High-resolution reconstruction of recent vegetation dynamics in a Mediterranean microtidal wetland: implications for site sensitivity and palaeoenvironmental research

The analysis of recent sediment sequences from coastal wetlands provides an opportunity to examine the response of these sites to environmental change and events, many of which are independently documented. This also permits an evaluation of rates of response to be made that can help in assessing changes identified in longer-term (Holocene) coastal sediment sequences. A short core from the Mulinello estuary, Augusta Bay, south east Sicily, was dated using 210Pb and 137Cs. Samples were analysed for pollen and spore content, and the results are presented here as both percentage and influx data. Temporal resolution of the pollen data is typically 5-15 years for the first 50 years of the record (circa 1895-1945 AD) and 2-5 years for the last 50 years (1945-1995 AD). Two phases of salt marsh expansion in the Bay occurred, up to the 1940s and from the 1960s to the mid 1980s. In the mid 1940s, the salt marsh underwent a significant decline, marked by a sudden fall in influx and percentage data for Chenopodiaceae. This correlates with an inwashing of catchment-derived pollen, particularly of resistant Lactucae grains, indicating more regular fluvial inundation. Climate records show the occurrence of significantly higher precipitation at this time. Since the construction of a port access road in the 1980s a second decline in the local halophyte community occurred. Pollen influx data enable a precise assessment of how quickly local colonisation of surfaces at the sampling site occurred. During both episodes of salt marsh colonisation, the transition from low-moderate to high Chenopodiaceae influx took less than 6 years. The data show that salt marsh communities can expand and decline very rapidly and that these variations can occur independently of significant changes in relative sea level