Showing papers in "Physics and Chemistry of The Earth in 2005"

Isocon analysis: A brief review of the method and applications

Abstract: Isocon analysis [Grant, J.A., 1986. The isocon diagram—a simple solution to Gresens’ equation for metasomatic alteration. Economic Geology 81, 1976–1982.] is a simple and effective means of quantitatively estimating changes in mass or volume or concentrations in mass transfer. It may be accomplished graphically by plotting an altered composition against an original composition with no significant manipulation of the data. Species that have remained immobile in the process define the isocon, which is a straight line through the origin. The paper reviews suggested means of identifying immobile species, graphical, statistical or by computation, and suggests that whatever the means, the geochemical characteristics of the species and of the process should be considered. It is shown that scaling of data need not affect the choice of immobile species or the slope of the isocon. Applications of the method to hydrothermal alteration, replacement, migmatites, shear zones, paleosols, silcretes, sedimentary exhalative deposits and fumarolic deposits are briefly reviewed.

Estimation of small reservoir storage capacities in a semi-arid environment: A case study in the Upper East Region of Ghana

Abstract: In semi-arid regions at the margins of the Sahel, large numbers of small reservoirs capture surface runoff during the rainy season, making water available during the dry season. For the local population, small reservoirs are important water sources which help them cope with droughts. The lack of knowledge of the number of existing reservoirs, their distribution, and their storage volumes hinders efficient water management and reservoir planning. The authors have developed a simple method that allows the estimation of reservoir storage volumes as a function of their surface areas. This function is based on an extensive bathymetrical survey that was conducted in the Upper East Region of Ghana. In combination with satellite imagery, this function can be used determine and monitor the storage volumes of large numbers of small reservoirs on a regional scale.

Sensitivity analysis for hydrology and pesticide supply towards the river in SWAT

Abstract: The dynamic behaviour of pesticides in river systems strongly depends on varying climatological conditions and agricultural management practices. To describe this behaviour at the river-basin scale, integrated hydrological and water quality models are needed. A crucial step in understanding the various processes determining pesticide fate is to perform a sensitivity analysis. Sensitivity analysis for hydrology and pesticide supply in SWAT (Soil and Water Assessment Tool) will provide useful support for the development of a reliable hydrological model and will give insight in which parameters are most sensitive concerning pesticide supply towards rivers. The study was performed on the Nil catchment in Belgium. In this study we utilised an LH-OAT sensitivity analysis. The LH-OAT method combines the One-factor-At-a-Time (OAT) design and Latin Hypercube (LH) sampling by taking the Latin Hypercube samples as initial points for an OAT design. By means of the LH-OAT sensitivity analysis, the dominant hydrological parameters were determined and a reduction of the number of model parameters was performed. Dominant hydrological parameters were the curve number (CN2), the surface runoff lag (surlag), the recharge to deep aquifer (rchrg_dp) and the threshold depth of water in the shallow aquifer (GWQMN). Next, the selected parameters were estimated by manual calibration. Hereby, the Nash–Sutcliffe coefficient of efficiency improved from an initial value of −22.4 to +0.53. In the second part, sensitivity analyses were performed to provide insight in which parameters or model inputs contribute most to variance in pesticide output. The results of this study show that for the Nil catchment, hydrologic parameters are dominant in controlling pesticide predictions. The other parameter that affects pesticide concentrations in surface water is ‘apfp_pest’, which meaning was changed into a parameter that controls direct losses to the river system (e.g., through the clean up of spray equipment, leaking tools, processing of spray waste on paved surfaces). As a consequence, it is of utmost importance that hydrology is well calibrated while––in this case––a correct estimation of the direct losses is of importance as well. Besides, a study of only the pesticide related parameters, i.e. application rate (kg/ha), application time (day), etc., reveals that the application time has much more impact than the application rate, which has itself a higher impact than errors in the daily rainfall observations.

Mental model mapping as a new tool to analyse the use of information in decision-making in integrated water management

Abstract: The solution of complex, unstructured problems is faced with policy controversy and dispute, unused and misused knowledge, project delay and failure, and decline of public trust in governmental decisions. Mental model mapping (also called concept mapping) is a technique to analyse these difficulties on a fundamental cognitive level, which can reveal experiences, perceptions, assumptions, knowledge and subjective beliefs of stakeholders, experts and other actors, and can stimulate communication and learning. This article presents the theoretical framework from which the use of mental model mapping techniques to analyse this type of problems emerges as a promising technique. The framework consists of the problem solving or policy design cycle, the knowledge production or modelling cycle, and the (computer) model as interface between the cycles. Literature attributes difficulties in the decision-making process to communication gaps between decision makers, stakeholders and scientists, and to the construction of knowledge within different paradigm groups that leads to different interpretation of the problem situation. Analysis of the decision-making process literature indicates that choices, which are made in all steps of the problem solving cycle, are based on an individual decision maker’s frame of perception. This frame, in turn, depends on the mental model residing in the mind of the individual. Thus we identify three levels of awareness on which the decision process can be analysed. This research focuses on the third level. Mental models can be elicited using mapping techniques. In this way, analysing an individual’s mental model can shed light on decision-making problems. The steps of the knowledge production cycle are, in the same manner, ultimately driven by the mental models of the scientist in a specific discipline. Remnants of this mental model can be found in the resulting computer model. The characteristics of unstructured problems (complexity, uncertainty and disagreement) can be positioned in the framework, as can the communities of knowledge construction and valuation involved in the solution of these problems (core science, applied science, and professional consultancy, and “post-normal” science). Mental model maps, this research hypothesises, are suitable to analyse the above aspects of the problem. This hypothesis is tested for the case of the Zwolle storm surch barrier. Analysis can aid integration between disciplines, participation of public stakeholders, and can stimulate learning processes. Mental model mapping is recommended to visualise the use of knowledge, to analyse difficulties in problem solving process, and to aid information transfer and communication. Mental model mapping help scientists to shape their new, post-normal responsibilities in a manner that complies with integrity when dealing with unstructured problems in complex, multifunctional systems.

