The mixing zone developed at freshwater-seawater interface is one of the most important features in complex coastal hydrogeologic systems, which controls subsurface flow and reactive transport dynamics. Freshwater-seawater mixing-zone development is influenced by many physical and chemical processes, such as characteristics of geologic formation, hydrodynamic fluctuations of groundwater and seawater levels, fluid-rock interactions, and others. Wide mixing zones have been found in many coastal aquifers all over the world. However, the mechanisms responsible for wide mixing zones are not well understood. In this thesis, two hypotheses were proposed to explain wide mixing zones in coastal aquifers: (1) kinetic mass transfer coupled with transient conditions, which create the movement of the mixing zone, may widen mixing zones; and (2) aquifer stratification may widen the mixing zone. The hypotheses were tested by both multiscale numerical simulations and laboratory experiments. Numerical simulations were based on a variable-density groundwater model by varying mass transfer parameters, including immobile porosity, mobile porosity, and mass transfer coefficient, and the hydraulic conductivity contrast between aquifer layers. Laboratory experiments were conducted in a quasi-two-dimensional tank, where real beach sands were installed and foodstuff dyes were used to visualize the development of freshwater-seawater mixing zone. Major conclusions included (1) the mixing zone can be significantly widened when the mass transfer timescale and the period of transient boundary is comparable due to the nonequilibrium mass transfer effects; and (2) a thick mixing zone occurs in low-permeability layer when it overlays upon a fast flow layer. These results not only improve the understanding of the dynamics of mixing-zone development and its associated geochemical processes in coastal aquifers, but also identify hydrogeologic conditions for the model of sharp-interface approximation to be valid. In addition to better understanding the mechanisms and dynamics of mixing zone, this thesis also investigates cost-effective management of coastal groundwater resources. To protect and conserve limited water recourses in coastal regions, interest in aquifer storage and recovery (ASR) has been growing in recent years. ASR is a promising strategy for water resources management and has been widely used in many contaminated and saline aquifers. However, its performance may be significantly constrained by mass transfer effects due to the mobilization of solutes initially residing in immobile domains. Better understanding of kinetic mass transfer effects on ASR is needed in order to aid the decision-making process. A numerical model is developed to simulate ASR performance by combining the convergent and divergent dispersion models with a first-order mass transfer model. By analyzing the concentration history at the pumping well, we obtain simple and effective relationships for investigating ASR efficiency under various mass transfer parameters, including capacity ratio and mass transfer timescales, and operational parameters. Based on such relationships, one can conveniently determine whether a site with mass transfer limitations is appropriate or not for ASR and how many ASR cycles are required for achieving a positive recovery efficiency (RE).

Anthropogenic activities are responsible for increases in atmospheric CO₂ and climate change. These increases are partly counterbalanced by natural processes, such as carbon uptake in land surfaces. These processes are themselves subject to climate change, creating a coupled carbon-climate system. I investigated the carbon sink that woody encroachment represents, using a Central Texas savanna as study site, and studied how climatic factors influence this carbon sink. Woody plant encroachment, a worldwide structural change in grassland and savanna ecosystems, alters many ecosystem properties, but the net effect on the carbon balance is uncertain. Woody encroachment represents one of the key uncertainties in the US carbon balance, and demands a more detailed understanding. To come to a process-based understanding of the encroachment effect on carbon dynamics, I analyzed patterns of carbon exchange using eddy-covariance technology. I expected the imbalance between carbon uptake and release processes associated with the encroaching trees specifically, to be responsible for the carbon sink. I also expected that the sink would vary in time, due to strong links between carbon fluxes and soil water in this semi-arid ecosystem. I further studied the ecophysiology of the dominant species, as well as soil respiration processes under different vegetation types, and scaled these findings in space and time. I found that the ecosystem was a significant carbon sink of 405 g C m⁻² yr⁻¹. The encroaching trees increased photosynthesis by 180% and decreased soil respiration by 14%, compared to the grassland, resulting in a strong carbon sink due to the encroachment process. The encroaching process also altered carbon dynamics in relation to climatic drivers. The evergreen species Ashe juniper effectively lengthened the growing season and widened the temperature range over which the ecosystem acts as a carbon sink. The drought resistance of the encroaching trees reduced the sensitivity of this savanna to drought. I conclude that encroachment in Central Texas savannas increased the carbon sink strength by increasing the carbon inputs into the ecosystem. Woody encroachment also reduced the sensitivity to climatic drivers. These two effects constitute a direct effect, as well as a negative feedback to the coupled carbon-climate system. / text

