This dataset contains measurements of sediment particle size distribution associated with denitrification rates from two saltmarshes in England (Old Hall in the Blackwater estuary, Warton Bank in the Ribble estuary) and in two seasons (Winter: December 2024/January 2025 and Summer: June/July 2025). The survey, laboratory measurements and data processing were done by Bangor University and UK Centre for Ecology and Hydrology for the Environmental Agency. Full details about this dataset can be found at https://doi.org/10.5285/56241997-8189-4455-9623-44cce052db11