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Please read the abstract in the 00front part of this document / Dissertation (MSc (Geology))--University of Pretoria, 2007. / Geology / unrestricted

Les sols sont définis comme étant caillouteux à partir d’une proportion supérieure à 35 % d’éléments grossiers. Les sols caillouteux - dont certains supportent des zones de grandes cultures - couvrent environ 30% de la superficie de l’Europe occidentale. Outre le fait qu’ils sont plus contraignants pour la production agricole car les opérations culturales y sont plus délicates, les sols caillouteux sont souvent des sols peu épais ; ils contribuent ainsi de façon significative à la recharge des nappes mais sont a priori très sensibles au lessivage hivernal du nitrate et des produits phytosanitaires. Malgré leur grande étendue géographique et leurs propriétés spécifiques, les sols caillouteux ont été peu étudiés. Devant ce déficit de connaissances et devant les problèmes spécifiques posés par les sols caillouteux (variabilité de la phase caillouteuse, échanges entre la phase caillouteuse et la fraction fine des sols), tant en termes de production végétale qu’en termes de protection de l’environnement, ce projet de thèse a eu pour objectifs de : i) déterminer la réserve utile des éléments grossiers de sols caillouteux d’origine sédimentaire ; ii) d’évaluer qualitativement et quantitativement la pierrosité de sols caillouteux à l’échelle parcellaire ; et iii) d’estimer la réserve utile effective de sols caillouteux et leur fonctionnement hydrique sur de grands territoires agricoles. Grâce à des analyses au laboratoire, nous avons montré que les cailloux étaient saturés en eau à -100 hPa et que les teneurs en eau à la capacité au champ et au point de flétrissement pouvaient s’exprimer simplement en fonction de la masse volumique, ce qui a permis de définir des fonctions de pédotransfert robustes et opérationnelles pour le calcul de l’humidité utile des éléments grossiers. Grâce à l’analyse du bruit du signal de la résistivité électrique, mesurée in situ par prospections géophysiques, il a été possible d’évaluer leur pierrosité volumique à l’échelle d’une parcelle. Enfin, à l’échelle régionale, nous avons montré que la non-prise en compte du volume de la phase caillouteuse et/ou de ses propriétés conduisait à des sous-estimations de 20 % de la réserve utile, ce qui avait pour conséquence une surestimation du déficit hydrique de 20 mm par an en moyenne, avec une grande variabilité spatiale. Ces travaux permettront, à terme, une meilleure gestion spatialisée des agrosystèmes, aux échelles locales et régionales. En effet, les nouvelles propriétés hydriques calculées permettront d’améliorer la compréhension du fonctionnement environnemental spatialisé des sols afin de mieux estimer certains risques (lessivage de nitrate, émissions de gaz à effet de serre par les sols, etc.). / Stony soils are soils containing a proportion of rock fragments larger than 35%. These soils - including intensive agricultural areas - cover about 30% of the surface of Western Europe. Stony soils are not only more stringent for agricultural production because the farming operations are usually more difficult, but also they are often thin; they then significantly contribute to the groundwater recharge, but are they are very sensitive to winter leaching of nitrate and pesticides. Despite their geographical spread and their specific properties, the stony soils have not been largely studied whereas they present specific scientific problems (variability of phase stony, exchanges between the stony phase and the fine fraction of soil). In that context, this thesis aimed at: i) determining the available water content of rock fragments from rock fragments of sedimentary origin; ii) assessing qualitatively and quantitatively the stoniness of stony soils at field scale; and iii) estimating the effective available water content of stony soils and their hydric functioning for large agricultural areas. From laboratory experiments, we demonstrated that rock fragments were saturated for a water potential of -100 hPa and that their water content at field capacity and at permanent wilting point could be easily estimated from their bulk density, which enable to define robust and operational pedotransfer functions for the estimation of the available water content of rock fragments. Thanks to the analysis of the signal noise of the electrical resistivity, measured in situ by geophysical prospectings, it was possible to assess the stoniness of stony soils at the plot scale. Finally, at the regional scale, we demonstrated that the available water content could be underestimated of about 20 % when the volume and/or properties of rock fragments were not taken into account, which induced overestimations of the hydric deficit of about 20 mm as a mean, with high spatial variability. This work will ultimately be used for a better spatial management of agricultural soils, at local and regional scales. Indeed, the new hydric properties will help in improving our knowledge of the environmental spatial soil functioning in order to better estimate some risks (nitrate leaching, greenhouse gas emissions from soils).

