SH Doerr | Swansea University (original) (raw)

Papers by SH Doerr

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT In most of the literature, ash is referred to as a highly wettable material (e.g. Cerdà ... more ABSTRACT In most of the literature, ash is referred to as a highly wettable material (e.g. Cerdà and Doerr, 2008; Etiegni and Campbell, 1991; Woods and Balfour 2010). However, the contrary was suggested in few articles, albeit with no further quantification (Gabet and Sternberg, 2008; Khanna et al., 1996; Stark, 1977). To clarify this question, water repellency measurements on ash using the Water Drop Penetration Times (WDPT) method were performed on ash from Mediterranean ecosystems and it was found to be water repellent (Bodí et al. 2011). Water repellency on ash from different wildfires ranged from 40 to 10 % occurrence with samples being extreme repellent (lasting more than 3600 s to penetrate). Part of the ash produced in the laboratory was also water repellent. After that, other ash samples had been found water repellent in wildfires in Colorado (unpublished results), Portugal (Gonzalez-Pelayo, 2009), or in prescribed fires in Australia (Bodí et al. 2011b; Petter Nyman, personnal communication). All the samples exhibiting water repellent properties had in common that were combusted at low temperatures, yielding in general ash with dark colour and contents of organic carbon of more than 18 % (Bodí et al. 2011a), although these properties were not exactly proportional to its water repellency occurrence or persistence. In addition, the species studied in Bodí et al. (2011) had been found to produce different levels of WR repellency, being ash from Pinus halepensis more repellent than that from Quercus coccifera and Rosmarins officinalis. Ash from Eucaliptus radiata had been found also very water repellent, as Pinus halepensis (unpublished data). The reasons of the existance of water repellent ash are that the charred residue produced by fire (an also contained in the ash) can contain aromatic compounds that have a lower free energy than water and therefore behave as hydrophobic materials with reduced solubility (Almendros et al., 1992 and Knicker, 2007). Specifically, studies of FT-IR spectroscopy in the WR ash reported in Bodí et al (2011) have been done, resulting that the more persistent water repellency coincided with higher levels of aliphatic, aromatic and carboxylic groups (Pavel Dlapa et al., under revision). The existence of water repellent ash indicate that i) after low severity fires, ash can be responsible in some occasions of the soil water repellency and ii) ash water repellency can be one of the ash properties that controls the variable hydrological response of ash covering the soil. Acknowledgments to the Spanish Ministry of Science and Innovation for the HYDFIRE project CGL2010-21670-C02-01.

Nanoscale, Jan 3, 2018

Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil ... more Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil organic matter (SOM) are critical to understanding the factors involved in soil composition and turnover. However soil nanoscience has been hampered by the lack of suitable methods to determine soil biophysical properties at nanometre spatial resolution with minimal sample preparation. Here we introduce for the first time an Atomic Force Microscopy (AFM)-based Quantitative Nano-Mechanical mapping (QNM) approach that allows the characterisation of the role of SOM in controlling surface nano-mechanical properties of soil aggregates. SOM coverage resulted in an increased roughness and surface variability of soil, as well as in decreased stiffness and adhesive properties. The latter also correlates with nano- to macro-wettability features as determined by contact angle measurements and Water Drop Penetration Time (WDPT) testing. AFM thus represents an ideal quantitative tool to complement ex...

European Journal of Soil Science, 2015

The potential of biochar to ameliorate soil water repellency has not been widely studied. Previou... more The potential of biochar to ameliorate soil water repellency has not been widely studied. Previous studies have focused on the potential for biochar to induce or exacerbate existing water repellency rather than alleviate it. This study investigates the effect of adding wettable biochar to water repellent soil by comparing the water drop penetration times (WDPT) of control and biochar-amended soil. The potential of wettable biochar to act as a physical amendment to water repellent soil was evaluated by mixing coarsely ground biochar (CGB, particle size range 250-2000 µm) or finely ground biochar (FGB, particle size range < 250 µm) with one strongly and one severely naturally water repellent soil in various quantities, and measuring the WDPT for each mixture. When biochar particles did not fall within the range of existing soil particle diameters, an initial increase in both mean WDPT (WDPT M) and variation in WDPT was observed with small additions of biochar. These effects possibly resulted from increased surface roughness and inhibition of infiltration by suspension of drops above the average soilair interface at a few hydrophobic points. Both CGB and FGB reduced soil water repellency, FGB more effectively than CGB. Adding 10% w/w FGB reduced soil WDPT by 50%, and 25% FGB eliminated repellency. Direct absorption of water by biochar and an increase in soil surface area in contact with water are likely the predominant physical mechanisms involved. This exploratory study suggests biochar has the potential to amend water repellent soil.

