Southwestern Niger Research Articles

Characterising the space–time structure of rainfall in the Sahel with a view to estimating IDAF curves

Abstract. Intensity–duration–area–frequency (IDAF) curves are increasingly demanded for characterising the severity of storms and for designing hydraulic structures. Their computation requires inferring areal rainfall distributions over the range of space scales and timescales that are the most relevant for hydrological studies at catchment scale. In this study, IDAF curves are computed for the first time in West Africa, based on the data provided by the AMMA-CATCH Niger network, composed of 30 recording rain gauges having operated since 1990 over a 16 000 km2 area in south-western Niger. The IDAF curves are obtained by separately considering the time (intensity–duration–frequency, IDF) and space (areal reduction factor, ARF) components of the extreme rainfall distribution. Annual maximum intensities are extracted for resolutions between 1 and 24 h in time and from point (rain gauge) to 2500 km2 in space. The IDF model used is based on the concept of scale invariance (simple scaling) which allows the normalisation of the different temporal resolutions of maxima series to which a global generalised extreme value (GEV) is fitted. This parsimonious framework allows one to use the concept of dynamic scaling to describe the ARF. The results show that coupling a simple scaling in space and time with a dynamical scaling that relates to space and time allows one to satisfactorily model the effect of space–time aggregation on the distribution of extreme rainfall.

Building a field- and model-based climatology of local water and energy cycles in the cultivated Sahel – annual budgets and seasonality

Abstract. In the sub-Saharan Sahel, energy and water cycling at the land surface is pivotal for the regional climate, water resources and land productivity, yet it is still very poorly documented. As a step towards a comprehensive climatological description of surface fluxes in this area, this study provides estimates of long-term average annual budgets and seasonal cycles for two main land use types of the cultivated Sahelian belt: rainfed millet crop and fallow bush. These estimates build on the combination of a 7-year field data set from two typical plots in southwestern Niger with detailed physically based soil–plant–atmosphere modeling, yielding a continuous, comprehensive set of water and energy flux and storage variables over this multiyear period. In the present case in particular, blending field data with mechanistic modeling makes the best use of available data and knowledge for the construction of the multivariate time series. Rather than using the model only to gap-fill observations into a composite series, model–data integration is generalized homogeneously over time by generating the whole series with the entire data-constrained model simulation. Climatological averages of all water and energy variables, with associated sampling uncertainty, are derived at annual to sub-seasonal scales from the time series produced. Similarities and differences in the two ecosystem behaviors are highlighted. Mean annual evapotranspiration is found to represent ~82–85% of rainfall for both systems, but with different soil evaporation/plant transpiration partitioning and different seasonal distribution. The remainder consists entirely of runoff for the fallow, whereas drainage and runoff stand in a 40–60% proportion for the millet field. These results should provide a robust reference for the surface energy- and water-related studies needed in this region. Their significance and the benefits they gain from the innovative data–model integration approach are thoroughly discussed. The model developed in this context has the potential for reliable simulations outside the reported conditions, including changing climate and land cover.

Millet response to microdose fertilization in south–western Niger: Effect of antecedent fertility management and environmental factors

Soil fertility is a major constraint to agricultural development in most of the Sahel, with P being the most limiting nutrient for millet production on acid sandy soils. To address this issue, microdose applications of P fertilizer have been widely advocated in recent years. However, little is known regarding the effect of farmer management practices and environmental factors on millet's yield response to this technique. For this purpose, 276 farmer demonstrations were setup across a 3-year period in the Fakara region, western Niger. Five strata were considered based on antecedent organic manure management (corralling or transported manure). At each demo site, conventional management was compared to basal microdose fertilizer application of DAP (2ghill−1), NPK (6ghill−1), or DAP (2ghill−1) with urea (1ghill−1) applied at tillering. Millet grain yields on control plots were low (84%<400kgha−1), reflecting the unfavorable environmental conditions of the area. On average, the application of DAP, NPK and DAP+urea increased grain yields by 43, 46 and 69kgha−1 (2001–2002). A positive response to microdose fertilization was observed for 92% of the sites where yields on control plots were <100kgha−1 but only for 32% of the sites where yields on control plots were >500kgha−1. In particular, the positive response to microdosing increased with later sowing given that late sowing tended to reduce yields on control plots. Higher rainfall during the early growing season favored a positive response to microdosing. On average over DAP and DAP+urea, 36% of the demonstrations had value-cost ratios (VCR)<1. However, for low yielding control plots (<200kggrainha−1), 26% of the demonstrations had VCR<1, whereas for high yielding plots (>400kggrainha−1), 55% had a VCR<1. Not accounting for labor, DAP and DAP+urea had similar economic returns. The use of NPK could not be recommended as the cost per unit P is 3 times higher than DAP. It appears that, for the Fakara study area, microdosing may best be targeted to areas with low expected yields. In particular, it may serve as a famine mitigation strategy in case of late sowing. Nevertheless, for poorly endowed areas such as the Fakara, the economic risk associated with microdosing (2gDAPhill−1) appears higher than has hitherto been reported and widespread adoption may not be warranted without institutional support.

