Green waste biochar effects on sandy soil physicochemical properties

The organic amendment of degraded soil in South East of Tunisia was used to restore the chemical, and physical properties of soil quality investigated in this study. Biochar derived from pyrolyzed green waste at 360°C was used like organic amendment.  Nines randomized plots with one square meter of the area of each plot in three replicates have been installed in the Institute of Arid Area in Mednine South East of Tunisia, with two rates of biochar 20 and 40 t/ha were investigated: 20 tons/ha (B20) (2 kg/m²) and 40 tons/ha (B40) (4 kg/m²). The results showed that biochar had a positive effect on soil's physical and chemical properties compared to non-amended soil (Untreated soil). Biochar supply at rates of 20 and 40 tons/ha, causes a decrease in electrical conductivity to achieve 2.66 mS/cm for the B40 dose after 1 year of amendment, also a decrease in the bulk density at the surface layer (0-20 cm) has been registered, the total porosity which was decreased with depth. The hydraulic conductivity is favored by the incorporation of biochar in the soil which increases the volume of voids and tends to create preferential flow paths

An interdisciplinary methodology to design integrated and innovative MAR systems in arid and semi-arid regions. Two case studies in Algeria and in Tunisia

Drought,  desertification, Managed Aquifer Recharge (MAR), Tunisia, Algeri

Dynamic hydrological modeling in drylands with TRMM based rainfall

This paper introduces and evaluates DryMOD, a dynamic water balance model of the key hydrological process in drylands that is based on free, public-domain datasets. The rainfall model of DryMOD makes optimal use of spatially disaggregated Tropical Rainfall Measuring Mission (TRMM) datasets to simulate hourly rainfall intensities at a spatial resolution of 1-km. Regional-scale applications of the model in seasonal catchments in Tunisia and Senegal characterize runoff and soil moisture distribution and dynamics in response to varying rainfall data inputs and soil properties. The results highlight the need for hourly-based rainfall simulation and for correcting TRMM 3B42 rainfall intensities for the fractional cover of rainfall (FCR). Without FCR correction and disaggregation to 1 km, TRMM 3B42 based rainfall intensities are too low to generate surface runoff and to induce substantial changes to soil moisture storage. The outcomes from the sensitivity analysis show that topsoil porosity is the most important soil property for simulation of runoff and soil moisture. Thus, we demonstrate the benefit of hydrological investigations at a scale, for which reliable information on soil profile characteristics exists and which is sufficiently fine to account for the heterogeneities of these. Where such information is available, application of DryMOD can assist in the spatial and temporal planning of water harvesting according to runoff-generating areas and the runoff ratio, as well as in the optimization of agricultural activities based on realistic representation of soil moisture conditions

The Use of geophysical methods to evaluate soil sediments behind gabion check dams in the dry regions of southern Tunisia.

This study aims to detect sediment at six gabions check-dams distributed in the upstream and downstream areas of the Koutine catchment located in an arid area in the southeast of Tunisia and characterized by an annual mean precipitation of less than 200 mm. The detection of sediment is based on the Electrical Resistivity Tomography (ERT) method associated with topographic measurements. About ten lines were arranged, with 72 electrodes. The results of resistivity data obtained during field measurements were inverted into subsurface structures using least squares inversion techniques. The preliminary results indicate that the sediment can be identified using an ERT contour method. The obtained results are calibrated based on samples collected for laboratory analysis. The accuracy of the high-density ERT method was justified. The density increases with the sediment deposit depth. Topographic methods were used to estimate the surface and the relief of deposed sediments in the area monitored by the gabions check-dams. This study provides an approach based on the high-density electrical resistivity tomography method and a topographic investigation to estimate sediment yield behind gabion check-dams that control catchments. The sedimentary deposit of eroded soils reduces the effectiveness of the recharge structures. Consequently, the improvement of permeability at the level of the retention basins (by cleaning the settlement basin and creating recharge wells) is of great importance. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence

An Integrated Cost–Benefit and Livelihood Approach for Assessing the Impact of Water Harvesting Techniques (WHTs) on Livelihoods: A Case Study in the Oum Zessar Watershed, South-East Tunisia

