Contributions of terrestrial organic carbon to northern lake sediments

Sediments of northern lakes sequester large amounts of organic carbon (OC), but direct evidence of the relative importance of their sources is lacking. We used stable isotope ratios of nonexchangeable hydrogen (delta H-2(n)) in topsoil, algae, and surface sediments in order to measure the relative contribution of terrestrial OC in surface sediments of 14 mountainous arctic and lowland boreal lakes in Sweden. The terrestrial contribution to the sediment OC pool was on average 66% (range 46-80) and similar between arctic and boreal lakes. Proxies for the supply of terrestrial and algal OC explained trends in the relative contribution of terrestrial OC across lakes. However, the data suggest divergent predominant sources for terrestrial OC of sediments in Swedish lakes, with dissolved matter dominating in lowland boreal lakes and particulate OC in mountainous arctic lakes.