Modeling wind erosion flux and its seasonality from a cultivated sahelian surface: A case study in Niger

Wind erosion can strongly affect the cultivated areas in semi-arid regions, through soil losses and/or decrease in nutrient contents. Additionally, dust emitted by aeolian erosion affects both the biogeochemical cycles and the Earth radiation budget. Modeling wind erosion and dust emission remains complex especially in semi-arid regions where vegetation interacts with the wind field and may act as a protection of the soil. An existing and widely used wind erosion model is tested in the present study to check the capacity to reproduce observations collected over a millet field and a neighboring bare plot in southwestern Niger during a three-year period. Observations of sediment horizontal fluxes and of vegetation growth and decay show that most of the eroded mass is due to major events occurring at the end of the dry season and at the beginning of the rainy season for the millet field, while erosion also occurs during the dry season for the bare soil plot. Horizontal erosion fluxes were computed with and without obstacles and compared to the measurements. Simulations were found in a good agreement with erosion measurements for both bare and millet plots, in terms of temporal dynamics, reproduction of the major events and annual quantities.Accumulated horizontal fluxes over the millet plot were found to be much lower than over the bare plot for both observations and simulations (respectively 235 to 565kgm−1y−1 and 332 to 526kgm−1y−1 over the millet plot; and 773 to 2692kgm−1y−1 and 1003 to 1986kgm−1y−1 for the bare plot). Total values over the 3-year period also show a much stronger (by a factor 3 to 4) wind erosion on the bare plot (5365kgm−1y−1 for observations, 4548kgm−1y−1 for simulations) than on the cropped one (1357kgm−1y−1 for observations, 1398kgm−1y−1 for simulations). Modeling is therefore able to represent anthropogenic impacts on wind erosion over typical Sahelian surfaces.

EFFECT OF MEDICAL WASTES ON PHYSICAL AND CHEMICAL PARAMETERS OF SOIL

Human beings are totally dependent on the environment for life itself. In Nigeria, like in other developing countries open dump is the only available option for solid waste disposal in the cities. This study is aimed at determining the physical and chemical parameters of soil from medical waste dumpsites in south western Niger Delta, Nigeria. Samples were collected from University of Benin Teaching Hospital, Irrua Teaching Hospital, Irrua, Stella Obasanjo Hospital, Benin City, Edo State, Federal Medical Center, Owo, Ondo State, and Central Hospital, Warri, Delta State with samples from non-medical waste dumpsites around the selected hospitals as controls. Soil samples collected from medical and non-medical waste dumpsites were analyzed using standard procedures. The pH and electrical conductivity values obtained were higher in medical than in non-medical waste dumpsites. The values of calcium, sodium, magnesium, zinc, chromium, cadmium and lead ions were lower in medical waste than in non-medical waste dumpsites. In contrast, the concentrations of potassium, iron, copper, nickel and manganese ions were higher in medical waste than in non-medical waste dumpsites. The mean values of heavy metals obtained in medical and non-medical waste dumpsites did not differ significantly (P&lt;0.05). There was heavy metal contamination of the soil from both medical and non-medical waste dumpsites as their values were above the WHO acceptable limits. The values of heavy metals from medical waste dumpsites were higher than the acceptable limit of WHO and FMEnvMeasures to reduce the contamination of soil from medical and non-medical waste dumpsites are advocated.

Well Log Sequence Stratigraphic and Palynological Analysis of Late Miocene to Pliocene Agbada Formation, Southwestern Niger Delta Basin, Nigeria

Sequence stratigraphic interpretation of Chev-1, 2, and 3 wells offshore western Niger delta basin was carried out based on the vertical relationship of the lithofacies associations, electronic well-log, palynologic and foraminiferal data and the existing stratigraphic framework of the Neogene succession in the Niger delta basin. Each well was analyzed in terms of the system tracts, maximum flooding surfaces and sequence boundaries. The recovered palynomorphs together with planktonic foraminifera suggest Late Miocene to Pliocene age. The palynological assemblages exhibit cyclic changes which are here related to the sedimentary evolution.Eighteen depositional sequences were recognized; there are five in Chev-1, ten in Chev-2 and seven in Chev-3. Three of those in Chev-1 and Chev-2 are correlatable while one is correlatable between Chev-2 and 3. These sequence stratigraphic data are matched with existing global standard biostratigraphic zonation scheme and global eustatic curve in order to allow a correlation of sequence beyond local and regional scales.

