Ground water flow in a sandy aquifer was modelled in this study, which was deduced from
available
recognition
of hydrogeological
conditions.
Since in
grain
water from
level
Ground
water flow
in a sandy aquifer
was modelled
thiscomposition
study, whichtests
wasand
deduced
measurements
at different
depths provedconditions.
no heterogeneity
in thecomposition
aquifer system,
waswater
possible
to
available
recognition
of hydrogeological
Since grain
testsit and
level
use
one
numerical
layer
of
Modflow
code
to
perform
the
simulations.
Because
only
part
of
the
aquifer
measurements at different depths proved no heterogeneity in the aquifer system, it was possible to use
was numerical
modelled, layer
first type
boundarycode
condition
was applied
to the channels
existing
fromof
the
northern,
one
of Modflow
to perform
the simulations.
Because
only part
the
aquifer
western,
and southern
while from
the
east, the
aquifer
recharge
fluxfrom
wasthe
imposed
as
was
modelled,
first type directions,
boundary condition
was
applied
to the
channels
existing
northern,
second
type
boundary
condition.
The
impermeable
layer
of
silty
loams
underlying
the
aquifer
was
western, and southern directions, while from the east, the aquifer recharge flux was imposed as second
treated
as a no-flow
boundary.
type
boundary
condition.
The impermeable layer of silty loams underlying the aquifer was treated as
a no-flow boundary.
2.5. Model Calibration
2.5. Model Calibration
A calibration process was performed using a trial and error procedure in order to estimate such
values
aquifer conductivity
eastern inflow
which
reasonablein
match
modeled
A of
calibration
process wasand
performed
using arate
trialfor
and
errora procedure
orderbetween
to estimate
such
and
observed
ground
water
levels
was
achieved.
Ground
water
levels
used
for
calibration
were
values of aquifer conductivity and eastern inflow rate for which a reasonable match between modeled
measured
in the
network
of piezometers
in 2012, and
surfacewater
waterlevels
levelsused
in channels
were gauged
and
observed
ground
water
levels was achieved.
Ground
for calibration
were
in that yearinasthe
well.
Moreover,
they were expressed
in surface
meters above
mean
Baltic seawere
levelgauged
datum.
measured
network
of piezometers
in 2012, and
water the
levels
in channels
Based
surveys, reasonable
assumed in
values
of above
hydraulic
conductivity
oflevel
the aquifer
in
that on
yeargeological
as well. Moreover,
they were expressed
meters
the mean
Baltic sea
datum.
variedon
from
16 to 30
m/day,reasonable
while theassumed
ground water
rate applied
on the
boundary
Based
geological
surveys,
values inflow
of hydraulic
conductivity
of eastern
the aquifer
varied
3/day/m [5]. Both parameters were changed individually, followed by a visual
ranged
from
0.5
to
2.1
m
from 16 to 30 m/day, while the ground water inflow rate applied on the eastern boundary ranged from
comparison
of observed
andparameters
modeled were
piezometer
heads
(Figure followed
4), correlation
coefficient,
and
0.5
to 2.1 m3 /day/m
[5]. Both
changed
individually,
by a visual
comparison
standard
deviation.
The conductivity
and inflow
values
were finally
considered
acceptable
when
of
observed
and modeled
piezometer heads
(Figure
4), correlation
coefficient,
and as
standard
deviation.
standard
deviation
reached
m and
correlation
coefficientas
was
equal to when
0.82. As
a consequence
of
The
conductivity
and
inflow0.3
values
were
finally considered
acceptable
standard
deviation
the calibration
procedure,
aquifer
conductivity
was set
as 25 As
m/day
and easternofflux
to 1.7
reached
0.3 m and
correlation
coefficient
was equal
to 0.82.
a consequence
theequal
calibration
m3/day/m. aquifer conductivity was set as 25 m/day and eastern flux equal to 1.7 m3 /day/m.
procedure,
Figure 4.
4. Scatter
modeled and
and observed
observed ground
ground water
water heads
heads with
with linear
linear correlation
correlation
Figure
Scatter diagram
diagram for
for modeled
coeffieicent
equal
to
0.82.
