ORIGINAL ARTICLE

Reclamation influence and background geochemistry of neutralsaline soils in the Po River Delta Plain (Northern Italy)

Dario Di Giuseppe • Barbara Faccini •

Micol Mastrocicco • Nicolo Colombani •

Massimo Coltorti

Received: 2 April 2013 / Accepted: 17 February 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract Reclaimed neutral saline sulphate soils consti-

tute a large part of the eastern part of Po Plain lowlands,

where intensive agricultural activities take place. The

knowledge of their geochemical features is essential to

develop the best management practices capable to preserve

this threatened environment. With this aim, three boreholes

were drilled in an agricultural field and a typical reclaimed

soil profile has been characterized for major and trace

element, pH, electrical conductivity, redox conditions and

water-soluble anions and ammonium. Statistical analysis

(cluster analysis and principal component analysis) has

been used to understand the relationship between elements

and grain size. The soil profile is characterized by high

salinity and high organic matter contents responsible for

high chloride, sulphate, and ammonium concentrations.

Heavy metal content is naturally high, since Po Plain

sediments are the result of ultramafic rocks erosion; in

addition, organic matter tends to concentrate heavy metals

by adsorption, mainly in peaty horizons. As a consequence

of chemical and zootechnical fertilization, high NO3-

contents have been found in the top soil, thus enhancing the

risk of nitrate discharge in the water system, especially in

relation to extreme climatic events.

Keywords Soil � Reclaim � Geochemistry � Agriculture �Redox � PCA

Introduction

Wetlands are critical and fragile environments were water

salinization and accumulation of heavy metals can easily

occur. The increasing demand of land for agricultural pur-

poses has led to the reclamation of large wetland areas

(Airoldi and Beck 2007) that may be affected by several

problems such as soil salinization (Mastrocicco et al.

2013a), decalcification (Van den Berg and Loch 2000),

gleying (Bini and Zilocchi 2004), and further increase in the

amount of the heavy metals (Bai et al. 2011; Molinari et al.

2013; Di Giuseppe et al. 2014). These processes can cause

extensive changes in the physical–chemical characteristics

of the soil, such as redox conditions, pH, and leaching of C,

N, P, S and Fe (Pornoy and Giblin 1997). Moreover, to

make this soil productive, a large use of fertilizers, espe-

cially nitrogen compounds, is required, causing a remark-

able pollution of the superficial and ground water. These

problems are rather common in Italy (D’Antona et al. 2009;

Mastrocicco et al. 2013b) and abroad (Rysgaard et al. 1996;

DelAmo et al. 1997; Bai et al. 2005; De Wit et al. 2005;

Netzer et al. 2011; Statham 2012).

To provide information on the water/soil system that

would be also useful for recognizing and interpreting geo-

chemical anomalies potentially induced by pollution pro-

cesses, the Po River Delta Plain in Northern Italy has been

studied. This sedimentary basin, bordered by the Alps and

the Apennine chains, hosts about 25 % of the Italian pop-

ulation and most of the Nation’s agricultural activities. In

particular, the soil profile, hereafter reported as reclaimed

soil profile (RSP), is located in the Province of Ferrara, next

Electronic supplementary material The online version of thisarticle (doi:10.1007/s12665-014-3154-4) contains supplementarymaterial, which is available to authorized users.

D. Di Giuseppe (&) � B. Faccini � M. Mastrocicco �N. Colombani � M. Coltorti

Physics and Earth Science Department, University of Ferrara,

Ferrara, Italy

e-mail: dgsdra@unife.it

N. Colombani

Department of Earth Sciences, ‘‘Sapienza’’ University of Rome,

Roma, Italy

123

Environ Earth Sci

DOI 10.1007/s12665-014-3154-4

to Codigoro town (45� 500 330’ N and 12�050400’ E), where

the ZeoLIFE Project (LIFE ? 10/ENV/IT/00321; Coltorti

et al. 2012; Di Giuseppe et al. 2012, 2013), aimed at

reducing nitrate pollution and correct agricultural soils, is

currently developing. The delta environment is character-

ized by high lateral mobility of the active channel belts,

with recurrent avulsion and channel bifurcation, which

redistribute the water and sediment fluxes throughout the

system (Bondesan et al. 1995; Stefani and Vincenzi 2005).

When the high-energy alluvial deposition outranged the

low-energy lacustrine conditions typical of organic depo-

sition, the peat levels were buried and incorporated into the

stratigraphic sequence (Miola et al. 2006).

The sedimentological and geochemical features of the

Po River sediments have been studied in detail, mainly

focussing on the spatial distribution of heavy metals in

relation to provenance and sedimentary facies (Amorosi

et al. 2002, 2003; Amorosi and Sammartino 2007; Bian-

chini et al. 2002, 2012; Amorosi 2012). On the other hand,

reclaimed saline soils are significantly different. Their

geochemical and pedological characteristics have been

extensively studied for acid sulphate soil (Unland et al.

2012; Burton et al. 2006; Ljung et al. 2009) but not so

intensely for neutral saline sulphate soils. These sediments

evolve from backswamp deposits peculiarly rich in organic

matter. In these environments, due to the rapid subsidence

enhanced by sediment compaction, the coalescence of

water pools has created large wetlands. In modern age, the

anthropic reclamation activity has drained off most of the

marshes, causing the deposition of a fine-grained surface

layer where drainage is difficult (Stefani and Vincenzi

2005). These soils have been drained by humans to take

advantage of new land and they are different from the

natural soil profiles existing worldwide. Nowadays, the

majority of the reclaimed lands is intensively exploited and

widely cultivated with highly nutrient-demanding crops

(mainly corn) which require a large use of fertilization and

chemical treatment. The consequence of such agricultural

practice in this ‘‘artificial’’ environment could lead to metal

pollution (Borghesi et al. 2011) and eutrophication of

channels and coastal lagoons (Frascari et al. 2002).

