This document discusses a study that investigated the effects of hydrocarbon contamination on water repellency and hydraulic properties in tropical sandy soils in Zimbabwe. The study compared two water repellency tests, measured water repellency and hydraulic properties in laboratory contaminated soils and field contaminated soils 1 and 5 years after accidental hydrocarbon spills, and evaluated the performance of models for predicting hydraulic properties. The key findings were that laboratory contamination induced water repellency and increased saturated hydraulic conductivity, while field contaminated soils did not show water repellency but had elevated electrical conductivity. Predictive models performed well for contaminated soils. The contamination may have transient effects on water repellency and hydraulic properties in these tropical soils.
This document discusses a study that investigated the effects of hydrocarbon contamination on water repellency and hydraulic properties in tropical sandy soils. The study compared two water repellency measurement tests and evaluated how hydrocarbon contamination impacted water repellency, soil moisture retention, and saturated hydraulic conductivity over time in both laboratory contaminated soils and field contaminated soils from an accidental spill. The study found that laboratory contaminated soils exhibited increased water repellency and saturated hydraulic conductivity, but field contaminated soils did not show water repellency. Predictions of hydraulic properties from pedotransfer functions matched measured field data, confirming their validity even on contaminated soils.
IRJET- Geotechnical Evaluation of Soils Found in Konso TownIRJET Journal
This document summarizes a study on the geotechnical evaluation of soils found in Konso town, Ethiopia. Soil samples were collected from 8 locations at different depths and tested in the laboratory to determine their engineering properties. The study found that moisture content, density, and specific gravity increased with depth while liquid limit and plastic limit decreased with depth. Unconfined compression strength ranged from 245 to 332 kN/m2. Shear strength parameters of cohesion and internal friction ranged from 160 to 191.34 kN/m2 and 10 to 12 degrees, respectively. Clay fraction content varied from 33 to 50.7% based on grain size distribution analysis. The soils properties were influenced by weathering factors like parent rock
This study examined the effects of treated municipal wastewater, magnetized wastewater, and normal water on soil chemical properties under furrow irrigation. Soil samples were taken from surface and subsurface layers after the first, third, and fifth irrigations and analyzed for salinity (EC) and pH. Results showed that soil salinity did not significantly differ between treatments in surface layers but increased significantly in subsurface layers under magnetized wastewater, likely due to increased salt mobility. Soil pH was reduced by wastewater but not significantly affected by magnetization. In conclusion, magnetizing wastewater increased salt accumulation in subsurface soils compared to untreated wastewater or normal water under furrow irrigation conditions.
Vegetation diversity on coal mine spoil heapshow important is the texture of ...EdytaSierka
Biologia, 2019
The relationship between the size of the particle fractions of the soil substrate and the diversity of the spontaneously developing vegetation was investigated on coal mine spoil heaps in Upper Silesia (Southern Poland). The analyses were based on 2567 research plots of developed spontaneous vegetation and their associated soil substrate samples collected from 112 coal mine spoil heaps. For each research plot the prevailing particle size fraction was determined (stones, gravel, sand, silt), the species composition and abundance was recorded and the species richness (S), Shannon-Wiener diversity index (H′), Simpson (C) and Evenness (E) indices were used to determine species diversity. From a total of 119 research plots (in all particle size fraction categories), the values of 15 physicochemical properties (pH, electrical conductivity, water holding capacity, moisture, carbon content, total N, available P, Mg and exchange cations Ca, Mg, K, Na, fine particles (%), gravel (%), stone (%)) were obtained to asses their impact on the floristic composition of vegetation patches using Canonical Correspondence Analysis (CCA). Additionally, functional traits of the dominant species of each vegetation patch (life forms, life strategies and socio-ecological groups), were selected to analyse their relation to substrate texture. It was shown that the highest species richness and the highest values for Shannon-Wiener diversity index, as well as Simpson and Evenness indices, were obtained in plots formed on stones. Moreover, the greatest variation in the participation of species representing different habitats, life forms, and life strategies was found on gravelly substrates. Contrary to our expectations, the vegetation diversity (in terms of both species and their functional traits) was not highest in habitats with a high composition of fine size particles.
Effect of Harvest of Air Relative Humidity on Water and Heat Transfer in Soil...IJERA Editor
In this work, the main objective is to analyze the effect of the harvest of air relative humidity on soil temperature, soil water storage and evaporation. An experiment work was conducted in order to evaluate the quantity of soil water adsorbed by harvesting of relative air humidity. This experimental work was conducted on hilly areas with various hypsographic and microclimatic conditions greatly affecting daily fluctuations of air humidity and soil characteristics. The metrological data needed by SISPAT model were obtained by using a Campbell Scientific equipments Station recorder on data loggers every half hour. A numerical model based on SiSPAT (Système d’Interaction Sol Plante Atmosphère) formulation is adopted. The general equations of the proposed model are based on heat and mass transfer in the soil, atmosphere and plant system. This study shows that Soil Water Adsorption (SWA) induce an increasing in the total evaporation and in soil water storage especially on the upper layers. The effect of Soil Water Adsorption on soil temperature appears for the first layers of soil and become absent in the profound zone because the vapour condensation phenomenon is very important at night for the first layers.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This document discusses a study that investigated the effects of hydrocarbon contamination on water repellency and hydraulic properties in tropical sandy soils. The study compared two water repellency measurement tests and evaluated how hydrocarbon contamination impacted water repellency, soil moisture retention, and saturated hydraulic conductivity over time in both laboratory contaminated soils and field contaminated soils from an accidental spill. The study found that laboratory contaminated soils exhibited increased water repellency and saturated hydraulic conductivity, but field contaminated soils did not show water repellency. Predictions of hydraulic properties from pedotransfer functions matched measured field data, confirming their validity even on contaminated soils.
IRJET- Geotechnical Evaluation of Soils Found in Konso TownIRJET Journal
This document summarizes a study on the geotechnical evaluation of soils found in Konso town, Ethiopia. Soil samples were collected from 8 locations at different depths and tested in the laboratory to determine their engineering properties. The study found that moisture content, density, and specific gravity increased with depth while liquid limit and plastic limit decreased with depth. Unconfined compression strength ranged from 245 to 332 kN/m2. Shear strength parameters of cohesion and internal friction ranged from 160 to 191.34 kN/m2 and 10 to 12 degrees, respectively. Clay fraction content varied from 33 to 50.7% based on grain size distribution analysis. The soils properties were influenced by weathering factors like parent rock
This study examined the effects of treated municipal wastewater, magnetized wastewater, and normal water on soil chemical properties under furrow irrigation. Soil samples were taken from surface and subsurface layers after the first, third, and fifth irrigations and analyzed for salinity (EC) and pH. Results showed that soil salinity did not significantly differ between treatments in surface layers but increased significantly in subsurface layers under magnetized wastewater, likely due to increased salt mobility. Soil pH was reduced by wastewater but not significantly affected by magnetization. In conclusion, magnetizing wastewater increased salt accumulation in subsurface soils compared to untreated wastewater or normal water under furrow irrigation conditions.
Vegetation diversity on coal mine spoil heapshow important is the texture of ...EdytaSierka
Biologia, 2019
The relationship between the size of the particle fractions of the soil substrate and the diversity of the spontaneously developing vegetation was investigated on coal mine spoil heaps in Upper Silesia (Southern Poland). The analyses were based on 2567 research plots of developed spontaneous vegetation and their associated soil substrate samples collected from 112 coal mine spoil heaps. For each research plot the prevailing particle size fraction was determined (stones, gravel, sand, silt), the species composition and abundance was recorded and the species richness (S), Shannon-Wiener diversity index (H′), Simpson (C) and Evenness (E) indices were used to determine species diversity. From a total of 119 research plots (in all particle size fraction categories), the values of 15 physicochemical properties (pH, electrical conductivity, water holding capacity, moisture, carbon content, total N, available P, Mg and exchange cations Ca, Mg, K, Na, fine particles (%), gravel (%), stone (%)) were obtained to asses their impact on the floristic composition of vegetation patches using Canonical Correspondence Analysis (CCA). Additionally, functional traits of the dominant species of each vegetation patch (life forms, life strategies and socio-ecological groups), were selected to analyse their relation to substrate texture. It was shown that the highest species richness and the highest values for Shannon-Wiener diversity index, as well as Simpson and Evenness indices, were obtained in plots formed on stones. Moreover, the greatest variation in the participation of species representing different habitats, life forms, and life strategies was found on gravelly substrates. Contrary to our expectations, the vegetation diversity (in terms of both species and their functional traits) was not highest in habitats with a high composition of fine size particles.
Effect of Harvest of Air Relative Humidity on Water and Heat Transfer in Soil...IJERA Editor
In this work, the main objective is to analyze the effect of the harvest of air relative humidity on soil temperature, soil water storage and evaporation. An experiment work was conducted in order to evaluate the quantity of soil water adsorbed by harvesting of relative air humidity. This experimental work was conducted on hilly areas with various hypsographic and microclimatic conditions greatly affecting daily fluctuations of air humidity and soil characteristics. The metrological data needed by SISPAT model were obtained by using a Campbell Scientific equipments Station recorder on data loggers every half hour. A numerical model based on SiSPAT (Système d’Interaction Sol Plante Atmosphère) formulation is adopted. The general equations of the proposed model are based on heat and mass transfer in the soil, atmosphere and plant system. This study shows that Soil Water Adsorption (SWA) induce an increasing in the total evaporation and in soil water storage especially on the upper layers. The effect of Soil Water Adsorption on soil temperature appears for the first layers of soil and become absent in the profound zone because the vapour condensation phenomenon is very important at night for the first layers.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
This document provides an overview of measuring soil moisture using digital image processing. It begins with an introduction stating that soil moisture content is important for crop growth and needs to be measured online. It then describes applying digital image processing techniques to images of soil layers to extract the gray value characteristic, and analyzing the relationship between gray value and soil moisture content. Experimental results showed an approximate linear relationship between soil moisture percentage and image gray value.
IRJET- Effect of Dumping on Geotechnical Properties of Soil: A ReviewIRJET Journal
Uncontrolled dumping of municipal solid waste has severe negative environmental and public health impacts and affects the geotechnical properties of soil. Previous studies have shown that dumping can decrease the specific gravity and increase the plasticity of soil. It also tends to increase the optimum moisture content and decrease the maximum dry density of soil. Dumping lowers the soil's angle of internal friction and increases its compression and consolidation properties. This review examines the methodologies and key findings of earlier investigations into the effects of dumping on soil index properties, strength characteristics, and hydraulic conductivity in order to understand how it changes geotechnical properties and to guide further research.
This report summarizes a study of 10 bioretention sites installed as part of a stormwater management program. Soil samples from the sites were analyzed and found to generally meet specifications, though phosphorus levels were lower than specified. Vegetation assessments found varying levels of vigor and survivorship among plant species and sites. Proper coordination from design to construction to maintenance is important for bioretention system success, but lack of communication can lead to issues. The study aimed to understand how inconsistencies impact vegetation success.
