Distribution and inventories of fallout radionuclides (239+240Pu, 137Cs) and 210Pb to study the filling velocity of salt marshes in Doñana National Park (Spain)

Journal of Environmental Radioactivity 89 (2006) 159e171 www.elsevier.com/locate/jenvrad

Distribution and inventories of fallout radionuclides (239þ240Pu, 137Cs) and 210Pb to study the filling velocity of salt marshes in Don˜ana National Park (Spain) C. Gasco´ a, M.P. Anto´n a,*, M. Pozuelo a, L. Clemente b, A. Rodrı´guez c, C. Yan˜ez b, A. Gonza´lez a, J. Meral a a

Centro de Investigaciones Energe´ticas, Medioambientales y Tecnolo´gicas, CIEMAT, Departamento de Medio Ambiente, Avda. Complutense 22, Madrid 28040, Spain b Consejo Superior de Investigaciones Cientı´ficas, Instituto de Recursos Naturales y Agrobiologı´a, CSIC-IRNA, Departamento de Geoecologı´a, Avda. Reina Mercedes s/n, Sevilla 41012, Spain c Universidad de Huelva, Departamento de Geodina´mica y Paleontologı´a, Avda. de las Fuerzas Armadas s/n, Huelva 21071, Spain Received 13 October 2005; received in revised form 30 March 2006; accepted 4 May 2006 Available online 27 June 2006

Abstract Within an extensive multinational and multidisciplinary project carried out in Don˜ana National Park (Spain) to investigate its preservation and regeneration, the filling velocity of the salt marshes has been evaluated through the calculation of their average sediment accumulation rates. 239þ240 Pu and 137Cs from weapons testing fallout and total 210Pb distribution profiles and inventories have been determined in some of the most characteristic zones of the park, namely, the ponds (or ‘‘lucios’’) and the waterjets (or ‘‘can˜os’’). Plutonium inventories range from 16 to 101 Bq m
2, 137 Cs values fluctuate between 514 and 3758 Bq m
2 and unsupported 210Pb values comprise between 124 and 9398 Bq m
2. Average sedimentation rates range from 3 to 5 mm y
1 (1952e 2002). These data are higher than those obtained by carbon dating for the period 6500 ADepresent, estimated as 1.5e2 mm y
1, suggesting an increase in the accumulation of sediments and the

* Corresponding author. Tel.: þ34 91 346 6664; fax: þ34 91 346 0005. E-mail address: [email protected] (M.P. Anto´n). 0265-931X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2006.05.004

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alteration of the park’s hydrodynamics caused by the re-channeling of the major rivers feeding the salt marshes. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Fallout radionuclides; Inventories; Radionuclides distribution; Accumulation rates; Don˜ana National Park

1. Introduction Don˜ana National Park is located in the province of Huelva (Andalusia), southwestern Spain, between the right bank of Guadalquivir River and the Atlantic Ocean (6  150 0000 e6  300 0000 W; 36  500 0000 e37  100 0000 N). Encompassing an area of approximately 507.2 km2, it is considered the most important biological reserve of the Iberian Peninsula, constituting a vital habitat for many types of migrating birds arriving from northern Europe to breed at this temperate latitude. The climatic regime of this zone is characterised by mild and stable temperatures throughout the year and a variable rainfall index (Siljestro¨m, 1985), with 50% of the total precipitation falling during the winter season (OctobereApril) and a seldom 5% reached during the summer time (MayeSeptember). The inter-annual rainfall variability is also noticeable, some years exceeding 700 mm, others hardly reaching 300 mm. This fact frequently leads to the flooding of the salt marshes during the winter months followed by a strong drought period in the summer, in which most of the water evaporates, revealing rich deposits of silt, raised sand banks and islands and cracked clay sediments. Two main rivers, Guadalquivir and Guadiamar have controlled the park’s hydrodynamics until recently. On the second half of the 20th century these river beds were modified and re-channeled with canals and dikes that reached to the park boundaries, acting as bottle necks during the flooding season, causing violent overflows (Gonza´lez Arteaga, 1993). Following the severe Azna´lcollar mine accident in 1998, the National Park was completely isolated from the mentioned rivers’ discharges by construction of a dike. The tidal influence on the salt marshes is non-existent nowadays, although it played a significant role during the Holocene period (Rodrı´guez-Ramı´rez et al., 1997). A detailed geological description of Don˜ana National Park is provided by Ruı´z et al., 2004. In summary, the park is dominated by sand sheets and groups of shifting dunes, some of which move very rapidly, others appear to be stabilized by the vegetation cover. About half of the total surface of the Park is salt marshes (or ‘‘marismas’’), described as swamps formed on clay soil filled with muddy sediments rich in calcium and magnesium. Characteristic features of the salt marshes are the natural ponds (or ‘‘lucios’’) and the waterjets (or ‘‘can˜os’’), and thus, they were selected for study in the above-mentioned project. Natural ponds are closed hollows where rainwater accumulates mainly during the winter, forming small lagoons (30e50 cm depth) that dry up during the summer. Waterjets are canals, variable in size, through which the water flows, depending on the season. Therefore, ‘‘lucios’’ and ‘‘can˜os’’ are representatives of accumulation and erosion zones, respectively. The environmental deterioration of Don˜ana National Park has been emphasized since the beginning of the 20th century, primarily provoked by agricultural farming, animal grazing and roaming and urban development in the Park surroundings, not forgetting the impact of the annual ‘‘El Rocı´o’’ pilgrimage.