Woody plant encroachment, that is, a substantial increase in the abundance of woody plants in a grassland or savanna, occurs in many parts of the world. It often has large effects on plant and animal populations and communities and on ecosystem properties and processes. However, little is known about the dynamics of woody plant encroachment and how these are affected by soils, by topography, and by the spatial pattern of the vegetation. Encroachment in turn can affect the spatial pattern of the vegetation. Using data from historical aerial photographs, I measured changes in woody plant cover and constructed, parameterized and compared a set of dynamic models of woody plant encroachment in central Texas savannas. These models predicted final woody cover from initial woody cover and the initial spatial configuration of woody plants. Then I incorporated soil and topography into these models to determine their effects. Finally, I examined the effects of encroachment on the spatial pattern of the vegetation. Incorporating negative density dependence in our models improved their fit, demonstrating that encroachment is density-dependent. A function that predicted the formation of new woody patches from a density-independent seed supply also improved the models' performance. The improvement in the models that resulted from incorporating the total length of woody-herbaceous edges confirmed that encroachment in this system occurs in part by the outward expansion of woody patches. The spatial pattern of the vegetation changed during woody plant encroachment. Spatial pattern (measured as degree of fragmentation) often had a non-linear relationship with cover. Furthermore, the spatial heterogeneity in fragmentation, that is, plot-to-plot variation in the degree of fragmentation, also changed during encroachment. Topography and soil type had, in general, little effect the dynamics of woody plant encroachment. Therefore, a relatively simple model of woody plant encroachment provided good predictions of woody cover at the end of the time periods. Other systems experiencing woody plant encroachment, forest succession, or invasion by non-native plants could be modeled using the same approach. / text

No description available.

An important basis for decisions regarding road investments is Cost Benefit Analysis (CBA), where all costs and benefits should be taken into account and expressed in monetary terms. A valuation of the cost for the encroachment caused by a new road in, for example, a recreation area or a residential area is, however, missing in road investment CBA. The purpose of this thesis is to develop approaches to deal with the encroachment costs. More specifically two approaches are developed. One approach is ”cost transfer” for typical cases. With this approach the encroachment cost is estimated ex post for a number of existing roads within each typical case. The results are to be used to estimate a calculation formula to use for CBA of planned road investments where the encroachment can be referred to a particular typical case. The typical case ”barrier to water” was chosen for a pilot study with the aim of developing the method for data collection, and study what is most important for the encroachment cost per affected individual. The other approach is a method, developed in the thesis, for estimating the encroachment cost ex ante for each specific object. The method is called COPATS, ”Combined Opinion Poll and Travel Survey”. It makes use of the fact that roads mean both positive and negative effects to a different degree for the affected people. Data of the residence location, visiting frequency in the encroachment area and travel pattern is collected by a postal questionnaire before deciding on a road investment. In the same questionnaire it is also asked whether the respondent is for or against the planned road. The encroachment cost can be estimated from the respondents´ balancing of the benefit of travel time savings, and possibly some other positive effects, against the negative encroachment caused by the planned road. A conclusion is that both alternatives seem to be possible ways of including encroachment costs as part of road investment CBA. To estimate calculation formulas for cost transfer in some common typical cases, a large number of further encroachment cost studies must though be made. COPATS is closer to practical application, but needs to be further developed in collaboration with road planners. / Ett viktigt beslutsunderlag inför väginvesteringar är cost-benefit analys (CBA), där alla kostnader och nyttor skall inkluderas och uttryckas i monetära termer. Vid CBA för väginvesteringar saknas dock värdering av kostnaden för det intrång som en ny väg orsakar, exempelvis i ett rekreationsområde eller bostadsområde. Syftet med avhandlingen är att utveckla tillvägagångssätt för hantering av intrångskostnader. Mer specifikt utvecklas två tillvägagångssätt. Det ena tillvägagångssättet kan beskrivas som en metod för ”cost transfer”. Intrångskostnaden beräknas ex post för ett antal existerande vägintrång inom varje ”typfall”. På denna grundval utarbetas en beräkningsformel som sedan kan användas vid CBA för planerade väginvesteringar där intrången kan hänföras till ett visst typfall. Typfallet ”barriär mot vatten” har valts för en pilotstudie med syftet att utveckla metodiken för datainsamling, samt undersöka vilka faktorer som har starkast påverkan på intrångskostnaden per exponerad individ. Det andra tillvägagångssättet är en i avhandlingen utvecklad metod för direkt beräkning ex ante av intrångskostnader för varje särskilt investeringsobjekt. Metoden kallas COPATS, ”Combined Opinion Poll and Travel Survey”. Den utnyttjar det faktum att vägar medför både positiva och negativa effekter i varierande grad för berörda personer. Genom en enkätundersökning före beslut om en väginvestering samlas uppgifter om bostadens läge, vistelsefrekvens vid vägsträckningen ifråga och resvanor in. I enkäten ställs också frågan om personen är för eller emot den planerade vägen. Intrångskostnaden kan sedan skattas på basis av respondenternas avvägning mellan fördelen av kortare restider samt eventuella andra positiva effekter och nackdelen av intrånget av den planerade vägen. En slutsats är att båda alternativen verkar vara framkomliga vägar för att få med intrångskostnader i CBA för väginvesteringar. För att få fram beräkningsformler för de vanligaste typfallen måste dock ett betydande antal ytterligare intrångsstudier göras. COPATS ligger närmare praktisk tillämpning, men behöver utvecklas ytterligare i samverkan med vägplaneringsansvariga.