The
heads
are
related
to
local
model
datum,
where
“0”
stands
90 m
coeffieicent equal to 0.82. The heads are related to local model datum, where “0” stands for 90 for
m above
aboveBaltic
meansea
Baltic
sea level.
mean
level.
The upper boundary condition (recharge flux through the surface into ground water system)
The upper boundary condition (recharge flux through the surface into ground water system) could
could be treated in the Modflow software (Processing Modflow-version 5.3.1. Copyright © 1991–2001
be treated in the Modflow software (Processing Modflow-version 5.3.1. Copyright © 1991–2001 W.H.
W.H. Chiang and W. Kinzelbach) as P-E—that is, precipitation rate minus evapotranspiration.
Chiang and W. Kinzelbach) as P-E—that is, precipitation rate minus evapotranspiration. Precipitation
Precipitation totals were achieved by linear interpolation over a wider area on the basis of the records
totals were achieved by linear interpolation over a wider area on the basis of the records from
from three stations: Warszawa (37 km), Siedlce (about 40 km), and Kozienice (about 37 km). However,
three stations: Warszawa (37 km), Siedlce (about 40 km), and Kozienice (about 37 km). However,
only meteorological data from Kozienice were used to calculate potential evapotranspiration
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according to Penman–Monteith method [10], since that station largely reflects the conditions outside
only meteorological data from Kozienice were used to calculate potential evapotranspiration according
the city area. It should be stressed that those values are not fully representative for the Całowanie
to Penman–Monteith method [10], since that station largely reflects the conditions outside the city
Peatland, and should also undergo calibration. Nevertheless, it was omitted in the present study so
area. It should be stressed that those values are not fully representative for the Całowanie Peatland,
as to keep the calibration procedure as simple as possible. On the basis of the ground water measurement
and should also undergo calibration. Nevertheless, it was omitted in the present study so as to keep the
availability, it was decided to run the model with a decade time step; hence, the input fluxes of
calibration procedure as simple as possible. On the basis of the ground water measurement availability,
precipitation and evapotranspiration were calculated as decade totals.
it was decided to run the model with a decade time step; hence, the input fluxes of precipitation and
In this study, it was decided that only the most uncertain parameters will undergo calibration
evapotranspiration were calculated as decade totals.
(hydraulic conductivity of the aquifer and inflow from east). The input from precipitation and
In this study, it was decided that only the most uncertain parameters will undergo calibration
evaporation could also have been subject to adjustments, as they come from interpolation for a wider
(hydraulic conductivity of the aquifer and inflow from east). The input from precipitation and
area, being influenced by spatial variability of hydrometeorological processes. Additionally, for
evaporation could also have been subject to adjustments, as they come from interpolation for a wider
further simulations, the calibrated inflow from the east remained constant, which most likely
area, being influenced by spatial variability of hydrometeorological processes. Additionally, for further
influenced model output. However, it was justified by the fact that no water level observations
simulations, the calibrated inflow from the east remained constant, which most likely influenced
existed from that direction, which would provide more accurate data for applying boundary
model output. However, it was justified by the fact that no water level observations existed from that
conditions.
direction, which would provide more accurate data for applying boundary conditions.
2.6. Model
and Exploitation
Exploitation
2.6.
Model Validation
Validation and
Next, the
the model
model was
was validated
validated on
Next,
on the
the basis
basis of
of ground
ground water
water levels
levels measured
measured throughout
throughout 2013.
2013.
In the
quality
of of
thethe
model
by visual
comparisons
(Figure
5) and
In
the simplest
simplestmanner,
manner,we
weestimated
estimatedthe
the
quality
model
by visual
comparisons
(Figure
5)
also also
by calculating
correlation
coefficients
between
modeled
and
all
and
by calculating
correlation
coefficients
between
modeled
andobserved
observedwater
watertables
tables for
for all
piezometers. The
but rather
rather
piezometers.
The achieved
achieved values
values (0.6–0.79)
(0.6–0.79) do
do not
not indicate
indicate good
good or
or very
very good
good quality,
quality, but
suggest aa satisfactory
satisfactory (or
(or acceptable)
acceptable) one.
one.
suggest
Figure 5. Comparison of the observed and modeled water tables for 2013. Each color pertains to an
individual piezometer.
piezometer.
