THE GEOCHEMISTRY OF RIVERS FROM NORTHERN SPAIN AND IMPLICATIONS FOR CHEMICAL WEATHERING

Over the past two decades many have realized that small mountainous rivers (SMR) contribute large amounts of sediment and organic matter to the world’s oceans. In addition, these watersheds have been documented to have some of the highest chemical weathering rates on the planet. Herein we present geochemical data from five rivers draining the Cantabrian Zone of northern Spain. We have analyzed samples draining both the Paleozoic rocks of the Iberian Massif in the western Cantabrian and the deformed Mesozoic-Cenozioc sediments of the eastern portion of the zone. Many of these rivers have steep topographic gradients and well-developed terraces and floodplains in their lower reaches. Four rivers have bicarbonate as the dominant anion while two of these have calcium as the major cation. The other two are Ca+Mg rich. The fifth river sampled, the Rio Villaviaosa, is Na-Cl dominated, but it is probable that we have sampled in a portion of the river that is still under tidal influence. Dissolved Si concentrations are relatively low suggesting that the major weathering reaction involves the dissolution of carbonate minerals. These data will be discussed and compared to geochemistry from other SMR that we have analyzed over the past decade and in addition we will assess the role these systems play in global CO₂ consumption.