The Role of Vegetation in Phosphorus Removal by Cold Climate Constructed Wetland: The Effects of Aeration and Growing Season

Abstract

The objective of this study was to evaluate the effectiveness and con- tribution of Schoenoplectus fluviatilis (Torr.) (river bulrush) to phosphorus (P) removal from dairy-farm effluent in a cold climate constructed wetland. After 3 years of operation (1,073 days), both nonaerated wetland cell 3 (C3) and aerated cell 4 (C4) exhibited a sharp decline in dissolved reactive phosphorus (DRP) stor- age, indicating wetlands saturation. The quantities of DRP stored during the three growing seasons (433 days) represented only 10.0%(C3) and 17.7%(C4) of the total amount of DRP (435.06 ± 2.3 g m �2 , 97.02 kg) added to each cell (C3 and C4) over the entire 3-year period. However, of the total DRP retained by both wetland cells during 1,073 days of operation, the quantities stored during the three grow- ing seasons (433 days) represented 50.3%(C3) and 36.50%(C4) of the total DRP retention. This indicated that vegetation had an important role in the overall DRP storage regardless of supplemental aeration. Overall, nonaerated C3 DRP mass removal efficiency during the 3-year period of investigation was low, averaging 19.9%. Aerated C4 DRP mass removal efficiency was 2.4-fold higher, averaging 48.4%. Belowground (BG) biomass had significantly higher (p < 0.001) P content than aboveground (AG) biomass, throughout the 3-year period of investigation.