The Fate and Metablism of Cyanobacteria after Flocculation using Modified Local Soil Technology

摘要

Chitosan modified local soil (CMLS) can flocculate cyanobacterial blooms, improve transparency and manipulate redox condition in the sediment. In order to understand the fate of algae after flocculation and the effects of light and O2 on the flocculated algae, the composition of phytoplankton community was studied from March to December 2009 in a controlled enclosure in Taihu Lake (China). Microcystis was the dominant species throughout the period except that diatom was dominant in March. In the incubation experiment, water samples of April, June and October were flocculated using CMLS and cultured under different irradiance and redox conditions. After 75 days, the dominant species in the April samples changed from cyanobacteria to green algae or diatom under light or air-open conditions, and that in the June samples changed from cyanobacteria to diatom only under dark and air-open conditions, while the cyanobacteria in the October samples remained dominant under all conditions. Photosynthesis and respiration experiments indicated that, after 75 days, flocculated algae could still maintain normal metabolism and contribute for oxygen enrichment under the air-open condition, but those under the air-closed and dark conditions could not sustain the normal metabolism. The results suggested that flocculated cyanobacteria could face different fates after they are flocculated by the CMLS technology. They could become biodegraded under anoxic and dark conditions when they are covered by the second layer of modified soils. They could maintain normal metabolism and contribute dissolved oxygen under light and aerobic conditions near the sediment, which may get back to water column.