Use of Floating Vegetated Mats to Remove Nutrients From Surface Waters.

Contamination of surface waters from point and nonpoint source pollution is an environmental concern.  Methods are needed to remove excess nutrients (N, P) contained in such surface waters.  Water bodies of concern may include streams, ponds, lakes, and wastewater lagoons.  A new concept for improving surface water quality is to grow vegetation on floating platforms in the water body.  Periodic harvesting and removal of the biomass serves as direct offsite removal of nutrients.  Research conducted by USDA-ARS and the University of Georgia at Tifton, GA has focused on determining the feasibility of growing vegetation on floating platforms to remove nutrients from contaminated waters.  Research has included both aquaculture wastewater and anaerobic swine lagoon wastewater.  Ongoing research at the University of Georgia Aquaculture Unit has shown that Variegated Japanese Water Iris (Iris ensata ‘Variegata’) grows well and removes N and P from the wastewater. At a commercial swine farm, on wastewater averaging 160 mg L^-1  Total N (128 mg L^-1  NH₄- N), Tifton 85 bermudagrass (Cynodon dactylon (L.) Pers.), Common bermudagrass (Cynodon dactylon (L.) Pers.) , and Fall Panicum (Panicum dichotomiflorum (L.) Michx.) were found to grow quite well.  These three species produced 3600, 3200, and 3100 g m^-2 biomass respectively over a two year period.  The greatest removal of nutrients from the wastewater was by the Tifton 85 bermudagrass, where in one growing season (3 cuttings) 690 and 250 kg ha^-1 of N and P were removed.  This paper explains the concepts and techniques involved in using floating vegetated mats to remove nutrients from contaminated waters and reports the findings of studies on both aquaculture and swine lagoon wastewater.