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  • 1.
    Andersson, Lotta
    et al.
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Wilk, Julie
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Todd, Martin
    University College of London.
    Hughes, Denis
    Research Rhodes University, South Africa.
    Earle, Anton
    University of Pretoria, South Africa.
    Kniveton, Dominic
    University of Sussex, UK.
    Layberry, Russel
    University of Sussex, UK.
    Savenije, Hubert
    Delft University of Technology, Netherlands.
    Impact of climate change and development scenarios on flow patterns in the Okavango River2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 331, no 1-2, p. 43-57Article in journal (Refereed)
    Abstract [en]

    This paper lays the foundation for the use of scenario modelling as a tool for integrated water resource management in the Okavango River basin. The Pitman hydrological model is used to assess the impact of various development and climate change scenarios on downstream river flow. The simulated impact on modelled river discharge of increased water use for domestic use, livestock, and informal irrigation (proportional to expected population increase) is very limited. Implementation of all likely potential formal irrigation schemes mentioned in available reports is expected to decrease the annual flow by 2% and the minimum monthly flow by 5%. The maximum possible impact of irrigation on annual average flow is estimated as 8%, with a reduction of minimum monthly flow by 17%. Deforestation of all areas within a 1 km buffer around the rivers is estimated to increase the flow by 6%. However, construction of all potential hydropower reservoirs in the basin may change the monthly mean flow distribution dramatically, although under the assumed operational rules, the impact of the dams is only substantial during wet years. The simulated impacts of climate change are considerable larger that those of the development scenarios (with exception of the high development scenario of hydropower schemes) although the results are sensitive to the choice of GCM and the IPCC SRES greenhouse gas (GHG) emission scenarios. The annual mean water flow predictions for the period 2020-2050 averaged over scenarios from all the four GCMs used in this study are close to the present situation for both the A2 and B2 GHG scenarios. For the 2050-2080 and 2070-2099 periods the all-GCM mean shows a flow decrease of 20% (14%) and 26% (17%), respectively, for the A2 (B2) GHG scenarios. However, the uncertainty in the magnitude of simulated future changes remains high. The simulated effect of climate change on minimum monthly flow is proportionally higher than the impact on the annual mean flow. © 2006 Elsevier B.V. All rights reserved.

  • 2.
    Bodin, Hristina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Persson, Jesper
    Swedish University of Agriculture Science, Sweden .
    Englund, Jan-Eric
    Swedish University of Agriculture Science, Sweden .
    Milberg, Per
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Influence of residence time analyses on estimates of wetland hydraulics and pollutant removal2013In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 501, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Hydraulic tracer studies are frequently used to estimate wetland residence time distributions (RTDs) and ultimately pollutant removal. However, there is no consensus on how to analyse these data. We set out to (i) review the different methods used and (ii) use simulations to explore how the data analysis method influences the quantification of wetland hydraulics and pollutant removal. The results showed that the method influences the water dispersion (N) most strongly and the removal least strongly. The influence increased with decreasing effective volume ratio (e) and N, indicating a greater effect of the method in wetlands with low effective volume and high dispersion. The method of moments with RTD truncation at 3 times the theoretical residence time (t(n)) and tracer background concentration produced the most dissimilar parameters. The most similar parameters values were those for gamma modelling and the method of moments with RTD truncation at tracer background concentration. For correct removal estimates, e was more important than N. However, the results from the literature review and simulations indicated that previously published articles may contain overestimated e and underestimated N values as a result of frequent RTD truncations at 3t(n), when using the method of moments. As a result, the removal rates may also be overestimated by as much as 14% compared to other truncation methods or modelling. Thus, it is recommended that wetland hydraulic tracer studies should use the same method, specifically, RTD truncation. We conclude that the choice of tracer data analysis method can greatly influence the quantifications of wetland hydraulics and removal rate.

  • 3.
    Ghosh, Devanita
    et al.
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences. Laboratory of Integrative Taxonomy and Molecular Ecology, Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal, India.
    Routh, Joyanto
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Bhadury, Punyasloke
    Laboratory of Integrative Taxonomy and Molecular Ecology, Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal, India.
    Characterization and microbial utilization of dissolved lipid organic fraction in arsenic impacted aquifers (India)2015In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 527, p. 221-233Article in journal (Refereed)
    Abstract [en]

