Effects of seawater exchange on water chemistry among coastal lakes with intermittent connections to the sea

Intermittently closed and open lakes and lagoons (ICOLLs) are a dynamic class of coastal waterbodies with the unique feature of intermittently connecting to the sea. Understanding the functioning and potential threats of these globally rare systems is important to their preservation and protection. Coastal dune lakes of northwest Florida are one example of an understudied group of ICOLLs which connect with the Gulf of Mexico for brief periods of time. Using a 17-year, monthly water chemistry dataset, we analyzed long-term patterns in water chemistry among 16 coastal dune lakes. Using salinity as a proxy for frequency of seawater inflows, principal component analysis and linear mixed-effects models indicated significant relationships between salinity and nitrogen, phosphorous, and pH. Salinity was positively associated with pH and phosphorus, and negatively associated with nitrogen, although relationships within individual lakes varied. Nonparametric trend analysis indicated lake-specific significant shifts in water chemistry in several systems, although a majority of systems did not exhibit notable long-term trends. Results indicate the significance of water exchange with the Gulf of Mexico on water chemistry of coastal dune lakes and have implications for management of ICOLLs globally