Browsing by Author "Wolski, P."
Now showing items 1-15 of 15
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Ramberg, L.; Lindholm, M.; Hessen, D.O.; Murray-Hudson, M.; Bonyongo, C.; Heinl, M.; Masamba, W.; Vanderpost, C.; Wolski, P. (Springer, http://www.springer.com, July 19, 2010)[more][less]
Abstract: The frequency of fires in the Okavango Delta seasonal floodplains peaked at an intermediate frequency of flooding. Floodplains are commonly burnt every 3–5 years. This study showed fundamental changes in ecosystem properties due to burning. A burnt seasonal floodplain in the aquatic phase had oxygen levels well above saturation, 100–200%, while the levels in the un-burnt control site were below saturation and, at night, could decline to 10–40% saturation. The total phosphorous and total nitrogen concentrations were similar on both floodplains but considerably enriched relative to inflowing water, due to nutrient release from the flooded soil-sediment and animal droppings. Zooplankton biomass was very high in both systems although the abundance of fish fry was ten times higher on the un-burnt floodplain. In a low flood year the un-burnt floodplain water had high nutrient levels, primary production, methane emission, and subsequent uptake of methane in biota, as well as a high zooplankton biomass. The very high flood the following year showed the opposite with much lower production at all levels owing primarily to greater dilution of nutrients. The abundance of fish, however, was much higher during the high flood year. Macrophytes and litter provide direct shelter for fish fry but also promote low oxygen levels when decaying. Large flooded areas result in high fish production by removing obstacles related to congestion. This interplay between hydroperiod and fire may be crucial for the maintenance of high biological productivity both in the aquatic and terrestrial phases in a very nutrient poor wetland landscape. Understanding these interactions is crucial for optimal management. URI: http://hdl.handle.net/10311/838 Files in this item: 1
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Wolski, P.; Masaka, T.; Raditsebe, L.; Murry-Hudson, M. (Botswana Society, NaN, 2005)[more][less]
Abstract: Seasonal changes in inundation area and peak flood occurrence in the Okavango Delta are analysed using a multiple regression technique. The multiple regression models developed constitute useful and simple tools for predicting inundation area and peak flood occurrence in the Okavango Delta. The regression model for monthly inundation area achieves a coefficient of determination of 0.80 and standard error of 538 km². Explanatory variables in the model are various expressions of long-term and short-term antecedent rainfall and inflow conditions. The model for flood peak occurrence can be used for accurate predictions only in the Jao-Boro distributary, for which it achieves a coefficient of determination of 0.85 and standard error of 15 days, with distance to Delta inlet and an expression of flood size as explanatory variables. Propagation of the flood in the two other analysed distributaries, Maunachira-Khwai and Mboroga-Santantadibe, is complex and its quantitative description appears to be beyond the capacity of a simple regression approach. Additionally, the analyses presented provide insight into the role of storage in the dynamics of flood in the system: hydrological inputs are accommodated in the large system storage, and hydrological response is strongly dependent on the factors affecting (slow!) release from that storage. Based on the analyses, the classic model of kinematic flood wave propagation has been adapted accordingly. URI: http://hdl.handle.net/10311/954 Files in this item: 1
Wolski 2005 Aspects of sea.pdf (2.080Mb) -
Characterization of arsenic occurrence in the water and sediments of the Okavango Delta, NW BotswanaHuntsman-Mapila, P.; Mapila, T.; Letshwenyo, M.; Wolski, P.; Hemond, C. (Elsevier Science B.V. Amsterdam; http://www.elsevier.com/wps/find/journaldescription.cws_home/768/description#description, NaN, 2006)[more][less]
Abstract: Detailed chemical analyses were performed on surface water, groundwater and sediment samples collected from the Okavango Delta between February and November 2003 in order to examine the distribution and geochemistry of naturally occurring As in the area. Surface water in the Okavango Delta, which is neutral to slightly acidic and has high dissolved organic C (DOC), was found to be slightly enriched in As when compared to a global value for stream water. Of the 20 new borehole analyses from this project, six were found to have values exceeding 10 ug/L. the current World Health Organization provisional guideline value for As. The results from field speciation indicate that As(III) is slightly more predominant than As(V). There is a positive correlation between As and pH and between As and DOC in the groundwater samples. For the sediment samples, there is a positive correlation between As and Co. As and Fe. As and loss on ignition (LOI) and between As and the percent fines in the sample. Reductive dissolution of oxides and hydroxides in the sediments with organic C as an electron acceptor is the likely mechanism for the release of As from the sediments into the groundwater. URI: http://hdl.handle.net/10311/135 Files in this item: 2
