Using 137Cs and 210Pbex measurements and

Soil & Tillage Research 135 (2014) 18–27

Contents lists available at ScienceDirect

Soil & Tillage Research
journal homepage: www.elsevier.com/locate/still

Using 137Cs and 210Pbex measurements and conventional surveys to
investigate the relative contributions of interrill/rill and gully erosion
to soil loss from a small cultivated catchment in Sicily
Paolo Porto a,b,*, Desmond E. Walling a, Antonina Capra b
a

Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, UK
Dipartimento di Agraria, Universita` degli Studi Mediterranea di Reggio Calabria, Agro-Forest and Environmental Sciences and Technologies, Contrada Feo di
Vito, Reggio Calabria 89122, Italy

b

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 19 March 2013
Received in revised form 21 August 2013
Accepted 31 August 2013

In many cultivated areas in semiarid Mediterranean regions, soil erosion is responsible for problems
related to both on-site and off-site impacts, including reduced crop productivity, water quality, and
degradation of freshwater ecosystems. In some areas of Sicily, where intense short duration rainfall
events are common, soil erosion is a very serious problem, especially on land subjected to continuous
tillage operations. The rates of soil loss in these areas and their impact differ according to the dominant
type of erosion. Several existing studies have focused on the impacts of either linear (gully- or ephemeral
gully-erosion) or interrill–rill erosion, but to date the relative magnitude of these two different types of
erosion, has rarely been assessed. This paper reports the results of a study aimed at comparing the
relative contribution of interrill–rill erosion and gully erosion to soil loss from a small cultivated
catchment located in Sicily (Italy). Surveys of ephemeral gullies (EG) in the study catchment carried out
at the event scale since 1999 are used to quantify soil loss attributable to EG erosion. 137Cs and 210Pbex
measurements are used to quantify the net soil loss from the catchment attributable to interrill–rill (IRR)
erosion. The study demonstrates that EG formation occurred 7 years out of 10, with a mean soil loss

averaged over a 10-year period equal to 26.5 t ha1 yr1. The rates of IRR erosion estimated using 137Cs
and 210Pbex measurements provided values of mean annual net soil loss of 38.8 t ha1 yr1 and
34.2 t ha1 yr1, respectively. The resulting ratios of soil loss attributable to EG to total soil loss
(IRR + EG) were 0.41 and 0.44 for the 137Cs and 210Pbex measurements, respectively. The results suggest
that the contributions of EG and IRR erosion are of a similar magnitude in semiarid regions of Sicily,
although the precise value of the ratio is likely to vary both spatially and temporally in response to
catchment morphology, soil erodibility and land use and inter-annual variability of rainfall magnitude
and erosivity. The findings are consistent with those of other studies that have attempted to compare the
relative efficacy of the two erosion types. The use of 137Cs and 210Pbex measurements in the study area
provided important insights into the relative importance of IRR and EG erosion and the same approach
could be employed in other locations where both forms of erosion occur and there is a need to quantify
their relative importance.
ß 2013 Elsevier B.V. All rights reserved.

Keywords:
Cs ;210Pbex
Interrill and rill erosion
Ephemeral gully erosion
Sediment redistribution
Sicily

137

1. Introduction
In recent decades, land degradation and soil erosion have been
increasingly recognised as a serious environmental problem in
semiarid Mediterranean regions. Recent studies carried out in
southern Italy have documented rates of soil erosion ranging from
10–85 t ha1 yr1, on cultivated land (Porto and Walling, 2012a,b)

* Corresponding author. Tel.: +39096557481.
E-mail addresses: P.Porto@exeter.ac.uk, paolo.porto@unirc.it (P. Porto),
D.E.Walling@exeter.ac.uk (D.E. Walling), acapra@unirc.it (A. Capra).
0167-1987/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.still.2013.08.013

and from 100–150 t ha1 yr1, in areas covered by forests (Porto et
al., 2011). These high erosion rates reflect both the nature of the
environment and the long-term impact of human activity. The
rainfall regime of Mediterranean areas, which is characterised by
events of extremely short duration and very high intensity

followed by long dry periods, is particularly conducive to erosion.
Human activity further increases the erosion risk through, for
example, creating bare surfaces on cultivated land after tillage
operations and land abandonment in marginal and improductive
areas. In Sicily, soil loss from cultivated lands reflects the general
situation in Southern Italy, but rates of soil loss differ according to
erosion type and land degradation processes. Erosion due to