To preserve this fragile environment or develop best

management practices, it is compulsory to define the geo-

chemical composition of the soils, i.e., the baseline on

which future human activities will be overimposed. This

study is aiming at describing, evaluating, and comparing

major and trace elements (Ni, Cr, V, Zn, Pb, Co, Cd, Cu, U,

As, Sr, Zr, S, Rb), organic matter, pH, electrical conduc-

tivity, and particle size vertical distribution in a typical

reclaimed saline soil. In addition, water-soluble cations and

anions in the soil, with particular emphasis to Nitrogen

species, are also taken into account. A multivariate statistic

approach [cluster analysis (CA) and principal component

analysis (PCA)] was adopted to assist the interpretation of

geochemical data, according to the procedure defined by

Facchinelli et al. (2001) and Tyler (2004).

Materials and methods

The study area

The geological setting of the Delta Plain, extending for more

than 730 km2, is dominated by the main branch of the Po river

and by its ancient and recent alluvial and delta deposits

(Fig. 1a). Sediments belonging to this environment occupy

an area extending from Ferrara to the Adriatic coast, shaping

up a fan-like delta limited to the North by the actual Po up to

the mouth of Maistra branch, and to the south by the Po di

Primaro–Reno fluvial system located just south of the Co-

macchio Lagoons. Within the delta system, three sedimen-

tological groups can be distinguished: the coarse deposits

(gravel and sand) of the interdistributary channels and their

banks (Fig. 1, Type Deposit 1 and 2), and the fine deposits

(silt, clay and peat) of brackish marsh and interdistributary

bays (Fig. 1, Type Deposit 3). The interdistributary bay is an

environment characterized by low-energy hydrodynamics,

where clayey and organic matter-rich sediments such as peat

(resulting from burial of swamp vegetation) prevail.

Moving eastward to the coast, the delta deposits are

interdigited with a series of sandy littoral stringy dune,

mainly elongated North–South, marking the ancient

coastline (Fig. 1, Type Deposit 4).

The areas enclosed between topographic highs (created

by paleochannels and paleodunes) are topographically

depressed areas (interdistributary bay) originally occupied

by vast marshy basins that are kept dry by the action of

mechanical water pumps (Figs. 1, 2). In 1860, the sur-

roundings of the actual city of Codigoro were almost

entirely occupied by lagoons that have been gradually dried

up in the subsequent decades (Bondesan 1990); today the

entire Codigoro Municipality lays on dry land.

Due to the soil lowering in the Po Plain that would cause

its flooding, the area belonging to the Municipality of

Codigoro is kept dry artificially by a network of draining

and irrigation channels. The lowering of the soils is caused

by the natural subsidence plus an induced subsidence

related to the human activity in the territory. The natural

subsidence is intrinsically linked to the general geological

characters of the Po Plain, with variable rates, usually

\2 mm/year (Teatini et al. 2011). The induced subsidence

is mainly related to water extraction from aquifers at low or

medium depth or gas at higher depth (Teatini et al. 2006).

The drainage of damp areas contributes also to increase this

subsidence, due to the compaction of the sediments no

longer submersed and sustained by water. The most

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Fig. 1 Regional framework of

Po Delta system. Scheme

integrated and modified from

Stefani and Vincenzi (2005)

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123

important drainage pump in the area is the Codigoro

dewatering pump, which allows the contemporaneous

drainage of two big channels conveying water at different

heights, the Acque Alte and the Acque Basse, located close

to the study site (Fig. 2).

The studied soil profile site is located between the main

distributary channel of the ancient Po Gaurus to the left and

a minor distributary channel to the right (Fig. 1). With a

height of ca. -3 m a.s.l., it resides in an intensely

agricultural area next to town of Codigoro, whose pre-

dominant crops are corn and wheat.

The site is only 13 km from the Adriatic coast. It is

characterized by a microclimate influenced by the sea.

Coastal area extends from the sea up to 30–40 km inward,

and includes 2/3 of the entire delta territory, with a broad

transitional zone where the sea mitigation gradually dis-

appears. Codigoro climate can be defined as ‘‘sub-coastal’’,

in contrast with the ‘‘sub-continental’’ climate

Table 1 Characteristics of the

soil profileHorizon Man depth (cm) Colour moist Structure Skeleton Texture CaCO3 %

Ap 0–50 Olive gray 5Y 4/2 Incoherent Angular Silty clay 8

Oe 50–140 Dark brown 10YR 3/3 Polyhedral Sub-angular Silty clay 3

Cg 140–400 Gray 5Y 5/1 Massive Clayey silt 10

Fig. 2 Site location. Three

boreholes (A, B, C). 3D view of

soil profile

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123

characterizing the western part of the Ferrara Province.

Rainfalls reach the regional pluviometric minimum, rep-

resented by an average annual value varying between 500

and 700 mm. Temperatures are affected by the proximity

of the sea. This is evident in particular during the cold

seasons, when marine thermoregulation contains the min-

ima over zero, reducing the number of night frosts (Moll-

ema et al. 2012).

Field sampling and laboratory analyses

Within the European project ZeoLife (LIFE ? 10/ENV/IT/

00321), three boreholes (A, B, C; Fig. 2) were drilled

manually in an agricultural field of six hectares with an

Ejielkamp Agrisearch auger equipment at the end of

October 2011. In all the boreholes, core samples were

collected every 30–50 cm down to a depth of 4 m. Samples

were stored in a cool box at 4 �C and immediately trans-

ported in laboratory for sedimentological and chemical

analysis. Each borehole was geo-referenced by a portable

global positioning system (GPS).

The total elements concentration of soils was deter-

mined using both X-ray fluorescence (XRF) (major and

trace elements) and ICP-MS (trace elements) technique at

the Department of Physics and Earth Sciences of the

University of Ferrara. The soil samples were air dried and

sieved at 2 mm. An aliquot of each sample was powdered

through an agate mill in preparation for chemical

investigations.

