Mineral Versus Organic Contribution to Vertical Accretion and Elevation

Home , Ebro Delta

Ecological Engineering 61 (2013) 12–22

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Ecological Engineering

j ournal homepage: www.elsevier.com/locate/ecoleng

Mineral versus organic contribution to vertical accretion and

elevation change in restored marshes (Ebro Delta, Spain)

a,∗ b b c a

Juan Calvo-Cubero , Carles Ibánez˜ , Albert Rovira , Peter J. Sharpe , Enrique Reyes

Department of Biology, East Carolina University, Greenville, NC, USA

Aquatic Ecosystems Program, IRTA. St. Carles de la Ràpita, Catalonia, Spain

US National Park Service, 120 Chatham Lane, Fredricksburg, VA 22405, USA

a r t i c l e i n f o a b s t r a c t

Article history: The Ebro Delta (Catalonia, Spain) is one of the most valuable coastal zones within the Mediterranean

Received 2 May 2013

Sea, supporting a highly productive rice agricultural system, as well as a myriad of coastal marsh habi-

Received in revised form 9 August 2013

tats. However, chronic reductions of ﬂuvial sediments coupled with accelerated relative sea-level rise

Accepted 20 September 2013

have created an environment where approximately half of the Ebro Delta is now vulnerable to ﬂood-

ing impacts. To assess relative sea-level rise (RSLR) mitigation options through marsh restoration within

Keywords:

abandoned deltaic rice ﬁelds, we established the experimentally restored marshes spanning three years.

Sea-level rise

We used two freshwater input type treatments (riverine irrigation and rice ﬁeld drainage water) and

Marsh restoration

three water level treatments (10, 20 and 30 cm deep). Our hypotheses were that: (1) vertical accretion

Root growth

and elevation change in oligohaline restored marshes would be primarily controlled by organic contrib-

Marsh elevation

Sediment inputs utions under sediment-deﬁcit conditions, and (2) both vertical accretion and elevation change would

−1

Paspalum distichum demonstrate higher rates compared with predicted RSLR in the Ebro Delta (5–8 mm yr ). Vertical accre-

−1

tion had higher mean values in both water type treatments (11.5 and 15.5 mm yr ) than elevation change

−1

(9.1 and 8.8 mm yr ). Vertical accretion (but not elevation change) was signiﬁcantly higher in drainage

water treatment receiving greater sediment mineral input, which caused higher surface soil mineral con-

tent. Conversely, experimentally restored marshes closer to rice ﬁelds in both water type treatments had

−1 −1

greater elevation change (11.3 and 17.8 mm yr ) than vertical accretion (8.3 and 15.1 mm yr ) due to

higher belowground biomass because of high weed colonization by Paspalum distichum L. These results

showed that vertical accretion and elevation change were generally controlled by mineral contribution,

although fast growing, ruderal plant species such as P. distichum can play a signiﬁcant role in marsh ele-

vation via root growth. The results supported the hypothesis that restored marshes using either water

type promote marsh elevation gains higher than predicted RSLR at least during the initial marsh devel-

opment (3 years). This study indicates that the use of agricultural runoff as a primary source of sediment,

nutrient, and freshwater is beneﬁcial for marsh restoration projects focused primarily on mitigating RSLR.

This research also highlights how nuisance species such as P. distichum can play a key role in mitigating

RSLR impacts when inexpensive and effective measures are needed to promote marsh elevation as the

primary restoration goal.

Published by Elsevier B.V.

1. Introduction the Natura 2000 network of the European Union (EU). Jux-

taposed with these natural areas there are 20,000 Ha of rice

The Ebro Delta is a vital coastal ecosystem in the western ﬁelds. Rice agriculture is the main economic activity within the

Mediterranean extending ∼330 km (Fig. 1) and is the second Delta comprising up to 60% of the land surface of the Ebro

most important special protection area for birds (SPA) in Spain Delta, providing an annual gross income of about D 60 million

(Seo/BirdLife, 1997). The Ebro Delta possesses a diverse number and a total rice production of 120,000 tons per year (Cardoch

of ecosystems including coastal lagoons, marshes and seagrasses, et al., 2002). Although rice agriculture development has trans-

which comprise the Ebro Delta Natural Park and are part of formed much of the Ebro Delta over the last two centuries

(Cardoch et al., 2002), rice ﬁelds provide signiﬁcant ecosystem

services such as seasonal habitat for migratory birds, preven-

∗ tion of saline intrusion and nutrient removal (Martinez-Vilalta,

Corresponding author. Tel.: +1 252 328 5778.

E-mail address: [email protected] (J. Calvo-Cubero). 1995).

0925-8574/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.ecoleng.2013.09.047

J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22 13

the global market by reduced production and subsequent increases

in rice prices, which may have important implications for food

security (Chen et al., 2012). Several studies in the Mediterranean

and Asian Deltas (e.g. Ebro, Nile, Ganges and Mekong Deltas) also

suggest potential population displacements, loss of biodiversity

and cultural heritage (Syvitski et al., 2009; Day et al., 2011).

One proposed measure to mitigate deltaic impacts is the intro-

duction of riverine sediments into marshes as a means of correcting

the sediment deﬁcit (e.g. Mississippi Delta, Rhone Delta and Ebro

Delta) (Ibánez˜ et al., 1997; DeLaune et al., 2003; Day et al., 2007).