Geoderma, 2016

Highlights • Soil organic layer chemical transformations during a boreal forest fire determined •... more Highlights • Soil organic layer chemical transformations during a boreal forest fire determined • Transformations correlated with temperature-time profiles during the fire • T and heating durations correlated with C%, thermal recalcitrance and aromaticity • Key changes occurred at higher T than found previously in laboratory experiments • Increases in boreal fire severity likely to lead to more recalcitrant soil carbon

Pyrogenic carbon (PyC; also known as black carbon or biochar), is viewed as an important carbon f... more Pyrogenic carbon (PyC; also known as black carbon or biochar), is viewed as an important carbon form that may contribute substantially to C sequestration in soils. However, big uncertainties arise when trying estimate PyC stocks in the environment. One of the main hurdles is the use of a wide range of methodologies used for PyC quantification, which can lead to variations in estimates of PyC quantities of several orders of magnitude. Another problem is that, as PyC is a continuum of compounds affected by different degrees of charring, the window of this continuum that is considered in a given study determines the amount of PyC quantified. When quantifying PyC in soils, two main approaches are currently taken: (i) estimation of charcoal content by visual detection, and (ii) estimation of PyC content in the bulk soil by various chemical, spectroscopic and/or thermal methods. The second approach is usually carried out for soil samples after sieving to < 2 mm. The aim of this contrib...

Cuadernos de Investigación Geográfica, 2012

Soil water repellency determines the water available in the soil system, the runoff generation an... more Soil water repellency determines the water available in the soil system, the runoff generation and the geomorphologic processes. This study examines the soil wettability during the summer of 2008 and 2009 in forest soils with different fire history, and in agricultural soils with different managements. Water repellency was assessed using the Water Drop Penetration Time test (WDPT). Results indicate that water repellency is more frequent and persistent in forest soils than in agricultural ones. In the former, water repellency is reduced a year after a fire and is not recovered during at least 12 years. In agricultural soils, it is found under no till treatment, whereas sites treated with herbicides or tillage were virtually unaffected. Water repellency is exhibited because of the increment of aboveground biomass and organic matter content as the vegetation is recovered following a wildfire or after abandoned crop fields, and after adding reaping or with green manure. In any case, wat...

ABSTRACT The use of high-speed videography has been shown to be very useful in some splash erosio... more ABSTRACT The use of high-speed videography has been shown to be very useful in some splash erosion studies. One methodological problem that arises in its application is the difficulty in tracking a large number of particles in slow motion, especially when the use of automatic tracking software is limited. With this problem, some studies simply assume a certain ejecting angle for all particles rather than actually tracking every particle. In this contribution, different combinations of variables (e.g. landing position, landing time or departing position, etc.) were compared in order to determine an efficient and sufficiently precise method for trajectory tracking when a large amount of particles are being ejected.

Pinus pinaster forest Prescribed fire Soil disturbance Following a prescribed fire in a Pinus pin... more Pinus pinaster forest Prescribed fire Soil disturbance Following a prescribed fire in a Pinus pinaster forest site located in the northwest Portugal, monitoring of any changes in selected soil characteristics and soil hydrology was undertaken to assess the effects of burning on the following: pH, electrical conductivity, water content, organic carbon and porosity. Thirty plots were established on a regular grid. At each sample plot before and after the fire, samples were collected (disturbed samples from depths of 0-1cm and 1-5cm; undisturbed core samples from 0-5cm). The results indicate that there was no measurable impact on the properties of the soil following this carefully conducted prescribed fire. The fire only affected the litter layer, as intended. Confirmation of this minimal impact on the soil was provided by regrowth of grasses and herbs already occurring two months after the fire. The implication is, therefore, that provided this wildfire-risk reduction strategy is carried out under existing strict guidelines, any impact on soil quality will be minimal.

