To foster the practical development of the constructed wetlands used for water quality enhancement in Turkey, 2 vertical subsurface flow pilot-scale constructed wetlands were implemented on the METU campus, Ankara, Turkey. Both of the wetlands were planted with Phragmites australis and operated identically at a flowrate of 3 m 3 .d −1 and a hydraulic loading rate (HLR) of 0.100 m.d −1 , intermittently. The main objective of the research was to quantify the effect of different substrates (gravel and blast furnace granulated slag) on the nutrient removal performance of the constructed wetlands in the prevailing climate of Ankara. According to the monitoring study (July 2002-January 2003), concentration based average removal efficiencies for the slag and gravel reed beds were as follows: TSS (64% and 62%), COD (49% and 40%), NH + 4 -N (88% and 58%), TN (41% and 44%), TP (63% and 9%) and PO 3− 4 -P (60% and 4%). In general, the treatment performance of the slag system was better than that of the gravel system.