After the
thevalidation,
validation,the
the
model
used
to calculate
ground
heads
for the assumed
After
model
waswas
used
to calculate
ground
water water
heads for
the assumed
channel
channel
water
levels,
so
as
to
estimate
potential
impact
on
Carex-dominated
sandy
wetland
and
find
water levels, so as to estimate potential impact on Carex-dominated sandy wetland and find relevance
relevance
to
restoration
goals.
We
found
it
to
be
a
practice
in
restoration
projects
to
make
use
of
to restoration goals. We found it to be a practice in restoration projects to make use of modelled ground
modelled
ground
water
head
distributions
for
scenario
comparisons
and
estimation
of
different
water head distributions for scenario comparisons and estimation of different management practices.
management
Here, theactual
first scenario
assumed
water levels
thesecond
main channels,
and
Here,
the first practices.
scenario assumed
water levels
in theactual
main channels,
andinthe
one involved
the
second
one
involved
raising
the
levels
by
0.5
m
to
find
out
if
such
hydrological
remediation
helps
raising the levels by 0.5 m to find out if such hydrological remediation helps to keep predefined ground
to keep
predefined
ground
water restoration.
tables on a site undergoing restoration.
water
tables
on a site
undergoing
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77 of
3.3.Results
Resultsand
andDiscussion
Discussion
3. Results
and
Discussion
On
of ground
groundwater
waterlevels
levelsfor
forthe
thecurrent
current
Onthe
thebasis
basisofof
ofdata
datacollected
collected for
for 2014,
2014, the
the simulation
simulation of
of
ground
water
levels
for
the
current
On
the
basis
data
collected
for
2014,
the
simulation
status
of
the
system
was
performed
with
the
use
of
the
validated
Modflow
model.
As
it
was
already
status of
of the
the system
system was
was performed
performed with
with the
the use of the validated
validated Modflow
Modflow model.
model. As
As it
it was
was already
already
status
mentioned,
the
input
values
for
that
year
involved
precipitation
and
evapotranspiration
fluxes,
ground
mentioned,
the
input
values
for
that
year
involved
precipitation
and
evapotranspiration
fluxes,
mentioned, the input values for that year involved precipitation and evapotranspiration fluxes,
water
inflow
from
the
eastern
direction,
and
measured
water
levels
in
the
main
ditches,
which
were
ground
water
inflow
from
the
eastern
direction,
and
measured
water
levels
in
the
main
ditches,
ground water inflow from the eastern direction, and measured water levels in the main ditches,
maintained
by
the
existing
hydraulic
structures.
The
physical
condition
of
those
structures
(as
it
was
which
were
maintained
by
the
existing
hydraulic
structures.
The
physical
condition
of
those
which were maintained by the existing hydraulic structures. The physical condition of those
structures
(as it
itiswas
was
stressed
before)
isanalysed
vital issue
issue
for
therespect
analysed
area,
with
respect to
to and
water
stressed
before)
a vital
issuebefore)
for theis
area,for
with
to area,
waterwith
management
the
structures
(as
stressed
aa vital
the
analysed
respect
water
management
and
the
maintenance
of
environmental
status.
On
the
basis
of
the
existing
assessment
maintenance
of
environmental
status.
On
the
basis
of
the
existing
assessment
of
the
structures
[5,7],
management and the maintenance of environmental status. On the basis of the existing assessment
of
thefound
structures
[5,7],
it was
was found
found
that
an allowable
allowable
riseisin
inequal
channel
water
table is
is
equal
to 0.5
0.5 m,
m,in
it of
was
that an
allowable
rise inthat
channel
water table
to 0.5
m, which
was
considered
the
structures
[5,7],
it
an
rise
channel
water
table
equal
to
which
was
considered
in
the
second
scenario.
the
second
which
wasscenario.
considered in the second scenario.
Groundwater
waterlevels,
levels,modeled
modeled with
with decade
decade time
time
step,
were
averaged
for
2014
(Figure
6)6)and
and
Ground
time step,
step, were
were averaged
averagedfor
for2014
2014(Figure
(Figure6)
and
Ground
water
levels,
modeled
with
subtracted
from
terrain
elevation
(Figure
7).
In
this
manner,
mean
ground
water
depths
were
determined.
subtracted
terrainelevation
elevation
(Figure
In this manner,
mean
ground
water
depths were
subtracted from
from terrain
(Figure
7). In7).
this manner,
mean ground
water
depths
were determined.
