Niencheski, L.F.H. and Windom, H.L., 2015. Chemistry of a surficial aquifer of a large coastal lagoon barrier and its relation to adjacent surface waters of Brazil.

The Holocene/Pleistocene barrier along the coast of southern Brazil, separating the Patos Lagoon (the largest in South America) from the South Atlantic Ocean, contains a surficial unconfined aquifer that connects to both water bodies. This has been the site of previous studies on surface-water chemistry and on the subterranean estuary (SE) and submarine groundwater discharge (SGD) along the barrier beach. In this paper we present the results of observations from monitoring wells placed in three transects across this barrier and make a preliminary assessment of spatial variations in chemistry of aquifer water, based on analyses of samples collected over a period of several years, and its relation to that of adjacent surface waters. In addition to general groundwater chemistry (DO, pH, Eh, and conductivity), dissolved nutrients (inorganic N, phosphate, and silicate) and trace metal (Ba, Cd, Co, Cu, Fe, Mo, Mn, Ni, U, V, and Zn) concentrations were also determined. From the results we conclude that the Patos Lagoon Barrier (PLB) aquifer serves as a reactive reservoir/filter of inputs from terrestrial runoff to the ocean. Processes occurring in the aquifer and at its interfaces with the ocean and lagoon influence nutrient composition and trace metal concentrations of adjacent surface waters and alter the land–sea flux of some dissolved trace metals.