Foraminiferal assemblages as bioindicators of potentially toxic elements in Biscayne Bay, Florida

• Main Author: Carnahan, Elizabeth A
• Format: Others
• Published: Scholar Commons 2005
• Subjects: Estuary; Heavy metals; Cu; Pb; Hg; Zn; Foram index; Benthic; Sediments; American Studies; Arts and Humanities
• Online Access: http://scholarcommons.usf.edu/etd/2810; http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3809&context=etd

Heavy-metal pollution is an issue of concern in estuaries such as Biscayne Bay that are heavily influenced by agricultural, urban, and harbor activities. The goals of this study were to provide a state of the bay assessment that can be used to interpret changes that have occurred over the past 60 years in Biscayne Bay, to provide a baseline to compare changes in the ecosystems during and after execution of the Comprehensive Everglades Restorations Plan (CERP), and to determine if benthic foraminiferal assemblages in Biscayne Bay reflect heavy-metal contamination in sediments. Surficial samples were collected at 147 sites throughout the bay. Analyses included geochemical assessment of the mud fraction for 32 chemical parameters, grain-size analysis, and assessment of foraminiferal assemblages at the genus level. Geochemical analyses revealed elevated concentrations of a suite of heavy metals in the sediments of the northern bay, between Miami and Key Biscayne, and the periphery of the southern bay from Black Creek Canal south to Turkey Point. Cluster analysis, multi-dimensional scaling, and multivariate-correlation analyses revealed three distinct foraminiferal assemblages. One assemblage, characteristic of the northern bay, was defined by stress-tolerant taxa including Ammonia, Cribroelphidium, Nonion, and Haynesina, which were present in low abundances. Distribution of this assemblage correlated with the most elevated concentrations of heavy metals. The assemblage that defined the southwestern margin of the bay was dominated by Ammonia and Quinqueloculina. This assemblage is characterized by the lowest diversities and highest abundances, and is likely influenced by both reduced salinity and elevated organic-carbon concentrations.