An investigation into the transient impacts of flood loadings on earthen embankments was conducted. Two embankments were instrumented and monitored over a period of four years. One of these embankments was a levee located along the Mississippi River just north of Cairo, Illinois. The other embankment was part of a catchment basin at the Engineer Research and Development Center located in Vicksburg, MS. Tensiometer and porous block sensors were used to monitor the pore water pressures in the embankments. It was found that when measuring the field soil water retention, tensiometers were more responsive than porous block sensors at low suctions; although, at shallower depths, the tensiometer performance was limited during periods of extended drying. It was shown that during the start of flooding, pore water pressures in the embankment soils were near −10 kPa at depths less than 2 m, which was greater than the normally assumed hydrostatic conditions. An investigation into flood hydrographs collected from across the United States showed that flood durations could be hundreds of days long. These hydrographs were collected over a period of 10 years. It was found that the recorded peak flood stage exceeded the major flood stage 11% of the time. An uncouple transient seepage model of a 2015 Mississippi River flood event that occurred at the Cairo levee showed that an uncoupled model could simulate the field measurements; however, the material properties that resulted in the most accurate simulation differed from those measured in the laboratory. Soil water retention characteristics of the embankment soils were assessed, and it was found that laboratory measured soil water retention curves could be used to bracket field measurements. Slope stability analyses were performed as a proxy to assessing the progression of the wetting front in the levees. Accounting for the increase in shear strength due to the presence of matric suction resulted in minimal impacts to stability factors of safety for levee embankments during flood loadings. The results of this investigation will help to improve the reliability of transient seepage analyses and provides guidance for future embankment monitoring investigations. / Doctor of Philosophy / An investigation into the movement of flood water through flood control embankments was conducted. Typically, analysis of this phenomenon is performed independent of the effects of time. For this investigation, the impacts of time were considered. When considering the effects of time dependent loadings, an initial distribution of water pressures must be considered. Typical assumptions regarding these distributions were investigated using four years of sensor measurements from two embankments. These measurements were also used to investigate appropriate material properties when considering saturated and unsaturated soil properties necessary for these analyses. Results show that typical assumptions may not be appropriate regarding initial water pressure distributions. Additionally, recommendations for assigning material properties were provided and it was found that these types of analyses can simulate flood loadings, but a range of material properties must be explored to understand the full range of performance. The impact of these results will lead to better predictions of embankment performance during flood loadings.

Soil improvement methods are used to minimize the consequences of liquefaction by changing the characteristics and/or response of a liquefiable soil deposit. When considering sites with previous development, the options for soil improvement are limited. Traditional methods, such as compaction and vibratory techniques, are difficult to employ because of adverse effects on adjacent structures. One potential method for soil improvement against soil liquefaction in developed sites is accelerated drainage through in situ vertical drains. Vertical drains expedite the dissipation of excess pore water pressures by reducing the length of the pore water drainage path. For more than thirty years, vertical gravel drains or stone columns have been employed to ensure the excess pore water pressure ratio remains below a prescribed maximum value. In recent years, the use of prefabricated vertical drains (PVDs) has increased because the drains can be installed with less site disruption than with traditional soil improvement methods. To date, little-to-no field or experimental verification is available regarding the seismic performance of sites treated with PVDs. The effectiveness of PVDs for liquefaction remediation was evaluated via small-scale centrifuge testing and full-scale field testing. A small-scale centrifuge test was performed on an untreated soil deposit and on a soil deposit treated with small-scale vertical drains. Compared to the untreated condition, the presence of the small-scale vertical drains provided numerous benefits including smaller magnitudes of excess pore water pressure generation and buildup, smaller induced cyclic shear strains, reduced times for pore pressure dissipation, and smaller permanent horizontal and vertical displacements. In addition, full-scale in situ field experiments were performed in an untreated soil deposit and in a soil deposit treated with full-scale PVDs using a vibrating mandrel as the dynamic source. In the untreated test area, the