PHOSPHORUS CYCLING IN THE ANOXIC GOLFO DULCE BASIN, COSTA RICA.
Submitted in Partial Fulfillment of the Requirements for the
BSc Environmental Science
School of Earth and Environment
University of Leeds
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in the lab and to and for your time and expertise outside of the lab. I
chose an area which would provide me with some practical experience and you all bore the
brunt of the learning curve!
Phosphorus is an essential nutrient for all life on Earth. Marine phosphorus cycling is
somewhat understood under euxinic and anoxic non-sulphidic scenarios. Less research has been
conducted into anoxic, nitrogenous environments such as the anoxic, nitrogenous Golfo Dulce
basin. Two cores: A (0-20cm depth – oxic water column) and B (2-54cm depth – anoxic water
depth intervals and subject to a
sequential extraction technique modified from the SEDEX method (Ruttenberg, 1993). SEDEX
differentiates and quantifies the operationally defined reactive P (PReactive) fractions: P loosely
adsorbed to samples sites (PLoose), bound to Fe (oxyhydr)oxides (PFe), organic matter (POrganic),
authigenic carbonate fluorapatite + biogenic apatite + CaCO3 (PAuthigenic) and bound to the nonreactive fraction: detrital apatite (PDetrital). Significant recycling from POrganic (C>500:1 POrganic)
to PReactive in core A (39-79C:1PReactive) and POrganic (C >378:1POrganic) to PReactive in core B (56104C:1PReactive) was observed. PFe was quantitatively the most significant P fraction in core A
(0.31-0.42) and core B (0.25-0.34). No significant trends were observed between PReactive
fractions and depth or PFe and Fe oxides in core A. In core B, PLoose and POrganic increased with
depth, PAuthigenic decreased with depth and PFe and Fe oxides were strongly correlated (R2=0.8).
We conclude that P is strongly liberated from OM in both the oxic and...