Constraints and opportunities for groundwater irrigation arising from hydrologic shifts in the Iullemmeden Basin, south-western Niger

Land-use-change-induced increases in shallow groundwater levels across parts of the Sahel in recent years have coincided with expanded use of groundwater for irrigation. This study was conducted to assess the potential linkages and livelihood implications based on a field survey of nine villages building on previous hydrological studies. The results show that irrigators lack effective means of production and mostly rely on manual methods. Borehole usage is more profitable and reliable than shallower wells. Overall incomes from irrigation are relatively small and severely constrained by the limited field scale due to high establishment and operating costs.

3d Seismic Structural Interpretation of a Part of Aloo-Field, Southwestern Niger Delta, Nigeria

Complexity of faulted subsurface configuration causing erroneous deductions in absence of well articulated interpretation approach led to a well refined 3D seismic data of part of ALOO-Field located in offshore southwestern Niger Delta. This study was aimed towards determining its subsurface structural features and retentive capacity of the reservoir for hydrocarbon. The methods employed include analysis of 3D seismic data using Petrel software; horizons and fault deductions from the seismic sectionwere used to generate structural maps which revealed different structural styles present in the studied area. Three distinct horizons were mapped. Depth structural maps generated for all surfaces of interest show subsurface features such as the geometry of the identified horizons, W-E trending growth fault, fault echelonsof which most of them dip to the east and fault assisted closures at the north-western-central part of the studied section. The dipping pattern of the identified faults coincides with that of the growth fault which enhances trapping mechanism for the hydrocarbon. Two principal structural trapping mechanisms present are growth fault and rollover anticline which are synonymous with Niger Delta. The study has demonstrated the importance of seismic structural interpretation in understanding the structural styles present and their retentive ability for hydrocarbon. Keywords-Fault echelons,Growth faults, Rollover anticline, Seismic Sections, and Structural styles.

Evolutionary dynamics of cycle length in pearl millet: the role of farmer’s practices and gene flow

In the Sahel of Africa, farmers often modify their cultivation practices to adapt to environmental changes. How these changes shape the agro-biodiversity is a question of primary interest for the conservation of plant genetic resources. We addressed this question in a case study on pearl millet in south western Niger where farmers used to cultivate landraces with different cycle length in order to cope with rain uncertainty. Early and late landraces were previously grown on distant fields. Nowadays, mostly because of human population pressure and soil impoverishment, it happens that the two types of landraces are grown on adjacent fields, opening the question whether gene flow between them may occur. This question was tackled through a comparative study among contrasting situations pertaining to the spatial distribution of early and late landraces. Observations of flowering periods showed that pollen flow between the two landraces is possible and has a preferential direction from early to late populations.

Drought sensitivity of patterned vegetation determined by rainfall-land surface feedbacks

[1] Vegetation pattern morphology is suggested as one indicator of system closeness to desertification. Using pattern morphology as an indicator requires understanding the timescales at which patterned vegetation systems respond to drought. Modeling these timescales requires accounting for rainfall intermittency and all the pathways controlling vegetation-precipitation feedbacks. In this paper, a model of rainfall initiation and intensity based on the dynamics of a single-column atmospheric boundary layer is coupled to a patterned vegetation model. The coupled climate-vegetation model, parameterized to represent a typical vegetation morphology in southwestern Niger, is used to investigate the timescales of desertification due to shifts in the total annual rainfall regime, and the effect of precipitation feedbacks on these timescales. Depending on the exact rainfall history, biomass and spatial morphology may not respond monotonically to a decrease in rainfall. The model results suggest changes in pattern morphology responding to shifts in annual rainfall require at least 4–5 years. Feedbacks acting through vegetation's influence on surface albedo and, to a lesser extent, surface evapotranspiration act to speed up the vegetation response to drought. Although the overall local-scale vegetation-precipitation feedback is positive, individual storm events may exhibit negative feedbacks, in which rainfall only occurs for low vegetation cover, depending on the free atmospheric conditions. Vegetation-precipitation feedbacks are sufficiently important to speed up changes in vegetation patterns, even in marginal drylands with low biomass levels.