huntsman-mapila_app_geochem.pdf (3.170Mb)license.txt (1.998Kb) -
Mladenov, N.; McKnight, D.M.; Wolski, P.; Ramberg, L. (The Society of Wetland Scientists, NaN, 2005)[more][less]
Abstract: In the Okavango Delta in Botswana, dissolved organic matter (DOM) transport is controlled by the slow movement of an annual flood ‘pulse’ across permanently and seasonally flooded wetlands, known respectively as the Permanent Swamp and Seasonal Swamp. We studied temporal and spatial variations in fluorescence index (FI) and specific UV absorbance (SUVA) of DOM to identify DOM sources and fate during the flood. Dissolved organic carbon (DOC) concentrations ranged from 2 to 25 mg C L21 in channels of the Delta, with seasonal floodplains having consistently higher concentrations. Chemical indices, such as DOC concentrations, conductivity, specific UV absorbance (SUVA), fluorescence, total dissolved nitrogen, and chlorophyll a, were analyzed for channel and floodplain sites in the Seasonal Swamp. DOC concentrations increased during the rising limb of the flood in the Seasonal Swamp. SUVA of whole water samples and fluorescence index (FI) of fulvic acids isolated from channel and floodplain sites changed in a manner indicating the release of DOM by leaching of plant litter during the flood. After the flood receded, DOC concentrations and fulvic acid content decreased, and microbially-derived sources of organic matter dominated. Along two river reaches, measuring over 400 km each, variations in DOC concentrations were primarily due to geomorphology, with the effects of the annual flood overprinted atop the spatial controls. Increasing downstream DOC concentrations were found to be a product of inundation of DOC-rich seasonal floodplains and evaporation-enriched waters downstream. Increasing SUVA, dissolved nitrogen, and fulvic acid content, and decreasing FI downstream suggested microbial processing of terrestrial DOM and possible release of nutrients incorporated in the DOM. URI: http://hdl.handle.net/10311/526 Files in this item: 1
Mladenov2005FLOODynamics.pdf (2.529Mb) -
Gumbricht, T.; Wolski, P.; Frost, P.; McCarthy, T.S. (Elsevier http://www.doi:10.1016/j.jhydrol.2003.11.010, NaN, 2004)[more][less]
Abstract: The pristine Okavango Delta wetland of northern Botswana is potentially under threat due to water abstraction from its tributaries. We have developed a statistical model which makes it possible to predict the extent of wetland loss which will arise from water abstraction. The model also permits prediction of the maximum area of flooding, and its spatial distribution, three months in advance of the flood maximum. The model was calibrated using maximum areas of seasonal inundation extracted from satellite imagery covering the period 1985–2000, which were correlated with rainfall and total flood discharge. A technique was developed to translate the modelled flood area into a flood map. The methodology can predict maximum area of flooding and its distribution with better than 90% accuracy. An important, although relatively minor, source of error in the spatial distribution of the flood arises from a secular change in flood distribution in the distal Delta which has taken place over the last 15 years. Reconstruction of flooding history back to 1934 suggests that the Delta may be subject to a quasi 80 year climatic oscillation. If this oscillation continues, the extent of flooding will increase in the coming decades. URI: http://hdl.handle.net/10311/428 Files in this item: 1
Gumbricht_JH_2004.pdf (1.267Mb) -
Gumbricht, T.; Wolski, P.; Frost, P.; McCarthy, T.S. (Elservier, www.elsevier.com, NaN, 2004)[more][less]
Abstract: The pristine Okavango Delta wetland of northern Botswana is potentially under threat due to water abstraction from its tributaries. We have developed a statistical model which makes it possible to predict the extent of wetland loss which will arise from water abstraction. The model also permits prediction of the maximum area of flooding, and its spatial distribution, three months in advance of the flood maximum. The model was calibrated using maximum areas of seasonal inundation extracted from satellite imagery covering the period 1985-2000, which were correlated with rainfall and total flood discharge. A technique was developed to translate the modelled flood area into a flood map. The methodology can predict maximum area of flooding and its distribution with better than 90% accuracy. An important, although relatively minor, source of error in the spatial distribution of the flood arises from a secular change in flood distribution in the distal Delta which has taken place over the last 15 years. Reconstruction of flooding history back to 1934 suggests that the Delta may be subject to a quasi 80 year climatic oscillation. If this oscillation continues, the extent of flooding will increase in the coining decades. URI: http://hdl.handle.net/10311/948 Files in this item: 1
