Flood & coastal defence • Pollution control & water quality • Biodiversity & conservation importance • Palaeoecology & Archaeology • Designations & conservation management

Palaeoecology

Modern saltmarshes have developed on sediment sequences which commonly have been deposited over thousands of years. Saltmarsh sediments usually consist of mainly grey anoxic silts/clays, but peat units are also frequently present. At the base of the sediment sequence a palaeosol (buried soil) formed on the basal land surface, pre-dating the local postglacial marine transgression, can often be seen. Reconstruction of the environmental history of the site (‘palaeoecology’) can be achieved by analysis of microfossils (e.g. diatoms, foraminifers, pollen) and macrofossils (e.g. seeds, mollusc shells and insects) from samples of sediments. These proxy indicators give a picture of changing local environmental conditions during sediment deposition. Generally, most clays and silts were deposited in intertidal environments, whereas peats formed in fresh to brackish water conditions. At some sites, the peat units include remains of in situ root systems and fallen trunks of ancient floodplain woodlands. Successive peat and clay units can be dated by radiocarbon, luminescence or palaeomagnetism, and the absolute levels of the contacts between these units can be determined in relation to OD. From this information, the environmental history of the locality can be established. That is, the date at which the basal land surface was influenced by rising sea-level and later successive phases of marine transgression or regression. The data can also contribute to an understanding of wider sea-level changes.

Consequently, saltmarsh sediment sequences are of considerable scientific significance, and their conservation is an important component of saltmarsh management.

Click on photograph above for an example of eroded saltmarsh overlying a palaeosol (buried soil).