Physico-chemical gradients and meromictic stratification in Cueva de la Mora and other acidic pit lakes of the Iberian Pyrite Belt

Abstract

A marked vertical trend of increasing temperature and dissolved metal concentrations is observed in the monimolimnia of some meromictic pit lakes of the Iberian Pyrite Belt (IPB) in SW Spain. Temperature differences between the chemocline and the pit lake bottom can be as high as 15°C (e.g. Herrerías), and the respective concentration of some metals (e.g. Fe) and metalloids (e.g. As) can increase by several orders of magnitude (e.g. Cueva de la Mora). The redox conditions also change drastically from the upper and oxygenated mixolimnion (strongly oxidizing) to the lower and anoxic monimolimnion (moderately reducing). Processes such as the inflow of metalsulphate laden ground water from flooded shafts and galleries, and other factors such as the pit geometry or the relative depth of the lakes, must be considered to account for the observed stratification pattern. The vertical profiles of physico-chemical parameters and water chemistry obtained in Cueva de la Mora and other meromictic pit lakes of the IPB are also compatible with a reactive bottom in which several geochemical and microbial reactions (including reductive dissolution of Fe 3? minerals, bacterial reduction of Fe 3? and SO 4 2-in pore waters within the sediments, and decomposition of organic matter) could be taking place.

Hydrochemical characterization of an acid mine drainage-affected reservoir: the Sancho Reservoir, Huelva, southwest Spain

“…This is in agreement with Sánchez-España et al (2009), who consider Schwertmannite a major controller of Fe(III) concentrations in the mine waters of the IPB.…”

Impact of Saline Mine Water: Development of a Meromictic Reservoir in Poland

“…The EC is low in the upper 1-2 m (mixolimnion zone) and gradually increases (chemocline zone) with depth, becoming stable in all seasons (monimolimnion zone) at a depth of 4-7 m with an EC of about 35,000 lS/cm. This type of permanent EC distribution in a vertical column of a reservoir is a characteristic of meromictic reservoirs (Dietz et al 2012;Espana et al 2009;Hongve 1980;Kazanci et al 2008;_ Zurek 2002). A similar survey in the Grunfeld reservoir showed no major differences in the EC values in the spring and autumn mixis periods (Fig.…”

Evidence for double diffusion in temperate meromictic lakes

“…Sánchez et al (2007) present microstructure profiles of temperature and salinity and particle concentration data from the ∼1 m thick bottom water body in the ∼35 m deep carstic Lake Banyoles in Spain, where a triple diffusive staircase was sustained. España et al (2009) give another example of step-like structures in the bottom-heated monimolimnion of a mining lake in Spain. The temperature and conductivity data support the assumption of the authors that this can be the result of double diffusive convection.…”