Nitrogen dynamics of the aquatic system is an important driving force for efficient sewage purification in single pond natural treatment wetlands at East Kolkata Wetland.

At East Kolkata Wetlands, though the domestic city sewage is purified very rapidly, the mechanisms of treatment remains inadequately explored. In this context, the present study investigated nitrogen dynamics of the single pond treatment systems during purification and explored its potential role in sewage treatment. For this purpose the concentrations of different forms of nitrogen present both in water and soil at different time points of purification were measured. The organic nitrogen content decreased sharply, in the early phase, with an increase in ammonium concentration. Notably the reduction in organic nitrogen was significantly higher than the increase in NH which can be attributed to the volatilization of NH under alkaline pH. This volatilization results in reduced oxygen demand. The nitrate-N concentration decreased sharply from soil with a concomitant increase in water column. However the reduction of nitrate in soil was significantly higher than the increase in water column. It indicated the occurrence of denitrification under anoxic condition wherein nitrate serves as terminal electron acceptor. Additionally a part of the nitrate supported planktonic growth. Thus it describes another mechanism of reducing oxygen demand. The initial NH-N concentration in the soil was very low and it increased gradually during purification due to increasing soil cation exchange capacity. Thus by trapping NH ion soil contributes towards preventing contamination of water. Thus at EKW, the cumulative activities in water and soil involved in nitrogen dynamics lead to overall reduction of the oxygen demand and contribute towards efficient sewage purification.