EXAMINATION OF ANTHROPOGENIC NUTRIENT ADDITIONS TO COASTAL MANGROVE COMMUNITIES: A MULTIPLE ISOTOPE APPROACH

Degree Awarded: M.S. Environmental Science. American UniversityABSTRACTCoastal areas in the United States and Central America have undergone major land-use change since the mid-1800s as agricultural and urban areas spread. Some coastal areas in the Gulf of Mexico supported then, and continue to support, mangrove communities. A consequence of land-use change and increasing human population has been an increase in nitrogen availability to coastal systems, including mangroves. While many records trace anthropogenically derived organic sources in the ocean using stable isotopes, fewer records evaluating the source of anthropogenic inorganic nitrogen affecting coastal areas using historical collections before 1950s are studied. This study uses stable isotope values of 14 big claw snapping shrimps (Alpheus heterochaelis) and 24 ivory barnacles (Balanus eburneus) across the Gulf of Mexico and the Caribbean Sea over 121 years to document how human derived nitrogen affected coastal communities. Overall, a significantly positive trend in stable nitrogen isotope (δ15N) values of the Caribbean Balanus eburneus from 1939 to 1972 was observed. Data was split for comparison given the increase in the quantity and rate of fertilizer use after 1960 in the Gulf of Mexico and the Caribbean as a consequence of the Green Revolution. Both δ15N and δ13C were significantly different between pre- and post-1960 stable isotope values. Increased mean δ15N values from pre- to post-1960 suggest that human population growth in the Caribbean Sea and the Gulf of Mexico is driving nitrogen enrichment. This study suggest that the signals of human perturbations of the C and N pools are detectable in historical specimens collected over wide geographic scales