In the
the first
first scenario,
scenario,
which
reflectedwhich
the current
current
statusthe
of the
the
system,
mean
ground
water depth
depth varied
varied
In
which
reflected
the
status
of
system,
mean
water
determined.
In the first
scenario,
reflected
current
status
ofground
the system,
mean
ground
from
0.3
to
0.9
m
in
the
middle
of
the
area,
and
near
the
canals
it
ranged
from
0.9
to
2.4
m.
We
found
from depth
0.3 to 0.9
m infrom
the middle
near the
canals
it ranged
from
to 2.4itm.ranged
We found
water
varied
0.3 to of
0.9the
m area,
in theand
middle
of the
area,
and near
the0.9
canals
from
that
the
calculated
depth
followed
patterns
typical
for
areas
surrounded
by
drainage-irrigation
that
the
calculated
depth
followed
patterns
typical
for
areas
surrounded
by
drainage-irrigation
0.9 to 2.4 m. We found that the calculated depth followed patterns typical for areas surrounded by
channels. Maximum
Maximum
depth values
values
were noted
noted
close
to channels,
channels,
whileclose
in the
theto
middle
of the
thewhile
area, in
near
channels.
depth
were
close
to
while
in
middle
of
area,
near
drainage-irrigation
channels.
Maximum
depth
values
were noted
channels,
the
piezometers
P4,
P5,
and
P6,
they
approached
land
surface
elevation.
piezometers
P5,
andpiezometers
P6, they approached
land
elevation. land surface elevation.
middle
of the P4,
area,
near
P4, P5, and
P6,surface
they approached
Figure6.6.
6.Mean
Meanground
groundwater
waterheads
heads for
for 2014
2014 related
related to
to
local
model
datum,
where
“0”
stands
for
9090m
mm
Figure
Mean
ground
water
heads
for
related
Figure
to local
local model
modeldatum,
datum,where
where“0”
“0”stands
standsfor
for90
above
mean
Baltic
sea
level.
abovemean
meanBaltic
Balticsea
sealevel.
level.
above
Figure
water depths
depthsfor
for2014.
2014.
Figure7.
7. Mean
Mean ground
depths
for
2014.
Figure
7.
Mean
ground water
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InIn
the
second
scenario,
which
involved
a 0.5
mm
rise
inin
channel
water
levels,
the
possible
increase
the
second
scenario,
which
involved
a 0.5
rise
channel
water
levels,
the
possible
increase
ininoverall
ground
water
table
approached
0.3
m,
except
for
the
vicinity
of
ditches,
where
it
overall ground water table approached 0.3 m, except for the vicinity of ditches, where itranged
ranged
from
0.4
to
0.6
m
(Figure
8).
It
was
initially
guessed
that
it
would
not
be
feasible
to
sufficiently
increase
from 0.4 to 0.6 m (Figure 8). It was initially guessed that it would not be feasible to sufficiently increase
water
a close-to-ditch
zone;
however,
subject
toto
change
watertables
tablesinin
a close-to-ditch
zone;
however,the
thewhole
wholeanalysed
analysedarea
areawas
wasindeed
indeed
subject
change
inin
ground
groundwater
watertable
tableasasa aresult
resultofofaltered
alteredditch
ditchlevels.
levels.
Figure
Mean
ground
water
depths
scenario
2—water
levels
ditches
raised
Figure
8. 8.
Mean
ground
water
depths
inin
scenario
2—water
levels
inin
ditches
raised
byby
0.50.5
m.m.
Next,
ground water
waterdepths
depths
were
utilized
to determine
the potential
of
Next,the
thecalculated
calculated ground
were
utilized
to determine
the potential
area ofarea
restored
restored
wetland.
this purpose,
previously
adopted
threshold
were imposed
on modelled
wetland.
