渦鞭毛藻シスト群集組成から見た大村湾における富栄養化の過程

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The eutrophication of Omura Bay, Kyushu, during the last ca. 350 years was reconstructed on the basis of sedimentary facies (mainly grain size), and dinoflagellate cyst assemblages in two cores (99 em and 74 em in length, respectively) collected at the center of the bay (st. 1) and Tsumizu Inlet (st. 2). Sedimentation rates were approximately 2.7mm・year-1 at st.1 and 2.1mm・ year-1 st. 2, as determined by the 210Pb method. The median diameter of core sediment varied from 8.1 to 10.3φ at St.1, and from 6.8 to 1O.2φ at st. 2. Dinoflagellate cysts mainly consisted of the Gonyaulacoid Spinijerites spp., Tuberculodinium vancampoae, the Protoperidinioid Brigantedinium spp., Votadinium carvum and the Gymnodinioid Pheopolykrikos hartmannii. At st.1, cyst abundance increased at two horizons: around 1800 and 1900 year depths. Around the 1800 year depth, the autotrophic group composed more than 80% in relative frequency. The heterotrophic group began to increase after 1900 and reached a maximum (48%) in the mid-1950s. At st.2, cyst assemblages of the lower part were similar to those at St.1, and the heterotrophs also increased around the 1900 year depth and recorded a maximum (ca. 80%) at the 1980 year depth. These data suggest that before 1900, the water quality of Omura Bay was probably in its natural oligotrophic condition, that eutrophication began about 1900, and that it accelerated during 1960s to 1980s.
日本プランクトン学会,Plankton Society of Japanの論文
1998-08-25

渦鞭毛藻シスト群集組成から見た大村湾における富栄養化の過程

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