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161

In this context, the preservation and regeneration possibilities of Don˜ana N.P. are being evaluated in the framework of an extensive study in which the evolution of the filling velocity of the salt marshes will be assessed through the calculation of mean accumulation rates. 2. Experimental 2.1. Sampling

Odiel River

River Guadiana

Huelva

o nt Ti

r ve Ri

Sevilla

Spain

alq

fC

adi

z

N

ad

lf o

Atlantic

Gu

Gu

uiv

ir R

ive

r

Portugal

Three sampling campaigns were carried out in Don˜ana National Park during the dry season (JuneeJulyeAugust) in the years 2000, 2001 and 2002. The sampled areas, their coordinates and characteristics are displayed in Fig. 1. As it can be observed some of the stations were located on erosion zones (La Madre, near the jetstream from which it is named and Juncabalejo,

Guadalquivir

Africa

Doñana National Park 0

Guadalquivir Marshland

30 km

La Madre

MariLópez

El Puntal Juncabalejo Huerto del Taraje

Membrillo

Sampling Stations

Coordinates

Type of area

La Madre

N 37º 05.235'

W 06º 26. 72'

Juncabalejo

36º 56.269'

06º 22.330'

Water Jet “Caño”

Huerto del Taraje

36º 56.483'

06º 19.655'

Intermediate Zone Pond “Lucio”

Water Jet “Caño”

El Puntal

36º 57.664'

06º 26.265'

MariLópez

37º 01.614'

06º 19.883'

Pond “Lucio”

Membrillo

36º 53.329'

06º 21.574'

Pond “Lucio”

Fig. 1. Location of sampling areas in Don˜ana National Park (Spain).

C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

162

sited in the confluence of Guadiamar and La Madre flows); others in accumulation areas such as Lucios El Puntal, MariLo´pez and Membrillo, and Huerto del Taraje in an intermediate zone, partially eroded, partially accumulative. Different sampling techniques have been employed, depending both on the radionuclide to be determined and on the level of humidity of the sediment, which in turn determines the drilling capacity of the device used. Thus, a PVC cylinder (30 cm long; f ¼ 8 cm) was used to take the samples for 137Cs, 241Am, 226Ra and 210Pb gamma measurements. The sediment so-obtained was frozen and sliced in the laboratory in 3 cm layers with a power saw, starting from the deeper sections to avoid cross-contamination while manipulating the sample. A boring device made of stainless steel cylinders of variable length (1 and 4 cm) allowed taking sediment cores 15 cm long to analyse plutonium, with a resolution of 1 cm on the upper layers and 4 cm from the third section down (Fig. 2). Sediment samples were dried in an oven at 58  C until reaching constant weight, and then ball-milled for homogenization. 2.2. Radiochemical analyses Aliquots of 10 g were used to analyse 239þ240Pu. Briefly, plutonium was extracted from the sediment with hot 8 M HNO3 (3), and then the sediment residue was discarded. Plutonium was purified from chemical and spectrometric interferents by employing ionic resins AG

A

B

D

E

C Fig. 2. Boring device employed to obtain sediment samples. (A) Introduction on the ground. (B) External view of device containing extracted sediment. (C,D) View of internal sediment section. (E) Sediment slice view.

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163

18 (20e50 mesh; 8 M HNO3 medium) and AG 18 (50e100 mesh; 12 M HCl medium). Finally, plutonium was electroplated onto stainless steel discs (Talvitie, 1972) and quantified by high-resolution alpha spectrometry. The average chemical recovery was 65  24%, calculated by using 242Pu as internal tracer. 137 Cs, 241Am, 226Ra and total 210Pb were measured by gamma spectrometry employing a coaxial hyperpure n-type germanium detector and Genie 2000 software for spectra analysis. Samples of 80e90 g were stored for a minimum of 28 days in sealed containers, to allow reequilibration of 222Rn and its daughter products. Unsupported 210Pb was obtained by subtracting 226Ra (calculated as the mean 214Pb and 214Bi concentrations) from total 210Pb. Quality control was achieved by analysing certified samples and by participating in intercomparison exercises organised by the International Atomic Energy Agency (IAEA); also by checking the tracer activity and by controlling the counting instrumentation (background levels, electronical adjustment, calibrations, etc.). Radionuclides’ inventories, defined as concentration of activity per surface unit (Bq m
2) for each sediment core were calculated using the following equation:

INVT ¼

n X Ai Dwi i¼1

Si

where Ai is radionuclide concentration of activity in each sediment layer (i) (Bq kg
1); Dwi the dry weight of each sediment layer (i) (kg); and Si is the surface area of each sediment layer (i) (m2). Only the layers with a radionuclide concentration higher than the minimum detectable activity (MDA) provided by the alpha measurement apparatus employed (estimated for 10 g samples counted for 600 000 s as 0.020 Bq kg
1) were considered in the inventory calculations. 2.3. Sedimentation rates Average sedimentation rates were calculated by assuming that the maximum penetration depth at which the radionuclides 137Cs and 239þ240Pu were detected corresponds to the year 1952, when they were firstly introduced into the environment following the atmospheric nuclear tests. By considering both the introduction and the sampling dates, and the number of centimeters of accumulated sedimentary material, a rough estimation of a mean sedimentation rate can be obtained. A simple model, such as CRS-MV (Constant rate of Supply-Modified Velocity) was employed when the unsupported 210Pb profile allowed so (Schell and Tobin, 1994). Knowing that detection of the first appearance of 137Cs and 239þ240Pu is dependant on the detection limits achieved by the instrumentation used, the results obtained (sedimentation velocities and associated uncertainties, lineal regression coefficients, etc.) were corroborated with those produced by pollen grain content analyses, as previously done by other authors in different scenarios (Robbins et al., 1978; Hancock et al., 2001). In this case, pollen from two vegetable species, namely Eucalyptus sp. and Parthenium argentatum (commonly known as Guayule) were employed. These species were introduced in the park between 1912 and 1929 and in 1951, respectively, the latter one being completely extinguished nowadays (Sousa, 2004). It should also be noted that only the sedimentation rate values that were double-checked with the pollen data have been taken into account.

C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

164

3. Results and discussion Results on activity concentrations and distribution profiles of 239þ240Pu, 137Cs, 241Am and natural radionuclides 210Pb and 226Ra are shown in Figs. 3e8. Activity concentrations range from 0.04  0.01 to 0.57  0.03 Bq kg
1 for 239þ240Pu, and from 1.0  0.1 to 19.4  0.7 Bq kg
1 for 137Cs. Total 210Pb values fluctuate between 20  2 and 69  1 Bq kg
1; 226Ra data range from 17  1 to 30  1 Bq kg
1 and 241Am results are below the detection limit achieved with the measuring conditions established for the employed instrumentation. As it can be observed, in some areas, such as La Madre, Juncabalejo and Huerto del Taraje, total 210Pb values are low, even equaling those of 226Ra, indicating the absence of unsupported 210 Pb (which has an atmospheric origin) and thus, the existence of important erosive phenomena. Artificial radionuclides concentrate mostly on the upper section of the sediment cores (5e9 cm), with profiles decreasing exponentially with depth, not showing the maximum concentration fallout peaks corresponding to 1963. This fact could be due either to the low sampling resolution achieved or to the loss of information accumulated on the top eroded sediment layers. Radionuclides’ penetration within the sediment column never exceeds 20 cm, being lower in Huerto del Taraje (15 cm), located as previously mentioned in a region that accumulates sedimentary material and also suffers erosion. When considering the ‘‘lucios’’ (El Puntal, MariLo´pez, Membrillo), it should be noted that 137 Cs and 239þ240Pu distribution profiles in Membrillo are very similar, with a growing tendency until reaching a maximum value (ascribed to 1963), then decreasing with depth. However, total 210Pb profile appears disturbed on the top 15 cm, displaying a decreasing pattern with depth. For MariLo´pez core, all the radionuclides present a maximum value on the surface and also on the 20 cm layer, likely caused by either an increase in the sedimentation or a higher LA MADRE Section cm

239,240Pu Bq·kg-1 1s

0-3 3-6 6-9 9-12 12-15 15-17.5 17.5-20.5 20.5-23.5 23.5-26.5

0.360 0.025 0.205 0.017 0.124 0.013 0.077 0.011 0.0650 0.0093 0.063 0.010 0.0673 0.0091 <0.020 ----------------

137Cs Bq·kg-1 1s

11.60 5.57 3.59 2.48 1.91 1.60 1.95 1.03 1.53

La Madre

0.3

0.4

0.5

0 0 5 10 15 20 25 30

5

10

241Am(

) Bq·kg-1 <1.5 <0.75 <1.2 <1.8 <0.91 <0.59 <1.0 <0.67 <1.0

1.8 1.3 1.8 1.3 1.6 1.2 1.3 1.9 0.84

La Madre Pbtotal Activity Concentration (Bq·kg-1)