Major (SiO2, TiO2, Al2O3, Fe2O3tot, MnO, MgO, CaO,

Na2O, K2O, P2O5, expressed in weight percent) and trace

(V, Cr, Cu, Zr, S) elements were analyzed by XRF on

powder pellets, using a wavelength-dispersive automated

ARL Advant’X spectrometer. Accuracy and precision

based on systematic re-analysis of standards are better than

3 % for Si, Ti, Fe, Ca and K, and 7 % for Mg, Al, Mn and

Na; for trace elements (above 10 ppm) they are better than

10 %. Additional trace elements (Co, Ni, Zn, Pb, Cd, U,

As, Rb, Sr, Ce, Pb) were analyzed using an X Series

Thermo-Scientific spectrometer (ICP-MS) after total dis-

solution with HF ? HNO3. Specific amounts of Rh, In and

Re were added to the analyzed solutions as an internal

standard, to correct for instrument drift. Accuracy and

precision, based on replicated analyses of samples and

standards, are better than 10 % for all elements, well above

the detection limit. As reference standards, the E.P.A.

Reference Standard SS-1 (a Type B naturally contaminated

soil) and the E.P.A. Reference Standard SS-2 (a Type C

naturally contaminated soil) were also analyzed to cross-

check and validate the results.Fig. 3 Massafiscaglia borehole stratigraphy and calibrated radiocar-

bon age (integrated and modified from Bondesan et al. 1995)

Fig. 4 Average texture of soil

profile

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pH-H2O was determined electrometrically in the

supernatant after shaking 5 g of soil at field moisture for

1 h with 25 ml H2O.

Particle size distribution of the soil horizons was esti-

mated by wet sieving. Each sample inside the polythene

bags has been adequately mixed. 150 g of samples were

Fig. 5 Average ECe, pH, organic matter, and Eh of soil profile

Fig. 6 Maximum, minimum, and average vertical distribution of major elements. The Y-axis shows the depth below ground in cm (cm b.g.l.) and

the X-axis represents the element concentration expressed in weight percent (wt%)

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123

treated with 160 ml of hydrogen peroxide to eliminate the

organic substance. The sand ([63 lm) was separated by

wet procedure through a mesh sieve. Silt and clay fractions

were analyzed using a Micromeritics Sedigraph 5100.

The organic matter content expressed in weight percent

(OM%) was measured by dry combustion (Tiessen and

Moir 1993). The soil water content was measured gravi-

metrically after heating the samples for 24 h at 105 �C

(Danielson and Sutherland 1986).

Distilled water (resistivity [18 MOmh/cm) was used to

extract the water-soluble cations (NH4?, K?, Ca?2, Mg?2,

Na?) and anions (NO3-, Cl-, Br-, F-, NO2

-, SO4-2,

PO4-3) from the soil samples, using a sediment to water

weight ratio of 1:5. The sediment and water were mixed

and sealed in bakers, then shaken for 1 h, and centrifuged

for 1 h at 25 �C to separate the sediment from the solution.

Soil water and groundwater samples were filtered through

0.22 lm Dionex polypropylene filters prior to anion

analysis. Anions in all water samples were analyzed using

an isocratic dual pump ion chromatography ICS-1000

Dionex. An AS-40 Dionex auto-sampler was employed to

run the analyses; quality control (QC) samples were run

every 10 samples and the standard deviation for all QC

samples was better than 4 %. NH4? was measured with a

double beam Jasco V-550 UV/VIS spectrophotometer

(Bower and Holm-Hansen 1980).

Results

Profile description

Sedimentological analyses in the three boreholes revealed a

slight vertical and lateral variability of silt and clay con-

tents, whereas sand content is always very low. Samples

from the first 80 cm ca. shift from clayey silt to silty clay

Table 2 Descriptive statistic and correlation matrix for major elements

Element Min. Mean Max. SD

SiO2 51.74 55.3 60.84 2

TiO2 0.62 0.7 0.81 0.1

Al2O3 12.32 16 19.6 2.1

Fe2O3 5.68 7.15 8.6 0.9

MnO 0.03 0.09 0.15 0

MgO 3.93 4.56 4.98 0.3

CaO 0.9 5.69 9.43 2.7

Na2O 0.48 0.92 1.42 0.3

K2O 2.26 2.99 3.75 0.4

P2O5 0.11 0.15 0.21 0

L.O.I.* 3.39 6.44 9.25 1.5

Sand% Silt% Clay% SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 L.O.I.

Sand% 1.00

Silt% 0.39 1.00

Clay% -0.76 -0.89 1.00

SiO2 -0.19 0.17 -0.02 1.00

TiO2 -0.67 -0.60 0.75 0.41 1.00

Al2O3 -0.67 -0.69 0.81 0.17 0.92 1.00

Fe2O3 -0.65 -0.57 0.72 0.08 0.81 0.91 1.00

MnO 0.56 0.46 -0.60 -0.52 -0.85 -0.85 -0.73 1.00

MgO 0.21 0.34 -0.34 0.02 -0.34 -0.28 -0.14 0.13 1.00

CaO 0.63 0.45 -0.63 -0.51 -0.91 -0.91 -0.83 0.92 0.18 1.00

Na2O 0.45 0.62 -0.66 0.35 -0.56 -0.73 -0.77 0.44 0.18 0.46 1.00

K2O -0.67 -0.71 0.82 0.14 0.91 0.98 0.85 -0.83 -0.38 -0.88 -0.68 1.00

P2O5 -0.11 -0.44 0.36 -0.49 0.13 0.33 0.46 -0.17 0.01 -0.08 -0.62 0.29 1.00

L.O.I.* 0.51 0.28 -0.44 -0.80 -0.77 -0.62 -0.55 0.77 0.03 0.77 0.14 -0.56 0.09 1.00

The concentration is expressed in weight percent

* L.O.I loss on ignition

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(see Table 1). From about 80 cm down to 150 cm, a layer

rich in clay and dark peat is observed. In the lower part of

the sequence, (150–400 cm) silt returns the prevalent grain

size. In the Shepard (1954) ternary classificative diagrams,

all samples fall in the clayey silt and silty clay fields; the

entire C2 log lay on the boundary between the two.

On average within the soil profile three main horizons

can be recognized, according to FAO (2006) (Table 1;

Fig. 2): (1) ‘‘Ap’’: the upper well aerated silty clay unit,

homogenized by anthropic activities and characterized by

the presence of carbonate inclusions and iron hydroxides,

(2) ‘‘Oe’’: a peaty silty clay layer, and (3) ‘‘Cg’’: the lower

undisturbed clayey silt anoxic unit, rich of yellowish

undecomposed organic matter and carbonate inclusions.

The age of RSP sediments is historical as found in a

deep core sampling carried out in Massafiscaglia (Fig. 3;

Bondesan et al. 1995), a locality close to the study area.

Surface sediments are younger than 1,500 years ago (Ste-

fani and Vincenzi 2005). This soil is classified as a Humi

Thionic Fluvisols Thapthohistic according to WRB clas-

sification (WRB 2007).

On average, the texture is silty clay in the upper layers

(Ap and Oe) and clayey silt in the lower layer (Cg) of the

profile (Fig. 5). In Ap horizon, the clay fraction (\2 lm)

makes up to the 50 % ca. of bulk dry weight, decreasing to

about 25 % in Cg level (Fig. 4). The contents of silt

(2–63 lm) increase slightly downwards. The content of

sand ([63 lm) is only 0.8–7 % in Ap horizon, whereas it

increases slightly above 10 % in the Cg horizon.

The pH-H2O ranges between 6.3 and 7.6 in the Ap

horizon; it decreases in the organic Oe layer (5.8–6.9), and

varies between 6.1 and 7.4 in the Cg horizon (Fig. 5).

Table 3 Descriptive statistic and correlation matrix for trace elements

Element Min. Mean e Max. SD

V 86.6 132 183 26.6

Cr 156 221 315 35.2

Co 14.0 19.3 29.9 3.4

Ni 95.7 142 226 27.7

Cu 24.3 50.6 76.3 14.3

Zn 77.5 105 147 18.4

As 7.4 13.7 22.2 3.5

Rb 72.5 134 202 33.1

Sr 103 198 285 56.0

Cd 0.7 1.3 2.4 0.4

U 1.2 3.1 9.5 2.1

Ce 2.7 22.9 78.1 21.7

Pb 12.4 20.9 31.4 5.0

S 1,138 6,816 17,466 4,950

Zr 82.5 134 202 31.2

V Cr Co Ni Cu Zn As Rb Sr Cd U Ce Pb S Zr

Cr 0.73 1.00

Co 0.53 0.21 1.00

Ni 0.62 0.49 0.86 1.00

Cu 0.96 0.72 0.50 0.61 1.00

Zn 0.86 0.55 0.74 0.78 0.83 1.00

As 0.50 0.28 0.18 0.22 0.56 0.26 1.00

Rb 0.95 0.73 0.54 0.61 0.91 0.88 0.39 1.00

Sr -0.78 -0.68 -0.55 -0.60 -0.74 -0.79 -0.29 -0.86 1.00

Cd 0.70 0.44 0.61 0.78 0.74 0.71 0.58 0.66 -0.57 1.00

U 0.67 0.69 0.19 0.41 0.65 0.68 0.11 0.72 -0.57 0.51 1.00

Ce 0.50 0.15 0.62 0.59 0.48 0.71 0.14 0.62 -0.46 0.55 0.36 1.00

Pb 0.87 0.64 0.56 0.59 0.88 0.77 0.39 0.81 -0.65 0.57 0.50 0.39 1.00

S -0.25 -0.18 -0.12 -0.16 -0.27 -0.09 -0.28 -0.05 -0.13 -0.02 0.09 0.13 -0.36 1.00

Zr -0.87 -0.56 -0.51 -0.51 -0.88 -0.72 -0.54 -0.76 0.58 -0.56 -0.50 -0.32 -0.80 0.37 1.00

The concentration is expressed in ppm

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The vertical distribution of soil horizons is quite peculiar

and it is typical of a developed fluvisols, having a buried

histic horizon between 80 and 140 from the surface

(Table 1). Ap horizon has skeleton, texture and structure

influenced by plowing, with strong concentration of plant

roots and rhizomes. Oe horizon has a thickness of about

60 cm and an average content of 14 % of partly decom-

posed organic matter (Fig. 5). The transition between Ap

and Oe is sharp and characterized by a change in the

organic matter content (average in horizon: from ca. 14 to

\8 %) and in colour from olive gray to very dark brown or

black.

The Cg horizon is always saturated with water, for the

presence of the water table near the surface. The transition

between Oe and Cg horizon is gradual and somewhat

variable among the tree boreholes. The soil salinity

increases rapidly from Ap to Cg horizon (Fig. 5). The

source of salinization is represented by soluble salts

accumulated during the depositional process, this is also

confirmed by groundwater salinity that in the area is

extremely elevated (up to 20 mS/cm).

Eh shows positive values (?310/?110 mV) in the upper

regions of the RSP (Ap and Oe horizons), whereas it rap-

idly changes towards negative values (-12/-200 mV)

with depth (Cg horizon) (Fig. 6).

Major and trace elements distribution in RSP

The extended data set of 33 chemical analyses carried out

on the ‘‘bulk’’ sample is reported in the journal repository

(Supplementary Table 1), while the maximum, minimum,

mean, standard deviation, and correlation matrix are

reported in Tables 2 and 3.