Environmental Earth Sciences, 2014

In order to decrease the risk of severe wildfire, prescribed fire has recently been adopted in Po... more In order to decrease the risk of severe wildfire, prescribed fire has recently been adopted in Portugal and elsewhere in the Mediterranean as a major tool for reducing the fuel load instead of manual or mechanical removal of vegetation. There has been some research into its impact on soils in shrublands and grasslands, but to date little research has been conducted in forested areas in the region. As a result, the impact of prescribed fire on the physico-chemical soil characteristics of forest soils has been assumed to be minimal, but this has not been demonstrated. In this study, we present the results of a monitoring campaign of a detailed pre-and post-prescribed fire assessment of soil properties in a long-unburnt P. pinaster plantation, NW Portugal. The soil characteristics examined were pH, total porosity, bulk density, moisture content, organic matter content and litter/ash quantity. The results show that there was no significant impact on the measured soil properties, the only effect being confined to minor changes in the upper 1 cm of soil. We conclude that provided the fire is carried out according to strict guidelines in P. pinaster forest, a minimal impact on soil properties can be expected.

Soil Research, 2005

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopr... more After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C–H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C–H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extrac...

Soil Research, 2005

The causes of soil water repellency are still only poorly understood. It is generally assumed tha... more The causes of soil water repellency are still only poorly understood. It is generally assumed that hydrophobic organic compounds are responsible, but those concerned have not previously been identified by comparison between samples taken from a water repellent topsoil and the wettable subsoil. In this study we separated, characterised, and compared the organic compounds present at 4 different depths in a sandy soil under permanent grass cover that is water repellent in the upper 0.30 m but wettable below this. Soil samples were extracted using a mixture of isopropanol and aqueous ammonia (7 : 3 v : v). Samples were wettable after extraction and re-application of the extract from each sample onto wettable sand induced water repellency. The chloroform-soluble portions of the extracts were analysed by gas chromatography and gas chromatography-mass spectrometry. The compounds identified at all soil depths included long-chain carboxylic acids (C16–C24), amides (C14–C24), alkanes (C25–C31...

Australian Journal of Soil Research, 2005

Copper is an important micronutrient and trace amounts are essential for crop growth. However, hi... more Copper is an important micronutrient and trace amounts are essential for crop growth. However, high concentrations of copper will produce toxic effects. Australia is increasingly developing production of crops in water repellent soils. Clay amendment, a common amelioration techniques used in Australia, has demonstrated agronomic benefits in increased crop or pasture production. The sorption and desorption of copper and the effect of clay treatment on copper behaviour in a water repellent soil collected from an experimental farm in South Australia is studied. We found that the water repellent soils amended with clay have an increased adsorption capacity of copper. Also the clay-amended soils had an increased ratio of specific sorption to total sorption of copper. The implications of this study to the sustainable agro-environmental management of water repellent soils is discussed.

Soil Research, 2005

Certain organic compounds derived from living organisms or their decaying parts are generally acc... more Certain organic compounds derived from living organisms or their decaying parts are generally accepted to induce soil water repellency. Water repellency may therefore be expected to increase with proximity to organisms releasing hydrophobic compounds. This hypothesis is tested here for Eucalyptus globulus trees, since eucalypt species are frequently associated with elevated repellency levels. In a young, first-rotation plantation on coastal dune sands in central Portugal, repeat measurements of water repellency using the ‘Molarity of an Ethanol Droplet’ (MED) test were carried out in situ between April 2001 and May 2002. On 25 dates, repellency was measured at initially 2 and later 3 distances on 2 sides of 8–11 randomly selected trees. On 15 occasions, additional repellency measurements were performed within small grids aside 3 of the selected trees. The postulated decrease in topsoil water repellency with increased distance from eucalypt tree stems was found to apply on several in...

Land Degradation & Development, 2002

... RA SHAKESBY,1* COA COELHO,2 S. SCHNABEL,3 JJ KEIZER,2 MA CLARKE,1 JF LAVADO CONTADOR,3 RPD WA... more ... RA SHAKESBY,1* COA COELHO,2 S. SCHNABEL,3 JJ KEIZER,2 MA CLARKE,1 JF LAVADO CONTADOR,3 RPD WALSH,1 AJD FERREIRA2 AND SH DOERR1 1Department of Geography, University of Wales Swansea, UK 2Departamento de Ambiente e Ordenamento ...

