Measurements of microbial processes, dissolution, water and porewater chemistry during experiments on two coral reef sediments

Two coral reef sediments have been subjected to OA scenarios in the laboratory. Sediments from Magnetic Island (year 2014, 3 pCO2 treatments) were investigated under diffusive conditions in flumes. Parameters studied were: oxygen fluxes, porewater pH and oxygen concentrations. Sulfate reduction rates and pigment concentrations as a measure for microphytobenthos abundance were measured at the end of the experiment. Sediments from Davies Reef (year 2015, 2 pCO2 treatments) were studied under advective conditions using stirred chambers. Microphytobenthos growth over the experimental period was studied using hyperspectral imaging. Porewater pH profiles were measured in different regions of the chambers. Fluxes of oxygen, total alkalinity (as a measure of CaCO3 dissolution), dissolved organic carbon and nutrients were measured using incubations. Pigment concentrations were measured at the end of the experiment as a measure for microphytobenthos abundance and to calibrate the hyperspectral imaging results. In both experiments, elevated pCO2 did not affect biotic processes. Elevated pCO2 caused an increase in dissolution of the Davies Reef sediments. The porewater pH measurements indicated that this is likely caused by the dissolution of high-magnesium calcites.