Restoration and meteorological variability highlight nested water supplies in middle altitude/latitude peatlands: Towards a hydrological conceptual model of the Frasne peatland, Jura Mountains, France

Peatlands and associated ecosystem services are sensitive to climate changes and anthropogenic pressures such as drainage. This study illustrates these effects on the Forbonnet bog (7 ha), belonging to the Frasne peatland complex (similar to 300 ha, French Jura Mountain), and shows how they can inform about the ecohydrological functioning of peatlands. The southern part of the Forbonnet bog was restored in 2015-2016 by backfilling of artificial drains dating from the end of the 19th century. Piezometric data from 2014 to 2018 allow to evaluate the restoration effect on the water table depth (WTD) and highlight the reactivation of lateral inflows from the surrounding raised peatland complex. Vertical electrical conductivity (EC) profiles permit to identify three main peat compartments depending on different water supplies arguing for a nested hydrological functioning. This involves (1) one-off karst groundwater inputs at the substratum/peat interface supplying the deepest peat layer, (2) lateral seepage inputs from the neighbouring raised wooded peatlands sustaining the intermediate peat level and (3) direct rainfall infiltrating the most superficial peat layer. This nested multi-reservoir model operates at various spatio-temporal scales and is consistent with the complex seasonal hydrological and physico-chemical response at the bog outlet, which will be increasingly affected by climate change in the coming decades.