The dataset comprises the bulk density taken from bulk density rings (3.1 centimetre (cm) height, 7.5 cm diameter) within each 1metre (m) x 1m quadrat. Samples were taken vertically at three depths within each quadrat to roughly quantify the following zones: 0 -10 cm, 10 - 20 cm and 20 - 30 cm. Sampling was conducted at six salt marsh sites at four spatial scales: 1 m (the minimal sampling unit) nested within a hierarchy of increasing scales of 1-10 m, 10-100 m and 100-1000 m. Three of the sites were in Morecambe Bay, North West England and three of the sites were in Essex, South East England. The Morecambe Bay samples were taken during the winter and summer of 2013. The Essex samples were taken during the winter, early spring and summer of 2013. This data was collected as part of Coastal Biodiversity and Ecosystem Service Sustainability (CBESS): NE/J015644/1. The project was funded with support from the Biodiversity and Ecosystem Service Sustainability (BESS) programme. BESS is a six-year programme (2011-2017) funded by the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC) as part of the UK's Living with Environmental Change (LWEC) programme. Full details about this dataset can be found at https://doi.org/10.5285/814be4cf-0ff2-46dd-b296-c4d9b913b6e4