Dissolved and Particulate Organic Matter Dynamics Relative to Sediment Resuspension Induced by the Tidal Cycle in Macrotidal Estuaries, Kyushu, Japan

Hiroyuki Takasu,Koji Uchino,Koichiro Mori

doi:10.3390/w12092561

Hiroyuki Takasu, Koji Uchino + Show 1 more

Open Access

https://doi.org/10.3390/w12092561

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Journal: Water	Publication Date: Sep 13, 2020
Citations: 10	License type: CC BY 4.0

Affiliation: Nagasaki University

Abstract

The tide-induced resuspension of sediments plays important roles in the efflux of particulate organic carbon (POC) from rivers to the coastal sea. Although dissolved organic carbon (DOC) comprises more than half of the riverine flux of organic carbon to the ocean, the influence of sediment resuspension induced by the tidal cycle on DOC dynamics is largely unknown. This study examined the dynamics of POC, particulate organic nitrogen (PON), DOC, humic-like and protein-like fluorescent dissolved organic matter (DOM) in relation to the tidal cycle in the Chikugo and Hayatsue River Estuaries, Kyushu, Japan. This study is the first to show both the particulate organic matter (POM) and DOM dynamics in relation to the tidal cycle in the macrotidal estuaries. We found that the turbidity changed with the tidal cycle and that there were significant positive correlations of turbidity with POC and PON in the Chikugo River mouth, suggesting that tide-induced sediment resuspension supplied POM to the water column. The DOC concentration, humic-like and protein-like fluorescent DOM were not correlated with turbidity but were negatively correlated with salinity. These results suggest that POM efflux, but not DOM efflux, can be accelerated by tide-induced sediment resuspension in the macrotidal estuaries.

Highlights

Estuaries, as transition zones between terrestrial and marine environments, are the most dynamic regions in the biosphere [1]
Coastal hypoxia has been a global phenomenon since the late 1950s, as it causes the deterioration of marine ecosystems [8]
Suzuki et al [17] reported that a strong tidal current in a macrotidal estuary can result in a high particulate organic carbon (POC) concentration due to active sediment resuspension

Summary

Introduction

As transition zones between terrestrial and marine environments, are the most dynamic regions in the biosphere [1]. An understanding of the mechanisms supplying organic matter from the Chikugo River estuary is essential to prevent hypoxia in the northern part of the Ariake Sea. Suzuki et al [17] reported that a strong tidal current in a macrotidal estuary can result in a high POC concentration due to active sediment resuspension. We examined the temporal variations in both POC and DOC concentrations in relation to the tidal cycle in the Chikugo River Estuary to understand the influence of tide-induced sediment resuspension on POC and DOC efflux from the estuary to the northern part of the Ariake Sea. Stable carbon isotope ratios of POC were measured to understand the source of particulate organic matter (POM). Humic-like and protein-like fluorescent dissolved organic matter (DOM), based on the fluorescence excitation-emission matrix (EEM), was measured to understand the influence of tide-induced sediment resuspension on labile DOM efflux

Materials and Methods

Ariake Sea

Results and Discussion

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