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El Hicha : en studie av saltstäppssediment

Pettersson, Hanna (2011) In Examensarbeten i geologi vid Lunds universitet
Department of Geology
Abstract (Swedish)
Det här examensarbetet i geologi är en studie av ökensediment. Det är tvärvetenskapligt mellan geologi och ekologi.
Sedimenten som har studerats kommer från en statlig försöksodling, El Hicha, på saltstäppen utanför El Akarit,
45 km norr om Gabes i södra Tunisien.
Första steget i studien var att ta sediementprover på försöksodlingen där Ministry of Rural Engineering, Water and
Forest odlar träd och buskar för att hitta arter som är tåliga mot saltstress och torka och har positiva effekter på odlingsjorden.
Olika arter kan hantera salter genom att exkludera eller inkludera joner. Därför förväntas jorden närmst
de olika arternas rotsystem ha olika saltinnehåll. Den elektriska konduktiviteten i jordprover från ett antal 2-meter
djupa... (More)
Det här examensarbetet i geologi är en studie av ökensediment. Det är tvärvetenskapligt mellan geologi och ekologi.
Sedimenten som har studerats kommer från en statlig försöksodling, El Hicha, på saltstäppen utanför El Akarit,
45 km norr om Gabes i södra Tunisien.
Första steget i studien var att ta sediementprover på försöksodlingen där Ministry of Rural Engineering, Water and
Forest odlar träd och buskar för att hitta arter som är tåliga mot saltstress och torka och har positiva effekter på odlingsjorden.
Olika arter kan hantera salter genom att exkludera eller inkludera joner. Därför förväntas jorden närmst
de olika arternas rotsystem ha olika saltinnehåll. Den elektriska konduktiviteten i jordprover från ett antal 2-meter
djupa profiler mättes och jämfördes. Jorden från tre arter valdes för vidare tester (Acacia salicina, Periploca laevigata
and Atriplex halimus). På Geocentrum i Lund analyserades proverna för att få halten organiskt kol och karbonater
och resultaten jämfördes sedan med kontrollprover tagna utanför odlingsområdet.
Metoden Loss On Ignition, glödförlust, användes för att analysera proverna. Resultatet visade att det inte var någon
statistisk skillnad mellan proverna för alla grupperna (arterna), varken när det gällde organiskt kol eller karbonater.
Medelvärdet för organiskt kol var högre än i undersökningen som utfördes 1997 och högre än medelvärdet för öken
- och halvökenjordar över lag i Tunisien. Att resultatet var så högt kan bero på att det inte togs hänsyn till det stora
gipsinnehållet i jorden när analysmetoden valdes. Gips (CaSO4·2H₂O) dehydreras inte fullständigt vid torkning vid
105°C. Istället bildas bassanit (CaSO4∙0.5H2O). En del av den viktförlust som noteras vid förbränning vid 550°C är
därför inte organiskt kol utan avgång av kristallint vatten från gips då anhydrit bildas (CaSO4).
Medelvärdet för karbonater var samma för de testade grupperna. Eftesom proverna innehöll dolomit, räknades inte
procenthalten karbonater ut som om proverna enbart innehöll kalciumkarbonat. Om förekomst av dolomit (CaMg
(CO3)2) ignorerades blev procenthalten den samma som i analysen 1997.
Utöver analyserna av organiskt kol och karbonater gjordes också en generell jordbeskrivning med förekommande
mineral, kemi, och aggregatsammansättning. Jordproverna innehöll få spår av organiskt bundna aggregat, men det
fanns mineraliserade microaggregat. Majoriteten av kornen var kvartskorn, men det förekom också gipskristaller
och ett fåtal zirkoner, titanmineral och aluminiumsilikat. Microaggregatens matrix bestod av Si, Ca och S med
mindre mängder K, Al, Fe, Na och Cl. Trots att jorden är salin fanns inga halitkristaller. Jordproverna från de odlade
fälten hade en mycket lägre elektrisk konduktivitet än kontrollprovet utanför området. Natrium och klor kan ha
sköljts ned till en lägre nivå i markprofilen eller så kan saliniteten vara ett resultat av höga halter av kalcium-, magnesium-
och sulfatjoner. (Less)
Abstract
This bachelor thesis is a study of desert soil. It is a thesis within the subject of bedrock geology but has a clear ecological
angle. The specific soil studied is from the salt flats in the area of El Akarit, 45 kilometers north of the city
of Gabes in southern Tunisia.
The first aim of the study was to sample soil from the test site El Hicha, where the Ministry of Rural Engineering,
Water and Forest is growing trees and shrub to find species that are salt and drought resistant and that might have
other abilities to improve the condition of the soil. Different species are known to handle high salt levels by excluding
or including ions. Therefore the soils around the different species were expected to have a different salt content.
... (More)
This bachelor thesis is a study of desert soil. It is a thesis within the subject of bedrock geology but has a clear ecological
angle. The specific soil studied is from the salt flats in the area of El Akarit, 45 kilometers north of the city
of Gabes in southern Tunisia.
The first aim of the study was to sample soil from the test site El Hicha, where the Ministry of Rural Engineering,
Water and Forest is growing trees and shrub to find species that are salt and drought resistant and that might have
other abilities to improve the condition of the soil. Different species are known to handle high salt levels by excluding
or including ions. Therefore the soils around the different species were expected to have a different salt content.
