Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea Mays)

Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ(15)N). Animal excrement is known to impact plant δ(15)N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.This paper presents isotopic (δ(13)C and δ(15)N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of (15)N enrichment in fertilized plants is very large, with δ(15)N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ(15)N values ranged between -0.3 and 5.7‰. Intraplant and temporal variability in δ(15)N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ(13)C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.The results presented in this study demonstrate the very large impact of seabird guano on maize δ(15)N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material

Kinetics of O-2 reduction on a Pt electrode covered with a thin film of solid polymer electrolyte

The kinetics of O-2 reduction on both oxidized and reduced Pt rotating disk surfaces covered with thin films (1 to 15 mu m) of recast polybenzimidazole (PBI) or Nafion have been examined in 0.1 M aqueous solutions of H3PO4, H2SO4, and HClO4 at 25.0 degrees C. Polymer films were deposited on a Pt disk electrode by a spin-coating technique. Experiments were performed formed at different rotation rates and potential scan rates. This investigation was undertaken to establish to what extent the solid polymer electrolyte influences the mechanism and kinetics of O-2 reduction. The number of electrons exchanged per O-2 molecule and kinetic parameters for O-2 reduction (reaction order with respect to O-2, Tafel slope/transfer coefficient, and exchange current density) are not changed in the presence of the polymer films, indicating that the reaction path and kinetics are not altered in the presence of recast PBI and Nafion films. The diffusion coefficient (D) and concentratio