Vertical variation in magnitude and partitioning of oxygen demand in a contaminated sediment

Abstract

Variation in oxygen demand (OD) with depth, of both the solids and porewaters, in a contaminated urban sediment was measured in order to predict the response of the sediment water system to future improvements in water quality and partial dredging. The OD (24 h) of the solid was relatively invariant with depth, and almost three orders of magnitude greater than that of the corresponding porewater. Porewater OD was also invariant with depth despite an increasing concentration of reduced species; the potential OD of these in the deepest samples was about 17% of that of the solid. Dissolved organic carbon (DOC) formed the major proportion of these reduced species, so the slow development of porewater OD may be a manifestation of the time required for the development of an oxic microbial flora, and its invariance suggests there may be a decrease in lability of DOC with depth. OD of the solid appeared to be limited by decreasing availability of dissolved oxygen (DO) suggesting that any deeper DO penetration into these sediments may increase OD beyond that exerted under present conditions.