Oxygen dynamics in crude oil contaminated salt marshes: II. Carbonaceous sediment oxygen demand model

The role of carbonaceous sediment oxygen demand (CSOD) due to oxidation of sulfides reduced in oxygen dynamics in crude oil contaminated salt marshes was investigated through a mathematical model. An existing CSOD model was calibrated from laboratory data sets through nonlinear regression. The effect of oil and fertilizer on CSOD was quantified by comparing three treatments (i) control (no oil and fertilizer amended) (ii) fertilized, and (iii) oiled and fertilized sediments. CSOD was directly proportional to sulfate reduction. Higher CSODs under oiled/fertilized and fertilized conditions were primarily due to increased sulfate reduction rates under these conditions. Reaction velocity for oxidation of dissolved sulfide in the aerobic layer, kappaH2S,d1, was significantly greater than that of particulate sulfide oxidation, kappaH2S,p1. This indicates that dissolved sulfides are dominant over particulate sulfides and directly related to CSOD in salt marshes. The CSOD was linearly dependent on the overlying dissolved oxygen concentration when crude oil and fertilizer were added.