Difference in temporal and spatial distribution pattern of cyanobacteria between the sediment and water column in Lake Chaohu

The evaluation about the relative distribution of cyanobacterial biomass between the sediment and water column would be indispensable to understand if benthic cyanobacteria are important to cyanobacterial biomass in the water column. A separation method for the rapid quantification of benthic cyanobacteria in Lake Chaohu was developed by density-gradient centrifugation. A 2(4) full factorial design and response surface methodology was employed to optimize the extraction protocol. Under the optimal operating parameters including 29% Percoll solution, 30 min centrifugation time, 7200 r/min centrifugation speed, and a 1:10 ratio between the volume of sediment and Percoll solution, the recovery rate of cyanobacteria in sediment was 96.73%. Temporal and spatial variations in cyanobacterial biomass in water and sediment were investigated monthly throughout a whole year. In general, cyanobacterial biomass per square centimeter in the water column showed high spatial-temporal changes, tending to increase in February and reaching a peak in April at some sites due to the growth of Dolichospermum. The second peak arrived in July and September and was caused by the rapid growth of Microcystis. Concurrently, cyanobacteria biomass per unit area in sediment showed a clear temporal change pattern, increasing from October and reaching a peak level in February at all the sampling sites. The average ratio of cyanobacterial biomass in water to that in sediment was lowest in January at 1.48 and increased to the highest level in July at 318.61. Although Microcystis and Dolichospermum were dominant species in the water column, only Microcystis was observed in the Percoll solution extraction from sediment. Microscopic observation revealed that a very small fraction of Microcystis cells could survive in sediment, and most of the cells decomposed when the water temperature increased after June. Therefore, the contribution of the recruitment of cyanobacteria could be negligible in Lake Chaohu.

Automated summary

The study developed a method to effectively separate benthic cyanobacteria in lake sediment and found significant spatial-temporal variations in cyanobacterial biomass in both the water column and sediment. Cyanobacterial biomass in the water column showed peaks in February and April, while sediment biomass showed peaks from October to February.