春季の有明海筑後川の高濁度汽水域における粒状有機物の動態

抄録

To elucidate the spatial and temporal dynamics of sources of particulate organic matter (POM) in the estuarine turbidity maximum, surveys (12 cruises) were conducted along the Chikugo River in the innermost Ariake Sea, Japan, from 24 February to 24 April 2005. To elucidate the influence of semi-lunar periodicity, surveys were conducted around the high slack tide in the daytime and were divided into three categories according to the tidal range; spring (>400 cm), medium (200–400 cm), and neap tides (<200 cm). At spring tides, the vertical mixing was strong and the turbidity maximum (>100 NTU) was formed at lower salinity (<5), synchronized approximately with both the maximum of particulate organic carbon and pheophytin concentrations (>5 mgl^-1 and >10μgl^-1, respectively). In contrast, the turbidity was low and higher chlorophyll a concentrations indicated active production of phytoplankton at neap tides. The POM in the surface water at spring tides had stable carbon isotope ratios (δ¹³C, mean±standard deviation: -25.3±0.9‰) and C/N atomic ratios (C/N, 11.6±2.0) significantly higher than those at neap tides (δ¹³C: -26.0±1.0‰, C/N: 7.9±1.4). The results indicate that the POM maximum accompanied by the estuarine turbidity maximum consists of resuspended detritus of both phytoplankton and terrestrial C₃ plants.