Photoreduction of Fe(III) in the Acidic Mine Pit Lake of San Telmo (Iberian Pyrite Belt): Field and Experimental Work

Abstract

Light

Microbial Diversity and Its Relationship to Physicochemical Characteristics of the Water in Two Extreme Acidic Pit Lakes from the Iberian Pyrite Belt (SW Spain)

“…The highest chlorophyll-a values were observed in the permanent chemocline, since its growth depends on parameters such as light and temperature, but also on nutrients, which showed higher values in the monimolimnion (N and P values; Table 1). In the shallower layer, a total Fe concentration of 9.5 mg/L was measured, of which 3.5 mg/L were Fe(II), suggesting photoreducing activity of dissolved Fe(III), which has been previously measured in this type of acidic pit lake [33], [41], [49], [50], [51]. On the other hand, hydrochemical characteristics of the monimolimnion were similar to the mine groundwater that floods underground mine sites.…”

“…In the chemocline PAR values were low, but sufficient to promote photosynthetic activity (Fig. 1A) in the first few meters of the water column despite intensely attenuated visible light (PAR) caused by the high concentration of dissolved solids [32], [33]. The chemocline appears to be the optimal place for phytoplankton growth since the highest measured nutrient (C, N, P) values were in the bottom layer (Table 1).…”

Changes in stratification and iron redox cycle of an acidic pit lake in relation with climatic factors and physical processes

“…At these depths and in spite of intense attenuation of visible light (PAR) in the upper layer ( Fig. 9) due to high dissolved solids concentration (Díez Ercilla et al, 2009;Schimmele and Herzsprung, 2000), PAR values are high enough to activate photosynthesis (Koschorreck and Tittle, 2002) as can be verified through vertical chlorophyll-a profiles (Fig. 9).…”

Geochemical processes in a highly acidic pit lake of the Iberian Pyrite Belt (SW Spain)

“…According to geochemical calculations with PHREEQC, around 99% of Fe is predicted to occur as Fe(III) in the mixolimnetic waters and less than 7% in the monimolimnion. The higher values of turbidity observed within the first 5 m of San Telmo waters may be linked to Fe(III) precipitation (increasing colloidal Fe) and microbiological activity, as highlighted by previous works dealing with San Telmo limnology (Sánchez-España et al, 2007;Diez-Ercilla et al, 2009).…”

“…2). This stratification of the mixolimnion is progressively formed at the beginning of the spring and disappears during the winter, when mixing takes places (Diez-Ercilla et al, 2009). The mixolimnetic waters show more oxidative conditions and lower EC values (807-883 mV; 5.3 mS/cm) than monimolimnetic waters (650 mV; 6.6 mS/cm).…”