Substratum phosphorus accumulation during maturation of gravel-bed constructed wetlands

Accumulation of phosphorus was investigated in the substrata and surface de posits of pilot-scale gravel-bed constructed wetlands after 2 (planted and unplanted) and 5 (planted only) years operation. Four different hydraulic l oading rates of farm dairy wastewaters provided mean cumulative total P (TP ) loadings ranging from similar to 520 to 2000 g m(-2) after 5 years operat ion. Mean substratum TP accumulations after 2 years operation ranged from 5 2 to 100 g m(-2) in the planted wetlands and from 40 to 51 g m(-2) in the u nplanted wetlands, both showing a general increase with wastewater loading. After 5 years operation, associated with declining wetland TP removal perf ormance, substratum TP accumulations in all the planted wetlands converged at similar values of 115 to 128 g m(-2). This represented 6 to 23% of their cumulative loadings. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.