Meiofauna analyses of saltmarsh development with changing sea-levels in the UK

Abstract

Coastal saltmarshes are vital ecosystems because (a) they physically buffer the land against storms and flooding from the sea and (b) ecologically they are high-productivity systems in estuaries and marine coastlines that shelter and support fish and bird populations. Saltmarshes are highly sensitive to sea level change. Any saltmarshes are now threatened by rising sea level, but how they will respond and at what rate is unclear. Managing saltmarshes is therefore necessary, but requires a good understanding of their development in order to predict how they might respond to sea level change. Current management practice in the UK is mainly managed realignment landward and future scenarios are predicted with computer models. Both use the hypothesis of facilitation succession, whereby saltmarsh progrades seawards. An alternative hypothesis is saltmarsh development by transgression landward due to rising sea level. This thesis critically examines how saltmarshes have developed under different sea-level change regimes in order to gain an insight into how they are likely to be affected by future sea level rise. Using established micropalaeontological techniques, Foraminifera tests and Ostracoda shells were extracted from sediment cores taken from saltmarshes representing a range of sea level change histories during the Holocene. Sampling of modern environments allowed saltmarsh vegetation zones to be characterised by foraminiferal and ostracod assemblages which were then used to reconstruct the development of saltmarshes over time as preserved in the cores. Sediment layers in the cores were dated using three techniques: Optically Stimulated Luminescence (OSL), radio carbon (14C) and 137Cs / 210Pb. The latter hypothesis is supported in southern England where marine transgression caused saltmarshes to migrate landwards, in contradiction to the facilitation succession hypothesis. In Scotland saltmarshes advanced seawards but due to a marine regression. Future studies should explore the applicability of these findings to saltmarshes outside the British Isles.