The reintroduced river water would also provide a source of nutri-

ent input, which theoretically would increase marsh elevation

by stimulating autogenic organic contribution via plant growth

(McKee and Mendelssohn, 1989; Day et al., 2008). Freshwater

inputs also reduce soil stressors such as hyper-salinity, anoxia

and toxins that typically inhibit plant growth (Day et al., 2011).

Several studies also emphasize that the organic contributions to

marsh elevation may be more relevant than mineral contributions

in sediment-deﬁcient deltas and estuaries (DeLaune and Pezeshki,

2003; Blum and Christian, 2004; Nyman et al., 2006). However,

more data are required to directly link organic contribution to

marsh elevation (Cahoon et al., 2006; Day et al., 2011; Fagherazzi

et al., 2012). In the Ebro Delta only marshes that maintain signiﬁ-

cant freshwater and sediment inputs will likely survive predicted

RSLR (Ibánez˜ et al., 2010). So it is important to understand under

which conditions the mineral and organic contributions to marsh

elevation can be optimized as a key restoration objective. For exam-

ple, the use of Paspalum Distichum L. during the establishment of

restored marshes may be a viable restoration practice to mitigate

RSLR due its ability to capture sediments, it’s tolerances to salinity,

water logging, and dry conditions, fast growth, and ability to repro-

duce from rhizomes, stolons, or seeds (Anderson and Ehringer,

2000; Carr, 2010; Wanyama et al., 2012). The practice of converting

rice ﬁelds into marshes in areas of low elevation has been proposed

in the Ebro Delta as a way to mitigate the effects of climate change

(e.g. by elevation gain and carbon sequestration) and improve the

water quality of agricultural runoff (Ibánez˜ et al., 1997). Recently,

several public efforts have restored rice ﬁeld land to freshwater

Fig. 1. The top map shows the location of the experimentally restored marshes marshes in the Ebro Delta using river irrigation water or rice ﬁeld

in the Ebro Delta (Catalonia, Spain). The bottom map shows its detailed location

drainage water to feed them (MARM, 2006; Ibánez˜ and Bertolero,

between an active organic rice ﬁeld and an old restored marsh dominated by Phrag-

2009). However, no previous experimental studies in the Ebro

mites australis (Cav.) Steudel and Typha latifolia L.

Delta and other Mediterranean deltas have assessed restoration

initiatives regarding abiotic and biotic factors controlling vertical

The marshes and rice ﬁelds within the Delta receive irrigation accretion and elevation change to keep pace with sediment deﬁcit

water from the Ebro River, which is the largest river of the Iberian and RSLR.

3 −1

∼

Peninsula (ﬂow ca. 400 m s ). A series of dams ( 170) were In this study we hypothesized that: (1) vertical accretion

built along the watercourse during the 1960s to support a vari- and elevation change in oligohaline restored marshes under low

ety of intensive water uses (Ibánez˜ and Prat, 2003). These dams sediment availability conditions are controlled by organic con-

retain an estimated 99% of the sediment that would normally be tributions as a function of water type and water level, and (2)

deposited within the Ebro Delta, thus creating a severe sediment oligohaline restored marshes can have rates of vertical accre-

deﬁcit (Ibánez˜ et al., 1996). Global eustatic sea-level rise (ESLR) has tion and elevation gain higher than RSLR under low sediment

−1

increased at a rate of 1–2 mm yr over the last century and it is availability conditions. To test these hypotheses, we conducted

−1

now higher than 3 mm yr (FitzGerald et al., 2008). However, pre- an experimental study during three years in a newly established

dicted relative sea-level rise (RSLR) in Ebro Delta may range from 5 experimentally restored marshes consisting of 72 experimental

−1 2

to 8 mm yr at the end of the present century, due to ESLR and land units (100 m each). Two different freshwater water input types

subsidence (Ibánez˜ et al., 2010). Both sediment reduction and RSLR (riverine irrigation water and rice ﬁeld drainage water) and three

∼

have created an environment where 40% of the emerged Ebro water levels (10, 20 and 30 cm deep) were used.

Delta plain has an elevation lower than 50 cm and ∼10% of the delta

is below sea level (Ibánez˜ et al., 1997). Thus, 50% of the Ebro Delta

is vulnerable to ﬂooding impacts and permanent submergence of 2. Methods

both marshes and rice ﬁelds (DMAiH, 2008; Alvarado-Aguilar et al.,

2012). This is not a problem unique to the Ebro Delta as similar 2.1. Experimental design

systems such as the Ganges, Mississippi, Nile, Rhone and Po Deltas,

all suffer from similar sediment deﬁcits (Syvitski et al., 2009). RSLR We carried out the ﬁeld experiment at an organic rice farm

impacts on worldwide deltaic rice agriculture would have effects on located in the southeast of the Ebro Delta (Catalonia, Spain) (Fig. 1,

14 J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22

Fig. 2. Design of the experimentally restored marshes. The two water treatments consisted of 36 experimental units receiving either irrigation or drainage water. Each

treatment included the water level factor (10, 20 and 30 cm depth) divided in 3 blocks via a complete randomized block design.

top). We established the experiment between an active organic Phragmites australis (Cav.) Steudel, Scirpus maritimus L. and Scirpus

rice ﬁeld to the West and an old restored marsh to the East sep- litoralis Schrad., since the study area is located in an old freshwater

arated by a bare soil strip (Fig. 1, bottom). We used a partly nested marsh area (abandoned distributary), which was transformed to

experimental design to compare plant biomass, vertical accre- rice cultivation in the previous century (Curcó et al., 1995).

