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  • 1.
    Baresel, Christian
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Destouni, Georgia
    Estimating subsurface nitrogen accumulation–depletion in catchments by input–output flow analysis2006In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 31, no 17, p. 1030-1037Article in journal (Refereed)
    Abstract [en]

    We use input-output analysis of nitrogen flows between various sources-sectors and natural waters in the Swedish Norrstrom drainage basin for investigating and bounding the implication range of some uncertainty sources for results of subsurface nitrogen accumulation-depletion in this basin. We quantify different possible base and extreme assumptions of nitrogen discharges and transport pathways from agriculture to surface and groundwater in the basin. The results are robust in showing considerable nitrogen accumulation-depletion flow interactions taking place between the basin's mobile water and accumulated nitrogen pools in soils, sediments and/or relatively immobile subsurface water zones for all different scenario assumptions. Similar scenario robustness is also found in resulting relative contributions of different active nitrogen source-sectors to nitrogen flows in natural water systems. In the Norrstrom basin, and possibly more generally, nitrogen accumulation-depletion flows to and from accumulated legacies for the future or from the past appear therefore to be more important for water quality than current nitrogen discharges from active source-sectors.

  • 2.
    Holmboe, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Petterson, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Effects of the injection grout Silica sol on Bentonite2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 17/18, p. 1580-1589Article in journal (Refereed)
    Abstract [en]

    Silica sol, i.e., colloidal SiO2, may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO2-colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO2-colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3 M NaCl), as well as dehydration and redispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO2-colloids affect the bulk/macro properties of bentonite. In order to study specific SiO2-colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO2-colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO2-colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO2-colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO2-colloids in Na+ dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca2+ dominated samples not subjected to excess NaCl, SiO2-colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and ungelled Silica sol should preferably be avoided.

  • 3.
    Karlberg, Louise
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Penning de Vries, Frits W T
    International Water Management Institute.
    Exploring potentials and constraints of low-cost drip irrigation with saline water in sub-Saharan Africa2004In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 29, no 15-18, p. 1035-1042Article in journal (Refereed)
    Abstract [en]

    Irrigation with saline water could provide an interesting opportunity to meet increasing food demands without competing with other pressing needs for fresh water such as domestic and industrial water use in water scarce regions. In sub-Saharan Africa, saline groundwater could be a plentiful and under-utilised resource; however, there is a lack of data to confirm this assumption. Saline water is deliberately and successfully used for irrigation of field and garden crops in several countries. The water saving characteristics and the distribution patterns of water in the soil under drip irrigation make this water application technique suitable for use in combination with saline water. Low-cost drip irrigation has already been successfully implemented in sub-Saharan Africa. It is suggested that low-cost drip irrigation with saline groundwater for the cultivation of horticultural crops can be a feasible option under conditions of water shortage, and has the potential to contribute to improved and sustainable crop production for smallholder farmers.

  • 4. Karpouzoglou, Timon
    et al.
    Barron, Jennie
    Wageningen University, Post Box 8130, Wageningen, 6700EW, Netherlands; Stockholm Resilience Centre, Stockholm University, Kräftriket 2B, Stockholm, SE106 91, Sweden.
    A global and regional perspective of rainwater harvesting in sub-Saharan Africa's rainfed farming systems2014In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 72-75, p. 43-53Article in journal (Refereed)
    Abstract [en]

    In semi-arid and sub-humid sub-Saharan Africa highly variable rainfall, frequent droughts and low water productivity are consistently undermining food security. Rainwater harvesting technologies (RWHTs) help utilise water more productively whilst raising yield levels. In this article it is argued that realising the potential of RWHTs for resilience building and climate adaptation requires a better understanding of global and regional processes influencing RWHTs adoption combined with pre-existing analysis at the household scale. On the basis of a systematic literature review, processes of influence in the diffusion and uptake of RWHTs are identified. These relate to shifting ideology associated with food production systems; the scope of investments in agriculture science and technology; emergent actors shaping development assistance; and patterns of farmer mobility. Drawing insights from theory on transformations for sustainability and development, this article adds to the understanding of connectedness between farm-level adoption of RWHTs, and regional to global level actors, institutions and processes.

