Phosphorous dynamics of the aquatic system constitutes an important axis for waste water purification in natural treatment pond(s) in East Kolkata Wetlands

• Eutrophication is prevented at EKW single pond system during sewage purification.
• Inhibition of eutrophication is attributed to rapid removal of phosphorous.
• Removal of particulate phosphorus has the largest contribution.
• Early onset of aerobic state and basic pH limits internal phosphorus loading.

Treatment wetlands provide effective means for sewage purification. Consistently, at East Kolkata Wetlands, a Ramsar site since 2002, the city sewage is purified within 9–12 days and rendered suitable for large scale fish cultivation. But the introduction of the sewage into these wetlands should greatly favour eutrophication event as it contains excess nutrients like phosphorus. Towards understanding the underlying mechanism of prevention of eutrophication, the current study investigated the phosphorus dynamics of the aquatic system during the purification process as phosphorus plays a critical role in regulating the trophic status of a wetland. For this purpose we measured total phosphorous, particulate phosphorous, and soluble phosphorous of the water coloumn at different time points of purification. The result showed that total phosphorous from the water coloumn was removed considerably with time and it can be attributed mainly to the rapid removal of particulate phosphorous during anoxic period of treatment. Besides, trophic status index indicated that wetland maintained a mesotrophic status after the onset of aerobic condition. Alkaline pH of the water column and onset of aerobic condition may also contribute towards maintaining this mesotrophic condition by inhibiting internal loading from sediment-associated phosphorus in the overlying water column. Thus the current study provides an insight into waste water purification wherein phosphorous dynamics plays an important role for the prevention of eutrophication.