6600 years of human and climate impacts on lake-catchment and vegetation in the Julian Alps (Lake Bohinj, Slovenia)

Abstract

Mountain grazing and ore processing had a significant impact on the Alpine environment in the last 5000 years, but few studies have so far focused on environmental changes of the south eastern Alps. This study investigates the vegetation history and sedimentary processes in the catchment of Lake Bohinj (Julian Alps, Slovenia), where a 12-m-long core was collected in the central part of the lake. Sediment in the early Holocene section of the core was partially reworked due to a major seismic event dated to 6711–6523 yr cal BP (Rapuc et al. 2018), therefore a detailed palaeoenvironmental reconstruction was performed only for the top 4.4 m of the core. Here the results of mineralogical, sedimentological, geochemical, stable isotope (δ13C and δ15N), and pollen analysis are presented in order to better understand the impact of people (agriculture, grazing, mining) on the environment, and climate-human interactions over the last 6600 years.The results of palynological research suggest that at ca. 6000 yr cal BP Lake Bohinj was surrounded by mixed forest composed of Picea, Abies, deciduous Quercus, with Fagus becoming dominant after ca. 3300 yr cal BP. In the Bronze and especially the Iron Age (3500–2500 yr cal BP), when the region was, according to archaeological data, densely populated, clearing of forests due to agriculture, livestock production and metallurgical activities was detected through Cerealia type pollen, Plantago lanceolata, and the decline of Abies. These activities probably triggered soil erosion recorded as increased sedimentation rates. In the subsequent centuries human impact on the environment continued (increased), but it seems that the watershed was not destabilised again. Several periods of high terrigenous input were recorded at 6100–6000, 5700–5550, 5000–4600, 3900, 3700–3550, 2300–2200 yr cal BP and could be associated with a mobilisation of river inflow from the eastern flysch bearing catchment, due to river migration during periods of wetter climate. These flood patterns match with periods of enhanced flood activity in the wider Alpine region.