Indigenous knowledge as decision support tool in rainwater harvesting

Abstract: Rainfall patterns in semi-arid areas are typically highly variable, both spatially and temporally. As a result, people who rely completely on rainwater for their survival have over the centuries developed indigenous knowledge/techniques to harvest rainwater. These traditional water-harvesting systems have been sustainable for centuries. The reason for this is that they are compatible with local lifestyles, local institutional patterns and local social systems. In order to develop sustainable strategies, it is therefore important to take into account of, and learn from, what local people already know and do, and to build on this. This paper explores how indigenous knowledge is used by farmers in the Makanya catchment, Kilimanjaro region, Tanzania to identify potential sites for rainwater harvesting (RWH). The paper draws on participatory research methods including focus group discussions, key informant interviews, field visits and participatory workshops. Initial findings indicate that farmers do hold a substantial amount of knowledge about the resources around them. As there are spatially typical aspects to indigenous knowledge, it could be extrapolated over a wider geographic extent. From the preliminary findings, it is being recommended that geographic information system (GIS) could be an important tool to collect and upscale the utility of diverse indigenous knowledge in the decision-making process.

Water demand management: A case study of the Heihe River Basin in China

Abstract: The study investigates the water supply and demand situation in the Heihe River Basin, China, and formulates a demand oriented water management approach in the irrigated agricultural sector in response to the increasing water shortage due to population growth and local economic development. This approach requires institutional reinforcement, water pricing reform and agricultural sector adjustment based on a virtual water trade analysis. It is also proposed to use a river basin water balance model for the water management authority to support decision-making. The paper reviews both technical and non-technical measures proposed for the Heihe River Basin management and concludes that with the growing water demand, the water authority can’t continue to supply the water without trying to actually influence the demand. Besides technical measures, e.g., through water saving measures and reservoir building, demand management has to come into force as an important part of integrated river basin management, so as to ensure the sustainable development of the Heihe River Basin.

Integrated Water Resources Management: Relevant concept or irrelevant buzzword? A capacity building and research agenda for Southern Africa

Abstract: This article examines the concept ‘Integrated Water Resources Management’ (IWRM) and inquires as to its relevance for the Southern African region. The paper first acknowledges the contributions made to IWRM by three regional initiatives—WaterNet, the Water Research Fund for Southern Africa (WARFSA), and the Southern African chapter of the Global Water Partnership. Then, three important aspects of IWRM are highlighted: that IWRM requires institutional capacity to integrate, which often is a scarce resource; that IWRM is neither solution nor recipe, but rather a perspective or way of looking at problems with a view to solving them through transparent and inclusive decision-making processes; and that IWRM should explicitly deal with the fact that water tends to build asymmetrical relationships between people, communities and nations. An IWRM agenda is subsequently set out, focussing on five critical issues: the dilemma between economic development and sustainability; the unresolved issue of water as an economic good; the place and role of rainfed farmers in IWRM; the importance of training and teaching; and the need for building reflexive capacity in the new and existing water institutions. The paper concludes that IWRM is a relevant, yet elusive and fuzzy concept. Evidence from Southern Africa and around the world shows that IWRM inspires a new generation of water managers and researchers to act creatively; assists in addressing the Millennium Development Goals (MDGs); and instils mutual respect, understanding and co-operation among water professionals in Southern Africa.

Livelihoods in the wetlands of Kilombero Valley in Tanzania: Opportunities and challenges to integrated water resource management

Abstract: You can egt full text in the following link http://www.sciencedirect.com/science/article/pii/S1474706505001154

Mobility of high field strength elements (HFSE) in magmatic-, metamorphic-, and submarine-hydrothermal systems

Abstract: High field strength elements (HFSE) are normally considered as ‘conservative’ elements in most geological settings. However, field and experimental evidence has suggested that these elements are actually mobile in some cases and can be transported by magmatic-, metamorphic-, and submarine-hydrothermal solutions, in particular in those extreme cases such as highly altered hydrothermal ore deposits and highly evolved products of crystal fractionation such as pegmatites or granitic bodies bordering to metamorphic rocks. In this paper, we combine our own data with those from the literature and focus our discussion on HFSE mobility at crustal fluid systems. We suggest that the mobility of HFSE is controlled by a number of factors, including P–T conditions, pH, and solution chemistry. The HFSE mobility can occur in a wide range of P–T conditions, and their solubility is generally enhanced at high pH conditions. The high F contents in the fluids also largely enhance the mobility of HFSE. The mobility of HFSE and formation of hydrothermal minerals such as zircon and titanite offer us a useful tool to directly date related hydrothermal events by U–Pb methods, which otherwise lack suitable minerals for isotope dating.

