Methodology for Analyzing Dissolved Oxygen Consumption in Benthic Chambers

Abstract

Dissolved oxygen (DO) consumption in the sediments of natural aquatic ecosystems occurs by mass flux across the water-sediment interface. This mass flux is determined as either the rate of oxygen consumption in the sediment or the rate of DO diffusion across the diffusive sublayer. The thickness of the diffusive sublayer is determined by the flow conditions in the turbulent water column. Consequently, feedback occurs between the biochemical consumption that occurs in the sediment and the flow that occurs in the water column. Together, these conditions define the DO flux across the water-sediment interface. Benthic chambers have been used to measure this flux in field and experimental conditions. However, these measurements do not account either for the fact that the flow inside a benthic chamber is not representative of field conditions or for the DO consumption in the water column. Thus, they can provide an inaccurate estimation of the sediment DO demanded in the field. This article aims to present and discuss an approach for analyzing a time series of DO depletion inside a benthic chamber. Based on this approach, the processes related to turbulent water transport in the column are separated from the processes that characterize biochemical consumption in the sediments and the water column. Under these conditions, the parameters related to biochemical consumption in the sediments can be used to compute the expected DO demanded of the sediments in field conditions. Sediment samples from a lagoon near the Universidad de Chile campus in Santiago, the capital city of Chile, were used to illustrate the application of the proposed method. In addition, dimensionless numbers were used to define the method's validity and limitations.