Despite broad interest in use of water harvesting techniques (WHTs) to reduce pressure on natural resources in arid zones, few ex post assessments are available on how WHTs impact livelihood sustainability. This paper assesses the impact of WHTs on the livelihood conditions of inhabitants in the Oum Zessar watershed in south-east Tunisia. We used an integrated impact assessment (IIA) framework incorporating extended cost–benefit analysis (ECBA) and the sustainable livelihoods approach (SLA). The former internalizes environmental impacts while the latter enables assessment of the contributions of WHTs to rural livelihoods in the watershed. We began by using ECBA to estimate the profitability of investments in WHTs. We then scaled up our impact perspective from the local level to the watershed level using SLA based on survey data from beneficiary households upstream, midstream and downstream. Our goal was to better understand and evaluate changes in livelihoods and associated environmental effects. We focused on the links between cost–benefit of WHTs and sustainable livelihoods, looking in particular at the capitals that connect the two. Our ECBA results suggest that WHT techniques did benefit the local population at both the private and the social level (IRR > 20%; NPV > 2000 TD/ha). Sensitivity analysis confirmed this result. SLA findings point to a central role of social capital in promoting sustainable livelihoods, followed by physical capital enhanced by WHTs construction, especially in the upstream and downstream segments of the watershed. Recommendations were derived from these outcomes for more integrated watershed management policy

The Use of geophysical methods to evaluate soil sediments behind gabion check dams in the dry regions of southern Tunisia.

This study aims to detect sediment at six gabions check-dams distributed in the upstream and downstream areas of the Koutine catchment located in an arid area in the southeast of Tunisia and characterized by an annual mean precipitation of less than 200 mm. The detection of sediment is based on the Electrical Resistivity Tomography (ERT) method associated with topographic measurements. About ten lines were arranged, with 72 electrodes. The results of resistivity data obtained during field measurements were inverted into subsurface structures using least squares inversion techniques. The preliminary results indicate that the sediment can be identified using an ERT contour method. The obtained results are calibrated based on samples collected for laboratory analysis. The accuracy of the high-density ERT method was justified. The density increases with the sediment deposit depth. Topographic methods were used to estimate the surface and the relief of deposed sediments in the area monitored by the gabions check-dams. This study provides an approach based on the high-density electrical resistivity tomography method and a topographic investigation to estimate sediment yield behind gabion check-dams that control catchments. The sedimentary deposit of eroded soils reduces the effectiveness of the recharge structures. Consequently, the improvement of permeability at the level of the retention basins (by cleaning the settlement basin and creating recharge wells) is of great importance. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence

Soil Erosion Estimates in Arid Region: A Case Study of the Koutine Catchment, Southeastern Tunisia

Soil erosion remains one of the principal environmental problems in arid regions. This study aims to assess and quantify the variability of soil erosion in the Koutine catchment using the RUSLE (Revised Universal Soil Loss Equation) model. The Koutine catchment is located in an arid area in southeastern Tunisia and is characterized by an annual mean precipitation of less than 200 mm. The model was used to examine the influence of topography, extreme rainstorm intensity and soil texture on soil loss. The data used for model validation were obtained from field measurements by monitoring deposited sediment in settlement basins of 25 cisterns (a traditional water harvesting and storage technique) over 4 years, from 2015 to 2018. Results showed that slope is the most controlling factor of soil loss. The average annual soil loss in monitoring sites varies between 0.01 and 12.5 t/ha/y. The storm events inducing the largest soil losses occurred in the upstream part of the Koutine catchment with a maximum value of 7.3 t/ha per event. Soil erosion is highly affected by initial and preceding soil conditions. The RUSLE model reasonably reproduced (R2 = 0.81) the spatiotemporal variability of measured soil losses in the study catchment during the observation period. This study revealed the importance of using the cisterns in the data-scarce dry areas as a substitute for the classic soil erosion monitoring fields. Besides, combining modeling of outputs and field measurements could improve our physical understanding of soil erosion processes and their controlling factors in an arid catchment. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence