Temperature effects on bank filtration: redox conditions and physical-chemical parameters of pore water at Lake Tegel, Berlin, Germany

In the city of Berlin, artificial groundwater recharge techniques, such as bank filtration and infiltration ponds, are an important source for drinking water production. Climate change with increasing surface water temperatures can influence the water purification processes during bank filtration mainly due the intensification of metabolic processes leading to a decrease of oxygen and an increase of anaerobic conditions. In Lake Tegel a significant increase of water temperature in the epilimnion of 2.4°C within the last 30 years was recorded. For a better understanding of induced bank filtration at Lake Tegel, redox processes and physical-chemical conditions within the surface sediment layers (0–26 cm depth) at the littoral infiltration zone were investigated. The influence of temperature in the range of 0–25°C on microbial catalysis of redox processes, such as reduction of nitrate and sulphate, was examined during the period March 2004–June 2005. High water temperatures (16–25°C) were accompanied by negative redox potentials (E_H=−47 mV) and decreasing N_inorg concentrations, while the amount of ammonia, Mn^2 + and Fe^2 + was rising. This indicates redox processes such as denitrification, Mn^4 + reduction, nitrate respiration and ammonification, as well as Fe^3 + reduction. The reduction of sulphate, however, has not yet become significant at Lake Tegel, but with increasing water temperature, sulphate reduction must be expected.