Changes in sedimentary environment and its impacts on the halophyte (Scirpus planiculmis) habitats in the Nakdong Estuary of Korea

Abstract

The Nakdong Estuary has experienced hydrological and topographic changes over the last century which have had negative effects on habitat loss and fragmentation. The population of Scirpus planiculmis 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. Temperature, salinity, pH, grain size, carbon and nitrogen stable isotope ratios (δ13C, δ15N) and element contents(major and minor) of sediment cores were measured at 2cm intervals. Both sediment cores contained more than 80% sand and the salinity of each core was higher than 16.3 psu. The mean pH of VA was slightly lower than that of NVA. At upper 10cm(root depth of S. planiculmis: about 9cm), especially, pH of VA was lower than that of NVA, indicating that sediment pH was not influenced by dam discharge but other reasons, such as secretion of acids as root exudate. δ13C and δ15N of sediment cores fell within the estuarine particulate organic matters(POM) and the highest δ13C value was observed at the surface indicating inputs of marine POM to the Nakdong Estuary. The geochemical environment of Nakdong Esutary would not be suitable for S. planiculmis growth, mainly due to coarse substrate and high salinity. It might result from decrease of dam discharge in Nakdong Estuary which could cause hydrological change. Those changes might influence the distribution and population of halophytes including S. planiculmis.