Phosphorus speciation and sedimentary phosphorus release from the Gulf of Mexico sediments: Implication for hypoxia

Abstract

Phosphorus (P) is an important macronutrient that can limit primary productivity in coastal marine ecosystems. This study provides a quantitative determination of abundance and chemical speciation of P and potential anaerobic P-release rates from northern Gulf of Mexico (GOM) sediments. Seven sediment cores were collected from shelf, slope and deep-sea sediments in the northern GOM. A sequential extraction method was used to operationally separate P pools into readily available-P, Fe/Al–P, alkali extractable organic-P, Ca/Mg–P, and residual-P. Ca/Mg–P was the most abundant form of sediment P (79.0 ± 9.4% of TP). Northern GOM sediments were found to release 0.02–4.4 mg kg−1 d−1 of bioavailable-P under anoxic sediment condition. P-release rate had significant positive correlation (P = 0.001) with the Fe/Al–P fraction, indicating this relatively small pool of TP (∼0.4–10.2%) is primarily releasing available-P to the water column during hypoxia events. The findings of this study suggest that the internal sedimentary P loading contributes substantial bioavailable-P to the P-limited water column which leads to increased primary production in the northern GOM, creating a positive feedback mechanism for hypoxia. Therefore, the action plan to reduce the GOM hypoxia zone needs to take internal sediment P loading into account when managing for watershed nutrient loading.