Hydromorphic conditions in forest soils due to mechanical soil compaction

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Manual Sampling of aqueous solutions

Surface water layer (LS) is in direct contact with atmospheric oxygen but soil solutions (SS) are in reductive environment. So sampling of SS and LS was carried out in different ways. Samples from LS were sampled directly with the help of a polypropylene pot while material and system of soil solution sampling was based on (Eleuterius, 1980), modified by (Maitre, 1991) and described by (Bourrié et al., 1999). The sampling of SS was not carried out directly by modified multiparametric probe system due to reported perturbation in recording by probe for one hour after each sampling, thus, a limitation of multiple sampling of soil solution during one day using same system (Cary, 2005). So, decontaminated with HNO3, perforated and inert tissue covered zero-tension lysimeters were used for sampling (figure 2B).
These polypropylene made pots were installed in the field some days before the sampling day, to allow chemical equilibrium, at some distance from probe to avoid any probe related external disturbances as shown (figure 2A). 15 plastic pots were installed at the depth range of 5-10 and having a distance of 20 cm among them.
At specific hours aqueous solutions were sampled from LS and SS at once. Each sampled solution was filtered: at 0.70 μm (optical filter) for dissolved organic carbon (DOC) and at 0.2 μm for others analysis, by a syringe with great care to avoid maximum from oxygen and light contact and were collected in 4 low density polypropylene small pots separately marked for analysis of cations, total dissolved carbon, alkalinity and anions. One drop of HNO3 acid was added to sampled solutions for cations to stop the further chemical reactions. Some non-conservative parameters were measured using calibrated electrodes in the field: temperature, pH, redox potential and electrical conductivity. The elements which are susceptible to any change in presence of oxygen were analysed immediately using colorimetric method with portable spectrometer (HACH DR/2010). Fe(II) by DPKBH complex (Pehkonen et al., 1992) modified by (Jaffrezic, 1997), sulphide by “methylene blue method”, ammonium by “indophenol blue method” and nitrite by “diazotation method using chromotropic acid”. Filtered solutions were covered with aluminium paper and were conserved in ice-bag. After arrival in laboratory they were preserved in refrigerator.

Use of graphical language TestPoint for alkalinity measurements

Measurement of alkalinity of all the samples were carried out by a digital burette that was connected to a computer and a high resolution voltmeter to measure the pH after each addition of acid for forward titration and base for back titration. A programme was written to verify and calibrate the pH electrodes, before the alkalinity measurements, and to control all the equipments in TestPoint-CEC (graphical language). Description of TestPoint, and procedure and methods to measure alkalinity by calibrated pH electrode is discussed in detail in this section.

Introduction, interest and principle of TestPoint language

Conventional manual acquisition, analysis and presentation of the data from electronic devices are very laborious and time consuming. So, in last decade, commercial measurement devices are largely controlled by the Personal Computers (PC) and an integrated efficient Soil and soil solution programming software package. In the beginning, preferred text-based languages in research institutions (Basic, C, Fortran and Pascal) were introduced to develop simple programs and control the instruments. But development of user interface in these conventional text-based languages is normally much time consuming task. Additionally, it takes much time and experience to learn programming, to get an overview of libraries with the graphical components and their use, and making changes in subroutines or add-ons. Graphical Programming Environments (GPEs) such as TestPointTM 1 by CEC (TestPoint, 2010), LabVIEWTM by National Instruments (NI, 2010), Delphi (Acacio et al., 2002) and VEE by Hewlett Packard (Greenbaum & Jefferson, 1998) have been available for few years. Learning and working with these packages is relatively easy and rapid. Features and prices of GPEs are different from each other. In LabVIEWTM, graphical programming codes are shown in graphical diagram which makes it different from other GPEs (Krauß et al., 1999). In TestPoint, each object in the panel allows the user to perform a definite set of actions by just dragging and dropping, and shows the programming codes alike to text-based languages (Fig. 3 and Fig. 4).