maximum induced excess pore pressure ratio reached about 0.95. In the treated test area, the vibratory installation of the first few drains generated significant excess pore pressures; however, significant excess pore pressures were not generated during the vibratory installation of additional drains because of the presence of the adjacent drains. Additionally, the vibratory installation of the drains caused significant settlement and significantly altered the shear wave velocity of the sand. Dynamic shaking after installation of all of the drains induced small accelerations, small cyclic shear strains, and negligible excess pore water pressures in the soil. The results of the field experiment indicate that the prefabricated vertical drains were effective at dissipating excess pore water pressures during shaking and densifying the site. / text

A indústria cimenteira busca alternativas para economia de recursos no processo produtivo, em especial envolvendo o uso de materiais residuais no cimento, como escórias siderúrgicas. A escória de aciaria, em particular, apresenta composição desfavorável para aplicação in natura, porém há metodologias na literatura de modificação do material para aplicações cimentícias. No entanto, ainda não se encontram avaliações da corrosão de armaduras de aço em compósitos cimentícios com essa adição, seja em meio sólido ou líquido (água de poro). Esse estudo avaliou, através de curvas de polarização e da espectroscopia de impedância eletroquímica (EIE), a resistência à corrosão do aço CA-50 em soluções representativas de águas de poro extraídas por pressão de pastas de cimento com 25 % de escória de aciaria in natura ou modificada por processo pirometalúrgico. Para efeitos comparativos, foi feita também a avaliação do desempenho do aço em meios de águas de poro indicadas na literatura como representativas de cimento Portland comum e de escória de alto forno. O efeito da presença de espécies agressivas na resistência à corrosão do aço foi avaliado adicionando-se 1,0 % de NaCl em massa às soluções estudadas. Nas águas de poro sem 1,0 % de cloreto, o aço CA-50 apresentou-se passivo e não mostrou indícios de corrosão nos ensaios nem de polarização nem de EIE durante 120 h de imersão. Entretanto, os ajustes dos diagramas com circuito elétrico equivalente (CEE) apontaram que as características de proteção da camada passiva formada nas águas de poro de cimento com escória de aciaria foram superiores, resultando em maior resistência à corrosão do aço CA-50 nestes meios. Por sua vez, nos meios com 1,0 % de NaCl, após polarização e EIE até 120 h, o aço sofreu corrosão para as águas de poro de cimento comum e escória de alto forno, porém não corroeu nas águas de poro representativas de cimentos com escórias de aciaria, cujo melhor desempenho foi associado à maior alcalinidade destes meios. A caracterização microestrutural por microscopia eletrônica de varredura após os ensaios de polarização anódica e de imersão mostrou que o principal produto de corrosão formado foi a lepidocrocita (?-FeOOH), comum em ataque do aço por cloretos. / The cement industry seeks alternatives to save resources in production processes, especially involving the use of residual materials in cements, such as slags. Steel slags present unfavorable composition for application as cement additions in natura, but there are methodologies in the literature for modifying this material for commercial application. However, there are no evaluations of the corrosion of steel reinforcements in cementitious composites with steel slags, either in solid or liquid medium (pore water). The present study employed polarization curves and electrochemical impedance spectroscopy (EIS) to evaluate the corrosion resistance of CA-50 steel in pore water solutions representative of cement pastes with 25 % steel slag in natura or modified by a pyrometallurgical process. For comparison purposes, the performance of CA-50 steel in the pore waters indicated in the literature as representatives of Portland cement and blast furnace slag activated with cement were also evaluated. The effect of aggressive species on the corrosion resistance of the steel was assessed by adding 1.0 % NaCl by mass to the pore water solutions. Without 1.0 % chloride addition, CA-50 steel exhibited good performance and showed no evidences of corrosion in all of the investigated media, both in anodic polarization and in EIS tests performed up to 120 h immersion. However, the fitting of the EIS diagrams with equivalent electric circuit (EEC) revealed that the protectiveness of the passive layer formed in pore waters representative of cements with steel slags were superior, indicating better corrosion resistance of CA-50 steel in these media. Conversely, when 1.0 % chloride was added to the pore waters, CA-50 steel presented pitting corrosion, and impedance decreases with immersion in the pore waters representative of pure cement and blast furnace slag, whereas no corrosion was detected by both methodologies in pore waters representatives of cements with steel slags, which superior performance was ascribed to their higher alkalinity. Microstructural characterization by scanning electron microscopy (SEM) after anodic polarization and immersion tests showed that the main corrosion product formed was lepidocrocite (?-FeOOH), usual of chloride attack of steel.

