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The high groundwater salinity of crystalline aquifers in semiarid areas is generally attributed to the dissolution and leaching of meteoric salts that have been progressively evapoconcentrated in the different hydrological compartments under dry climate conditions. A numerical model, simulating water and salt balances, was developed from a case study in Northeast Brazil to: (1) test the validity of this hypothesis, through the quantification of all relevant water cycle processes in the studied watershed, and (2) demonstrate how changes in land cover can impact groundwater salinity. Computations showed that the aridity and the high evapo(transpi)ration rates from the unsaturated zone and/or surface water (ponds, reservoirs) cannot lead to the observed aquifer salinization levels, but only to concentrations of a few tens or hundreds of mg L–1 (Cl–). The only process that can induce a high groundwater salinity, with chloride concentrations up to several g L–1, is the transpiration of groundwater by the deep roots of the vegetation, with a rate reaching 100% of the annual recharge. In this case study, the vegetation involved is the native Caatinga forest. Simulations of the long-term dynamics of groundwater salinity indicate that aquifer areas with high salinity are relicts of the Caatinga pre-colonization period during which subterranean endorheic conditions were prevailing. Following the Caatinga deforestation linked to colonial agricultural development, aquifer recharge increased and endorheism ceased. Consequently, these aquifers may have now been experiencing a desalination process for about three centuries. The desalination spatial variability drivers are explained in the paper. [ABSTRACT FROM AUTHOR]

Small and shallow alluvial aquifers in arid and semi-arid regions compose an important water system that smallholder farmers rely on for irrigation and livestock feeding. Geological settings and the small scale of these aquifers suggest the need for governance at the local level, but research supporting its development is still scarce. Treating a case of alluvial aquifers exploited by smallholder farmers located in the Brazilian semi-arid region as a common pool resource (CPR), this paper analyses the governance of a social-ecological system (SES) for which an alluvial aquifer is an essential source of water. The paper applies the SES Framework to analyse the SES in light of Ostrom's principles for sustainable CPR management to answer the questions: (1) can the governance arrangements support sustainable common pool resource management of the alluvial aquifers? (2) what opportunities are there to make the management of the aquifer more sustainable through community-based governance? (3) can Ostrom's design principles lead the transition to more sustainable governance of alluvial aquifers? Despite a water policy aiming for decentralisation and participatory governance, gaps in the implementation of these policies are identified. Taking into account the challenges imposed by the aquifer characteristics to impact efficient groundwater exploitation, equity in water distribution and conservation of the CPR, the analysis reveals opportunities to improve CPR management by supporting the community to increase participation in the governance of the aquifer in coordination with existing policies. This work concludes with suggestions that could empower community progress towards more sustainable governance of the aquifer. [ABSTRACT FROM AUTHOR]