Are benthic nutrient fluxes from intertidal mudflats driven by surface sediment characteristics?

A broad sampling program was carried out in the spring of 2019 on the Brittany coast to assess how the surface sediment characteristics drive the benthic effluxes of ammonium (NH4+) and phosphate (PO4) from intertidal mudflats. A total of 200 sediment samples were characterized by their porosity, grain-size, elemental composition and pigment contents, as well as the benthic fluxes of NH4+ and PO4 determined by core incubations. The results showed that (1) a high phaeopigment and iron-bound phosphorus content (Fe-P) and a low porosity were significantly related to the high PO4 flux, and (2) a high porosity and the TN:Org-P ratio in the sediment organic matter (SOM) were related to the high NH4+ flux. This indicated that PO4 fluxes would be more driven by the redox status of the sediment through the desorption of Fe-P under specific anoxic conditions during the algal decomposition. NH4+ fluxes would be more driven by high NH4+ recycling rates from SOM mineralization and high sediment-water exchanges, enhancing the diffusion of NH4+ to the overlying water. The present study allowed to highlight the large variability in the benthic nutrient fluxes at the regional scale, as a result of the connections between microbial (SOM mineralization), chemical (adsorption-desorption) and physical (diffusion) processes.

Automated summary

The study conducted a broad sampling program on the Brittany coast in the spring of 2019 to assess how surface sediment characteristics affect the benthic effluxes of ammonium and phosphate, revealing the driving factors behind these nutrient fluxes. Results showed that different sediment characteristics lead to variations in ammonium and phosphate fluxes, which are influenced by chemical and biological processes in the sediment.