Sedimentary Processes of Tidal Flat and the Responses to Typhoon Events and Anthropogenic Influences in the Luoyuan Bay of China

Key words: 
• tidal flat /
• anthropogenic influence /
• typhoon event /
• sedimentary records /
• Luoyuan Bay

Abstract: Situated at the junction of land and sea, tidal flat is very sensitive to typhoon event and anthropogenic influence. In order to reveal the histories of regional typhoon events and strong anthropogenic influences, two sediment cores were collected in inner Spartina alterniflora marsh and middle-upper intertidal flat in the Luoyuan Bay for sedimentary records extraction. The sediment cores were cut with 1 cm interval for grain size and radio isotope dating. The results of grain size analysis indicate that the sediment on tidal flat of Luoyuan Bay is mainly composed by fine fractions. The mean grain sizes of core sediments in inner Spartina alterniflora marsh and middle-upper intertidal flat are 5.41 μm~45.00 μm and 5.4 μm~68.82 μm, respectively; however, there are several interfaces where sediment characteristics vary obviously. The mean sedimentation rates in inner Spartina alterniflora marsh and middle-upper intertidal flat calculated from ²¹⁰Pb are 1.96 cm/a and 1.23 cm/a, respectively. However, the mean sedimentation rates increased from 0.56 cm/a during 1909~1946 to 2.36 cm/a during 1946~1966 at upper intertidal flat due to strong reclamations, and the introduction of Spartina alterniflora led to the mean sedimentation rate increased to 5.10 cm/a during the early marsh formation, and with increasing of the marsh age, the mean sedimentation rate decreased to 2.83 cm/a. The sedimentary records of core sediments collected from inner Spartina alterniflora marsh and middle-upper intertidal flat not only recorded the typhoon events which brought the strong effects on the Luoyuan Bay in recent 170 years, and but also recorded the several large scale reclamation from 1950's.