  • 5.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    A model for the viscosity of dilute smectite gels2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 17-18, p. 1792-1798Article in journal (Refereed)
    Abstract [en]

    A simple yet accurate model describing the viscosity of dilute suspensions of sodium montmorillonite in dilute homoionic solutions is presented. Taking the clay particle and the surrounding clouds of ions as a whole as an uncharged but soft, coin-like particle, the Huggins’ equation for a suspension of uncharged particles is extended in the model to account for not only the primary and the secondary electroviscous effects, but also the multi-particle interaction. The agreements between the predicted and measured results are excellent. The Huggins’ coefficient obtained compares favorably with available data, while the intrinsic viscosity reduces to the Simha’s equation in the large limit of ionic strength, suggesting that the model is robust.

  • 6.
    Liu, Longcheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Analysis of fluid flow and solute transport through a single fracture with variable apertures intersecting a canister: Comparison between fractal and Gaussian fractures2006In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 31, no 14-okt, p. 634-639Article in journal (Refereed)
    Abstract [en]

    Canisters with spent nuclear fuel will be deposited in fractured crystalline rock in the Swedish concept for a final repository. The fractures intersect the canister holes at different angles and they have variable apertures and therefore locally varying flowrates. Our previous model with fractures with a constant aperture and a 90 degrees intersection angle is now extended to arbitrary intersection angles and stochastically variable apertures. It is shown that the previous basic model can be simply amended to account for these effects. More importantly, it has been found that the distributions of the volumetric and the equivalent flow rates are all close to the Normal for both fractal and Gaussian fractures, with the mean of the distribution of the volumetric flow rate being determined solely by the hydraulic aperture, and that of the equivalent flow rate being determined by the mechanical aperture. Moreover, the standard deviation of the volumetric flow rates of the many realizations increases with increasing roughness and spatial correlation length of the aperture field, and so does that of the equivalent flow rates. Thus, two simple statistical relations can be developed to describe the stochastic properties of fluid flow and solute transport through a single fracture with spatially variable apertures. This obviates, then, the need to simulate each fracture that intersects a canister in great detail, and allows the use of complex fractures also in very large fracture network models used in performance assessment.

  • 7.
    Liu, Longcheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Permeability and expansibility of natural bentonite MX-80 in distilled water2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 17-18, p. 1783-1791Article in journal (Refereed)
    Abstract [en]

    Natural bentonite MX-80 differs from the purified and fully Na-exchanged bentonite in that it contains approximately 20.0% accessory minerals, in addition to the montmorillonite particles. Since the accessory minerals and montmorillonite particles have very different physical and chemical properties, natural bentonite MX-80 is found to expand much more slowly in distilled water, leading actually to a three-component system that has very different hydraulic properties from that of the fully Na-exchanged bentonite. To better understand and simulate the special features of expansion of natural bentonite MX-80 in distilled water, the focus is put primarily on the development of a Kozeny-Carman-like equation for its hydraulic permeability in the same way as it was done for Na-exchanged bentonite. With this permeability model, the dynamic force balance model that was originally developed for colloidal expansion of montmorillonite in a two-component system is applied to the natural MX-80 system. Without making any changes to the model, however, two strategies are used to account for both physical and chemical effects of the accessory minerals. The "lumped" strategy assumes that the accessory minerals are stuck onto the montmorillonite particles in such a way that they behave just like one solid component. The "stepwise" strategy changes the pore water chemistry gradually from initially distilled water to eventually achievement of the equilibrium condition. These strategies are simple but proved to function well. The agreement between the simulations and the experimental results indicates that the two-component dynamic force balance model works well in predicting the general features and the behavior of upward expansion of natural bentonite MX-80 in distilled water in a vertical test tube.