O Litoral Norte de São Paulo é uma região pouco impactada e com elevada sensibilidade ecológica e que reúne perspectivas de grande crescimento econômico com novas instalações de empresas ligadas à exploração do PRÉ-SAL. O presente estudo tem como objetivo analisar a toxicidade dos sedimentos dos Municípios de Ubatuba e Caraguatatuba com os procedimentos da Avaliação e Identificação da Toxicidade (AIT), somente a fase I, proposto pela USEPA (1991; 2007). O ensaio de toxicidade crônico de desenvolvimento embriolarval do ouriço do mar Lytechinus variegatus. Foi extraída a água intersticial dos sedimentos, coletados em quatro enseadas, pelo método de sucção descrito por Winger & Lasier (1991), sendo dois pontos de coleta na Enseada de Ubatuba - Perequê-Açu e Itaguá, um na Enseada do Flamengo, um na Enseada do Mar Virado e uma na Enseada de Caraguatatuba. A AIT evidenciou como agente causador da toxicidade, de modo geral, os compostos pH dependentes e dos metais. As amostras do Perequê-Açu e de Caraguatatuba apresentaram toxicidade em todas as amostras analisadas, as demais amostras não presentaram nenhuma relação entre a toxicidade e a sazonalidade. / São Paulo north coast is a poor impacted region and with high ecological sensitivity which gathers perspectives of great economic growth with new facilities related to the operation of the Pre-Salt companies. The aim of the present study is to analyze the toxicity of sediments from the municipalities of Ubatuba and Caraguatatuba with the procedures of the Toxicity Identification Evaluation (TIE), only the phase I, proposed by USEPA (1991, 2007). The test of chronic toxicity of embriolarval development of sea urchin Lytechinus variegates. Pore water was extracted from the sediments collected in four bays, by the suction method described by Winger & Lasier (1991), being two collection points in Ubatuba Bay - Perequê-Açu and Itaguá, one in Flamengo Bay, one the Mar Virado Bay and one in Caraguatatuba Bay. The TIE evidenced as a causative agent of toxicity, in general, the compounds of pH dependent and of metals. The samples of Perequê-Açu and Caraguatatuba showed toxicity in all samples, the other samples showed no relationship between toxicity and seasonality.

O Litoral Norte de São Paulo é uma região pouco impactada e com elevada sensibilidade ecológica e que reúne perspectivas de grande crescimento econômico com novas instalações de empresas ligadas à exploração do PRÉ-SAL. O presente estudo tem como objetivo analisar a toxicidade dos sedimentos dos Municípios de Ubatuba e Caraguatatuba com os procedimentos da Avaliação e Identificação da Toxicidade (AIT), somente a fase I, proposto pela USEPA (1991; 2007). O ensaio de toxicidade crônico de desenvolvimento embriolarval do ouriço do mar Lytechinus variegatus. Foi extraída a água intersticial dos sedimentos, coletados em quatro enseadas, pelo método de sucção descrito por Winger & Lasier (1991), sendo dois pontos de coleta na Enseada de Ubatuba - Perequê-Açu e Itaguá, um na Enseada do Flamengo, um na Enseada do Mar Virado e uma na Enseada de Caraguatatuba. A AIT evidenciou como agente causador da toxicidade, de modo geral, os compostos pH dependentes e dos metais. As amostras do Perequê-Açu e de Caraguatatuba apresentaram toxicidade em todas as amostras analisadas, as demais amostras não presentaram nenhuma relação entre a toxicidade e a sazonalidade. / São Paulo north coast is a poor impacted region and with high ecological sensitivity which gathers perspectives of great economic growth with new facilities related to the operation of the Pre-Salt companies. The aim of the present study is to analyze the toxicity of sediments from the municipalities of Ubatuba and Caraguatatuba with the procedures of the Toxicity Identification Evaluation (TIE), only the phase I, proposed by USEPA (1991, 2007). The test of chronic toxicity of embriolarval development of sea urchin Lytechinus variegates. Pore water was extracted from the sediments collected in four bays, by the suction method described by Winger & Lasier (1991), being two collection points in Ubatuba Bay - Perequê-Açu and Itaguá, one in Flamengo Bay, one the Mar Virado Bay and one in Caraguatatuba Bay. The TIE evidenced as a causative agent of toxicity, in general, the compounds of pH dependent and of metals. The samples of Perequê-Açu and Caraguatatuba showed toxicity in all samples, the other samples showed no relationship between toxicity and seasonality.

