A comparison of oxygen, nitrate, and sulfate respiration in coastal marine sediments

Abstract

Aerobic respiration with oxygen and anaerobic respiration with nitrate (denitrification) and sulfate (sulfate reduction) were measured during winter and summer in two coastal marine sediments (Denmark). Both aerobic respiration and denitrification took place in the oxidized surface layer, whereas sulfate reduction was most significant in the deeper, reduced sediment. The low availability of nitrate apparently limited the activity of denitrification during summer to less than 0.2 mmoles NO ₃ ⁻ m⁻² day⁻¹, whereas activities of 1.0–3.0 mmoles NO ₃ ⁻ m⁻² day⁻¹ were measured during winter. Sulfate reduction, on the contrary, increased from 2.6–7.6 mmoles SO ₄ ²⁻ m⁻² day⁻¹ during winter to 9.8–15.1 mmoles SO ₄ ²⁻ m⁻² day⁻¹ during summer. The aerobic respiration was high during summer, 135–140 mmoles O₂ m⁻² day⁻¹, as compared to estimated winter activities of about 30 mmoles O₂ m⁻² day⁻¹. The little importance of denitrification relative to aerobic respiration and sulfate reduction is discussed in relation to the availability and distribution of oxygen, nitrate, and sulfate in the sediments and to the detritus mineralization.