Dissolved Organic Carbon Source Attribution in the Changjiang Outflow Region of the East China Sea.

Yong Du,Haiyan Jin,Xiaoyu Zhang,Jianyu Chen,Zhihua Mao,Shuchang Ma,Lei Bi

doi:10.3390/s21248450

Abstract

The variable optical properties of chromophoric dissolved organic matter (CDOM) under the complicated dynamic marine environment make it difficult to establish a robust inversion algorithm for quantifying the dissolved organic carbon (DOC). To better understand the main factors affecting the relationship between the DOC and the CDOM when the Changjiang diluted water (CDW) interacts with the marine currents on the wide continental shelf, we measured the DOC concentration, the absorption, and the fluorescence spectra of the CDOM along the main axis and the northern boundary of the CDW. The sources of DOC and their impacts on the relationship between the optical properties of the DOC and CDOM are discussed. We reached the following conclusions: There are strong positive correlations between the absorptive and fluorescent properties of the DOC and the CDOM as a whole. The dilution of the terrestrial DOC carried by the CDW through mixing with saline sea water is the dominant mechanism controlling the characteristics of the optical properties of the CDOM. CDOM optical properties can be adopted to establish inversion models in retrieving DOC in Changjiang River Estuary. It is concluded that the introduction of extra DOC from different sources is the main factor causing the regional optical complexity leading to the bias of DOC estimation rather than removal mechanism. As whole, the input of polluted water from Huangpujiang River with abnormally high and Fs(355) will induce the overestimation of DOC. In the main axis of CDW, the impact from autochthonous DOC input to the correlation between DOC and CDOM can be neglected in comparison with conservative dilution procedure. The relationship between the DOC and the CDOM on the northern boundary of the CDW is more complicated, which can be attributed to the continuous input of terrestrial material from the Old Huanghe Delta by the Subei Coastal Current, the input of materials from the Yellow sea by the Yellow Sea Warm Western Coastal Current, and the input of materials from the Changjiang Basin by the CDW. The results of this study suggest that long-term observations of the regional variations in the DOM inputs from multiple sources in the interior of the CDW are essential, which is conducive to assess the degree of impact to the DOC estimation through the CDOM in the East China Sea.

Highlights

As the third longest river in the world, the Changjiang River delivers 0.5–0.8% of the riverine dissolved organic carbon (DOC) to the global oceans [1], exerting a significant influence on the carbon budget and the marine eco-environment of the East China Sea (ECS)and the western Pacific Ocean
Since C1 represents the humic-like component, the strong correlation between C1 and the DOC found in this study indicates the dominant control of the terrestrial materials in the study area and the decreasing impact of the terrestrial materials along the three sections
The ability of the optical properties of the chromophoric dissolved organic matter (CDOM) to reflect the main intrinsic mechanism impairing the correlation between the optical properties of the DOC and the CDOM in the Changjiang diluted water (CDW) were investigated, and it was found that in addition to the hydrodynamic environment, phytoplankton, and microbial activities, the material sources may have a profound impact on the spatial CDOM

Summary

Introduction

As the third longest river in the world, the Changjiang River delivers 0.5–0.8% of the riverine dissolved organic carbon (DOC) to the global oceans [1], exerting a significant influence on the carbon budget and the marine eco-environment of the East China Sea (ECS)and the western Pacific Ocean. As the third longest river in the world, the Changjiang River delivers 0.5–0.8% of the riverine dissolved organic carbon (DOC) to the global oceans [1], exerting a significant influence on the carbon budget and the marine eco-environment of the East China Sea (ECS). In most studies that have focused on the estuary, more effort was devoted to understanding the impact of the estuarine effects on the conservative behavior of the DOC and to determining the feasibility of an inversion algorithm for determining the DOC from the CDOM [14]. Concerning the amount of terrestrial DOC and its geochemical behaviors on the wide continental shelf when encountering saline oceanic currents and the impacts on the marine ecological system, studies of the changes in the DOC content and species after the Changjiang diluted water (CDW) enters the ECS need to be performed

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Discussion

Conclusion