Abstract
AbstractMany studies have viewed lakes as quasi‐static systems with regard to the rate of organic carbon (OC) burial, assuming that the dominant control on BE is sediment mineralization. However, in systems undergoing eutrophication or oligotrophication (i.e., altered nutrient loading), or climatic forcing, the changes in primary production will vary on both longer (> 10 yr) and shorter (seasonal) timescales, influencing the rate of OC accumulation and subsequent permanent burial. Here, we consider the extent to which permanent OC burial reflects changing production in a deep monomictic lake (Rostherne Mere, UK) that has been culturally eutrophied (present TP > 200 μg L−1), but has undergone recent reductions in nutrient loading. We compare multi‐year dynamics of OC fluxes using sediment traps to longer‐term burial rates estimated from two 210Pb‐dated sediment cores. The recent sediment record demonstrates that most of the autochthonous OC is preserved (∼95% of OC captured in the deep trap and 86% of the NEP in the contemporary system), contrary to widely held assumptions that this more labile, algal‐dominated OC component is not well preserved in lake sediments. A revised method for calculating BE for lakes which have undergone changes in primary productivity in recent decades is developed, which reduces some of problems inherent in existing approaches using historical sediment records averaged over the last 25–150 yr. We suggest that an appreciation of lakes in all biomes as ecosystems responding dynamically to recent human impact and climate change (for example) can improve up‐scaled regional and global estimates of lake OC burial.
Highlights
Many studies have viewed lakes as quasi-static systems with regard to the rate of organic carbon (OC) burial, assuming that the dominant control on BE is sediment mineralization
Estimates of global C burial by lakes are between 0.02 Pg C yr21 and 0.07 Pg C yr21, with most lakes burying between 4.5 g C m22 yr21 and 14 g C m22 yr21 (Tranvik et al 2009), rates are considerably higher in agriculturally dominated landscapes of Europe (60–100 g C m22 yr21; Anderson et al 2014) and North America
Across the study the uncorrected winter OC collection mean is similar between the shallow trap and deep trap (5-yr average 243.4 g C m22 yr21 and 248.2 g C m22 yr21, respectively; Table 1), with the deep trap collecting more in 3 of the 4 yr (2011–2014; Table 2)
Summary
Many studies have viewed lakes as quasi-static systems with regard to the rate of organic carbon (OC) burial, assuming that the dominant control on BE is sediment mineralization. A portion of the organic carbon (OC) that settles to the bottom of a lake will be mineralized and either recycled or degassed as CO2, or potentially undergo methanogenesis and degassed as CH4 (Fahrner et al 2008), and the remainder will be buried Burial of this OC in lake sediments can be considered as removal of atmospheric or terrestrial C from the active pool over geological timescales. Estimates of global C burial by lakes are between 0.02 Pg C yr and 0.07 Pg C yr, with most lakes burying between 4.5 g C m22 yr and 14 g C m22 yr (Tranvik et al 2009), rates are considerably higher in agriculturally dominated landscapes of Europe (60–100 g C m22 yr21; Anderson et al 2014) and North America Other drivers have been argued to have a bearing on OC BE, such as basin morphometry (Ferland et al 2012), changes in sunlight (Cory et al 2014; Koehler et al 2014; Tranvik 2014), sediment flocculation (Von Wachenfeldt et al 2008; Sobek et al 2009), OC molecular properties (Kellerman et al 2015), and mineral sorption (Maerki et al 2006)
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