Effects on the Underlying Water Column by Extensive Floating Treatment Wetlands

Floating treatment wetlands (FTWs) are an emerging engineering option with promise for simultaneous water quality improvement and habitat creation. Relatively little research has been published regarding their construction or effects on the underlying water column. In this field-scale experiment, four different extensive FTW designs were constructed using minimal materials, including drainpipe, burlap, mulch, utility netting, and reused polyethylene bottles. The FTWs were then planted with spp. (cattail) and L. (common rush). Over 28 mo, the water column beneath FTWs in two test ponds was compared to that in an open water control pond. The ponds (190 ± 10 m) were fed with well water enriched with nitrate to emulate agricultural ponds. Although observed differences were relatively small, statistically significant differences were noted. With respect to the control, waters underneath FTWs had lower dissolved oxygen, sulfate, nitrate, and pH, dampened diurnal temperature fluctuations, and greater alkalinity. The FTWs created habitat and were colonized by species of insects, birds, amphibians, snails, and spiders. Results indicated that spp. is suitable for FTW creation. However, a more supportive planting matrix is suggested to encourage faster plant growth and protect against wind and wave action damage. Although plant growth was limited, results suggest that FTWs may be applied to encourage less aerobic and more organic rich and thermally insulated conditions for water quality improvement in agricultural ponds and other aquatic systems while also creating valuable habitat.