Zoning of the central and western parts of the Seto Inland Sea based on the principal component analysis of sediment parameters and comparison between the 2016 and previous surveys

Abstract

Total organic carbon (TOC), total nitrogen (TN), δ¹³C and δ¹⁵N in sediments collected from 135 stations in the central and western parts of the Seto Inland Sea in July 2016 by Ministry of the Environment, Japan (MOF) were analyzed to evaluate the bottom environment. The principal component analysis based on these parameters plus C : N ratio and six parameters provided by MOF shows that the area is divided into four zones: zone A characterized by fine and organically enriched sediments, zone B characterized by coarse sediments showing low contents of organic matter, zone C1 characterized by low δ¹³C and δ¹⁵N values and the nearshore location and zone C2 characterized by low δ¹³C and δ¹⁵N and the offshore location. The terrestrial organic matter ratio in the sediment of zone C1 was high (37%), whereas the ratio in zone C2 must be low, considering low values of the C : N ratio. The comparison in the sediment parameters between the 2016 and previous surveys shows no clear trend in the sediment parameters during the 30 years except for TOC and TN in sediments collected from zone A in Hiroshima Bay.