Seasonal change of chlorophyll-a and bacteriochlorophyll in Lake Fukami-ike.

Abstract

Lake Fukami-ike is a small lake having a maximum depth of 8.5m, and is well protected from the wind. Lake water stratified from March to October and circulated from November to Mardi. Anoxic condition prevailed below 4-5 in depth from April to October. From 1956 to 1957, SHIMODAIRA found that the amount of chlorophyll-a in the euphotic layer was low during the stagnation period, and high during the circulation period. The same pattern of seasonal change in chlorophyll-a was observed in this study. It was suggested that such a seasonal change in chlorophyll-a amount might be caused by 1) the interruption of upwards nutrient transportation from the tropholytic layer due to a distinct stagnation of water and the consumption of nutrients by photosynthetic sulfur bacteria growing near the top of anoxic layer in summer, and 2) the sequential change of circulation and stagnation of water which gives a favorable condition for phytoplankton growth in winter.