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This review examines the role of soil and sediment organisms as bioindicators in environmental pollution assessment. As fundamental elements of terrestrial ecosystems, soils harbour a rich and diverse biodiversity that plays a key role in regulating ecological processes. The use of bioindicators provides a sensitive and specific approach to detecting the effects of chemical, biological, and physical pollutants on soil health. The review presents a detailed analysis of the types of contaminants commonly encountered, the soil organisms used as bioindicators, and the criteria for selecting the most appropriate bioindicators. It also discusses assessment methods, including soil sampling and analysis techniques, and the biological and ecological indices used to measure contamination. Regional case studies illustrate the practical application of bioindicators for assessing soil quality in different geographical contexts. The review also highlights current challenges to the use of bioindicators, such as technical limitations and the variability of organism responses, and suggests perspectives for future research, including technological innovation and the integration of bioindicators into environmental policy.

In arid and semi-arid regions, managing agricultural water for irrigation is essential to cope with water scarcity and maximize crop yields. In this study, an experiment was conducted on a potato crop in the Manouba region (lower valley of Medjerda, Tunisia). The experimental protocol consisted of four water treatments utilizing water-saving irrigation techniques: FI (Full Irrigation 100%): irrigation with 100% of crop water requirements. DI (Irrigation 75%): deficit irrigation with the application of 75% of crop water requirements. PRDRight (Irrigation 50% on the right side): Irrigation by partial root drying. PRDLeft (Irrigation 50% on the left side): Irrigation by partial root drying. Simulation of soil water profiles was carried out by the Hydrus-1D model. The soil hydraulic properties were calibrated according to the experimental conditions using an inverse modeling technique. According to the obtained results, simulated soil water profiles were close to those measured. Indeed, the calculated NRMSE values are low, indicating the reliability of Hydrus-1D as a decision support tool to optimize water irrigation management. These results were then used to investigate the effects of a 2 °C temperature increase on soil water loss, and it was determined that the impact was insignificant. HIGHLIGHTS Arid and semi-arid need irrigation water saving techniques.; Deficit irrigation and partial root drying techniques can be a good alliterative to drip irrigation.; Simulation of water flow in the unsaturated soil allows the estimation of soil water storage.; Soil water loss under irrigation saving techniques is related to the applied irrigation doses.; The increase in temperature has no significant effect on deep percolation.;

In arid and semi-arid regions like Tunisia, irrigation water is typically saline, posing a risk of soil and crop salinization and yield reduction. This research aims to study the combined effects of soil matric and osmotic potential stresses on tomato root water uptake. Plants were grown in pot and field experiments in loamy-clay soils and were irrigated with three different irrigation water qualities: 0, 3.5, and 7 dS/m. The Hydrus-1D model was used to simulate the combined dynamics of subsurface soil water and salts. Successful calibration and validation of the model against measured water and salt profiles enabled the examination of the combined effects of osmotic and matric potential stresses on root water uptake. Relative yields, indirectly estimated from actual and potential transpiration, indicated that the multiplicative stress response model effectively simulated the measured yields and the impact of saline water irrigation on crop yields. The experimental and modeling results provide information to aid in determining the salinity levels conducive to optimal crop growth. The findings indicate that the selected salinity levels affect tomato growth to varying degrees. Specifically, the salinity levels conducive to optimal tomato growth were between 0 and 3.5 dS/m, with a significant growth reduction above this salinity level. The gradual salinization of the root zone further evidenced this effect. The scenario considering a temperature increase of 2 °C had no significant impact on crop yields in the pot and field experiments.

The project ‘Research and Training on Irrigation with Saline Water in Tunisia’, with the project report published by UNESCO in 1970, was set up to specify Tunisian standards for the use of saline water and to mitigate their effects on crop yields. The objective of this study is to assess the risk of long-term soil salinization by considering the agricultural practices mentioned in the project for the ‘Water Quality’ experiment in the semi-arid region of Cherfech (Tunisia). A Hydrus-1D model was used to simulate the movement of water and the transfer of salts. Soil hydraulic and solute transport parameters were estimated using inverse modeling. Calibration and validation of the model were made for the water and salt profiles carried out with four irrigation qualities QA, QB, QC and QD. Four scenarios over 50 years were studied: (i) S1 with rainfall (400 mm) only; (ii) S2 with rainfall and irrigation (1,400 mm); (iii) S3 with a 2 °C increase in temperature; (iv) S4 with the addition of 100 mm·d−1 of rainfall. The four scenarios highlighted the high risk of soil salinization, especially for the QB, QC and QD qualities after 20 years of irrigation and the deep dynamics of water and salts beyond the root zone which increases the risk of groundwater salinization. HIGHLIGHTS Saline water in Tunisia is a significant constraint on development.; The UNESCO project report Research and Training on Irrigation with Saline Water in Tunisia of 1970 is the only local reference for decision makers.; Inverse modeling is an essential tool to estimate soil transport parameters.; Assessment of soil salinization under different climate change scenarios.; Use of saline water based on the project practices can lead to the destruction of agricultural soils after 20 years.;