Ap and Og show different composition with respect to

Cg horizon. As already shown by Bianchini et al. (2012),

the chemical composition of the soil is strongly influenced

by the grain size, and possibly by the elementary com-

plexation of the organic fraction (Twardowska and Kyziol

2003). The anthropic factor should also be taken into

account since: (1) generally the upper layer (Ap) contains

most of the anthropic contamination, while the underlying

layer essentially represents the lithogenic input, (2) the

upper layer (Ap) is affected by annual plowing to an

average depth of 40 cm, (3) after the reclamation, a series

of drains were installed in the field at an average spacing of

10 m and at a depth varying from 0.85 m in the central part

of the field to 1.35 m b.g.l. at the northern and southern

boundaries of the field. On the other hand, Cg horizon has

not been affected by human activity, in fact, the chemical

composition of the deeper samples is similar in all three

holes.

The vertical distribution of major elements is shown in

Fig. 6. The Ap horizon is characterized by low SiO2, TiO2,

Al2O3, K2O, Na2O, Fe2O3 and high MnO, CaO and P2O5.

Oe horizon has the highest TiO2, Al2O3, K2O, Fe2O3 and

the lowest MnO, CaO and Na2O contents of the whole

profile. SiO2, CaO, MnO, Na2O increase, while K2O,

Fe2O3, Al2O3 and TiO2 decrease in Cg.

Trace elements taken into account in this study were

chosen on the basis of their environmental relevance. Some

of them, although considered micronutrients essential for

the plant growth, become harmful contaminants above

Fig. 7 Maximum, minimum, and average vertical distribution of trace elements. The Y-axis shows the depth below ground in cm (cm b.g.l.) and

the X-axis represents the element concentration expressed in ppm

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critical concentrations (Hermanescu et al. 2011); others,

such as As and Cd, are particularly toxic and undesired in

soils and waters (Kapaj et al. 2006; Bernard 2008).

Oe horizon is remarkably enriched in Ni, V, Zn, Co, Cu,

Pb, Cd, Cr, As, U, and Rb. Ap is characterized by Ni, V,

Zn, Co, Cu, Pb, Cd, Cr, As, content intermediate between

Oe and Cg. This latter has the lowest heavy metal and U

concentrations, with the highest Zr, Sr and S contents

(Fig. 7).

Discussion

Statistical analysis of data

Statistical analysis using CA and PCA methods was carried

out to identify groups of variables which are correlated and

highlight their possible genetic relationships. R-mode

cluster analysis was performed on chemical parameters,

grain size (clay %, silt % and sand %) and organic matter

content (O.M.) using the between-groups linkage based on

Pearson correlation coefficients. This method is the most

appropriate to evidence correlation between variables

(Facchinelli et al. 2001; Le Maitre 1982). The results of CA

(dendrogram) are shown in Fig. 8. The distance axis rep-

resents the degree of association between groups of

variables. The lower the value on the axis, the more sig-

nificant the association. Weighted pair group (WPG)

average linkage methods (MVSP software, demo version)

have also been used, for validation. Results are very similar

and in both cases, two distinct main groups can be envis-

aged: Group A, associated with the finer fraction of the

soil, and Group B, representative of the coarser fraction.

Group A is further subdivided into three sub-groups of

variables defined as cluster 1, 2 and 3. Al2O3 and K2O

(principal elementary components of the clay minerals) are

key factors, since all the other elements of the group are

strongly correlated with them. In turn they are related to

clay, indicating that the Group A represents clay minerals.

Cluster 1 probably identifies Illite and Smectite (potas-

sium-rich clay minerals), as V, Cu, Rb, Zn, Pb, Cr, and U

are associated with these mineral phases. On the contrary,

Ni, Co, and Cd do not correlate well with major elements

(cluster 2), suggesting the paucity of serpentine, a mineral

commonly found in Po plain soils from other sites (Bian-

chini et al. 2002, 2012, 2013). This probably reflects the

progressive serpentine destabilization in supergene envi-

ronment observed by Kierczak et al. (2007). Cluster 3 is

constituted by As, P2O5 and S, which are relatively more

distant from the key factors. This suggests that these ele-

ments are not related to the genesis of clay minerals but

have been associated with clay sediments at a later stage

Fig. 8 Cluster dendrogram

highlighting relationships

between distinct parameters of

RSP

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well after their deposition. As in fact could have been

chelated by the abundant organic matter, which typically

includes P2O5 and S among their constituents (Chou and

De Rosa 2003); alternatively, it could derive from the

agricultural use of the soil after its reclamation (Chou and

De Rosa 2003).

Group B is divided into two sub-groups corresponding

to the silty (cluster 4) and sandy (cluster 5) soil fraction. Zr

and Na2O correlate slightly with silt suggesting the per-

sistence of zircon and alkali feldspar in the coarser grain

size. The presence of zircon in the coarse fraction is

common in soils derived sedimentary rocks. On the other

hand, the presence of alkali feldspar has already been

identified in the soils of Po Plain (Bianchini et al. 2012).

Calcium and magnesium are positively correlated with

sand. This indicates that CaO and MnO are mostly con-

tained in the carbonate fraction (mainly of biogenic origin),

and that their content is higher in the sand rather than in the

finer fraction of the soil.

PCA was carried out grain size, O.M., major and trace

elements. Parameters used are: (1) extraction method:

PCA, and (2) rotation method: Varimax with Kaiser nor-

malization; rotation converged in four iterations. The

results of PCA are reported in Tables 4 and 5.

Given the results of the initial eigenvalues, five principal

components were considered, which account for over 85 %

of the total variance. The eigenvalues of the five extracted

components are greater than one.

F1 positively correlates clay %, TiO2, Al2O3, Fe2O3,

K2O, V, Cr, Cu, Rb, and Pb, whereas sand %, CaO, L.O.I.

