Influence of seasonal variation in water quality on the microalgal diversity of sewage wastewater

• Microalgal diversity was analyzed in a canal near fields (India).
• Sampling at monthly intervals revealed the dominance of members of Cyanophyta.
• Diversity indices revealed low microalgal diversity in sewage wastewater.
• High species richness was positively correlated with the nitrate level.
• Phormidium sp. was the dominant genus present throughout the year.

An investigation was undertaken to assess the variation in microalgal diversity vis a vis physicochemical characteristics of sewage wastewater at monthly time intervals. Diversity analyses revealed the presence of algal members belonging to all major divisions, with a predominance of Cyanophyta. Shannon-Wiener and Simpson's diversity indices illustrated low microalgal diversity in sewage wastewater. Highest chemical oxygen demand (COD) of 14,000 mg L− 1 was recorded in December 2012. Spectrometric analyses of sewage wastewater revealed the presence of heavy metals, with Cr ranging from 3 to 4 mg L− 1 being detected in all the samples collected over the year. A positive correlation was found between COD and total heavy metal concentration (r = 0.77). The indices of microalgal diversity showed a positive correlation with nutrients and a negative correlation with COD and heavy metal concentrations, implying the significant role of these factors in influencing the algal population. Phormidium sp. was the dominant genus present throughout the year.