To assess and describe saltmarsh abrupt changes in the past, we took a palaeoecological approach that involved the extraction of sediment cores from the Ebro delta (Catalonia, Spain) and from different estuaries around Wales (United Kingdom). Cores were analysed in the laboratory using an X-ray fluorescence scanner, that provided information on the geochemical characteristics of the different sediment layers observed. This information can hint to possible habitat changes along the core. We additionally dated some of the cores using 14C, to pair known historical land use changes with observed abrupt shifts along the core. In addition, for a subset of cores we estimated organic carbon stocks. The data gathered, allowed us to identify abrupt changes in the sedimentary record in most of the saltmarsh areas studied, with some changes likely indicating transitions from vegetated to unvegetated states. Saltmarshes known to be dynamic for their level of exposure to incoming storms, for example, showed many transitions along the paleorecord, whereas others were more stable (being continuously vegetated all along the core length). We also found strong evidence for a negative relationship between saltmarsh carbon storage capacity and the number of abrupt changes along cores.
To mechanistically examine the drivers of saltmarsh resilience to disturbances, our manipulative experimental approach involved the set-up of disturbance (simulated shift to unvegetated state) and control plots (fully vegetated) within salt marshes, in six regions around the United Kingdom. Contextual variables were also measured at each plot (or site, depending on the variable), namely: temperature, wave forcing, inundation period, shore elevation, sediment stability, sediment accretion rates, and vegetation and sediment properties. After two growing seasons post-disturbance, we returned to the same plots and assessed vegetation recovery in terms of the standing biomass in each plot. The results from this study show that a combination of abiotic (sediment accretion, mean annual temperature, clay-silt fraction in the sediment) and biotic variables (initial above-ground biomass) drive saltmarsh resilience (i.e. vegetation recovery) along the coasts of the United Kingdom.
To assess the level of awareness towards saltmarshes in the Ebro delta and in Wales, we developed questionnaires and questions for semi-structured interviews, thanks to collaboration with social scientists. We also formulated questions to assess the perceived threats/challenges these ecosystems face, and the perceived benefits we get from them. The target respondents were the general public and different stakeholders. In another survey using similar questions, the target respondents were professionals involved in saltmarsh management and/or research around the world. A key finding from this public perceptions study was the low levels of public awareness and uncertainty associated with saltmarshes and their societal benefits. In contrast, professionals directly involved in saltmarsh management or research were of course much more certain when asked about their knowledge of these ecosystems, but we found strong geographical differences in terms of the most important perceived benefits, or the perceived level of protection enjoyed by these systems, which has important implications to scale down the implementation of international conservation goals.
Dissemination of these results has been done through scientific manuscripts (some already published, others in preparation) and conferences, while many efforts have gone to disseminating these results also to the general public through social media, press releases, and workshops/talks to secondary school teachers and pupils.
