Nutrient removal through oyster habitat restoration in the Indian River Lagoon
AuthorGallagher, Sean M.
AdvisorSchmidt, Casey A.
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In 2016, an algae bloom in the Indian River Lagoon (IRL) caused a state of emergency in Florida. As with many estuaries, nutrient loading has led to periodic eutrophication in the IRL. Previous studies have found oyster bed restoration promotes seasonal ecosystem services of phosphorus sequestration and denitrification; however, benefits over longer periods are not well understood. In the Mosquito Lagoon of the IRL, oyster beds have decreased from 24.07 ha to 14.46 ha due to boat traffic (40% decline). Since 2009, restoration has repaired 19 beds and half an acre of oyster habitat. Our study in 2016 determined whether restoration has increased ecosystem services in Mosquito Lagoon since 2009. Hypotheses for the study were that control sediments represented conditions at damaged oyster beds during restoration, that ecosystem services increased as oyster beds recovered, that services were limited by sediment components, and that service limitation from sediment components decreased with restoration. Recalcitrant phosphorus was significantly higher in oyster beds than in control sediments. In addition, bioavailable phosphorus converted to recalcitrant forms with bed restoration. Denitrification was significantly higher in oyster beds than in controls, and there was a small, weak decrease in denitrification in restored beds over time due to increasing nitrogen limitation. Restored oyster beds removed 5,318 kg/ha of nitrogen and 91 kg/ha of phosphorus in new oyster tissue and shell. Sediment in restored beds also provided 796 kg/ha/yr of denitrification and sequestered 9 kg/ha of phosphorus. On average, a 20 year oyster restoration project could remove nitrogen at $570/kg (30% of other methods) and phosphorus at $121,000/kg (9 times other methods).