Influence of plant species and submerged zone with carbon addition on nutrient removal in stormwater biofilter

The type of plant species and the presence of a submerged zone (SZ) with carbon (C) addition may influence nitrogen (N) and phosphorus (P) removal in stormwater biofilters under wet-dry climatic patterns. A glasshouse experiment using two plant species (Baumea juncea and Melaleuca lateritia) with/without SZ and C addition, in addition to two plant species (Baumea rubiginosa and Juncus subsecundus) and a no-plant as control with SZ and C addition was conducted to investigate the removal of NH4-N, NOx-N, total dissolved N (TDN) and total N (TN) and filterable reactive P (FRP), total dissolved P (TDP) and total P (TP) from the stormwater in biofilter columns during 20 months of plant growth and 16 months of water sampling runs. All plants grew vigorously and developed well in the biofilters, but plant growth and nutrient removal (except for NH4-N and FRP removal) were enhanced in the planted treatments with rather than without SZ. The removal of N was significantly higher in the planted treatments with SZ than in the no-plant treatment with SZ. The removal of TP significantly increased in the treatments with SZ regardless of the plant presence or absence. Although different plant species contributed differently to nutrient removal from the stormwater, it was not possible to discriminate the relative performance of the four plant species with SZ. The benefits of a SZ with C addition for nutrient removal in the planted biofilters could be due to increased denitrification and improved plant growth.