Distribution of yttrium and rare earths in Florida Bay sediments

The distribution of yttrium and rare earth elements (YREEs) in surface sediments was measured on samples collected from 40 stations in Florida Bay (June 2000 and February 2001). Florida Bay is the largest shallow carbonate estuary in South Florida with nearly pristine conditions. It receives fresh waters from some rivers and several canals from the Everglades which contribute rare earth elements and metals to the Bay. This paper is the first extensive study of YREEs in Florida Bay. Concentrations of YREEs (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were determined by ICP-MS. The YREEs show a similar distribution pattern for the two months studied. The maximum concentrations were found in the western and north-central zones (near the Everglades) and the minimum concentrations were found in the south-central zone near the Florida Keys. The pattern of YREEs in Florida Bay sediments correlated strongly with those in the North American Shale Composite, indicating a dominant crustal source for these elements. However, the REE concentrations in Florida Bay sediments are depleted with respect to NASC. All REEs exhibited a strong correlation with Fe and Al from continental input and river runoff from the Everglades. The heavy REEs and Y showed a strong correlation with Al (R2 > 0.84). The light and medium REEs showed a strong correlation with Fe (R2 > 0.9). Correlations of all the YREEs with Mn were slightly lower (R2 ∼ 0.7–0.75). The concentration of all the YREEs, Al and Fe are dependent on the bottom types and zones in the Bay, except Mn which decreases as it moves from the land to the sea.