Industrial tailings in Lake Traunsee (Salzkammergut, Austria)

Abstract

Tailings from salt work and a soda work have been pumped into the southern part of Traunsee (bay of Ebensee) for more than 50 years. Solid wastes have accumulated to form a pile > 40 m high with a total volume of > 3 × 106 m3. The sandy silty mud consists of calcite and other phases of CaCO3, brucite, CaO resp. Ca(OH)2 and gypsum. The chemical environment of the mud is characterized by extreme alkaline pore water (pH > 10 up to 12.5; total amount of pore water: 3 × 106 t) and highly negative Eh-values. These values result from the pumped tailings and from postdepositional chemical processes such as dissolution resp. reaction of CaO, brucite and gypsum and precipitation of CaCO3. The high water content of the mud and the steep slopes (> 15°) are responsible for frequent debris flows near the waste inlet, and occasional turbidity currents flow down to the distal basin floor. One particular current may transport up to 4 × 105 m3 of alkaline mud as far as 6 km from the inlet into the profundal basin plain, intercalating with natural lake sediments. Sedimentation rates in the northern part of Traunsee within the last decades are isotopically measured as 0.4–0.5 cm/a. In the central basin the sedimentation rates within the last 50 years are in the range of 2–3 cm/a. Up to 75% of the profundal sediments consist of industrial tailings and turbidites. Thus, within a substantial portion of the profundal zone (about 15%) the benthic fauna and the chemical environment of the sediments are influenced by the alkaline tailings.