Application of the SWAT model on the Medjerda river basin (Tunisia)

Abstract: The Medjerda river basin (Northern Tunisia) is experiencing an intensification of agriculture and the irrigated area is increasing rapidly. The SWAT (Soil and Water Assessment Tool) model, a soil, water, sediment, and nutrient transformation and fate simulator for agricultural watersheds, was applied to this catchment to study the potential impact of land management scenarios. The model was able to represent the hydrological cycle even though some discrepancies were observed, probably due to a lack of sufficient rainfall data, and due to the lack of representation of reservoirs. It was predicted that converting all agricultural land to irrigated crop introduced significant changes on nitrate concentration in surface water. However, the concentration was still below the limit of potability. It was also predicted that drastic reduction in the load of ammonium and phosphorus could be achieved by collecting and treating wastewater from major urban areas.

Political challenges to implementing IWRM in Southern Africa

Abstract: Southern African states are undertaking comprehensive water sector reforms. While motives for reform are partially local, they are in large part driven by the interests and ideologies of Western states and civil societies. Within the Southern African Development Community (SADC), national (water, sanitation, irrigation) master plans are being written or revised. In several states, new Water Acts are in place and new institutions have been created to improve delivery. The stated goal of these activities is integrated water resources management (IWRM) defined simply as equitable, efficient and sustainable use of the resource. This article summarizes findings of social science-oriented scholarship on water management in the region, in particular that published in three special issues of Physics and Chemistry of the Earth (vol. 27, nos. 11–22; vol. 28, nos. 20–27; vol. 29, nos. 15–18). Evidence shows, among other things, that governments have been reluctant to devolve power to stakeholders; that rural dwellers are suspicious of the motives behind reform; that already empowered actors dominate new institutions touting broad-based participation; that efforts to fully recover costs in urban areas have been met with widespread civil resistance; and that new institutions have undermined existing forms of cooperation and conflict resolution, making matters worse not better. At the same time, these studies show the utility of decision support tools, capacity building exercises and research and knowledge production—all positive outcomes that should not be discounted. The paper argues that difficulties with reform reflect the highly political nature of the undertaking. Specifically, the new water architecture proposes a profound realignment of decision making power in already fragile, underdeveloped states. As a result, what may have started as a project now constitutes a context wherein differently empowered actors negotiate and renegotiate roles and rights to resources. Thus, to achieve sustainable, equitable and efficient water use in the Southern African region, it is important to reflect on the political nature of these activities and to reconsider (and be prepared to revise or discard) the basic assumptions and ideologies driving the reform process.

Nitrogen transformation in horizontal subsurface flow constructed wetlands I: Model development

Abstract: In this paper a mathematical model for prediction of nitrogen transformation in horizontal subsurface flow constructed wetlands was developed. Two horizontal subsurface flow constructed wetlands were designed to receive organic loading rate below 50 kg/ha/d and hydraulic loading rate of 480 m 3 /ha/d from a primary facultative pond. Two rectangular shaped units each 11.0 m long, 3.7 m wide and 1.0 m deep and bottom slope of 1% were constructed and filled with 6–25 mm diameter gravel pack to a depth of 0.75 m. Each unit was planted with Phragmites mauritianus with an initial plant density of 29,000 plants/ha. The plants were allowed to grow for about four months before sampling for water quality parameters commenced. Samples were collected daily for about three months. Dissolved oxygen, pH and temperature were measured in situ and ammonia, total Kjeldahl nitrogen, nitrates, nitrite and Chemical Oxygen Demand were measured in the laboratory in accordance with Standard Methods. The mathematical model took into account activities of biomass suspended in the water body and biofilm on aggregates and plant roots. The state variables modelled include organic, ammonia, and nitrate–nitrogen, which were sectored in water, plant and aggregates. The major nitrogen transformation processes considered in this study were mineralization, nitrification, denitrification, plant uptake, plant decaying, and sedimentation. The forcing functions, which were considered in the model, are temperature, pH and dissolved oxygen. Stella II software was used to simulate the nitrogen processes influencing the removal of nitrogen in the constructed wetland. One of the two-wetland units was used for model calibration and the second unit for model validation. The model results indicated that 0.872 gN/m 2 d was settled at the bottom of the wetland and on gravel bed and roots of the plants. However, 0.752 gN/m 2 d (86.2%) of the settled nitrogen was regenerated back to the water body, which means that only 13.8% of the settled nitrogen was permanently removed. Denitrification and nitrification were responsible for transformation of 0.436 gN/m 2 d and 0.425 gN/m 2 d, respectively. Uptake of nitrogen by plants was 0.297 gN/m 2 d out of which 0.140 gN/m 2 d was returned to the water body as plants decay. It was found that the major pathways leading to permanent removal of nitrogen in a horizontal subsurface flow constructed wetland system in descending order are denitrification (29.9%), plant uptake (10.2%) and net sedimentation (8.2%). A total nitrogen removal of 48.9% was achieved in this study.