Relation of compaction and other soil properties to erosion resistance of soilarya_gooners
The document discusses a study that investigated the effect of soil compaction and other properties on erosion resistance. Seven Texas soils were tested in a hydraulic flume. Tests measured erosion rates under varying water flows and tractive forces. Soil samples were analyzed to determine physical properties like clay content and compaction levels. The results aimed to identify which soil properties best indicate a soil's erosion resistance and how compaction impacts resistance. Understanding these relationships could help protect soils from water erosion.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
Geotechnical evaluation of some soils from part of southwestern nigeria, usab...Alexander Decker
This document discusses using soils from southwestern Nigeria as liners in waste disposal landfills. Five soil samples were collected and tested to evaluate their geotechnical properties according to British standards. The results showed that the soils have low to medium plasticity, with clay content ranging from 42-82%. Maximum dry densities ranged from 1.46-1.96 g/cm3 under standard Proctor compaction and 1.57-2.09 g/cm3 under modified Proctor compaction. Permeability values were all below 2.99 x 10-9 m/s, meeting regulatory standards. Therefore, the soils were found to be suitable for use as landfill liners based on their geotechnical properties
1) The study investigated how seasonal temperature changes affected the release of dissolved organic carbon (DOC) and phenols from soils treated with different plant litter types over 22 months.
2) The researchers found that seasonal soil temperature positively correlated with DOC loss from litter-free soils, but this correlation diminished over time for soils treated with grass and ash litter.
3) Phenol concentrations in the senescing litters were small, resulting in minor losses to water. The variety of dissolved phenols in litter-amended soil leachates increased over time and was influenced by litter type.
Long-term litter manipulation treatments in a temperate forest showed that:
1) Plots with added litter (REF, DL, DLF) had significantly higher soil CO2 efflux rates compared to the control, indicating litter additions increased decomposition.
2) The δ13C values of soil CO2 in litter addition plots were more depleted compared to the control, suggesting litter carbon contributed more to respiration.
3) Neither temperature nor respiration rates explained the δ13C values, implying the isotope signatures of soil organic matter pools did not change with decomposition rates across treatments.
This document compares methods for extracting and quantifying water-transportable phenols from different land uses. Solid phase extraction (SPE) was used to extract dissolved organic matter from water samples collected from grassland, woodland, and moorland sites. SPE followed by thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (THM) was shown to be an effective approach for isolating and quantifying lignin-derived phenols. All the different land uses exported similar amounts of lignin per unit weight of organic carbon in the drainage water. A significant proportion of lignin phenols may be lost from soils in particulate form, so total phenol loss is likely greater than previously estimated from dissolved phenols
Three sentences:
The document summarizes a study that examines how vehicular traffic impacts elemental cycling and microbial communities in roadside soils. Soil samples from locations near a highway and a nature preserve were analyzed to compare salt concentrations, carbon mineralization rates, and the microbial reduction and oxidation of antimony. Preliminary results found higher salt levels and slower mineralization rates in roadside soils compared to the nature preserve, and microcosms showed evidence of microbially-mediated antimony redox reactions occurring in both soil types.
This project investigated using native Rio Grande cottonwood trees and zeolite to improve water quality in nearby urban streams and drains. Six test plots were established, with cottonwood trees planted in soil with or without added zeolite. Data on soil properties, plant health, weather, and water quality was collected. Initial results found the cottonwoods survived well and established baseline data on soil and plant conditions prior to irrigation testing.
Upflow Evapotranspiration System for the Treatment of On-Site Wastewater Effl...Arne Backlund
Sean Curneen †
and Laurence Gill †,*
Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Dublin 2,Ireland; E-Mail: curneens@tcd.ie
Water 2015, 7, 2037-2059; doi:10.3390/w7052037
water ISSN 2073-4441
www.mdpi.com/journal/water
This document summarizes a study on water and cation movement in an Indonesian Ultisol. The study characterized the soil's hydraulic properties and internal drainage, finding that nearly 94% of applied water drained below 112.5 cm depth within 6 hours. Macropores accounted for 26-40% of topsoil porosity and facilitated this drainage. A field experiment examined cation levels and movement over 2 years under different fertilization and residue removal treatments. Results showed 1% of applied K, 5% of applied Ca, and 24% of applied Mg accumulated in the 30-90 cm depth, while 33% of applied K, 26% of applied Ca, and 8% of applied Mg were unaccounted for and likely leached below
This document summarizes a study of groundwater quality in and around Vallanadu Hills in Tamil Nadu, India using GIS. 36 water samples were collected from the area and tested for parameters like pH, turbidity, electrical conductivity, alkalinity, and concentrations of silica, iron, calcium, magnesium, potassium, carbonates, bicarbonates, chlorides, nitrates, and total dissolved solids. The quality was classified using various methods and standards like the WHO. Total dissolved solids exceeded 1000 mg/L in many locations indicating unsuitable quality for drinking and domestic use. Hardness was also high (over 300 mg/L) in many locations suggesting very hard water. GIS was used to
The Changing of Soil Reaction and Exchangeable Aluminum on two Different Soil...Agriculture Journal IJOEAR
The document summarizes a study on the effects of dolomite application on soil reaction and exchangeable aluminum in two different soil orders: Ultisols Kentrong and Inceptisols Jatinangor in Indonesia. Dolomite applications significantly increased soil pH and decreased exchangeable aluminum in Ultisols Kentrong. In Inceptisols Jatinangor, dolomite increased soil pH insignificantly and did not significantly affect exchangeable aluminum. The results indicate that liming effects differ between soil orders depending on their inherent acidity levels.
Assessment of the Water Quality of Lake Sidi Boughaba (Ramsar Site 1980) Keni...journal ijrtem
Sidi Boughaba Lake, part of a wetland complex of Morocco (Ramsar site in 1980) is located on
the Atlantic coast of northwestern Morocco, oriented NNE - SSW and located in an interdunal depression. The
existence of this body of water is due to the fact that the topographic surface is at a lower cost than that of the
piezometric surface of the coastal water table, rainwater and runoff water. The objective of this study is to
determine the physical and chemical characteristics of the waters of this lake. Thus, several water samples were
taken monthly in the period 2016-2017. Parameters such as: temperature, pH, electrical conductivity (EC),
chloride (Cl-
), turbidity (NTU), calcium (Ca2+) and magnesium (Mg2+). The results obtained show that the
distribution of the analyzed elements in Lake waters is quite variable between seasons, as well as between stations.
However, the analysis showed that the studied waters are very mineralized, with an EC between 7 g/l and 14.8
g/l. This mineralization is essentially evaporitic and is controlled by various processes, such as evaporation and
marine influence by aerosol.
Assessment of the Water Quality of Lake Sidi Boughaba (Ramsar Site 1980) Keni...IJRTEMJOURNAL
Sidi Boughaba Lake, part of a wetland complex of Morocco (Ramsar site in 1980) is located on
the Atlantic coast of northwestern Morocco, oriented NNE - SSW and located in an interdunal depression. The
existence of this body of water is due to the fact that the topographic surface is at a lower cost than that of the
piezometric surface of the coastal water table, rainwater and runoff water. The objective of this study is to
determine the physical and chemical characteristics of the waters of this lake. Thus, several water samples were
taken monthly in the period 2016-2017. Parameters such as: temperature, pH, electrical conductivity (EC),
chloride (Cl-
), turbidity (NTU), calcium (Ca2+) and magnesium (Mg2+). The results obtained show that the
distribution of the analyzed elements in Lake waters is quite variable between seasons, as well as between
stations. However, the analysis showed that the studied waters are very mineralized, with an EC between 7 g/l
and 14.8 g/l. This mineralization is essentially evaporitic and is controlled by various processes, such as
evaporation and marine influence by aerosol.
This document summarizes a study that monitored changing groundwater-surface water interactions during a drought in a Scottish montane catchment. Synoptic surveys were carried out along the stream network on four occasions as flows declined. Samples were analyzed for major ions, isotopes, and other tracers. Initial surveys showed relatively homogeneous stream chemistry from riparian peat soils. Later, stream chemistry became more enriched with weathering-derived solutes as groundwater dominance increased. However, these changes showed spatial variability, implying different groundwater sources influenced flows differentially during the recession. Isotope data also indicated some streams were influenced by evaporation from peat soils. The surveys inferred heterogeneous groundwater bodies contributed variably to flows,
This document evaluates the use of portable X-ray fluorescence (PXRF) spectrometry to measure soil salinity. 122 soil samples were collected from salt-impacted soils in Louisiana and analyzed using standard laboratory methods and PXRF. Standard analyses included particle size analysis, organic matter content, and electrical conductivity (EC) using a saturated paste. PXRF was used to quantify elemental concentrations. Simple and multiple linear regression models were developed to correlate elemental concentrations measured by PXRF (particularly Cl) to EC values. Both models produced acceptable correlations (R2 values of 0.83 and 0.90) between EC and PXRF data, though multiple regression using additional parameters like sand, clay and organic matter content was recommended
This study evaluated the use of portable X-ray fluorescence (PXRF) spectrometry to measure soil salinity. PXRF allows for rapid, in-situ measurements with minimal sample preparation. The study collected 122 soil samples from saline soils in coastal Louisiana and analyzed them using standard methods like electrical conductivity (EC) as well as PXRF. Simple and multiple linear regression models found good correlation (r2 of 0.83-0.90) between soil EC and elemental concentrations measured by PXRF, especially when including additional parameters like chloride, sulfur, potassium, calcium, sand, clay and organic matter. While both models performed well, multiple linear regression is recommended for predicting soil EC from PXRF data.
C:\fakepath\Impact of tsunami on soil propertiessekaran
The document discusses the impact of tsunamis on soil properties based on various research studies. It describes how tsunami waves can deposit mud and sediments on top of soils, increasing salinity and changing the soil profile. Research findings showed that salts in affected soils were quickly leached due to rainfall but nutrient imbalances from high sodium and low calcium levels remained, affecting crop growth. Studies analyzed changes in soil physical and chemical properties from tsunami deposits and found that while salinity reduced over time, issues like low fertility and compaction persisted in some areas.
This document provides an overview of measuring soil moisture using digital image processing. It begins with an introduction stating that soil moisture content is important for crop growth and needs to be measured online. It then describes applying digital image processing techniques to images of soil layers to extract the gray value characteristic, and analyzing the relationship between gray value and soil moisture content. Experimental results showed an approximate linear relationship between soil moisture percentage and image gray value.
IRJET- Effect of Dumping on Geotechnical Properties of Soil: A ReviewIRJET Journal
Uncontrolled dumping of municipal solid waste has severe negative environmental and public health impacts and affects the geotechnical properties of soil. Previous studies have shown that dumping can decrease the specific gravity and increase the plasticity of soil. It also tends to increase the optimum moisture content and decrease the maximum dry density of soil. Dumping lowers the soil's angle of internal friction and increases its compression and consolidation properties. This review examines the methodologies and key findings of earlier investigations into the effects of dumping on soil index properties, strength characteristics, and hydraulic conductivity in order to understand how it changes geotechnical properties and to guide further research.
This report summarizes a study of 10 bioretention sites installed as part of a stormwater management program. Soil samples from the sites were analyzed and found to generally meet specifications, though phosphorus levels were lower than specified. Vegetation assessments found varying levels of vigor and survivorship among plant species and sites. Proper coordination from design to construction to maintenance is important for bioretention system success, but lack of communication can lead to issues. The study aimed to understand how inconsistencies impact vegetation success.
