The results show that Schoenoplectus californicus had allometric growth between 31.2 to 98.4 and relative abundance between 21 to 108 individuals m(-2), during the fall and spring seasons, respectively. These results are influenced by the nitrogen content (between 0.05 to 2.0 kg N ha(-1) d(-1)) present in the constructed wetland. In this same period, the increase in Schoenoplectus californicus biomass (similar to 28%) is related to a decrease in nitrogen loading between 2.0 to 0.05 kg N ha(-1) d(-1). Aboveground biomass was greater (500 to 724 g m(-2)) than belowground biomass (4.8 to 22.7 g m(-2)). Due to nutrient translocation in spring-summer, the N:P ratio aboveground ranged from 9 to 16, while belowground the ratio varied from 7 to 10.