For thisFor
purpose,
previously
adopted
threshold
valuesvalues
were imposed
on modelled
depths
depths
for scenarios.
both scenarios.
the mean
was found
be between
the assumed
upper
and
for both
If theIfmean
waterwater
table table
was found
to be to
between
the assumed
upper
and lower
lower
to 0.45
m), claimed
we claimed
restoration
target
to reached.
be reached.
current
status
limitlimit
(0.35(0.35
to 0.45
m), we
the the
restoration
target
to be
In In
thethe
current
status
of of
the
the
system,
only
about
16%
of
the
area
(92.6
ha)
was
found
to
maintain
the
predefined
ground
water
system, only about 16% of the area (92.6
found to maintain the predefined ground water
table
range.
In the
second
scenario
(channel
waterwater
tablestables
raisedraised
by 0.5),bythat
area
extends
to 29% (171.6
table
range.
In the
second
scenario
(channel
0.5),
that
area extends
to 29%
ha).
On ha).
these
we canweexpect
moremore
favorable
initial
conditions
for for
thethe
maintenance
ofof
(171.6
Onsurfaces,
these surfaces,
can expect
favorable
initial
conditions
maintenance
vulnerable
Carex
or
Molinia
habitats
underlain
by
sandy
soils
within
a
flooding
terrace.
The
remaining
vulnerable Carex or Molinia habitats underlain by sandy soils within a flooding terrace. The remaining
part
rise
ininthe
part(71%
(71%ofofthe
thearea)
area)would
wouldbebestill
stillsubject
subjecttotolower
lowerwater
watertable
tableand
andinsufficient
insufficientcapillary
capillary
rise
the
soil,
not
reaching
the
root
zone.
We
findings
should
bebe
soil,
not
reaching
the
root
zone.
Wewish
wishtotoemphasize
emphasizethat
thatthe
theabove-mentioned
above-mentioned
findings
should
treated
aredirectly
directlydependent
dependentonon
adopted
criteria.
Having
assumed
treatedasasrelative,
relative, because
because they are
thethe
adopted
criteria.
Having
assumed
other
other
allowable
of hydrologic
characteristics,
weachieve
might aachieve
different
view
on the
allowable
limitslimits
of hydrologic
characteristics,
we might
differenta view
on the
conservation
conservation
wetlands
the water
obtained
waterThe
levels.
The appropriateness
of hydrological
of wetlandsofversus
the versus
obtained
levels.
appropriateness
of hydrological
criteriacriteria
for the
forassessment
the assessment
of wetland
restoration
has been
already
been discussed
in literature
scientific [6,12]
literature
[6,12]
of wetland
restoration
has already
discussed
in scientific
considering
considering
mean
water
levels
and its
extremesvalues),
(threshold
values),
as well
as other hydrological
mean water
levels
and its
extremes
(threshold
as well
as other
hydrological
characteristics
characteristics
(e.g.,
flooding
frequency
is
mainly
based
on
expert
knowledge,
resulting
mostly fromof
(e.g., flooding frequency is mainly based on expert knowledge, resulting mostly from observations
observations
of reference
ecosystems)
[8]. Withinwe
those
we dynamics
find suchthat
water
level
reference ecosystems)
[8]. Within
those ecosystems,
find ecosystems,
such water level
the existing
dynamics
that the existing
habitat conditions
propertiesfirst
andofplant
communities
all)can
arebe
habitat conditions
(soil properties
and plant(soil
communities
all) are
preserved first
well of
and
preserved
well
and
can
be
treated
as
patterns
for
nature
conservation.
At
present,
empirical
attempts
treated as patterns for nature conservation. At present, empirical attempts were made to relate ground
were
made
towith
relate
ground
water
levelsorwith
habitat
quality
or type or for
to find
optimum
water
levels
certain
habitat
quality
typecertain
or to find
optimum
hydrographs
particular
plant
hydrographs
for
particular
plant
groups
within
an
ecosystem
[8].
This
still
seems
to
be
subject
to
groups within an ecosystem [8]. This still seems to be subject to discussion, because for hydrologic
discussion,
because
for hydrologic
aspects,
the water
levels
soil water
content however,
are the
aspects, the
water levels
and resultant
soil water
content
areand
the resultant
most important
parameters;
most
important
ecological
issues
also
need
to be
addressed;
i.e., thecycling,
seed
other
ecologicalparameters;
issues also however,
need to beother
addressed;
i.e., the
seed
bank,
light
availability,
nutrient
bank,
light
availability,
nutrient
cycling,
etc.