Relation of compaction and other soil properties to erosion resistance of soilarya_gooners
The document discusses a study that investigated the effect of soil compaction and other properties on erosion resistance. Seven Texas soils were tested in a hydraulic flume. Tests measured erosion rates under varying water flows and tractive forces. Soil samples were analyzed to determine physical properties like clay content and compaction levels. The results aimed to identify which soil properties best indicate a soil's erosion resistance and how compaction impacts resistance. Understanding these relationships could help protect soils from water erosion.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
Geotechnical evaluation of some soils from part of southwestern nigeria, usab...Alexander Decker
This document discusses using soils from southwestern Nigeria as liners in waste disposal landfills. Five soil samples were collected and tested to evaluate their geotechnical properties according to British standards. The results showed that the soils have low to medium plasticity, with clay content ranging from 42-82%. Maximum dry densities ranged from 1.46-1.96 g/cm3 under standard Proctor compaction and 1.57-2.09 g/cm3 under modified Proctor compaction. Permeability values were all below 2.99 x 10-9 m/s, meeting regulatory standards. Therefore, the soils were found to be suitable for use as landfill liners based on their geotechnical properties
1) The study investigated how seasonal temperature changes affected the release of dissolved organic carbon (DOC) and phenols from soils treated with different plant litter types over 22 months.
2) The researchers found that seasonal soil temperature positively correlated with DOC loss from litter-free soils, but this correlation diminished over time for soils treated with grass and ash litter.
3) Phenol concentrations in the senescing litters were small, resulting in minor losses to water. The variety of dissolved phenols in litter-amended soil leachates increased over time and was influenced by litter type.
Long-term litter manipulation treatments in a temperate forest showed that:
1) Plots with added litter (REF, DL, DLF) had significantly higher soil CO2 efflux rates compared to the control, indicating litter additions increased decomposition.
2) The δ13C values of soil CO2 in litter addition plots were more depleted compared to the control, suggesting litter carbon contributed more to respiration.
3) Neither temperature nor respiration rates explained the δ13C values, implying the isotope signatures of soil organic matter pools did not change with decomposition rates across treatments.
This document compares methods for extracting and quantifying water-transportable phenols from different land uses. Solid phase extraction (SPE) was used to extract dissolved organic matter from water samples collected from grassland, woodland, and moorland sites. SPE followed by thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide (THM) was shown to be an effective approach for isolating and quantifying lignin-derived phenols. All the different land uses exported similar amounts of lignin per unit weight of organic carbon in the drainage water. A significant proportion of lignin phenols may be lost from soils in particulate form, so total phenol loss is likely greater than previously estimated from dissolved phenols
Three sentences:
The document summarizes a study that examines how vehicular traffic impacts elemental cycling and microbial communities in roadside soils. Soil samples from locations near a highway and a nature preserve were analyzed to compare salt concentrations, carbon mineralization rates, and the microbial reduction and oxidation of antimony. Preliminary results found higher salt levels and slower mineralization rates in roadside soils compared to the nature preserve, and microcosms showed evidence of microbially-mediated antimony redox reactions occurring in both soil types.
This project investigated using native Rio Grande cottonwood trees and zeolite to improve water quality in nearby urban streams and drains. Six test plots were established, with cottonwood trees planted in soil with or without added zeolite. Data on soil properties, plant health, weather, and water quality was collected. Initial results found the cottonwoods survived well and established baseline data on soil and plant conditions prior to irrigation testing.
Upflow Evapotranspiration System for the Treatment of On-Site Wastewater Effl...Arne Backlund
Sean Curneen †
and Laurence Gill †,*
Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Dublin 2,Ireland; E-Mail: curneens@tcd.ie
Water 2015, 7, 2037-2059; doi:10.3390/w7052037
water ISSN 2073-4441
www.mdpi.com/journal/water
This document summarizes a study on water and cation movement in an Indonesian Ultisol. The study characterized the soil's hydraulic properties and internal drainage, finding that nearly 94% of applied water drained below 112.5 cm depth within 6 hours. Macropores accounted for 26-40% of topsoil porosity and facilitated this drainage. A field experiment examined cation levels and movement over 2 years under different fertilization and residue removal treatments. Results showed 1% of applied K, 5% of applied Ca, and 24% of applied Mg accumulated in the 30-90 cm depth, while 33% of applied K, 26% of applied Ca, and 8% of applied Mg were unaccounted for and likely leached below
This document summarizes a study of groundwater quality in and around Vallanadu Hills in Tamil Nadu, India using GIS. 36 water samples were collected from the area and tested for parameters like pH, turbidity, electrical conductivity, alkalinity, and concentrations of silica, iron, calcium, magnesium, potassium, carbonates, bicarbonates, chlorides, nitrates, and total dissolved solids. The quality was classified using various methods and standards like the WHO. Total dissolved solids exceeded 1000 mg/L in many locations indicating unsuitable quality for drinking and domestic use. Hardness was also high (over 300 mg/L) in many locations suggesting very hard water. GIS was used to
The Changing of Soil Reaction and Exchangeable Aluminum on two Different Soil...Agriculture Journal IJOEAR
The document summarizes a study on the effects of dolomite application on soil reaction and exchangeable aluminum in two different soil orders: Ultisols Kentrong and Inceptisols Jatinangor in Indonesia. Dolomite applications significantly increased soil pH and decreased exchangeable aluminum in Ultisols Kentrong. In Inceptisols Jatinangor, dolomite increased soil pH insignificantly and did not significantly affect exchangeable aluminum. The results indicate that liming effects differ between soil orders depending on their inherent acidity levels.
Assessment of the Water Quality of Lake Sidi Boughaba (Ramsar Site 1980) Keni...journal ijrtem
Sidi Boughaba Lake, part of a wetland complex of Morocco (Ramsar site in 1980) is located on
the Atlantic coast of northwestern Morocco, oriented NNE - SSW and located in an interdunal depression. The
existence of this body of water is due to the fact that the topographic surface is at a lower cost than that of the
piezometric surface of the coastal water table, rainwater and runoff water. The objective of this study is to
determine the physical and chemical characteristics of the waters of this lake. Thus, several water samples were
taken monthly in the period 2016-2017. Parameters such as: temperature, pH, electrical conductivity (EC),
chloride (Cl-
), turbidity (NTU), calcium (Ca2+) and magnesium (Mg2+). The results obtained show that the
distribution of the analyzed elements in Lake waters is quite variable between seasons, as well as between stations.
However, the analysis showed that the studied waters are very mineralized, with an EC between 7 g/l and 14.8
g/l. This mineralization is essentially evaporitic and is controlled by various processes, such as evaporation and
marine influence by aerosol.
Assessment of the Water Quality of Lake Sidi Boughaba (Ramsar Site 1980) Keni...IJRTEMJOURNAL
Sidi Boughaba Lake, part of a wetland complex of Morocco (Ramsar site in 1980) is located on
the Atlantic coast of northwestern Morocco, oriented NNE - SSW and located in an interdunal depression. The
existence of this body of water is due to the fact that the topographic surface is at a lower cost than that of the
piezometric surface of the coastal water table, rainwater and runoff water. The objective of this study is to
determine the physical and chemical characteristics of the waters of this lake. Thus, several water samples were
taken monthly in the period 2016-2017. Parameters such as: temperature, pH, electrical conductivity (EC),
chloride (Cl-
), turbidity (NTU), calcium (Ca2+) and magnesium (Mg2+). The results obtained show that the
distribution of the analyzed elements in Lake waters is quite variable between seasons, as well as between
stations. However, the analysis showed that the studied waters are very mineralized, with an EC between 7 g/l
and 14.8 g/l. This mineralization is essentially evaporitic and is controlled by various processes, such as
evaporation and marine influence by aerosol.
This document summarizes a study that monitored changing groundwater-surface water interactions during a drought in a Scottish montane catchment. Synoptic surveys were carried out along the stream network on four occasions as flows declined. Samples were analyzed for major ions, isotopes, and other tracers. Initial surveys showed relatively homogeneous stream chemistry from riparian peat soils. Later, stream chemistry became more enriched with weathering-derived solutes as groundwater dominance increased. However, these changes showed spatial variability, implying different groundwater sources influenced flows differentially during the recession. Isotope data also indicated some streams were influenced by evaporation from peat soils. The surveys inferred heterogeneous groundwater bodies contributed variably to flows,
This document evaluates the use of portable X-ray fluorescence (PXRF) spectrometry to measure soil salinity. 122 soil samples were collected from salt-impacted soils in Louisiana and analyzed using standard laboratory methods and PXRF. Standard analyses included particle size analysis, organic matter content, and electrical conductivity (EC) using a saturated paste. PXRF was used to quantify elemental concentrations. Simple and multiple linear regression models were developed to correlate elemental concentrations measured by PXRF (particularly Cl) to EC values. Both models produced acceptable correlations (R2 values of 0.83 and 0.90) between EC and PXRF data, though multiple regression using additional parameters like sand, clay and organic matter content was recommended
This study evaluated the use of portable X-ray fluorescence (PXRF) spectrometry to measure soil salinity. PXRF allows for rapid, in-situ measurements with minimal sample preparation. The study collected 122 soil samples from saline soils in coastal Louisiana and analyzed them using standard methods like electrical conductivity (EC) as well as PXRF. Simple and multiple linear regression models found good correlation (r2 of 0.83-0.90) between soil EC and elemental concentrations measured by PXRF, especially when including additional parameters like chloride, sulfur, potassium, calcium, sand, clay and organic matter. While both models performed well, multiple linear regression is recommended for predicting soil EC from PXRF data.
C:\fakepath\Impact of tsunami on soil propertiessekaran
The document discusses the impact of tsunamis on soil properties based on various research studies. It describes how tsunami waves can deposit mud and sediments on top of soils, increasing salinity and changing the soil profile. Research findings showed that salts in affected soils were quickly leached due to rainfall but nutrient imbalances from high sodium and low calcium levels remained, affecting crop growth. Studies analyzed changes in soil physical and chemical properties from tsunami deposits and found that while salinity reduced over time, issues like low fertility and compaction persisted in some areas.
Certain soils develop water repellent characteristics over time and become hydrophobic. This reduces their water holding capacity and can cause issues like poor plant growth and increased erosion. Hydrophobicity is caused by organic compounds like plant waxes coating soil particles. It is more common in coarse-textured sandy soils and soils affected by events like wildfires. Remediation methods include adding clay or other amendments to mask the hydrophobic layers, applying wetting agents, or biodegrading the hydrophobic compounds with microbes.
impacts of biodegradable organics on soil and gwMarwan Haddad
This study investigated the impact of biological oxygen demand (BOD) on soil and groundwater in two areas of the West Bank - Jericho and Talkarem. Soil samples were collected from each area and subjected to simulated rainfall in columns, with some columns receiving water containing BOD and others receiving only water. The concentration of BOD, total dissolved solids (TDS), and dissolved oxygen (DO) were measured in the leachate from the columns over time, simulating the effects of 1, 10, and 25 years of rainfall. The results showed that BOD concentration increased with time and depth in the soil columns, and was generally higher in Talkarem soil than Jericho soil. TDS levels also
Assessment of shallow aquifers contamination by failure of on site sewage dis...Alexander Decker
1) The study assessed potential contamination of shallow groundwater aquifers in Ughelli, Nigeria by nearby on-site sewage disposal systems.
2) Water samples were tested for parameters like pH, electrical conductivity, bacteria, nutrients and metals. While most samples met standards, some had high bacteria levels and nutrient concentrations indicating contamination from sewage.
3) The shallow aquifers and permeable soils allow contamination from sewage systems to potentially spread, especially during wet seasons with high recharge. Proper disposal and treatment of groundwater is recommended.