International Journal of Wildland Fire, 2013

Pyrogenic carbon (PyC) produced during vegetation fires represents one of the most degradation re... more Pyrogenic carbon (PyC) produced during vegetation fires represents one of the most degradation resistant organic carbon pools and has important implications for the global carbon cycle. Its long-term fate in the environment and the processes leading to its degradation are the subject of much debate. Its consumption in subsequent fires is considered a potential major mechanism of abiotic PyC degradation; however, no quantitative data supporting this removal pathway have been published to date. To address this gap, we quantified consumption of residual PyC at the forest floor during an experimental fire, representative of a typical boreal wildfire, complemented by exploratory laboratory heating experiments. Labelled PyC (pinewood charcoal from a slash pile burn), in granular form contained in stainless steel mesh bags and as individual pieces, were placed at ~2-cm depth within the forest floor. The median mass loss of granular charcoal was 6.6%, with 75% of the samples losing <15%,...

Geomorphology, 2009

Information on post-fire sediment and nutrient redistribution is required to underpin post-fire c... more Information on post-fire sediment and nutrient redistribution is required to underpin post-fire catchment management decisions. Fallout radionuclide budgets (210 Pb xs , 137 Cs and 7 Be) were derived to quantify soil redistribution and sediment yield in forested terrain following a moderately severe wildfire in a small (89 ha) water supply catchment in SE Australia. Application of these techniques in burnt terrain requires careful consideration of the partitioning of radionuclides between organic and mineral soil components. Beryllium-7 and 210 Pb xs were shown to be closely associated with ash, litter and soil organic matter whereas 137 Cs was more closely associated with subsurface coarse mineral soil. Comparison of the three tracer budgets indicated that the dominant sediment source areas were ridgetops and steep valley sideslopes, from which burnt surface material was conveyed to the stream network via pre-existing gullies. Erosion was predominantly driven by sheetwash, enhanced by soil water repellency, and modified by bioturbation which both supplies subsurface sediment and provides sinks for erosive overland flow. Footslope and riparian zones were not important sediment source areas. The estimated event-based (wildfire and subsequent rainfall) sediment yield is 58 ± 25 t km − 2 , based on fallout 7 Be measurements. The upper estimate of total particulate phosphorus yield (0.70 kg ha − 1) is more than 10 times that at equivalent unburnt sites. This illustrates that, soon after fire, burnt eucalypt forest can produce nutrient loads similar to those of agricultural catchments. The tracer budgets indicate that wildfire is an important control on sediment and phosphorus inputs to the stream network over the decadal timeframe and the pulsed nature of this release is an important concern for water quality management.

Geoderma, 2010

Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies h... more Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies have systematically investigated the relationship between these variables. Specifically the hypothesis that the pH may control repellency via changes in the variable surface charge of soil material has not yet been tested. In previous work, methods for changing soil pH have also involved changes in soil moisture, but it has been argued that the potential influence of soil moisture changes needs to be eliminated before the actual relationship between pH and SWR can be isolated. The paper addresses this research gap using a new method, which enables adjustment of the pH of soils with low moisture content via the gas phase and thus involves minimal change in moisture content, allowing the response of SWR to pH changes to be evaluated. The method was applied to 14 soil samples from Germany, The Netherlands, the UK, and Australia, using the water drop penetration time (WDPT) as the indicator of SWR. Additionally, sessile drop contact angles (Θ sess) were measured on the four samples from Germany and the titratable surface charge of these four soils was measured at selected pH values using a particle charge detector (PCD). Changes in SWR with soil pH were found to be influenced by the density and type of sites able to interact with protons at the available surfaces of organic and mineral materials in soil. The maximum SWR occurred for soil at natural pH and where the charge density was minimal. As pH increased, negative surface charge increased due to deprotonation of sites and WDPT decreased. Two types of behaviour were observed: i) a decrease in repellency with decreasing pH, probably because of a sufficient number of proton accepting surface sites with a significant amount of positive surface charge, ii) no decrease in repellency with decreasing pH in soils with insufficient proton accepting surface sites to develop significant positive surface charge. The data suggest that the availability and relative abundance of proton active sites at mineral surfaces, and those at organic functional groups influence the response of the soil samples to changes in pH. The variety of geographic origins and histories of the soils examined provides a distinction between site specific and more widely applicable soil characteristics of pH dependent SWR.

