No abstract

The Kumozu River delta, in central Japan, is a fluvial-wave dominated delta facing Ise Bay in the Pacific Ocean. We reconstructed the Holocene evolution of the Kumozu River delta area in response to sea-level changes using sedimentary facies analyses, grain-size analyses, and radiocarbon dating of two new cores, KM and KM , obtained from the delta plain as well as previously published data. The core sediments, in ascending order, consisted of fluvial gravelly sand, tidemud and upward-coarsening delta-front muddy sand, and modern fluvial sand and mud. The maximum flooding surface (MxFS) was identified between the estuarine and deltaic sediments, and was dated at about calibrated radiocarbon years ago (cal kyr BP). At that time the shoreline was located near the site of core KM , about km inland from the present shoreline. Before the MxFS, the present delta area was a fluvial environment until cal kyr BP, and then changed to an estuarine environment during cal kyr BP. After the MxFS, the Kumozu River delta formed and prograded eastward in the incised valley between Pleistocene terraces during cal kyr BP. After deltaic sediments filled the incised valley, the delta advanced into Ise Bay and became lobate. Delta-front migration shows that the delta prograded northeastward, mainly during and cal kyr BP, and southeastward during cal kyr BP.

Abstract:This study aims to clarify the main ion concentrations in paddy field surface soil from 0 to 100 cm in depth along the coast of the Red River Delta, Northern Vi etnam, represented by Nam Dinh Province. There is a relation between total dissolved solid (TDS) and Na+ concentra tion. Na+ and Cl concentrations in paddy fields increase gradually and the abundance of Cl concentration in soil proclaims the influence of seawater intrusion. Washing is reported to reduce the high salinity in the cultivation-layer soil of paddy fields. Furthermore, the impact of seawa ter intrusion on soil salinity of coastal paddy fields has been considered. The top soil layer of coastal salt-affected paddy fields has the highest sodium absorption ratio (SAR) values, and shows the strongest salinity influence in both the flood season and the dry season. Soil samples near the Day River mouth have high SAR values with considerable Na+ concentrations in the dry sea son. The exchange selectivity between Ca2+, Mg2+ and Na+ has also been studied by considering changes in the SAR under different conditions of soil composition and land cover. In coastal agri cultural land, the SAR in the surface soil layer can be used to evaluate the influence of salinity. The SAR in cultivated soil is used to assess the influence of salinity problems on the paddy field.