This document summarizes a study that used remote sensing techniques to monitor and map soil salinity in the Tuz Lake region of Turkey from 1990 to 2015. The study analyzed 25 Landsat satellite images from 1990, 2002, 2006, 2011 and 2015 to calculate soil salinity indices and generate salinity maps for each time period. Field measurements of soil electrical conductivity from 2002 were used to relate the satellite-derived indices to actual soil salinity. Land cover data from 2000-2006 and 2006-2012 was also analyzed to detect changes that could impact salinity levels. The results showed the salinity index that combined the blue and red bands had the best correlation to field measurements. The maps produced can help track changes in salt-affected areas
Impact of Climate Change on Groundwater ResourcesC. P. Kumar
This document summarizes the impact of climate change on groundwater resources. It discusses how climate change can affect factors like precipitation, temperature, and evapotranspiration, which then impact groundwater recharge and levels. Higher temperatures and variability in rainfall from climate change could mean more fluctuations in groundwater levels and potential saline intrusion in coastal aquifers. Quantifying the full impact on groundwater requires downscaling climate models and coupling them with hydrological models to estimate changes in groundwater recharge over time. Key concerns are potential decreases in groundwater supplies and quality issues, as groundwater serves as a major global source of potable water.
This document summarizes a study that evaluated the effect of non-uniform longitudinal slopes due to inappropriate tillage on water advance and recession in furrow irrigation. 12 furrows of varying slopes were tested over 5 irrigation events. Results showed advance times varied significantly between furrows, from 19-50 minutes for the first irrigation. Recession times also varied widely between furrows, from 9-29 minutes. The results indicate that non-uniform slopes due to inappropriate tillage have a significant impact on advance and recession times in furrow irrigation, affecting irrigation uniformity and efficiency. More accurate land preparation and uniform furrows are needed to improve water distribution and use.
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
This study measured soil penetration resistance (PR) and soil moisture in 10 citrus orchards in Vietnam with different ages over one year. The results showed that PR increased with the age of the raised beds and varied seasonally with changes in soil moisture. PR was more strongly correlated with volumetric water content than water potential (pF values). Bulk density of the subsoil layers increased significantly with the age of the raised beds, indicating greater compaction over time. The PR and soil moisture data provided insights into soil structure and compaction that could help minimize degradation in the orchards.
This document summarizes a study that examined the effects of 13 years of nitrogen and water addition on the availability of soil base cations and micronutrients along an 80 cm soil profile in a semi-arid grassland. The authors found that nitrogen addition decreased exchangeable calcium and magnesium in the top 10 cm of soil but increased available iron, manganese, and copper, with effects increasing with higher nitrogen addition rates. Nitrogen addition also increased available iron, manganese, and copper in deeper soil layers but to a lesser degree than in topsoils. Water addition increased exchangeable sodium throughout the soil profile and increased calcium, magnesium, and sodium in some soil layers. Soil pH was positively correlated with base cations
11.[40 51]correlates in groundwater quality parameters and textural classes o...Alexander Decker
This document summarizes a study that investigated the physicochemical status of groundwater in Ekakpamre, Nigeria, a community located in the oil-rich Niger Delta region. 10 groundwater samples were collected from boreholes about 1 km apart and analyzed along with soil samples from around the boreholes. The study found that clay-rich soils appeared to influence certain groundwater quality parameters like dissolved oxygen, total petroleum hydrocarbons, and potassium levels. While groundwater quality was generally similar across sampling locations, levels of lead and cadmium exceeded regulatory limits for drinking water in some samples, posing a potential public health risk. Principal component analysis identified three components that accounted for 100% of the variability in the original water quality data
Impacts of Changing land cover and Climate on Hokersar wetland in KashmirShakil Romshoo
The document discusses changes in land cover and climate impacts on the Hokersar wetland in the Indian Himalayas over several decades. Significant changes were observed in the wetland area, which shrank from 18.75 km2 in 1969 to 13 km2 in 2008, with water depth also reducing drastically. Marshy lands providing habitat for migratory birds declined from 16.3 km2 to 5.62 km2 during this period. Land cover in the surrounding catchment also changed substantially, with decreases in forest cover and water bodies, and increases in settlements. The wetland changes were found to correlate with land cover changes and variability in the catchment's hydrometeorological conditions. Urbanization, deforestation
In this study, the spatiotemporal changes in the land cover system within a Himalayan wetland and its catchment were assessed and correlated using a time series of satellite, historical, and field data. Significant changes in the spatial extent, water depth, and the land system of the Hokersar wetland were observed from the spatiotemporal analysis of the data from 1969 to 2008.
This document summarizes recent advances in removing uranium from contaminated soils using chemical and biological techniques. It discusses soil washing using water or chemical additives to dissolve and extract uranium. Soil acidification and addition of chelating agents like citric acid were found to maximize uranium solubility and extraction. Sodium bicarbonate achieved 75-90% uranium removal efficiency from contaminated soils. The document reviews various chemical leaching solutions for uranium removal and their effectiveness.
Soil solution changes affected by biosolids and aluminumAlexander Decker
The document summarizes the results of an incubation experiment investigating the effects of biosolids and water treatment residuals (WTRs) on soil solution chemistry when applied to Troy soils. Key findings include:
1) Soil solution pH and electrical conductivity increased significantly with higher WTR and biosolid application rates and longer incubation times, reflecting their liming effect and supply of elements.
2) Concentrations of nutrients and elements like calcium, potassium, sodium, and phosphorus in the soil solution changed significantly over incubation time and with WTR/biosolid additions.
3) Trace elements like copper, nickel, manganese, and zinc also showed changes in soil solution concentration during incubation and with amendments.
This study assessed the baseline water quality and ecology of 7 streams near Geneva Marsh in Crawford County, Pennsylvania before construction of a proposed tire burning plant. Land use in the watersheds was analyzed using GIS and remote sensing. Water quality parameters like phosphorous and macroinvertebrate communities were assessed. Results showed urban land use decreased phosphorous and agricultural land use decreased sensitive macroinvertebrate taxa. The 3 streams with the highest agricultural and urban land use (Towpath, Shafer Run, and Williams Run) were identified for further monitoring after plant construction.
11.soil solution changes affected by biosolids and aluminumAlexander Decker
This document summarizes an incubation experiment that investigated the effects of biosolids and aluminum-based drinking water treatment residuals (Al-WTRs) on soil solution chemistry in Troy soils over time. Soil samples were treated with different rates of biosolids (0, 25, 50 g/kg) and WTRs (0, 20, 40, 80 g/kg) and incubated for various times. The results showed that soil solution pH and electrical conductivity increased with higher WTR application rates. Concentrations of elements like calcium, potassium, sodium, and aluminum in the soil solution changed significantly over incubation time and with biosolids and WTR application rates. The results provide insights into how biosolids and
Similar to Takawira, Gwenzi & Nyamugafata 2014 geoderma hydrocarbons (1) (20)
2. Wallach and Jortzick, 2008) and amelioration and management prac-
tices (e.g. Dlapa et al., 2004). The causes of hydrophobicity include
plant derived waxes, humic and fulvic acids and organic compounds
from forest fires (Arcenegui et al., 2007; Doerr et al., 2000; Huffman
et al., 2001; Ritsema et al., 1993; Scott, 2000). Water repellency influ-
ences water redistribution via reduced infiltration, enhanced surface
runoff and erosion, and preferential flow or fingering (Doerr et al.,
2000). These changes in hydrological balance, may in turn impact on
soil–plant water relations, resulting in impeded seed germination,
stunted plant growth and reduced plant productivity (Mainwaring
et al., 2004). Other researchers have investigated the potential to ame-
liorate water repellency and the associated impacts through localized ir-
rigation, tillage, and application of clays and surfactants or wetting
agents (Buczko et al., 2006; Dlapa et al., 2004; Kostka, 2000). Several
methods exist for evaluating the occurrence and severity of soil water
repellency, the molarity of ethanol droplet (MED) and the water droplet
penetration test (WDPT) being the most prominent (Dekker and
Jungerius, 1990; Dekker and Ritsema, 1994; King, 1981). However,
comparative studies on their performance particularly on hydrocarbon
contaminated soil are limited. Therefore uncertainty exists about the
sensitivity and comparability of results between the two methods.
In comparison to other areas, little is known about the occurrence of
water repellency in the predominant tropical soils of southern Africa.
The reason for this lack of information is unclear, but could be indicative
of the general lack of hydrological research in the region. An exception is
a study by Scott (2000) documenting water repellency and reduced in-
filtration and enhanced runoff in an exotic eucalyptus timber and pine
plantation, and natural Acacia dominated miombo woodland in South
Africa. The miombo woodlands are the dominant native vegetation
type in southern Africa, covering over 3.6 million km2
across 11 coun-
tries (Timberlake and Chidumayo, 2011). The miombo woodlands con-
sist predominantly of deciduous broad-leaved leguminous trees with a
well-developed grass understory, giving rise to frequent and wide-
spread veld fires. Although documented cases of naturally-occurring
or fire-induced water repellency are scarce in the region, soil contami-
nation through anthropogenic activities could potentially cause water
repellency. In particular, wastewater irrigation, soil application of bio-
solids and hydrocarbon contamination may introduce hydrophobic
organic compounds into the soil system. However, compared to
naturally-occurring and fire induced hydrophobicity, little is known
about the impacts of contamination on water repellency and soil hy-
draulic properties.
Aislabie et al. (2004) noted that few studies exist on the impacts of
hydrocarbon contamination and associated additives on water repellen-
cy and moisture retention. In an arid region, wastewater irrigation has
been reported to cause water repellency (Wallach et al., 2005). A
study conducted in Canada on weathered oil-contaminated sites
showed that some long-chain and polycyclic aliphatic organic com-
pounds of petroleum origin were water repellent (Roy et al., 1999).
On Barrow islands in Australia, George et al. (2011) observed that
flowline additives associated with oilfield installation had no effect on
water repellency. In the Antarctic region, hydrocarbon-contaminated
soils were weakly hydrophobic, but impacts on moisture retention
were negligible (Aislabie et al., 2004). Elsewhere, hydrocarbon contam-
ination was also reported to alter soil field capacity, porosity, soil bulk
density and optimum water content even at low hydrocarbon contam-
ination levels (Adams and Cruz, 2008; Adams et al., 2008; Caravaca and
Rolda, 2003; Rahman et al., 2010). In other studies, soil contamination
by petroleum hydrocarbons was reported to increase the moisture re-
tention of soil at high suction values (Burckhard et al., 2004; Hyun
et al., 2008), while a decline in water retention was observed by Roy
and McGill (1998). These changes often result in reduced plant growth
and productivity (Adams and Cruz, 2008). In summary, the findings of
these earlier studies are inconsistent, and often contradicting. More-
over, the bulk of these studies were drawn from cool and humid tem-
perate and arctic conditions (Adams and Cruz, 2008; Balks et al., 2002;
Foght and Waterhouse, 2004; Quyum, 2000). By contrast, there is a pau-
city of information on the impacts of hydrocarbon contamination on
water repellency and hydraulic properties in tropical environments typ-
ical of southern Africa. Unlike temperate and Arctic environments, the
tropics experience distinct warm to hot and seasonally dry climatic con-
ditions, resulting in diverse soil types. These unique climatic and soil
characteristics constrain the extrapolation and generalization of find-
ings obtained in other environments.
