Effects of warming and CO_2 enrichment on O_2 consumption, porewater oxygenation and pH of subtidal silt sediment

摘要

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O-2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 degrees C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ Delta pCO(2): 253-396 mu atm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O-2 consumption (R-vol), the maximum in the volume-specific O-2 consumption at the bottom of the oxic zone (R-vol(,)bmax) and the volume-specific net O-2 production (P-n,P-vol), and decreased the O-2 penetration depth (O-2-pd) and the depth of R-vol,R-bmax (depth(bmax)). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on R-vol, R-vol,(bmax), P-n,P-vol, O-2-pd, or depth(bmax) and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.