Of marsh and mangrove: coupled biophysical and anthropogenic drivers of 20th century wetland conversion in Tampa Bay Estuary, Florida (USA)

Abstract

Dense mangrove swamps currently dominate tidal wetlands of the Tampa Bay Estuary System on the central peninsular Gulf Coast of Florida (USA). Late-19th century Coast and Geodetic Survey topographical charts and Government Land Office surveys, however, depict wetland systems dominated by salt marsh—therefore suggesting mangrove dominance as a product of 20th century encroachment. To clarify the primary drivers of ecosystem change, this study integrates sedimentological, paleobotanical, and radiometric analyses of sediment cores collected in 2018 with analyses of aerial photography taken between 1940 and 1997. Results empirically ground truth the wetland conversions inferred through analytical comparisons of historical and modern mapping and establish a high-resolution chronology for coastal environmental change. These results showed that salt marsh and salt prairie habitats persisted within Tampa Bay study areas until the mid-20th century. Mangrove forest rapidly encroached the study areas over a 20 year interval, between 1960 and 1980, immediately following intensive ditching for mosquito control. The findings demonstrate how coastal geoengineering, mangrove autoecology, and sea-level rise interacted across the late-20th century to accelerate the creation of novel seascapes.