Description of the study area
The sampling area is located in the upstream part of the Loire basin. The Loire river is the largest river in France (1012 km) and the upper section is 448 km long with a drainage area of 17,570 km² (15% of the total basin area). The coal district is located in the Ondaine-Furan corridor (OFC), two small tributaries of the upper Loire main stream (Fig. 1). It was in operation since the early 18th century up to the late 1980s. In the early 20th century, it became the 1st French coal producer (4.9 million tons/year in 1918; Barau, 2008). The local economy of the study area was thereby essentially based on this industrial coal mining extraction and led to the setting of over 70 coking and/or gas plants (Fig. 1). Furthermore, related metallurgy activities, weapon, paper mill, smelting and glass plant industries were very active along the OFC.