Surface water is exposed to contaminants which change the natural hydrological parameters and consequent contaminant dispersion. Water self-depuration is an ecological process aiming to restore the natural watercourse balance, which depends on the quality and quantity of topical and di use contributions. The main goal of this ff research is the evaluation of surface water quality in the Águeda River (Portugal-Spain transboundary watershed) and its self-depuration ability considering di erent predicted scenarios. Biochemical oxygen demand ff (BOD 5), dissolved oxygen (DO), dry residue, Ptotal, Ntotal, pH, temperature and microbiological parameters were analyzed, in thirty-six surface water samples. Simulation of di erent quality scenarios was undertaken using Qual2Kw software and the river's self-de-ff puration ability discussed. The obtained model's calibration achieved a score of 95% con dence interval, for fi almost analyzed parameters. The calibrated model was used for two prediction scenario construction. The rst fi one, intending to assess the in uence of topical contaminated discharge and the second one, aiming to evaluate fl the in uence of minimum ow rates, representing an extremely dry year. The two considered scenarios revealed fl fl that self-depuration capacity is more a ected by the presence of minimum ow rates than topical discharges, ff fl attesting a large potential for self-depuration along the Águeda River.

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Neste trabalho são propostos os padrões de distribuição espacial para contaminantes em águas subterrâneas – Urânio e Arsénio, na bacia transfronteiriça do rio Águeda. Os mapas obtidos permitem avaliar o risco ambiental associado às atividades antrópicas desenvolvidas na área em estudo, constituindo as atividades mineiras um importante fator de risco ambiental. Pretende-se, ainda, contribuir para uma melhoria na gestão dos sistemas de águas e possibilitar a futura definição de políticas de atuação conjunta, em casos transfronteiriços, tal como é apresentado neste trabalho.