Soil Organic Carbon Emissions Research Articles

Changes of lake organic carbon sinks from closed basins since the Last Glacial Maximum and quantitative evaluation of human impacts

BackgroundClosed basins occupy 21% of the world’s land area and can substantially affect global carbon budgets. Conventional understanding suggests that the terminal areas of closed basins collect water and carbon from throughout the entire basin, and changes in lake organic carbon sinks are indicative of basin-wide organic carbon storages. However, this hypothesis lacks regional and global validation. Here, we first validate the depositional process of organic carbon in a typical closed-basin region of northwest China using organic geochemical proxies of both soil and lake sediments. Then we estimate the organic carbon sinks and human impacts in extant closed-basin lakes since the Last Glacial Maximum (LGM).ResultsResults show that 80.56 Pg organic carbon is stored in extant closed-basin lakes mainly found in the northern mid-latitudes. Carbon accumulation rates vary from 17.54 g C m−2 yr−1 during modern times, 6.36 g C m−2 yr−1 during the mid-Holocene and 2.25 g C m−2 yr−1 during the LGM. Then, we evaluated the influence by human activities during the late Holocene (in the past three thousand years). The ratio of human impacts on lake organic carbon storage in above closed basins is estimated to be 22.79%, and human-induced soil organic carbon emissions in the past three thousand years amounted to 207 Pg.ConclusionsWhile the magnitude of carbon storage is not comparable to those in peatland, vegetation and soil, lake organic carbon sinks from closed basins are significant to long-term terrestrial carbon budget and contain information of climate change and human impact from the whole basins. These observations improve our understanding of carbon sinks in closed basins at various time scales, and provide a basis for the future mitigation policies to global climate change.

Soil organic carbon enrichment of dust emissions: magnitude, mechanisms and its implications for the carbon cycle

ABSTRACTSoil erosion is an important component of the global carbon cycle. However, little attention has been given to the role of aeolian processes in influencing soil organic carbon (SOC) flux and the release of greenhouse gasses, such as carbon dioxide (CO2), to the atmosphere. Understanding the magnitude and mechanisms of SOC enrichment in dust emissions is necessary to evaluate the impact of wind erosion on the carbon cycle. This research examines the SOC content and enrichment of dust emissions measured using Big Spring Number Eight (BSNE) wind‐vane samplers across five land types in the rangelands of western Queensland, Australia. Our results show that sandy soils and finer particulate quartz‐rich soils are more efficient at SOC emission and have larger SOC dust enrichment than clay‐rich aggregated soils. The SOC enrichment ratios of dusts originating from sites with sand‐rich soil ranged from 2·1–41·9, while the mean enrichment ratio for dusts originating from the clay soil was 2·1. We hypothesize that stronger inter‐particle bonds and the low grain density of the aggregated clay soil explain its reduced capacity to release SOC during saltation, relative to the particulate sandy soils. We also show that size‐selective sorting of SOC during transport may lead to further enrichment of SOC dust emissions. Two dust samples from regional transport events were found to contain 15–20% SOC. These preliminary results provide impetus for additional research into dust SOC enrichment processes to elucidate the impact of wind erosion on SOC flux and reduce uncertainty about the role of soil erosion in the global carbon cycle. Copyright © 2013 John Wiley & Sons, Ltd.

Usefulness of the carbon-13 tracer technique for characterizing terrestrial carbon pools

Application of the carbon-13 (13C) tracer technique to soil organic carbon emission is relatively new to many researchers and only a few results have been reported to date. This mini-review paper cites some well-documented research in organic carbon pool studies using the 13C tracer technique. The 13C abundance in soil usually remains at a stable level under a set of natural conditions. Variations in 13C reflect different sources and types of organic components from natural environments. An important feature of 13C discrimination in the soil C pool has permitted researchers to assess the dynamic nature of the pool. This discrimination may reflect a selective preference at early stage of residue decomposition by soil microbes. Crop rotation and residue input to humic substances can change the 13C abundance, which is a possible way to estimate soil C emission. However, the dynamic relationship between 13C abundance in the soil C pool and C emission is still in an early stage of development. Restrictions due to requirement of long-term experiments and duration of vegetation changes may affect its wide-spread adoptions in C emission studies.