Geochimica et Cosmochimica Acta, 2006

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT In most of the literature, ash is referred to as a highly wettable material (e.g. Cerdà ... more ABSTRACT In most of the literature, ash is referred to as a highly wettable material (e.g. Cerdà and Doerr, 2008; Etiegni and Campbell, 1991; Woods and Balfour 2010). However, the contrary was suggested in few articles, albeit with no further quantification (Gabet and Sternberg, 2008; Khanna et al., 1996; Stark, 1977). To clarify this question, water repellency measurements on ash using the Water Drop Penetration Times (WDPT) method were performed on ash from Mediterranean ecosystems and it was found to be water repellent (Bodí et al. 2011). Water repellency on ash from different wildfires ranged from 40 to 10 % occurrence with samples being extreme repellent (lasting more than 3600 s to penetrate). Part of the ash produced in the laboratory was also water repellent. After that, other ash samples had been found water repellent in wildfires in Colorado (unpublished results), Portugal (Gonzalez-Pelayo, 2009), or in prescribed fires in Australia (Bodí et al. 2011b; Petter Nyman, personnal communication). All the samples exhibiting water repellent properties had in common that were combusted at low temperatures, yielding in general ash with dark colour and contents of organic carbon of more than 18 % (Bodí et al. 2011a), although these properties were not exactly proportional to its water repellency occurrence or persistence. In addition, the species studied in Bodí et al. (2011) had been found to produce different levels of WR repellency, being ash from Pinus halepensis more repellent than that from Quercus coccifera and Rosmarins officinalis. Ash from Eucaliptus radiata had been found also very water repellent, as Pinus halepensis (unpublished data). The reasons of the existance of water repellent ash are that the charred residue produced by fire (an also contained in the ash) can contain aromatic compounds that have a lower free energy than water and therefore behave as hydrophobic materials with reduced solubility (Almendros et al., 1992 and Knicker, 2007). Specifically, studies of FT-IR spectroscopy in the WR ash reported in Bodí et al (2011) have been done, resulting that the more persistent water repellency coincided with higher levels of aliphatic, aromatic and carboxylic groups (Pavel Dlapa et al., under revision). The existence of water repellent ash indicate that i) after low severity fires, ash can be responsible in some occasions of the soil water repellency and ii) ash water repellency can be one of the ash properties that controls the variable hydrological response of ash covering the soil. Acknowledgments to the Spanish Ministry of Science and Innovation for the HYDFIRE project CGL2010-21670-C02-01.

Nanoscale, Jan 3, 2018

Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil ... more Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil organic matter (SOM) are critical to understanding the factors involved in soil composition and turnover. However soil nanoscience has been hampered by the lack of suitable methods to determine soil biophysical properties at nanometre spatial resolution with minimal sample preparation. Here we introduce for the first time an Atomic Force Microscopy (AFM)-based Quantitative Nano-Mechanical mapping (QNM) approach that allows the characterisation of the role of SOM in controlling surface nano-mechanical properties of soil aggregates. SOM coverage resulted in an increased roughness and surface variability of soil, as well as in decreased stiffness and adhesive properties. The latter also correlates with nano- to macro-wettability features as determined by contact angle measurements and Water Drop Penetration Time (WDPT) testing. AFM thus represents an ideal quantitative tool to complement ex...

European Journal of Soil Science, 2015

The potential of biochar to ameliorate soil water repellency has not been widely studied. Previou... more The potential of biochar to ameliorate soil water repellency has not been widely studied. Previous studies have focused on the potential for biochar to induce or exacerbate existing water repellency rather than alleviate it. This study investigates the effect of adding wettable biochar to water repellent soil by comparing the water drop penetration times (WDPT) of control and biochar-amended soil. The potential of wettable biochar to act as a physical amendment to water repellent soil was evaluated by mixing coarsely ground biochar (CGB, particle size range 250-2000 µm) or finely ground biochar (FGB, particle size range < 250 µm) with one strongly and one severely naturally water repellent soil in various quantities, and measuring the WDPT for each mixture. When biochar particles did not fall within the range of existing soil particle diameters, an initial increase in both mean WDPT (WDPT M) and variation in WDPT was observed with small additions of biochar. These effects possibly resulted from increased surface roughness and inhibition of infiltration by suspension of drops above the average soilair interface at a few hydrophobic points. Both CGB and FGB reduced soil water repellency, FGB more effectively than CGB. Adding 10% w/w FGB reduced soil WDPT by 50%, and 25% FGB eliminated repellency. Direct absorption of water by biochar and an increase in soil surface area in contact with water are likely the predominant physical mechanisms involved. This exploratory study suggests biochar has the potential to amend water repellent soil.