210

0

15

Depth (cm)

0.2

28.2 16.6 27.2 28.6 20.5 20.0 24.2 23.0 20.80

5.4 2.8 4.1 5.5 2.7 1.9 4.9 2.3 3.1

Cs Activity Concentration (Bq·kg-1)

Depth (cm)

Depth (cm)

0.1

46.6 22.9 13.9 29.9 21.3 19.8 20.5 17.1 21.9

137

Pu Activity Concentration (Bq·kg-1)

0.0

0.53 0.35 0.34 0.34 0.31 0.26 0.22 0.14 0.20

226Ra Bq·kg-1 1s

La Madre

239,240

0 5 10 15 20 25 30

210Pb( ) Bq·kg-1 1s

20

0 5 10 15 20 25 30

Fig. 3. Radionuclides’ activity concentrations and distribution profiles in station La Madre.

40

60

C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

165

JUNCABALEJO Section cm

239,240Pu Bq·kg-1 1s

137Cs Bq·kg-1 1s

0-6 6-9 9-12 12-15 15-21 21-24 24-27 27-30

0.451 0.034 0.125 0.017 0.069 0.014 0.062 0.017 0.0380 0.0080 <0.020 <0.020 <0.010

13.50 0.69 4.75 0.24 1.53 0.26 1.60 0.27 1.56 0.28 <0.91 <0.91 <0.85

210Pb( ) Bq·kg-1 1s

Juncabalejo

0.3

0.4

0.5

0

5

Pbtotal Activity Concentration (Bq·kg-1)

10

15

0 5 10 15 20 25 30 35

0 Depth (cm)

0.2

210

Cs Activity Concentration (Bq·kg-1)

Depth (cm)

Depth (cm)

0.1

0 5 10 15 20 25 30 35

<1.1 <0.62 <1.1 <1.1 <0.94 <1.1 <0.92 <0.90

Juncabalejo

137

Pu Activity Concentration (Bq·kg-1)

Am( ) Bq·kg-1

1.0 0.97 1.2 1.6 1.1 1.8 1.0 0.97

21.5 23.10 25.2 22.6 22.8 23.3 21.5 19.90

Juncabalejo

239,240

0.0

3.6 2.3 3.4 3.5 3.8 3.8 5.7 3.6

40.4 32.9 30.7 25.1 27.8 27.0 24.2 26.1

241

226Ra Bq·kg-1 1s

20

40

60

0 5 10 15 20 25 30 35

Fig. 4. Radionuclides’ activity concentrations and distribution profiles in station Juncabalejo.

clay content. El Puntal sediment exhibits the lowest concentrations out of the three compared ‘‘lucios’’, with a homogeneous 239þ240Pu and 210Pb distribution profiles on the upper 10 cm and a global decreasing pattern from then down. 137Cs distribution presents a maximum in the 6e9 cm section. Radionuclides’ penetration reaches down to 30 cm, except for El Puntal,

HUERTO DEL TARAJE Section cm

239,240Pu Bq·kg-1 1s

137Cs Bq·kg-1 1s

0-3 3-6 6-9 9-12 12-15 15-18 18-21 21-24 24-27 27-30

0.427 0.024 0.335 0.023 0.327 0.030 0.216 0.022 0.0481 0.0078 <0.020 <0.020 <0.010 <0.010 <0.020

15.70 0.69 9.92 0.49 8.08 0.34 6.05 0.39 1.47 0.27 0.59 0.22 <0.93 <0.97 <0.88 <0.86

Huerto del Taraje

0.3

0.4

0.5

0 0 5 10 15 20 25 30 35

5

10

15

<0.95 <0.90 <0.51 <0.90 <0.90 <0.87 <0.96 <1.2 <1.1 <0.89

0.99 1.6 0.86 1.0 1.1 1.1 1.1 1.2 1.1 1.0

Huerto del Taraje Pbtotal Activity Concentration (Bq·kg-1)

0

20

Depth (cm)

0.2

) Bq·kg-1

210

Cs Activity Concentration (Bq·kg-1)

Depth (cm)

Depth (cm)

0.1

19.40 20.5 19.90 21.3 22.5 21.8 22.1 23.5 22.0 21.0

3.7 3.7 3.8 3.7 3.8 3.7 3.5 3.7 3.3 3.2

137

Pu Activity Concentration (Bq·kg-1)

0.0

39.3 25.4 22.0 26.7 29.2 28.1 25.9 32.3 27.1 20.30

241Am(

226Ra Bq·kg-1 1s

Huerto del Taraje

239,240

0 5 10 15 20 25 30 35

210Pb( ) Bq·kg-1 1s

20

40

0 5 10 15 20 25 30 35

Fig. 5. Radionuclides’ activity concentrations and distribution profiles in station Huerto del Taraje.