The electro-kinetic characteristics of different material bioreactor columns for treating water and waste water are experimentally studied. Separate columns of unsaturated gravels (~6mm) and ball clay were assessed for electro-kinetic characteristics by dosing water at a hydraulic loading rate of 50ml/min and 10ml/min. Similarly locally available organic materials such as sawdust, Moringa oleifera sheets and textile clothe pieces were also empirically analyzed. Size effects of the bio-reactor columns were also studied. The effluent from textile clothe and gravel reactor respectively showed an increase in pH while a depreciation in pH in the effluent was observed in the Moringa Oleifera reactor and sawdust reactor. This may be due to leaching of acidic organic components for sawdust and Moringa Oleifera . In gravels effluent pH depreciated with increase in flow rate but the general trend of the effluent pH curve showed an initial improvement before it slowed down to an asymptote for a specific constant dosage and height. A multi-parameter stochastic linear model for change in pH as a function of column height, dosage rate, time for specific volume discharge and change in electrical conductivity between influent and effluent was derived. A general stochastic model was also developed to characterize pH change in any bioreactor irrespective of the material media. Thirty centimeters of gravel exhibited an increase in conductivity with increase in flow rate while conductivity dipped with increasing flow rate when the gravel column height was halved. The measure of organic compounds in water decreased with increasing percolation rate through gravel. The chemical oxygen demand ratio within the gravel improved to unity showing increased containment of organic compounds with time. Organic textile clothes reactor also illustrated increased conductivity with increasing flow but conductivity dipped with increase in column height. For Moringa Oleifera reactors, a dosage of water at 10ml/min showed a significant improvement in conductivity with increase in column height. An initial depreciation in temperature curve was observed within clay and gravel reactor. With increase in depth there was an increase in temperature within the gravel as the saturation by water improved. In sawdust reactors this was not the trend. A birth process model is proposed to simulated temperature within a bioreactor as a function of time irrespective of any specific material used as bioreactor media.

The use of coarse-grained fill materials has grown significantly in recent years especially on account of their use in dams and transportation networks. This study investigates compressibility of various coarse-grained fill materials in dry and wet loading conditions in oedometer test. Four materials were used in the experiments, which falls into GP, GW, GM and GC categories respectively. GP material is a weathered rock obtained from Eymir Lake region. This material was chosen especially to be able to investigate degradation and particle breakage due to compaction and compression. GW, GM and GC materials were obtained by using the material called &lsquo / bypass&rsquo / which is a fill material used in the construction of metro of Eryaman. Using these four materials, large-scale double oedometer tests were carried out to investigate compressibility in both dry and wet conditions. The double oedometer testing technique is used to investigate the effect of soaking on compressibility behaviour of compacted fill materials. Various compactive efforts were used in the compaction stage to investigate the effect of compactive effort on compressibility and degradation of the four gravelly materials. Gradations of the post-test samples were obtained and particle breakage due to compaction using various compactive efforts and particle breakage due to compression were determined. It is found that amount of compression does not necessarily depend on the dry density of the material and fine fraction is also a dominating property regarding the compressibility in coarse-grained fill materials. The vertical strains induced by soaking are on the order of 12% - 20% of the compression measured in dry loading case for the well-graded coarse-grained fill materials tested. Besides, there is significant particle breakage in the compaction process and no further particle breakage in the oedometer test for GP material.

