Project title: WESTLOGs - Recent evolution of Portuguese W coast ESTuaries: high resolution studies from marshes geoLOGical recordS: 2009-2011. $214,000.
Estuaries are highly productive environments that have been strongly impacted by human activities during the last 200 years. Within the estuaries, marshes are the most suitable environment to search for the record of regional and global forcing events due to the approximately constant sedimentation in these sub-environments, that often represents the most continuous post-glacial geological record available on shore (e.g. Davis & Fitzgerald, 2004). In the last decades, several researchers around the world studied salt marshes in the scope of defining environmental proxies, like foraminifera and ostracoda, to be used in palaeoclimatic and palaeogeographic interpretations, namely within the context of sea level rise and Global Change evaluation (e.g. Cearreta et al. 2000, 2007; Gehrels, 1994; Hayward et al. 1999; Horton & Edwards, 2000; Scott & Medioli, 1980). The application of microfossil proxies rests upon the principle of uniformitarism implying that their interpretation must be supported by a robust and site specific data base build upon the study of modern living communities (e.g. Leorri et al. 2008).
The results obtained from MicroDyn project - POCTI/CTA/45185/2002 - funded by FCT (finalized in December 2008), allowed to recognise the importance of several micropalaeontological proxies in present tidal marshes of the Portuguese west coast. These microfaunistical studies were followed by synoptic measurements of estuarine and interstitial waters parameters, sampling to geochemical analyses of sediment and waters, the determination of estuarine tidal levels and the altitude of sampling points, filling a gap of crucial information from modern marsh analogues (e.g. Cardoso et al. 2008; Fatela et al. 2007, 2009; Moreno et al. 2006, 2007, Antunes et al. 2008). For instance, the distribution of living assemblages of marsh benthic foraminifera, appeared clearly related with the elevation above mean tide level, meaning that this proxies have a major potential to be included or compared with palaeoecological data from any estuary around the world (e.g. Gehrels et al. 2001; Hayward et al. 2004; Horton & Edwards, 2006; Leorri et al. 2008; Scott & Leckie, 1990; Sen Gupta, 2002). Nevertheless, concerning the main species, the assemblages composition depends on the geochemical constraints of marsh sediment and interstitial waters seen as a consequence of marine influence inside the estuary (Fatela et al. 2007, 2009; Moreno et al. 2006, 2007). This data from Portuguese marshes are essential to support reliable interpretation of the geological record in a regional as well as in a global context. The team experience and the body of knowledge provided by MicroDyn must be now applied to the study of recent palaeoenvironmental evolution of east North Atlantic estuaries.
High-resolution studies of the geological record, focused on the last centuries, may deliver a prospective dimension of past anthropogenic impacts and so, a double benefit of funding may be achieved with our proposal: the understanding of the path followed by coastal systems until the present, and the acquisition of future evolving scenarios.
The paleoenvironmental models of recent evolution of Atlantic estuaries from Portuguese west coast will be searched in an integrated mode, improving the advantages of the team joined in the last years. We have developed the capacity to discuss and interpreted the site results from micropaleontology, sedimentology, geochemistry and geodesy within the global mechanisms like sea level rising. This proposal will fill a gap providing high-quality data from the Iberian Atlantic coast to examine the issue of recent changes in the rate of relative sea-level rise. Advances in high-resolution sea-level reconstruction have been made in the last few years through the development of foraminifera-based transfer functions (e.g. Gehrels et al. 2001; Horton & Edward 2006; Leorri et al. 2008). This group have been used as 'proxies' for elevation by quantifying the relationship between faunal data and elevation. In spite of the influence of local factors, studies from Europe, North America and South America, indicate that the strong correlation between foraminiferal assemblage zones distribution and marsh elevation can be recognized worldwide. These relationships are then employed to reconstruct past tide levels from core assemblages contained within sedimentary sequences, in connection with the other microfaunistical groups and the changes of estuarine dynamics delivered by sedimentological studies. The geochemical analysis of the same sediment cores, dated by C14, Pb210 and Cs137, will be used to determine the base line of estuaries contamination and its evolution, assessing the results of growing and decline of mining and industrial activities, along the XIX and XX centuries, and the results of Portuguese environmental protection policy developed in the last 20 years.