Anthropogenic Changes Over The Last 100 Years In Dove Sound, Upper Florida Keys, USA

Thomas S. Harmon

A thesis submitted in partial fulfillment of the requirements for the degree of Masters of Science, Department of Environmental Science, College of Arts & Sciences, University of South Florida, Saint Petersburg

Abstract

Dove Sound located near Key Largo, Florida (USA) was investigated to determine potential anthropogenic influences from land use alteration such as highway and residential developments. The sediment load and nutrient flux was investigated using 210Pb dating of a sediment core, combined with stable isotope values δ15N, δ13C and pigment analysis. A 210Pb CRS model 130 year horizon was determined for the upper 12cm of the core. Mass sedimentation rates over this time period increased approximately 10 fold from 5.0 ±0.97 mg cm-2 yr-1 (10-12cm depth interval) to 48.58±3.61 mg cm-2 yr-1 (0-1cm depth interval). Reduction in the atomic C/N values combined with analysis of sedimentary pigments indicates an upcore shift from macrophyte grasses to algae, which included cryptophytes. Evidence suggests Dove Sound is undergoing eutrophication from an increase in nutrient supply and/or increase in water column residence time. This affects autochthonous productivity with shifts in primary producer abundance. This study does not support previous studies indicating septic wastes as the common nutrient source