La protection à long terme des ressources en eau souterraine implique détudier le comportement de leau et des éventuels contaminants quelle véhicule depuis lentrée dans le milieu souterrain (recharge) jusquà lexutoire naturel (émergence, cours deau) ou forcé (pompage) de la nappe. Au cours de ce transit, de nombreux phénomènes dorigine physique ou chimique sont susceptibles daffecter la mobilité et les concentrations du ou des contaminants. Il sagit donc de tenir compte du pouvoir atténuateur, retardateur, voire auto-épurateur du milieu souterrain à leur égard, les conséquences pouvant être positives (dispersion, dilution, dégradation du contaminant) ou négatives (difficultés de reprise du contaminant, impact à long terme de la contamination, ). Lobjectif de cette recherche est de développer une approche conceptuelle et mathématique visant à létude in situ et à la modélisation de la mobilité et du piégeage temporaire ou définitif des solutés au sein du milieu souterrain variablement saturé en eau. Une classification des processus physico-chimiques influençant la mobilité des solutés est proposée, reposant sur trois critères : (1) un distinction entre processus « microscopiques », ayant cours à léchelle de quelques pores et processus « macroscopiques », ayant cours à léchelle du terrain ; (2) une distinction entre processus physiques (affectant tout type de contaminant, indépendamment de sa nature chimique) et processus chimiques (affectant certains contaminants, en fonction de leurs propriétés chimiques spécifiques) ; (3) une distinction entre processus à léquilibre (indépendant du temps) et processus cinétiques (dépendant explicitement du temps). Sur base de cette analyse, le modèle conceptuel considéré comporte trois éléments principaux : ladvection, la dispersion hydrodynamique et un processus de stockage-déstockage de soluté au sein dune phase immobile liquide (effet deau immobile) ou solide (sorption cinétique), représenté par une équation de transfert de premier ordre. Suivant le schéma conceptuel, les adaptations et développements réalisés au sein du code éléments finis SUFT3D, en vue de permettre la simulation du comportement dun soluté dans le milieu souterrain variablement saturé, sont décrits. La détermination des paramètres gouvernant les processus de migration et de piégeage des solutés repose sur linterprétation dessais de traçage réalisés in situ, en milieu saturé et non saturé. Une part importante de la recherche a donc été consacrée à lamélioration des techniques de traçage et dinterprétation des résultats en termes dévolution de la concentration et dévolution de la masse restituée du traceur, cette dernière étant plus adaptée à lévaluation et à la quantification des effets de retard. En vue de représenter de manière plus physique et plus précise linjection dun traceur, une nouvelle approche conceptuelle, mathématique et numérique est élaborée, considérant explicitement les interactions puits aquifère. A laide de ce modèle, divers tests numériques démontrent limpact des conditions dinjection du traceur sur les résultats de traçage, pouvant potentiellement conduire à des erreurs dinterprétation en termes didentification des processus agissant et de quantification des paramètres calibrés. En vue dune interprétation correcte des résultats de traçage, le contrôle des conditions dinjection est donc primordial. Deux études expérimentales servent de base et dillustration aux développements réalisés. Une campagne dessais de traçage en milieu saturé a été réalisée dans la plaine alluviale de la Meuse, à Hermalle-sous-Argenteau. Ces essais permettent de valider et dillustrer lapproche développée en vue de représenter précisément linjection des traceurs et les interactions puits aquifère, de mettre en évidence une série de problèmes conceptuels et pratiques rencontrés lors de la réalisation des essais de traçage, dexaminer le comportement chimique de plusieurs traceurs artificiels et de mettre en évidence les propriétés hydrodispersives des formations alluviales. La deuxième étude a eu pour objectif détudier les mécanismes de migration de substances dissoutes au sein de la zone non saturée surmontant la nappe aquifère des craies en Hesbaye. Les résultats de ces tests permettent de proposer une approche unifiée visant à représenter le comportement hydrodynamique et hydrodispersif des craies fissurées sous des conditions variables de recharge, donc de saturation en eau. Cette étude permet également de mettre en évidence le lien entre les propriétés physiques et hydrodynamiques des limons éoliens en Hesbaye.