60

C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

166

EL PUNTAL Section cm

239,240Pu Bq·kg-1 1s

137Cs Bq·kg-1 1s

0-3 3-6 6-9 9-12 12-15 15-18 18-21 21-24 24-27 27-30

0.281 0.024 0.254 0.021 0.250 0.019 0.219 0.023 <0.030 <0.010 <0.020

7.70 0.60 7.31 0.41 8.72 0.48 7.14 0.41 1.31 0.24 <0.97 <0.87 <0.49 <0.87 <0.49

----------------------------------------------

El Puntal Pu Activity Concentration (Bq·kg-1) 0.3

0.4

0 5 10 15 20 25 30 35

0

5

10

) Bq·kg-1 <1.0 <0.94 <0.93 <1.0 <0.88 <1.0 <0.88 <0.50 <1.1 <0.53

1.8 1.7 1.0 1.0 1.1 1.3 1.1 0.92 1.1 0.88

El Puntal Pbtotal Activity Concentration (Bq·kg-1)

210

15

0 5 10 15 20 25 30 35

20

0

40

60

0 5 10 15 20 25 30 35

Depth (cm)

0.2

20.7 22.30 21.2 20.9 22.6 22.9 21.9 21.40 22.6 20.30

4.5 4.1 3.7 3.4 3.6 3.6 3.6 2.3 3.3 2.1

137

Depth (cm)

Depth (cm)

0.1

41.1 40.0 36.7 30.2 31.0 24.3 28.9 38.3 25.0 25.4

241Am(

226Ra Bq·kg-1 1s

El Puntal Cs Activity Concentration (Bq·kg-1)

239,240

0.0

210Pb( ) Bq·kg-1 1s

Fig. 6. Radionuclides’ activity concentrations and distribution profiles in station El Puntal.

where radioelements are detectable just until a depth of 12 cm, due to its location on one of the sides of the depression and not in its center, covered with water at the time of sampling. 238 Pu has not been quantified for any of the sediment cores analysed, presenting results that were always below the minimum detectable activity achieved for our alpha analyses. Therefore, the ratio 238Pu/239þ240Pu could not be calculated. However, the location of the studied area,

MARILÓPEZ Section cm

239,240Pu Bq·kg-1 1s

137Cs Bq·kg-1 1s

0-4 4-8 8-12 12-16 16-20 20-24 24-28 28-32

0.561 0.037 0.565 0.030 0.498 0.028 0.231 0.019 0.361 0.023 0.0418 0.0080 <0.010 <0.010

19.40 0.73 16.40 0.71 16.40 0.73 8.49 0.46 12.90 0.64 1.95 0.36 <0.49 <0.97

MariLópez Pu Activity Concentration (Bq·kg-1) 0.4

26.3 22.4 28.2 27.9 28.1 29.9 28.1 23.8

0.6

0 0 5 10 15 20 25 30 35

5

10

15

) Bq·kg-1 <0.72 <1.1 <1.2 <1.1 <1.3 <1.3 <0.63 <1.2

1.1 1.8 2.1 1.3 2.3 1.4 1.2 1.2

MariLópez Pbtotal Activity Concentration (Bq·kg-1)

210

20

0

Depth (cm)

0.2

3.5 3.9 5.3 3.7 4.7 4.2 4.3 3.9

MariLópez Cs Activity Concentration (Bq·kg-1)

Depth (cm)

Depth (cm)

0.0

62.4 45.8 39.9 41.4 57.2 37.8 25.7 28.3

241Am(

226Ra Bq·kg-1 1s

137

239,240

0 5 10 15 20 25 30 35

210Pb( ) Bq·kg-1 1s

20

40

0 5 10 15 20 25 30 35

Fig. 7. Radionuclides’ activity concentrations and distribution profiles in station MariLo´pez.

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C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

167

MEMBRILLO 239,240Pu Bq·kg-1 1s

Section cm 0-2 2-6 6-10 10-15 15-17 17-21 21-25 25-30

0.323 0.360 0.492 0.415 0.344 0.131 0.189 0.0450

0.025 0.028 0.038 0.032 0.036 0.017 0.017 0.0088

137Cs Bq·kg-1 1s

210Pb( ) Bq·kg-1 1s

226Ra Bq·kg-1 1s

12.10 14.20 15.80 17.90 12.00 6.00 4.90 1.80

64.0 68.3 59.8 69.00 52.7 25.0 23.8 39.2

24.3 24.0 23.4 22.2 19.8 20.20 24.0 26.2

Membrillo Pu Activity Concentration (Bq·kg-1) 0.4

0.6

0

5

10

15

0 5 10 15 20 25 30 35

<2.4 <1.3 <2.3 <2.8 <1.8 <0.98 <1.7 <2.3

Membrillo Pbtotal Activity Concentration (Bq·kg-1)

20

0

Depth (cm)

