The effect of sediment resuspension on organic matter reactivity and organic carbon content within a mid-latitude fjord in Scotland

A laboratory-based experiment was conducted to evaluate how resuspension affects the amount and composition of the organic matter in the surface sediments of Loch Etive, a fjord in Western Scotland with a pronounced gradient of organic carbon content and organic matter reactivity. Sediment samples collected from the fjord's frequently hypoxic upper basin and its more well-mixed lower basin were completely resuspended in well-oxygenated seawater to simulate a potential maximum disturbance event. Resuspension of the sediments resulted in a loss of organic carbon and a decrease in the labile organic matter in all sediments over the 120-h measurement period. Organic carbon loss was greatest in sediments from the upper hypoxic basin of the fjord, where both initial organic carbon and labile organic matter content were highest. The largest changes occurred in the first 24 h (first-order organic carbon decay rates (k-values) ranged from 0.403 to 0.951 d⁻¹) while average rates for the whole incubation period were lower (ranging from 0.071 to 0.151 d⁻¹), implying that the first 24 h after a seabed disturbance may be crucial for OC loss. This research highlights the importance of considering organic carbon content and organic matter reactivity in developing protections for the management of carbon-rich marine sediments.