The Distribution of Sedimentary Organic Matter and Implication of Its Transfer from Changjiang Estuary to Hangzhou Bay, China

Fanglu Xu,Haiyan Jin,Zhongqiang Ji,Kui Wang,Pei Sun Loh

doi:10.4236/ojms.2016.61010

Abstract

In this study, a comparison was made between the Changjiang Estuary and the Hanghzou Bay, in terms of the sources and diagenesis of the sedimentary organic matter (OM). To achieve this purpose, surface sediments from the estuary and bay were analyzed for lignin-derived phenols, stable carbon isotope and TOC/TN (total organic carbon/total nitrogen) molar ratio. The signal of land-derived OM decreased, and the vanillic acid to vanillin ratio, (Ad/Al)v, increased with increasing distance from the Changjiang Estuary and the Hangzhou Bay. These results corresponded with the contribution of the terrigenous OM from the rivers to the coastal zone, and the predominance of marine OM farther offshore, and that the land-derived OM underwent decomposition during transport along the estuary and bay. It should be noted that besides the Qiantang River, Hangzhou Bay is also receiving more than half of its materials from Changjiang Estuary, which flows into the Hangzhou Bay at the north, and leaves via the southern part of the bay. This important aspect of the hydrological cycle in Hangzhou Bay corresponded to higher Λ (total lignin in mg/100 mg OC), higher TOC and C/N ratios and more elevated (Ad/Al)v and (Ad/Al)s values in the bay than the Changjiang Estuary, thus, rendering the bay as a site for the accumulation and rapid cycling of terrigenous OM.

Highlights

Estuaries are zones of connection between land and ocean, which are vulnerable to the effects of global climate change
We investigated the sources, distribution and fate of sedimentary organic matter (OM) along the Changjiang Estuary, and the Hangzhou Bay, with the aim that a comparison between the estuary and bay would give us better insights into the dynamics of the terrigenous OM in the Hangzhou Bay
Our results are consistent with previous studies in this region, which found higher contribution of vascular plant signal near the coastal zone and the dilution with marine OM farther offshore: such was the case in Changjiang Estuary [20]-[22] [30]-[32] as well as in Hangzhou Bay [32] [33]

Summary

Introduction

Estuaries are zones of connection between land and ocean, which are vulnerable to the effects of global climate change. The warming of water has resulted in the changing of the timing and magnitude of phytoplankton bloom in estuaries [1], extreme weather condition, such as cyclone event has caused flash flood, which in turn, increased the contribution of river discharge into the adjacent estuary [2], and the sea level rise due to the effect of global warming on the hydrological cycle of estuaries, causing an increased intrusion of sea water farther upstream [3] Based on these reasons, some measures have been put in place to assess the vulnerability of the coastal zone, so that proper management in terms of sedimentation, land subsidence, land rehabilitation and reclamation can be carried out [4]. Because of its importance as a sediment passage and trap between the Changjiang and Qiantang Rivers, Hangzhou Bay could be vulnerable to the changes in sediment load from the Changjiang River [9]

Methods

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Discussion

Conclusion