Abstract
Lakes are a key feature of arctic landscapes and can be an important component of regional organic carbon (OC) budgets, but C burial rates are not well estimated. 210Pb-dated sediment cores and carbon and organic matter (as loss-on-ignition) content were used to estimate OC burial for 16 lakes in SW Greenland. Burial rates were corrected for sediment focusing using the 210Pb flux method. The study lakes span a range of water chemistries (conductivity range 25–3400 µS cm−1), areas (< 4–100 ha) and maximum depths (~ 10–50 m). The regional average focusing-corrected OC accumulation rate was ~ 2 g C m−2 y−1 prior to ~ 1950 and 3.6 g C m−2 y−1 after 1950. Among-lake variability in post-1950 OC AR was correlated with in-lake dissolved organic carbon concentration, conductivity, altitude and location along the fjord. Twelve lakes showed an increase in mean OC AR over the analyzed time period, ~ 1880–2000; as the study area was cooling until recently, this increase is probably attributable to other global change processes, for example, altered inputs of N or P. There are ~ 20,000 lakes in the study area ranging from ~ 1 ha to more than 130 km2, although over 83% of lakes are less than 10 ha. Extrapolating the mean post-1950 OC AR (3.6 g C m−2 y−1) to all lakes larger than 1000 ha and applying a lower rate of ~ 2 g C m−2 y−1 to large lakes (> 1000 ha) suggests a regional annual lake OC burial rate of ~ 10.14 × 109 g C y−1 post 1950. Given the low C content of soils in this area, lakes represent a substantial regional C store.
Highlights
Lakes play a significant role in the terrestrial carbon (C) cycle (Cole and others 2007)
The release of C from terrestrial pools into surface and subsurface runoff increases input to streams and lakes, where it can be processed and released as CO2 (Kling and others 1991; Sobek and others 2003). It is unclear whether the recent productivity increases widely postulated to occur in arctic lakes is a response to higher mean annual temperatures (Michelutti and others 2005) or enhanced deposition of reactive nitrogen (Hastings and others 2009; Wolfe and others 2013) and whether these production increases are translated into increased C burial
It is unknown whether the increased C burial associated with greater aquatic primary production will balance the C lost as soil carbon is transferred from the terrestrial to aquatic systems (Schuur and others 2008)
Summary
Lakes play a significant role in the terrestrial carbon (C) cycle (Cole and others 2007). The release of C (as DOC) from terrestrial pools into surface and subsurface runoff increases input to streams and lakes, where it can be processed and released as CO2 (Kling and others 1991; Sobek and others 2003) It is unclear whether the recent productivity increases widely postulated to occur in arctic lakes is a response to higher mean annual temperatures (Michelutti and others 2005) or enhanced deposition of reactive nitrogen (Hastings and others 2009; Wolfe and others 2013) and whether these production increases are translated into increased C burial. Calculation of patterns of whole-lake deposition and accumulation of important elements and metals, such as Hg, P or C (Molot and Dillon 1996; Fitzgerald and others 2005; Engstrom and Rose 2013), requires cores from multiple depositional areas of the lake to adequately capture the spatial variability or application of a correction factor to account for spatial variability The contribution of lake OC burial to regional C sequestration in this area is considered
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