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| Titel |
Mapping Zn, Cu and Cd contents at the small catchment level after dispersion of contaminants by agricultural practices |
| VerfasserIn |
E. Vidal Vázquez, J. M. Mirás-Avalos, J. Paz-Ferreiro |
| 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 |
250030553
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| Zusammenfassung |
| Dispersion of trace metals into the rural environment through the use of sewage sludge,
fertilizers and manure has been worldwide reported. In El Abelar (Coruña province, Spain),
pig slurry was discharged during years intensively into an agricultural field by means of a
device which constituted a point source of contamination. The application point was
located near the head of an elementary basin, so that slurry was dispersed by runoff
into neighboring grassland and maize fields. In addition, diffuse pollution was also
present in the study area as a consequence of cattle grazing. Water quality was
monitored during and after slurry application at the outlet of a small catchment (about
10.7 ha in surface) draining the study fields. High levels of nutrients, including
heavy metals, were found in drainage water. The main objectives of this paper are to
determine the spatial variability of Cu, Zn and Cd as extracted by NO3H, EDTA and
Ca2Cl and to evaluate the risk of accumulation of these heavy metals at the small
catchment level. A set of 55 soil samples were taken from the top soil layer (0-20 cm)
of the studied catchment, following a random sampling scheme. Fe, Mn, Cu, Zn
and Cd contents were determined i) after digestion by nitric acid in a microwave
(USEPA-SW-846 3051) ii) after extraction with EDTA and iii) after extraction with Cl2Ca.
Element contents in the extracts were determined by ICP-MS. Summary statistics
indicate that variability in Cu, Zn and Cd contents over the study area was very
high. For example, after NO3H digestion Zn contents ranged from 29.66 to 141.77
3 mg kg-1 and Cu contents varied from 10.45 to 72.7 3 mg kg-1. High Cu and
Zn contents result from accumulation as a consequence of slurry discharge. Also,
some hot spots with high levels of Cd (> 3 mg kg-1 after NO3H) with respect to
background values were recorded. Geostatistics provides all necessary tools to analyze the
spatial variability of soil properties over a landscape. The spatial dependence of the
extracted heavy metals was assessed by semivariogram analysis. When a pattern of
spatial dependence was found, kriging was used to construct contour maps of metal
contents. Indicator kriging was also used to map the probability that a local threshold is
exceeded. This probability map can also be used for decision making processes such as
the determination of areas where additional samples should be collected. In cases
where extractable trace elemet contents did not show spatial structure at all, hence,
non-geostatistical techniques such as the inverse distance method were used to
attempt to interpolate these metal fractions. The used mapping methods illustrate how
poor the studied site was managed from an environmentally point of view. The
spatial distribution of the study soil elements appear to depend largely on both, the
discharge pattern and the morphological characteristics of the area where slurry was
applied.
Acknowledgements. This work was financed by MEC (Spain) under project
CGL2005-08219-C02-01. |
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