19

P. Porto et al. / Soil & Tillage Research 135 (2014) 18–27

concentrated flow is very severe on many unprotected farm fields
and the presence of various gully types can be observed in many
areas of the region. The initiation and development of channels
routinely obliterated by tillage and other farm operations,
commonly referred to as ephemeral gullies (EG), constitutes a
severe problem (Capra, 2013). Growing crops can be removed by
scour as these small gullies develop, the crops at the lower end of
the gully can be buried by the sediment discharged from the

ephemeral gully and deposited in an alluvial fan. Furthermore,
filling operations reduce the long-term productivity of the
farmland. Although the importance of EG erosion is well
recognised, even at the local scale (Capra and Scicolone, 2002;
Capra et al., 2005) little research has focused on this erosion type
and most soil erosion prediction studies have relied on generalised
empirical models (Capra et al., 2005; Capra et al., 2009a,b; Di
Stefano et al., 2013).
In contrast, IRR erosion rates are better understood in Sicily and
over the last 50 years many different approaches have been
employed to predict IRR erosion, in order to assess soil erosion risk
and develop effective strategies to control erosion and sedimentation in these areas. These different approaches are based on
different types of models that range from empirical-parametric
approaches such as SEDD (Ferro, 1997; Ferro and Porto, 2000),
through conceptual models, which correlate soil loss to physical
parameters depending on soil erodibility and land use (Novara et
al., 2011), topography (Bagarello et al., 2011) or rainfall erosivity
(Agnese et al., 2006), to recent physically-based models, such as
WEPP (Nearing et al., 1989), which aim to simulate both the
detachment and transport of soil particles (Amore et al., 2004).

The results provided by these studies demonstrate that IRR
erosion is also an important problem in Sicily, although there is a
need for further calibration and validation of the models
employed for local conditions, in order to increase confidence
in their output.
The use of fallout radionuclides and more particularly caesium137 (137Cs) and excess lead-210 (210Pbex) to document rates of soil
and sediment redistribution in the landscape has attracted
increasing attention in recent years (Mabit et al., 2008; Ritchie
and Ritchie, 2007; Walling, 2010; Zapata, 2002) and the approach
is now being successfully employed in Mediterranean areas (e.g.
Benmansour et al., 2013; Estrany et al., 2010; Gaspar et al.,
2013a,b; Navas et al., 2013; Porto et al., 2006, 2013). This approach
is able to overcome several of the limitations associated with more
traditional methods of documenting erosion and soil redistribution. Of particular importance is its potential to provide retrospective information on medium-term average rates of soil
redistribution on the basis of a single site visit and representative
distributed data for fields and larger areas, without the need to
disturb the system by installing measuring equipment. For some
applications, particularly those requiring spatially distributed
information on soil redistribution rates, fallout radionuclides
arguably provide an essentially unique means of assembling

data that cannot be obtained using alternative approaches. By
virtue of their different half-lives and fallout origins, 137Cs and
210
Pbex provide information relating to different periods of time.
137
Cs measurements are primarily used to generate information
on mean annual erosion rates over the past ca. 50 years and
210
Pbex measurements are able to provide information relating

to a longer period of up to ca. 100 years (Walling and He,
1999a,b).
The study reported here aims to quantify EG and IRR erosion
rates in a small cultivated catchment located in Sicily (Italy), to
compare their relative contribution to the total soil loss from the
catchment and thereby provide important information on soil
erosion rates in the study region. An empirical approach, based on
field measurements was used to quantify the erosion rates
associated with EG erosion, while the rates IRR erosion were
estimated using 137Cs and 210Pbex measurements. To the authors’

knowledge this is the first attempt to undertake such a comparison
in Italy.
2. The study area
The study area (Fig. 1) comprises a small 0.86 ha catchment
located in Sicily, Italy. This catchment is part of a larger drainage
area (80 ha in size) belonging to a national network of
experimental catchments for erosion studies. The data-set of EG
measurements in the study area extends over 18 years (from
1995 to 2013). The study catchment is characterised by an
altitudinal range of 325 to 355 m above sea level, a mean slope of
28% and a single main drainage line with a NW–SE orientation
(Capra and Scicolone, 2005) (see Table 1). The catchment is a
tributary (W-side) of the middle reaches of the Simeto river, and
is developed on the oldest allochthonous units of the Apennines–
Maghrebian Chain (Imerese Unit, Upper Trias–Middle Miocene),
which underlie the syn- and post-orogenic units (Burdigalian and
lower Tortonian) (Longhitano and Colella, 2007). The dominant
soil type is Vertic Xerocrept, which is very common in Sicily.
Particle size analysis carried out for 10 soil samples collected
within the catchment, indicated the presence of silty clay loam

and silt loam textural classes (see Table 1 for details) with
negligible stone content.
The catchment has been cultivated since the early 1950s. The
main crop is durum wheat that requires two tillage operations in
summer or early autumn with a cultivator and one ploughing
operation carried out every few years (generally a minimum of 3
years). The climate of the study area is typically Mediterranean
with a mild wet winter and a warm dry summer. The mean annual
rainfall for the period 1971–2007 is ca. 500 mm, with a coefficient
of variation of ca. 40%. More than 80% of the rainfall occurs during
the period extending from October to May.
An active ephemeral gully (EG) develops along the main swale
in the centre of the catchment during the rainy season in most
years (Fig. 1). As is usually the case for cultivated land, the EG is
obliterated by infilling with soil from areas immediately adjacent
to the channel, using ordinary tillage equipment. However, the EG
frequently recurs in the same place during the next rainy season.
The extent and development of the EG system in the catchment has
been documented since 1995, but measurements at the event level
did not commence until 1999 (Capra and Scicolone, 2002, 2005).

