Coastal wetlands represent important ecosystems performing several functions leading to services. Out of those, the estimation of carbon sequestration and storage capacity is receiving increasing attention for emissions abatement and climate mitigation. Phragmites australis - dominated wetlands have the capacity to sequester large amounts of carbon given the large biomass formed annually, however the storage capacity depends on various factors including the environmental conditions that are site-specific. The aim of this study was to develop a method that could be used to quantify the storage capacity, from site-specific plant growth drivers (temperature, light, soil nutrients) and environmental attributes (e.g., particle size of soil). This was achieved with a combination of sampling (above- and below-ground plant biomass, nutrients and carbon content, soil nutrients and carbon at different depths) across the whole Venice Lagoon area where P. australis forms habitats under different conditions, using a PCA approach to link biotic and abiotic variables. To upscale the results, a modelling approach in two steps was used, taking first under consideration plant growth under different nutrient availabilities and then simulating the fate of carbon under different conditions (likelihood of material remaining in the area, its decomposition rate, the burial efficiency of soil). The results confirmed a positive effect of nutrient availability, mediated by soil moisture, on plant biomass and storage capacity, in alignment with the model results. Soil type was one the main driver of carbon storage. The knowledge of environmental dynamics and drivers of P. australis - dominated wetlands can be useful to support carbon management in order to mitigate climate change. Our model, with a calibration on different environmental conditions, has the potential to predict carbon sequestration and storage enabling it to be used as a management tool for different ecosystems.