Editorial: Understanding change in the ecological character of wetlands

Abstract

The world’s wetlands of international importance are overseen by host nations under processes established through the intergovernmental Convention on Wetlands, commonly known as the Ramsar Convention. Signatory nations to the Convention are required to list at least one wetland as internationally important (known as Ramsar sites) and describe and maintain their ecological character (Gardner and Davidson 2011). Wetlands that satisfy one of a suite of ecological criteria, many of which relate to wetland biodiversity, may be listed as internationally important; the list of internationally important wetlands currently contains 2231 sites covering 214 936 005 ha (17March 2016). The signatories are also required to report on any likely and actual variations in the ecological character of the wetland that may bring it to a state where it may be considered degraded (Finlayson 1996). They are then required to mitigate this degradation or follow prescriptions to delist and offset, with the former being potentially biophysically complex (Alexander et al. 2011) and the latter potentially bedevilled by complex processes (Pittock et al. 2010). As outlined in theMillenniumEcosystemAssessment (MEA 2005), many wetlands, including those listed as Ramsar sites, are increasingly under pressure from (1) anthropogenic climate change causing changes in their hydrology, and (2) the direct impacts of people, notably by modification to their water regimes (increasing water use and/or decreasing water quality), changes in land use, and the introduction or facilitation of invasive species. The Ramsar site description, which is provided at the time of listing of a wetland as internationally important, provides a baseline against which change can be measured. However, as outlined in thisSpecial Issue ofMarineF MacKay et al. 2009). Other techniques to understand the condition or trajectory of change in a wetland include palaeoecology. While these approaches, which are largely sediment-based, may not reconstruct the nature of waterbird or fish populations over time, they are capable of reporting on long-term changes in water quality, sediment load, plant and algal communities and invertebrates, particularly ostracods, cladocerans and chironomids. These records can extend the knowledge of change back centuries or even millennia, but with decreasing resolution over longer periods. With the scope or potential of these approaches being increasingly articulated (Gell 2012), there is an opportunity, or even a need, for contemporary ecologists andmanagers to explore the ecological heritage of their wetlands. Finlayson et al. (2016) also report that there are now many palaeoecological records from sediment sequences collected from Ramsar wetlands across the world, as shown by the papers included in this special issue (Gell and Finlayson 2016). These records show the extent of change through time, with some revealing variation in response to low-frequency climate cycles and others revealing the pervasive andmore recent impacts from industrial development. These studies can be used to reveal how well the ecological condition of awetland at the time of listing as internationally important represents the historical condition and variability of the wetland or if it is a consequence of more recent humanmodification. As explained by Gell et al. (2016), this can create considerable tension in discussions about the ‘ecological character’ of Ramsar-listed wetlands, as well as the ‘limits of acceptable change’, and what constitutes a ‘degraded state’, and can obfuscate the obligations of a signatory nation to remediate or offset adverse ecological change in a wetland of international significance. These issues provided the background for the workshop ‘RamsarWetlands: Understanding Change in Ecological Character’ at Queenscliff, Victoria, Australia, 5–8 November 2013. Sponsored by the International Geosphere-Biosphere Programme (now Future Earth) project PAGES (Past Global Changes), this meeting brought together what was possibly an eclectic group of palaeoecologists andwetlandmanagers andecologists. It included representatives from PAGES and from the Ramsar Convention’s CSIRO PUBLISHING