Regeneration of Nutrient and Detritus Formation from Aerobic Decomposition of Natural Phytoplankton

Abstract

Respiration and short-term decomposition processes of natural phytoplankton communities collected from eutrophic Lake Kasumigaura were examined eight times in each season from 1983 to 1985 under dark and aerating conditions. The lag periods were observed for the increase of nutrient and the decrease of cell components during the initial period of the incubation. This fact suggested that most of the phytoplankters were living in the initial few days under these conditions. Since the nutrient regeneration seemed to be unrelated to the oxygen consumption rate, it was considered that the change in nutrient concentration had to be measured directly for estimation of the regeneration rate?and this measurement was useful to distinguish between decomposition and respiration processes of phytoplankton. The decomposition process could be described as a first order process in the initial period. The relative rates of decrease of the measured parameters were as follows; chlorophyll>nitrogen>carbon. Decomposition and nutrient regeneration rates seemed to be affected by water temperature and the algal species composition. Bluegreen algae easily decomposed at high temperature, but diatoms did not. About 70-90% of cell carbon and nitrogen were easily mineralized to C02 and dissolved inorganic nitrogen, and only about 10-30% changed to detritus carbon and nitrogen. About 24% of cell phosphorus was regenerated in average and the remainder was in the particulate form. © 1991, The Japanese Society of Limnology. All rights reserved.