The Effects of Artificial Floating Wetland Island Construction Materials on Plant Biomass

Julie A. Vogel

A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science, Department of Environmental Science and Policy, College of Arts and Sciences, University of South Florida St. Petersburg


Two artificial floating wetland island types were constructed to determine if floating wetland islands made from ‘natural’ environmentally sensitive materials would perform similarly to those islands made of ‘artificial’ plastic derived materials with regard to vegetation dynamics, biomass, plant percent cover, carbon, nitrogen, and phosphorus content, material durability, and buoyancy. The islands were placed in an urban lake in St. Petersburg, FL and initially transplanted with Pontederia cordata (pickerelweed), Schoenoplectus tabernaemontani (bulrush), Canna flaccida (golden canna), and Sagittaria lancifolia (duck potato). Islands were measured through the growing season for percent cover, weight, and plant category composition. At the end of the study, biomass was harvested and oven dried. Nitrogen, carbon, and phosphorus content were analyzed for each species. All floating wetland islands remained buoyant throughout the study. The substrate on the ‘natural’ bamboo islands disintegrated within one month in the aquatic environment, which was not sufficient for most bamboo island vegetation to establish and create a self-sustaining buoyant root mat. Biomass from three of eight bamboo islands was harvested. Vegetation dynamics depended on raft type. Emergent macrophytic vegetation decreased 13% on average across all islands. Conversely, floating aquatic vegetation (FAV) increased on average 39%. Mean algae cover was greatest on the open PVC islands (58%) and less than half that for all other islands. Ludwigia grandiflora (primrose ix willow) was not initially transplanted to any of the floating wetland islands, but averaged 40% on all harvested islands by the end of the study, greater than any other emergent macrophyte on average. Mean island weights varied for island groups (PVC open: 15 kg; Bamboo unharvested: 18 kg; Bamboo harvested: 22 kg; PVC enclosed: 23 kg). Weight increases resulted from biomass growth (PVC open: 131 g/m2; Bamboo harvested: 1,461 g/m2; PVC enclosed: 1,511 g/m2), mainly from Ludwigia grandiflora (2,123 g/m2). Islands with greater biomass had a greater mass of nitrogen, phosphorus and carbon content. Percent nitrogen, phosphorus and carbon were dependent on species rather than raft type. Ludwigia grandiflora and Pistia stratiotes (water lettuce) had the greatest percent of N (3.7% and 3.9%) and P (0.2% and 0.4%) over other island species. Island location and enclosure led to differences in percent cover within the island groups. The parameter of lakeward or landward accounted for 44% of variation in the total mean percent cover (p<0.001). The parameter or north or south accounted for 32% of variation (p=0.002). Enclosure accounted for 24% of variation (p=0.014).