Wind erosion characteristics of Sahelian surface types

AbstractThe assessment of wind erosion magnitudes for a given area requires knowledge of wind erosion susceptibilities of the dominant local surface types. Relative wind erosion potentials of surfaces can hardly be compared under field conditions, as each erosion event is unique in terms of duration, intensity and extent.The objective of this study was to determine and compare relative wind erosion potentials of the most representative surface types over a transect comprising most parts of southwestern Niger. For this purpose, mobile wind tunnel experiments were run on 26 dominant surface types. The effects of surface disturbance were additionally determined for 13 of these surfaces. The results, namely measurements of wind fields and mass fluxes, can be classified according to specific surface characteristics.Three basic surface groups with similar emission behaviour and aerodynamic characteristics were identified: (1) sand surfaces, (2) rough stone surfaces and (3) flat crusted surfaces. Sand surfaces feature a turbulent zone close to the surface due to the development of a saltation layer. Their surface roughness is medium to high, as a consequence of the loss of kinetic energy of the wind field to saltating particles. Sand surfaces show the highest mass fluxes due to the abundance of loose particles, but also fairly high PM10 fluxes, as potential dust particles are not contained in stable crusts or aggregates. Rough stone surfaces, due to their fragmented and irregular surface, feature the highest surface roughness and the most intense turbulence. They are among the weakest emitters but, due to their relatively high share of potential dust particles, PM10 emissions are still average. Flat crusted surfaces, in contrast, show low turbulence and the lowest surface roughness. This group of surfaces shows rather heterogeneous mass fluxes, which range from moderate to almost zero, although the share of PM10 particles is always relatively high. Topsoil disturbance always results in higher total and PM10 emissions on sand surfaces and also on flat crusted surfaces. Stone surfaces regularly exhibit a decrease in emission after disturbance, which can possibly be attributed to a reorganization which protects finer particles from entrainment.The results are comparable with field studies of natural erosion events and similar wind tunnel field campaigns. The broad range of tested surfaces and the standardized methodology are a precondition for the future regionalization of the experimental point data. Copyright © 2010 John Wiley &amp; Sons, Ltd.

A new species of the bee genus Chiasmognathus from southwestern Niger (Hymenoptera: Apidae)

A new species of the bee genus Chiasmognathus from southwestern Niger (Hymenoptera: Apidae)

Contribution of geophysical surveys to groundwater modelling of a porous aquifer in semiarid Niger: An overview

Subsurface geophysical surveys were carried out using a large range of methods in an unconfined sandstone aquifer in semiarid south-western Niger for improving both the conceptual model of water flow through the unsaturated zone and the parameterization of numerical a groundwater model of the aquifer. Methods included: electromagnetic mapping, electrical resistivity tomography (ERT), resistivity logging, time domain electromagnetic sounding (TDEM), and magnetic resonance sounding (MRS). Analyses of electrical conductivities, complemented by geochemical measurements, allowed us to identify preferential pathways for infiltration and drainage beneath gullies and alluvial fans. The mean water content estimated by MRS (13%) was used for computing the regional groundwater recharge from long-term change in the water table. The ranges in permeability and water content obtained with MRS allowed a reduction of the degree of freedom of aquifer parameters used in groundwater modelling.

Uses of Local Plant Species by Agropastoralists in South-western Niger

Knowledge pertaining to local plant species in West African Sahel has been poorly documented despite the central role local vegetation plays in the everyday lives of the rural people. An ethnobotanical study was conducted between April and November 2005 to document knowledge and uses of local herbaceous and woody species by the agropastoralists in South-western Niger. One hundred and twenty three voucher reference samples were collected consisting of 87 and 36 herbaceous and woody species, respectively. The voucher specimens were used for individual interviews of the agropastoralists, guided by a semi-structured questionnaire. In each interview session, an interviewee was shown voucher reference samples and was asked to identify each of them. For each plant species identified, questions were asked about its utilization and the plant part(s) being used. Major uses of local plant species are for traditional medicine, human consumption, animal feed, household construction and firewood. Mean use value of woody species was significantly higher for all use categories (p < 0.001) than for the herbaceous species. These results confirm that “apparent” plants, perennial woody species, are used by the agropastoral communities more intensively than the “non-apparent” short life cycle herbaceous species.

