Floodplain-mire interactions and palaeoecology : implications for wetland ontogeny and Holocene climate change

• Main Author: Mansell, Lauren Joanne
• Published: Queen's University Belfast 2012
• Subjects: 577.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579790

There has been increasing interest in combining proxy records from raised mire and floodplain ecosystems in order to provide greater clarity concerning Holocene climate and environment change. However, there are a number of questions still to be addressed concerning this approach. Perhaps most pertinent is that there has been limited research as to how these systems interact and react to change in a local landscape context. For instance, do ecosystems register events such as increased wetness in a synchronous manner and to what extent do they experience different thresholds? It has become increasingly apparent that chronologically aligning these records is challenging. This study provides a palaeoenvironmental reconstruction across a transect from raised mire to floodplain, using the Humberhead Levels in South Yorkshire as a case study. Coleoptera and pollen were used as environmental indicators, while multiple fraction dating and Bayesian modelling were used to produce age-depth models. These results were compared with previous research undertaken in the region in order to explore wider environmental signals. Floodplain-peat development (c. 8000-3000 cal BC) was intrinsically linked to rising sea-levels, causing base-levels to rise, leading to plaudification and the formation of rheotrophic mire-peat communities, from at least c. 5000 cal BC. The mire communities reached ombrotrophy by c. 2800 cal BC and were no-longer influenced by base-level flow. Consequently, the floodplain and mire ecosystems stopped registering synchronous episodes of change, such as increased wetness. Although the floodplain and lagg fen ecosystems continued to experience similar changes, they also recorded a number of asynchronous hydrological events. These systems may have experienced different thresholds. That floodplain, mire and lagg fen communities do not always register similar or simultaneous environmental changes highlights that more caution should be taken when combining different datasets in order to infer wider regional reconstructions.