Assessing the effects of land use change on soil physical properties and hydrological processes in the sub-humid tropical environment of West Africa

Abstract: Land use is a key parameter in the hydrologic cycle. Tropical Africa is affected by intense land use change since decades, particularly deforestation and conversion to agricultural land. The aim of this study is to analyse the effects of land use change on the hydrologic processes and soil physical properties in a small catchment (Aguima catchment) in central Benin. Results from pedological, pedobiological and hydrological investigations within the Aguima catchment were taken into account. The effects of land use change on hydrologic processes were analysed by comparing two sub-catchments of the Aguima catchment with different land use (savannah/forest and agricultural land use). The study is part of the GLOWA IMPETUS project, which examines the effects of global change on the water cycle and water availability on a regional scale in Morocco and Benin. The investigations of this study revealed that due to reduced activity of the macrofauna the infiltration capacity is significantly lower in cultivated soils than in savannah and forest. This causes higher surface runoff and soil loss rates, which was also determined on erosion plots. The increased soil loss on fields has effects on soil physical properties like increase of gravel content and reduction of field capacity. The impact of reduced vegetation cover on the soil water dynamics was examined with soil moisture measurements on different land use. Due to higher evapotranspiration and water withdrawal the soil water content on forest and savannah plots was lower than on agricultural fields. The difference in the water yield of the forested and cultivated catchments was over 120 mm in the dry year 2001 and about 70 mm in the wetter year 2002.

Using ASTER remote sensing data set for geological mapping, in Namibia

Abstract: The present study deals with the estimation of the advanced spaceborne thermal emission and reflection radiometer (ASTER) data for geological application. Visible, near-infrared and short wave infrared reflectance data (9 ASTER bands) have been processed and interpreted in framework of a mapping project concerning the western margin of the Kalahari desert. A methodology has been applied to apparent reflectance images corrected to illumination effects. A Principal Component Analysis (PCA) has been realised on the 9 ASTER bands in order to reduce the redundancy information in highly correlated bands. PCA results enable the validation and the revision of the lithological boundaries defined on previous geological map and provide information for characterising new lithological units corresponding to surficial formations previously unrecognised. A supervised classification realised from PCA results and based on the geological map shows that lithological units may have similar spectral signature, a strong spectral variability or a spectral homogeneity. The processing of ASTER remote sensing data set can thus be used as a powerful tool for geological mapping

Contemporary “green” water flows: Simulations with a dynamic global vegetation and water balance model

Abstract: “Green water”—the water stored in the soil and productively used for plant transpiration—is an important quantity particularly in rainfed agriculture (in contrast to “blue water” available in streams and lakes, on which irrigation relies). This study provides preliminary estimates of contemporary (1961–1990) global green water flows (i.e. plant transpiration), using a well-established, process-based dynamic global vegetation and water balance model, LPJ. Transpiration is analysed with respect to differences between a simulation that accounts for human land cover changes and a simulation under conditions of potential natural vegetation. We found that historic land cover change usually reduced the green water flow to the atmosphere, resulting in a global decrease of ∼7% in total. To further explore how the biophysical setting influences the green water flow, we analyse the ratio between soil moisture-limited canopy conductance of carbon and water and energy-controlled potential conductance. This plant physiology-based ratio measures the degree to which actual green water flow falls below the potential flow that would occur when the soil is saturated, thus it represents a measure of the water limitation of terrestrial vegetation. We found that plant water limitation is lowest in the wet tropics and at high latitudes, where soil moisture is high enough to meet the atmospheric demand for transpiration. The present results are preliminary, since irrigation is not yet accounted for, and because the model simulations are compromised primarily by the quality of the input data. A more comprehensive and consistent assessment of global green and blue water flows and limitations using an enhanced LPJ model is identified as a prime task for future studies.