124f. / Submitted by Oliveira Santos Dilzaná (dilznana@yahoo.com.br) on 2013-07-12T15:33:25Z No. of bitstreams: 1 cabilda de facinorosos moradores.pdf: 2195234 bytes, checksum: c1907aec3d40bf37733520d32bf4209b (MD5) / Approved for entry into archive by Ana Portela(anapoli@ufba.br) on 2013-07-15T19:23:42Z (GMT) No. of bitstreams: 1 cabilda de facinorosos moradores.pdf: 2195234 bytes, checksum: c1907aec3d40bf37733520d32bf4209b (MD5) / Made available in DSpace on 2013-07-15T19:23:42Z (GMT). No. of bitstreams: 1 cabilda de facinorosos moradores.pdf: 2195234 bytes, checksum: c1907aec3d40bf37733520d32bf4209b (MD5) Previous issue date: 2009 / O presente trabalho pretende analisar a revolta dos índios da Aldeia de Pedra Branca no ano de 1834. Situada na região do atual município de Santa Terezinha, no Centro-norte Baiano, Pedra Branca testemunhou uma insurreição realizada por seus habitantes, predominantemente kiriri-sapuiá. O significado histórico do levante, suas causas e consequências estarão em foco. Ao mesmo tempo, será dada ênfase às estratégias dos índios para resistir a um processo de usurpação das suas terras e de controle sobre os seus destinos. Disputas entre autoridades locais, num cenário de incertezas e tensões motivadas pela crise política do Período Regencial (1831-1840), deram contorno peculiar ao movimento, fornecendo as bases para que alianças fossem tecidas pelos rebelados, fato que foi decisivo para o rumo dos acontecimentos. O estudo desta revolta também é importante para mostrar a presença do índio na história do Brasil, colocando-os na condição de sujeitos históricos; This present thesis intends to analyze the uprising of Pedra Branca’s village in 1834. Placed in region of Santa Terezinha Town, in Center-north of Bahia, Pedra Branca witnessed a riot carried by its inhabitants out, predominantly Indians kiririsapuiá. The historical meaning, its causes and consequence will be in focus. At the same time, Indians’ strategies in order to resist to process of their lands’ encroachment and control of their destines will be emphasizes. Disputes involving local authorities, in scenery of uncertainties and tensions aroused by political crisis during Period of Regence (1831-1840), rendered peculiar characteristics to the movement, providing the basis for rebels to weave alliances, which were a decisive factor to the course of the events. This research is important showing the presence of Indian in Brazilian history, putting them under conditions of historical subjects. / Salvador

