Identifying increased inputs of terrestrial phosphorus to sediments of the southwestern Everglades and Florida Bay

Increased inputs of terrestrial phosphorus are a key factor in enhanced coastal eutrophication. Yet, precise determination of increases in terrestrial phosphorus in the sedimentary record is complicated by a variety of post-depositional processes. A method that takes these complications into consideration and produces a better record is needed. In this study, spatial and temporal patterns of terrestrial total phosphorus (TP) were determined for both pre-development (1900–1920s) and post-development (>1990s) sediments from the southwestern (SW) Everglades and Florida Bay. A two-component model for sediment sources [(Al + TOC) and CaCO3], coupled with the TOC/TOP ratios for TOP sources, was used to identify sediments containing mainly terrestrial TP. A strong spatial and temporal relationship between terrestrial TP and (Al + TOC) in pre- and post-development sediments from the more terrestrial sites suggests that aluminosilicates and organic matter play major roles in delivering terrestrial TP to area sediments. Terrestrial TP has been the predominant source of phosphorus to the sediments at the mouth of Shark River Slough (SRS), the west coast of the SW Everglades and western Florida Bay over the past century. Anthropogenic inputs of terrestrial TP, based on an enrichment factor calculated using [Terrestrial TP/(Al + TOC)] for pre- and post-development sediments, showed a 2- to 3-fold increase for sediments from the west coast of the SW Everglades and northwestern Florida Bay during the past century. In contrast, no such increases were found for the mouth of SRS. These findings suggest that anthropogenic inputs of terrestrial TP were most likely derived from freshwater runoff along the southwest coast of Florida. Our approach and results support and help focus current management efforts for the Everglades–Florida Bay as well as other coastal systems.