<p>Nedbrytning av organiskt material är en nyckelfaktor som påverkar omvandlingar av de många grundämnen som utgör eller är associerade till just organiskt material. En stor del av nedbrytningen av akvatiskt organiskt material (OM) sker i gränsskiktet mellan sediment och vatten. Eftersom så många biogeokemiska cykler styrs av nedbrytningen av OM är det viktigt att ha kunskap om processer och påverkansfaktorer både på mikro- och makronivå. Mineraliseringshastigheten av OM är en vanligt förekommande mätparameter, men vanligtvis inkluderar mätningarna inte de naturliga processer som kan påverka nedbrytnings-hastigheterna, t.ex. fysiska krafter.</p><p>Syftet med den här studien är att studera mineraliseringshastigheten av det OM som finns naturligt i ytsediment i söt- och brackvatten när det utsätts för fysiska krafter som orsakar förändringar i redox-förhållanden, resuspension eller advektivt porvattenflöde. Fem</p><p>laborativa experiment har utförts för att belysa syftet:</p><p>Åldrat ytsediment från en sötvattens å utsattes för olika redox förhållanden där oxisk respiration, sulfatreduktion respektive metanogenes gynnades. Resultaten visade ingen skillnad i mineraliseringshastighet beroende på behandling. Detta motsäger studier utförda i marina miljöer, där anoxiska förhållanden ger en lägre mineraliseringshastighet än oxiska.</p><p>Vidare gjordes två studier på brackvattensediment där effekten av resuspension var i centrum. Den ena studien fokuserade på frekvens och varaktighet av resuspensionstiderna, den andra på olika typer av sediment. Studierna visade att väldigt korta resuspensionstider med upp till 48 timmars stillhet mellan varje resuspension ökade mineraliseringstakten med fem gånger jämfört med diffusivt utbyte, och mer än dubblerades i jämförelse med kontinuerlig resuspension eller resuspension i långa perioder. Resuspensionen under kort tid var troligen gynnande då resuspension fysiskt stör bildningen av stabila bakteriesamhällen. Mineraliseringshastigheterna i sediment som domineras av väldigt fin, fin eller medium sand visade lika hastigheter, medan grov sand visade en signifikant lägre mineraliseringshastighet. Likheterna mellan de tre första sedimenttyperna kan dock ha påverkats av tillgång på lättnedbrytbart OM då sediment och vatten hämtades in under en algblomning.</p><p>Till sist studerades effekten på mineraliseringshastigheten av advektivt porvattenflöde. Detta gjordes på åldrat sediment dels från en sötvattensbäck dels från en brackvattenstrand. Inget av de två sedimenttyperna visade någon skillnad i mineraliseringshastighet i jämförelse med diffusivt styrda system. Det är i motsats till tidigare marina studier, men är i linje med den första studien, där mineraliseringshastigheten var oberoende av redox-förhållande.</p><p>Den generella slutsatsen från den här studien är nödvändigheten att studera samma aspekter i olika typer av akvatiska system, eftersom responsen verkar vara annorlunda beroende på system, t.ex. söt- brack- och saltvatten. Faktorer som kan förklara de här skillnaderna finns ännu inte, vilket gör att småskaliga studier och modeller blir viktiga verktyg för att utreda detta.</p> / <p>Organic matter mineralisation is a key parameter that affects most other element transformations associated with organic matter. A substantial part of aquatic organic matter (OM) mineralisation takes place at the interface between sediment and water. Understanding OM mineralisation is important at both the micro and macro scales, since it drives many biogeochemical cycles. OM mineralisation rates are widely measured, but generally not all the natural factors possibly affecting the rates, such as physical forcing, are considered.</p><p>This thesis examines the mineralisation rates of indigenous OM in fresh and brackish surface sediments, subjected to different physical forces inducing changed redox conditions, resuspension, and advective pore water flow. Five experiments were performed to this end.</p><p>Aged surface sediment from a freshwater river was subjected to different redox conditions favouring oxic respiration, sulphate reduction, and methanogenesis, respectively. Results indicated no difference in mineralisation rate irrespective of treatment. This contradicts what has been found in marine environments, where anoxic mineralisation rates are lower than oxic ones.