Groundwater monitoring for assessing artificial recharge in the Mediterranean coastal aquifer of Korba (Northeastern Tunisia).

Groundwater (GW) artificial recharge with treated wastewater (TWW) is seen as a promising technical solution to overcome groundwater overexploitation and seawater intrusion and to ascertain future water resources availability. While these introduced recharge systems have shown positive impacts in many areas across the world, their effective contribution to GW recharge is still not well quantified in water-stressed regions such as Tunisia. The scarcity of on-site data with accurate temporal and spatial measurements and resolution in such areas hinders the clear assessment of these recharge systems' performances. This article presents an approach based on the on-site monitoring of groundwater level and salinity measurements and recharge rate records spanning over the 6-year period to investigate the performances of a wastewater-based recharge system located in the Korba-El Mida site in Tunisia. The analysis showed that the artificial recharge did not have an impact on groundwater level. Controversially, a decrease in water salinity in and around the study site was observed. Findings emphasize on the weak wastewater volumes applied to the recharge system and the clogging phenomena that occurred in the pool and in the vadose zone. Furthermore, analyzing the information over a short period of time could be misleading as the results of a 6-year period of monitoring show clearly that the way the site was managed and the local conditions have a role in understanding and interpreting the results even if the artificial recharge was appropriately designed.

Assessment of Agriculture Pressures Impact on the Joumine River Water Quality Using the PEGASE Model.

The protection of the aquatic environment while managing the risk of water scarcity in the Mediterranean region is challenging. Ensuring future sustainability of water resources needs improved monitoring networks and early warning system of future trends of water quality. A specific concern is given to nonpoint source pollution from agriculture, which is often the main source of water quality degradation in rivers. In this work, we focused on the Joumine river basin, a rural-catchment situated north Tunisia dominated by agricultural activities and exposed to eutrophication problems. Aiming to present an assessment framework of the spatial-temporal water quality variability and quantify "pressure-impact" relationships, we used a physically based modeling approach involving the river/basin integrated model PEGASE (Planification Et Gestion de l'ASsainissement des Eaux). PEGASE simulates watercourses physicochemical quality depending on the morphology of the drainage network, hydrometeorological conditions and natural and anthropogenic influences. Simulation results showed a better description of Joumine river water quality and helped in identifying exposed areas to nutrients export. Results have also emphasized the contribution of different pollution sources. We were able to examine the potential impact of agriculture diffuse pollution and we found that Nitrate is the element mostly threatening water quality. The nutrients patterns suggest that climate and farming practices are important factors controlling their transfer. These findings demonstrate that the adopted assessment approach in investigating the behavior of the studied hydrosystem can be a useful support to develop an appropriate surface water quality management program in a semiarid context.

Modeling water quality to improve agricultural practices and land management in a tunisian catchment using the soil and water assessment tool.

Agriculture intensification has impaired water quality. In this study, the risk of pollution by nitrates was assessed by experimental monitoring, spatial integration of farm census, and modeling of water quality using the Soil and Water Assessment Tool (SWAT), version 2009, over the period of 1990 to 2006 for a catchment located northern Tunisia. Under a semiarid climate, the water quality is influenced by the predominating agriculture activities. The hydrological results are compared with the observed flows derived from measurements at the outlet of the Joumine watershed. Model performance showed good statistical agreements, with a Nash-Sutcliffe efficiency of 0.9 and a value of 0.92 after monthly calibration. The model predicted the timing of monthly peak flow values reasonably well. During the validation period, SWAT simulations were nearly as accurate, with Nash-Sutcliffe efficiency and values of 0.89 and 0.92, respectively. The model was used to simulate NO concentrations. The predicted NO concentration values were compared with in situ measured concentrations. The simulated and measured NO-N concentrations varied in the same range of 0 to 5 mg L at the E3 and E5 locations. The calibrated model was then used for simulating the impact of the best management practice scenarios to reduce NO loads to the river. The first set-up consisted of reducing the N fertilizer application by 20 and 100% from the current state. These two scenarios induced a reduction in NO loads by 22 and 72%, respectively. The second set-up consisted of using vegetation filter strips. The last scenario combined filter strips and a reduction of 20% in N fertilizer application. Results showed NO reduction rates of 20 and 36%, respectively. The SWAT model allowed managers to have several options to improve the water quality in the Joumine watershed.

Hydrology, biogeochemistry and metabolism in a semi-arid mediterranean coastal wetland ecosystem.

A LOICZ Budget Model is applied to the Ichkeul Lake, a wetland ecosystem of the South Mediterranean-North African region, to evaluate its functioning in order to boost water management. The Ichkeul Lake water and nutrient budget, net ecosystem metabolism (NEM), nutrient availability, and their seasonal changes are estimated using field data. A considerable anthropogenic-driven amount of nitrogen is transferred into N2/N2O to the atmosphere during the dry season with predominance of denitrification-anammox processes. The primary production is impacted by forcing the ecosystem respiration to reduce the NEM so that the system is functioning as heterotrophic. Climate change and anthropogenic pressures are expected to exacerbate the current trends of water quality degradation, with possible negative impacts on Palearctic birds' population. Mitigation actions are possible, through the implementation of National Wetland Management Strategies that include nutrient load and water resources management.