Knowledge of soil hydraulic properties is crucial for understanding
the hydrology and remediation of contaminated sites (Gwenzi et al.,
2011). Soil hydraulic properties particularly saturated hydraulic
conductivity (Ks) and soil moisture retention (SMR) influence soil mois-
ture storage, deep drainage, runoff and infiltration, and provide key
inputs for water balance and solute transport models (Gwenzi,
2010; Gwenzi et al., 2011; Holländer et al., 2009). Most existing water
and solute transport models rely on hydraulic properties estimated
from pedotransfer functions derived for uncontaminated natural soils
(Bohnhoff et al., 2009; Holländer et al., 2009). Hydrocarbon contamina-
tion could potentially cause water repellency and associated changes in
hydraulic properties. Consequently, PTFs for Ks and SMR developed for
uncontaminated natural soils may fail to predict field measurements
on such contaminated soils. Therefore, there is need to evaluate the ca-
pacity of existing pedotransfer functions to predict saturated hydraulic
conductivity and soil moisture retention for hydrocarbon contaminated
soils. In the current study we investigated the hypothesis that hydrocar-
bon contamination induces water repellency and reduces moisture re-
tention and saturated hydraulic conductivity in inherently wettable
tropical sandy soils. The objectives of the study were; (1) to compare
the water droplet penetration test (WDPT) to the molarity of ethanol
droplet (MED) as water repellency tests, (2) to investigate whether
hydrocarbon contamination induces water repellency and changes in
soil hydraulic properties, and (3) to evaluate the performance of
pedotransfer functions for soil moisture retention curve and saturated
hydraulic conductivity.
2. Materials and methods
2.1. Description of study sites
The study was conducted on two field sites in Zimbabwe; Ruwa
(E 031° 13′ 04.0″, S 17°52′ 52.7″, altitude: 1521 m asl) and Goromonzi
(E 031° 24′ 10.9″, S 180° 07′ 54.0″, altitude: 1609 m asl). The sites
were located along the Mutare highway, approximately 10 (Ruwa)
and 30 km (Goromonzi) from Harare, the capital city of Zimbabwe.
The highway links Zimbabwe to the international seaport of Beira in
Mozambique, and is frequently used by oil tankers for the transport of
oil and other petroleum products. The two sites were approximately
10 km apart, and had similar soils, vegetation types and climatic condi-
tions. The climate of the area is tropical, characterized by distinct warm
wet summers (27 °C) and cool dry winters (17.5 °C). Average annual
rainfall is about 800 mm, occurring mainly in summer stretching from
November to February. Soils are predominantly in-situ sands derived
from granites. They are classified as Harare 6G.2 according to the
Zimbabwe soil classification system, corresponding to Udic Kandiustalf
(USDA, 1994) and Gleyic Luvisol (FAO, 1988) (Nyamapfene, 1991). Nat-
ural vegetation in the study area is miombo woodlands consisting of de-
ciduous trees and a grass understorey.
Two sampling sites representing hydrocarbon-contaminated and
uncontaminated soils (control) were selected within each study site.
Contaminated soils were selected from sites that experienced a
large spillage of petroleum hydrocarbons through road accidents in-
volving oil tankers. Petroleum hydrocarbon contamination occurred in
2007 at Ruwa and 2012 at Goromonzi. Sampling was conducted be-
tween January and April 2012, approximately 5 and 1 year later, respec-
tively. No clean-up or remediation was conducted at the Ruwa
site, while at Goromonzi, post-contamination remediation involved
280 A. Takawira et al. / Geoderma 235–236 (2014) 279–289
3. application of nutrient solution containing 9:1 phosphorus to nitrates at
a rate of 20 l ha−1
diluted in 200 l. The application of the nutrient solu-
tion was meant to promote vegetation growth. Field observations
showed that contaminated sites differed from the control sites in
terms of soil color and smell. Moreover, compared to the control sites,
sedges and grasses growing on the contaminated sites were sparse, yel-
lowish and stunted. Control sampling areas were uncontaminated sites
identified within natural undisturbed miombo woodlands approxi-
mately 1 km from the road and upstream of the contaminated area.
The identification of contaminated and control sites was conducted
with the assistance of officials from the Hazardous Substances Inspec-
torate of the Zimbabwe Environmental Management Agency (EMA).
EMA documents and maintains an up-to-date database of all freights
and accidents involving hazardous substances in Zimbabwe. The agency
also provides emergency response services including the clean-up and
remediation of contaminated sites. Therefore historical information in-
cluding the nature of the hydrocarbons, year of contamination and
post-contamination clean-up and rehabilitation activities were readily
available for the study sites. Additional information on the spatial extent
of the contamination, and whether there were any fire outbreaks were
obtained from local people who witnessed the accidents, and have lived
in the study sites since then.
To address the study objectives, soil samples for laboratory simula-
tion of hydrocarbon contamination were collected from the control
sites. Contaminated and control field soil samples were also collected
from both sites for general soil characterization, water repellency tests
and measurement of hydraulic properties. Details of the sampling pro-
tocol are described in Section 2.2.
2.2. Evaluation of water repellency
2.2.1. Laboratory hydrocarbon contaminated soils
Disturbed composite samples from the control within each site were
used for laboratory simulation of hydrocarbon contamination. Each
composite sample weighing approximately 50 kg consisted of five ran-
dom sub-samples collected from the top 10-cm depth using a spade.
The samples were air-dried under room conditions, thoroughly mixed
and then passed through a 2-mm sieve. Six levels of hydrocarbon con-
tamination replicated three times were tested; control (0.0), 30, 60,
120 and 150 mg of diesel per gram of soil. These contamination levels
are consistent with experimental values used in previous studies
(Adams and Cruz, 2008; Millioli et al., 2009) and concentrations mea-
sured in field contaminated soils (Aislabie et al., 2004). To facilitate ho-
mogeneous mixing with soil, the corresponding volume of diesel was
added to a 200-ml flask, and the volume made up to the mark with ac-
etone (Awada et al., 2004). The acetone was expected to evaporate
without altering the water repellency properties of the soil. Neverthe-
less, a control soil treated with 170 ml of acetone only was included to
confirm that acetone had no effect on water repellency. For each repli-
cate, one kilogram of soil was weighed into a container. The diesel–ace-
tone solution was then added and thoroughly mixed by hand. The soil
was then kept for 14 days under room conditions (25–26 °C). The soil
was mixed at two-day intervals during the aging process.
The contaminated soils were then oven-dried at 60 °C for 48 h, and
then allowed to equilibrate for two days under room conditions
(Contreas et al., 2008). A portion of soil from each replicate was then
put in a petri dish and the surface smoothened. Two methods were
compared for the evaluation of water repellency, namely, the water
drop penetration time method (WDPT) (Letey, 1969; Watson and
Letey, 1970) and the molarity of ethanol droplet test (MED) (King,
1981). For the WDPT, a syringe was used to place a droplet on the
smoothed surface and time required for the water droplet to penetrate
the soil surface recorded using a stopwatch. The WDPT values of each
sample were given by the average of seven drops of distilled water
placed onto the smoothened surface of 30–40 g of soil placed in a
petri dish (Contreas et al., 2008). Samples were classified as hydrophilic
or wettable (below 5 s), slightly water repellent (5–60 s), strongly
water repellent (60–600 s), severely water repellent (600–3600 s)
and extremely water repellent (more than 3600 s) (Dekker and
Jungerius, 1990; Dekker and Ritsema, 1994).
In the MED test water repellency was recorded as the molarity of
ethanol in a droplet of water needed to penetrate the soil within 10 s
(King, 1981). Solutions ranging from 0 to 6 M concentration at 0.2 M in-
tervals were used for the MED test (Roy et al., 1999). Results of the MED
tests were evaluated using the criteria developed by King (1981). The
classification system consists of four categories; non-water repellent
(MED = 0), low water repellency (0 b MED b 1), moderate water repel-
lency (MED = 1–2.2) and severe water repellency (MED N 2.2) (King,
1981).
2.2.2. Field hydrocarbon contaminated soils
To investigate the impacts of hydrocarbon contamination under
field conditions, contaminated and control soils were collected from
both sites. The soils were used for general characterization, water repel-
lency test and measurement of soil moisture retention and saturated
hydraulic conductivity. Metal cores (7 cm diameter and 5 cm height)
were used to collect undisturbed samples for the determination of
field water repellency, soil bulk density (Blake and Hartge, 1986) and
total porosity. As will be presented later, comparison of the MED and
WDPT data showed that the two methods gave similar results. There-
fore, the WDPT, which was quicker and cheaper, was used in subse-
quent water repellency tests conducted on field samples.
2.3. Determination of soil chemical properties
Soil pH, electrical conductivity (EC) and organic carbon (SOC) were
measured on triplicate samples from the contaminated and control
sites. Soil pH and electrical conductivity were measured in 1:5 soil:
water suspension using standard methods (Gwenzi et al., 2011;
Rayment and Higginson, 1992). Briefly, the soil–water suspension
were shaken for 1 h on a mechanical shaker and allowed to settle for
30 min (Gwenzi et al., 2011). Soil pH and electrical conductivity were
measured using EC and pH electrodes, respectively (model: Mettler To-
ledo). The modified Walkley–Black method was used for determining
SOC on samples passed through a 0.5-mm sieve (Okalebo et al., 1993).
The method is based on wet oxidation of soil organic carbon using po-
tassium dichromate with external heating at 145 °C.
2.4. Determination of soil hydraulic properties
Particle size distribution, soil bulk density, total porosity, soil mois-
ture retention and saturated hydraulic conductivity were measured to
evaluate the effects of hydrocarbon contamination on hydraulic proper-
ties. Particle size analysis was done using a combination of wet sieving
and sedimentation (Gee and Bauder, 1986). The core method (Blake
and Hartge, 1986) was used for the determination of bulk density
using metallic cores measuring 7 cm by 5 cm. The soil cores were
then oven dried at 105 °C for 24 h. Total porosity (n) was calculated as;
n = 1 − ρb/ρs, where ρb is the dry bulk density of the soil (kg m−3
),
and ρs is the particle density assumed to be 2650 kg m−3
(Hillel, 1998).
The pressure plate method was used to determine soil moisture re-
tention curves on core samples collected from the field (Klute and
Dirksen, 1986). Saturated hydraulic measurements were conducted on
repacked laboratory contaminated soils. Samples were subjected to suc-
tions of 2, 5, 10, 33, 100 and 200 kPa and allowed to equilibrate in the
pressure plate chamber. At equilibrium, samples were oven-dried at
105 °C and then weighed to determine soil moisture content at each
suction level. Single- and dual-porosity PTF models were then fitted to
the data using the RETC software (van Genuchten et al., 1991).
Section 2.5 presents the details of the PTFs investigated and the perfor-
mance evaluation criteria.
281A. Takawira et al. / Geoderma 235–236 (2014) 279–289
4. As water repellency tests showed that all field contaminated sam-
ples were non-water repellent, evaluation of the effect of hydrocarbon
contamination on Ks was limited to laboratory contaminated samples.
Ks was determined by the constant-head method (Reynolds and
Elrick, 2002) using a set-up developed by Verboom (1991). The setup
was originally designed and applied to investigate the effect of electro-
lytes on hydraulic conductivity of Zimbabwean soils (Verboom, 1991).
