Document Type



Master of Science (MS)



First Advisor's Name

James W. Fourquerean

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Steven Oberbauer

Third Advisor's Name

William Anderson

Date of Defense



This experiment investigated causes of seasonality of δ15N and δ13C values in Thalassia testudinum leaf tissue by manipulating plant demand and nutrient supply in situ for 13 months. I clearly demonstrated that seagrass elemental content, stable C and N isotopic content, morphology and the concentration of NH4+ seagrass porewaters directly respond to manipulations of resources and also by the plant demand for nutrients to support growth. Isotopic values displayed marked seasonality with heavier values found in summer (δ15N=5.0% δ13C=-5.7%o) and lighter values in winter (δ15N=1.7%o δ13C= -9.4%o). Calculations of Δ (δ15N source DIN- δ15N plant product) indicate that T. testudinum is able to strongly fractionate against source pool DIN. Interpretation of an enriched N signature as pollution-derived must first recognize the isotopic seasonality of the plant demand relative to the nutrient supply. Only when these links have been explained can the full relevance of δ15N values be applied.



Included in

Biology Commons



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