Calcium Carbonate and Temperature as Tools for Manipulation of Coastal Sediment Acidification: A Laboratory Study

Abstract

The spread of low-pH sediments (also known as dead muds) has brought about the need for laboratory studies involving acidified sediment. CO 2 bubbling is traditionally used to acidify the sediment; however, allowing the native sediment bacteria to do the acidification is a more natural approach. The objective of the current study was to test if the surface sediment could be acidified using the sediment bacteria and determine how long the sediment chemistry stayed stable for. The pH of sediment taken from near Dobbins Island in Beals, ME, was monitored in sediment containers distributed evenly among 20-gallon aquaria containing artificial seawater for 74 days. Half of these aquaria were kept at 6.5°C while the other half were kept at 24°C. Each sediment bed had a depth of 15 cm and had pore water samples taken via syringe at the top, middle and bottom of the sediment column every 2-3 days. Crushed razor clam (Ensis leei) shell was applied to half of these sediment beds on day 33. The results show surface sediment pore water chemistry can be kept at acidified conditions (~6.0 pH/ ~500 µmol kg-1 total alkalinity/ less than 0.04 aragonite saturation state) or ambient collection site conditions (~6.8 pH/ ~4000 µmol kg-1 total alkalinity/ 0.10-0.25 aragonite saturation state) for month-long periods by incubating the sediment in recirculating aquaria or applying crushed E. leei shell respectively. Higher temperatures reduce the incubation time needed to acidify the sediment but shorten the period the surface sediment remains at 6.0 pH for. Before using the method, researchers should run a preliminary experiment with a batch of the sediment they intend to use to insure the sediment acidification intensity and duration meets their needs.