Nutrient content of wetland plants in constructed wetlands receiving municipal effluent in tropical Australia

Abstract

Several pilot wetlands have been constructed in Queensland to treat municipal wastewater. The wetlands are in tropical, subtropical and arid geographical locations. Most wetlands are free water surface and contain a variety of macrophyte types and species. A total of 49 native and 11 exotic species of wetland plants have been identified. This paper examines tissue nutrient content in different species and plant components from 7 wetlands.

Most species translocated to the constructed wetlands flourished indicating their ability to tolerate nutrient enriched waters, and tended to have higher tissue nutrient concentrations than their controls in natural wetlands. Submerged and free floating species exhibited higher nutrient concentrations than floating leaved and emergent species. Maximum dry weight nutrient concentrations (mg.g⁻¹) were recorded in duckweed 18 mgP.g⁻¹; 58 mgN.g⁻¹; Ceratophyllum 14 mgP.g⁻¹, 35 mgN.g⁻¹; Monochoria cyanea (a native relative of the water hyacinth) 13 mgP.g⁻¹, 30 mgN.g⁻¹; waterlilies: Nymphoides indica 16 mgP.g⁻¹, 40 mgN.g⁻¹; aquatic vines Ipomoea diamantinensis 10 mgP.g⁻¹, 53 mgN.g⁻¹, I. aquatica 9.5 mgP.g⁻¹, 53 mgN.g⁻¹; Ludwigia peploides 10 mgP.g⁻¹, 52 mgN.g⁻¹; and the water ferns Ceratopteris thalictroides 10 mgP.g⁻¹, 31 mgN.g⁻¹,Marsilea 10 mgP.g⁻¹, 43 mgN.g⁻¹. Emergent species with the highest nutrients (P or N) were Eleocharis sphacelata 9.4 mgP.g⁻¹, 31.7 mgN.g⁻¹, Baumea articulata 8.7 mgP.g⁻¹, 24 mgN.g⁻¹,Typha domingensis 7.2 mgP.g⁻¹, 51.8 mgN.g⁻¹ and Cyperus involucratus 7 mgP.g⁻¹, 44.6 mgN.g⁻¹.

Pooled data showed no significant difference between tissue nutrient content in plant components, though nitrogen was highest in the leaves and phosphorus highest in the roots of most species. There was some evidence of spatial variation in tissue nutrient content between different wetlands but it has not been possible to correlate this with nutrient loadings or removal efficiencies.