0.2

2.1 1.2 1.4 1.5 1.1 0.80 1.3 1.4

) Bq·kg-1

210

137

Depth (cm)

Depth (cm)

0.0

8.0 5.4 7.5 0.90 4.8 2.6 5.3 7.7

Membrillo Cs Activity Concentration (Bq·kg-1)

239,240

0 5 10 15 20 25 30 35

0.70 0.60 0.95 0.95 0.60 0.30 0.40 0.52

241Am(

20

40

60

80

0 5 10 15 20 25 30 35

Fig. 8. Radionuclides’ activity concentrations and distribution profiles in station Membrillo.

where no sources of artificial radionuclides exist and the low activities obtained in our analyses indicate that global fallout from atmospheric nuclear tests is the only source term of the investigated anthropogenic radionuclides. Comparison of the data produced in this work with those published in the literature became a tough task due to the scarce number of references dealing with the distribution of 239þ240Pu, 137 Cs (pre-Chernobyl accident) and 210Pb in salt marshes in Spain. 239þ240 Pu activity concentrations compare well with those obtained in the Arabia Saudi desert (0.28e0.50 Bq kg
1) as reported by Shabana and Al-Shammari in 2001, and in Mun˜overos (Spain) where an average concentration of 0.246  0.023 Bq kg
1 in the upper 5 cm of soil has been informed (Baeza et al., 2004). Both Arabia Saudi and Mun˜overos present similar rainfall indexes (100e300 mm y
1 and 450 mm y
1, respectively) to that of Don˜ana N.P. (633 mm y
1) (Pastor et al., 2004). Radionuclides’ inventories are shown in Table 1. 239þ240Pu inventories range from 16 to 101 Bq m
2, 137Cs values fluctuate between 514 and 3758 Bq m
2, and total 210Pb and unsupported 210Pb values comprise between 3398e18 529 and 3367e11 328 Bq m
2. It is noticeable Table 1 239,240 Pu,

137

Cs, total

210

Pb and unsupported

210

Pb inventories in Don˜ana

Sampling stations

239,240

Pu (Bq m
2)  1 s

137 Cs (Bq m
2)  1 s

210

Pbtotal (Bq m
2)  1 s

210

La Madre Juncabalejo Huerto del Taraje El Puntal MariLo´pez Membrillo Average values

16.35  0.65 29.5  1.7 48.2  1.9 31.7  1.7 82.8  2.4 101.1  3.5 54.6  5.4

514  16 816  31 1371  34 988  31 2620  59 3758  97 1787  133

3398  188 9304  449 9986  423 10 960  403 13 910  556 18 529  864 11 328  1312

124  188 2063  473 1951  443 3158  424 4413  539 9398  885 3367  1294

Pbuns ¼ 210Pbtotal
226Ra (226Ra values range between 20 and 25 Bq kg
1).

a 210

Pbunsa (Bq m
2)  1 s

168

C. Gasco´ et al. / J. Environ. Radioactivity 89 (2006) 159e171

that a wide range of values were obtained for the same radionuclide in different areas; several factors affect the accumulation of radionuclides on the sediments, such as the granulometric facies of the sediment, the erosion processes, orography (ponds or waterjets), etc. MariLo´pez and Membrillo present the highest inventories for all the selected radionuclides, due to their location in extensive depressed areas, allowing the accumulation of sedimentary material (and its associated radionuclides) and avoiding the erosion caused by seasonal floodings. 239þ240 Pu inventories are in good agreement with that obtained in salt marshes located in an undisturbed zone only affected by global fallout in the Camarge area, in the Rhone River delta (South of France), namely 84  1 Bq m
2 (Miralles et al., 2004). They also display a good concordance with data from Mediterranean continental shelf sediments, with values ranging from 10 to 120 Bq m
2 (Gasco´ and Anto´n, 1997; Gasco´ et al., 2002). Fallout plutonium is completely deposited on shelf sea-bottom sediments, taking into account its strong tendency to associate to the water column particulate material, and for this reason both inventories in marine and marshland zones are comparable. Following a survey dealing with atmospheric test fallout in UK, a strong correlation between nuclear weapons fallout and mean annual rainfall has been demonstrated (Cawse, 1983). Using a least squares fit procedure, it has been proven that total 239þ240Pu inventory satisfies the following equation: I239þ240 Pu ¼ 48R þ 16 where R is the average annual rainfall expressed in m y
1. Applying this relation to Don˜ana sediment cores, total 239þ240Pu inventory is estimated as 46 Bq m
2, considering a mean annual rainfall of 633 mm y
1 (average value since 1930) (Pastor et al., 2004). The mean 239þ240Pu inventory for Don˜ana sediments has been estimated as 55 Bq m
2. The fairly good concordance between the exposed results suggests that the sediment cores collected and analysed provide a fine estimate of the total amount of plutonium deposited on the investigated park. 137 Cs inventories are about five times higher in Don˜ana sediments than in Spanish Mediterranean marine shelf sediments (160e730 Bq m
2). Caesium behaves conservatively, with just about 40% being accumulated on marine sediments between 0 and 500 m depth (Gasco´ et al., 2002). Moreover, the clay fraction clearly prevails in Don˜ana sediments and the direct correlation between clay content and 137Cs concentration has been established by several scientists (Ligero et al., 2001; Elejalde et al., 2000). The connection between 137Cs inventories and the rainfall index has been proven by a number of authors (Huh and Su, 2004; Hien et al., 2002), indicating its variation with latitude as well. The broad range of inventories encountered in Don˜ana sediments is mainly attributed to the location of the sampled areas (either accumulation e ‘‘lucios’’ e or eroded e ‘‘can˜os’’ e sites), in concordance with published findings, mentioning a 76% maximum variation due to rainfall and latitude (Legarda et al., 2001). The average 137Cs inventory has been estimated to be 1787  133 Bq m
2 in this work, comparing well with that provided for 52 Alora soils (1400 Bq m
2) in Ma´laga (southeastern Spain) following investigations about soil erosion (Schoorl et al., 2004). Total and unsupported 210Pb inventories have not been compared with other marshland sediments due to the lack of available information. As expected, these values are lower than those reported for marine shelf sediments (4000e14 000 Bq m
2), considering that the content of

