Sediment and pore water chemistry analyses
The remaining sediment in the frozen 215 ml containers were thawed, homogenized, and 15 ml sediment from each sample was dried at 60ºC for seven days for C/N analysis. In addition, 20 ml of sediment from each sample was centrifuged at 2200 × g to extract the pore water for ammonium (NH4+) and phosphate (PO43-) analyses. The dried sediment was ground, homogenized, and 1 ml dry weight sediment per sample stored in a desiccator prior to freeze drying, re-grinding, re-homogenizaton and treated with HCl to remove inorganic carbon. Samples were subsequently weighed into tin capsules. Concentrations of total OC and total nitrogen were determined on an elemental analyser (Flash 2000, Thermo Scientific). The pore water was collected after centrifugation by filtering 10 ml of the supernatant through a 0.45 µm polyethersulfone membrane filter (Filtropur S 0.45, Sarstedt). NH4+ and PO43- were determined colorimetrically (Multiskan GO spectrophotometer, Thermo Scientific) and NH4+ analysis followed the modified salicylate-hypochlorite method by Bower and Holm-Hansen (1980), and PO43- analysis followed the standard methods for seawater analyses (Grasshoff, Kremling, & Ehrhardt, 2009).