tion and elevation change in response to water type and water We initiated the experiment in August 2009 and ran it for 3 years

level treatments. Water type comprised 2 treatments: riverine (Appendix 1). The hydroperiod for the experiment (seasonal ﬂood-

irrigation water (IW) and rice ﬁeld drainage water (DW) applied ing and draw down periods) was coincident with the regional rice

to 36 experimental units (EUs) for each treatment. The water level harvest/planting regime. During the ﬁrst year, the EUs were fully

factor consisted of 3 water level treatments of 10, 20, and 30 cm ﬂooded from August to December. In the second and third years,

in depth. These water level treatments were applied inside each the EUs were ﬂooded from June to December. Targeted water levels

−1

water type using a complete randomized block design with three were maintained using an average water in-ﬂow rate of 4.5 L s .

blocks. Therefore, each water type included 3 blocks and where The EUs were individually isolated using plastic lined wooden walls

each block included 12 EUs; 4 replicate EUs for each three water to prevent/limit water loss.

levels (Fig. 2). We included a block design to account for the varia-

tion in our experimental units from plant colonization effects from 2.2. Water and soil analysis

the active rice ﬁeld on the West side of the experiment. The cho-

sen water types and levels were based on readily available water Physical and chemical parameters were analyzed monthly from

sources and a realistic range of potential water levels found in rice 2009 to 2011 for both water type inﬂows (3 samples per month

ﬁelds and marshes of the Ebro Delta. Freshwater from both IW and and water type). Dissolved oxygen (DO2), temperature, conduc-

DW favors the development of a helophytic marsh dominated by a tivity and pH were measured using an YSI 556 multiprobe (YSI

J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22 15

Table 1

Incorporated, Yellow Springs, OH, USA). Three water samples per

Mean and standard error of water characteristics of both water type inﬂows. An

month were collected for both water type inﬂows during 2010

asterisk indicates a signiﬁcance difference (˛ = 0.05) on repeated measures ANOVA

and 2011 to measure total suspended solids (TSS), and total inor- −

results between water type inﬂows for water nutrient content (TP, P-PO4 , TN, N-

− +

ganic suspended solids (TISS) according to the UNE-EN 872 norm NO3 and N-NH4 ) and sediment inputs (TSS and TISS).

(AENOR, 1996). TSS and TISS analysis quantiﬁes both total and

Parameter Water type inﬂows

mineral sediment inputs in both water types that may cause ver-

Irrigation water Drainage water

tical accretion and elevation change response. In addition, three

◦

water samples per month for both water type inﬂows during 2010 Temperature ( C) 20.67 ± 1.74 20.56 ± 2.72

± ±

were analyzed for the following nutrients: total phosphorus (TP) pH 8.59 0.20 7.73 0.25

−1

DO2 (mg L ) 7.75 ± 0.94 5.55 ± 0.75

and total nitrogen (TN); inorganic dissolved nutrients; phosphate

−1

± ±

3− − + Conductivity (mS cm ) 1.22 0.10 1.48 0.18

(P-PO4 ), nitrate (N-NO3 ) and ammonium (N-NH4 ), following −1

TP (mg L ) 0.08 ± 0.01 0.18 ± 0.02*

− −

standard methods (Grasshoff et al., 1999). Water nutrient analy- 1

P-PO4 (mg L ) 0.10 ± 0.04 0.13 ± 0.04

−1

± ± sis quantiﬁes nutrient inputs in both water types that may cause a TN (mg L ) 1.18 0.04 1.05 0.21

− −1

± ±

N-NO (mg L ) 1.40 0.17* 0.54 0.13 plant growth response. 3

+ −1

N-NH4 (mg L ) 0.05 ± 0.01 0.22 ± 0.09*

Furthermore, the same physical and chemical parameters were −1

TSS (mg L ) 4.38 ± 0.67 26.66 ± 3.83*

analyzed from a subset of 26 randomly selected EUs (Fig. 2) from the −1

TISS (mg L ) 2.49 0.51 23.16 3.36*

surface and sub-soil (0.5 m depth) from 2009 to 2011 to monitoring

water characteristics that may inﬂuence plant growth. Superﬁ-

cial soil core samples (above marker horizons) were collected sampled at the end of the experiment (May 2012). SET stations

in May 2011 within a 36 EUs subset to analyze soil parameters were established adjacent to the marker horizons in 26 randomly

(i.e. mineral matter content, bulk density and mineral particle selected EUs (Fig. 2) and SETs readings were taken every three

size) that may impact vertical accretion. Samples of known vol- months since August 2009 until May 2012. In this study we use ver-

ume were weighted to determine wet weight and dried to a tical accretion to refer to surface accretion processes due to mineral

◦

constant weight at 60 C. Soil bulk density was calculated from sedimentation, leaf litter deposition and root growth. We refer to

these data (Page et al., 1982). Organic matter content was mea- elevation change as the change of marsh elevation due to vertical

◦

sured by loss-on-ignition at 500 C during 12 h and mineral matter accretion, subsurface soil expansion by root growth and shallow

was derived from organic matter percentage following Pont et al. subsidence by compaction and decomposition.

