Keeping above the waves? The response of coastal freshwater peatlands to sea-level rise.

Global mean sea-level (GMSL) is rising and is projected to do so for centuries, if not millennia, even after anthropogenic greenhouse gas emissions cease. The rate of GMSL rise is accelerating, having already increased from ~2.1 mm/year in 1993 to ~4.5 mm/year in 2023. With high emissions, we cannot rule out a rise of 15 m by 2300. Understanding coastal responses to sea-level rise (SLR) is a priority for policymakers and land managers, particularly as coastal processes increasingly affect inland areas. While much research has focused on saltwater wetlands such as mangroves and saltmarshes, freshwater peatlands have received less attention despite their significant ecosystem services: they store at least twice as much carbon as forests globally, attenuate floods, improve water quality, and enhance biodiversity. SLR poses a potential major threat to coastal freshwater peatlands. There is some evidence that peatlands have historically increased their accumulation rates in response to rising sea-levels, but these mechanisms remain poorly understood. Without this understanding, we cannot predict their response to future SLR. This research has global relevance with many low-lying wetlands around the world, and findings could help indicate where to prioritise management efforts. This project adopts a past-present-future approach to investigate the response of coastal freshwater peatlands to SLR, combining palaeoecology, contemporary ecohydrological monitoring, modelling, and mapping. The study focuses on two contrasting UK sites: Cors Fochno, a Welsh estuarine ombrotrophic bog, and Wheatfen, a floodplain fen in Norfolk. Research questions include: 1) How have peatlands responded to SLR throughout the Holocene? 2) Can peatlands keep pace with SLR? 3) What changes might we expect to see in coastal freshwater peatlands as sea-levels rise in the future?