Phytoplankton and benthic infauna responses to aeration, an experimental ecological remediation, in a polluted subtropical estuary with organic-rich sediments

Abstract

Fine-grained organic-rich sediments (FGORS) are accumulating in estuaries worldwide, with multi-faceted negative ecosystem impacts. A pilot experiment was carried out in a residential canal of the Indian River Lagoon estuary (IRL, Florida, USA) using an aeration treatment intended to mitigate the harmful ecological effects of organic-rich sediment pollution. Planktonic and benthic communities were monitored, and environmental data collected throughout the aeration process. Results were compared against control conditions to evaluate the efficacy of aeration in the mitigation of FGORS. During the aeration process, hurricane Irma impacted the study area, bringing heavy rainfall and spawning a brown tide event (Aureoumbra lagunensis). The overall thickness and volume of FGORS, and the organic content of surface sediments did not change during the aeration treatment. Dissolved oxygen was higher and ammonium concentrations were lower in aeration canal bottom water compared to the control canal. During treatment, aeration did facilitate benthic animal life when temperatures dropped below 25°C, likely due to water column mixing and the increased capacity of water to hold dissolved gasses. In general, aeration did not significantly change the planktonic community composition relative to the control canal, but, during the post-bloom period, aeration helped to weaken the brown tide and phytoplankton densities were 35–50% lower for A. lagunensis in aeration canal surface water compared to the control canal. Aeration has important management applications and may be useful for mitigating algal blooms in flow-restricted areas and promoting benthic communities in cooler environments.

Nutrient fluxes from recent deposits of fine-grained, organic-rich sediments in a Florida estuary

“…Capping fine-grained sediments can prevent resuspension, and mitigate fluxes by creating an oxic surface layer that promotes coupled nitrification-denitrification plus sorption of phosphorus and through consolidation of sediments. Although aeration was unable to improve sediment conditions in highly organic sediments from BRL, it may be a viable option to preserve areas near the tipping point (e.g., Harris et al, 2015;Ma et al, 2023). We should continue to investigate methods to promote coupled nitrificationdenitrification and sequestration of P. For example, some benthic habitats can be modified to promote bioirrigation and thereby restore ecosystem services, including nutrient removal (e.g.…”

“…Approaches that address geochemical processes may include aeration, alterations to hydrology (increased circulation), removal of impaired sediments (dredging) and targeted habitat and shoreline restoration. These approaches have varying degrees of success in the IRL system and globally (e.g., Harris et al, 2015;Fox and Trefry, 2018;Ma et al, 2023).…”