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169

Table 2 Mean sedimentation rates in some sediment cores expressed in mm y
1  1 s Station La Madre Juncabalejo Huerto del Taraje El Puntal MariLo´pez Membrillo

210

Pb CRS-MV (R2)

3.34  0.84 (0.93) 3.5  1.0 (0.92)

Pollen (eucalyptus) a

4.9 (2.9e6.0)

5.1 (3.0e6.3)a 3.44  0.85 (0.92) 3.6 (2.1e4.4)a 3.25  0.63 (0.98)

137

Cs and

239,240

Pu

3.96  0.73 5.20  0.41 4.59  0.63 2.76  0.63 5.31  0.83 5.61  0.83

R2: Coefficient of linear correlation. a Range depending on the eucalyptus introduction date considered: 1912 or 1929.

210

Pb in marine water noticeably exceeds that of fresh waters, mainly due to the high concentration of 238U in salty waters. Average sedimentation rates have been estimated using different approaches, as presented in Table 2. Sedimentation rates range from 3 to 5 mm y
1, depending on the considered area, either ‘‘lucios’’ or ‘‘can˜os’’. As previously explained in Section 2.3, the methods applied for the estimation of the sedimentation rates are arguable, and for this reason, only the mean results obtained in La Madre, Huerto del Taraje and MariLo´pez will be considered and discussed, since they were cross-checked with the information supplied with the eucalyptus pollen content in the sediments. In La Madre, the average sedimentation rates were obtained either through CRS-MV (3.34  0.84 mm y
1) or artificial radionuclides (3.96  0.73 mm y
1) falling within the sedimentation range obtained with the pollen procedure (2.9e6.0 mm y
1). For Huerto del Taraje, a value of 4.59  0.63 mm y
1 is confirmed by the pollen range (3.0e6.3 mm y
1). For MariLo´pez pond, a mean sedimentation rate of 5.31  0.83 mm y
1 has been reported in good concordance with the range estimated via pollen content (2.1e4.4 mm y
1). The evolution of the filling velocity of the studied salt marshes has been investigated by determining the old (last 6000 years), recent (1952e2002) and current (2000e2004) average sedimentation rates. In the Holocene, some authors (Ruı´z et al., 2004) provided a 1.5e2 mm y
1 sedimentation rate for the period 6500epresent using 14C. In this work, the accumulation rates produced for the time 1952e2002 range between 3 and 5 mm y
1. Sedimentation rates for the last couple of years were estimated by measuring, with the help of a graduated magnifying glass, the thickness of the sedimentary material accumulated on some ceramic plates located in the drilling points. The results obtained fluctuate between 0.3 and 2 mm y
1 (Rodrı´guez et al., 2005). These data point to an increase in the sedimentation rates in recent times, in concordance with the anthropogenic modification (re-channeling, dikes construction) of the Guadalquivir and Guadiamar River beds. The decrease observed in the last 2e3 years corresponds to the hydric isolation of the park from the mentioned rivers following Azna´lcollar mine accident. 4. Conclusions The activity concentrations and inventories of 137Cs, 239þ240Pu and 210Pb in Don˜ana salt marshes match well with those obtained in other regions with similar rainfall indexes and climatic characteristics. The artificial radionuclides distribution profiles do not show (except for Membrillo station) the maximum concentration fallout peaks corresponding to 1963, being homogenized on the upper layers due to alternation of humid and dry periods in the area, the location on eroded sites and/or disturbation provoked by animal grazing.

