The Sedimentological and Ecological Signature of Dredge Fill Deposition on an Estuarine Seagrass Meadow, Boca Ciega Bay, Florida

Abstract: Dredge and fill is a construction method that has been utilized extensively within Boca Ciega Bay (St. Petersburg, FL) over the last century to develop and expand coastal infrastructure. This includes the Tierra Verde bridge, which was originally constructed in 1961 and then demolished and rebuilt in 2021. This project investigates the nature and extent of sedimentological and ecological impacts of sediment fill deposited in seagrass meadows for the construction of the Tierra Verde bridge. To do so, twelve marine sediment cores were collected along transects on the east and west sides of the bridge, including a control transect by Indian Key. Using visual core descriptions, quantitative sedimentological and XRF analyses, and molluscan diversity, sedimentary units were defined in each core. Units characterized by relatively high percentages of gravel, higher concentrations of elements such as P, Ca, and Si, and high abundances of molluscs are hypothesized to represent fill material. These units vary considerably, but generally contain sediment that is lighter in color and more coarse than the surrounding sediment. There are no sedimentary units in control site cores that resemble the suspected fill units. Molluscan diversity is greater in units underlying hypothesized fill units in comparison to units directly overlying those units, suggesting that the event has made a measurable impact upon the molluscan community. Forthcoming age data will continue to elucidate the timing and nature of natural and suspected anthropogenic sedimentation patterns near the Tierra Verde bridge as well as potential ecological impacts associated with fill deposition.