(2002). The determination of particle size distribution in mineral

soil material was performed using wet sieving and sedimenta- 2.5. Statistical analysis

tion technique (ISO11277, 2002). The following particles sizes

classes were measured: clay (d < 2 ␮m), ﬁne silt (2 ␮m < d < 16 ␮m), A repeated measures analysis of variance (ANOVA) of ﬁxed

medium silt (16 ␮m < d < 45 ␮m), coarse silt (45 ␮m < d < 63 ␮m) effects (Type III test) was performed to test differences in sedi-

and sand (63 ␮m < d < 2000 ␮m). ment input (TSS and TOSS) and nutrient content (total nutrients and

dissolved inorganic nutrients) on both water type inﬂows, which

2.3. Aboveground and belowground plant biomass may cause a different response of vertical accretion and elevation

change in the experimentally restored marshes. Multivariate Prin-

Maximum aboveground biomass (MAB) or peak standing crop cipal Component Analysis (PCA) was carried out to explore the

was measured to obtain an estimate of plant growth (Cronk and relationships between abiotic and biotic variables with vertical

Siobhan Fennessy, 2001) that may affect vertical accretion and ele- accretion and elevation change and identify underlying factors that

vation change. Accordingly, three random subsamples of 0.25 m control them. Kaiser–Meyer–Olkin’s (KMO) measure of sampling

were sampled from the previously identiﬁed 36 EUs subset in the and Barlett’s test of sphericity were used to assess the appropri-

last growing season of the experiment (August 2011) following ateness and adequacy of the PCA (McGarigal et al., 2000). A partly

a direct method from Schubauer and Hopkinson (1984). Plants nested ANOVA of ﬁxed effects (Type III test) was used to test differ-

◦

were separated by species and dried to constant weight (at 60 C). ences on the main response variables (plant biomass, surface soil

Maximum belowground biomass (MBB) was analyzed to obtain properties, vertical accretion and elevation change) among water

information of root growth contribution to vertical accretion and types and water levels (Quinn and Keough, 2002). Differences in

elevation change. MBB was sampled in the last dormant season of response variables among block effects were also analyzed to test

the experiment (May 2012) by collecting two soil core subsamples vertical accretion and elevation change response to vegetation col-

from the 36 EUs subset (50 cm long, 11.8 cm internal diameter). onization. In the presence of signiﬁcant differences ( < 0.05) in

To improve the efﬁciency of core extraction, we sealed the top ANOVA results, pairwise comparisons were made with the Tukey

with a screw top cap before extracting the core from the sed- test. All statistical analyses were performed using SPSS software

iment (Schurman and Goedewaagen, 1971). Each soil core was version 20 (IBM, 2010).

sectioned and washed with tap water through 1 mm mesh sieve to

remove inorganic sediments. The plant material was then sealed 3. Results

◦

into labeled plastic bags and stored at 2–5 C. Each thawed sam-

ple was sorted into live and dead roots and litter. All samples were 3.1. Water characteristics

◦

dried to constant mass at 60 C and weighed (Curcó et al., 2002).

Both water type inﬂows were characterized as oligohaline

2.4. Vertical accretion and elevation change and oxygenated waters (Table 1). The ANOVA indicated DW

inﬂow had signiﬁcantly higher TSS (F1,4 = 59,247, P < 0.001), TISS

Vertical accretion and elevation change were determined using (F1,4 = 58,285, P < 0.001), N-NH4 (F1,4 = 73.8, P = 0.001) and TP

marker horizons (Kaolinite) (Cahoon and Turner, 1989) and surface (F1,4 = 29.81, P = 0.05) compared to IW (Table 1). IW inﬂow had

−

elevation tables (SETs), respectively (Cahoon et al., 2002). Marker signiﬁcantly higher N-NO3 (F1,4 = 51.67, P = 0.002) with no signiﬁ-

2 3−

horizons were laid upon a 1 m marsh surface in the center of the cant differences for TN (F1,4 = 0.32, P = 0.6) and P-PO4 (F1,4 = 5.26,

36 EUs subset in August 2009 and two random subsamples were P = 0.084) (Table 1). Experimentally restored marshes had

16 J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22

Table 2

Mean and standard error of surface and soil water characteristics in the experimentally restored marshes as a function of water type and water level treatments.

Parameter Irrigation water Drainage water

10 cm 20 cm 30 cm 10 cm 20 cm 30 cm

Surface water Mean 20.00 19.56 19.51 20.26 19.98 19.65

◦

temperature ( C) S.E. 0.27 0.16 0.09 0.20 0.25 0.12

Soil water temperature Mean 20.55 20.47 20.32 20.31 20.44 20.30

◦

( C) S.E. 0.05 0.07 0.17 0.23 0.20 0.15

Surface water pH Mean 7.59 7.78 7.72 7.71 7.74 7.65

S.E. 0.08 0.06 0.09 0.06 0.04 0.09

Soil water pH Mean 6.68 6.65 6.77 6.65 6.76 6.80

S.E. 0.07 0.05 0.12 0.08 0.04 0.03

Surface water DO2 Mean 5.23 5.14 5.09 5.61 4.84 4.35

−1

(mg L ) S.E. 0.59 0.35 0.43 0.54 0.26 0.77

−1

Soil water DO2 (mg L ) Mean 0.31 0.52 0.49 0.51 0.37 0.36

S.E. 0.03 0.09 0.08 0.11 0.07 0.04

Surface water Mean 1.98 1.60 1.30 1.91 1.98 1.64

−1

conductivity (mS cm ) S.E. 0.44 0.12 0.06 0.15 0.16 0.04

Soil water conductivity Mean 70.96 73.40 53.17 76.42 73.51 50.60

−1

(mS cm ) S.E. 1.39 3.49 8.20 2.54 1.54 4.26

oligohaline surface waters and hyperhaline soil waters (0.5 m negatively to higher water levels in DW treatment (Fig. 4). Plant

depth) due to saline intrusion characteristic of current conditions composition of the EUs corresponded to a oligohaline marsh veg-

within the Ebro Delta (Table 2). Experimentally restored marshes etation dominated by S. maritimus L. and S. litoralis Schrad., with

had oxygenated surface waters and sub-oxygenated soil waters high colonization by the weed P. distichum as a consequence of