Table 4 Total variance explained

Total variance explained

Component Initial eigenvalues Extraction sums of squared loadings Rotation sums of squared loadings

Total % of Variance Cumulative% Total % of Variance Cumulative% Total % of Variance Cumulative%

1 17.236 57.455 57.455 17.236 57.455 57.455 9.162 30.539 30.539

2 3.978 13.259 70.714 3.978 13.259 70.714 5.200 17.334 47.873

3 1.832 6.106 76.820 1.832 6.106 76.820 4.388 14.627 62.500

4 1.500 4.999 81.819 1.500 4.999 81.819 4.122 13.741 76.241

5 1.069 3.562 85.381 1.069 3.562 85.381 2.742 9.140 85.381

6 0.899 2.998 88.379

7 0.740 2.466 90.845

8 0.618 2.061 92.907

9 0.491 1.637 94.544

10 0.389 1.296 95.839

11 0.293 0.977 96.816

12 0.237 0.791 97.607

13 0.195 0.649 98.256

14 0.134 0.446 98.702

15 0.093 0.309 99.011

16 0.076 0.252 99.263

17 0.066 0.221 99.485

18 0.048 0.160 99.644

19 0.030 0.098 99.743

20 0.027 0.088 99.831

21 0.019 0.062 99.893

22 0.013 0.043 99.936

23 0.009 0.031 99.967

24 0.004 0.013 99.980

25 0.003 0.009 99.989

26 0.002 0.007 99.996

27 0.001 0.002 99.999

28 0.0001 0.001 100.000

29 5.470E-7 1.823E-6 100.000

30 1.558E-8 5.193E-8 100.000

Environ Earth Sci

123

and Sr are negatively correlated with this component. P2O5

has positive loading in F2, where SiO2, Na2O, S, and Zr are

negatively correlated. Component F3 includes Co, Ni, Zn,

and Cd. U and O.M. are positively loaded in F4 and cor-

relate negatively with silt % and MgO, while As is isolated

in the fifth component (F5).

The statistical treatment (CA and PCA) suggests a

lithogenic control over the distribution of SiO2, TiO2,

Al2O3, Fe2O3, K2O, Na2O, V, Cu, Rb, Pb, Cr, Zr. These

elements have in fact the largest weight in F1 and F2 and

are very well correlated with clay, silt or sand fractions,

belonging to minerals which are direct products of parental

rock weathering. F1 includes CaO, Sr and L.O.I., indicating

a carbonatic fraction, found as shell fragments along the

whole soil profile. S and P2O5 are represented in F2. As

described below, sulphur present in the RSP clearly influ-

ences soil salinity and is associable to the large organic

matter present in the whole RSP profile, since the marsh

peat is the principal pool for organic C, N, and P and other

elements, e.g., Fe and S (Portnoy 1999). F3 can be iden-

tified as a secondary lithogenic factor, probably related to

further degradation of clay minerals (Serpentine), mainly

happening during transport and after deposition. F4 may

represent the fraction of the soil, where U is complexed

with organic matter (Bednar et al. 2007 and references

therein).

The fifth factor (F5) identifies an element with different

origin, unrelated to lithogenesis. Arsenic shows higher

concentrations in the first 20 cm of the Ap horizon, clearly

indicating an anthropogenic input. Common sources of As

Table 5 Component matrixes (five factors selected) for grain size, O.M., major, and trace elements

Component matrix Rotated component matrix

Component Component

1 2 3 4 5 1 2 3 4 5

% Sand -0.694 -0.143 -0.126 0.035 -0.204 % Sand -0.468 -0.402 0.016 -0.230 -0.357