Geoderma, 2016

Highlights • Soil organic layer chemical transformations during a boreal forest fire determined •... more Highlights • Soil organic layer chemical transformations during a boreal forest fire determined • Transformations correlated with temperature-time profiles during the fire • T and heating durations correlated with C%, thermal recalcitrance and aromaticity • Key changes occurred at higher T than found previously in laboratory experiments • Increases in boreal fire severity likely to lead to more recalcitrant soil carbon

Pyrogenic carbon (PyC; also known as black carbon or biochar), is viewed as an important carbon f... more Pyrogenic carbon (PyC; also known as black carbon or biochar), is viewed as an important carbon form that may contribute substantially to C sequestration in soils. However, big uncertainties arise when trying estimate PyC stocks in the environment. One of the main hurdles is the use of a wide range of methodologies used for PyC quantification, which can lead to variations in estimates of PyC quantities of several orders of magnitude. Another problem is that, as PyC is a continuum of compounds affected by different degrees of charring, the window of this continuum that is considered in a given study determines the amount of PyC quantified. When quantifying PyC in soils, two main approaches are currently taken: (i) estimation of charcoal content by visual detection, and (ii) estimation of PyC content in the bulk soil by various chemical, spectroscopic and/or thermal methods. The second approach is usually carried out for soil samples after sieving to < 2 mm. The aim of this contrib...

Cuadernos de Investigación Geográfica, 2012

Soil water repellency determines the water available in the soil system, the runoff generation an... more Soil water repellency determines the water available in the soil system, the runoff generation and the geomorphologic processes. This study examines the soil wettability during the summer of 2008 and 2009 in forest soils with different fire history, and in agricultural soils with different managements. Water repellency was assessed using the Water Drop Penetration Time test (WDPT). Results indicate that water repellency is more frequent and persistent in forest soils than in agricultural ones. In the former, water repellency is reduced a year after a fire and is not recovered during at least 12 years. In agricultural soils, it is found under no till treatment, whereas sites treated with herbicides or tillage were virtually unaffected. Water repellency is exhibited because of the increment of aboveground biomass and organic matter content as the vegetation is recovered following a wildfire or after abandoned crop fields, and after adding reaping or with green manure. In any case, wat...

ABSTRACT The use of high-speed videography has been shown to be very useful in some splash erosio... more ABSTRACT The use of high-speed videography has been shown to be very useful in some splash erosion studies. One methodological problem that arises in its application is the difficulty in tracking a large number of particles in slow motion, especially when the use of automatic tracking software is limited. With this problem, some studies simply assume a certain ejecting angle for all particles rather than actually tracking every particle. In this contribution, different combinations of variables (e.g. landing position, landing time or departing position, etc.) were compared in order to determine an efficient and sufficiently precise method for trajectory tracking when a large amount of particles are being ejected.

Pinus pinaster forest Prescribed fire Soil disturbance Following a prescribed fire in a Pinus pin... more Pinus pinaster forest Prescribed fire Soil disturbance Following a prescribed fire in a Pinus pinaster forest site located in the northwest Portugal, monitoring of any changes in selected soil characteristics and soil hydrology was undertaken to assess the effects of burning on the following: pH, electrical conductivity, water content, organic carbon and porosity. Thirty plots were established on a regular grid. At each sample plot before and after the fire, samples were collected (disturbed samples from depths of 0-1cm and 1-5cm; undisturbed core samples from 0-5cm). The results indicate that there was no measurable impact on the properties of the soil following this carefully conducted prescribed fire. The fire only affected the litter layer, as intended. Confirmation of this minimal impact on the soil was provided by regrowth of grasses and herbs already occurring two months after the fire. The implication is, therefore, that provided this wildfire-risk reduction strategy is carried out under existing strict guidelines, any impact on soil quality will be minimal.