(Table 2). the proximity of a rice ﬁeld (Curcó, 2000). There were no signiﬁ-

cant differences in MAB between water types (F1,26 = 1.1, P = 0.309)

3.2. Relationships between forcing and response variables

and water levels (F2,26 = 2.1, P = 0.145) nor was there a signiﬁcant

block effect (F4,26 = 1.6, P = 0.192). It should be noted, however,

Principal Component Analysis results indicated a strong rela-

that the MAB data displayed an increasing trend (higher biomass)

tionship of vertical accretion with surface soil properties along

from block 1 to block 3 (area closest to an existing rice ﬁeld)

component 1 (Fig. 3, top), which is explained by water type

under both water types (Fig. 4, top). This observed trend closely

variation (Fig. 3, bottom). A secondary relationship of elevation

tracked the biomass of P. distichum (Fig. 4, center). P. distichum was

change with plant biomass appears along component 2 (Fig. 3,

the most signiﬁcant contributor to MAB of any other species and

top), which is explained by block variation (Fig. 3, bottom). KMO’s

was found in EUs independent of the IW or the DW treatments

measure of sampling adequacy (0.60) and Bartlett’s test of spheric-

(F1,26 = 4.1, P = 0.057) water level (F2,26 = 0.57, P = 0.571) or block

ity (P < 0.0001) indicated the appropriateness of the PCA. The ﬁrst

(F4,26 = 2.1, P = 0.111). MBB was signiﬁcantly different among water

two components explained a total of 43.13% of the variance, with

levels (F2,26 = 8.0, P = 0.002) and blocks (F2,26 = 3.2, P = 0.028), but not

component 1 contributing 26.89% and component 2 contributing

among water types (F1,26 = 3.5, P = 0.072). MBB only showed sig-

16.24%. An oblimin rotation was performed to aid in the inter-

niﬁcant differences between water levels in the DW treatment for

pretation of these two components (McGarigal et al., 2000). The

pairwise comparisons (Tukey), where MBB was signiﬁcantly higher

PCA rotation solution showed a number of medium (±0.40) and

in the 10 cm water level than in the 30 cm water level (P = 0.014)

high (±0.60) loadings (correlations) indicating the relationships

and higher than the 20 cm water level but not signiﬁcant (P = 0.059)

of abiotic and biotic variables with vertical accretion and eleva-

(Fig. 4, bottom). A signiﬁcant block effect was observed when look-

tion change in both components (Fig. 3, top). Along component 1

ing speciﬁcally at MBB in the IW treatment, where block 3 had

appears a direct relationship between vertical accretion (−0.56)

signiﬁcantly higher MBB than blocks 2 and 1 (P = 0.01 and P = 0.001,

and ﬁner grain sizes; namely clay (−0.75) and ﬁne silt (−0.6).

respectively). In the DW treatment, block 3 had signiﬁcantly higher

These variables were all opposed to soil bulk density (0.42) and

MBB than block 1 (P = 0.042) for pairwise comparisons (Tukey)

coarser grain sizes; medium silt (0.93), coarse silt (0.94) and sand

(Fig. 4, bottom).

(0.94). Component 2 shows a direct relationship between elevation

change (−0.81), MAB (−0.65) and MBB (−0.52). These variables

were all opposed to surface water pH (0.75) and DO2 (0.55), soil 3.4. Surface soil properties response among treatments

water pH (0.60) and soil bulk density (0.57). Scores of EUs explained

two main underlying factors controlling forcing and response vari- Surface soil mineral content was greater in DW treatment,

ables relationships (Fig. 3, bottom). The ﬁrst factor was the water as well as bulk density, sand and silt content. Mineral con-

type variation along component 1, which explained vertical accre- tent also increased in both water type treatments with the

tion and surface soil properties relationships. The second factor was higher water levels, and decreased in blocks closer to rice ﬁeld

the block variation along component 2, which explained elevation cultivation. Mineral content responded in all treatments signif-

change, plant biomass and water parameters relationships. icantly: among water types (F1,28 = 4.7, P = 0.039), water levels

(F2,28 = 4.6, P = 0.019) and blocks (F4,28 = 4.8, P = 0.004) (Fig. 5, top).

3.3. Plant biomass response among treatments Pairwise comparisons between water levels only showed sig-

niﬁcant differences in mineral content in DW treatment: 10 cm

MAB and MBB were signiﬁcantly higher in blocks closer to the with 20 cm (P = 0.04) and 30 cm (P = 0.005). Pairwise compar-

rice ﬁeld due to P. distichum L colonization, and MBB also responded isons between blocks showed signiﬁcant differences in mineral

J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22 17

and clay content varied inversely among water levels and blocks in

both water type treatments.

