Selection of Native Wetland Plants for Water Treatment of Urban Runoff
Field sampling was conducted in relatively undisturbed wetlands as well as in wetlands impacted by urban runoff to obtain information on ranges of biomass, nutrients and heavy metals accumulation in different type of common wetland plant species. The above ground biomass of erect emergent macrophytes, tules and cattails, (Scirpus spp., Typha spp.) ranged from 560 g to 3015 g of dry mass per square meter with the average nitrogen concentration of 0.9%. The creeping or soft emergent macrophytes such as water primrose, water cress and pennywort (Ludwigia peploides, Nasturtium aquaticum, Hydrocotyle verticillata, Sagittaria latifolia) usually reached significantly lower biomass (average of about 450 gm-2) but the biomass was richer in nitrogen (3%). Representatives of the second group were also characterized by significantly faster decomposition rates. Methods of propagation of plants from rhizome and stem cuttings were elaborated. A greenhouse experiment carried out to determine the dependence of growth characteristics on water level showed that Hydrocotyle verticillata seemed to be most sensitive to low water levels followed by Nasturtium aquaticum. Ludwigia peploides grew well at all five tested water levels. Both Hydrocotyle verticillata and Nasturtium aquaticum were more sensitive to high nitrogen concentrations than Ludwigia peploides. The mesocosm experiment studying the effect of four different water levels on the growth and biomass allocation in tall erect emergents (Scirpus californicus, S. acutus, Typha domingensis, Phragmites australis) and short emergents (Polygonum sp., Scirpus robustus, Sagitta ria latifolia and Ludwigia peplaides) showed that with the exception of Typha domingensis, Sagitta ria latifolia and Scirpus robustus, all other species allocated more biomass into belowground organs in the low water level treatment than in the high water treatment. Results of this experiment in combination with the observations from the field are crucial for proper species selection for various treatment purposes.
Five species, Scirpus californicus, S. acutus, Typha domingensis, Sagitta ria latifoia and Ludwigia peploides, were grown in outdoor hydroponic cultures in a heavy metal experiment. Zinc, lead, cadmium and copper in the concentrations of 0.1, 1 and 10 ppm of were added to the nutrient solution in the cultures. After two weeks of exposure to the heavy metals, plants were measured, harvested, biomass was sorted into roots, rhizomes, stems and leaves, dried and analyzed for concentrations of individual metals. There were no statistically significant differences in the growth expressed as the percentage increment of total length between the control and all concentrations of all metals. However, there were species and organ specific differences in the accumulation of individual metals. Most metals were accumulated in roots, specifically adventitious roots. Ludwigia peploides seemed to be the most efficient in the accumulation of all metals tested.