Environmental Earth Sciences, 2014

In order to decrease the risk of severe wildfire, prescribed fire has recently been adopted in Po... more In order to decrease the risk of severe wildfire, prescribed fire has recently been adopted in Portugal and elsewhere in the Mediterranean as a major tool for reducing the fuel load instead of manual or mechanical removal of vegetation. There has been some research into its impact on soils in shrublands and grasslands, but to date little research has been conducted in forested areas in the region. As a result, the impact of prescribed fire on the physico-chemical soil characteristics of forest soils has been assumed to be minimal, but this has not been demonstrated. In this study, we present the results of a monitoring campaign of a detailed pre-and post-prescribed fire assessment of soil properties in a long-unburnt P. pinaster plantation, NW Portugal. The soil characteristics examined were pH, total porosity, bulk density, moisture content, organic matter content and litter/ash quantity. The results show that there was no significant impact on the measured soil properties, the only effect being confined to minor changes in the upper 1 cm of soil. We conclude that provided the fire is carried out according to strict guidelines in P. pinaster forest, a minimal impact on soil properties can be expected.

Soil Research, 2005

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopr... more After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C–H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C–H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extrac...

Soil Research, 2005

The causes of soil water repellency are still only poorly understood. It is generally assumed tha... more The causes of soil water repellency are still only poorly understood. It is generally assumed that hydrophobic organic compounds are responsible, but those concerned have not previously been identified by comparison between samples taken from a water repellent topsoil and the wettable subsoil. In this study we separated, characterised, and compared the organic compounds present at 4 different depths in a sandy soil under permanent grass cover that is water repellent in the upper 0.30 m but wettable below this. Soil samples were extracted using a mixture of isopropanol and aqueous ammonia (7 : 3 v : v). Samples were wettable after extraction and re-application of the extract from each sample onto wettable sand induced water repellency. The chloroform-soluble portions of the extracts were analysed by gas chromatography and gas chromatography-mass spectrometry. The compounds identified at all soil depths included long-chain carboxylic acids (C16–C24), amides (C14–C24), alkanes (C25–C31...

Australian Journal of Soil Research, 2005

Copper is an important micronutrient and trace amounts are essential for crop growth. However, hi... more Copper is an important micronutrient and trace amounts are essential for crop growth. However, high concentrations of copper will produce toxic effects. Australia is increasingly developing production of crops in water repellent soils. Clay amendment, a common amelioration techniques used in Australia, has demonstrated agronomic benefits in increased crop or pasture production. The sorption and desorption of copper and the effect of clay treatment on copper behaviour in a water repellent soil collected from an experimental farm in South Australia is studied. We found that the water repellent soils amended with clay have an increased adsorption capacity of copper. Also the clay-amended soils had an increased ratio of specific sorption to total sorption of copper. The implications of this study to the sustainable agro-environmental management of water repellent soils is discussed.

Soil Research, 2005

Certain organic compounds derived from living organisms or their decaying parts are generally acc... more Certain organic compounds derived from living organisms or their decaying parts are generally accepted to induce soil water repellency. Water repellency may therefore be expected to increase with proximity to organisms releasing hydrophobic compounds. This hypothesis is tested here for Eucalyptus globulus trees, since eucalypt species are frequently associated with elevated repellency levels. In a young, first-rotation plantation on coastal dune sands in central Portugal, repeat measurements of water repellency using the ‘Molarity of an Ethanol Droplet’ (MED) test were carried out in situ between April 2001 and May 2002. On 25 dates, repellency was measured at initially 2 and later 3 distances on 2 sides of 8–11 randomly selected trees. On 15 occasions, additional repellency measurements were performed within small grids aside 3 of the selected trees. The postulated decrease in topsoil water repellency with increased distance from eucalypt tree stems was found to apply on several in...

Land Degradation & Development, 2002

... RA SHAKESBY,1* COA COELHO,2 S. SCHNABEL,3 JJ KEIZER,2 MA CLARKE,1 JF LAVADO CONTADOR,3 RPD WA... more ... RA SHAKESBY,1* COA COELHO,2 S. SCHNABEL,3 JJ KEIZER,2 MA CLARKE,1 JF LAVADO CONTADOR,3 RPD WALSH,1 AJD FERREIRA2 AND SH DOERR1 1Department of Geography, University of Wales Swansea, UK 2Departamento de Ambiente e Ordenamento ...