The set-up consisted of a plastic permeameter consisting of two double
rings; an outer ring with an internal diameter of 59 mm attached to
inner ring with internal diameter of 37 mm. Laboratory contaminated
bulk samples from the previous experiment were repacked in the plas-
tic permeameters to a bulk density of approximately 1500 kg m−3
. Wire
gauze was placed on the soil surface to reduce the impact of water drop-
lets. A burette was used to provide a constant supply of water by
allowing water to fall on the soil surface from a height of 25 cm to main-
tain a constant head of 2 cm above the soil column. The soil column had
a height of 5 cm and a diameter of 37 mm. To reduce edge effects, out-
flow data were collected from the internal ring and used to compute Ks.
Outflow data were measured using a balance to the nearest 0.00 g and
time monitored using a stopwatch. Cumulative outflow data were plot-
ted against time to obtain a straight line whose gradient represented av-
erage flow rate. Darcy's law was used to calculate Ks using a hydraulic
head of 7 cm and column dimensions of 5 cm height and diameter of
37 mm (Reynolds et al., 2000, 2002).
2.5. Evaluation of pedotransfer functions
To evaluate the capacity of existing pedotransfer functions (PTFs),
laboratory-measured saturated hydraulic conductivity (Ks) and soil
moisture retention curve (SMRC) data were compared to PTF model
predictions. Specifically, four prominent PTFs for estimating Ks were
evaluated (Sobieraj et al., 2001; Tietje and Hennings, 1996). These
PTFs have been investigated in previous studies conducted on natural
soils and artificial substrates including mine wastes (Gwenzi et al.,
2011; Sobieraj et al., 2001; Tietje and Hennings, 1996). The van
Genuchten (1980) model is the most widely used PTF for prediction of
soil moisture retention curves (Ippisch et al., 2006). Three forms of the
single-porosity van Genuchten (1980) model; VG1, VG2 and VG3
were used for SMRC prediction. The three forms differed in the value
of the van Genuchten parameter, m (Table 1). RETC software (version
6.02) (van Genuchten et al., 1991) was used for model fitting and esti-
mation of the air-entry value (α) and pore size distribution (n) param-
eters. Table 1 presents the PTF models and their input data on particle
size distribution and soil bulk density.
2.6. Data analysis
Shapiro–Wilk's and Barlett's tests were used to test data normality
and homogeneity of variances, respectively, at 5% level. Two-sample t-
test and analysis of variance (ANOVA) were conducted to test effects
of site, hydrocarbon contamination, and interactions on water repellen-
cy and hydraulic properties. Non-normal data were transformed to
achieve normality, and those that failed to meet assumptions for para-
metric tests were analyzed using non-parametric statistical tests. Re-
gression was used to test the relationship between the two methods
for determining water repellency, and relations between hydrocarbon
contamination levels, water repellency (WR) and hydraulic properties.
Statistical tests were done at p = 0.05 using Minitab version 16.0 statis-
tical package. Least significant differences (lsd) were used for the sepa-
ration of treatment means at probability level (p) of 0.05. Correlation
was used to evaluate the performance of PTF models for SMRC using
the coefficient of determination (r2
) to assess the goodness of fit.
Given that Ks varies considerably with method of measurement
(Gwenzi, 2010; Gwenzi et al., 2011; Johnston et al., 2009; Muñoz-
Carpena et al., 2002), comparison of measured Ks values to those pre-
dicted by PTF model focused on evaluating whether values were within
the same orders of magnitude. Therefore, box-and-whisker plots show-
ing median, minimum, maximum and 25th and 75th percentile values
of measured and predicted values were used for this purpose.
3. Results
3.1. General soil properties
The soils at the two study sites were classified as well-sorted pre-
dominantly fine sandy loam and fine loamy sand with approximately
80–88% sand (Fig. 1). At both sites, the differences in particle size distri-
bution between the control and contaminated soils were considered in-
sufficient to justify classifying into different textural classes according to
the USDA Soil Classification (Fig. 1). Therefore, the soils were considered
to have comparable particle size distribution.
The soils at both sites had mean bulk density values of
1350–1613 kg m−3
. Soil bulk density, porosity, SOC and EC varied
significantly (p b 0.05) between the control and contaminated sites,
but the trend was inconsistent (Table 2). The Ruwa control site had sig-
nificantly (p = 0.002) lower bulk density, and hence higher total poros-
ity than the contaminated site, while comparable values were observed
for the Goromonzi sites (Table 2). On the other hand, the Goromonzi
contaminated site had higher SOC than the control, while those for
the Ruwa soils were comparable. Soil EC was consistently higher for
the contaminated sites than the control. All soils were characterized
by similar slightly acidic soil pH. No remarkable pH differences were ob-
served between the contaminated soil and the control at the Goromonzi
site. The pH of the Ruwa contaminated soil was significantly higher than
that of the control.
3.2. Soil water repellency
Laboratory-contaminated soil samples were used to compare the
WDPT and the MED tests. The average time for the WDPT and the
MED increased exponentially with increasing concentration of hydro-
carbon contamination, with coefficients of determination (r2
) of 0.94
and 0.91, respectively (Fig. 2(a)). Accordingly, for any given concentra-
tion of hydrocarbon contamination, the mean time for WDPT and that of
MED were also positively correlated (p b 0.001, r2
= 0.97–0.99)
(Fig. 2(b)), demonstrating that the two methods yielded qualitatively
similar results.
The WDPT showed that hydrocarbon contamination exceeding
30 mg g− 1
caused soil water repellency at both sites. Significant
(p b 0.05) differences in WDPT were observed among all treatments ex-
cept the control and the 30 mg g−1
concentration, which were similar
Table 1
Pedotransfer functions used to predict soil moisture retention curve (SMRC) and saturated
hydraulic conductivity (Ks, mm h−1
). Input data for PTFs are moisture retention data for
SMRC and sand (Sa): 50–2000 μm, silt (Si): 2–50 μm and clay (C): ≤2 μm and dry soil
bulk density (ρb) for Ks.
Reference Pedotransfer function
Soil moisture retention curve (SMRC):
1. Van Genuchten (1980) (VG1)
θ hð Þ ¼
θr þ θs −θr
1þ αhj j
n
½ Š
m h≤0
θs hN0
(
2. Van Genuchten (1980)
(Mualem) (VG2)
VG1 with m = 1–1/n
3. Van Genuchten (1980)
(Burdine) (VG3)
VG1 with m = 1–2/n
Saturated hydraulic conductivity (mm h−1
):
1. Puckett et al. (1985) Ks = 156.96 exp[−1975C]
2. Dane and Puckett (1994) Ks = 303.84 exp[−0.144C]
3. Cosby et al. (1984) Ks = 25.4 × 10[−0.6 + 0.0126Sa − 0.0064C]
4. Jabro (1992) Ks = 10 × 10[9.56–0.81log(Si) − 1.09log(C) − 4.64ρ
b
]
In the van Genuchten model, θ is the volumetric water content, h is pressure head (cm); θr
and θs are the residual and saturated water contents, respectively. The parameter α is re-
lated to the inverse of the air-entry value, and n is a measure of the pore-size distribution
(van Genuchten, 1980).
282 A. Takawira et al. / Geoderma 235–236 (2014) 279–289
5. (Fig. 3). According to the classification system of Dekker and Ritsema
(1994), the soils from both sites were grouped into three water repel-
lency classes; non-water repellent (control and 30 mg g−1
), slightly
water repellent (60.0 mg g−1
) and strongly water repellent (120 and
150 mg g−1
). The control and contaminated field soils at both sites
were classified as wettable (Dekker and Ritsema, 1994), with very low
WDPT time (b1 s), which were approximately 5-times lower than 5-s
minimum for a slightly wettable soil. At both sites, the WDPT for
the control soils in a native miombo woodland were significantly higher
(p = 0.05) than that of the contaminated soils. The results of the MED
test for both Ruwa and Goromonzi soils were qualitatively similar to
that of the WDPT. Based on MED, the control and 30 mg g−1
were
classified as non-water repellent (MED = 0), while the 60, 120 and
150 mg g−1
hydrocarbon concentrations were classified as severely
water repellent with (MED: 5–8). Both WDPT and MED tests classified
the control soils treated with acetone as non-water repellent, demon-
strating that acetone used as a solvent for the petroleum hydrocarbons
had no effect on the observed water repellency. WDPT was strongly
and positively correlated to the concentration of hydrocarbon contami-
nation, with regression coefficients (r) of 0.90 and 0.95 for Ruwa and
Goromonzi, respectively. For Goromonzi, the times for WDPT and
MED were related to hydrocarbon concentration (mg g−1
) (HC)
by power functions; WDPT = 1.10e0.033 ∗ HC
, r2
= 0.94 and MED =
1.32e0.037 ∗ HC
, r2
= 0.91, respectively. A similar relationship was
obtained for Ruwa.
3.3. Impact of hydrocarbons on soil hydraulic properties
3.3.1. Soil moisture retention curve
Soil moisture content for the control and contaminated soils de-
clined gradually for suctions below 100 kPa for both sites, followed by
a rapid decline at 200 kPa (Fig. 4). The effect of hydrocarbon contamina-
tion was more pronounced for laboratory-contaminated soils than field
samples. Hydrocarbon contamination significantly (p b 0.01) reduced
soil moisture retention in laboratory contaminated soils (Fig. 4). At
low suction ranges (2–33 kPa), the 120 and 150 mg g−1
treatments
had consistently lower (p b 0.05) moisture content than the other treat-
ments (0–60 mg g−1
), which were comparable. On the other hand, the
effects of hydrocarbon contamination on soil moisture retention of field
samples were inconsistent between sites. At Ruwa, the control soil had
significantly (p b 0.05) higher moisture content at 2-kPa suction than
the contaminated soil, but no significant effects were observed at
other suction levels (Fig. 4). At Goromonzi, for any given suction, soil
moisture retention of the contaminated soils was similar to that of the
control (Fig. 4).
Evaluation of PTFs for SMRC only focussed on single-porosity models
of van Genuchten with various functions (e.g. Mualem, 1976) for esti-
mating the pore size distribution parameter (n). The soil moisture re-
tention curves for the laboratory contaminated soils was best
described by the single porosity van Genuchten (1980) model (VG1)
(r2
= 0.92–0.99, p ≤ 0.003) (Fig. 4(a)). Similar results were observed
for the control and contaminated soils at both sites (p b 0.001, r2
=
0.98) (Fig. 4(b) and (c)). No attempts were made to fit double or
dual-porosity models (e.g. Mualem, 1976), which are often used on
well-structured soils and those with a substantial proportion of rock
fragments and fractures, where both preferential and matrix flow are
dominant. This was motivated by the fact that particle size distribution
and soil moisture retention data showed no evidence of bimodality.
The effects of hydrocarbon contamination on the van Genuchten
parameters n, α and air-entry value 1
α
À Á
of field- and laboratory-
contaminated soils were also investigated. Under laboratory simulation
hydrocarbon contamination had a significant effect (p b 0.05) on n, α
and air-entry value particularly at concentrations above 30 mg g−1
(Table 3). In general, hydrocarbon contamination significantly in-
creased α, and consequently reduced the air-entry value. On the other
hand, the pore size distribution index n for laboratory contaminated
Fig. 1. Semi-logarithmic plot of particle size distribution for control (○) and hydrocarbon contaminated (●) field soils at Goromonzi (a) and Ruwa (b).
Table 2
Summary properties of field soil samples from Goromonzi and Ruwa used in the study. Values shown are mean ± standard error (SE) for sample size n = 3 except for soil bulk density
and total porosity (n = 5).