Geomorphology and geography of the Rhône delta

The left branch of the Rhône river extends to Fos-sur-Mer and the right branch until Grau du Roi, so the current Rhône delta includes all the downstream alluvial lands of Beaucaire-Tarascon with total area of 150,000 hectares. The natural limits of the delta are formed by:
-On the right side by the old Rhône river terraces of Costière du Gard.
-On the left side by Alpilles range and durancian sediments of Crau.
The Rhône splits into two branches at Arles. First one by length is the Petit Rhône, flowing west and then south-west until it joins the sea near Saintes-Maries-de-la-Mer. The second one is the Grand Rhône, flowing towards Southeast and falls in sea at Port-Saint-Louis.
The delta is subdivided into three units:
-La Grande Camargue, between the two branches of the Rhône, 75000 ha, which is subdivided into Upper (Haut), Middle (Moyenne) and Lower (Basse) Camargue.
-La Petite Camargue on the right side of the Petit Rhône.
-Tarascon plain.
The elevation of the delta is about six meters to the north and decreases southward. The slope is very low, about 0.027% at Upper Camargue, while it varies around 0.007% at Lower Camargue; where many depressions are often less than the 0 NGF around the lagoon of Vaccarès (6500 hectares). The alluvial ridges confined to the northern part of lagoon and marshes, together with the raising of existing banks, form the delta landforms of Upper and Middle Camargue. So, there are two distinct morphological units. Upper and Middle Camargue have a morphology dominated by fluviatile coastal plain and lacustrine deposits while Lower Camargue results from both marine and continental origin (fluvial, lagunal, eolian or littoral sediment) (Boyer et al., 2005) . Upper and Middle Camargue seem protected from salt rise, while in Lower Camargue, the deposition of salts on the soil surface are observable. The crops cultivation in the Camargue is linked to the delta geomorphology. In Upper and Middle Camargue rice cultivation is carried out on the stream beds (30000 hectares of crops), while in Lower Camargue, pond (16000 hectares), saline soils (19,000 ha) and salt industry are present (Marinos, 1969). In an area of so low altitude, the consequences of sea level rise are very severe and manifold: from the disappearance of land (Sabatier & Provansal, 2002) to the salinization of soils by advancing of the salt wedge. Camargue has been subjected to strong anthropic influence. Particularly, the canalisation and sea wall construction cut off the area from its natural water supply (DDA des Bouches du Rhône, 1970). Hard engineering practices were also carried out in 1980 at various beaches in Rhônedelta to combat the problem of shore erosion and weak redistribution of sandy inputs of  Rhône river. The Camargue is now protected from marine invasions but efficiency of theseengineering structures is in question against increasing aggressiveness of climatic agents (Sabatier et al., 2009).

Hydrogeology of Rhône delta

In Rhône delta two aquifers are identified, within the Quaternary deposits, with limited communication with one another. Plaisancian marls which outcrop along the Costière and the Crau, constitute the impervious basement of the whole plain of the Camargue. They are overlain by Astian sandstones, sandy layers and by the gravels and conglomerates of the Villafranchian and old Quaternary, which represent a confined aquifer system, separated by peat beds and lenses from the phreatic aquifer system of recent alluvia (Griolet, 1972). The latter one is a low permeable, heterogeneous and unconfined aquifer which is not a continuous entity but is the sum of more or less independent small aquifers. The groundwaters range from freshwater zone to saline or hypersaline waters (up to 100 mS/cm) and water flow between these two zones is little bit restricted (Ambrosy, 2003). According to water table and salinity maps, aquifer is mainly recharged by the surface waters from the reliefs of the Alpilles and Crau while to some extent by irrigation (Marinos, 1969). The bottom of this aquifer is more clayey and corresponds to a confining layer for the second aquifer.
This second aquifer is constituted by the fluvial Pleistocene gravels. In the east of the Rhône River, in the Crau plain, it is a fresh unconfined aquifer greatly exploited for drinking water and industries (Fig. 1.3) while in the West of the Rhône River, in Camargue, the aquifer is confined and artesian in places. The end of the aquifer under the sea could be located around the continental shelf edge (around 30 km from the shoreline). Permeability varies between 10-5 m/s and 10-2 m/s and the groundwater electrical conductivity (EC) rises from NE to SW from 4 mS/cm up to 58 mS/cm. Hydrogeological studies carried out at the beginning of the 1970s have previously mentioned the poor water quality of the confined aquifer. Over 30 years, the situation has worsened; the piezometers showed salinity 2 g/l in 1969, now they show high salinity up to 38 g/l. The rapid increase of salinity in the confined aquifer is linkedto increased sea water intrusion. The intrusion of seawater can modify the groundwater chemistry by cation exchange (< 20% seawater intrusion) or SO4 and high Mg2+ in groundwater. These reactions can increase Ca2+ and HCO3 water and can shift the carbonate equilibrium and leads to dolomite/or magnesian calcite precipitation (De Montety et al., 2008).

