Macrofauna, Sediment Characteristics, and Benthic Biogeochemical Fluxes across a Coastal Breakwater System

The dataset includes measurements of macrofaunal community structure (density, biomass, species richness, and functional traits), sediment characteristics (grain size distribution, porosity, organic matter content, organic carbon and total nitrogen concentrations, delta 13C), porewater oxygen and nutrient concentrations (nitrate, ammonium, phosphate), and benthic fluxes of oxygen and nutrients. Total denitrification and coupled nitrification–denitrification rates were quantified using the isotope pairing technique.

Sampling was conducted in June 2021 and June 2022, at the onset of the saltmarsh growing season. The data represent discrete observations, with short-term incubations performed under controlled laboratory conditions.

The study was carried out in an intertidal saltmarsh located in Rivière-du-Loup Bay, within the St. Lawrence Estuary (Quebec, Canada). Five sites were sampled, including locations behind the breakwater, immediately seaward of the structure, and lateral to it, as well as natural reference sites with and without vegetation. Biogeochemical fluxes and sediment processes were measured on intact sediment cores in the laboratory.

These data support the assessment of how coastal artificialization through breakwater construction alters benthic ecosystem functioning, with a specific focus on nitrogen cycling. The dataset informs whether modified, unconsolidated mud habitats can sustain benthic fluxes and denitrification rates comparable to those of natural saltmarshes, thereby contributing to evaluations of functional resilience and trade-offs in coastal protection strategies.