    The coupled role of organic matter (OM) and microbial activity is widely acknowledged in arsenic (As) biogeochemical cycling in sedimentary environments. However, little is known about OM characteristics particularly the dissolved fraction in the Bengal Delta Plain aquifers – one of the worst As impacted regions in the world. Ongoing investigations in As-rich aquifers in Nadia district (West Bengal, India) indicate presence of arsenite As(III) oxidizing bacterial communities in the Grey Sand Aquifers (GSA), but absent in Brown Sand Aquifers (BSA). In this study, we investigate the key differences in dissolved organic carbon (DOC) characteristics and its relationship with differences in elemental concentrations, distribution of biomarkers, and utilization of DOC by in situ microbial communities in BSA and GSA. We demonstrate a new approach using ENVI™ C-18 DSK discs to pre-concentrate DOC from large volumes of water, and further extract the OM and separate it into different lipid fractions using the solid phase extraction technique. The aquifers show marked heterogeneity in terms of their DOC characteristics and elemental profiles irrespective of their grey or brown color. DOC indicates variable inputs of terrestrial derived OM sources, and OM derived from decomposition and/or microbial cellular components. DOC in the aquifers consist of predominantly n-alkanoic acids (∌80%) followed by n-alkanes and n-alcohols. The GSAs indicate high iron (Fe) and manganese (Mn) concentrations, and presence of mature petroleum derived hydrocarbons in DOC. BSA has comparatively lower concentrations of Fe and Mn, and shows absence of mature hydrocarbons in DOC. Experiments in presence of indigenous bacteria from groundwater with DOC lipid extracts as the sole carbon source indicate higher growth in the GSA samples implying preferential use of DOC. The potential availability of DOC in these aquifers can influence the community composition of indigenous heterotrophic microbial flora, which in turn can affect elemental cycles including that of As.

  • 4.
    Hughes, Denis
    et al.
    Rhodes University, South Africa.
    Andersson, Lotta
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Wilk, Julie
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Savenije, Hubert
    Delft University of Technology.
    Regional calibration of the Pitman model for the Okavango River2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 331, no 1-2, p. 30-42Article in journal (Refereed)
    Abstract [en]

    This paper reports on the application of a monthly rainfall-runoff model for the Okavango River Basin. Streamflow is mainly generated in Angola where the Cuito and Cubango rivers arise. They then join and cross the Namibia/Angola border, flowing into the Okavango wetland in Botswana. The model is a modified version of the Pitman model, including more explicit ground and surface water interactions. Significant limitations in access to climatological data, and lack of sufficiently long records of observed flow for the eastern sub-basins represent great challenges to model calibration. The majority of the runoff is generated in the wetter headwater tributaries, while the lower sub-basins are dominated by channel loss processes with very little incremental flow contributions, even during wet years. The western tributaries show significantly higher seasonal variation in flow, compared to the baseflow dominated eastern tributaries: observations that are consistent with their geological differences. The basin was sub-divided into 24 sub-basins, of which 18 have gauging stations at their outlet. Satisfactory simulations were achieved with sub-basin parameter value differences that correspond to the spatial variability in basin physiographic characteristics. The limited length of historical rainfall and river discharge data over Angola precluded the use of a split sample calibration/validation test. However, satellite generated rainfall data, revised to reflect the same frequency characteristics as the historical rainfall data, were used to validate the model against the available downstream flow data during the 1990s. The overall conclusion is that the model, in spite of the limited data access, adequately represents the hydrological response of the basin and that it can be used to assess the impact of future development scenarios. © 2006 Elsevier B.V. All rights reserved.

  • 5.
    Kgathi, D.L.
    et al.
    Harry Oppenheimer Okavango Research Centre, University of Botswana, Private Bag 285, Maun, Botswana.
    Kniveton, D.
    University of Sussex, Falmer, Brighton, United Kingdom.
    Ringrose, S.
    Harry Oppenheimer Okavango Research Centre, University of Botswana, Private Bag 285, Maun, Botswana.
    Turton, A.R.
    CSIR Environmentek, P.O. Box 395, Pretoria, 0001, South Africa.
    Vanderpost, C.H.M.
    Harry Oppenheimer Okavango Research Centre, University of Botswana, Private Bag 285, Maun, Botswana.
    Lundqvist, J.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Seely, M.
    Desert Research Foundation of Namibia (DRFN), P.O. Box 2022, Windhoek, Namibia.
    The Okavango, a river supporting its people, environment and economic development2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 331, no 1-2Article in journal (Refereed)
    Abstract [en]

    The Okavango basin comprises the Cuito and Cubango active catchment areas in Angola, in addition to the Kavango-Okavango non-active catchment in northern Namibia and Botswana. The Okavango River water and its ecosystem resources are critically important sources of livelihoods for people in the basin. Pressures from livelihoods and development are already impacting on the environment. These pressures may increase in the future due to the rapid increase in population, the peace process and associated resettlement activities in Angola, and major development initiatives in Botswana and Namibia. For instance, possible future increase in water abstraction from the Okavango River may affect the long-term environmental sustainability of the Okavango Delta by minimizing channel shifting and thereby reducing spatial biodiversity. The paper argues that while conservation of the natural environment is critical, the pressing development needs must be recognized. The reduction of poverty within the basin should be addressed in order to alleviate adverse effects on the environment. The paper recommends that the development of sustainable tourism and community-based natural resource management initiatives may be appropriate strategies for reaching the Millennium Development Goals of poverty alleviation and achievement of environmental sustainability in the Okavango Basin. These initiatives have a comparative advantage in this area as demonstrated by the performance of the existing projects. © 2006 Elsevier B.V. All rights reserved.