</p><p>Further, two studies of resuspension of brackish sediments were performed, one addressing the impact of the frequency and duration of the resuspension events, and the other addressing the impact of resuspension on different types of sediments. The studies found that very brief resuspension events followed by calm periods of up to 48 h increased mineralisation rates by five times compared to diffusion, and more than doubled the rate compared to continuous or long-term resuspension. The short-term events were possibly favoured because resuspension physically disturbs the arrangement of a stable bacteria community. Mineralisation rates on sediments dominated by very fine, fine, or medium-grained sand were the same, while coarse sand displayed a significantly lower rate. The similar rates of the three first sediment types could stem from access to labile OM, due to an ongoing algae bloom when the sediment and water samples were collected.</p><p>Finally, the effect of advective pore water flow on aged sediment from one fresh and one brackish sediment was studied. Neither of the sediments displayed a mineralisation rate different from those occurring in incubations in which only diffusive exchange occurred. This contradicts the findings of previous marine studies, but is in line with the first study, which did not detect different mineralisation rates irrespective of redox conditions.</p><p>The general conclusion is that it is necessary to study the same physical forces in different aquatic environments, since responses appear to differ, for example, between freshwater, brackish, and marine environments. Factors explaining these differences have not yet been expressed, making small-scale studies and modelling a challenge for future research.</p>

Based upon the upper bound limit analysis, the stability numbers have been developed for a two-layered soil slope both for an associated flow rule material and for a homogeneous slope with non-associated flow rule material. The failure surface was assumed to be an arc of logarithmic spiral and it automatically ensures the kinematics admissibility of the failure mechanism with respect to the rigid rotation of the soil mass about the focus of the logarithmic spiral. The effect of the pore water pressure and horizontal earthquake body forces was also included m the analysis. For a non-associated flow rule material, the stress distribution along the failure surface was developed with the assumption of interslice forces given by Fellenius and Bishop. The stability numbers have been found to reduce appreciably with increases m the (i) horizontal inclination (β) of slope, (ii) pore water pressure coefficient, ru and (iii) horizontal earthquake acceleration coefficient (kh). The values of the stability numbers for a non-associated co-axial flow rule, with dilatancy angle ψ =0, have been found to be considerably lower as compared to the associated flow rule material. For a given height of the slope, with associated flow rule, the values of the stability numbers have been found to increase with increase in the thickness of a layer with greater value of the friction angle Φ. The results have been given in the form of non-dimensional stability charts, which can be used for readily obtaining either the value of the critical height or the factor of safety The methodology can be easily extended even for multi-layered soil slopes with different values of cohesion (c), bulk unit weight (γ) and friction angle (Φ). An attempt has also been made in this thesis to study experimentally the effect of the frequency of the excitation and the addition of non-plastic fines on the liquefaction resistance of the material Shake table studies, generating uni-axial sinusoidal horizontal vibrations, were earned out for this purpose. During the period of excitation of the material, the settlement at the surface of the sample increases continuously with time up to a certain peak value and thereafter, it becomes almost constant. For the excitation of the material with higher frequency, more number of cycles was seen to reach the final settlement. With the continuous excitation of the material, the magnitude of the pore water pressures increases up to a certain peak value and there after, its magnitude decreases till it again becomes the hydrostatic pressure as it was before the excitation of the material. The peak magnitude of the pore water pressure tends to be higher for the excitation with smaller frequency especially at greater depths from the ground surface. The addition of non-plastic fines tends to increase the magnitude of the settlement as well as the increase in the pore water pressure.

