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The Tinto and Odiel rivers in southwest Spain drain the world's largest sulfide mineral formation: the Iberian Pyrite Belt which has been worked since 2,500 BC. The Tinto and Odiel estuarine zones include both an extensive area of salt marsh and an intensively industrialized urban area. As a consequence of pyrite oxidation, the Tinto and Odiel rivers are strongly acidic (pH < 3) with unusually high and quite variable metal concentrations. In this study, seasonally varying concentrations of dissolved major and trace elements were determined in the acid mine drainage affected estuary of the Ría de Huelva. During estuarine mixing, ore-derived metal concentrations exhibit excellent correlations with pH as the main controlling parameter. As pH increases, concentrations of dissolved ore-associated elements are attenuated, and this process is enhanced during the summer months. The decrease in Fe and Al concentrations ranged from 80 to 100 % as these elements are converted from dissolved to sediment-associated forms in the estuary. Coprecipitation/adsorption processes also removed between 60 and 90 % of the originally dissolved Co, Cu, Mn, Pb, Zn, and Th; however, Cd and Ni exhibited a greater propensity to remain in solution, with an average removal of approximately 60 %. On the other hand, As and U exhibited a different behavior; it is likely that these elements remain in dissolved forms because of the formation of U carbonates and soluble As species. Concentrations of As remain at elevated levels in the outer estuary (average = 48 μg L(-1)) which exceeds concentrations present in the Tinto River. Nevertheless, the estuary has recently witnessed improvements in water quality, as compared to results of several previous studies reported in the 1990s.

The 20th century has been characterized by an exponential population growth, with a high density in coastal zones. The aim of this work is to study the impact of land use changes on the hydrological cycle, and possible consequences in marine environment. The study has focused on the relationship between coastal urbanisation and submarine groundwater discharge (SGD) that may cause an alteration in the biogeochemical cycles of marine ecosystems. An analysis of land use changes, historical salinities and nutrients data in the Maresme (Barcelona) coastal zone have revealed that the percentage of urban and forest zone land use has increased since 1990, corresponding to a decrease of nutrients in coastal waters through SGD. These impacts may cause changes in coastal biogeochemical cycles, like the decrease in chlorophyll concentrations. Results denote the correlation between land use, coastal aquifer dynamics and the effects of SGD in coastal environments.

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