The origin of high silicon content in potentially medicinal groundwater of Gran Canaria (Canary Islands, Spain). Modelling of chemical water-rock interactions

Abstract

Groundwater of Gran Canaria (Canary Island, Spain) have been appreciated and used as an element of health tourism since the 19th Century. This activity was abandoned in the second half of 20th Century when springs disappeared due to groundwater drawdown. The chemistry of groundwater from 19 intakes in volcanic rocks of the north part of Gran Canaria was studied by applying geochemical modelling for quantifying processes responsible for high Si concentrations.Studied groundwater has temperature of 16.3 degrees C-25.5 degrees C, pH of 4.40-7.40, and usually HCO3-(Cl)-Mg-Ca-Na hydrochemical types. At near-neutral pH, fresh groundwater usually has 0.1-0.3 mM of Si. In studied groundwater Si concentrations are 0.42 to 1.82 mM, and show positive correlation with ionic strength and temperature. Volcanic bedrocks consist of, generally, easily reactive silicate minerals. Weathering is not supported by low rainfall; however, it shall be intensified by high influx of salts from marine aerosols and lithogenic carbon dioxide into groundwater. Geochemical modelling has found water-mineral reactions which reflect properly diversity of bedrock mineralogy. Based on those chemical reactions, contributions of particular silicate minerals to the pool of silicon dissolved in groundwater were calculated. Understanding the processes responsible for water chemistry might help in proper management and protection of groundwater.The Si-rich waters might be found in numerous places of Gran Canaria in all volcanic rocks. Silicic acid is the only form of silicon which is biologically available, and is regarded as a component which provides balneotherapeutic benefits. Many studies have showed beneficial and essential aspects of silicon in humans. Studied groundwater from Gran Canaria has an unexploited balneotherapeutic potential, and due to very high Si contents they seem to be ideal for testing the health benefits of such waters to humans. Hydrogeochemical methods, including geochemical modelling, provide effective tools for protection of such medicinal waters.