SEGH Articles

# Studying the effects on soil organic matter of wildfires in central Portugal

01 January 2013
The main objective of this study is testing the efficacy of pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) as a fast analytical technique to detect wildfire-induced molecular alterations of the SOM in Mediterranean Leptosols.

Sílvia Regina Marques Faria, is a PhD student at the Universidade de Aveiro http:// www.cesam.ua.pt/silviaregina) undertaking a project entitled “WildFIRE effects on forest Soil Organic Matter stocks and losses by runoff”. She was a joint poster winner at the 9th ISEG meeting in Aveiro in July 2012. Her work is in collaboration with (IST-ITN), Sacavém, Portugal and (IRNAS-CSIC), Seville, Spain.

In Mediterranean ecosystems, forest fires are a common phenomenon and widely considered to be the main factor of disturbance. In the case of the Mediterranean Basin, the Iberian Peninsula has the highest risk of wildfire occurrence, and certainly in relative terms Portugal is affected most by wildfires, devastating on average 100,000 ha each year and dramatically larger areas in dry years like 2003 and 2005.

Wildfires result in the transformation of vegetation and litter, leaving charred residues, and thus influence the carbon cycle by changing: (i) the amounts of soil organic matter (SOM); and (ii) the proportions amongst the carbon pools with different degrees of stability. In addition to affecting the carbon cycle, fires also affect the amounts and availability of nitrogen within soil organic matter. Especially char and other highly stable soil carbon pools are dificult to determine with solvent-based methods, so that pyrolysis-based analysis methods offer several advantages.

The main objective of this study is testing the efficacy of pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) as a fast analytical technique to detect wildfire-induced molecular alterations of the SOM in Mediterranean Leptosols.

To this end, the topsoil of two slopes with adjacent patches of burnt and unburnt Maritime Pine (Pinus pinaster) and eucalypt plantations (Eucalyptus globulus) were sampled in the Serra de Lousã, central Portugal. Compounds released by analytical pyrolysis showed alterations in the SOM due to fire. At desorption step (300 ºC), the marked presence of labile carbohydrate- derived compounds and of long chain n-alkanes distribution pointed to the incorporation of fresh plant material and/or low wildfire severity. Pyrolysis at 500 ºC revealed an increase of low molecular weight molecules for certain homologous series in fire-affected soils, suggesting the occurrence of thermal breakdown and cracking of long-chain components. Also the presence of several thermo-labile markers indicated that the wldfire severity had been low. Elemental analysis indicated marked fire-induced increases in total organic carbon (TOC) and total nitrogen (TN) for the pine stand as opposed to noticeable decreases for the eucalypt stands. The pH and CEC results were consistent with the contrast in fire-induced changes in TOC and TN. Probably, this contrast between the two sites was not due to differences in direct fire effects (especially fire severity) but to indirect fire effects i.e. in particular needle/leaf fall from partially combusted tree canopies.

Sílvia Regina Marques Faria

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Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Fertilizer usage and cadmium in soils, crops and food 2018-06-23

### Abstract

Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent $$\hbox {Cd}^{2+}$$ , $$\hbox {Mg}^{2+}$$ and $$\hbox {F}^-$$ ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

• Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

### Abstract

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

• Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

### Abstract

Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.