SPATIO-TEMPORAL EVIDENCE OF ANTHROPOGENIC NITROGEN IN FLORIDA WATERS USING STABLE ISOTOPE ANALYSIS OF MANATEE BONES
Degree awarded: M.S. Biology. American University
Nutrient pollution from human activities leads to coastal eutrophication and degradation of critical habitat for threatened species, including the Florida manatees (Trichechus manatus latirostris). Recovery of these damaged habitats relies on water quality assessments over a long period of time. With the absence of long-term diet and water quality data, manatee bones will serve as proxies for environmental reconstruction. Isotopic composition of skeletal nitrogen (N) reflects plants that manatees consume and the predominant N source driving primary productivity within the ecosystem. Sewage, as a consequence of rapid coastal development, is isotopically distinct from natural sources of N. Thus, δ15N values are predicted to increase over time and would be highest in densely-populated areas. Collagen in manatee bones were analyzed from 173 necropsied individuals since 1975. Mean δ15N values have decreased from 8.8 / in the 1970s to 6.3 / in 2010 mainly because fertilizer is the source of depleted N. Coastal and regional mean δ15N values were very high, suggesting a mixing of enriched N sources that include sewage and atmospheric deposition.