Land use as a key driver of increased organic carbon burial in boreal lakes

The abundant lakes in the boreal region are an active zone for cycling of organic carbon, functioning as simultaneous sources and sinks of atmospheric carbon dioxide. While previous studies have documented increased carbon loading and accelerated carbon accumulation to inland waters, the catchment level drivers of this increase remain ambiguous. Using caesium-137 dating and C-N analysis, we calculated the post year 1986 carbon accumulation rates from lake sediment cores collected from 213 individual lakes in boreal Finland. The linkages between carbon accumulation rates, lake morphometry and catchment land use were statistically investigated.  We show that modern sediment carbon accumulation rates in boreal lakes are significantly higher than over the Holocene epoch, mainly due to increased terrestrial OC inputs. Extensive ditch excavation enhances the delivery of terrestrial OC to lakes, which has resulted in elevated carbon accumulation in lakes with high percentage of ditched area in their catchment. Recalcitrant terrestrial carbon from forested and peatland areas is buried more effectively, whereas increased soil erosion and enhanced mineralization of labile OC from agricultural runoff reduces the relative burial of terrestrial OC.

Presentation Preference: Oral

Primary Presenter: Tuomas Junna, Geological Survey of Finland (tuomas.junna@gtk.fi)

Authors:

Tuomas Junna, Geological Survey of Finland  (tuomas.junna@gtk.fi)

Eero Asmala, Geological Survey of Finland  (eero.asmala@gtk.fi)

Jari Mäkinen, Geological Survey of Finland  (jem.makinen@outlook.com)

Pirkko Kortelainen, Finnish Environment Institute  (pirkko.kortelainen@syke.fi)

Tom Jilbert, University of Helsinki  (tom.jilbert@helsinki.fi)

Karoliina Koho, Geological Survey of Finland  (karoliina.koho@helsinki.fi)