HAS - Working papers
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- Água subterrânea : conhecer para proteger e preservarPublication . Midões, Carla; Fernandes, Judite; Costa, Cristina Gomes da
- Assessing and modelling hard rock aquifer recharge based on complementary methodologies : a case study in the Gabbros of Beja Aquifer System, South PortugalPublication . Paralta, Eduardo; Oliveira, M.The "Gabbros of Beja" Aquifer System extends for approximately 350 km2 and is one of the most important reservoirs of groundwater in the context of hard rocks aquifers of South Portugal (Alentejo Region). The average annual rainfall in the area is about 500 to 600 mm. Groundwater resources are used for public supply over 3 councils and irrigation. During drought cycles consumption increases and pumping rates decrease with correspondent management difficulties and conflicts between private and public interests. The correct assessment of annual recharge is of utmost importance for regional planning and management of groundwater resources under semiarid climate conditions. Moreover the aquifer was recently declared vulnerable to nitrate diffuse pollution of agriculture origin and recharge mechanisms are the major natural factor controlling contamination of shallow waters in the "Gabbros of Beja" aquifer. Recharge assessment and modelling was performed on the base of several complementary methodologies: 1) water balance based on historical data of annual pumping rates; 2) chloride mass balance between groundwater and rainfall compositions; 3) daily sequential water balance modelling of hydrological parameters using Balseq model, and 4) soil and vadose zone daily water balance modelling using lumped model Earth and piezometric water level curves for calibration. Results of direct and indirect methods show that annual average recharge should be between 10% and 20% or even more of annual rainfall.
- Assessing the impacts of agriculture on groundwater quality using nitrogen isotopes : preliminary results on the Gabbros of Beja Aquifer System, South PortugalPublication . Paralta, Eduardo; Fernandes, Rosa M.; Carreira, P.; Ribeiro, Luís F.This paper intends to present preliminary results of nitrogen isotope assessment and source identification and characterization of nitrate non-point pollution in the context of official publication of ''Gabbros of Beja'' Vulnerable Region (Portaria 1100/2004, 3 of September). Research is based on funding project ''Assessing the impacts of agriculture on groundwater quality using nitrogen isotopes'' in progress in the rural region of Beja (south Portugal), under semiarid conditions in the period 2004-2007. Supported by previous hydrogeological characterization of ''Gabbros of Beja'' hard rock aquifer, seasonal groundwater chemistry and nitrate content evolution under different land use scenarios is possible to use nitrate isotopes and oxygen isotopes to trace nitrogen origin of nitrates in groundwater and nitrogen cycle. Stable nitrogen isotopes (15N/14N ratios) can offer a direct means of source identification of the pollutants in groundwater systems, In the research area the two major sources of nitrate were identified in agricultural areas, fertilizer and manure, which present different isotopic d15N signatures. The relative contributions of these two sources to groundwater or surface water can be estimated by mass balance. The analysis of d18O of nitrate in conjunction with d15N improves the ability to trace nitrate sources and cycling. Preliminary results are not conclusive that major source of nitrate-N in groundwater comes from agriculture. Further work is necessary under regular hydrological conditions. It is intended to give scientific proves to support political decisions, taking into account the sustainable development of the region and the appropriate use of nitrogen fertilizers on the basis of several European and national directives, namely vulnerable regions and EC Water Framework Directive.
- Sistema Aquífero Monforte-Alter do Chão : resultados obtidos no âmbito do Estudo dos Recursos Hídricos Subterrâneos do Alentejo, ERHSAPublication . Fernandes, Judite; Francés, Alain Pascal