Pragmatic Encroachment and Epistemic Value”. Some philosopherswho defend pragmatic encroachment” and sensitive invariantism” argue thatchanges in the importance of being right and signiicant increases of the costsof error in given contexts can alter the standards of knowledge. If this view werecorrect, it could explain to some extent the practical value of knowledge. Thispaper argues that the pragmatic encroachment thesis is wrong. It discusses threepossible sources of encroachment on epistemic notions: on belief, on justiication,and on knowledge, and rejects the idea that the epistemic standards change withpractical stakes. Pragmatic factors can be relevant to the formation of belief andto the context of inquiry, although they are not relevant to epistemic evaluation.Epistemic value cannot depend upon such factors. / Algunos filósofos que defienden la intrusión pragmática y el invariantismo sensible sostienen que, en ciertos contextos, los cambios en la importancia de estar en lo cierto y los aumentos significativos de los costos del error pueden alterar los estándares del conocimiento. Si esta postura fuese correcta, podría explicar, hasta cierto punto, el valor práctico del conocimiento. El presente artículo sostiene que la tesis de la intrusión pragmática es incorrecta. Discute tres fuentes posibles de intrusión en nociones epistémicas: en la creencia, en la justificación y en el conocimiento, y rechaza la idea de que los estándares epistémicos cambian según lo que se ponga en juego a nivel práctico. Los factores pragmáticos pueden ser relevantes para la formación de creencias y para el contexto de indagación, pese a que no son relevantes para la evaluación epistémica. El valor epistémico no puede depender de tales factores.

abstract: Woody plant encroachment is a worldwide phenomenon linked to water availability in semiarid systems. Nevertheless, the implications of woody plant encroachment on the hydrologic cycle are poorly understood, especially at the catchment scale. This study takes place in a pair of small semiarid rangeland undergoing the encroachment of Prosopis velutina Woot., or velvet mesquite tree. The similarly-sized basins are in close proximity, leading to equivalent meteorological and soil conditions. One basin was treated for mesquite in 1974, while the other represents the encroachment process. A sensor network was installed to measure ecohydrological states and fluxes, including precipitation, runoff, soil moisture and evapotranspiration. Observations from June 1, 2011 through September 30, 2012 are presented to describe the seasonality and spatial variability of ecohydrological conditions during the North American Monsoon (NAM). Runoff observations are linked to historical changes in runoff production in each watershed. Observations indicate that the mesquite-treated basin generates more runoff pulses and greater runoff volume for small rainfall events, while the mesquite-encroached basin generates more runoff volume for large rainfall events. A distributed hydrologic model is applied to both basins to investigate the runoff threshold processes experienced during the NAM. Vegetation in the two basins is classified into grass, mesquite, or bare soil using high-resolution imagery. Model predictions are used to investigate the vegetation controls on soil moisture, evapotranspiration, and runoff generation. The distributed model shows that grass and mesquite sites retain the highest levels of soil moisture. The model also captures the runoff generation differences between the two watersheds that have been observed over the past decade. Generally, grass sites in the mesquite-treated basin have less plant interception and evapotranspiration, leading to higher soil moisture that supports greater runoff for small rainfall events. For large rainfall events, the mesquite-encroached basin produces greater runoff due to its higher fraction of bare soil. The results of this study show that a distributed hydrologic model can be used to explain runoff threshold processes linked to woody plant encroachment at the catchment-scale and provides useful interpretations for rangeland management in semiarid areas. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2013

Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2020 / Bush encroachment is a major problem in arid and semi-arid savannas characterized by a grass layer interspersed with a shrub stratum. Land cover change as a result of rapid proliferation of woody species in previously open rangelands alters herbaceous species and impacts soil properties. So far, little is known about the threshold at which woody plant density and cover affects herbaceous cover and the underlying mechanisms driving bush encroachment in arid and semi-arid rangelands are still debated. The objectives of this dissertation were to (1) to assess woody species composition and structure along an encroachment gradient and to explore the relationship between woody vegetation and herbaceous vegetation. (2) To determine the effect of increasing tree density and cover on grass species richness, diversity, evenness and selected soil nutrients in a bush encroached rangeland. In order to address these objectives, a semi-arid rangeland was demarcated into three encroachment gradients spanning from open to intermediate and intensive. Within each encroachment gradient six plots of 10 m x 10 m were randomly selected, whereby woody and herbaceous vegetation were assessed and soil properties determined. A discernible increase in woody species diversity and evenness was found along the transition from open to intensive bush encroached rangeland. Leguminous woody species Vachellia spp. and Dichrostachys cinerea were dominant along the bush encroachment gradient. Tree height was found to be positively correlated with long crown diameter (LCD) and short crown diameter (SCD). Furthermore, increasing tree density resulted in a 53% decline in grass species richness (GR). A decline in GR mirrored an increase in the composition of the decreaser species Panicum maximum (90%). Increasing woody plant density and cover also increased macro-nutrients; total carbon, nitrogen, phosphorus, exchangeable calcium and magnesium by 21%-159% in the shallow rangeland soils. Such quantitative information will assist rangeland managers to better understand the effects of varying bush encroachment intensities on herbaceous species composition, richness and soil properties in semi-arid savanna rangelands.

No description available.