Occurrence of red tides in Lake Nakaumi related to annual variation in water quality and C:N:P ratio of phytoplankton

概要

論文の詳細を見る
Frequent water quality monitoring, identification of phytoplankton species, and measurement of C:N:P ratios were conducted to clarify the time series in the occurrence of a red tide by a dinoflagellate, Prorocentrum minimum, in Lake Nakaumi, a coastal lagoon with a two-layered structure. In late autumn 1996, when vertical mixing by seasonal winds started, a red tide from P. minimum occurred after a supply of NO3-N due to a freshet in an upper layer where PO4-P had excessively accumulated. That red tide continued throughout the winter, strengthened in spring, and disappeared in mid-May 1997 when fluxes of inorganic nitrogen and phosphorus to the upper layer decreased. During the period from autumn 1996 to spring 1997, the C:N:P ratio of suspended material gradually increased from 130:14:1 to 300:30:1. Compared with the early 1980s, the concentration of PO4-P in the central lake increased in the lower layer during the warmer seasons. Consequently, water quality in the upper layer changed from P to N deficiency in late autumn. P. minimum was dominant enough to absorb the supplied NO3-N under excess phosphorus conditions. The change toward N deficiency in the water quality was considered to be the reason why almost all red tides recently formed were due to P. minimum rather than to the diatom, Skeletonema costatum.
日本陸水学会の論文