Gumbricht JOH 2004.pdf (2.449Mb) -
Bartsch, A.; Wagner, W.; Scipal, K.; Sabel, D.; Wolski, P. (Elsevier, March 17, 2008)[more][less]
Abstract: This paper elaborates on recent advances in the use of ScanSAR technologies for wetland-related research. Applications of active satellite radar systems include the monitoring of inundation dynamics as well as time series analyses of surface soil wetness. For management purposes many wetlands, especially those in dry regions, need to be monitored for short and long-term changes. Another application of these technologies is monitoring the impact of climate change in permafrost transition zones where peatlands form one of the major land cover types. Therefore, examples from boreal and subtropical environments are presented using the analysed ENVISAT ASAR Global mode (GM, 1 km resolution) data acquired in 2005 and 2006. In the case of the ENVISAT ASAR instrument, data availability of the rather coarse Global Mode depends on request priorities of other competing modes, but acquisition frequency may still be on average fortnightly to monthly depending on latitude. Peatland types covering varying permafrost regimes of the West Siberian Lowlands can be distinguished from each other and other land cover by multitemporal analyses. Up to 75% of oligotrophic bogs can be identified in the seasonal permafrost zone in both years. The high seasonal and interannual dynamics of the subtropic Okavango Delta can also be captured by GM time series. Response to increased precipitation in 2006 differsfrom flood propagation patterns. In addition, relative soil moisture maps may provide a valuable data source in order to account for external hydrological factors of such complex wetland ecosystems. URI: http://hdl.handle.net/10311/767 Files in this item: 1
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Kiker, G.; Munoz-Carpena, R.; Wolski, P.; Cathey, A.; Gaughan, A.; Kim, J. (Inderscience, http://www.inderscience.com, NaN, 2008)[more][less]
Abstract: In this paper, we present a review and conceptual design to integrate hydrological/ecological models, global uncertainty and sensitivity analysis, integrative modelling and decision analysis for complex and adaptive transboundary challenges. The research uses the transboundary issues within the Okavango River basin, a shared water resource among the nations of Angola, Namibia and Botswana, as an example for constructing these integrated tools. The objective of this paper is to present a design that integrates a set of tools that builds systematically on past basin modelling research to incorporate the inherent uncertainty within the system and its application for answering practical management questions. URI: http://hdl.handle.net/10311/864 Files in this item: 1
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Ringrose, S.; Vanderpost, C.; Matheson, W.; Wolski, P.; Huntsman-Mapila, P.; Murray-Hudson, M.; Jellema, A. (Elsevier Ltd; www.elsevier.com/locate/jaridenv, January NaN, 2007)[more][less]
Abstract: This work seeks to determine whether riparian woody plant variables respond to drying and salinity regimes in the semi-arid distal Okavango Delta, northern Botswana. Structural and compositional variables were obtained from 47 field sites. Mapping using satellite imagery illustrated differences in the character of riparian zones in terms of species composition and provided data on flood frequency. Salinity data plots show increases downstream. Results imply that woody plant variables respond to desiccation-driven change due to water-table lowering (reduced recharge) and increased salinization through distinct changes in tree and shrub height, plant density and species richness. In the wetter, intermediate distributaries, key biotic indicators of ecosystem change comprise structural variables such as decreases in canopy cover per cent and tree height and increases of shrub height, which are indicative of mainly ground-water declines. Biotic indicators in the less frequently flooded receiver channels comprise plant density and species richness increases involving mainly brackish ground-water-tolerant and dryland species which are indicative of both ground-water declines and/or salinization. These indicators could provide useful parameters for use in long- and short-term monitoring aimed at assessing desiccation-driven change in different parts of the Okavango Delta and possibly other semi-arid wetlands. The indicators are important as a less-expensive alternative to drilling as a means of verifying ground-water declines and/or salinization. URI: http://hdl.handle.net/10311/161 Files in this item: 2
