NUTRIENT RELEASE FROM COASTAL AQUIFERS OF VARYING LITHOLOGY UNDERGOING SALTWATER INTRUSION

Coastal interfaces are hotspots for critical biogeochemical processes that cycle nutrients. The process of saltwater intrusion into coastal aquifers may be responsible for the release of nutrients, such as phosphorus and nitrogen, in amounts significant enough to drastically alter coastal wetlands and marine ecosystems. Brackish groundwater discharging to surface waters in the Florida Everglades contains elevated phosphate concentrations due to the release of phosphate from limestone as the saltwater intrusion front progresses. Elevated levels of phosphorus and nitrogen have been recorded in many other coastal settings with varying lithology. This study compares the release of nutrients due to saltwater intrusion from three geologic materials: carbonate aquifers, siliciclastic aquifers, and soils in order to compare which coastal settings may be most susceptible to increased nutrient loads as sea level continues to rise.

Nutrient concentrations from the various lithologies upon exposure to salt water were obtained from the literature. Published results from both field and laboratory studies were considered. Higher concentrations of phosphorus were found to be released from carbonate material than siliciclastic materials. Phosphorus was reported to be released from soils exposed to brackish waters. The results of this investigation indicate that phosphorus can be released from all three geologic materials upon exposure to saltwater intrusion. Understanding that nutrients can be released from geologic materials upon exposure to saltwater is important in understanding the overall effects of sea level rise in coastal regions.