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Published on: October 24, 2025
Macroalgae detritus accelerates degradation of recalcitrant organic matter in coastal marine sediments
Julie Lyhne Ehrenreich1, Annette Bruhn2, Daniel Taylor3
1Department of Ecoscience, Aarhus University, Aarhus, Denmark.
Abstract:
The supply of macroalgal detritus to marine sediments may impact the degradation dynamics of pre-existing organic matter in the sediment. This was investigated in sediment sampled from a shallow coastal estuary (Limfjorden, Denmark). Measurements of oxygen (O2) consumption, the release of dissolved inorganic carbon (DIC), and the exchange of dissolved inorganic nutrients (NO2-, NO3-, NH4+, and PO43-) between sediment and bottom water in macroalgae-amended and unamended sediment cores showed a clear impact of macroalgae additions, with elevated carbon (C) turnover in these cores. The differences in total DIC release between unamended cores and macroalgae-amended cores were more than 100% and up to 298% of the added macroalgae C. The macroalgae addition, therefore accelerated the degradation of pre-existing organic matter in the sediment. This observation, known as a "priming effect," is well described in soils and freshwater systems but has only recently been considered in marine systems. Results from this experiment suggest that short term priming (
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