Until 1998, rainfall data were collected using an autographic rain
gauge equipped with a chart recorder, located about 600 m away
from the study area. In 1999, a digital recording rain gauge was
installed in the basin. A comparison of the rainfall measured by
both gauges over a period of 4 months showed good agreement
between the two gauges (Capra et al., 2009b).

Table 1
Characteristics of the study catchment.
Drainage area (ha)

Min altitude
(m asl)

Max altitude
(m asl)

Mean slope (%)

Sand (%)

Silt (%)

Clay (%)

Organic
matter (%)

Bulk density
(g cm3)

0.86

325

355

28

4–15

62–79

17–28

0.98–1.13

1.14–1.17

20

P. Porto et al. / Soil & Tillage Research 135 (2014) 18–27

Fig. 1. The study area and the study catchment, showing the ephemeral gully system that developed in 2008.

3. The measurement programme
3.1. The ephemeral gully system
The measurement programme for the ephemeral gully system
involved field surveys undertaken after each erosive event. When
the time interval between two erosive events was too short to visit
the site, a single measurement subsumed both events. The surveys
involved surveying the main branch of the EG (see Fig. 1) and its
tributaries (if present). A post processing differential GPS with a
planimetric accuracy of 12 cm (Capra and Scicolone, 2002) was
used to establish the spatial co-ordinates of points located along the
channel at about 5 m intervals in the longitudinal direction. Cross
sections were measured at about every 5 m of channel, or whenever a
change in the EG cross section or the entry of tributaries was
observed. As it was possible to treat the cross section of the EG as a
trapezium (or a rectangle) (Capra et al., 2011), the channel widths
(upper and lower) and depths were measured with a steel tape
graduated every 5 mm. All the measures were made by the same
expert operator.
The length of the EG was computed from the co-ordinates of the
survey points. The volumes of material removed by erosion to
create each channel segment were calculated using the end area
method (i.e. the product of the mean area of two successive cross
sections and the distance between them). The total volume of soil
eroded from the EG was calculated as:
V¼

n
n
X
X
Ai1 þ Ai
 Li
Vi ¼
2
i¼1
i¼1

(1)

where V is the total volume of soil eroded from the EG (m3); n is the
number of segments; Vi is the volume of eroded soil from each

segment (m3); Ai1 is the downstream cross sectional area of the
segment (m2); Ai is the upstream cross sectional area of the
segment (m2); and Li is the distance between adjacent cross
sections (m). The data relating to the volume of soil removed from
the gulley system were converted to values of mass using
representative values of in situ bulk density for the material
removed.
3.2. Soil sampling of

137

Cs and

210

Pbex

In order to use 137Cs and 210Pbex measurement to estimate rates
of interrill–rill erosion within the study catchment, two separate
soil sampling programmes were undertaken. The first aimed to
establish the magnitude and spatial distribution of soil redistribution rates within the catchment and involved two sampling
campaigns. During the first campaign, undertaken in 2009,
replicate bulk soil cores were collected at 30 sites, using an
11 cm diameter steel core tube inserted to depth of 45 cm.
Deeper cores were collected from sites where there was the
possibility of deposition. These soil cores, which were collected at
the intersections of an approximate 20 m  20 m grid, were
supplemented by a further 52 bulk cores collected in the same
way from sites selected to improve the coverage of topographic
variability, during a second sampling campaign in 2010 (see
Fig. 1). In all cases the sampling points were selected to avoid the
zone occupied by the EG and the zone from which soil was moved
for infilling the gully, and are therefore seen as being representative of the soil redistribution occurring on the slopes of the
catchment beyond the EG. The second sampling programme,
undertaken in 2010, aimed to obtain information on the local
reference inventory and the depth distribution of 137Cs and 210Pbex
both at the reference site and in the cultivated soil profile of the

21

P. Porto et al. / Soil & Tillage Research 135 (2014) 18–27

catchment. Since it was not possible to identify a site that was both
undisturbed and unaffected by soil redistribution within the study
catchment, the samples used to establish the reference inventory
were collected from an area of permanent pasture with minimal
slope adjacent to the study catchment. In this case, eight separate
cores were collected from an area of ca. 25 m2 using an 11 cm
diameter steel core tube inserted to depth of 60 cm, in order to take
account of micro-scale variability in the reference inventory (cf.
Owens and Walling, 1996). Each core was sectioned using the same
depth increments, which ranged from 1 to 4 cm, and the individual
depth increments from the eight cores were bulked. Bulking was
undertaken to reduce the mass of material that needed to be
transported to the laboratory in the UK, where the samples were
assayed for 137Cs and 210Pbex, and because of limitations on the
total number of samples that could be assayed. Additional
sectioned cores were also obtained from two sampling sites
within the catchment selected to be representative of an eroding
and a depositional site (see Fig. 1), using the same procedure as
employed at the reference site.
3.3. Laboratory analyses for

137

Cs and

210

Pbex

All bulk core and depth incremental samples collected from the
catchment and from the reference area were oven dried at 105 8C
for 48 h, disaggregated and dry sieved to separate the