BACTERIAL ESTABLISHMENT DURING THE FIRST YEAR OF OPERATION OF AN UNSATURATED AND A PARTIALLY SATURATED VERTICAL FLOW CONSTRUCTED WETLANDS

Based on seven sampling campaigns during the first year of operation of an unsaturated (UVF) and a partially saturated vertical (SVF) subsurface flow constructed wetland the dynamics of nitrogen transforming bacteria were unravelled. Ammonia oxidizing populations (Nitrosomonas and Nitrosospira) showed large variations throughout the study, especially in the top layer of both wetlands, whereas in the bottom layers lower abundance and no temporal variation was found. Nitrite oxidizing bacteria (Nitrobacter and Nitrospira) displayed little fluctuations and were identified in higher abundance in the bottom of the UVF wetland, and the top of the SVF wetland. Denitrifying bacteria exhibited no significant changes over time in both wetlands. In addition, the saturation of the bottom part of the SVF caused denitrification to occur over time in greater magnitude in the SVF wetland than in the UVF wetland, coinciding with the greater abundance of denitrifiers in this wetland configuration.