On farm evaluation of the effect of low cost drip irrigation on water and crop productivity compared to conventional surface irrigation system

Abstract: This on-farm research study was carried out at Zholube irrigation scheme in a semi-arid agro tropical climate of Zimbabwe to determine how low cost drip irrigation technologies compare with conventional surface irrigation systems in terms of water and crop productivity. A total of nine farmers who were practicing surface irrigation were chosen to participate in the study. The vegetable English giant rape ( Brassica napus ) was grown under the two irrigation systems with three fertilizer treatments in each system: ordinary granular fertilizer, liquid fertilizer (fertigation) and the last treatment with no fertilizer. These trials were replicated three times in a randomized block design. Biometric parameters of leaf area index (LAI) and fresh weight of the produce, water use efficiency (WUE) were used to compare the performance of the two irrigation systems. A water balance of the inflows and outflows was kept for analysis of WUE. The economic profitability and the operation, maintenance and management requirements of the different systems were also evaluated. There was no significant difference in vegetable yield between the irrigation systems at 8.5 ton/ha for drip compared to 7.8 ton/ha in surface irrigation. There were significant increases in yields due to use of fertilizers. Drip irrigation used about 35% of the water used by the surface irrigation systems thus giving much higher water use efficiencies. The leaf area indices were comparable in both systems with the same fertilizer treatment ranging between 0.05 for surface without fertilizer to 6.8 for low cost drip with fertigation. Low cost drip systems did not reflect any labour saving especially when manually lifting the water into the drum compared to the use of siphons in surface irrigation systems. The gross margin level for surface irrigation was lower than for low cost drip irrigation but the gross margin to total variable cost ratio was higher in surface irrigation systems, which meant that surface irrigation systems gave higher returns per variable costs incurred. It was concluded that low cost drip systems achieved water saving of more than 50% compared to surface irrigation systems and that it was not the type of irrigation system that influenced the yield of vegetables significantly but instead it is the type of fertilizer application method that contribute to the increase in the yield of vegetables. It was recommended that low cost technologies should be used in conjunction with good water and nutrient management if higher water and crop productivity are to be realized than surface irrigation systems.

Active biomonitoring in freshwater environments: early warning signals from biomarkers in assessing biological effects of diffuse sources of pollutants

Abstract: Effluents are a main source of direct and continuous input of pollutants in aquatic ecosystems. Relating observed effects to specific pollutants or even classes of pollutants remains a very difficult task due to the usually unknown, complex and often highly variable composition of effluents. It is recognized that toxicants interfere with organism integrity at the biochemical level and give rise to effects at the individual level and is manifested in reduced ecologically relevant characteristics such as growth, reproduction and survival, and ultimately at the ecosystem level. By integrating multiple endpoints at different ecologically relevant levels of organization within one test organism, it should be possible to gain understanding in how different levels of organization within this organism respond to toxic exposure and how responses at these different levels are interrelated. This paper presents results from a field study in the Rietvlei Wetland system, Gauteng, South Africa using the freshwater mollusk (Melanoides tuberculata) and freshwater fish (Oreochromis mossambicus) as bioindicator organisms. Active biomonitoring (ABM) exposures were conducted where organisms were exposed for 28 days in an effluent dominated river during high flow conditions in April 2003. The river receives effluent from a wastewater treatment plant and an industrial complex, so that up to 75% of the total flow of the river is effluent-based. Effects of field exposure were determined using cellular biomarkers e.g. DNA damage, HSP 70, metallothionein, acetylcholine esterase, lactate dehydrogenase and ethoxyresorufin-odeethylase activity. The results clearly indicate that although the traditional mortality-based whole effluent toxicity testing did not indicate any toxicity, the in situ exposed organisms were stressed. A multivariate statistical approach was particularly useful for integrating the biomarker responses and highlighting sites at which more detailed analysis of chemical contamination would be useful. Based on the individual biomarker results contributing towards the distinct groupings it is possible to conclude that Site 1 is subjected to organic pollutants, whereas Sites 2 and 3 undergo a combination of metallic and organic pollutant stress. However, it is essential that a rapid and sensitive biomarker that is representative of the responses of a suite of biomarkers be tested before ABM can be implemented as a routine biomonitoring practice in water resource management. � 2005 Elsevier Ltd. All rights reserved.

Adaptation strategies to climate change and climate variability: A comparative study between seven contrasting river basins

Abstract: Adaptation strategies to climate change and climate variability to enhance food quantity and security and environmental quality and security have been explored for seven contrasting basins in the context of the ADAPT project. For the seven basins as much as possible established modeling frameworks were used, where the focus was on the linkage between field scale models to explore farm scale water management and basin scale models dealing with water resources issues. Climate change projections were scaled to local conditions where the HadCM3 and the ECHAM4 General Circulation Models as well as the seven basins required different adjust- ment factors in this downscaling. For the seven basins selected, impacts and adaptation strategies at field scale indicated that overall food production will increase in the future as a result of enhanced CO2 levels, but that variation in yields will increase too. Linking this to the basin scale and including also environment focused adaptation strategies showed for the one example basin presented here, Walawe in Sri Lanka, that food security was more difficult to maintain than total food production and that environmental quality can be maintained by selecting the appropriate adaptation strategies. Results from the relatively complex modeling frame- work were converted to easily understandable graphs that have been used in discussions regarding adaptation strategies with various stakeholders.