By sampling a number of 2 meter deep soil profiles and measuring the electrical conductivity of the samples, three
species were chosen for further tests (Acacia salicina, Periploca laevigata and Atriplex halimus). They were tested
for organic carbon and carbonates and the results were compared with two controls from outside the agriculture
area.
The Loss On Ignition method was used to analyze the soil samples at the university laboratory in Sweden. The results
showed that there was no statistical difference between the samples for all groups tested, both regarding organic
carbon and carbonates. However, the average percentage of organic carbon was higher than the initial survey
in 1997 and higher than desert and semi desert soils in Tunisia in general. This could be because the gypsum content
of the soil was not considered when the method Loss On Ignition was chosen. Gypsum, (CaSO4·2H₂O), is not
fully dehydrated at 105°C. Instead the mineral bassanite (CaSO4·0.5H₂O) have been formed. Some of the weight
loss at 550ºC that was thought to have been organic carbon is therefore water loss from bassanite dehydration, formation
of anhydrite (CaSO4).
The average carbonate content was equal for all groups. Since the samples contained dolomite, the carbonate percentage
was not calculated as being only calcium carbonate. If the dolomite was ignored the percentage was approximately
the same as in the previous analyze made in 1997.
In addition to the test of organic carbon and carbonates a general soil description with minerals, chemistry, structure
and aggregate composition was made. The soil showed few signs of organic aggregates, but had mineralized micro
aggregates. The majority of the soil particles were silicon grains, but there were also gypsum crystals and a few
zircons, titanium minerals and aluminum silicates. The micro aggregates had a matrix consisting of Si, Ca and S,
with lower amounts of K, Al, Fe, Na and Cl present. Despite the soil being very saline there were no halite crystals.
The soil samples from the cultivated fields had a much lower electrical conductivity than the control sample from
outside the research area. The sodium and chlorine could have been washed to a lower level in the ground or the
soil salinity could be a result of high levels of calcium, magnesium and sulphate ions. (Less)
Please use this url to cite or link to this publication:
author
Pettersson, Hanna
supervisor
organization
alternative title
El Hicha : a study of salt flat sediments
year
type
M2 - Bachelor Degree
subject
keywords
salin jord, organiskt kol, karbonater, gips, LOI, SEM, EDS, Tunisien, saline soil, organic carbon, carbonates, gypsum, Tunisia
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
278
language
Swedish
additional info
Mr Hafedh Nasr - INRGREF (Institut National de Recherche en Genie Rural, Eaux et Forets / National Institute of Rural Engineering, Water and Forests), Tunisien.
id
2278375
date added to LUP
2012-01-09 17:23:40
date last changed
2012-01-09 17:23:40
@misc{2278375,
  abstract     = {This bachelor thesis is a study of desert soil. It is a thesis within the subject of bedrock geology but has a clear ecological
angle. The specific soil studied is from the salt flats in the area of El Akarit, 45 kilometers north of the city
of Gabes in southern Tunisia.
The first aim of the study was to sample soil from the test site El Hicha, where the Ministry of Rural Engineering,
Water and Forest is growing trees and shrub to find species that are salt and drought resistant and that might have
other abilities to improve the condition of the soil. Different species are known to handle high salt levels by excluding
or including ions. Therefore the soils around the different species were expected to have a different salt content.
By sampling a number of 2 meter deep soil profiles and measuring the electrical conductivity of the samples, three
species were chosen for further tests (Acacia salicina, Periploca laevigata and Atriplex halimus). They were tested
for organic carbon and carbonates and the results were compared with two controls from outside the agriculture
area.
The Loss On Ignition method was used to analyze the soil samples at the university laboratory in Sweden. The results
showed that there was no statistical difference between the samples for all groups tested, both regarding organic
carbon and carbonates. However, the average percentage of organic carbon was higher than the initial survey
in 1997 and higher than desert and semi desert soils in Tunisia in general. This could be because the gypsum content
of the soil was not considered when the method Loss On Ignition was chosen. Gypsum, (CaSO4·2H₂O), is not
fully dehydrated at 105°C. Instead the mineral bassanite (CaSO4·0.5H₂O) have been formed. Some of the weight
loss at 550ºC that was thought to have been organic carbon is therefore water loss from bassanite dehydration, formation
of anhydrite (CaSO4).
The average carbonate content was equal for all groups. Since the samples contained dolomite, the carbonate percentage
was not calculated as being only calcium carbonate. If the dolomite was ignored the percentage was approximately
the same as in the previous analyze made in 1997.
In addition to the test of organic carbon and carbonates a general soil description with minerals, chemistry, structure
and aggregate composition was made. The soil showed few signs of organic aggregates, but had mineralized micro
aggregates. The majority of the soil particles were silicon grains, but there were also gypsum crystals and a few
zircons, titanium minerals and aluminum silicates. The micro aggregates had a matrix consisting of Si, Ca and S,
with lower amounts of K, Al, Fe, Na and Cl present. Despite the soil being very saline there were no halite crystals.
The soil samples from the cultivated fields had a much lower electrical conductivity than the control sample from
outside the research area. The sodium and chlorine could have been washed to a lower level in the ground or the
soil salinity could be a result of high levels of calcium, magnesium and sulphate ions.},
  author       = {Pettersson, Hanna},
  keyword      = {salin jord,organiskt kol,karbonater,gips,LOI,SEM,EDS,Tunisien,saline soil,organic carbon,carbonates,gypsum,Tunisia},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {El Hicha : en studie av saltstäppssediment},
  year         = {2011},
}