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The article presents a study examining the late-Holocene Epoch sea level based on a reconstruction from a salt marsh in the Malltraeth estuary in North Wales. Information is provided on how the research can inform modeling of past and future relative sea-level changes in the British Isles.

Introduction: Marshes contribute to habitat and water quality in estuaries and coastal bays. Their importance to continued ecosystem functioning has led to concerns about their persistence. Outcomes: Concurrent with sea-level rise, marshes are eroding and appear to be disappearing through ponding in their interior; in addition, in many places, they are being replaced with shoreline stabilization structures. We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay, the largest estuary in the United States, to better understand the effects of sea-level rise and human pressure on marsh coverage. Discussion: Approximately 30 years ago, an inventory of York River estuary marshes documented the historic extent of marshes. Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution. Marsh change varied spatially along the estuary, with watershed changes between a 32% loss and an 11% gain in marsh area. Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/ riverine section of the estuary and where forested hummocks on marsh islands have become inundated. Marshes showed little change in the small tributary creeks, except in the creeks dominated by fringing marshes and high shoreline development. Conclusions: Differential resilience to sea-level rise and spatial variations in erosion, sediment supply, and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient, with consequences for their unique communities. [ABSTRACT FROM AUTHOR]

As sea level rise accelerates and land development intensifies along coastlines, tidal wetlands will become increasingly threatened by coastal squeeze. Barriers that protect inland areas from rising sea level prevent or reduce tidal flows, and impermeable surfaces prevent wetland migration to the adjacent uplands. As vegetation succumbs to submergence by rising sea levels on the seaward edge of a wetland, those wetlands prevented from inland migration will decrease in area, if not disappear completely. Tools to identify locations where coastal squeeze is likely to occur are needed for coastal management. We have developed a ''Coastal Squeeze Index'' that can be used to assess the potential of coastal squeeze along the borders of a single wetland and to rank the threats faced by multiple wetlands. The index is based on surrounding topography and impervious surfaces derived from light detection and ranging and advanced spaceborne thermal emission and reflection radiometry imagery, respectively, and uses a fuzzy logic approach. We assume that coastal squeeze varies continuously over the coastal landscape and tested several fuzzy logic functions before assigning a continuous weight, from 0 to 1, corresponding to the influence of slope and impervious surfaces on coastal squeeze. We then combined the ranked variables to produce a map of coastal squeeze as a continuous index. Using this index, we compare the present and future threat of coastal squeeze to marshes in Wells and Portland, Maine, in the United States and Kouchibouguac National Park in New Brunswick, Canada. [ABSTRACT FROM AUTHOR]

Climate change-induced rises in sea level threaten to drastically reduce the areal extent of important salt marsh habitats for large numbers of waterfowl and waders. Furthermore, recent changes in management practice have rendered existent salt marshes unfavourable to many birds, as lack of grazing has induced an increase in high-sward communities on former good-quality marshes., Based on a high-resolution digital elevation model and two scenarios for projected rise in near-future sea levels, we employ an Arc Map allocation model to foresee the areal loss in salt marsh associated with these changes. In addition, we quantify the areal extent of inadequate salt marsh management in four EU Special Protection Areas for Birds, and demonstrate concurrent population dynamics in four species relying on managed habitats. We conclude by investigating potential compensation for climate change-induced salt marsh losses by means of more efficient management., Our models indicate that by the end of this century 15·3-43·6% of existent salt marshes will be flooded due to rising sea levels, and that inadequate managed salt marsh presently makes up around 51·1% of total marshes. Thus, re-establishing extensive areas of well-managed marshes might counterbalance the loss expected from rising sea levels during the next century., In addition to positive effects on plant diversity, this will benefit energetically challenged herbivorous waterfowl such as light-bellied brent geese Branta bernicla hrota L. and increase potential recovery of wader populations with unfavourable conservation status such as black-tailed godwit Limosa limosa L., dunlin Calidris alpina L. and ruff Philomachus pugnax L., Synthesis and applications. Implementing environmentally friendly management schemes based on extensive grazing (around 1 cow per hectare) is an important initiative to counteract the accelerating climate change-induced habitat loss in near-coastal areas across the globe, and to secure priority salt marsh habitats that support internationally important populations of breeding, wintering and staging waterfowl. However, this may only be a temporary solution that will have to be supplemented by increased reintegration with the sea and managed retreat of seawalls or near-coastal agricultural areas to effectively safeguard the future salt marsh biome. [ABSTRACT FROM AUTHOR]

Diatoms, vascular vegetation, sediment data and water salinity from contemporary intertidal environ ments in Roudsea Marsh, northwest England, are used to define altitudinal relationships between diatom assem blages and reference water levels. Comparison of these data with the high-resolution diatom biostratigraphy of a fossil marsh sequence allows identification of fluctuations of relative sea level in the mid- and late Holo cene. Two oscillations in relative sea level are recorded. A rise in sea level (> 0.6 m) led to the inundation of the site after 6000 BP and was followed by a fall in sea level (c. 1 m) around 4700 BP. A second rise in sea level (> 0.5 m) occurred before 2420 BP and was followed by a relatively stable or smaller rise of sea level during the last millennium. The use of diatom groups based on marsh altitude was successful. [ABSTRACT FROM PUBLISHER]