Deciphering the impact of land-uses on terrestrial organic matter and mercury inputs to large boreal lakes of central Québec using lignin biomarkers

• Lignin biomarkers allow to powerfully follow terrestrial OM transfers to lakes.
• Hg dynamics in large lake ecosystems radically differ from that of small ones.
• Lake with large watershed shows some buffering capacity to land-use disturbance.
• Logging and mining activities are not necessarily discernible in large lake sediments.

To evaluate watershed impacts of anthropogenic activities on terrestrial organic matter (TOM) and total mercury (THg) dynamics in large boreal lake ecosystems, we studied sediment cores retrieved in eight large lakes of Québec (Canada). Two lakes with pristine watersheds were considered as reference lakes and six lakes with watersheds affected by different types of anthropogenic activities (e.g. logging and/or mining activities) were used to illustrate the influence of land-use on TOM and Hg cycling in lakes. A Geographical Information System (GIS) approach was used to correlate the evolution of anthropogenic land-uses from 1979 to 2010 (e.g. logging and mining activities) to TOM and THg contents measured in sediment cores. In each core, THg concentrations gradually increased over the recent years. Using lignin biomarkers, we noticed that the presence of both intense logging and mining activities in the watershed does not necessarily correspond to noticeable changes in the relative amount of terrestrial organic matter (TOM) exported from the watershed to the sediments and by extension to the level of THg measured in sediments. Apparently large-scale watersheds show some “buffering” capacity to land-use disturbance.