Land clearing, climate variability, and water resources increase in semiarid southwest Niger: A review

The water table in southwestern Niger has been rising continuously for the past decades (4 m rise from 1963 to 2007), despite a ∼23% deficit in monsoonal rainfall from 1970 to 1998. This paradoxical phenomenon has been linked with a change in land use from natural savannah to millet crops that have expanded in area sixfold since 1950 and have caused soil crusting on slopes that has, in turn, enhanced Hortonian runoff. Runoff concentrates in closed ponds and then recharges the aquifer; therefore, higher runoff increases aquifer recharge. At the local scale (2 km2), a physically based, distributed hydrological model showed that land clearing increased runoff threefold, whereas the rainfall deficit decreased runoff by a factor of 2. At a larger scale (500 km2, 1950–1992 period), historical aerial photographs showed a 2.5‐fold increase in the density of gullies, in response to an 80% decrease in perennial vegetation. At the scale of the entire study area (5000 km2), analytical modeling of groundwater radioisotope data (3H and 14C) showed that the recharge rate prior to land clearing (1950s) was about 2 mm a−1; postclearing recharge, estimated from groundwater level fluctuations and constrained by subsurface geophysical surveys, was estimated to be 25 ± 7 mm a−1. This order of magnitude increase in groundwater fluxes has also impacted groundwater quality near ponds, as shown by a rising trend in groundwater nitrate concentrations of natural origin (75% of δ15N values in the range +4 to +8‰). In this well‐documented region of semiarid Africa, the indirect impacts of land use change on water quantity and quality are much greater than the direct influence of climate variability.

Hydrological modelling and associated microwave emission of a semi-arid region in South-western Niger

summary Studying surface–atmosphere feedback is often limited by the accuracy of the land surface observations (particularly soil moisture estimates) or the performance of the land surface models. To further our understanding of soil moisture effects on land–atmosphere fluxes, improvements in soil moisture mapping over large regions are necessary. The aim of this study was to obtain accurate soil moisture mapping over a 120 by 100 km 2 area in West Africa using the considerable amount of measurements available from local and regional scales, recorded during the African monsoon multidisciplinary analysis (AMMA) experiment. The modelling strategy was based on the use of a land surface model (LSM), employed to provide high-resolution soil moisture mapping over the studied area. A microwave emission model was then used to simulate associated microwave brightness temperatures (TB) to compare with the Advanced microwave scanning radiometer (AMSR) at the same spatial (25 by 20 km 2 ) and temporal resolution (daily). Discrepancies between observed and simulated TB were analysed and used to calibrate the LSM and the microwave emission models to match the specific hydrology and soil microwave behaviour of the studied area. Nevertheless, a positive bias of the near-surface soil moisture remained and the land surface model was still unable to reproduce the rapid dynamic of the near-surface soil moisture observed at the local and regional scales in this climatic context. To solve this problem, a secondary surface soil layer was added to match in situ soil moisture measurements as well as satellite microwave measurements. Additionally, the choice of the soil permittivity model was found to be of prior importance in order to perform suitable microwave brightness temperatures. Finally, a soil moisture retrieval algorithm based on AMSR and meteosat second generation (MSG) measurements was proposed in order to improve the quality of the soil moisture estimates over the studied area (the root mean square error decreases from 5.4 % vol. to 2.8 % vol).

Botanical Knowledge and its Differentiation by Age, Gender and Ethnicity in Southwestern Niger

Indigenous knowledge is unevenly distributed. Individual knowledge level may be affected by many factors such as gender, age, ethnicity, profession, religious and cultural beliefs, abundance and usefulness of the species. This study documents indigenous knowledge of herbaceous and woody plant species of farmers and herders in southwestern Niger. Specifically, we examine the effects of age, gender, and ethnicity on knowledge of local vegetation. Results from the study showed that on average a higher proportion of woody species was identified by the respondents compared to herbaceous species. Both gender and ethnicity had a significant effect on the identification of herbaceous species but no effect on identification of woody species. Respondents in lower age group (10 to 30 years) identified lower number of species compared to other age classes. There seems to be a curvilinear relationship between age of respondents and number of plant species identified. Results from this study reaffirm the uneven distribution of indigenous knowledge within a given area due to social factors. The main challenge is how to incorporate these social differences in knowledge of native plant species into sustainable management and conservation of community natural resources.