Recent advances in nanotechnology have led to the production of materials with nanoscale dimensions (nm) and properties distinctly different from their bulk (>100 nm) counterparts. With increased use, it is inevitable that nanomaterials will accumulate in the environment and there is concern that the novel properties of nanomaterials could result in detrimental environmental and human health effects. In particular, there has been concern recently regarding the use of silver (Ag) based nanomaterials as antimicrobial agents in consumer and medical products. Current regulations dealing with the discharge of metals into the environment are based on total concentrations with no consideration for the form (e.g., ionic, nanoparticle, colloid) which can largely determine toxicity. Methods for the identification and characterization of nanoparticulates within complex matrices are lacking and the development of robust methods for this purpose are considered a high priority research area. This research focuses on the development and application of a novel method for characterizing Ag manufactured nanoparticles (MNPs) within terrestrial environments, in particular in soil pore water, with applications relevant to other metal MNPs as well. The method was then applied to understand the dynamics and behavior of Ag MNPs in soil and soil amended with sewage sludge biosolids.

The use of geosynthetics in landfill construction introduces potential planes of weakness. As a result, there is a requirement to assess the stability along the soil/geosynthetic and geosynthetic/geosynthetic interfaces. Stability is governed by the shear strength along the weakest interface in the system. Repeatability interface shear strength testing of a geomembrane/geotextile interface at low normal stresses suitable for capping systems showed considerable variability of measured geosynthetic interface shear strengths, suggesting that minor factors can have a significant influence on the measured shear strength. This study demonstrates that more than one test per normal stress is necessary if a more accurate and reliable interface shear strength value is to be obtained. Carefully controlled inter-laboratory geosynthetic interface shear strength comparison tests undertaken on large direct shear devices that differ in the kinematic degrees of freedom of the top box, showed the fixed top box design to consistently over estimate the available interface shear strength compared to the vertically movable top box design. Results obtained from measurement of the normal stress on the interface during shear with use of load cells in the lower box of the fixed top box design, raise key questions on the accuracy, reliability and proper interpretation of the interface shear strength data used in landfill design calculations. Tests on the geocomposite/sand interface have shown the interface friction angle to vary with the orientation of the geocomposite's main core, in relation to the direction of shearing. Close attention needs to be paid to the onsite geocomposite placement in confined spaces and capping slope corners, as grid orientation on the slope becomes particularly important when sliding is initiated. Attempts to measure the pore water pressure during staged consolidation and shear along a clay/geomembrane interface in the large direct shear device suggest that this interface is a partial drainage path.

Nedbrytning av organiskt material är en nyckelfaktor som påverkar omvandlingar av de många grundämnen som utgör eller är associerade till just organiskt material. En stor del av nedbrytningen av akvatiskt organiskt material (OM) sker i gränsskiktet mellan sediment och vatten. Eftersom så många biogeokemiska cykler styrs av nedbrytningen av OM är det viktigt att ha kunskap om processer och påverkansfaktorer både på mikro- och makronivå. Mineraliseringshastigheten av OM är en vanligt förekommande mätparameter, men vanligtvis inkluderar mätningarna inte de naturliga processer som kan påverka nedbrytnings-hastigheterna, t.ex. fysiska krafter. Syftet med den här studien är att studera mineraliseringshastigheten av det OM som finns naturligt i ytsediment i söt- och brackvatten när det utsätts för fysiska krafter som orsakar förändringar i redox-förhållanden, resuspension eller advektivt porvattenflöde. Fem laborativa experiment har utförts för att belysa syftet: Åldrat ytsediment från en sötvattens å utsattes för olika redox förhållanden där oxisk respiration, sulfatreduktion respektive metanogenes gynnades. Resultaten visade ingen skillnad i mineraliseringshastighet beroende på behandling. Detta motsäger studier utförda i marina miljöer, där anoxiska förhållanden ger en lägre mineraliseringshastighet än