Considering groundwater use to improve the assessment of groundwater pumping for irrigation in North Africa

Groundwater resources in semi-arid areas and especially in the Mediterranean face a growing demand for irrigated agriculture and, to a lesser extent, for domestic uses. Consequently, groundwater reserves are affected and water-table drops are widely observed. This leads to strong constraints on groundwater access for farmers, while managers worry about the future evolution of the water resources. A common problem for building proper groundwater management plans is the difficulty in assessing individual groundwater withdrawals at regional scale. Predicting future trends of these groundwater withdrawals is even more challenging. The basic question is how to assess the water budget variables and their evolution when they are deeply linked to human activities, themselves driven by countless factors (access to natural resources, public policies, market, etc.). This study provides some possible answers by focusing on the assessment of groundwater withdrawals for irrigated agriculture at three sites in North Africa (Morocco, Tunisia and Algeria). Efforts were made to understand the different features that influence irrigation practices, and an adaptive user-oriented methodology was used to monitor groundwater withdrawals. For each site, different key factors affecting the regional groundwater abstraction and its past evolution were identified by involving farmers’ knowledge. Factors such as farmer access to land and groundwater or development of public infrastructures (electrical distribution network) are crucial to decode the results of well inventories and assess the regional groundwater abstraction and its future trend. This leads one to look with caution at the number of wells cited in the literature, which could be oversimplified.     

Agricultural groundwater use and rural livelihoods in sub-Saharan Africa: A first-cut assessment

The rapid expansion in agricultural groundwater use in the last few decades has transformed rural economies in large parts of the developing world, in particular South Asia and North China. There has been no such “Groundwater Revolution” in most of sub-Saharan Africa and little is known about the actual role of groundwater use in supporting agricultural livelihoods in the region or opportunities to expand this role in the future. Published literature has been reviewed to paint a preliminary, region-wide picture of the contribution groundwater makes to agriculture, and in turn to rural livelihoods, within sub-Saharan Africa. The findings indicate that groundwater is used on only 1–2 million hectares of cropped area, directly contributing to the livelihoods of 1.5–3% of the rural population. Groundwater also plays a critical role in the vital livestock sector as well as an important indirect role in the supply of domestic water to agricultural households. While data are lacking, these latter two roles likely surpass the direct importance of groundwater to crop production. This suggests that an understanding of the value of agricultural groundwater use in support of rural livelihoods in sub-Saharan Africa should be based on different models than have typically been applied in Asia.

Adjustment preferences to groundwater depletion in the American high plains

This paper explores the adjustments that residents in one part of the High Plains prefer in coping with the depletion of the Ogallala aquifer. The authors identify 31 possible adjustment policies and report on public preferences, examining differences among socioeconomic groups and also the preferred governmental agencies to administer specific programs. Adjustments involving improved water use efficiency were most favored; those entailing financial incentives were least liked. The local groundwater management district was the preferred agency overall. Most significant differences in preference were between those in agribusiness and those outside agriculture.     

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

Groundwater resources are important sources of drinking water in Africa, and they are hugely important in sustaining urban livelihoods and supporting a diverse range of commercial and agricultural activities. Groundwater has an important role in improving health in sub-Saharan Africa (SSA). An estimated 250 million people (40% of the total) live in urban centres across SSA. SSA has experienced a rapid expansion in urban populations since the 1950s, with increased population densities as well as expanding geographical coverage. Estimates suggest that the urban population in SSA will double between 2000 and 2030. The quality status of shallow urban groundwater resources is often very poor due to inadequate waste management and source protection, and poses a significant health risk to users, while deeper borehole sources often provide an important source of good quality drinking water. Given the growth in future demand from this finite resource, as well as potential changes in future climate in this region, a detailed understanding of both water quantity and quality is required to use this resource sustainably. This paper provides a comprehensive assessment of the water quality status, both microbial and chemical, of urban groundwater in SSA across a range of hydrogeological terrains and different groundwater point types. Lower storage basement terrains, which underlie a significant proportion of urban centres in SSA, are particularly vulnerable to contamination. The relationship between mean nitrate concentration and intrinsic aquifer pollution risk is assessed for urban centres across SSA. Current knowledge gaps are identified and future research needs highlighted.     

Assessment of groundwater quality in the flood plains of upper Palar River, India

Groundwater is generally presumed to be good for human consumption and is used as a main source of drinking water. Although there are numerous reasons for groundwater pollution, anthropogenic sources are consid-ered as the prime ones. In this study, twenty-two groundwater samples were collected from the flood plains of upper Palar River during the pre- and post-monsoon seasons to assess the extent of pollution and effects on human health. Physico-chemical characteristics of groundwater were analyzed and compared with those of drinking water standards recommended by the World Health Organization (WHO) and the Bureau of Indian Standards (BIS). The Piper’s tri-linear diagram shows the nature of alkali earth with the high contents of alkalies and prevailing sulphate in the pre-sent samples. The univariate statistics and correlation analysis were performed to find out the relationships between the variables. The tannery effluents, solid wastes and sewage were suspected to be the predominant sources of pollu-tion in the area.     