A spatially explicit assessment of current and future hotspots of hunger in Sub-Saharan Africa in the context of global change

Hunger knows no boundaries or borders. While much research has focused on undernutrition on a national scale, this report evaluates it at subnational levels for Sub-Saharan Africa (SSA) to pinpoint hotspots where the greatest challenges exist. Undernutrition is assessed with a spatial resolution of 30 arc-minutes by investigating anthropometric data on weight and length of individuals. The impact of climate change on production of six major crops (cassava, maize, wheat, sorghum, rice and millet) is analyzed with a GIS-based Environmental Policy Integrated Climate (GEPIC) model with the same spatial resolution. Future hotspots of hunger are projected in the context of the anticipated climate, social, economic, and bio-physical changes. The results show that some regions in northern and southwestern Nigeria, Sudan and Angola with a currently high number of people with undernutrition might be able to improve their food security situation mainly through increasing purchasing power. In the near future, regions located in Ethiopia, Uganda, Rwanda and Burundi, southwestern Niger, and Madagascar are likely to remain hotspots of food insecurity, while regions located in Tanzania, Mozambique and the Democratic Republic of Congo might face more serious undernutrition. It is likely that both the groups of regions will suffer from lower capacity of importing food as well as lower per capita calorie availability, while the latter group will probably have sharper reduction in per capita calorie availability. Special attention must be paid to the hotspot areas in order to meet the hunger alleviation goals in SSA.

Contribution of magnetic resonance sounding to aquifer characterization and recharge estimate in semiarid Niger

To improve the knowledge of the regionally important Continental Terminal 3 (CT3) aquifer in south-western Niger, fifteen magnetic resonance soundings (MRS) were carried out in December 2005 in the vicinity of wells and boreholes. The output MRS geophysical parameters, i.e. water content and decay constants versus depth, were compared to hydrogeological characteristics, i.e. water table depth, total porosity, specific yield and transmissivity estimated from direct measurements, pumping tests and transient groundwater modelling. The MRS-determined parameters were then used to estimate the rates of groundwater recharge. Contained in poorly consolidated Tertiary sandstones, the CT3 aquifer's water table has continuously risen by 4 m in total over the past four decades. Additionally, a significant portion of this increase has occurred in the past decade alone, with an annual rise now ranging between 0.1 and 0.3 m depending on the monitored well. Increase in groundwater recharge due to land clearance and deforestation explains this situation. According to previous estimations, the pre-clearing recharge ranged from 1 to 5 mm per year in 1950–60 s, while more recent recharge rates (1990s–2000s) range from 20 to 50 mm per year. These recharge values are directly affected by estimated aquifer specific yield value, while the spatial variation of rates of water table rise can be attributed to large scale hydrodynamic heterogeneities in the aquifer. However, few field measurements were available to confirm these assumptions. The main results of this study are: (1) The water table depth and aquifer transmissivity are estimated from MRS output parameters with an average accuracy of ± 10% and ± 9% respectively. (2) The MRS-determined water content is linked to both the total porosity and the specific yield of the aquifer, but no quantitative formulation can be proposed as yet. (3) Using the average MRS-determined water content over the investigated area, i.e. 13%, the groundwater recharge rates can be estimated to be ~ 2 mm per year in the 1950–1960s (pre-clearing period), and ~ 23 mm per year for the last decade. (4) The variations in specific yield and transmissivity cannot explain by themselves the spatial variability of the rise of the water table. (5) The ranges in transmissivity and water content obtained from MRS are more realistic than the groundwater modelling outputs. Therefore, MRS could be used to better constrain the aquifer parameters in groundwater modelling with a dense site network. Finally, this work illustrates how MRS can successfully improve characterisation and transient multi-year groundwater balance of commonly found sedimentary aquifers, particularly when integrated with well observations and pumping tests.

Intensification scenarios in south-western Niger: Implications for revisiting fertilizer policy

In semi-arid south-western Niger, external fertilizer inputs are a complement of livestock-mediated nutrient transfers for maintaining soil fertility. This paper discusses scenarios of intensification for different farm household types in an area representative of the wetter parts of semi-arid Sahel. Twenty-five-year projections suggest that soil fertility may not always or irreversibly deteriorate under intensification, and that nitrogen is the main external input required. Owning animals allows some households to achieve food security and maintain soil fertility by capturing and mobilizing soil nutrients. Intensification will bring various benefits to livelihoods, but these will be unevenly distributed. The results of this paper should caution scientists and policy-makers against the often heard warning of inevitable losses in soil fertility in the Sahel associated with intensive technologies, and against extrapolating conclusions attained at specific locations or social groups. Endogenous coping strategies based on using local inputs can also be effective and should be explored in addition to a continued attention for the need for more targeted uses of external inputs.