  • 8.
    Moreno, Luis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Erosion of sodium bentonite by flow and colloid diffusion2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 17-18, p. 1600-1606Article in journal (Refereed)
    Abstract [en]

    Smectite gel formed at the outer part of a bentonite buffer in granitic rock could expand into rock fractures with seeping water. Such a gel can release colloids into low ionic strength waters. In addition the gel/sol can itself slowly flow downstream when it has reached a low particle concentration sufficient to decrease the viscosity to allow flow. The erosion due to the combined effects of particle diffusion and gel/sol flow is modelled for a thin fracture into which the gel expands influenced by various forces between and on particles. Some of the forces such as the electrical double layer force and viscous force are strongly influenced by the ionic strength of the pore water. Changes in the ionic strength due to diffusion and dilution of ions in the expanding clay are modelled simultaneously with the gel expansion, flow of gel and colloid release to the seeping water. The model includes description of flow of the seeping fluid, which gradually turns from pure water to sol to more dense gel as the smectite source is approached. The model also describes expansion of the gel/sol and colloid release and flow and diffusion of ions in the system. The coupled models are solved using a numerical code. The results show that the gel will flow with a non-negligible flowrate when its volume fraction is below 1%, but that the erosion and loss of smectite is not much influenced by the concentration of sodium in the clay or in the approaching seeping water, if they are kept below the Critical Coagulation Concentration, CCC.

  • 9. Stein, C.
    et al.
    Ernstson, Henrik
    Stockholm Resilience Center, Sweden;University of Cape Town, South Africa.
    Barron, J.
    A social network approach to analyzing water governance: the case of the Mkindo catchment, Tanzania2011In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, no 14-15, p. 1085-1092Article in journal (Refereed)
    Abstract [en]

    The governance dimension of water resources management is just as complex and interconnected as the hydrological processes it aims to influence. There is an increasing need (i) to understand the multi-stake- holder governance arrangements that emerge from the cross-scale nature and multifunctional role of water; and (ii) to develop appropriate research tools to analyze them. In this study we demonstrate how social network analysis (SNA), a well-established technique from sociology and organizational research, can be used to empirically map collaborative social networks between actors that either directly or indirectly influence water flows in the Mkindo catchment in Tanzania. We assess how these collabo- rative social networks affect the capacity to govern water in this particular catchment and explore how knowledge about such networks can be used to facilitate more effective or adaptive water resources man- agement. The study is novel as it applies social network analysis not only to organizations influencing blue water (the liquid water in rivers, lakes and aquifers) but also green water (the soil moisture used by plants). Using a questionnaire and semi-structured interviews, we generated social network data of 70 organizations, ranging from local resource users and village leaders, to higher-level governmental agencies, universities and NGOs. Results show that there is no organization that coordinates the various land and water related activities at the catchment scale. Furthermore, an important result is that village leader play a crucial role linking otherwise disconnected actors, but that they are not adequately inte- grated into the formal water governance system. Water user associations (WUAs) are in the process of establishment and could bring together actors currently not part of the formal governance system. How- ever, the establishment of WUAs seems to follow a top-down approach not considering the existing infor- mal organization of water users that are revealed through this social network analysis. Instead of imposing institutional arrangements, we argue that it is more promising to identify and build on existing social structures. Social network analysis can help to identify existing social structures and points for interventions to increase the problem solving capacity of the governance network.

  • 10.
    Wold, Susanna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Eriksen, Trygve
    Diffusion of humic colloids in compacted bentonite2007In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 32, no 07-jan, p. 477-484Article in journal (Refereed)
    Abstract [en]

    Through-diffusion experiments in bentonite with humic colloids in the size range of 1-10 nm were carried out. Bentonite was compacted to 0.6-1.8 g/cm(3) dry density and equilibrated with 0.01 and 0.1 M NaClO4 solutions. Experiments with Eu(Ill) diffusing in the absence and presence of humics were run in parallel, as well as Co(ll) diffusing through compacted bentonite in the presence of hurnics. The hurnic colloid diffusion experiments were run for 60 days and the humic concentration in the outlet solutions measured at time intervals. The experimental breakthrough curves for humic substances (HS) as well as the HS, Co(II) and Eu(III) profiles in the bentonite were simulated using the finite difference based computer code ANADIFF. Regardless of the compaction and ionic strength of solutions, hurnic colloids diffused through the compacted bentonite. The effects of hurnic colloids on both Co(H) and Eu(111) sorption as well as on diffusion were significant. The apparent diffusivity (D-a) increased significantly for both Co(II) and Eu(III) when hurnic colloids were present and the distribution coefficient (K-d) values decreased.

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