  • 6. Stålnacke, P.
    et al.
    Grimvall, Anders
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Mathematics, Statistics .
    Libiseller, Claudia
    Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Mathematics, Statistics .
    Laznik, M.
    Kokorite, I.
    Trends in nutrient concentrations in Latvian rivers and the response to the dramatic change in agriculture2003In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 283, no 1-4, p. 184-205Article in journal (Refereed)
    Abstract [en]

    In recent years, the use of fertilisers in the Baltic countries (Estonia, Latvia, and Lithuania) has decreased at an unprecedented rate. The import of mineral fertilisers and feed stuff became almost non-existent, and extensive slaughtering of livestock reduced the amount of manure. In Latvia, the purchase of mineral fertilisers decreased by a factor of 15 between 1987 and 1996 and the number of livestock decreased with a factor of almost 4 during the same time period. Such abrupt and comprehensive changes in land use have never before occurred in the history of modern European agriculture. Here, the impact that this dramatic reduction has had on concentrations of nutrients in Latvian rivers is examined. To discern temporal changes, statistical analyses were undertaken on time series of nutrient concentrations and relationships between concentrations and runoff at 12 sampling sites in ten Latvian rivers covering drainage areas from 334 to 64,000 km2. Considering the study period 1987-1998, only four of the 12 sites showed statistically significant downward trends (one-sided test at the 5% level) in the dissolved inorganic nitrogen (DIN = NO3-N + NO2-N + NH4-N) data. There are probably two main explanations for the weak DIN trends. Firstly, long water-transit times in the soilwater and groundwater may have caused substantial time lag between changes in input and output of nitrate in the studied catchments. Secondly, the loss of DIN might have been dominated by mineralisation of large pools of organic nitrogen that have accumulated over several years. These inferences are supported by (i) a hydrograph recession analysis and (ii) indications of DIN transformation processes, presumably denitrification, in smaller streams and channels, based on measurements in small agricultural catchments (1-4 km2) in Estonia and Latvia. Formal testing of trends in phosphorus data revealed that marked drops occurred in riverine concentrations at six sites in 1987-1998. A joint analysis of concentration time series for all sampling sites for 1987-1998 showed weak statistical significance for downward trends in NH4-N, NO 3-N, and DIN (p ? 0.04) and substantial significance for PO 4-P (p < 0.01). Thus, the extensive decrease in agricultural intensity that began in the early 1990s has led to only a slow and limited (especially regarding nitrogen) response in Latvian rivers. The difference noted between nitrogen and phosphorus also suggests that factors other than reduced fertiliser application influenced the inertia of the water quality response. Our findings, along with those obtained in similar studies, show that large cuts in nutrient inputs do not necessarily cause an immediate response, particularly in medium-sized and large catchment areas.

  • 7.
    Wilk, Julie
    et al.
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Kniveton, Dominic
    Department of Physics, Chemistry and Environmental Science University of Sussex.
    Andersson, Lotta
    Linköping University, The Tema Institute, Centre for Climate Science and Policy Research . Linköping University, The Tema Institute, Department of Water and Environmental Studies.
    Layberry, Russell
    Department of Physics, Chemistry and Environmental Science University of Sussex.
    Todd, Martin
    University College of London.
    Hughes, Denis
    Institute of Water Research Rhodes University.
    Ringrose, Susan
    Harry Oppenheimer Okavango Research Centre University of Botswana.
    Vanderpost, Cornelius
    Harry Oppenheimer Okavango Research Centre University of Botswana.
    Estimating rainfall and water balance over the Okavango River Basin for hydrological applications2006In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 331, no 1-2, p. 18-29Article in journal (Refereed)
    Abstract [en]

    A historical database for use in rainfall-runoff modeling of the Okavango River Basin in Southwest Africa is presented. The work has relevance for similar data-sparse regions. The parameters of main concern are rainfall and catchment water balance, which are key variables for subsequent studies of the hydrological impacts of development and climate change. Rainfall estimates are based on a combination of in situ gauges and satellite sources. Rain gauge measurements are most extensive from 1955 to 1972, after which they are drastically reduced due to the Angolan civil war. The sensitivity of the rainfall fields to spatial interpolation techniques and the density of gauges were evaluated. Satellite based rainfall estimates for the basin are developed for the period from 1991 onwards, based on the Tropical Rainfall Measuring Mission (TRMM) and Special Sensor Microwave Imager (SSM/I) datasets. The consistency between the gauges and satellite estimates was considered. A methodology was developed to allow calibration of the rainfall-runoff hydrological model against rain gauge data from 1960 to 1972, with the prerequisite that the model should be driven by satellite derived rainfall products from 1990 onwards. With the rain gauge data, addition of a single rainfall station (Longa) in regions where stations earlier were lacking was more important than the chosen interpolation method. Comparison of satellite and gauge rainfall outside the basin indicated that the satellite overestimates rainfall by 20%. A non-linear correction was derived by fitting the rainfall frequency characteristics to those of the historical rainfall data. This satellite rainfall dataset was found satisfactory when using the Pitman rainfall-runoff model (Hughes, D., Andersson, L., Wilk, J., Savenije, H.H.G., this issue. Regional calibration of the Pitman model for the Okavango River. Journal of Hydrology). Intensive monitoring in the region is recommended to increase accuracy of the comprehensive satellite rainfall estimate calibration procedure. © 2006 Elsevier B.V. All rights reserved.

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