Assessing the hydrogeological resilience of a groundwater-dependent Mediterranean peatland: Impact of global change and role of water management strategies.

Mediterranean peatlands remain largely under-documented, except for detailed biological data such as fauna and flora taxa lists, and yet are increasingly threatened by water withdrawal and agriculture practices. This lack of information, particularly on their hydrogeological functioning, makes it impossible to evaluate their response to changing climate conditions. A pilot study on a representative Mediterranean peatland on the island of Corsica (France) was conducted to evaluate recharge modalities in the peatland using a coupled water-level monitoring, geochemical and isotope multi-tracing approach (electric conductivity, major ions, δ18O, δ2H, 3H, 87Sr/86Sr). The goal was to understand how water budgets in peatland ecosystems were maintained throughout the year, especially during the summer. Despite the remarkable stability of the peatland water level, the recharge contributions of varied water bodies through an alluvial aquifer vary significantly from one season to another. An end-member mixing analysis (EMMA) indicates that the peatland is mainly recharged by an alluvial aquifer. During fall-winter, the alluvial aquifer on which the peatland depends is recharged by the rainfall, a river, and shallow groundwater (colluvium). During spring-summer, water supply is provided mostly by a river, shallow, and deep groundwater (fractured granite). However, this specific hydrogeological functioning is not taken into account by environmental management policies making peatlands vulnerable to anthropogenic and climatic pressures. Thus, their actual status regarding water and aquatic environment management policies is discussed to provide recommendations for better consideration and preservation.

Impact of irrigated agriculture on groundwater resources in a temperate humid region.

The groundwater irrigation expansion, and its multiple potential impacts on the quantity and quality of water resources, is not just restricted to areas that are water limited. In this study we present the seasonal impacts irrigation practices can have on groundwater resources in a temperate humid region, where the average annual rain/PET ratio is 1.0. In this system the irrigation expansion is solely supported by groundwater pumping, but despite this only 5 boreholes are monitored for hydraulic head data. In this study, we compensate the scarce hydrophysical dataset by incorporating environmental tracers (major ions, δ18O, δ2H and δ13C) and dating tracers (3H, CFC, SF6 and 14C). Results indicate that at 9 of the 15 irrigation sites investigated, groundwater pumping for irrigation has induced the mixing of recent groundwater (up to <1year) with older waters. The origin of the older waters was from either the deeper marl aquifer, or the shallow sand-clay aquifer (SCB) that has a 14C mean residence time (MRT) of up to 9700years. Secondly, although high nitrate loads in infiltrating waters were being diverted via the artificial subsurface drainage system, increases in fertiliser loads have resulted in higher NO3 concentrations in younger groundwater (NO3: 9-45mg/L, MRT <20years), compared with older groundwater (NO3≤9mg/L, MRT>20years). The changes in flow pathways, induced by irrigation, also results in seasonal declines in groundwater NO3 concentrations due to mixing with older waters. In temperate humid areas, such evaluations of the seasonal evolution of water residence time, mixing process, and agrochemical contaminants are an important contribution to real water resources management in irrigated catchments.

Mechanism of degradation of the quality of natural water in the Lakes Region of the Ethiopian rift valley.

The natural waters of the Lakes Region in the Main Ethiopian Rift (MER) show serious problems of chemical quality. The high content of fluoride reaches 300 mgl(-1) and affects the health of the population who live in this area. Furthermore, the alkaline and sodic characteristics (8 2(Ca + Mg)]. which results from the weathering and dissolution of the volcanic rocks. The predictive qualities of the model AQUA were tested in the context of this region. A simulation of the concentration of the waters by evaporation has shown chemical variations relatively similar to those obtained with field data which include the minor chemical elements such as the fluoride or the dissolved silica. For field data, enrichment is more variable and may represent localised conditions of mineralization. This model is then used to study a method of defluoridation by supplying these waters with calcium in the form of gypsum. This method also allows the reduction of the alkalinizing and sodifying characteristics of the waters without reaching the fluoride standard concentration accepted for drinking waters. For drinking purpose, waters of the Ethiopian rift should undergo another method of defluoridation.

Nitrate pollution study in the aquifer of Dakar (Senegal).

Dakar is a peninsula inhabited by a population of about 2 million people in 1996. In some dug wells and piezometers, the nitrate content (NO3.) in the groundwater is above the World Health Organization (WHO) limit of 50 mg/l. In the unconfined part of the aquifer of the peninsula, all the samples from wells are contaminated by high nitrate contents which increased over time from 100 mg/l in 1987 to more than 250 mg/l in 1996. Only a limited area is affected by nitrate pollution in the confined layer. The results indicate anthropogenic pollution, a fact which indicates the increasing risk of pollution of drinking-water resources. Studies in the unsaturated zone and familiarity with the sanitation practices in the area indicate that the horizontal and vertical flux are linked mainly to defective septic tanks and direct organic waste elimination into the soil by more than 40% of the inhabitants. The correlation between tritium values (3H) and nitrate shows that the source of nitrate is recent. The relation of oxygen 18 (18O) to deuterium (2H) in water with high nitrate levels indicates that the concentrations of nitrate have been identified in evaporated points.