3.5. Vertical accretion and elevation change response among

treatments

Vertical accretion showed a signiﬁcant increase in DW treat-

ment compared to IW treatment due to signiﬁcantly higher mineral

sediment input, which promoted higher surface soil mineral con-

tent. Elevation change appeared to be affected by block effects

due to P. distichum colonization and all three parameters (ele-

vation change, MAB of P. distichum L and MBB) increased in

block 3 closest to rice cultivation. In both water type treatments,

mean values (±standard error) of vertical accretion (11.5 ± 0.8

−1

and 15.5 ± 0.6 mm yr ) were higher than those for elevation

−1

change (9.1 ± 1.4 and 8.8 ± 2.8 mm yr ). ANOVA results showed

vertical accretion was signiﬁcantly higher in the DW treatment

than the IW treatment (F1,21 = 9.5, P = 0.006) (Fig. 6, top). Verti-

cal accretion did not show signiﬁcant differences among water

levels (F2,21 = 0.4, P = 0.681) but showed signiﬁcant differences

among blocks (F4,21 = 2.8, P = 0.05). Vertical accretion signiﬁcantly

increased on blocks closer to rice ﬁeld cultivation (block 3) in the

DW treatment, possibly in response to sediment capture by the

combination of higher sediment input and substantially higher

aboveground biomass of P. distichum. Block 3 displayed substan-

tially higher vertical accretion than block 1 (P = 0.075) and block

2 had signiﬁcantly higher vertical accretion rates than block 1

(P = 0.05) for pairwise comparisons (Fig. 6, top). In the IW treat-

ment, vertical accretion signiﬁcantly changed among blocks, where

block 3 had signiﬁcantly lower accretion than block 1 (P = 0.013)

and block 2 (P = 0.034) for pairwise comparisons (Fig. 6, top).

Elevation change did not show signiﬁcant differences among

water types (F1,16 = 0.1, P = 0.797) and water levels (F2,16 = 0.1,

P = 0.868) but it showed signiﬁcant differences among blocks

(F4,16 = 4.2, P = 0.016) (Fig. 6, bottom). Particularly, block 3 in both

water type treatments had higher elevation change (11.3 ± 2.3

−1

and 17.8 ± 2.9 mm yr ) than vertical accretion (8.3 ± 1.3 and

−1

15.1 ± 1.3 mm yr ). This positive difference when subtracting ver-

tical accretion rates from elevation change rates points out that

signiﬁcantly higher belowground biomass in block 3 also con-

tributed to elevation change by root growth due to high weed

colonization by P. distichum from rice ﬁeld edge. Block 3 of the DW

treatment had signiﬁcantly higher rates of elevation change than

either block 2 or 1 (P = 0.043 and P = 0.042, respectively) for pair-

wise comparisons (Fig. 6, bottom). In the IW treatment, elevation

change did not show any signiﬁcant differences between blocks

Fig. 3. Principal Component Analysis of the forcing and response variables. Factor although it displayed an increasing trend from the block 1 to the

loadings of the variables (top) and scores of experimental units classiﬁed by water block 3 (Fig. 6, bottom).

type treatments and block effects (bottom).

4. Discussion

content in both water type treatments. Block 3 had signiﬁcantly

lower mineral content than block 1 (P = 0.02) in the IW treat- Marsh development and stability are dependent on allogenic

ment. Block 2 had signiﬁcantly lower mineral content than block (e.g. ﬂooding, sediment inputs) and autogenic factors (e.g. plant

1 (P = 0.04). There were signiﬁcant differences in bulk density growth) (Singer et al., 1996; Waller et al., 1999). Initial stages of

between water types (F1,28 = 12.9, P = 0.001) but not between marsh succession are usually controlled by mineral contributions

water levels (F2,28 = 1.1, P = 0.365) and blocks (F4,28 = 0.1, P = 0.979) that control the optimal elevation to favor vegetation coloniza-

(Fig. 5, center). There were no signiﬁcant differences for any par- tion and development (Morris et al., 2002). Mature marshes may

ticle size content between water types, water levels and blocks have greater organic contribution (e.g. leaf litter deposition and

(Fig. 5, bottom): sand (F1,28 = 1.7, P = 0.205; F2,28 = 1.5, P = 0.249; and root growth) because a more extensive plant community cover is

F4,28 = 2.4, P = 0.071), silt (F1,28 = 2.4, P = 0.129; F2,28 = 1.1, P = 0.338; developed and marsh elevation gain causes higher isolation from

and F4,28 = 2.9, P = 0.061) and clay (F1,28 = 3.8, P = 0.062; F2,28 = 0.8, marine and riverine sediment sources (Brinson et al., 1995; Mitsch

P = 0.462; and F4,28 = 2.5, P = 0.082). Two general trends of particle and Gosselink, 2007). Under a sediment-deﬁcit scenario, autogenic

size content appeared among treatments. First, both sand and silt organic contributions may be critical to marsh stability and survival

increased in DW treatment inversely to clay content. Secondly, silt to support the balance between elevation gain and RSLR (DeLaune

18 J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22

Fig. 4. Partly nested ANOVA results of mean (±SE) plant biomass response among water types, water levels and blocks. Where there were signiﬁcant main effects (˛ = 0.05)

on ANOVA results among water levels and block effects, Tukey pairwise comparisons were tested within each water type treatment and different letters denotes signiﬁcant

differences.

and Pezeshki, 2003; Blum and Christian, 2004; Nyman et al., 2006; gain, especially when the weed P. distichum colonized rapidly and

Langley et al., 2009; Kirwan and Guntenspergen, 2012). In our densely the experimentally restored marshes. The observed overall

study, mineral contributions controlled vertical accretion and ele- mean rates of vertical accretion and elevation change also support

vation change in the establishment of oligohaline restored marshes the hypothesis that oligohaline restored marshes often have eleva-

even under sediment-deﬁcit conditions. Higher mean vertical tion gains higher than RSLR in the Ebro Delta, at least during the

−1

accretion rates (11.5 ± 0.8 and 15.5 ± 0.6 mm yr ) than elevation initial phase of marsh establishment.

−1

change (9.1 ± 1.4 and 8.8 ± 2.8 mm yr ) in both water type treat- Vertical accretion responded positively to higher mineral input

ments suggests that the surface accretion processes via mineral from the rice ﬁeld drainage water but vertical accretion was not

sedimentation overall controlled marsh elevation. However, sub- affected by plant colonization among blocks. Our results show a

soil expansion via root growth also caused a positive elevation signiﬁcant higher surface soil mineral content in DW treatment due

J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22 19

Fig. 5. Partly nested ANOVA results of mean (±SE) surface soil properties response among water types, water levels and blocks. An asterisk indicates signiﬁcant increase

( = 0.05) between water type treatments. Where there were signiﬁcant main effects (˛ = 0.05) on ANOVA results among water levels and block effects, Tukey pairwise

comparisons were tested within each water type treatment and different letters denotes signiﬁcant differences.

to signiﬁcant higher mineral input that contributes signiﬁcantly to organic contribution to marsh elevation. An alternative explana-

vertical accretion. The multivariate analysis results also pointed out tion is that agricultural run-off may also contain herbicides, which

the strong relationship between vertical accretion and surface soil may reduce plant germination (Reynoldson and Zarull, 1993; Jurik

mineral properties along the component 1, which was explained et al., 1994). The use of herbicides in rice ﬁelds of the Ebro Delta such

by primary source of variation due to water type treatments. Sim- as molinate, propanil and 2–4 MCP is the most common way to con-

ilar plant growth in both water type treatments and lower surface trol weeds (Echinochloa spp., Cyperus spp. and Scirpus spp.; Manosa˜

soil organic content in the DW treatment may indicate that higher et al., 2001), so herbicide content in DW treatment could also affect

nutrient levels from drainage waters did not enhance accretion via plant communities of the experimentally restored marshes.

organic contribution as several studies have already pointed out We also hypothesize that P. Distichum enhanced positive eleva-

(Craft and Richardson, 1993; Rybczyk et al., 2002; Brantley et al., tion change rates via fast root growth in the initial stages of the

2008). A possible explanation is that small differences in nutrient experimentally restored marsh development (i.e. within the ﬁrst

content between water type inﬂows may require a longer time of three years) (Anderson and Ehringer, 2000; Wanyama et al., 2012).

fertilization to cause differences in plant growth and subsequent Both elevation change and MBB increased signiﬁcantly in blocks

20 J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22

Fig. 6. ANOVA results of mean (±SE) vertical accretion and elevation change response among water types, water levels and blocks. An asterisk indicates signiﬁcant increase

(˛ = 0.05) between water type treatments. Where there were signiﬁcant main effects (˛ = 0.05) on ANOVA results among water levels and block effects, Tukey pairwise

−1

comparisons were tested within each water type treatment and different letters denotes signiﬁcant differences. The dashed line represents global (3 mm yr ) and regional

−1

projections (5 mm yr ) of ESLR means (IPCC, 2007; Marcos and Tsimplis, 2008). The shaded area represents predicted RSLR for the Ebro Delta (Ibánez˜ et al., 2010).

closest to rice cultivation (block 3), where P. distichum colonization Europe, Asia and the Paciﬁc (Curcó, 2000; CABI, 2012). Though

appears to originate from the earth berm edge that divided the a vigorous invader of newly reclaimed marshland, this species is

adjacent rice ﬁeld and the experimental study. The multivariate documented to be a minor contributor in natural and restored

analysis results also pointed out this strong relationship between oligohaline marshes in mature succession stages (Comín et al.,

elevation change and both MAB and MBB along the component 2, 2001; Curcó, 2001). These ﬁndings suggest that initial invasions

which was explained by a secondary source of the variation due to by this plant in the restored marshes (at least in the Ebro Delta)

block effects. On close examination, our results also point out that should not be of great concern and perhaps even encouraged when

water levels may indirectly control elevation change inﬂuencing the overarching goal of the marsh restoration is RSLR abatement

root growth in DW treatment. Prolonged higher water levels dur- and passive water treatment.

ing the experiment may have caused a physiological stress reducing Previous works have highlighted marsh ecosystems services

root productivity in higher water levels (Mendelssohn and Morris, providing coastal protection to human populations against storm

2000). Both elevation change and MBB increased signiﬁcantly with surges and RSLR (Gedan et al., 2011; Shepard et al., 2011). Our

lower water levels in the DW treatment. Oppositely, there was a study strongly supports the use of restored marshes as natural

30% decrease of soil water DO2 from 10 cm to 30 cm water level buffers against RSLR. Experimentally restored marshes receiving

treatment that may reduce root growth. Finally, root growth could rice ﬁeld drainage water balanced RSLR rates due to a combination

not affect vertical accretion rates because most of root growth may of a signiﬁcant mineral contribution (sediment input) to verti-

have occurred below the placed marker horizons and may only cal accretion and high organic contribution (root production) to

affect elevation change (Cahoon et al., 1999, 2006). elevation change. To note, the experimentally restored marshes

Our results support the idea that wetland restoration initiatives had higher overall mean values in both water type treatments of

−1

with the primary goal of maximize marsh elevation gain should vertical accretion (11.5 ± 0.8 and 15.5 ± 0.6 mm yr ) and eleva-

−1

consider the inclusion of vegetated buffers to mitigate or pro- tion change (9.1 ± 1.4 and 8.8 ± 2.8 mm yr ) than brackish natural

mote the edge effects of plant colonization (Murcia, 1995; Wu and marshes in the Ebro Delta. For example, in riverine sites, the aver-

Mitsch, 1998; Feagin and Wu, 2006). Interestingly, P. distichum is age rate of vertical accretion and elevation change were 5.03 ± 0.33

−1

considered a major weed of rice ﬁelds and restored marshes in and 6.61 ± 2.36 mm yr , respectively (Ibánez˜ et al., 2010).

J. Calvo-Cubero et al. / Ecological Engineering 61 (2013) 12–22 21

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natural marshes located in Northwestern Mediterranean Deltas

wetlands from abandoned rice ﬁelds for nutrient removal, and biological com-

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± ±

such as the Po Delta (10.7 4.2 and 7.3 2.1 mm yr , respec- munity and landscape diversity. Restor. Ecol. 9, 201–208.

−

1 Craft, C., 2007. Freshwater input structures soil properties, vertical accretion, and

tively) and the Rhône Delta (12.5 ± 3.2 and 11.4 ± 3.2 mm yr ,

nutrient accumulation of Georgia and U.S. tidal marshes. Limnol. Oceanogr. 52,

respectively) (Day et al., 2011). These ﬁndings suggest that exper- 1220–1230.

imentally restored marshes result on higher vertical accretion and Craft, C.B., Richardson, C.J., 1993. Peat accretion and N, P, and organic C accumu-

lation in nutrient-enriched and unenriched Everglades Peatlands. Ecol. Appl. 3,

elevation change rates than natural marshes because of water

446–458.

input and turnover was large enough to favor sedimentation even

Cronk, J.K., Siobhan Fennessy, M., 2001. Wetland Plants. CRC Press, Boca Raton, FL.

under low suspended sediment availability. Using freshwater in Curcó, A., 2000. La vegetació del delta de l’Ebre (IV): Les comunitats nitróﬁes. Acta

marsh restoration projects located in sediment-deﬁcient deltas Bot. Barc. 46, 143–178.

Curcó, A., 2001. The vegetation of the Ebro Delta (V): helophytic and hygrophilous

and estuaries has the potential to be a positive option for the

communities. Lazaroa 22, 67–81.

main restoration goals seeking to mitigate RSLR, since freshwater

Curcó, A., Canicio, A., Ibánez,˜ C., 1995. Mapa d’habitats potencials del delta de l’Ebre.

may enhance vertical accretion and elevation change via auto- Butlletí del Parc Nat. Delta Ebre 9, 4–12.

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Neubauer, 2008).

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Acknowledgements

Day, J.W., Christian, R.R., Boesch, D.M., Yanez-Arancibia, A., Morris, J., Twilley, R.R.,

Naylor, L., Schaffner, L., Stevenson, C., 2008. Consequences of climate change on

the ecogeomorphology of coastal wetlands. Est. Coasts 31, 477–491.

This study has been funded by the Government of Spain

Day Jr., J.W., Boesch, D.F., Clairain, E.J., Kemp, G.P., Laska, S.B., Mitsch, W.J., Orth,

(Ministerio de Medio Ambiente, Research Project 056/RN08/04.3,

K., Mashriqui, H., Reed, D.J., Shabman, L., Simenstad, C.A., Streever, B.J., Twilley,

development of techniques to compensate subsidence and sea- R.R., Watson, C.C., Wells, J.T., Whigham, D.F., 2007. Restoration of the Mississippi

Delta: lessons from Hurricanes Katrina and Rita. Science 315, 1679–1684.

level rise in coasts and wetlands of the Ebro Delta, 2009–2011). We

DeLaune, R.D., Jugsujinda, A., Peterson, G.W., Patrick, W.H., 2003. Impact

would like to thank Lluis Jornet, David Mateu, Rosa Valmana˜ and

of Mississippi River freshwater reintroduction on enhancing marsh

Dr. Walter Tzilkowski for technical support and assistance in ﬁeld- accretionary processes in a Louisiana estuary. Est. Coast. Shelf Sci. 58,

653–662.

work and lab analysis. We also thank three anonymous reviewers

DeLaune, R.D., Pezeshki, S.R., 2003. The role of soil organic carbon in maintaining

for constructive comments helped us to improve this manuscript.

surface elevation in rapidly subsiding U.S. Gulf of Mexico coastal marshes. Water

Air Soil Pollut.: Focus 3, 167–179.

DMAiH, 2008. Framework Study N1: Ebro Delta. Framework Studies for Later Use in

Appendix A. Supplementary data

Deﬁning a Strategy for Preventing and Adapting to Climate Change in Catalonia.

Departament de Medi Ambient i Habitatge, Barcelona, Spain.

Supplementary data associated with this article can be Fagherazzi, S., Kirwan, M.L., Mudd, S.M., Guntenspergen, G.R., Temmerman, S.,

D’Alpaos, A., van de Koppel, J., Rybczyk, J.M., Reyes, E., Craft, C., Clough, J., 2012.

found, in the online version, at http://dx.doi.org/10.1016/j.ecoleng.

Numerical models of salt marsh evolution: ecological, geomorphic, and climatic

2013.09.047.

factors. Rev. Geophys., 50.

Feagin, R.A., Wu, X.B., 2006. Spatial pattern and edge characteristics in restored ter-

race versus reference salt marshes in Galveston Bay. Wetlands 26, 1004–1011.

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