The Role of Bedrock Geology in the Aqueous Chemistry of Cantabrian Rivers

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The Ohio State University

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The relationship between the bedrock and the aqueous chemistry of rivers in northern Spain has yet to be investigated. This study’s goal is to do just that, to relate the geology of the bedrock to the chemistry of each river and to determine which minerals in the bedrock are being weathered. While the majority of the rivers have very similar chemistries and flow through fairly similar lithologies, one river stands out from the rest. This river, the Ría de Villaviciosa, is the only river that flows through an evaporite deposit, and its chemistry reflects this difference in lithology. It is the only river that has an excess of Cl- when compared to Na+, and it is the only river not dominated by bicarbonate. The Ría de Villaviciosa also has a high concentration of lithium when compared with the other rivers. This could be due to the presence of a lithium evaporite mineral or due to lithium substitution for magnesium and/or iron. Using PHREEQC, a geochemical modeling software, to determine the minerals being weathered by each river, it can be seen that the Ría de Villaviciosa is the only river that is oversaturated with respect to any mineral; it is oversaturated with respect to quartz. This could be misleading, as the concentration of aluminum was not measured in this study, so aluminosilicate weathering is not considered by PHREEQC as an input for SiO2 in these rivers. These rivers all flow through primarily sedimentary rocks, but the differences in bedrock lithologies can be seen in the chemistry of the rivers. Even slight differences in lithologies are reflected in slight difference in chemistries of each river, and significant differences in lithologies show significant differences in chemistries of the rivers.


2014 Denman Undergraduate Research Forum Winner, Honorable Mention


geochemistry, Río Asón, Río Sella, Ría de Villaviciosa, Río Narcea, Río Nalón