Effects of diel oxygen cycling and benthic macrofauna on sediment oxygen demand

Abstract

Shallow marine soft sediments serve an important function by remineralizing organic matter, which consumes dissolved oxygen in the process. Sediment oxygen demand (SOD) depends on overlying water oxygen concentration but can also be altered by mixing and irrigating activities of sediment macroinfauna. Oxygen patterns in shallow coastal waters can vary substantially on short time scales, frequently following a diel cycle. However, little is known about whether and how the presence of macrofauna in sediment may affect SOD throughout a diel cycle. In this field study, we examined how sediment oxygen demand varied over a diel oxygen cycle and with sediment macroinfaunal presence. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. We found that sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. There was an interaction between the effects of faunal biomass and DO on SOD, suggesting that where macroinfauna are present they drive greater SOD during nightly low oxygen, presumably by enhancing their irrigation. SOD was also highly variable on a sub-diel timescale, and more variable in sediments with more macroinfauna. This indicates that sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna. High temporal and spatial resolution measurements, particularly on the diel scale, are critical to accurately estimate sediment metabolism.