Soils as a Key Component of the Critical Zone 4

Foreword ix

André Mariotti

Introduction xiii

Guilhem Bourrié

Chapter 1. Water Quality in Soils 1
Guilhem Bourrié, Fabienne Trolard

1.1. Elementary weathering reactions 3

1.2. Weathering as a CO2 sink 4

1.3. Neoformations 5

1.3.1. Neoformation reactions 5

1.3.2. Arenization and pedogenesis 6

1.4. The weathering rate of rocks 11

1.4.1. Mass balance of granite weathering 11

1.4.2. Influence of soil heterogeneity: dilution and dissolution 11

1.5. Aluminum dynamics in solution 13

1.5.1. Application of the model of partial charges to the polyacid nature of aluminum 13

1.5.2. Aluminum hydroxide solubility as a function of pH 13

1.5.3. Field data 15

1.5.4. Aluminum condensation 16

1.6. Formation paths of aluminum hydroxides 16

1.6.1. The reaction mechanisms of aluminum 16

1.6.2. Kinetic interpretation 16

1.6.3. "Amorphous" aluminous gels 18

1.6.4. Aluminum toxicity 18

1.6.5. Aluminization of interlayers of clay minerals 19

1.7. Exchange acidity and lime requirement 19

1.8. The gibbsite-kaolinite-quartz system 21

1.8.1. Equilibrium and non-equilibrium 21

1.8.2. Gibbsite, a ubiquitous minera 23

1.8.3. The significance of the biogeochemical cycle of silicon 23

1.9. The dynamics of iron 25

1.9.1. Iron: the main indicator of hydromorphy 25

1.9.2. Soil color 28

1.9.3. Qualitative field tests 28

1.9.4. rH measurements 30

1.9.5. Study methods of the iron redox state in soil solution 32

1.9.6. Study methods of solid constituents in hydromorphic soils 35

1.9.7. Fougerite: mineralogical structure, composition and stability 38

1.9.8. Application of the model of partial charges to the determination of the Gibbs free energy of fougerite 41

1.9.9. Formation paths of iron oxides 41

1.9.10. Iron dynamics according to aerobiose/anaerobiose variations 42

1.9.11. Fougerite reactivity: influence on other biogeochemical cycles 51

1.9.12. Fougerite and the origin of life 55

1.10. Clay minerals formation 56

1.10.1. The precursors of clay minerals 56

1.10.2. The genesis of clay minerals by hydroxide silicification 57

1.11. Subtractive weathering and pedogenesis 59

1.11.1. A general subtractive evolution in temperate or tropical environment 59

1.11.2. The pedological reorganization of matter 59

1.11.3. The descent of horizons in landscapes 60

1.11.4. Soils in pedogenesis-erosion-transport-sedimentation cycles 61

1.12. Bibliography 62

Chapter 2. Irrigation, Water and Soil Quality 73.
Guilhem Bourrié, Nassira Salhi, Rabia Slimani, Abdelkader Douaoui, Belhadj Hamdi-Aïssa, Gihan Mohammed, Fabienne Trolard

2.1. Irrigation and global changes 73

2.2. The different salinization paths 74

2.2.1. Alkalinity and the sense of variation of pH 75

2.2.2. The acid sulfated path 77

2.2.3. The neutral saline path 78

2.2.4. The alkaline path 80

2.3. From irrigation water to groundwater 81

2.3.1. The salt balance 81

2.3.2. The coupling of the crop model STICS and the geochemical model Phreeqc 81

2.3.3. Proton balance and the rhizosphere effect 84

2.3.4. Simulation of soil-water-plant interactions 89

2.4. Equilibrium and non-equilibrium in saline soils 101

2.5 The use of deep groundwater 107

2.6. Sodification and soil degradation 114

2.7. Perspectives for irrigation 119

2.8. Appendix: relationship between d18O and log[Cl-] 120

2.9. Bibliography 121

Chapter 3. The Regulation of Phosphorus Transfer 127
Jean-Marcel Dorioz

3.1. Introduction 127

3.2. Phosphorus in the environment 129

3.2.1. The three issues of P 129

3.2.2. Principal characteristics of the dynamics of P in the environment 131

3.2.3. Biogeochemical control of PO4-P ions in solution and phosphorus cycle 135

3.2.4. Binding capacity and bioavailability measurements 138

3.2.5. Trophic impacts of external P load 141

3.3. Phosphorus cycle in anthropized lands 144

3.3.1. (Re)distribution, anthropogenic motion and phosphorus reserves 144

3.3.2. Diffuse phosphorus flows and soil usage patterns 148

3.4. The role of soils in diffuse transfers at the watershed level 150

3.4.1. Constitution of reserves in soil cover 151

3.4.2. P load acquisition of surface waters: from soil reserves to hydrochemical flows 153

3.4.3. P load attenuation in buffer zones: from hydrochemical flows to buffer zone deposits 161

3.5. The watershed as a P transfer system 175

3.5.1. Overall functioning 175

3.5.2. Spatial and time organization of the transfer system 178

3.5.3. Export patterns and states of the system 178

3.6. Considerations on diffuse P management 180

3.6.1. Is it possible to reasonably overlook diffuse P? 180

3.6.2. Controlling agricultural diffuse P transfers 181

3.7. Conclusion 183

3.8. Bibliography 184

List of Authors 189

Index 191