Phosphorus Sorption Dynamics in Shallow Groundwater, Coastal Everglades, Florida, USA

For this dissertation I studied phosphorus (P) sorption dynamics in the shallow groundwater of the southern Everglades. In particular, I examined how the ambient water type governs soluble reactive P (SRP) availability through adsorption/desorption reactions with the aquifer matrix. Chapter 2 investigated how P sorption dynamics of the mangrove root zone sediment are affected by high bicarbonate brackish groundwater compared to both fresh groundwater and saltwater. The results from chapter 2 show that the sediment exhibited exceptionally low sorption efficiency in the high bicarbonate brackish water, which would allow ambient water SRP concentration to be maintained at a higher level. Chapter 3 is a detailed analysis of how P sorption dynamics in two bedrock samples are affected by incremental increases in saltwater content in a freshwater-saltwater transition zone. The results of chapter 3 indicate that a sorption edge occurs at 3 mM Cl- concentration. In water exceeding this Cl- concentration, SRP would be expected to desorb from the bedrock due to a sharp decrease in sorption efficiency between the freshwater saltwater. These results suggest that SRP is active in the ion exchange front of saltwater intrusion, with a rapid increase in SRP availability expected at the leading edge of saltwater intrusion. A landward incursion of 3 mM Cl- concentration water would be expected to raise ambient SRP concentration along the affected aquifer zone, in turn increasing SRP availability in the ecosystem where the transitional waters discharge to the surface. Chapter 4 investigates the kinetics SRP release accompanying saltwater intrusion using a column of carbonate aquifer solids and alternating inflow between fresh groundwater and saltwater. The results show an immediate and high magnitude increase in SRP concentration when saltwater flows into the column. The combined results of this dissertation show that, in the southern Everglades and possibly other carbonate coastlines as well, water type strongly controls P sorption behavior of the sediment and bedrock, and may have a direct influence on the local ecology through increased P availability. A fundamental understanding of the abiotic exchange mechanisms between SRP and the aquifer solids can aid in the successful management and protection of this unique and important ecosystem