. Characterization of amino acids in hypersaline sediments in Ganh Hao, Vietnam

PHAM QUYNH HUONG; NGUYEN VAN HIEN; LARA, R.J.

Manila

Congreso; 1st ASEAN Mangrove Congress on Research and Development; 2012

1st ASEAN Mangrove Congress on Research and Development

Amino acids are a major source of organic nitrogen in sediments and soils and are also used as indicators for organic matter diagenesis. Several studies have been conducted to characterize the composition and distribution of amino acids in the marine and coastal marine sediments. However, research on amino acids and organic matter degradation in hypersaline areas is comparatively scarce, although a deeper knowledge of the dynamics of these sensitive ecosystems is needed for coastal protection. Therefore, this study was designed to investigate the amino acid composition and state of organic matter degradation in sediments at Ganh Hao, a hypersaline coastal area in the Mekong Delta, Vietnam. Replicate forty-centimeter sediment cores were taken from 8 stations along transect through replanted mangroves in an abandoned saltpan and a naturally regenerated mangrove in the mud flat toward the sea. Amino acids, total organic carbon and nitrogen in the sediments were quantified from the samples collected at 00-05, 05-10, 10-15 and 30-35 cm in the dry seasonThe composition pattern (mole %) of individual amino acids in the sediments from all stations was alike, regardless of the sediment physical-chemical properties and occurrence of plants. Total hydrolysable amino acids (THAA) accounted for 26% and 10% of the nitrogen and organic carbon, respectively. There was a systematically downcore decrease in THAA concentration at most of the sampling stations, except the replanted forests in abandoned saltpan, probably due to the artificial disturbance in soil preparation before planting. Aspartic acid, glycine, glutamic acid and alanine were the most dominant amino acids in the study area while taurine and methionine were found as traces only. Aspartic acid to beta-alanine (ASP : β-ALA) and glutamic acid to gamma-amino butyric acid (GLU : γ-ABA) ratio was ca. 7 and 8, respectively, indicated a high degradation state in the study areas. Sediments in the replanted forest contained more refractory organic matter relative to the natural regenerated mangrove and the seashore sediments. Sediment pH, salinity and clay content probably influenced the organic matter degradation in the study area.