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Average sedimentation rates estimated for recent times (1952e2002) point to an increase in the amount of sedimentary material deposited on the salt marshes when compared to preanthropogenic rates (Holocene). Man-modification of Don˜ana’s hydrodynamics by re-channeling of the two major river beds crossing the park (Guadalquivir and Guadiamar) has been appointed as the main reason for the sedimentation enhancement, provoking a decrease on the hydric retention capacity of the salt marshes, which, in turn influences the fauna and flora distribution of the area. Acknowledgments We acknowledge Dr. M.B. Ruı´z-Zapata from Universidad Alaca´ de Henares (Madrid) for her work on the pollen content. A special mention to Dr. D. Dierig from the US Water Conservation Laboratory in Phoenix, TX, for providing pollen from Parthenium argentatum (or Guayule), extinguished in Spain nowadays. We also thank Organismo Auto´nomo de Parques Nacionales (Ministerio de Medio Ambiente) for the partial funding that enabled this work. References Baeza, A., Herna´ndez, S., Guille´n, F.J., Moreno, G., Manjo´n, J.L., Pascual, R., 2004. Radiocaesium and natural gamma emitters in mushrooms collected in Spain. The Science of The Total Environment 318 (1e3), 59e71. Cawse, P.A., 1983. Ecological Aspects of Radionuclides Release. In: Coughtrey, P.J. (Ed.). Blackwell, Oxford, p. 47. Elejalde, C., Herranz, M., Legarda, F., Romero, F., 2000. Determination and analysis of distribution coefficients of 137Cs in soils from Biscay (Spain). Environmental Pollution 110 (1), 157e164. Gasco´, C., Anto´n, M.P., 1997. Influence of the submarine orography on the distribution of long-lived radionuclides in the Palomares marine ecosystem. Journal of Environmental Radioactivity 34 (2), 111e125. Gasco´, C., Anto´n, M.P., Pozuelo, M., Meral, J., Gonza´lez, A.M., Papucci, C., Delfanti, R., 2002. Distribution of Pu, Am and Cs in margin sediments from the western Mediterranean (Spanish coast). Journal of Environmental Radioactivity 59 (1), 75e89. Gonza´lez Arteaga, J., 1993. Las Marismas del Guadalquivir: etapas de su aprovechamiento econo´mico. Tesis doctoral, Universidad de Sevilla Ed. Hancock, G.J., Olley, J.M., Wallbrink, J.P., 2001. Sediment Transport and Accumulation in Western Port. In: Technical Report 47/01. CSIRO Land and Water, Environmental Hydrology, Canberra. Hien, P.D., Hiep, H.T., Quang, N.H., Huy, N.Q., Binh, N.T., Hai, P.S., Long, N.Q., Bac, V.T., 2002. Derivation of 137Cs deposition density from measurements of 137Cs inventories in undisturbed soils. Journal of Environmental Radioactivity 62 (3), 295e303. Huh, C.-A., Su, C.-C., 2004. Distribution of fallout radionuclides (7Be, 137Cs, 210Pb and 239,240Pu) in soils of Taiwan. Journal of Environmental Radioactivity 77 (1), 87e100. Legarda, F., Elejalde, C., Herranz, M., Romero, F., 2001. Distribution of fallout 137Cs in soils from Biscay. Radiation Physics and Chemistry 61 (3e6), 683e684. Ligero, R.A., Ramos-Lerate, I., Casas-Ruiz, M., Sales, D., Lopez-Aguayo, F., 2001. Relationships between sea-bed radionuclide activities and some sedimentological variables. Journal of Environmental Radioactivity 57 (1), 7e19. Miralles, J., Radakovitch, O., Cochran, J.K., Veron, A., Masque´, P., 2004. Multitracer study of anthropogenic contamination records in the Camargue, Southern France. Science of The Total Environment 320 (1), 63e72. Pastor, F., Ferna´ndez, F., Garcı´a, J.P., Tovar, I., Sampedro, L., 2004. Boletı´n Hidrolo´gico semanal. Informacio´n Pluviome´trica. Ed. Subdireccio´n General de Planificacio´n y Uso Sostenible del Agua, Servicio de Recursos Hı´dricos. n  30. Robbins, J.A., Edgington, D.N., Kemp, W.L.A., 1978. Comparative 210Pb, 137Cs, and pollen geochronologies of sediments from Lakes Ontario and Erie. Quaternary Research 10, 256e278. Rodrı´guez-Ramı´rez, A., Rodrı´guez Vidal, L., Clemente, L., Ca´ceres, L.M., 1997. Evolucio´n reciente de la red hidrogra´fica de las marismas del Guadalquivir. In: Rodrı´guez Vidal, J. (Ed.), Cuaternario Ibe´rico. Huelva, pp. 137e139.

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