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| Titel |
Assessing soil redistribution on slope transects at different temporal scales by using radiotracers. |
| VerfasserIn |
L. Gaspar, A. Navas, J. Machín |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023502
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| Zusammenfassung |
| Soil erosion and sediment deposition represent a serious problem throughout the world,
because of their impact on sustainable agricultural production as well as on environmental
conservation. The isotopic techniques based on the use of fallout radionuclides 137Cs,
210Pbexand 7Be as tracers allow to obtain estimates of soil redistribution rates within
undisturbed and cultivated landscapes over a range of different timescales. Increasing risk of
erosion under climate change regimes precise data on soil erosion rates at different temporal
scales. The 137Cs technique (T1-2=30.17 years), an artificial radionuclide coming from
nuclear test, is the most widely used of the fallout radionuclides, and provides results of
medium-term average rates of soil redistribution. 210Pbex (T1-2= 22.26 years), a natural
geogenic radionuclide, offers estimates to quantify large-term soil erosion rates, and reflect a
longer period of time, between 100 and 150 years than the 40 years with 137Cs
.
The study area is located in the subhumid mountain in the north of Spain. To document
soil redistribution, 24 soil cores spaced 50 m apart were collected along slope transect. The
site selected to establish the local reference inventory was situated in the upper part of the
transect, on a flat area under natural forest. The reference inventory for 137Cs is 1570 Bq m-2
and for 210Pbex is 1891Bq m-2. Comparison of 137Cs versus 210Pb profiles for the
uncultivated soils show that the maximum concentrations of both radionuclides occur at
the surface horizon. For the cultivated soils the two radionuclides are relatively
uniformly distributed with depth. However 210Pbex concentrations show some evidence
of increasing slightly towards the surface. The areal activity density (inventory)
showed large variations, between 489.2 – 6080.1 Bq m-2 for 137Cs, and 117.6 –
7788.3 Bq m-2 for 210Pbex. The 137Cs and 210Pbex inventories at the middle of the
slope were extremely low in cultivated soils, and the highest inventories were found
at the bottom of the slope in flat areas where the sediment is accumulated. The
mean 137Cs,210Pbex inventories measured in cores collected from the upper part of
the transect, with an average slope of 24%, were 1699 Bq m-2 and 1713Bq m-2,
respectively, for the midslope (21% slope) were 1713 Bq m-2 and 1720 Bq m-2, and for
the lower part of the transect (15% slope) were higher with values from 2296 Bq
m-2 and 2325 Bq m-2. The estimates of erosion and sedimentation rates based on
conversion models by using 137Cs measurements provide a maximum erosion and
sedimentation rates of 31.9 Mg ha-1 year-1 and 24.5 Mg ha-1 year-1, respectively. The
highest erosion rate occurred in cultivated areas at the midslope, while the highest
sedimentation rates are found at the bottom part of the transect. Comparison with
previous research along the slope that documented soil redistribution after a 22 mm
storm event by using 7Be reflect that erosion dominated at most sampling points
along the transect, and estimated soil losses ranged between 5.5 and 40 Mg ha-1
year-1.
The pattern of radionuclides redistribution along the transect reflects the effects of water
erosion on different types and land uses according to the slope gradient and soil properties.
The results obtained confirm the potential for using 137Cs and 210Pbexfor assessing soil
redistribution on slope transects at different temporal scales in Mediterranean environments. |
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