Organic matter mineralization in intertidal sediments along an estuarine gradient

A seasonal study of organic matter mineralization rates was made at 8 intertidal stations in the Westerschelde Estuary (The Netherlands). Organic matter mineralization rates, based on the gaseous emission of carbon dioxide and methane, showed significant dynamic temporal and spatial variability at various scales. Annual rates of organic matter mineralization varied from 8 to about 339 mol C m−2 yr−1. The temperature dependence of organic matter degradation was described using an Arrhenius-type equation. Activation energies ranged from 54 to 125 kJ mol−1 and correlated negatively with depth-integrated rates of mineralization. Spatial differences in mineralization were mainly due to differences in the lability of the organic matter, since the quantity of organic matter was similar between stations on an areal or volume basis. Average first-order decomposition rate constants ranged from 0.2 to 7 yr−1 and decreased towards the seaward end of the estuary due to ageing of riverinederived material. Intertidal sediments were estimated to account for about 25% of the total carbon retention in the Westerschelde estuary.