Abstract
The application of biochar as an organic amendment in polluted soils can facilitate their recovery by reducing the availability of contaminants. In the present work, the effect of biochar application to acid soils contaminated by heavy metal spillage is studied to assess its effect on the quantity and composition of soil organic matter (SOM), with special attention given to soil humic acids (HAs). This effect is poorly known and of great importance, as HA is one of the most active components of SOM. The field experiment was carried out in 12 field plots of fluvisols, with moderate and high contamination by trace elements (called MAS and AS, respectively), that are located in the Guadiamar Green Corridor (SW Spain), which were amended with 8 Mg·ha−1 of olive pit biochar (OB) and rice husk biochar (RB). The results indicate that 22 months after biochar application, a noticeable increase in soil water holding capacity, total organic carbon content, and soil pH were observed. The amounts of oxidisable carbon (C) and extracted HAs in the soils were not altered due to biochar addition. Thermogravimetric analyses of HAs showed an increase in the abundance of the most thermostable OM fraction of the MAS (375–650 °C), whereas the HAs of AS were enriched in the intermediate fraction (200–375 °C). Spectroscopic and chromatographic analyses indicate that the addition of biochar did not alter the composition of the organic fraction of HAs, while Cu, Fe, and as were considerably accumulated at HAs.
Highlights
Soil pollution is one of the main environmental problems at a global scale
This study demonstrates that the combination of elemental, chromatographic, and spectrospic analyses provides valuable information concerning the impact of biochar on the composition of humic acids (HAs) and the selective metal–HA interactions
HAs, without variations with the application of biochar as an amendment, and the only remarkable difference was the greater abundance of recalcitrant OM in the HAs of the moderately acid contaminated sites (MAS), in comparison with that of the acid contaminated sites (AS)
Summary
Soil pollution is one of the main environmental problems at a global scale. It affects2.5 million sites in the European Union alone, with mineral oil and heavy metals the main contaminants contributing around 60% to soil contamination [1]. Soil pollution is one of the main environmental problems at a global scale. 2.5 million sites in the European Union alone, with mineral oil and heavy metals the main contaminants contributing around 60% to soil contamination [1]. The high concentration of trace elements in soils is quite frequent in the Iberian Pyritic Belt, which is located in the southwest part of the Iberian Peninsula. These soils present serious functional problems, including difficulties for the development and establishment of microbial communities, as well as for the germination and growth of vegetation [3]. Recent estimates suggest that every year approximately 5 to 6 million ha of arable land are lost because of soil contamination, soil degradation, and marginalisation, which is an irreversible action
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