Irrigation in Tunisia is threatened all over the country. The irrigated coastal area of Dyiar-Al-Hujjej has observed a drop in agricultural activity following a seawater intrusion. Thus, yields have become disrupted in direct relation to the quantities of fresh water supplied and transferred over a distance of 100 km. For the sustainability of this area, the feasibility of using desalinated water to stabilize the irrigation water supply was analyzed. When all crop water requirements are to be met with desalinated water, the net income is negative for crops currently grown, except strawberry. All the open-field crops remain unprofitable even in the case of agro-industrial development, except tomatoes. A blending between desalinated seawater and aquifer saltwater also leads to a negative income for the main crops. The introduction of greenhouses to replace the same open-season crops is beneficial when desalinated water is used. The use of desalinated water in irrigation faces the high cost of desalination (0.5 US $/m3) while the average price of irrigation water in Tunisia is 0.05 US $/m3. Desalination can be recommended only in the case of crops with low need for water and high added value.

In semi-arid regions like Tunisia, agricultural use of saline waters raises soil salinization risk. A land-parcel was selected in the semi-arid region of Ariana for simulating water and salts dynamics in order to assess the ability of Hydrus-1D model in various field conditions and to assess the environmental risks due to the salinization process. Four water qualities were used (C1 = 1 dS m−1, C2 = 7 dS m−1, C3 = 14 dS m−1 and C4 = 21 dS m−1) to irrigate four plots with same dose. Monitoring of the soil moisture was carried out by gravimetric method and soil salinity by measuring the electrical conductivity of the saturated paste up to 80 cm in depth. The model was calibrated during 7 days and the validation was carried out during 383 days. The measured water and saline profiles are similar to the simulated profiles which demonstrate the ability of Hydrus-1D for reproducing water and salts dynamics in such conditions. The soil salinization risk is higher with the use of C3 and C4 water qualities for irrigation. The model can be a powerful tool to assess the environmental risks related to the irrigation with saline waters in semi-arid regions. Keywords: Soil, Salinization, Risk assessment, Hydrus-1D, Tunisia

Arid and semi-arid regions face the risk of soils and aquifers salinization. Rainy events are rare which is characteristic of these regions. They play a significant role in the leaching of salts from topsoil to deeper layers, which increases the risk of aquifers salinization. For this reason, a plot was selected in the semi-arid region of Bou Hajla (Central Tunisia). The simulation of water and salts dynamics was carried out by Hydrus-1D. Model calibration was realised on a flood irrigation experiment during 10 days and in a depth of 4 m. The hydrodynamic parameters were determined by inverse modelling. Model validation was performed successfully during 577 days. The simulation of water and salts dynamics has allowed the analysis of two scenarios: (i) the effect of a very rainy event (> 50mm/day) on the dynamics of salts. This type of event allows leaching of the accumulated salts in the topsoil which promotes their burial in the depth; (ii) the long-term evolution of the saline profile in 20 years showed the cyclical nature of salts leaching in the topsoil, the permanent accumulation of salts in the depth of around 2 m, and a continuous leaching in the deeper layers (around 4 m), which may increase groundwater contamination risk.

Olive mill effluents (OME) are characterized by their nutrients content and their adhesive and hydrophobic properties. An experiment was carried out at an olive growing area in Tunisia, “Sidi Bou Ali”, to identify the impact of spreading over OME on physical soil characteristics. Three treatments were in situ monitored, namely T0 (Control), T1 (25 m3/ha) and T2 (50 m3/ha), over a period of 4 months. Measurements were conducted monthly corresponding respectively to D1, D2, D3 and D4. Water retention curves were established by a physical capillary model in porous medium. Results showed that the two applied OME doses induced a decrease in water retention, especially for potential matrixes above pF 2 corresponding to the water available range. No significant differences were found between the treated soil plots T1 and T2. doi:10.14456/WJST.2014.27

Soil hydraulic properties are necessary for modeling water flow and solute transport in the vadose zone. However, direct measurement of these characteristics in field conditions is tedious, time-consuming and expensive. In this study, a laboratory method was used to characterize soil water retention curves of three soil samples in the region of Bouhajla (Central Tunisia). For experimental purposes, volumetric water content and pressure head values were measured using the gravimetric method and Watermark sensor, of a small disturbed soil core, respectively, during a drying cycle under the effect of evaporation. The van Genuchten model was fitted to the measured retention curves with the RETC software to determine residual water content (θr), saturated water content (θs) and the two shape parameters; α and n. Strong correlations were found between the fitted and measured retention curves. The van Genuchten model was also fitted to the retention curves measured by pressure chamber (as the reference method). The results were evaluated by calculating the root mean square error (RMSE) and the geometric mean error ratio (GMER). Statistical analysis proved the success of the proposed method for estimating van Genuchten soil retention parameters of the studied soils. A Mann-Whitney test performed at the significance level of 0.05 showed no significant difference between the two methods.