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 (similar to 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. (c) 2015 Elsevier Ltd. All rights reserved.