From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / Mulches have been used for evaporation suppression in facilitating vegetable production under arid lands conditions. A study was undertaken in order to evaluate the effectiveness of plastic aprons, supplied by the FAO, as compared to gravel mulches. The vinyl aprons were 6 mils thick and about 1 meter square. Squash plants (Cucurbita pepo) were planted with gravel or plastic aprons or in bare areas and under different watering schedules. The yields under plastic aprons were considerably greater than under gravel and required slightly less water. Bare soil yields lagged far behind. Soil temperatures under the plastic aprons were consistently higher over 24 hours than bare soil, which within limits, would facilitate faster crop growth. Additionally, the apron collects and diverts rainfall to the plant. The vinyl used lasts only 2 seasons, and gravel would probably be a more suitable mulch for developing countries where capital is scarce.

A series of glasshouse and laboratory experiments was carried out to enable comparison of two woody perennial legumes, gorse and broom, with other legumes, nodulated non-legumes and other biological nitrogen fixing systems. Both species had distinct juvenile phases in which broom closely resembled herbaceous species in appearance, but adult plants of both species bore little resemblance to each other or to other legume species. Nodule development was similar to that of other legumes, but mature nodules exhibited structural adaptations to longevity - meristematic activity, a well developed vascular system and numerous cytoplasmic granules in cortical cells. Acetylene reduction and ¹⁵N₂ fixation continued for much longer following excision than has been observed in other legumes. In all experiments, broom nodules exhibited higher rates of acetylene reduction and nitrogen fixation than did gorse nodules. The first detectable product of nitrogen fixation in excised nodules - ammonia - was rapidly incorporated into amide and ∝ amino groups and another unidentified fraction. The principle free amino acid in nodules and sap was asparagine. Its preponderance increased as plants aged. Whole nodulated plants and excised nodules of both species exhibited a relatively low temperature optimum for growth and nitrogen fixation (22°C). They were very sensitive to elevated temperatures. Results indicated that gorse and broom have relatively low light requirements. When aeration was sufficient, combined nitrogen had little effect on growth of nodulated plants. Nodulation in both species was reduced by increasing amounts of combined nitrogen. High levels (100 mg/1) of nitrate and ammonia caused considerable inhibition of nitrogen function. Both species showed large responses to phosphate, but were able to grow and fix nitrogen when supplied with low amounts of phosphate. Boron deficiency reduced nitrogen fixation. Nodulation was increased to compensate for this. Considerable amounts of nitrogen can be contributed to the ecosystem in gorse end broom litter. Direct transfer between gorse or broom and Pinus radiate is likely to be small and may be masked by competition for other nutrients. These findings are discussed with respect to the use of gorse and broom to overcome nitrogen deficiency in reafforestation on the Moutere Gravels, in Nelson, N.Z.

From the Proceedings of the 1978 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 14-15, 1978, Flagstaff, Arizona / Water yield studies and flood control surveys often necessitate estimating transmission losses from ungaged watersheds. There is an immediate need for an economical method that provides the required accuracy. Analysis of relations between stream order, drainage area, and volume of channel alluvium existing in the various orders is one means of estimating loss potential. Data needed for the stream order survey are taken from aerial photos. Stream order is analyzed using stereophoto maps. Stream lengths taken from the maps are combined with average channel width and depth data (determined by prior surveys) to estimate volumes of alluvium involved. The volume of channel alluvium in a drainage network is directly related to the stream order number of its channels. Thus, a volume of alluvium within a drainage network (with a known transmission loss potential) may be estimated by knowing the order of each length of channel and the drainage areas involved. In analyzing drainage areas of 56-mi² or less, 70 to 75 percent of the total drainage network length is contained within first and second order channels; yet, these constitute less than 10 percent of the total transmission loss potential of the areas. Analysis of stream order and drainage area versus volume of alluvium relations allows preliminary estimates of transmission loss potential to be made for ungaged areas.