In two saltmarshes, Old Hall in the Blackwater (southeast England) and Warton Bank in the Ribble (northwest England), we took vegetation and soil samples every six to eight weeks from August/September 2024 to January 2025 to characterise seasonal denitrification and vegetation dynamics. The data includes, vegetation species and diversity; seawater and porewater samples (NO3-, NH4+, PO43-); seawater ion concentrations (Cl-, Na2+, K+, Br-, Mg3+ and Ca2+); moisture and organic matter content in the sediment. A key ecosystem service in coastal systems is the remediation of nutrient pollution through sediment burial, vegetative uptake and microbial processing. Denitrification is a facultative anaerobic process where microbial activity transforms nitrate (NO3-), which in high concentrations can be environmentally harmful, into the environmentally benign dinitrogen gas (N2). Denitrification's magnitude is considered particularly important in saltmarsh systems compared to other habitats, although an intermediate product, nitrous oxide (N2O), can also be given off and contribute to climate change. Full details about this dataset can be found at https://doi.org/10.5285/72962722-bd56-4b3e-b397-90ceec6c821e
