Abiotic mineralization of dissolved organic phosphorus for improved nutrient retention in a large-scale treatment wetland system

The Everglades Stormwater Treatment Areas (STAs) in South Florida are large treatment wetlands that were constructed and managed to reduce phosphorus (P) loads to the Everglades Protection Area. Most P in inflow waters originates from urban, agricultural, and equestrian runoff, as well as discharges from Lake Okeechobee. To effectively reduce dissolved organic P (DOP) in the outflow of the STAs, DOP must be mineralized to soluble reactive phosphorus (SRP) (Ged and Boyer, 2013), and then removed through uptake by aquatic vegetation or co-precipitation with calcite during photosynthesis. In order to explore the effects of sunlight and photolytic processing on dissolved P mineralization within the STAs, a series of photochemical experiments were conducted. First, DOM entering the STAs was measured and found to be highly aromatic (mean SUVA = 0.38) and dominated by large molecular weight molecules (75% of bulk DOM > 10KDa) that are reactive to photolytic degradation. Model molecules, such as phytic acid, and site water from the STAs were exposed to light and produced SRP from DOP after exposure to high energy UV radiation. Additionally, analysis of excitation emission matrices (EEM) found that aromatic and humic structures were photolytically degraded during UV exposure. These findings suggest that photolysis is a significant process in DOM and P cycling in the STAs, and if leveraged in SAV dominated areas, could benefit P removal by co-precipitation with calcite. These findings suggest that vegetation management strategies could be employed to maximize UV photolytic reactions to optimize P retention. •DOM entering Everglades STAs are humified and photo-bleached but still photoreactive.•Photomineralization of DOP was observed in model molecules and agricultural runoff.•Photolysis is a key process in DOM cycling and can improve DOP retention in the STAs.