Geochemical characteristics of halophyte (Scirpus planiculmis) habitats in the Nakdong Estuary, Korea

Abstract

The Nakdong Estuary has experienced hydraulic and topographic changes over the last century. These alterations in the physical environment have had negative effects on habitat loss and fragmentation. The population of Scirpus planiculmis, which is a major food plant for wintering birds in Nakdong Estuary, has decreased over the last decade. To identify factors that influence S. planiculmis population, 2 short core samples (about 30cm) were collected at vegetation area (VA)and non-vegetation area (NVA) in June, 2018. In sediment cores, temperature, salinity and pH were measured at 2cm intervals in situ. Grain size, stable carbon isotope ratios (δ13C) and elements (major and minor) contents were analyzed in laboratory. Both sediment cores contained more than 80% sand but the percentage of silt and clay in NVA core was higher than VA core. The result of Principal Component Analysis indicates that sediment grain size influences the elemental composition of sediment. Salinity between VA (17.7±0.81 psu) and NVA (17.8±0.69) was similar, but pH was different between VA(6.75±0.28) and NVA (7.03±0.16). At upper 10cm (root depth of S. planiculmis: about 9cm), especially, pH of VA (6.44～6.72) was about 0.69 lower than that of NVA (7.18～7.33), indicating that sediment pH was not influenced by dam discharge but other reasons, such as secretion of acids as root exudates. δ13C of sediment cores ranged from -25.3 to -22.6.