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- Predicting the impact of management and climate scenarios on groundwater nitrate concentration trends in southern PortugalPublication . Costa, Luis; Hugman, Rui; Stigter, Tibor Y.; Monteiro, José PauloThe dynamics related to evolution of nitrate-contaminated groundwater are analyzed with focus on the impact of intrinsic aquifer properties, agricultural activities and restoration measures at Campina de Faro aquifer (M12), southern Portugal. Agricultural practices in the region developed in the 1970s and resulted in high abstraction rates, nitrate contamination and salinization. Despite the implementation of the European Union (EU) Nitrates Directive since 1997, nitrate levels still show increasing trends at some locations, constituting a threat to the chemical status of M12 and consequent nitrate discharge to Ria Formosa coastal lagoon. Simultaneously, groundwater levels are not dropping consistently, despite apparent overexploitation. A groundwater flow and mass transport model is developed for M12 to assess the evolution of nitrate under different scenarios. Model results reveal that M12 has a hydraulic connection with northernmost aquifers, a process not properly assessed so far. Results further show that nitrate contamination in the upper Plio-Quaternary layer of M12 is extremely persistent and mostly linked to unbalanced fertilizer application practices and irrigation return flows. The response of M12 to implementation of good agricultural practices in compliance with EU policies is slow, indicating that good qualitative status would be impossible to reach by the required EU deadlines. Integration of climate change scenarios into the transport model reveals that despite the implementation of restoration measures, there could be a retardation of the nitrate levels' decrease in the upper aquifer as a result of enhanced evapoconcentration caused by lower recharge, higher water demands and incomplete mixing within the aquifer.
- Numerical modelling assessment of climate-change impacts and mitigation measures on the Querença-Silves coastal aquifer (Algarve, Portugal)Publication . Hugman, Rui; Stigter, Tibor; Costa, Luis; Monteiro, José PauloPredicted changes in climate will lead to seawater intrusion in the Querença-Silves (QS) coastal aquifer (south Portugal) during the coming century if the current waterresource-management strategy is maintained. As for much of the Mediterranean, average rainfall is predicted to decrease along with increasing seasonal and inter-annual variability and there is a need to understand how these changes will affect the sustainable use of groundwater resources. A densitycoupled flow and transport model of the QS was used to simulate an ensemble of climate, water-use and adaptation scenarios from 2010 to 2099 taking into account intra- and interannual variability in recharge and groundwater use. By considering several climate models, bias correction and recharge calculation methods, a degree of uncertainty was included. Changes in rainfall regimes will have an immediate effect on groundwater discharge; however, the effect on saltwater intrusion is attenuated by the freshwater–saltwater interfaces’ comparatively slow rate of movement. Comparing the effects of adaptation measures demonstrates that the extent of intrusion in the QS is controlled by the long-term water budget, as the effectiveness of both demand and supply oriented measures is proportional to the change in water budget, and that to maintain the current position, average groundwater discharge should be in the order of 50 × 106 m3 yr−1.