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

Universidade de Aveiro www.cesam.ua.pt/silviaregina

Keep up to date

SEGH Events

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

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

  • Characteristics of PM 2.5 , CO 2 and particle-number concentration in mass transit railway carriages in Hong Kong 2017-08-01

    Abstract

    Fine particulate matter (PM2.5) levels, carbon dioxide (CO2) levels and particle-number concentrations (PNC) were monitored in train carriages on seven routes of the mass transit railway in Hong Kong between March and May 2014, using real-time monitoring instruments. The 8-h average PM2.5 levels in carriages on the seven routes ranged from 24.1 to 49.8 µg/m3, higher than levels in Finland and similar to those in New York, and in most cases exceeding the standard set by the World Health Organisation (25 µg/m3). The CO2 concentration ranged from 714 to 1801 ppm on four of the routes, generally exceeding indoor air quality guidelines (1000 ppm over 8 h) and reaching levels as high as those in Beijing. PNC ranged from 1506 to 11,570 particles/cm3, lower than readings in Sydney and higher than readings in Taipei. Correlation analysis indicated that the number of passengers in a given carriage did not affect the PM2.5 concentration or PNC in the carriage. However, a significant positive correlation (p < 0.001, R 2 = 0.834) was observed between passenger numbers and CO2 levels, with each passenger contributing approximately 7.7–9.8 ppm of CO2. The real-time measurements of PM2.5 and PNC varied considerably, rising when carriage doors opened on arrival at a station and when passengers inside the carriage were more active. This suggests that air pollutants outside the train and passenger movements may contribute to PM2.5 levels and PNC. Assessment of the risk associated with PM2.5 exposure revealed that children are most severely affected by PM2.5 pollution, followed in order by juveniles, adults and the elderly. In addition, females were found to be more vulnerable to PM2.5 pollution than males (p < 0.001), and different subway lines were associated with different levels of risk.

  • Comparison of chemical compositions in air particulate matter during summer and winter in Beijing, China 2017-08-01

    Abstract

    The development of industry in Beijing, the capital of China, particularly in last decades, has caused severe environmental pollution including particulate matter (PM), dust–haze, and photochemical smog, which has already caused considerable harm to local ecological environment. Thus, in this study, air particle samples were continuously collected in August and December, 2014. And elements (Si, Al, V, Cr, Mn, Fe, Ni, Cu, Zn, Mo, Cd, Ba, Pb and Ti) and ions ( \({\text{NO}}_{3}^{-}\) , \({\text{SO}}_{4}^{2-}\) , F, Cl, Na+, K+, Mg2+, Ca2+ and \({\text{NH}}_{4}^{+}\) ) were analyzed by inductively coupled plasma mass spectrometer and ion chromatography. According to seasonal changes, discuss the various pollution situations in order to find possible particulate matter sources and then propose appropriate control strategies to local government. The results indicated serious PM and metallic pollution in some sampling days, especially in December. Chemical Mass Balance model revealed central heating activities, road dust and vehicles contribute as main sources, account for 5.84–32.05 % differently to the summer and winter air pollution in 2014.

  • Annual ambient atmospheric mercury speciation measurement from Longjing, a rural site in Taiwan 2017-08-01

    Abstract

    The main purpose of this study was to monitor ambient air particulates and mercury species [RGM, Hg(p), GEM and total mercury] concentrations and dry depositions over rural area at Longjing in central Taiwan during October 2014 to September 2015. In addition, passive air sampler and knife-edge surrogate surface samplers were used to collect the ambient air mercury species concentrations and dry depositions, respectively, in this study. Moreover, direct mercury analyzer was directly used to detect the mercury Hg(p) and RGM concentrations. The result indicated that: (1) The average highest RGM, Hg(p), GEM and total mercury concentrations, and dry depositions were observed in January, prevailing dust storm occurred in winter season was the possible major reason responsible for the above findings. (2) The highest average RGM, Hg(p), GEM and total mercury concentrations, dry depositions and velocities were occurred in winter. This is because that China is the largest atmospheric mercury (Hg) emitter in the world. Its Hg emissions and environmental impacts need to be evaluated. (3) The results indicated that the total mercury ratios of Kaohsiung to that of this study were 5.61. This is because that Kaohsiung has the largest industry density (~60 %) in Taiwan. (4) the USA showed average lower mercury species concentrations when compared to those of the other world countries. The average ratios of China/USA values were 89, 76 and 160 for total mercury, RGM and Hg(p), respectively, during the years of 2000–2012.