Carbon (C) and nitrogen (N) burial within new intertidal and saltmarsh sediments from the Blackwater estuary, Essex were investigated. These sediments were created as part of a 'managed realignment' of coastal sea defences in the East of England to address issues such as loss of intertidal habitat, the effects of relative sea level rise and the unfeasibility of maintaining aging sea defences. The fluxes of greenhouse gases (CH4 & N20) from the sediments were quantified using non-steady state chambers and their ability to offset a portion of the C burial to give net carbon sequestration was investigated. C and N contents in natural intertidal sediments were higher than in managed realignment (MR) sediments and comparable to saltmarsh sediments from around the East coast of England. Mature MR sites possessed C and N burial rates at least as great as natural marshes and if increased sedimentation in these predominantly low lying intertidal areas is accounted for, the mature MR sites far outstrip natural marsh C burial rates. Less mature, MR midmarsh areas had lower C and N burial rates more inline with those found in intertidal mudflats. Both natural and MR intertidal areas were small sources of the powerful greenhouse gases CH4 (0.10-0.40 g m'2 y(l) and N20 (0.03-0.37 g M-2 y('). These gas fluxes reduced net C sequestration within the MR marshes by as much as 49%, but by only 2% from natural saltmarshes. The current C sequestration of Blackwater estuary managed realignment sites is -690 tonnes of CO2eq yr' (carbon dioxide equivalents). If the total area identified as potentially suitable for MR to take place is reverted back to intertidal area this will sequester -10200 tonnes of CO2eq yr' and -440 tonnes of N per year. Another -480 tonnes N will be removed through denitrification and -80-320 tonnes P yr"' will be buried within the new intertidal areas.