Microbial activity and temperature in soil solutions

Temperature in all the plots were significantly affected by the air temperatures and solar cycles during the early period of rice cultivation while this influence of air temperature was moderated by the shadow of long rice plants after the end July. In all plots, irrigation or watering, depending on the temperatures of the irrigated water, decreased the temperatures of the soil solution significantly but this effect of newly waters remained only during 2-3 days.
This effect of newly waters is less observable in R 204 as compared to R 178 and R 179 due to high temperatures and high variations of daily temperatures in 2004. The temperature of R 179 remained, at average 1.3°C, higher than R 178 during all the period of the rice cultivation period and every decrease of temperatures by the newly waters is relatively during shorter time in R 179 than R 178. This higher temperature can be linked to the difference of post harvest management practices in both plots. It is reported that incorporation of rice residuals under anaerobic conditions influence the composition, diversity and population of microorganisms (Mandal et al., 2004). The practice of incorporation of rice residuals and floodings increase the microbial biomass by second year of this practice and cause the change in the relative abundances of specific groups of microorganisms (Bossio & Scow, 1997). It increases the microbial activity, microbial biomass and microbial respiration in the soil as compared to burning of rice straw (Devevre & Horwath, 2000; Singh et al., 2007). So, this increase in the microbial respiration and activity may be responsible for higher temperatures in the R 179. Temperatures of soil solution in the R 179 can also be higher due to change in radiant energy balance and insolation as thickness in both plots (Mandal et al., 2004).

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Presence of phasing and dephasing in the physical parameters

Dynamics of physical parameters during the rice cultivation period, visually, showed a daily variation but this visual daily variation necessitates a statistical confirmation. “Fourier analysis” and “cross-covariance analysis” are useful tools to observe the daily variations in the physical parameters and to see, if exist, a correlation among recorded physical parameters.
These types of analysis are frequently used in physics, geodynamics and climatology, so, these analyses were carried out on our data.
Fourier analysis was carried out in excel while Cross-covariance analysis was carried out by using the Matlab software. Fourier analysis describes the structure of data by indicating the presence of any periodicity in the long term recorded signals and help us to present the data in the form of periodogram. Cross-covariance analysis gives us information about correlations between the data structures of two physical parameters and shows if two parameters are in the same phase.
In this study, Fourier analysis was carried out on all the plots (R 178, R 179 and R 204) for the data obtained throughout the rice cultivation period. Cross-covariance analysis was carried out for all physical parameters (Temperature, EC, Eh and pH) for three plots for complete data. All the results are discussed hereunder.

Table of contents :