Characteristic Goromonzi Ruwa
Control Contaminated Control contaminated
Soil bulk density (kg m−3
) 1600 ± 44.1 1470 ± 30.9 1350 ± 51.2 1613 ± 30.9
Total porosity (%) 39.7 ± 1.7 44.4 ± 1.2 49.1 ± 1.9 39.7 ± 1.8
Soil organic carbon (%) 1.12 ± 0.03 1.43 ± 0.01 0.97 ± 0.03 0.91 ± 0.01
pH (1:5 soil:water) 6.2 ± 0.1 6.0 ± 0.0 6.0 ± 0.0 6.4 ± 0.0
EC (1:5 soil:water) (μS m−1
) 37 ± 0.9 61 ± 1.3 37 ± 2.5 80 ± 3.6
283A. Takawira et al. / Geoderma 235–236 (2014) 279–289
6. soils generally decreased with increasing hydrocarbon contamination.
Field contaminated soils had significantly lower α (p b 0.05) and
hence higher air-entry value than the uncontaminated control, but ef-
fects on n were not significant at both field sites.
3.3.2. Saturated hydraulic conductivity
Hydrocarbon contaminated laboratory soils caused a significant in-
crease in Ks at both sites (Fig. 5), but site effects were not significant.
At Goromonzi, all hydrocarbon contaminated soils had significantly
higher (p b 0.001) Ks than the control. A similar trend was observed at
Ruwa, but the 30 mg g−1
treatment had Ks similar to that of the control.
Although site had no significant effect on Ks, Ruwa had slightly higher
Ks (4.27 × 10−5
m s−1
) than Goromonzi (3.27 × 10−5
m s−1
).
A significant linear relationship (p b 0.05) was observed between
the level of hydrocarbon contamination (HC) and Ks at both Ruwa
(Ks = 5 × 10−7
∗ HC + 1 × 10−5
, r2
= 0.88) and Goromonzi (Ks =
3 × 10−7
∗ HC + 9 × 10−5
, r2
= 0.78).
Evaluation of five PTFs on Goromonzi soil revealed that predicted
median Ks values (1.0–4.0 × 10−5
m s−1
) were of similar orders of
magnitude to laboratory-measured ones (2 × 10−6
–2.4 × 10−5
m s−1
)
(Fig. 6(a)). The Puckett, and Dane and Puckett PTF models yielded the
closest estimate of Ks for the control and the 30 mg g−1
hydrocarbon con-
centration, but tended to under-estimate Ks for higher level of hydrocar-
bon contamination (60–150 mg g−1
). The opposite trend was observed
for the Jabro PTF model, which over-predicted Ks for low hydrocarbon
concentrations (control and 30 mg g−1
) by approximately an order of
magnitude, but gave estimates comparable to laboratory measured
values for higher hydrocarbon concentrations (60–150 mg g−1
)
(Fig. 6(a)). The performance of PTFs on Ruwa soil was generally
comparable to that of Goromonzi soil. The only exception was that the
Puckett, and Dane and Puckett PTF models performed equally well for
the 60 mg g−1
hydrocarbon contamination (Fig. 6(b)). The Jabro PTF
model also tended to under-predict the median Ks for all samples, but
its values were within the range for the 150 mg g−1
hydrocarbon con-
tamination. For both soils, laboratory-measured Ks showed higher vari-
ability than predicted values. However, it is noteworthy that the
evaluation of PTFs compared predicted values based on input data mea-
sured on control and contaminated field samples to those measured on
the control and laboratory-contaminated samples. This was motivated
by the findings of the current and previous research (e.g. Roy et al.,
1999) demonstrating that hydrocarbon contamination of laboratory
soils had negligible effects on the input data for the PTFs for Ks (PSD,
bulk density and soil organic carbon).
4. Discussion
Hydrocarbon contamination via accidental spills, leakages from
oilfield installations and disposal of used petroleum products potential-
ly alters soil hydrological and ecological functions. Understanding the
impacts of hydrocarbon contamination on soil and chemical properties
is critical for remediation of contaminated sites. The current study in-
vestigated water repellency and hydraulic properties of laboratory and
field contaminated sandy loam and loamy sands derived from granitic
parent material in tropical Zimbabwe. The soils were inherently wetta-
ble, and consisted predominantly of sand fraction (80–91%). Here, we
discuss the key findings on general soil properties, water repellency, hy-
draulic properties and evaluation of prominent PTFs for the prediction
of SMRC and Ks, and highlight the implications.
The time for WDPT and MED tests were positively correlated, indi-
cating that the two methods gave comparable results. Although previ-
ous research (e.g. Dekker and Ritsema, 1994) has reported that the
WDPT test tends to be less sensitive than the MED test, our results
showed that for soils similar to those studied here, either of the two
methods may be used for water repellency evaluation. This observation
Fig. 2. (a) Relationships between hydrocarbon contamination and time for WDPT ( ) and MED (○) water repellency tests, and (b) correlation between time for WDPT and MED for lab-
oratory contaminated Goromonzi soil. Similar results were obtained for the Ruwa soil (data not shown).
Fig. 3. Effect of concentration of hydrocarbon contamination on water repellency mea-
sured by the water droplet penetration test (WDPT) on Ruwa (○) and Goromonzi (●)
laboratory-contaminated soils. Data are mean of three replicates. Errors bars show 1 stan-
dard error.
284 A. Takawira et al. / Geoderma 235–236 (2014) 279–289
7. is consistent with a few earlier studies showing agreement between
WDPT and MED results (e.g. Badía et al., 2013). In this regard, consider-
ing that no special reagents are required for the WDPT, this method is
ideal for rapid water repellency evaluation under field conditions, par-
ticularly where laboratory facilities are lacking.
Subsequent water repellency evaluation based on the WDPT and
MED tests both revealed that the uncontaminated soils were wettable.
Following hydrocarbon contamination, all samples became water repel-
lent except the 30 mg g−1
treated sample, evidently confirming our
original hypothesis that hydrocarbon contamination induces water re-
pellency in inherently wettable tropical sandy soils. In earlier studies,
water repellency has been documented in natural sandy soils (Dekker
and Ritsema, 1994; Mainwaring et al., 2004; Wahl, 2008), while limited
evidence exists for hydrocarbon contaminated soils. In these studies,
water repellency has been attributed to fire, type and vegetation spe-
cies, and hence soil organic carbon (Wahl, 2008). Here, we present the
first evidence suggesting that uncontaminated sandy soils associated
with the miombo woodlands of southern Africa are inherently wettable.
However, hydrocarbon contamination through spills, leakages and dis-
posal of petroleum hydrocarbons has the capacity to induce water re-
pellency. In this case, we attribute the induced water repellency to the
presence of hydrophobic long-chain aliphatic and aromatic compounds
in petroleum hydrocarbons.
Contrary to our expectation, Ks increased linearly (p b 0.05) as the
concentration of hydrocarbons increased between 30 and 150 mg g−1
.
Although elucidating the exact mechanisms was beyond the scope of
the current study, we hypothesize that the presence of hydrophobic pe-
troleum hydrocarbons caused a drop in the dielectric constant of water.
The resulting reduction of electrostatic interactions between the dipolar
water molecules and the charged soil matrix triggers rapid and exten-
sive outflow of pore water. Indeed, a recent study by Calla et al.
(2011) show that the dielectric constant of saline water dropped
when the diesel increased from 0 to 120% by weight. Further evidence
supporting this hypothesis is provided by the two laboratory
studies on the effects of liquid hydrocarbons as soil permeants on
Ks (Fernandez and Quigley, 1985, 1988). Fernandez and Quigley
(1985) observed that decreasing the dielectric constant from 80 to 2 in-
creased Ks of clay soils by 5 orders of magnitude from 5 × 10−9
to 1 × 10
−4
cm s−1
. As a result, using alcohol and liquid aromatics as permeants
at 30% of the pore volume increased Ks by 10 and 1000 fold, respectively
(Fernandez and Quigley, 1985). However, the magnitude of increase ob-
served on the predominantly sandy soils used in the current study
Fig. 4. Soil moisture retention curves for laboratory contaminated soils (a) and field contaminated soils (●) and control (○) at Ruwa (b) and Goromonzi (c) sites. RETC software
(version 6.02) was used to fit the single-porosity van Genuchten (VG) pedotransfer function to measured data (van Genuchten et al., 1991).
285A. Takawira et al. / Geoderma 235–236 (2014) 279–289
8. appears lower than values reported for clay (Fernandez and Quigley,
1985), probably reflecting the textural differences.
Laboratory simulated contamination above 30 mg g−1
significantly
reduced soil moisture retention at low suctions, suggesting enhanced
soil water loss. However, the impacts of hydrocarbon contamination
on SMRC of field contaminated soils were less pronounced and showed
no clear trend, further suggesting that under tropical conditions, the im-
pacts could be transient. Earlier research investigating impacts of hydro-
carbon contamination on SMRC have yielded inconsistent results (e.g.
Ellis and Adams, 1961; Roy and Mcgill, 1998). For example, Roy and
McGill (1998) observed that wettable soils had higher moisture reten-
tion than water repellent ones, while Ellis and Adams (1961) observed
the opposite. Although the mechanisms accounting for this inconsisten-
cy observed in earlier studies (e.g. Roy and McGill, 1998) are unclear,
this could reflect differences in soils, levels of contamination and age ef-
fects. For example, while recent hydrocarbon contamination may re-
duce water retention as observed under laboratory conditions, aging
of hydrocarbons may increase soil organic matter content and hence
moisture retention. Moreover, the effect of aging on hydrocarbon con-
centrations could also account for the inconsistent effects of field con-
tamination on SOC and SMRC observed between the two sites. In the
current study, the observed reduction in moisture retention for
Table 3
van Genuchten parameters α, air-entry value 1
α
À Á
and n for laboratory and field hydrocar-
bon contaminated soils. Data are means of three replicates ± standard errors. Means
followed by different letters for laboratory contaminated soils and each field site are signif-
icantly different at probability level p = 0.05.
Treatment α (kPa−1
) 1
α kPað Þ n
Laboratory-contaminated soils:
Hydrocarbon concentration (mg g−1
soil)
0 0.056 ± 0.007a
18.4 ± 2.0a
1.216 ± 0.135a
30 0.049 ± 0.000a
20.3 ± 0.1a
1.723 ± 0.115b
60 0.287 ± 0.028b
3.6 ± 0.4b
1.147 ± 0.071ac
120 0.382 ± 0.015b
2.6 ± 0.1b
1.072 ± 0.064ac
150 0.744 ± 0.116c
1.4 ± 0.2b
1.031 ± 0.026ac
p value b0.001 b0.001 0.002
Field contaminated soils:
Goromonzi:
Control 0.304 ± 0.012a
3.3 ± 0.1a
1.356 ± 0.086a
Contaminated soil 0.047 ± 0.021b
22.0 ± 0.3b
1.568 ± 0.092a
p value b0.001 0.02 0.374
Ruwa:
Control 0.505 ± 0.042a
2.0 ± 0.2a
1.612 ± 0.101a
Contaminated soil 0.301 ± 0.023b
3.3 ± 0.1b
1.631 ± 0.097a
p value 0.015 0.03 0.257
Fig. 5. Effects of hydrocarbon contamination levels on constant-head saturated
hydraulic conductivity (Ks) of laboratory contaminated sandy soils from Goromonzi
(a) and Ruwa (b) sites. Data are means ± standard error (SE) for three replicates.
Means with different letters are significantly different using least significant difference
(lsd) at p = 0.05.