% Silt -0.735 0.311 0.161 -0.339 0.288 % Silt -0.350 -0.176 -0.537 -0.647 -0.001

% Clay 0.856 -0.148 -0.051 0.221 -0.102 % Clay 0.475 0.320 0.369 0.567 0.176

SiO2 0.146 0.931 -0.123 -0.113 -0.051 SiO2 0.658 0.063 -0.621 -0.144 -0.274

TiO2 0.926 0.293 -0.036 0.061 0.018 TiO2 0.767 0.405 0.025 0.398 0.192

Al2O3 0.982 0.049 -0.055 -0.045 0.026 Al2O3 0.713 0.426 0.263 0.349 0.300

Fe2O3 0.900 -0.057 0.056 -0.317 0.057 Fe2O3 0.608 0.533 0.345 0.083 0.374

MnO -0.831 -0.382 0.247 0.129 0.001 MnO -0.897 -0.245 -0.037 -0.171 -0.132

MgO -0.335 0.022 -0.429 -0.631 -0.007 MgO 0.142 -0.346 0.157 -0.725 -0.060

CaO -0.878 -0.395 0.029 0.189 -0.032 CaO -0.838 -0.453 0.020 -0.141 -0.191

Na2O -0.745 0.540 0.061 0.164 -0.108 Na2O -0.283 -0.287 -0.664 -0.203 -0.494

K2O 0.974 0.038 -0.024 0.074 0.038 K2O 0.660 0.414 0.229 0.455 0.300

P2O5 0.350 -0.654 -0.183 -0.269 -0.233 P2O5 0.063 0.097 0.827 -0.027 0.111

L.O.I. -0.592 -0.674 0.226 0.123 0.074 L.O.I. -0.879 -0.181 0.246 -0.052 0.091

V 0.965 -0.184 -0.088 0.017 0.032 V 0.586 0.361 0.438 0.422 0.361

Cr 0.746 0.123 -0.530 -0.019 -0.069 Cr 0.831 -0.053 0.301 0.256 0.094

Co 0.624 -0.027 0.623 -0.291 -0.220 Co 0.163 0.921 0.177 0.026 0.065

Ni 0.726 0.046 0.383 -0.178 -0.264 Ni 0.365 0.760 0.206 0.157 0.006

Cu 0.947 -0.220 -0.070 0.059 0.119 Cu 0.534 0.336 0.413 0.453 0.440

Zn 0.922 0.013 0.239 -0.013 -0.194 Zn 0.511 0.676 0.266 0.380 0.109

As 0.443 -0.430 0.001 -0.140 0.693 As 0.074 0.067 0.246 0.064 0.899

Rb 0.964 0.062 -0.044 0.018 0.045 Rb 0.688 0.407 0.223 0.397 0.302

Sr -0.863 -0.329 0.064 0.238 -0.042 Sr -0.822 -0.423 -0.047 -0.096 -0.219

Cd 0.761 -0.023 0.340 0.152 0.237 Cd 0.279 0.544 0.020 0.450 0.445

U 0.708 0.218 -0.225 0.458 -0.136 U 0.599 0.079 0.040 0.678 -0.046

Ce 0.593 0.174 0.551 0.021 -0.047 Ce 0.204 0.744 -0.110 0.264 0.109

Pb 0.857 -0.257 -0.031 -0.053 -0.080 Pb 0.470 0.394 0.507 0.330 0.263

S -0.127 0.812 0.187 0.156 0.306 S 0.185 0.034 -0.890 -0.005 -0.013

Zr -0.792 0.440 0.022 0.011 -0.075 Zr -0.313 -0.316 -0.564 -0.354 -0.432

OM 0.670 -0.095 -0.179 0.432 0.103 OM 0.386 0.034 0.182 0.661 0.256

Environ Earth Sci

123

in soil are arsenate pesticides and industrial pollutants

(Sparks 2003; Nriagu 1994).

Major and trace element distribution

The vertical distribution of major elements is concordant

with the results of the statistical analysis (Fig. 7; Table 2)

Correlation matrix highlights that Al2O3 and K2O correlate

significantly with TiO2 (r [ 0.9) and Fe2O3 (r [ 0.8),

indicating the presence of metal-rich phyllosilicates (e.g.,

chlorite, smectite) within the fine fraction of these soils. In

RSP, high concentrations of these elements are found in

surface horizons, where the grain size is finer (Figs. 4, 6).

The increase of Na2O and S downward clearly demon-

strates a salinity gradient due to soluble salts accumulation

during the depositional process of the salt marshes. Profile

tends to be enriched in P2O5 and As toward the surface,

probably due to the contribution of fertilizers, especially

raw pig slurry (Jin and Chang 2011). It is thus possible that

the upper layer is contaminated by anthropogenic inputs:

on the other hand, heavy metals and Rb enrichment factor

is correlated to the grain size difference between the

horizons.

It has to be noted that the absolute concentrations of

some potentially toxic heavy metals, such as Cr and Ni, are

high if compared with the limits established by local reg-

ulations (Italian Legislative Decree 152/06) for agricultural

and residential land use (Cr: 150 ppm and Ni: 120 ppm).

This fact has to be interpreted as a natural–geogenic–

anomaly, typically observed in soils evolved from the Po

River alluvial sediments, which derive from the weathering

of parent rocks including femic/ultrafemic lithologies

(Amorosi et al. 2002; Bianchini et al. 2002, 2012; Bo-

nifacio et al. 2010). This conclusion is supported by the

high Ni and Cr content of ancient bricks (and mortars) from

historical buildings of the region made with local sedi-

ments analogous to those considered in this study and

manufactured in times preceding any significant form of

anthropogenic pollution (Bianchini et al. 2004, 2006).

The vertical distribution of heavy metals shows a

marked enrichment in the Oe horizon (Fig. 7). Comparing

the heavy metals of Oe with the values found by Amorosi

et al. (2002) in neighbouring areas, all the elements are

significantly higher (Table 6). This confirms that deposits

rich in organic matter formed in anaerobic and waterlogged

ecosystems are effective in trapping metals from the

interacting waters (Syrovetnik et al. 2007).

Soluble anions and cations distribution

The determination of the soluble anions and cations in

distilled water is important to provide information useful

for the agricultural activities, in fact they can be con-

sidered representative of the mobile water phase (Ure

1996). The concentrations of dissolved NO3-, Cl-, Br-,

F-, NO2-, SO4

-2, PO4-3, NH4

?, K?, Ca?2, Mg?2, and

Na? are reported in Table 7 and Fig. 9. In this figure,

inverse distance interpolation (IDW, ArcGIS 9.3 soft-

ware) method was also applied to study the vertical

spatial variability of NO3-, Cl-, NH4

? and Na?. This

interpolation is based on a simple principle of geography

that things close to one another are more alike and is

often used to create a continuous surface from sampled

point values (Cheng et al. 2007). All samples display a

remarkably high chloride (Cl- up to 1,788 ppm) and

sulphate (SO4-2 up to 6,158 ppm) contents, coupled with

very high sodium concentration (Na? up to 1,495 ppm)

that prevails over the other cations (Fig. 9). ‘‘Sodium

adsorption ratio’’ (SAR) is an index widely used to

define the soil salinity (Sposito and Mattigod 1977),

expressed as the ratio between the concentrations of

sodium (Na) and the sum among the magnesium and

calcium (Ca ? Mg):

Table 6 Maximum, minimum and average values of heavy metals.

Comparison between RSP and Amorosi et al. (2002)

V Cr Co Ni Cu Zn As

Amorosi et al. (2002)

Max 130 223 22 148 43 117 14

Med 110 175 18 109 35 101 10

Min 91 146 14 77 24 88 7

Oe horizon

Max 184 316 30 227 76 138 22

Med 158 260 21 166 64 122 15

Min 99 208 14 112 33 95 7

Table 7 Concentration of dissolved anions and cations

Max Med Min SD

F- 9.8 2.8 0.4 2.3

Cl- 1,789 382 5.9 526

NO2- 7.9 1.5 0.0 1.9

Br- 4.9 1.3 0.0 1.5

NO3- 151.2 20.3 0.8 29.5

PO4-3 2.2 0.3 0.0 0.5

SO4-2 6,158 1,119 30 1,195

NH4? 87.0 27.5 0.0 30.4

Na? 1,495 410 22.1 402

Mg?2 205 84.8 11.7 54.9

K? 102.1 41.1 6.3 26.7

Ca?2 1,461 305 122 250

Environ Earth Sci

123

Fig. 9 Vertical distribution of

selected anions and cations

Environ Earth Sci

123

SAR ¼ Naffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

ðCa + Mg)p

=2:

The studied RSP soil displays extreme SAR values (up

to 127), with the highest values typically recorded in the

deep horizons. The concentration of soluble components is

comparable with those measured in soils and sediments

from coastal sectors of the Po River plain (Marinari et al.