International Journal of Wildland Fire, 2013

Pyrogenic carbon (PyC) produced during vegetation fires represents one of the most degradation re... more Pyrogenic carbon (PyC) produced during vegetation fires represents one of the most degradation resistant organic carbon pools and has important implications for the global carbon cycle. Its long-term fate in the environment and the processes leading to its degradation are the subject of much debate. Its consumption in subsequent fires is considered a potential major mechanism of abiotic PyC degradation; however, no quantitative data supporting this removal pathway have been published to date. To address this gap, we quantified consumption of residual PyC at the forest floor during an experimental fire, representative of a typical boreal wildfire, complemented by exploratory laboratory heating experiments. Labelled PyC (pinewood charcoal from a slash pile burn), in granular form contained in stainless steel mesh bags and as individual pieces, were placed at ~2-cm depth within the forest floor. The median mass loss of granular charcoal was 6.6%, with 75% of the samples losing <15%,...

Geomorphology, 2009

Information on post-fire sediment and nutrient redistribution is required to underpin post-fire c... more Information on post-fire sediment and nutrient redistribution is required to underpin post-fire catchment management decisions. Fallout radionuclide budgets (210 Pb xs , 137 Cs and 7 Be) were derived to quantify soil redistribution and sediment yield in forested terrain following a moderately severe wildfire in a small (89 ha) water supply catchment in SE Australia. Application of these techniques in burnt terrain requires careful consideration of the partitioning of radionuclides between organic and mineral soil components. Beryllium-7 and 210 Pb xs were shown to be closely associated with ash, litter and soil organic matter whereas 137 Cs was more closely associated with subsurface coarse mineral soil. Comparison of the three tracer budgets indicated that the dominant sediment source areas were ridgetops and steep valley sideslopes, from which burnt surface material was conveyed to the stream network via pre-existing gullies. Erosion was predominantly driven by sheetwash, enhanced by soil water repellency, and modified by bioturbation which both supplies subsurface sediment and provides sinks for erosive overland flow. Footslope and riparian zones were not important sediment source areas. The estimated event-based (wildfire and subsequent rainfall) sediment yield is 58 ± 25 t km − 2 , based on fallout 7 Be measurements. The upper estimate of total particulate phosphorus yield (0.70 kg ha − 1) is more than 10 times that at equivalent unburnt sites. This illustrates that, soon after fire, burnt eucalypt forest can produce nutrient loads similar to those of agricultural catchments. The tracer budgets indicate that wildfire is an important control on sediment and phosphorus inputs to the stream network over the decadal timeframe and the pulsed nature of this release is an important concern for water quality management.

Geoderma, 2010

Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies h... more Soil water repellency (SWR) is widely thought to be influenced by soil pH, however, few studies have systematically investigated the relationship between these variables. Specifically the hypothesis that the pH may control repellency via changes in the variable surface charge of soil material has not yet been tested. In previous work, methods for changing soil pH have also involved changes in soil moisture, but it has been argued that the potential influence of soil moisture changes needs to be eliminated before the actual relationship between pH and SWR can be isolated. The paper addresses this research gap using a new method, which enables adjustment of the pH of soils with low moisture content via the gas phase and thus involves minimal change in moisture content, allowing the response of SWR to pH changes to be evaluated. The method was applied to 14 soil samples from Germany, The Netherlands, the UK, and Australia, using the water drop penetration time (WDPT) as the indicator of SWR. Additionally, sessile drop contact angles (Θ sess) were measured on the four samples from Germany and the titratable surface charge of these four soils was measured at selected pH values using a particle charge detector (PCD). Changes in SWR with soil pH were found to be influenced by the density and type of sites able to interact with protons at the available surfaces of organic and mineral materials in soil. The maximum SWR occurred for soil at natural pH and where the charge density was minimal. As pH increased, negative surface charge increased due to deprotonation of sites and WDPT decreased. Two types of behaviour were observed: i) a decrease in repellency with decreasing pH, probably because of a sufficient number of proton accepting surface sites with a significant amount of positive surface charge, ii) no decrease in repellency with decreasing pH in soils with insufficient proton accepting surface sites to develop significant positive surface charge. The data suggest that the availability and relative abundance of proton active sites at mineral surfaces, and those at organic functional groups influence the response of the soil samples to changes in pH. The variety of geographic origins and histories of the soils examined provides a distinction between site specific and more widely applicable soil characteristics of pH dependent SWR.

Geochimica et Cosmochimica Acta, 2006