Fig. 6. Box-and-whisker plot comparison of saturated hydraulic conductivity (Ks) values
measured by constant-head laboratory method and predicted by three pedotransfer func-
tion models (Puckett, Dane and Puckett and Jabro) for Goromonzi (a) and Ruwa (b) soils.
Data shown are median, minimum, maximum, and 25th and 75th percentile values.
286 A. Takawira et al. / Geoderma 235–236 (2014) 279–289
9. laboratory contaminated soils was consistent with increased soil hy-
draulic conductivity attributed to the reduced dielectric constant of
water in the presence of hydrocarbons. Water repellency tests on field
samples showed that soils from both control and contaminated sites
were wettable. Unlike other sandy soils in Australia (King, 1981) and
Netherlands (Dekker and Ritsema, 1994; Ritsema et al., 1993), results
showed that sandy soils derived from granites associated with miombo
natural woodlands are inherently wettable. Contrasting water repellen-
cy results on similar textures probably reflected the effects of vegetation
type and species on the amount and forms of soil organic carbon. How-
ever, t-test comparisons indicate that the WDPT for control soils were
higher than that of the contaminated soils. This observation implies
that the organic compounds causing water repellency were relatively
higher in natural woodlands than contaminated soils. Despite the
large pulse spills, our findings on field contaminated soils indicate no
water repellency. There is lack of information on the persistence of
hydrocarbon-induced water repellency in tropical soils. However, the
findings of few studies conducted in temperate and arctic regions sug-
gest that hydrocarbon-induced water repellency persists long after con-
tamination (Roy and McGill, 1998). Several reasons could account for
the putative lack of persistence in the current study. First, given that
the Ruwa site was contaminated in 2007, there exists a possibility that
breakdown of hydrocarbons could have occurred during the 5-year
post contamination period. Moreover, contrary to the low temperatures
that could retard microbial activity in the temperate and arctic regions
(e.g. Roy et al., 1999), relatively high temperatures associated with trop-
ical conditions in Zimbabwe could account for the lack of persistence.
Second, the application of nutrient solution to promote revegetation
could also have stimulated native microbes responsible for the decom-
position of hydrocarbons. The stimulation of microbial activity causing
hydrocarbon degradation through nutrient application has been report-
ed in previous studies (Garcia-Blanco, 2004; Garcia-Blanco et al., 2007).
However, determining the key mechanism accounting for the observed
lack of persistence will require conducting further experimentation
comparing similar sites with and without nutrient addition.
Despite the lack of water repellency, residual signature of hydrocar-
bon contamination was evident at both sites. For instance, EC was con-
sistently higher in contaminated soils than the control soils, signifying a
residual salt load. The high EC could be associated with fuel additives
and/or soluble products of hydrocarbon decomposition. At Goromonzi,
the recently (b1 year) contaminated soil had higher SOC than the con-
trol. The enhanced soil structural stability arising from the relatively
higher SOC could account for the significantly lower density and more
porous soils observed on the contaminated soil than the control. At
Ruwa, the 5-year old contaminated site had significantly higher pH,
bulk density and lower porosity than the control. An increase in soil
pH on soils contaminated with flowline additives for oil pipelines has
also been reported under tropical conditions in the Barrow Island in
Australia (George et al., 2011). The high bulk density, and low total po-
rosity were attributed possibly to compaction associated with its close
proximity to the road compared to the control. The control and contam-
inated sites had comparable SOC, suggesting that over the 5-year period,
carbon derived from hydrocarbon could have undergone rapid decom-
position to background levels.
Evaluation of PTFs showed that the single-porosity van Genuchten
function developed initially for uncontaminated natural soils provided
the best fit for soil moisture retention. The good fit for both control,
and laboratory and field contaminated soils supports earlier observa-
tions indicating that the impact of hydrocarbon contamination on
SMRC was minimal. However, laboratory simulated hydrocarbon con-
tamination increased α and reduced the air-entry value, an observation
consistent with the reduced moisture retention in Fig. 4(a). The oppo-
site effect was observed for field contaminated soil suggesting improved
moisture retention on contaminated soils evident in soil moisture re-
tention curves in Fig. 4(b) and (c). Although the mechanisms are un-
clear, this could reflect changes in the nature and amount of soil
organic carbon especially for the Goromonzi site. However, in general,
the values of n and α were comparable to those reported for natural
sandy soils (2.0 to 3.2 kPa) (e.g. Wang et al., 2009; Zhu and Mohanty,
2002). Exceptions were laboratory (0 and 30 mg g−1
) and field contam-
inated soils from Goromonzi which had comparatively higher air entry
values than the other treatments, probably due to fitting errors associat-
ed with the RETC software. Overall, the van Genuchten parameters
appeared more sensitive to hydrocarbon contamination than the
laboratory-measured soil moisture retention data. Therefore, we infer
that water and solute transport models based on the van Genuchten
function may be applied to the studied soils with minimum bias in
model outputs.
Evaluation of PTFs for Ks indicate that the Puckett, and Dane and
Puckett models provide Ks estimates closer to the measured values
than the Jabro model, which tended to over-estimate. The opposite
trend was observed for the 60–150 mg g−1
hydrocarbon contamina-
tion, where the Jabro model provided a better estimate than the other
two. The discrepancy between measured and observed Ks for the
60–150 mg g−1
was associated with the observed unexpected increase
in Ks with hydrocarbon contamination. These PTFs, originally developed
for natural uncontaminated soils, do not account for the phenomenon
associated with hydrocarbon contamination. It is also noteworthy that
the PTFs for Ks used in the current study all involve clay as an input. Con-
sidering that the soils studied here contained 80–88% sand, it is also
likely that the variation of predicted Ks among PTFs possibly reflects dif-
ferences in input parameters. Overall, both measured and predicted Ks
values were within the range reported in literature for such textural
classes (Sobieraj et al., 2001; Tietje and Hennings, 1996). Although the
capacity of PTFs to predict measured hydraulic properties of uncontam-
inated soils has been reported in earlier studies (Dikinya, 2005; Kool
and Parker, 1988), our results further confirm the validity of such
models on hydrocarbon contaminated soils investigated in the current
study.
The induced water repellency and increase in saturated hydraulic
conductivity have implications on hydrological and ecological functions
of contaminated soils. Water repellency alters the water balance
through reduced infiltration, enhanced surface runoff and erosion, and
reduced soil moisture. In a seasonally dry environment, reduced soil
moisture may have adverse impacts on soil-plant-water relations, caus-
ing shifts in plant species through invasion by alien species and vegeta-
tion die-off. Indeed, field observations showed that contaminated sites
had sparse, yellowish and stunted vegetation consisting predominantly
of sedges and grass species, indicative of reduced vegetation growth and
vigor and possibly mortality. Moreover, enhanced surface runoff may
transport hydrocarbons and other associated contaminants into surface
water bodies, posing significant public and environmental risks. The ob-
served increase in Ks on contaminated soils suggests that once saturat-
ed, rapid water and contaminant transport including preferential flow
may occur in the sub-surface into groundwater systems. The generally
high residence times of groundwater in aquifers, coupled with anaero-
bic conditions and low microbial activity in the saturated zone, imply
that hydrocarbons and other contaminants tend to persist in groundwa-
ter systems. This will exert a strong influence on groundwater remedi-
ation and clean-up, and pose significant public and environmental
risks particularly in southern Africa, where approximately 90% of rural
households depend on groundwater sources for domestic supply.
5. Summary, conclusions and outlook
Hydrocarbon contamination of soils occurs frequently yet limited re-
search has investigated water repellency and changes in soil hydraulic
properties induced by such contamination. In addition, comparison of
water repellency methods and evaluation of existing PTFs for estimating
hydraulic properties on such soils have been lacking. The current study
measured water repellency and hydraulic properties, and evaluated
PTFs on laboratory-and field-contaminated tropical sandy soils. The
287A. Takawira et al. / Geoderma 235–236 (2014) 279–289
10. WDPT and MED methods for water repellency evaluation gave compa-
rable results. Laboratory simulated hydrocarbon contamination of soils
induced water repellency (WR) and a significant increase in saturated
hydraulic conductivity (Ks) in an inherently wettable sandy soil. The in-
crease in Ks was attributed to the reduction of the dielectric constant of
water caused by the presence of hydrophobic hydrocarbons. Contrary to
studies conducted in temperate and arctic environments where WR
persists for over 20 to 50 years after hydrocarbon contamination, the
current study showed that hydrocarbon contaminated field soils were
wettable, as evidenced by WDPT far below the minimum threshold for
water repellent soils. This indicates that under tropical conditions,
such induced water repellency could be transient or non-persistent.
The induced water repellency could potentially offset the hydrological
balance and adversely affect soil–plant–water relations and soil ecology.
On recently contaminated sites, the associated increase in Ks may trigger
rapid movement of water and contaminants into the groundwater sys-
tems, and influence remediation or clean-up process. Non-persistence
of water repellency in the tropics could be attributed to high biodegra-
dation rates stimulated by warm conditions. At the Goromonzi site, nat-
ural breakdown could have been further stimulated by nutrients added
to promote revegetation of the contaminated sites. The fact that both
relatively old (5 years) and recent (b1 year) sites had similar water re-
pellency further suggests that this breakdown could be rapid under
tropical conditions. However, the residual signature of hydrocarbon
contamination on field samples was evident through stunted vegetation
and changes in electrical conductivity, pH, soil organic carbon, bulk den-
sity and total porosity. Despite these changes in soil properties, the re-
sults suggest that the existing PTFs provide reliable estimations of
SMRC and Ks as evidenced by values within the same order of magni-
tude. By inference, water and solute balance models relying on these
PTFs to estimate storages and fluxes may yield outputs with minimum
bias. Coupled with additional field data, these data are sufficiently accu-
rate for large-scale simulation of water and solute transport on contam-
inated soils using existing models based on the PTFS evaluated here.
In general, the findings support the hypothesis that hydrocarbon
contamination induces water repellency and reduces moisture reten-
tion on inherently wettable tropical sandy soils. However, the positive
linear relationship between hydrocarbon contamination and Ks
contradicted the original hypothesis, an observation attributed to a de-
crease in the dielectric constant of water. Future research should focus
on elucidating the key mechanisms responsible for the increased Ks in
hydrocarbon contamination. Further field investigations based on a
contamination chronosequence or gradient are also required to confirm
our laboratory findings. Such studies will also provide comprehensive
information on the temporal evolution of water repellency and hydrau-
lic properties, and the fate and degradation mechanisms of hydrocar-
bons under tropical conditions.
Acknowledgments
We are grateful to staff from the Hazardous Substance Inspectorate
of the Zimbabwe Environmental Management Agency (EMA) for de-
tailed site information, and their time and effort during site identifica-
tion and sampling. We also thank staff from the Department of Soil
and Agricultural Engineering at the University of Zimbabwe for assis-
tance during laboratory analyses. Laboratory reagents were partly pro-
vided by WG's biochar research project funded by the Swedish
International Foundation for Science (IFS) Grant Number C/5266-1.
The authors are solely responsible for the experimental design, data col-
lection and interpretation, manuscript compilation and conclusions
drawn thereof. We are also grateful to Professor Jirka Simunek of
the Department of Environmental Sciences, University of California Riv-
erside for help with interpretation of RETC results. The manuscript also
benefited from valuable comments provided by two anonymous re-
viewers, to whom we are sincerely thankful.
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