Isotope (δ13C-TOC, δ15N-TN) and Elemental (C/N Ratios) Compositions of Surface Sediments from the Barrier Islands in the Nakdong River Estuary, South Korea

Abstract

The Nakdong River Estuary (NRE) in South Korea is a typical, artificially-manipulated estuary and blocked by two large dam. The Noksan Dam, built in 1934, blocks the flow of the West Nakdong River, and the NRE Dam was completed between 1983 and 1987 to regulate the flow of the East Nakdong River (called the Eulsuk River locally). Consequently, the saltwater wedge that once reached approximately 40 km upstream is now blocked at the dam, considerably reducing the tidal prism. We investigated the isotopic (δ13CTOC, δ15NTN) and elemental (C/N ratios) compositions of organic matters in various composition in the NRE. In May 2015, 94 surface sediment samples were collected on and around three islands in the NRE. The mean grain size of the barrier island system ranged from 1.1 to 8.9 Φ (average 3.9 Φ) in mean grain size, and they were composed of various sediment types, including muddy Sand (S), sandy Mud (sM), and Mud (M). The C/N ratios (average,5.88) imply that the organic matter in the study area was of marine origins, as indicated by the lower ratios between 4 and 10. The carbon isotopic values (δ13CTOC) ranged from &#8211 28.2 to &#8211 16.8 ‰VPDB (average, &#8211 22.5 ‰VPDB), with a nitrogen isotopic values (δ15NTN) in the range of 6.2&#8211 12.5 ‰AIR (average, 9.4 ‰AIR) and C/N ratios in the range of 4.6&#8211 7.3 (average, 11.3). These results suggest that the microphytobenthos contribution was great and 1987 to regulate the flow of the East Nakdong River (called the Eulsuk River locally). Consequently, the saltwater wedge that once reached approximately 40 km upstream is now blocked at the dam, considerably reducing the tidal prism. We investigated the isotopic (δ13CTOC, δ15NTN) and elemental (C/N ratios) compositions of organic matters in various composition in the NRE. In May 2015, 94 surface sediment samples were collected on and around three islands in the NRE. The mean grain size of the barrier island system ranged from 1.1 to 8.9 Φ (average 3.9 Φ) in mean grain size, and they were composed of various sediment types, including muddy Sand (S), sandy Mud (sM), and Mud (M). The C/N ratios (average,5.88) imply that the organic matter in the study area was of marine origins, as indicated by the lower ratios between 4 and 10. The carbon isotopic values (δ13CTOC) ranged from &#8211 28.2 to &#8211 16.8 ‰VPDB (average, &#8211 22.5 ‰VPDB), with a nitrogen isotopic values (δ15NTN) in the range of 6.2&#8211 12.5 ‰AIR (average, 9.4 ‰AIR) and C/N ratios in the range of 4.6&#8211 7.3 (average, 11.3). These results suggest that the microphytobenthos contribution was great