Total, above and below ground biomass, growth, and tissue nutrient concentration of three species growing in two contrasting environments (a horizontal flow, constructed wetland fed tertiary effluent at Bolivar, South Australia, and a natural wetland, Bool Lagoon, south-eastern South Australia) were compared to determine relative performance of each species.

Overall Baumea articulata and Phragmites australis performed poorly in trenches compared with natural wetland. Total biomass was 4.0 and 2.7, compared with 7.7 and 10.9 kg/m2 however, above ground (AG)/below ground (BG) ratios were similar at both locations (1 (Baum) and 0.42(Phrag)). Below ground mass was restricted to the top 25cm in the trenches but penetrated to > 50cm in the natural wetland. Phragmites showed a marked decline in standing biomass during the winter period in both environments but Baumea increased standing biomass in the trenches. Although the mean tissue nutrient concentrations of N and P for plants grown in trenches were higher than their natural counterparts [3.18(Baum), 2.56(Phrag) vs. 0.68(Baum), 0.49(Phrag) mg P/g DWt.; 12.99(Baum), 23.06(Phrag) vs. 5.39(Baum), 8.92(Phrag) mg N/g DWt.], this was offset by the lower biomass of the plants in the trenches.

In contrast, the semi-emergent Triglochin procerum performed exceptionally well in the trenches, compared with the other species, and with itself growing in Bool Lagoon. Total biomass was 15.4 kg/m2, AG/BG ratio was 6. Triglochin continued to grow vigorously throughout the winter and had a mean tissue concentration of 5.19 mg P, 22.63 mg N and 368 C/g dry weight.

These data suggest that the effective removal of nitrogen and phosphorus by harvesting was 5 times higher for Triglochin than for Baumea or Phragmites in the trenches. The nitrogen concentrations in Triglochin suggest a protein content of 16–18% which compares favourably with lucerne.

Author notes

Present Address: Water Research Laboratory, Faculty of Science and Technology, University of Western Sydney - Hawkesbury, Bourke Street, Richmond, N.S.W., Australia