license.txt (1.998Kb)Ringrose_et_al_JAE_07.pdf (1.322Mb) -
Wolski, P.; Murry-Hudson, M.; Fernkvist, P.; Liden, A.; Huntsman-Mapila, P.; Ramberg, L. (Botswana Society, NaN, 2005)[more][less]
Abstract: Groundwater under islands in the Okavango Delta is a known sink of inorganic dissolved minerals, preventing salinisation of this virtually enclosed evaporation-dominated hydrological system. The Okavango Delta is an oligotrophic, yet very productive system, and it is important to understand sources, pathways and recycling of nutrients in order to fully comprehend its ecology. In order to investigate the role of islands as nutrient sinks, concentrations of nitrogen and phosphorus, as well as major inorganic ions were measured in island and floodplain groundwater. The electrical conductivity was found to be up to 50 times higher in the island centre groundwater than in the surrounding floodplain groundwater. The amount of total phosphorus was found to be up to 400 times higher and total nitrogen up to five times higher in the interior of the island than in the surrounding floodplain. These show that major nutrients are, like other inorganic ions, accumulated under islands. Importantly, the ratio of nitrogen to phosphorus was 5:1 in floodplain water and water in island fringe soils, but 1:4 in island centres. his indicates an intensive removal of nitrogen along the floodplain-island groundwater flow path by the floodplain fringe and riparian biota, resulting in a relative enrichment in P. URI: http://hdl.handle.net/10311/950 Files in this item: 1
Wolski 2005 Islands.pdf (1.469Mb) -
Mladenov, N.; McKnight, D.M.; Wolski, P.; Murray-Hudson, M. (Elsevier, www.elsevier.com/locate/ecolmodel, NaN, 2007)[more][less]
Abstract: In order to examine dissolved organic matter (DOM) fluxes in seasonal wetland systems that expand and contract seasonally, a time-variable model of dissolved organic carbon (DOC) was developed for a seasonal floodplain in the Okavango Delta of Botswana. The model simulates DOC concentrations from March 2001 to November 2002, during which time DOC concentrations varied between 8 and 31mgCL−1. The model uses a continuously stirred tank reactor (CSTR) approach to describe the hydrologic and biogeochemical controls on DOC leached from litter within the floodplain and transported into the floodplain from upstream. In 2002, a fire burned the floodplain and less litter was available for leaching than in 2001. The model was driven by observations of discharge, water temperature, upstream DOC concentrations, and DOC leaching rates from leaching experiments. Leaching experiments with sedges and grasses indicated that on average 23mgDOCg−1 were leached during the first day ofwetting and 0.6mgDOCg−1 d−1 were continuously leached afterwards. Leaching experiments also showed a decreased amount of DOC released from burned litter and soils than from unburned litter and soils. A two-pool first-order decaymodel that represents both rapidly (0.14 d−1 (at 22 ◦C)) and slowly (0.045 d−1) decaying pools of DOC provided the best representation of observed patterns in DOC concentration in 2001. The decay rate of the first pool decreased by nearly half in 2002, when an estimated 78% of litter was removed by fire. Upstream DOC transport into the floodplain was the dominant source of DOC (representing approximately 70% and 75% of the DOC input in 2001 and 2002, respectively), followed by DOC leaching from litter and DOC originating from microbial sources. In 2001, decomposition (representing approximately 36% of the DOC loss), outflow to an adjacent floodplain (36%) and infiltration (28%) were the major removal mechanisms for DOM from the study floodplain. The large amount of DOC transported by infiltration implies storage of DOC in the subsurface, whichmay influence subsurface heterotrophic activity. In light of future climate change anticipated for the region, a scenario using a 2 ◦C increase in average water temperature and 10% reduction in upstream DOC mass was performed and resulted in significant (11%) reduction in annual DOC mass within the study floodplain. URI: http://hdl.handle.net/10311/497 Files in this item: 1
Mladenov2007Simulation.pdf (2.048Mb) -
Gieske, A.S.; Wubett, M.T.; Timmermans, W.J.; Parodi, G.N.; Wolski, P.; Arneth, A. (SPIE, http://link.aip.org, NaN, 2004)[more][less]
