Phosphorus Uptake in Floating Wetlands: A Mass Balance Approach

Anthropogenic eutrophication of coastal waters, primarily attributed to agricultural runoff and wastewater disposal, is a phenomenon that disrupts marine ecosystems on a global scale. Mass-inputs of nutrients can cause hypoxic zones in aquatic environments, leading to toxic algal blooms and species decline. In an attempt to mitigate the effects of nutrient enrichment, Floating Treatment Wetlands (FTWs) have been employed as a restoration strategy to mimic a natural wetland’s ability to remove excess nutrients from flowing water. Studies have supported the success of FTWs in freshwater lakes, however, literature regarding the behavior of FTWs in estuarine waters is lacking. Here, we report preliminary findings from a mesocosm experiment that aimed to measure uptake of phosphorus by FTWs from brackish water over a 5-week period.

FTWs for this experiment were constructed from a media made from synthetic fibers in which Spartina patens was established and allowed to expand. Chlorophyll content, temperature, pH, and dissolved oxygen were measured within mesocosms daily, and phosphorus concentrations in water flowing into and out from mesocosms were measured weekly. We depended on a mass-balance equation to determine changes in phosphorus concentrations as water flowed throughout the mesocosms. Our data revealed an average Δ Flux Total Phosphorus of -477.95 mg/wk for FTW mesocosms during week 1, indicating the existence of a source releasing phosphorus into the mesocosms. Seedlings used to plant the mesocosms were fertilized with Osmocote at an application rate that corresponds to the magnitude of this phosphorus flux. By week 5 no Osmocote remained and the FTW mesocosms showed an average Δ Flux Total Phosphorus of 739.09 mg/wk, which implies that there is still potential for the FTWs to remove nutrients from mesohaline estuarine settings