Search

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. 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.

Endemic planktonic diatoms are a major component of Lake Baikal sediments during interglacial periods. To investigate how these diatom assemblages are altered during sediment formation, quantitative plankton monitoring (1995–1998) was integrated with sediment trapping over 2 yr (1996–1997) in Baikal's southern basin (depth ~1,400 m). The traps consisted of both open (~6 monthly) and sequential (~2 weekly) collectors deployed throughout the water column. Sedimentation was seasonal, with diatom species composition, valve abundance, and total dry massreflecting changes in the planktonic communities. Sedimented assemblages were transmitted largely intact to the deepest traps (~1,300–1,390 m); some compositional blurring occurred from differential sinking rates and dissolution of diatom valves. A rapid mass flux event of Aulacoseira skvortzowiiand A. baicalensiswas recorded in summer 1997 with particle sinking rates between 60 and 100 m d−1and dry mass fluxes >5 g m−2d−1. Although dissolution was evident for all species, more delicate taxa were preferentially affected (e.g., A. skvortzowiivegetative cells and fine Synedraspecies), whereas Nitzschia acicularisvalves were almost entirely dissolved within the water column. Comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment, with sedimentary diatom accumulation rates being only about 1% of trap deposition and plankton production rates. Dissolution was significant in explaining 5–30%