2012; Cidu et al. 2013), but seems to be a natural (geo-

genic) feature inherited from the original depositional

environment, i.e., a wetland characterized by highly saline

brackish water (Mastrocicco et al. 2013b). Further source

of salinization is represented by the groundwater that in the

area is extremely saline (up to 13 mS/cm), taking into

consideration that the depth of the water table (and the

related capillary fringe) of the phreatic aquifer is extremely

superficial and sometimes (for example in July and August,

when the channel levels are artificially rose for irrigation

purposes) tends to approach the surface. In this context, the

general decrease of EC (Fig. 5), Cl-, and Na? toward the

surface (Fig. 9) is probably related to the percolation of

rain and irrigation waters that ‘‘wash’’ and desalinize the

superficial horizons.

NH4? content is negligible in Ap and Oe horizons, but

increases significantly from about 150 down to 400 cm

(Fig. 9). As the permeability of the soil is extremely low

(few cm/day, Mastrocicco et al. 2013a), the percolation of

ammonium derived from fertilization in depth can be ruled

out; moreover, nitrification processes in the upper part of

the RSP, where oxidizing conditions are met, would

quickly transform ammonium into nitrate thus preventing

NH4? transfer into the lower levels of soil column. The

high ammonium values found in Cg horizon can be related

to the natural presence of considerable amounts of organic

matter in reducing conditions (Mastrocicco et al. 2013a)

which slowed down its rate of decomposition. High

ammonium contents are also found in groundwater

(48.6–64.6 ppm) during autumn and winter, when the level

of channels is artificially lowered and surface water income

through the drains does not affect the overall groundwater

composition.

A reverse trend is observed for nitrates that are higher,

close to the surface, as an effect of agricultural fertilization,

but tend to decrease with depth (Fig. 9). The drastic

decrease of NO3-, at a depth of ca 100–120 cm, can be due

to the denitrification processes mediated by biological

activity, i.e., biochemical reactions triggered by soil bac-

teria that participate to the decomposition of the organic

matter (Rivett et al. 2008). These data indicate that the

investigated zone is less vulnerable to nitrates than

expected (Castaldelli et al. 2013; Mastrocicco et al. 2013b),

and that the fertilizers nitrogen load is metabolized along

the soil profile. However, in concomitance with extremely

dry and hot seasons (like the period September 2011–

August 2012) the precipitation and accumulation of NO3--

soluble salts within the first 0–30 cm of soil, leading to

salinity stress for plant roots, with crop loss and local N

concentration, that can result in a massive nitrate discharge

in the channels after heavy rainfalls, when NO3- is sud-

denly mobilized, percolates through soil cracks and is

conveyed in the drainage system (Mastrocicco et al.

2013a).

Conclusion

A typical RSP has been characterized through grain size

and geochemical analyses together with data statistical

treatment. This kind of soil is artificial, as it would be

naturally submersed, and has very peculiar features. It is

characterized by high salinity, presence of peat levels and/

or horizons and by high organic matter contents responsi-

ble for high chloride, sulphate and ammonium values in the

soil. Redox conditions are reducing, beside the first 150 cm

where tillage, cracks and the presence of a sub-irrigation

drainage system allows air circulation. Ferrara Province

reclaimed soils lay below sea level: their hydrology is

totally regulated by anthropic interventions; the whole area

is mechanically kept dry with drain pumps and the water

table undergoes seasonal variations linked to agricultural

cycles and land use. RSP heavy metal content is naturally

high, since these soils originate from Po plain sediments

derived from the erosion of ultramafic rocks; moreover,

heavy metal adsorption by organic matter tends to further

concentrate them, especially in peaty horizons. Reclaimed

soils undergo intensive agricultural exploitation, as testified

by the high NO3- content due to fertilization.

For all the above-mentioned features, the reclaimed soil

constitutes a particularly vulnerable and fragile environ-

ment. Further studies are needed to check the amount of

heavy metals and metalloids effectively adsorbed by the

cultivated crops, as well as the solubility of these elements

in groundwater and in the surface hydrological system.

Sediment low permeability and bacterial de-nitrification

processes could prevent groundwater from high level of

nitrate pollution. However, the actual meteorological con-

ditions are strongly affected by the ongoing climatic

changes, with long dry season alternated to temporally

concentrated heavy rainfall. The hot and prolonged spring-

summer temperatures can favour nitrate salt deposition and

accumulation in soil, quickly flushed away by flash floods

and massively input into the channels through the drains. In

spite of the application of the Nitrate and Water Frame-

work Directives (91/676/CEE; 2000/60/CE), nitrogen pol-

lution is still a major menace to lowlands and coastal

Environ Earth Sci

123

lagoons and further studies are required to better under-

stand the complex processes of nitrate release into the

environment.

Swamp reclamation supplied inhabitable land and cul-

tivable soils; however, they are a delicate system whose

management is difficult both from environmental (nitrate

pollution), economic (high needs of power for water

pumps), and agricultural (highly saline soils subject to a

quick depletion of nutrients) points of view. An accurate

and continuous monitoring of the reclaimed areas is rec-

ommended for a correct conservation of the territory and

the limitation of heavy pollution phenomena.

Acknowledgments Authors thank Dr. Umberto Tessari and Dr.

Renzo Tassinari for their analytical support. This work has been

supported by EC LIFE ? funding to ZeoLIFE project (LIFE ? 10

ENV/IT/000321).

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