Hydro-economic evaluation of rainwater harvesting and management technologies: Farmers’ investment options and risks in semi-arid Laikipia district of Kenya

Abstract: Smallholder farmers in Laikipia district of Kenya, like their counterparts in water scarce semi-arid environments, are facing the challenge of improving agricultural productivity and livelihoods. A number of viable options are available, but high hydrological risks and low economic capability are discouraging the poor and risk-averse farmers. Rainwater harvesting and management (RHM) is one of the promising options, whose impacts are unfortunately also affected by hydrological risks related to unreliable rainfall. The paper presents a hydro-economic analysis of RHM systems with the aim of analyzing some of the factors that affect their adoption by smallholder farmers. Hydro-economic analysis included hydrological reliability of RHM systems, agro-hydrological risks and economic analysis. Agro-hydrological risk focused on dry spell and drought analysis, which affect soil moisture availability and hence crop production. Hydrological reliability assessed the ability of a RHM system to harvest and store adequate runoff to meet supplemental irrigation requirement to bridge dry spells and mitigate the impacts of persistent droughts. Economic analysis addressed benefit-cost analysis and profitability of RHM in terms of increasing crop production and stabilizing yields. The study was conducted in Kalalu and Matanya , which are in two different agro-climatic zones and represent land-use changes in the recently settled areas of Laikipia district. The results provide a basis for farmers to make informed decisions on agricultural investments under hydrologic risks and uncertain production systems. RHM systems for supplemental irrigation were found to be an economically viable option for improving agricultural production and livelihoods of smallholder farmers in drought prone rural areas.

Effects of land-use changes on the hydrologic response of reclamation systems

Abstract: Our study investigates the possible effects of recent land-use changes on the frequency regime of floods for reclaimed lands. We modelled the runoff concentration behaviour of a reclaimed area of 76 km 2 , located in the Po River plain near the city of Bologna (northern Italy), through the combined application of a semi-distributed rainfall-runoff model, which captures the key features of surface and sub-surface flows, and a hydrodynamic streamflow routing model. Three land use data from 1955, 1980 and 1992 were available. We implemented the rainfall-runoff model to the three land-use scenarios and analysed the hydrological–hydraulic behaviour of the study area for numerous rainfall events associated with different recurrence interval. The results of our study show a rather significant sensitivity of the flood frequency regime of the reclaimed land to land-use changes, and the sensitivity tends to increase as the recurrence interval of the rainfall event decreases.

An assessment of the effect of human faeces and urine on maize production and water productivity

Abstract: The key challenge facing many catchment authorities in Zimbabwe and elsewhere is the challenge of feeding the growing populations within their catchment boundaries. Modern agricultural practices continue to mine valuable crop nutrients through increased food production to satisfy ever-increasing food demand. In recent diagnostic survey of smallholder agricultural sector in the Manyame catchments of Zimbabwe it was revealed that exhausted soils depleted of their natural mineral and organic constituents by many years of cropping with little fertilization or manuring were the major factors contributing to low yields and poor food security in this sector in Zimbabwe. The objective of the study was to assess the effect of using sanitized human excreta on maize production and water productivity. The study involved six volunteer farmers with four 10 m × 10 m trial plots each with the following treatments the control, commercial fertilizer treatment urine only plot, and the feacal matter and urine plot. Harvest determination was carried by weighing the yield from each of the treatment plots and comparisons done. Water productivity was computed by calculating the amount of water used to produce a tone of maize per ha. The study showed that human excreta improves maize crop production and water productivity in rain-fed agriculture. The study recommends that the ecological sanitation concept and the reuse of human excreta both humanure and (ecofert) urine can be considered as alternative excreta management options in catchment areas.

Hydrological and ecological impacts of dams on the Kafue Flats floodplain system, southern Zambia

Abstract: Developmental changes in river basins in Africa have become a reality. Many wetland ecosystems have been impacted by dams and other hydrological interventions resulting in both foreseen and unexpected consequences. The Kafue Flats in southern Zambia is an extensive floodplain system that lies within the middle Kafue river basin. The floodplain is about 255 kin long and 60 km wide, covering an area of approximately 6,500 km(2). It is currently sandwiched between two large dams which are approximately 270 km apart. These dams have completely altered the hydrological regime of the system. Backwater from the downstream dam and releases from upstream have created a permanently flooded area within the floodplain that was not present in the past. Elsewhere, flooding has been reduced. The ecological consequences of these changes for the floodplain, which hosts two national parks (both Ramsar sites), have been extensive. Hydrological and vegetation changes have impacted the habitat for important wildlife communities including the endemic antelope, Kobus leche kafuensis. The most dramatic change in vegetation is associated with the colonisation of parts of the floodplain by the invasive alien plant, Mimosa pigra. This paper discusses these changes and their potential consequences. (c) 2005 Elsevier Ltd. All rights reserved.

Palmer drought severity index as soil moisture indicator: physical interpretation, statistical behaviour and relation to global climate

Abstract: Palmer Drought Severity Index (PDSI) series, based on monthly homogenised temperature and precipitation data, are analysed for the 1901–1999 period at three stations in West-Hungary, i.e. in an objectively separating region of the country, concerning spatial variations of the monthly PDSI fluctuations. All displayed results represent computations by the Thorthwaite-type potential evapotranspiration. Some comparison with those index-series, computed by the Blaney–Criddle method is given in the Discussion. Series of PDSI exhibit strong correlation with series of two independent soil moisture estimations. Having the regression coefficient standardised by standard deviation of the soil-moisture, we obtain similar coefficients during the year (allowing for only 10–30% difference). This means, PDSI can be considered as a soil-moisture indicator. It is shown that the monthly standard deviation of PDSI exhibit small variation, ca. 10%, with a minimum in the summer period. Distribution of monthly PDSI can be considered as Gaussian, according to the Kolmogorov–Smirnoff test, whereas according to the χ2-test this is true for more than 2/3 of the cases. Exceptions all fall in the second half of the year. Finally, multi-annual relation of PDSI to the global temperature trends are analysed using the method of “slices” (Mika, 1988), dividing the local and global values into uniform time sequences, the so called time-slices and calculating regression coefficients between the local PDSI and two hemispherical temperature variables. One of the latter is the hemispherical mean, the other is the continent–ocean air temperature contrast. This correlation is always negative and frequently significant, which means that in the 20th century local soil moisture conditions became drier parallel to the hemispherical changes.

Prediction of flow characteristics using multiple regression and neural networks: A case study in Zimbabwe

Abstract: The feasibility of predicting flow characteristics from basin descriptors using multiple regression and neural networks has been investigated on 52 basins in Zimbabwe. Flow characteristics considered were average annual runoff, base flow index, flow duration curve, and average monthly runoff . Mean annual runoff is predicted using linear equations from mean annual precipitation, basin slope, and proportion of a basin underlain by granite and gneiss. A multiple regression equation is derived to predict the base flow index from mean annual precipitation, slope, and proportion of a basin with grasslands. Findings indicate that a neural network predicts the base flow index with comparable accuracy to multiple regression. Differences in lithology and land cover type were not significant in explaining the base flow index. An exponential model was able to describe flow duration curves, and coefficients of this model could be predicted from the base flow index. Best predictions of flow duration curves were made by a neural network from base flow index, slope, and proportion of a basin with grasslands. The distribution of mean annual runoff into monthly flows was predicted by a neural network from base flow index, slope, and proportion of a basin with grasslands. The study found the base flow index to be important for predicting flow characteristics, and recommends studies aimed at improving prediction of the base flow index.

Comparison of measured changes in seasonal soil water content by rainfed maize-bean intercrop and component cropping systems in a semi-arid region of southern Africa

Abstract: Seasonal water content fluctuation within the effective root zone was monitored during the growing season for a maize-bean intercrop (IMB), sole maize (SM) and sole bean (SB) in Free State Province, Republic of South Africa. Comparisons were undertaken for progressive depths of extraction 0–300 mm; 300–600 mm and 600–900 mm respectively. These enabled the understanding of water extraction behavior of the cropping systems within the different soil layers including the topsoil surface normally influenced by soil surface evaporation. Additive intercrops have been known to conserve water, largely due to the early high leaf area index and the higher total leaf area. In this study, the combined effect of the intercrop components seemed to lower the total water demand by the intercrop compared to the sole crops. During the two seasons (2000/2001 and 2001/2002) the drained upper limit (DUL) and crop lower limits (CLL) were determined. The maize-bean intercrop, sole maize and sole bean had CLL of 141 mm/m, 149 mm/m and 159 mm/m respectively. The DUL was 262 mm/m for the site and therefore the potential plant extractable soil water for the cropping systems were: 121 mm/m (IMB); 114 mm/m (SM) and 103 mm/m (SB). Overall, the intercrop did not have significantly different total soil water extraction during both seasons, although it was additive, showing that it had higher water to biomass conversion.

An assessment of the water quality of drinking water in rural districts in Zimbabwe. The case of Gokwe South, Nkayi, Lupane, and Mwenezi districts

Abstract: Zimbabwe generally receives an average rainfall of 675 mm per annum of which only a maximum of 10% finds its way to rivers as runoff. Gokwe, Nkayi, Lupane and Mwenezi are some of the driest districts in Zimbabwe having mean annual runoffs (MAR) in the range 17–70 mm. River flows especially in Nkayi and Lupane are seasonal and often dry in the period June to November every year. The Kalahari sands predominantly found in such areas as Gokwe, Nkayi, and Lupane promote rapid percolation of rainwater leaving little runoff. The main source of water for domestic purposes in these areas is groundwater with very little reliance on surface water. This study analyzed the water quality of water points in Gokwe South, Nkayi, Lupane, and Mwenezi districts. Parameters analyzed were pH, temperature, dissolved oxygen (DO), turbidity and electrical conductivity (EC). Water quality perceptions from the villagers and the research team were investigated and possible correlations studied. Water quality perceptions included, taste and soap consumption and colour. The uses of the water at domestic level as well as available alternatives to borehole water were investigated. The pH generally ranged from 6.5 to 8.0, which is within the Canadian guidelines. DO was 0.3–5.9 mg/l while turbidity ranged from 0 to 259 NTU with Mwenezi having the highest turbidity value. Conductivity ranged from 70 to 9800 μS/cm with the lowest and highest values recorded in Gokwe and Mwenezi. It was found out that the water quality in terms of taste and odour was 97% satisfactory for Gokwe South, 85% Nkayi, 64% Lupane, and 62% for Mwenezi. High soap consumption which is related to hardness was perceived to be least in Lupane (14%) and highest in Mwenezi with 81%. In general taste complaints also corresponded to high soap consumption but the opposite was not true. It was observed that there was no clear correlation between the quality parameters studied and perceived quality as for example satisfactory taste responses were obtained at EC values higher than the threshold minimum value for objection.

Effects of a semi-formal urban settlement on groundwater quality: Epworth (Zimbabwe): Case study and groundwater quality zoning

Abstract: Rapid urbanisation and lack of low cost accommodation in the City of Harare, Zimbabwe, led to a lot of people settling (formally or otherwise) on previously cultivated land in Epworth, south-east of the city. Groundwater quality in different parts of Epworth, a semi-formal settlement in Zimbabwe, was investigated. Water samples for water quality analysis were collected from 10 shallow boreholes and 20 shallow wells across the settlement. Results showed significantly elevated levels of nitrates and coliform bacteria in most parts of the settlement. Levels of coliforms were highest in the old parts of the settlement (>10,000 cfu). High nitrate levels (20–30 mg/l) can be related to more densely settled areas, with a higher density of pit latrines. The groundwater quality generally decreased downflow (to the south-east). Na, Zn, Cu, Co, Fe, PO4 were also determined, of which only iron showed substantially high levels. Groundwater quality results were used to delineate parts of the settlement into water use zones. Three broad zones were defined: Zone 1 (water drinkable after boiling), Zone 2 (water for agricultural use only), and Zone 3 (water unsuitable for domestic or agricultural purposes). The results also showed that most parts of the settlement have no safe groundwater for human consumption and Zone 1 could be faced with high nitrate levels in future. It is too late to prevent contamination of groundwater in this settlement. As a cost-effective measure to reduce health risk, the local authority could consider the provision of a limited water supply, via communal taps, starting in those areas in Zones 2 and 3 except for the south-east where there area already communal taps. A health education campaign on the risks of drinking polluted groundwater in this settlement is also necessary. The development of a sewage system is an alternative although it is expensive with the current situation. Furthermore, although a proper sewage reticulation system would prevent further groundwater contamination, the levels of nitrate will remain high, until flushed by recharge.

The impact of Mpererwe landfill in Kampala–Uganda, on the surrounding environment

Abstract: Mpererwe landfill site receives solid wastes from the city of Kampala, Uganda. This study was carried out to assess and evaluate the appropriateness of the location and operation of this landfill, to determine the composition of the solid waste dumped at the landfill and the extent of contamination of landfill leachate to the neighbouring environment (water, soil and plants). Field observations and laboratory measurements were carried out to determine the concentration of nutrients, metals and numbers of bacteriological indicators in the landfill leachate. The landfill is not well located as it is close to a residential area (

The Palmer Drought Severity Index (PDSI) as an indicator of soil moisture

Abstract: Detailed observation of soil moisture time series has of practical importance either in strategic preparing of researches or in professional planning. Meteorological-related spatial and temporal connections of soil moisture were investigated on monthly Palmer Drought Severity Index (PDSI) time series of five meteorological stations in Eastern Hungary (Miskolc, Nyiregyhaza, Debrecen, Kecskemet and Szeged) for the period 1901–1999. The calculated PDSI values were compared with the soil moisture content of the upper one meter soil layer. The measured soil moisture time series come from the authors ([Dunkel, Z., 1994; Lambert, K., et al., 1993 (in Hungarian)]). Both the used soil moisture time series and the Palfai-index, expressing numerically daily hydrological extremes ([Palfai, I.,1991]), confirmed our result independently of each other according to which PDSI is a good indicator of the soil moisture fluctuations in the upper one meter soil layer of the Great Hungarian Plain. On the basis of the regression coefficients of the linear connection, the index values can be expressed in physical unit of the water content in the upper one meter soil layer, as well. As a result of our examinations, the index has favourable statistical features; namely, the distribution of monthly samples is normal. Analysing spatial and temporal connections of the varied hydrometeorological relations of the selected region, average spatial and strong temporal correlations were established and these results are functions of intra-annual variability of precipitation.

Extreme floods in the Meuse river over the past century: aggravated by land-use changes?

Abstract: Recent floods in the Meuse river increased the public’s concern about the risk of flooding. It is often assumed that the rapid land-use changes in the basin since the 1950s have aggravated these floods. This possibility has provided the motivation to analyse the flood peaks in the Meuse river and causal extreme precipitation in the basin during the past century. The historical land-use changes in the basin were also evaluated. The results indicate that both the flood peaks in the Meuse river and the antecedent precipitation depths in the basin have significantly increased since the early 1980s. Over the past century, the forest area in the upstream basin has changed little and most changes in the forest types, agricultural land and urbanisation occurred before the 1980s. The apparent changes in frequency and magnitude of floods in the Meuse river over the last two decades can apparently be broadly ascribed to climate variability.