Abstract: Land surface temperatures are important in global change studies, in estimating radiation budget, heat balance studies and as control for climate models. Several algorithms for estimating land surface temperature and emissivity spectra for multispectral thermal infrared images were developed recently for use with data from the Advanced Spacebome Thermal Emission and Reflection Radiometer (ASTER) on the TERRA platform. Similar methods are also used with the MODIS instrument. In this study, surface temperature and broadband emissivities were determined from the five TIR channels of ASTER instrument in an area on the southern fringe of the Okavango Delta (Botswana). MODTRAN 4 was used to determine the necessary atmospheric corrections while software was developed to facilitate MODTRAN post-processing. The results were compared with micrometeorological observations from a flux tower, with a LANDSAT 7 image of the same day, and finally also with reported ASTER surface temperature and emissivities for the same image (high level ASTER product). Results indicate that the surface temperature depends rather sensitively on atmospheric transmissivity and relatively large temperature differences are found between results from imagery analysis and flux tower. No relation was found between broad-band emissivity and NDVI, contrary to earlier findings in Botswana. URI: http://hdl.handle.net/10311/1015 Files in this item: 1
gieske_procSPIE_2003_pw.pdf (317.2Kb) -
Mitsch, W.J.; Nahlik, A.; Wolski, P.; Bernal, B.; Zhang, L.; Ramberg, L. (Springer, http://www.springer.com, NaN, 2010)[more][less]
Abstract: This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m−2 year−1 in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m−2 year−1 over the same period. Methane emissions averaged 1,080 mg-C m−2 day−1 in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m−2 day−1). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly. Description: Some symbols may not come as they are in the abstract. URI: http://hdl.handle.net/10311/832 Files in this item: 1
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Ringrose, S.; Matheson, W.; Wolski, P.; Huntsman-Mapila, P. (Elsevier; www.elsevier.com/locate/jaridenv, NaN, 2003)[more][less]
Abstract: Vegetative response aspects of climate change studies include the determination of vegetation cover changes across climatic gradients. Vegetation characteristics and soil moisture measurements were obtained from four locations with decreasing rainfall along the Botswana Kalahari transect. These are referred to as Pandamatenga, (698mmyear_1), Maun (460 mmyear_1), Okwa (407 mmyear_1) and Tshane (365 mmyear_1). Trends in major vegetative cover and soil components included species types and richness assessments which reflected certain changes southward but also showed interesting degrees of variability. This occurred despite the apparent homogeneity of the Kalahari sands and predominantly semi-arid savanna shrubâ woodland vegetation cover. Despite linear decreases, both in rainfall and soil moisture content, results indicated high soil moisture variability at the Okwa location which relates to unique climatic and geological factors. Also many species are unique to specific locations for instance Pandametanga is characterized by Zambesian species while the Maun location is characterized by Colophosphermum mopane. This changes southwards as Acacias become more dominant and significantly co-occur with Grewia flava. While the average total numbers of plants decreased, total numbers of different species varied little from the wetter to the drier end of the moisture gradient. The association between rainfall and woody cover is negative implying that canopy cover extents (in terms of vegetation density) increase along the gradient due to increases in bush encroachment in drier areas. Therefore, while representing a continuum in terms of species numbers, in other respects (e.g. species types and ground cover components) vegetation zones in the Kalahari may be regarded as discontinuous units. Differences between mapped vegetation zones may be accounted for in terms of relatively unique ecosystem factors which function partly in response to geological conditions and partly in response to local (as opposed to regional) climatic factors. This appears to have led to ecosystem adaptive measures (in terms of species responses) rarely mirrored elsewhere along the gradient. Hence adaptability in terms of species migrations in response to relatively rapid climate changes may not readily take place over the Kalahari in Botswana. URI: http://hdl.handle.net/10311/175 Files in this item: 2
license.txt (1.998Kb)ringrose_jae_2003.pdf (3.823Mb) -
Andersson, L.; Gumbricht, T.; Hughes, D.; Kniveton, D.; Ringrose, S.; Savenije, H.; Todd, M.; Wilk, J.; Wolski, P. (Elsvier, www.elsevier.com, September 8, 2003)[more][less]
Abstract: As part of the EU-funded project ‘Water and Ecosystem Resources in Regional Development––Balancing Societal Needs and Wants and Natural Resources Systems Sustainability in International River Basin Systems’ (WERRD) (www.okavangochallenge.com), work is carried out aiming to improve and develop scientific methods that will facilitate the understanding of fluctuations of hydrological and ecosystem variables and likely human-induced trends concerning key characteristics of the Okavango River Basin in Southern Africa. URI: http://hdl.handle.net/10311/980 Files in this item: 1
Andersson_PhysChemEarth_2003_Pw.pdf (1.840Mb)
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