Part 1. Objectives of study and methods applied
Chapter 1. Introduction and objectives
1.1 Concept of hydromorphism
1.2 Types of hydromorphism depending on its origin
1.3 Hydromorphism caused by soil compaction
1.3.1 Soil compaction and its causes
1.3.2 Voluntary soil compaction and non voluntary soil compaction
1.3.3 Effects of soil compaction
1.4 Redox potential as an indicator of hydromorphic conditions
1.4.1 Heterogeneity in redox conditions in the soil
1.5 Factors affecting the hydromorphism and redox conditions of the soil
1.5.1 Soil oxygenation
1.5.2 Organic matter
1.5.3 Microorganisms
1.6 Effects of redox reactions on the soil
1.7 Effect of crop residual management practices on redox conditions
1.8 Interest and objectives of the study
1.9 Order of presentation of work
Chapter 2 Material and Methods
2.1 Methods of soil study
2.1.1 X-Ray diffraction
2.1.2 Selective extraction of iron oxides
2.2 Methods of aqueous study
2.2.1 In situ long term measurements by multiparametric probe
2.2.2 Manual Sampling of aqueous solutions
2.3 Use of graphical language TestPoint for alkalinity measurements
2.3.1 Introduction, interest and principle of TestPoint language
2.3.2 Verification of pH electrodes using high resolution voltmeter
2.3.3 Measurement of alkalinity by calibrated pH electrodes
2.4 Conclusion
Part 2. Hydromorphic conditions in the rice culture
Chapter 1. Presentation of studied area in Camargue
1.1 Camargue
1.1.1 Geology of the Rhône delta
1.1.2 Geomorphology and geography of the Rhône delta
1.1.3 Hydrogeology of Rhône delta
1.1.4 Pedology of Rhône delta
1.1.5 Climate of Rhône delta
1.1.6 Ecology of Rhône delta
1.1.7 Rice cultivation in Camargue
1.1.8 Major processes in the rice growing field
1.1.9 Mineralogy of rice cultivated soils in Camargue
1.2 Characteristics of the studied plots
1.3 Conclusion
Chapter 2 Dynamics of physical parameters of surface waters in rice culture by multiparametric probe
2.1 Introduction
2.2 Effects of the crop residual management practices on the evolution of the physical characteristics during rice culture
2.2.1 Major differences and similarities in physical parameters
2.2.2 Evolution of the temperature during the rice culture in three plots
2.2.3 Evolution of EC during the rice culture in three plots
2.2.4 Evolution of the pH during the rice culture in three plots
2.2.5 Evolution of the redox potential during the rice culture in three plots
2.3 Effect of the major events on the evolution of the physical characteristics during rice culture
2.3.1 Hydraulic and other management practices
2.3.2 Meteorological events during rice culture
2.4 The pe-pH diagram to calculate the stability fields of different forms of iron during the rice cultivation period
2.4.1 The effect of variations in pe-pH on different forms of iron in three plots
2.4.2 Different stages in the variations of pe-pH in rice culture
2.5 Interpretations and discussions
2.5.1 Redox potentials
2.5.2 pH
2.5.3 Electrical conductivity (EC)
2.5.4 Microbial activity and temperature in soil solutions
2.6 Presence of phasing and dephasing in the physical parameters
2.6.1 Fourier analysis
2.6.2 Covariance analysis
2.7 Conclusion
Chapter 3 Physico-chemical properties of surface waters during day cycle 
3.1 Introduction
3.2 Evolution of physical characteristics at different stages
3.2.1 The redox potentials presented as electron activity (pe)
3.2.2 The pH
3.2.3 Temperature
3.2.4 Electrical conductivity (EC)
3.3 Comparison of probe and multimeter measurements in SS
3.3.1 Difference in redox potentials
3.3.2 Difference in pH
3.3.3 Difference in temperature
3.3.4 Difference of electrical conductivity (EC)
3.3.5 Relation between T, pH, pe and EC
3.4 Evolution of unstable elements at different stages
3.4.1 Reduced iron (Fe2+)
3.4.2 Ammonium (NH4 +)
3.4.3 Nitrite (NO2 -)
3.5 Evolution of anions at different stages
3.5.1 Chloride (Cl-)
3.5.2 Bromide (Br-)
3.5.3 Sulphate (SO4 2-)
3.5.4 Fluoride (F-)
3.5.5 Nitrate (NO3 -)
3.6 Evolution of cations at different stages
3.6.1 Calcium (Ca2+)
3.6.2 Magnesium (Mg2+)
3.6.3 Potassium (K+)
3.6.4 Total iron (Fe)
3.6.5 Manganese (Mn)
3.6.6 Zinc (Zn2+)
3.6.7 Sodium (Na+)
3.6.8 Aluminium (Al3+)
3.7 Evolution of silicon and alkalinity at different stages
3.8 Evolution of dissolved organic carbon (DOC) at different stages
3.9 Synthesis of results
3.10 Interpretations and discussions
3.10.1 Impact of biotic factors on physical parameters
3.10.2 Interaction between air temperature and physical parameters
3.10.3 Statistical approach by using the correlations of different parameters .
3.10.5 The processes affecting the evolution of the elements at different stages
