PALEOLIMNOLOGICAL EVIDENCE OF HISTORICAL LAND USE CHANGE FROM MULTIPLE SITES ON THE ISLAND OF ST. CROIX, USVI

The island of St. Croix has been acquired by various governments throughout its history. With every new period of occupation different environmental stressors were applied to the island, including nearly complete deforestation of the island for sugarcane cultivation in the late 1700’s. The island is currently undergoing an economic shift to ecotourism and there is an increasing focus on sustainability efforts. By studying the impacts of historic anthropogenic activities on sensitive island ecosystems, efforts can be directed towards improving and maintaining ecosystem health and sustainability. This study focuses on sediment cores recovered from Sugar Bay, an embayment at the mouth of Salt River; and two upland ponds, Fredensborg Pond and Lower Windsor Pond located within, or very near, the Salt River watershed. The combination of upland and nearshore sedimentary records is intended to provide a novel spatiotemporal perspective on the dramatic terrestrial land use change and resulting sedimentary dynamics in the nearshore environment that may have severely impacted sensitive marine habitats such as coral reefs and mangrove forests. Preliminary loss on ignition (LOI), carbon-nitrogen ratio (C/N), and bulk sedimentary δ13C and δ15N data indicate significant temporal change in vegetation and sediment source in the Salt River watershed. In Sugar Bay, there is a notable shift in sediment stratigraphy with a recent increase in organic content and decreased shell/carbonate concentrations. These stratigraphic changes correlate with a gradual decrease in C/N ratios suggesting a decreased contribution of terrestrial organic matter to the bay in recent times. In Lower Windsor Pond and Fredensborg Pond, δ13C values increase markedly with depth, likely due to the predominance of sugarcane, a C₄-photosynthetic crop, in the watershed historically. Forthcoming isotopic analyses and forthcoming short-lived radioisotope and radiocarbon dates will help to elucidate the relationship between historical anthropogenic land usage and sedimentation rates.