Historical reconstruction of organic carbon decay and preservation in sediments on the East China Sea shelf

Abstract

[1] Sediment cores were collected from the East China Sea inner shelf in 2010 to study the decay and preservation of organic carbon (OC). The highest sediment mass accumulation rate (0.61 ± 0.20 g cm À2 yr À1 ), derived from 210 Pb, was found near the river mouth and decreased alongshore to the south (0.17 ± 0.004 g cm À2 yr À1 ), and in an offshore direction (0.31 ± 0.08 g cm À2 yr À1 ). Average total OC content was higher at inner shelf stations (0.52%) than those offshore (0.38%). The δ 13 C was more depleted at nearshore (À23.49‰ to À21.97‰) than offshore (À22.49‰ to À21.60‰) stations. Principal component analysis indicated that terrestrial OC, as indicated by lignin-phenols (Λ 8 ) values, was preserved in sediment closer to the coast (0.22-0.44), while offshore sediment was more composed of lignin-poor (0.12-0.24) degraded OC that was likely hydrodynamically sorted. Marine-derived OC, as indicated by plant pigments, was significantly more abundant in the sediment mixed layer than the underlying accumulation layer. Historical flooding events were detected in Λ 8 profiles in two of the six cores located at midshelf stations. Despite the magnitude of the 2010 flood in East China, we did not see any signature of this event with the chemical biomarker in these two cores. This may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment. The total OC standing stock since 1900 was approximately 1.62 ± 1.15 kg C m À2 , about one tenth of all the middle and lower lakes in the Changjiang catchment basin. This work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from Chinese rivers (due to river diversions and dams) affect carbon cycling in the East China Sea.Citation: Li, X., T.

Nutrient dynamics from the Changjiang (Yangtze River) estuary to the East China Sea

“…The PBE for STP in the study area was almost 100%. The high PBE in the study area may be related to the low benthic PO 4 3 − flux and the high sediment accumulation rate, which are related to high levels of terrigenous input and pre-aged organic matter (Li et al, 2013;Wu et al, 2013). The concentrations of STP and SOP in this study are comparable to those previously reported (Meng et al, 2014).…”

An 800-year record of terrestrial organic matter from the East China Sea shelf break: Links to climate change and human activity in the Changjiang Basin

“…6(A), the Σ8 of inner shelf surface sediments in the ECS is higher than that of outer shelf sediments, and the Σ8 in Bohai sediments lies between values from the inner and outer shelf sediments (Li et al, 2012(Li et al, , 2013bWu et al, 2013). The Σ8 of the P4 sediments is higher than of the outer shelf sediments, but comparable with that of inner shelf sediments.…”

“…The behavior of BSi was very similar that of OC (Liu S.M., unpublished data). The k d of OC and TN in P4 were much lower than for inner shelf sediments (Li et al, 2013b;Zhu et al, 2014), which implies that active materials in P4 degrade more slowly than in shallow regions due to hydrodynamic condition. In the inner shelf, the water depth is mostly o 50 m, and shallow water encourages resuspension and conveys oxygen to the sediments.…”

“…The ISM controls Table 2 Comparison of bulk parameters, lignin phenols index between P4 core and the surface sediments in the ECS and Bohai. The data of surface sediments are from Li et al (2012), Wu et al (2013) and Li et al (2013b). (n.d.: not detected).…”

Historical reconstruction of organic carbon inputs to the East China Sea inner shelf: Implications for anthropogenic activities and regional climate variability

“…Moreover, more than 50,000 dams (including dams on farmers' fields and dams higher than 100 m) have been constructed in the Changjiang catchment since the 1950s, which has led to significant decreases of riverine sediment discharge and changes in the aquatic ecosystems (Yang et al, 2005(Yang et al, , 2011bZhang et al, 2014). Also, there has recently been an increase in the number of studies on historical reconstruction of eco-environmental evolution of the Changjiang Estuary and adjacent ECS shelf, including the history of eutrophication, phytoplankton community changes, hypoxia, Changjiang flooding and drought events, and the response to monsoons (Hu et al, 2014;Jiang et al, 2014;Li et al, 2011Li et al, , 2013Liu et al, 2015;Wang et al, 2014aWang et al, , 2014bZhao et al, 2012). However, little remains known about the relative importance of anthropogenic activities and regional climate variability on eco-environmental evolution in different areas of the Changjiang Estuary and adjacent ECS shelf.…”