Hydrochemical characteristics of groundwater in the plains of Phalgu River in Gaya, Bihar, India

Assessment of groundwater quality is essential to ensure sustainable use of it for drinking, agricultural, and industrial purposes. The chemical quality of groundwater of Gaya region has been studied in detail in this work to delineate the potable groundwater zones. A total of 30 groundwater samples and 2 surface water samples were collected in and around Gaya district of Bihar. The major cations follow the trend: Ca²⁺?>?Mg²⁺?>?Na⁺?>?K⁺. The domination of calcium ions in the groundwater is due to weathering of rocks. The K⁺ ranged between 0.2 and 47.95 ppm, suggesting its abundance the below desired limit; but some samples were found to be above permissible limit. K⁺ weathering of potash silicate and the use of potash fertilizer could be the source. The major anions abundance followed the order HCO ₃ ^? ?>?Cl^??>?SO ₄ ^2? ?>?NO ₃ ^? ?>?PO ₄ ^3? . Dissolution of carbonates and reaction of silicates with carbonic acid accounts for the addition of HCO ₃ ^? to the groundwater and oxidation of sulphite may be the source of SO ₄ ^2? . Principal component analysis was utilized to reflect those chemical data with the greatest correlation and seven major principal components (PCs) representing >80 % of cumulative variance were able to interpret the most information contained in the data. PC1, PC2 and PC3 reflect the hydrogeochemical processes like mineral dissolution, weathering and anthropogenic sources. PC4, PC5, PC6 and PC7 show monotonic, random and independent relationships.     

Hydrochemical framework of groundwater in the Ankobra Basin,Ghana

Hydrochemical and stable isotope (¹⁸O and ²H) analyses of groundwater samples were used to establish the hydrochemistry of groundwater in the Ankobra Basin. The groundwater was generally mildly acidic, low in conductivity and undersaturated with respect to carbonate phases. Major ions except bicarbonate were low and dissolved silica was moderately high. Silicate minerals weathering is probably the main process through which major ions enter the groundwater. Groundwater samples clustered tightly along the Global Meteoric Water Line suggesting integrative, smooth and rapid recharge from meteoric origin. The majority of the boreholes and a few hand dug wells cluster towards the Ca–Mg–HCO₃ dominant section of the phase diagram, in conformity with the active recharge and short residence time shown by the isotope data. Aluminium, arsenic, manganese, iron and mercury were the only trace metals analysed with concentrations significantly above their respective detection limits. Approximately 20%, 5%, 40% and 25% respectively of boreholes had aluminium, arsenic, iron and manganese concentrations exceeding the respective WHO maximum acceptable limits for drinking water. The relatively large percentage of boreholes with high concentration of aluminium reflects the acidic nature of the groundwater.     

Intra-urban patterns of domestic solid waste recycling in sub-Saharan Africa: towards an exploratory search for insights in Gaborone,Botswana

Botswana is among those developing countries that are rapidly transitioning from predominantly rural to urban societies. Gaborone, its capital city, is seriously confronted by formidable challenges of sustainable metropolitan management, including the proper handling of solid domestic waste. Although the international convention of the 3-Rs, namely, Recycle, Reduce, Reuse is generally accepted; its implementation remains elusive. It is therefore of utmost importance to unravel significant determinants of the gap between nominal acceptance and praxis in order to influence policy. This preliminary case study, consequently, sought to identify the underlying factors that differentiate waste recycling practices from high, medium, and low socio-economic areas Gaborone. Key informants, including municipal officials and company representatives, in charge of city solid waste management, were interviewed. A probit model was used to analyze those factors that could influence recycling and waste separation practices. Results showed that tenure, gender, income, affluence, location of house increase the likelihood of recycling while age, education level, household size and source of waste management information did not influence the likelihood of recycling. Stakeholders should place greater emphasis on positive environmental awareness, and appropriate reward systems for recycling domestic solid waste and recycling should be tailored according to the locational needs.     

Mapping composite vulnerability to groundwater arsenic contamination: an analytical framework and a case study in India

Natural Hazards - Groundwater arsenic (As) contamination affects millions of people in South Asia. In this paper, we propose a composite vulnerability framework to identify, for mitigation, the...     

Spatiotemporal variation of groundwater quality in an arid area experiencing long-term paper wastewater irrigation,northwest China

Groundwater is crucial for multiple uses over the world, especially in arid and semiarid regions. However, human activities significantly decreased groundwater quality. In this study, the spatiotemporal variation of groundwater quality was evaluated in an arid area where long-term paper wastewater irrigation has been implemented. For this study, seven wells were regularly monitored for physicochemical parameters over a period of 1 year. Statistical and graphical approaches were applied to interpret the spatiotemporal variation of groundwater quality parameters in the wastewater irrigation zone. Correlation analysis was also carried out to reveal the sources of some major ions. The results indicate that the groundwater type in the study area is dominated by the Cl–Na, followed by the HCO₃–Na, the HCO₃–Ca·Mg, and the SO₄·Cl–Ca·Mg types. Groundwater in the area is significantly contaminated locally with fluoride, nitrite and ammonia, and the chemical oxygen demand levels were increased in some groundwater monitoring wells. Most contaminants showed an increasing trend from the Yellow River water irrigation zone toward the wastewater irrigation zone. Rock weathering, mineral dissolution, and cation exchange are important processes controlling groundwater quality, but human activities, such as wastewater irrigation, play an undeniable role in affecting groundwater quality in this area. The results of this study contribute to the understanding of the formation and circulation of groundwater under human activities and provide a scientific basis for regional water quality evaluation, water quality improvement, and protection.     