3.10.6 Evolution of chemical properties of surface waters
3.10.7 Transfer of elements between SS and LS
3.11 Conclusion
Chapter 4 Thermodynamic approach to physico-chemical parameters
4.1 Introduction
4.2 The pe-pH diagram to show the rhizosphere effect
4.3 Thermodynamic calculations using software PHREEQC
4.3.1 Calculation of index of saturation
4.3.2 Presentation of PHREEQC
4.4 Evolution of ionic strength at different stages of rice culture
4.5 Effect of post harvest practices in the rice culture on the pCO2
4.6 Effect of different post harvest practices on the SI of iron minerals
4.7 The evolution of SI of different minerals in rice culture
4.7.1 Calcite (CaCO3)
4.7.2 Aragonite (CaCO3)
4.7.3 Dolomite (CaMg(CO3)2)
4.7.4 Anhydrite (CaSO4) and Gypsum (CaSO4: 2H2O)
4.7.5 Smithsonite (ZnCO3)
4.7.6 Pyrochroite (Mn (OH)2) and Rhodochrosite (MnCO3)
4.7.7 Manganite (MnOOH)
4.7.8 Quartz (SiO2) and Chalcedony (SiO2)
4.7.9 Halite (NaCl)
4.7.10 Fluorite (CaF2)
4.7.11 Talc (Mg3Si4O10(OH)2)
4.7.12 Saturation indexes of soil clay minerals in rice culture
4.7.13 The SI of phosphate minerals
4.8 The SI of minerals without rhizosphere effect on physical parameter
4.8.1 Effect of rhizospheric activity absence on Iron minerals
4.8.2 Effect of rhizospheric activity absence on other minerals and pCO2
4.9 Comparison of SI for some minerals in R 204 with other plots
4.10 Conclusion
Chapter 5 Kinetics of pH in rice culture under hydromorphic conditions
5.1 Introduction
5.2 Interpretations of pH at equilibrium or “pH stat”
5.3 Calculations of time of relaxation for all plots
5.4 Daily variations during the study of pH kinetics
5.4.1 Time of relaxation for daily pH kinetics for plot R
5.4.2 Relation of pH and other physical parameters for R
5.5 Interpretations and discussions
5.6 Conclusion
Conclusion Part 2
Part 3 Hydromorphic conditions in forest soils due to mechanical soil compaction
Chapter 1 Presentation of site and problem description
1.1 General presentation of site
1.1.1 Climate of site
1.1.2 Soil characteristics
1.1.3 Preparation of site
1.1.4 Instrumentation of site for in situ, long term measurements
1.1.5 Evidence of hydromorphic degradation of soil after soil compaction.
1.2 Presentation of selected block
1.3 Conclusion
Chapter 2 Results obtained by X-ray diffraction
2.1 Major identified minerals in soil samples
2.2 Percentage of organic and non-organic carbon in different profiles
2.3 Identification of different clay minerals in soil samples
2.4 Comparison of different profiles for their clay minerals
2.5 Quantification of clay minerals in different soil profiles
2.6 Conclusion
Chapter 3 Effect of soil compaction on the reactivity of iron oxides
3.1 Kinetics of extraction in compacted and non-compacted soils
3.2 Association of elements in soil profiles
3.3 Effect of soils compaction on kinetics of selective chemical extraction
3.4 Extracted elements concentrations at various depths in all soil profiles
3.5 Conclusion
Part 4 Conclusion and perspectives
1. Conclusion
1.1 Site characteristics
1.2 Material and methods used
1.3 Use of multiparametric probe in rice culture
1.3.1 Evolution of physical parameters in rice culture
1.3.2 pH control in rice culture
1.3.3 Periodicity and relation among physical parameters
1.3.4 Effects of anthropic actions and meteorological events in rice culture
1.3.5 Effect of different post-harvest methods on the physical parameters
1.4 Effect of rhizospheric activity on physico-chemical parameters
1.5 Chemical composition of surface waters in paddy plots
1.6 Effect of Post harvest practices on physico-chemical parameters
1.7 Diurnal patterns in physico-chemical parameters in rhizosphere
1.8 Major chemical processes controlling the elements concentrations
1.9 Nature of hydromorphism in compacted forest soils
2. Perspectives
2.1 Automation of data acquisition
2.2 Hydromorphic conditions in rice culture and forest
Part 5 : Annexes
Annex 1: Chemical analysis of rice plots (source: Cassard R, 2009)
Annex 2: Chemical analysis of soil of Azerailles (Haut Bois) (source: Ranger and Brethes 2008).
Annex 3: X- ray diffraction (diffractograms) for clay minerals of compacted soils (T) and non compacted soils (C) of Nancy.
Annex 4: Interview with farmer about major field operations in paddy plots (R 178 and R 179) of Camargue (Source: Cassard R, 2009)
Annex 5: Chemical composition of surface waters of Camargue: (soil solution (SS) and surface water layer (LS)), and results of chemical selective extraction by reagents CB-CBD are available in computer format on demand.


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