oxiska. Vidare gjordes två studier på brackvattensediment där effekten av resuspension var i centrum. Den ena studien fokuserade på frekvens och varaktighet av resuspensionstiderna, den andra på olika typer av sediment. Studierna visade att väldigt korta resuspensionstider med upp till 48 timmars stillhet mellan varje resuspension ökade mineraliseringstakten med fem gånger jämfört med diffusivt utbyte, och mer än dubblerades i jämförelse med kontinuerlig resuspension eller resuspension i långa perioder. Resuspensionen under kort tid var troligen gynnande då resuspension fysiskt stör bildningen av stabila bakteriesamhällen. Mineraliseringshastigheterna i sediment som domineras av väldigt fin, fin eller medium sand visade lika hastigheter, medan grov sand visade en signifikant lägre mineraliseringshastighet. Likheterna mellan de tre första sedimenttyperna kan dock ha påverkats av tillgång på lättnedbrytbart OM då sediment och vatten hämtades in under en algblomning. Till sist studerades effekten på mineraliseringshastigheten av advektivt porvattenflöde. Detta gjordes på åldrat sediment dels från en sötvattensbäck dels från en brackvattenstrand. Inget av de två sedimenttyperna visade någon skillnad i mineraliseringshastighet i jämförelse med diffusivt styrda system. Det är i motsats till tidigare marina studier, men är i linje med den första studien, där mineraliseringshastigheten var oberoende av redox-förhållande. Den generella slutsatsen från den här studien är nödvändigheten att studera samma aspekter i olika typer av akvatiska system, eftersom responsen verkar vara annorlunda beroende på system, t.ex. söt- brack- och saltvatten. Faktorer som kan förklara de här skillnaderna finns ännu inte, vilket gör att småskaliga studier och modeller blir viktiga verktyg för att utreda detta. / Organic matter mineralisation is a key parameter that affects most other element transformations associated with organic matter. A substantial part of aquatic organic matter (OM) mineralisation takes place at the interface between sediment and water. Understanding OM mineralisation is important at both the micro and macro scales, since it drives many biogeochemical cycles. OM mineralisation rates are widely measured, but generally not all the natural factors possibly affecting the rates, such as physical forcing, are considered. This thesis examines the mineralisation rates of indigenous OM in fresh and brackish surface sediments, subjected to different physical forces inducing changed redox conditions, resuspension, and advective pore water flow. Five experiments were performed to this end. Aged surface sediment from a freshwater river was subjected to different redox conditions favouring oxic respiration, sulphate reduction, and methanogenesis, respectively. Results indicated no difference in mineralisation rate irrespective of treatment. This contradicts what has been found in marine environments, where anoxic mineralisation rates are lower than oxic ones. Further, two studies of resuspension of brackish sediments were performed, one addressing the impact of the frequency and duration of the resuspension events, and the other addressing the impact of resuspension on different types of sediments. The studies found that very brief resuspension events followed by calm periods of up to 48 h increased mineralisation rates by five times compared to diffusion, and more than doubled the rate compared to continuous or long-term resuspension. The short-term events were possibly favoured because resuspension physically disturbs the arrangement of a stable bacteria community. Mineralisation rates on sediments dominated by very fine, fine, or medium-grained sand were the same, while coarse sand displayed a significantly lower rate. The similar rates of the three first sediment types could stem from access to labile OM, due to an ongoing algae bloom when the sediment and water samples were collected. Finally, the effect of advective pore water flow on aged sediment from one fresh and one brackish sediment was studied. Neither of the sediments displayed a mineralisation rate different from those occurring in incubations in which only diffusive exchange occurred. This contradicts the findings of previous marine studies, but is in line with the first study, which did not detect different mineralisation rates irrespective of redox conditions. The general conclusion is that it is necessary to study the same physical forces in different aquatic environments, since responses appear to differ, for example, between freshwater, brackish, and marine environments. Factors explaining these differences have not yet been expressed, making small-scale studies and modelling a challenge for future research.