Valuing scarce observation of rainfall variability with flexible semi-distributed hydrological modelling - Mountainous Mediterranean context.

To represent spatial and temporal variability in rainfall adequately, rainfall-runoff models must compromise among modelling objectives, data availability, conceptualization options, and the actual variability in rainfall. This is of utmost importance for challenges of integrated water management in the rapidly changing Mediterranean context. We evaluated the sensitivity of the SWAT model to combinations of spatial rainfall variability and catchment subdivision in a data-scarce mesoscale mountainous Mediterranean context. The case study focused on the Joumine catchment, in northern Tunisia, which is emblematic of agro-hydro-chemical changes and challenges. The double-mass curve method was used to verify the consistency of rainfall time series from 1991 to 2003, indicating proportionality between annual rainfall at the reference gauge and that of the nearest gauge. The rainfall lapse rate at the Joumine catchment was 69.9 mm per 100 m of altitude. Seven sets of rain gauges and five subdivision configurations of the catchment were simulated. Differences between measured and predicted streamflow at the outlet were assessed using three indices of model fit. Predicted streamflow was extremely sensitive to spatial rainfall variability but relatively insensitive to catchment subdivision. Daily predictions were most accurate for the wettest year (2002-2003) and least accurate for the driest year (1993-1994).

Quantifying hydrological responses of small Mediterranean catchments under climate change projections.

Catchment flow regimes alteration is likely to be a prominent consequence of climate change projections in the Mediterranean. Here we explore the potential effects of climatic change on the flow regime of the Thau and the Chiba catchments which are located in Southern France and Northeastern Tunisia, respectively. The Soil and Water Assessment Tool (SWAT) hydrological model is forced with projections from an ensemble of 4 climate model (CM) to assess changes and uncertainty in relevant hydrological indicators related to water balance, magnitude, frequency and timing of the flow between a reference (1971-2000) and future (2041-2071) periods. Results indicate that both catchments are likely to experience a decrease in precipitation and increase in temperature in the future. Consequently, runoff and soil water content are projected to decrease whereas potential evapotranspiration is likely to increase in both catchments. Yet uncertain, the projected magnitudes of these changes are higher in the wet period than in the dry period. Analyses of extreme flow show similar trend in both catchments, projecting a decrease in both high flow and low flow magnitudes for various time durations. Further, significant increase in low flow frequency as a proxy for hydrological droughts is projected for both catchments but with higher uncertainty in the wet period than in the dry period. Although no changes in the average timing of maximum and minimum flow events for different flow durations are projected, substantial uncertainty remains in the hydrological projections. While the results in both catchments show consistent trend of change for most of the hydrologic indicators, the overall degree of alteration on the flow regime of the Chiba catchment is projected to be higher than that of the Thau catchment. The projected magnitudes of alteration as well as their associated uncertainty vary depending on the catchment characteristics and flow seasonality.

Modelling climate change impacts on and adaptation strategies for agriculture in Sardinia and Tunisia using AquaCrop and value-at-risk.

In Europe, there is concern that climate change will cause significant impacts around the Mediterranean. The goals of this study are to quantify the economic risk to crop production, to demonstrate the variability of yield by soil texture and climate model and to investigate possible adaptation strategies. In the Rio Mannu di San Sperate watershed, located in Sardinia (Italy) we investigate production of wheat, a rainfed crop. In the Chiba watershed located in Cap Bon (Tunisia), we analyze irrigated tomato production. We find, using the FAO model AquaCrop that crop production will decrease significantly in a future climate (2040-2070) as compared to the present without adaptation measures. Using "value-at-risk", we show that production should be viewed in a statistical manner. Wheat yields in Sardinia are modelled to decrease by 64% on clay loams, and to increase by 8% and 26% respectively on sandy loams and sandy clay loams. Assuming constant irrigation, tomatoes sown in August in Cap Bon are modelled to have a 45% chance of crop failure on loamy sands; a 39% decrease in yields on sandy clay loams; and a 12% increase in yields on sandy loams. For tomatoes sown in March; sandy clay loams will fail 81% of the time; on loamy sands the crop yields will be 63% less while on sandy loams, the yield will increase by 12%. However, if one assume 10% less water available for irrigation then tomatoes sown in March are not viable. Some adaptation strategies will be able to counteract the modelled crop losses. Increasing the amount of irrigation one strategy however this may not be sustainable. Changes in agricultural management such as changing the planting date of wheat to coincide with changing rainfall patterns in Sardinia or mulching of tomatoes in Tunisia can be effective at reducing crop losses.