Fluoride ions in groundwater of the Turkana County,Kenya, East Africa

Acta Geochimica - Groundwater samples were evaluated throughout Turkana County (Kenya, East Africa) while looking for drinking water sources. Some samples showed high concentrations of fluoride...     

A Weichselian deglaciation model applied to the Early Permian glaciation in the northeast Karoo Basin,South Africa

It generally is assumed that the Early Permian Gondwana deglaciation in South Africa started with a collapse of the marine ice‐sheet. The northeast part of the Karoo Basin became ice‐free as a result of this collapse. The deglaciation here probably took place under temperate glacial conditions. Three glacial phases have been identified. Phase 1: the marine ice retreat of 400 km over the northeast Karoo Basin, which may have been completed over a few thousand years. The glaciers grounded in the shallower areas around the shore of the basin. Phase 2: the smaller, now mainly continental ice‐sheet here re‐stabilised and remained more or less stationary for several tens of thousand years. During this phase, between 50 and 200 m of massive glaciomarine mud with dropstones accumulated in the open, marine basin that became ice‐free during Phase 1. Isostatic uplift, as a response to the first rapid deglaciation phase, can be traced in the inland part of the region. Phase 3: the final deglaciation may have taken 10 to 20 kyr. After this time no new ice sheet was built up over southern Africa. The entire Early Permian deglaciation of the northeast Karoo Basin was completed within thousands rather than millions of years. Phases 1 and 3 had lengths similar to typical Quaternary deglaciations, whereas Phase 2 was a long, stable phase, more similar to a full Quaternary glaciation. Copyright © 2001 John Wiley & Sons, Ltd.     

Application of environmental isotopes to groundwater recharge studies in a semi-arid fractured crystalline basement area of Dodoma, Tanzania

The distribution of ¹⁸O and ²H in various water sources indicates that groundwater recharge is due to local rainfall occurring within the basins. Groundwater recharge takes place under a bypass flow mechanism and matrix diffuse flow and is 3% and 2% of the long-term mean annual rainfall of 550 mm for the Makutapora and Hombolo basins, respectively. Chloride mass balance indicates that 60% and 40% of the total groundwater recharge takes place through macropores and matrix flow, respectively. Sporadic variations in ¹⁸O, ²H and chloride among adjacent boreholes suggest existence of a discrete fractured aquifer and/or dominance of local recharge. The relationship between δ²H and chloride indicates that groundwater salinization is due to the leaching of surficial and soil salts during high intensity rainfall, which causes high surface runoff and flash floods. It has been concluded that the isotopic and chemical character of groundwater in fractured semi-arid areas may provide the most effective complementary means of groundwater recharge assessment and therefore is very useful in the management of the water resources.     

An evaluation of the genesis and suitability of groundwater for irrigation in the Volta Region,Ghana

Stable isotope data and concentrations of the major cations and anions of groundwater from the northern part of the Volta Region, Ghana, were used to determine the source of recharge and the suitability of groundwater in the area for irrigation. This study finds that the delta deuterium (δD) and delta Oxygen-18 (δ¹⁸O) data from the area fall along the global meteoric water line (GMWL). An equation of regression derived for the relationship between δD and δ¹⁸O bears very close semblance to the equation which describes the GMWL. On the basis of this, groundwater in the study area is probably meteoric and fresh. The apparently low salinities and sodicities of the groundwater seem to support this interpretation. The suitability of groundwater for domestic and irrigation purposes is related to its source, which determines its constitution. A plot of the sodium adsorption ratio (SAR) and electrical conductivity (EC) data on a semilog axis, suggests that groundwater serves good irrigation quality in the area. Sixty percent (60%), 20% and 20% of the 67 data points used in this study fall within the medium salinity–low sodicity (C2–S1), low salinity–low sodicity (C1–S1) and high salinity–low sodicity (C3–S1) fields, which ascribe good irrigation quality to groundwater from this area. Salinities range from 28.1 to 1,956 μS/cm, whilst SAR values fall within the range 0–3. Extremely low sodicity waters of this kind, with salinities lower than 600 μS/cm, have the tendency to affect the dispersive properties of irrigation soils when used for irrigation. About 50% of the groundwater in the study area fall within this category and need prior treatment before usage.     

Magnetotellurics applied to the study of the crustal structures in Senegal (West Africa)

Abstract

In Senegal, magnetotellurie (MT) method has been used in an attempt to resolve the principal structural features by their electrical response. On the basis of numerical modelling of data, an unified model of possible crustal structure is presented for the West african margin. The results are in agreement with other independent geophysical and geological information.