A large carbon pool in lake sediments over the arid/semiarid region, NW China

Abstract

Carbon burial in lake sediments is an important component of the global carbon cycle. However, little is known about the magnitude of carbon sequestered in lake sediments over the arid/semiarid region of China (ASAC). In this study, we estimate both organic and inorganic carbon burial since ~ad 1800 based on nine lakes in ASAC, and discuss the most plausible factors controlling carbon burial. Our estimates show that the annual organic carbon burial rate (OCBR) ranges from 5.3 to 129.8 g cm−2 year−1 (weighted mean of 49.9 g cm−2 year−1), leading to a standing stock of 1.1–24.0 kg cm−2 (weighted mean of 8.6 kg cm−2) and a regional sum of ~108 Tg organic carbon sequestered since ~ad 1800. The annual inorganic carbon burial rate (ICBR) ranges from 11.4 to 124.0 g cm−2 year−1 (weighted mean of 48.3 g cm−2 year−1), which is slightly lower than OCBR. The inorganic carbon standing stock ranges from 2.4 to 26.0 kg cm−2 (weighted mean of 8.1 kg cm−2), resulting in a sum of ~101 Tg regional inorganic carbon burial since ~ad 1800, which is slightly lower than the organic carbon sequestration. OCBR in ASAC shows a continuously increasing trend since ~ad 1950, which is possibly due to the high autochthonous and allochthonous primary production and subsequently high sedimentation rate in the lakes. This increasing carbon burial is possibly related to both climatic changes and enhanced anthropogenic activities, such as land use change, deforestation, and eutrophication in the lake. Furthermore, OCBR and ICBR are expected to continuously increase under the scenario of increasing precipitation and runoff and enhanced anthropogenic activities. The results of this research show that the buried carbon in lake sediments of the ASAC region constitutes a significant and large carbon pool, which should be considered and integrated into the global carbon cycle.