This
may
lead
to
more
interdisciplinary
eco-hydrological
etc. This may lead to more interdisciplinary eco-hydrological approaches. As of yet, the formulation of
approaches.
As of yet,
thetoformulation
of particular
tends which
to be questionable,
and
one has
to
particular criteria
tends
be questionable,
and one criteria
has to decide
environmental
qualities
could
decide
which to
environmental
qualities
couldThe
be assigned
particular moisture
ranges.
The soil
be assigned
particular moisture
ranges.
soil watertomanagement
approach
we decided
to water
present
management
approach
welevels
decided
to present
helpswhich
to maintain
levelscontent
for sandy
soilroot
types,
helps to maintain
water
for sandy
soil types,
secure water
8% oxygen
in the
zone
which secure 8% oxygen content in the root zone as an effect of capillary rise in the soil. It is then
Sustainability 2016, 8, 1324
9 of 10
as an effect of capillary rise in the soil. It is then transparent from the soil point of view, and directly
related to its basic physical properties, but again may not be sufficient for other ecohydrological issues.
4. Conclusions
Results of hydrogeological surveys along with the recognition of dominating plant species within
the Southern Całowanie Peatland revealed the need for a wise use of the existing drainage network.
Carex and Molinia stands were still preserved on a sandy flooding terrace, especially where ground
water tables would not fall 1.5 m below the land surface. This corresponds with the results of ground
water modeling for the current status of the hydrological system. Another feature that is consistent
with the depicted geological setting is a high organic matter content of the topsoil. All of the above
findings undoubtedly suggest that there are perquisites for swamp-forming processes, and the realistic
restoration potential is supported by the modelled ground water table response to increased channel
water levels. Having analysed the modelling results as well as the application of hydrologic criteria,
we were able to form the following conclusions:
(1)
(2)
(3)
(4)
Channel water level clearly exerts an influence on ground water table with a typical pattern; that is,
the highest drawdown takes place close to channels, and the maximum elevation of the water table
is present in the middle of the area. We try to describe that influence as conductivity-dependent,
because its large values for existing sandy soils may cause high exchange between canals and
ground water horizons, undoubtedly contributing to the preservation of the natural values of
a flooding terrace.
Depth to water table was analysed according to the adopted criteria, which describe sandy soil
wetness due to effective capillary rise. According to that criteria, maximum allowable depth to
water table may not be higher than 0.45 m, the mean depth should be equal to 0.40 m, and the
minimum reaching 0.5 m. The assumed threshold values of ground water table (0.3 to 0.45 m
below land surface) were achieved on maximum 29% of the area if the channel water levels
were increased by 0.5 m in the second analysed scenario. The first scenario (which reflected the
actual status of the system) guarantees proper water levels only on 16% of the area. We wish to
stress that the restoration target was achieved when ground water table position was between
the adopted extremes. This was indeed an assumption. First of all, the criteria seem to be relative,
and we also claim that the prescribed water level range is directly assumed as a permanent
feature of well-preserved habitats (and their plant species composition), and may be used for
scenario comparisons in hydrologic and water management analyses. The appropriateness of
the applied threshold values results from their extensive use over the area of Poland and firm
relation to crucial soil properties.
Hydrologic conditions on sandy terrace favorable for dominating Carex species and widespread
Molinia meadows were possible in the middle of the area. As shown by the modelling results, they
were not achieved in close-to-channel zones, which would require other hydrologic remediation.
Adaptive channel water management is no doubt an option for the maintenance of habitats on
sandy deposits of flat river valleys. More detailed scenario studies are indispensable for the
decision making on the extent of restoration area.
Author Contributions: The study was completed with cooperation between all authors. Andrzej Brandyk
conceived and designed the experiments, prepared the conceptual model and wrote material and methods as
well as discussion. Grzegorz Majewski performed field measurements, and Adam Kiczko prepared the figures,
modeling data and part of the results. Andrzej Boczoń and Michał Wróbel took part in fieldwork and results
discussion, Paola Porretta-Tomaszewska elaborated the conclusions.
Conflicts of Interest: The authors declare no conflict of interest.
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Chichester, UK, 1995.
Grygoruk, M.; Bańkowska, A.; Jabłońska, E.; Janauer, G.; Kubrak, J.; Mirosław-Światek,
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D.; Kotowski, W.
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