Ecological effects of sea level rise on freshwater wetland communities of the wet-dry tropics of Australia

Globally, freshwater coastal ecosystems are under pressure from multiple threats, including climate change, urbanisation, over-exploitation, and invasive species (Traill et al. 2010; Boulton et al. 2014; Blankespoor et al. 2014). Climate change and specifically sea level rise (SLR) has the potential to severely impact freshwater ecosystems (Blankespoor et al. 2014; Grieger et al. 2020). For example, Bayliss et al. (2018), has shown that all of the freshwater floodplains in Kakadu National Park, Australia, will be exposed to sea water by 2132, and most low-lying coastal freshwater floodplains of Northern Australia are expected to be impacted to a similar extent. Griegar et al. (2020) and Herbert et al. (2015) have undertaken reviews on the impacts of climate change on freshwater coastal wetlands and the global ecological impacts of wetland salinization, respectively. The majority of studies on the impacts of SLR on freshwater coastal wetlands have been done within the United States of America, with very few focused on fauna or food webs globally (Grieger et al. 2020). Despite the scale of SLR impacts on Northern Australia’s coastal freshwater ecosystems, there is currently very little research on how SLR will affect fauna ranging from invertebrates to fish and waterbirds, and no research on the potential food web consequences. Most effects have been inferred from studies in other geographic locations and have focused on the salinity tolerances of organisms, such as the increasing salinity of inland wetlands in south-eastern Australia (Nielsen et al. 2003; Brock et al. 2005; Nielsen et al. 2008).
Firstly, I aim to synthesise the ecological impacts of SLR on freshwater coastal ecosystems globally, through a topic modelling literature review that will focus on novel comparisons of invertebrate and vertebrate taxonomic groups, biogeographic regions, climate regions, time-period, and ecological processes and functions which have not been reviewed previously. Secondly, in a laboratory microcosm experiment I will determine if off-channel wetlands in the Northern Territory contain a similar biomass and taxonomic composition of
phytoplankton, benthic algae, macrophytes, and aquatic invertebrates emerging from sediment cores inundated with varying salinity concentrations. Thirdly, in an outdoor mesocosm experiment I will test how SLR may affect a bottom-up trophic cascade through changes in biomass production and fatty acid profiles of primary producers, consumers and secondary consumers exposed to varying salinity treatments. Lastly, I will undertake field-based measurements of biomass and fatty acid profiles of primary producers, consumers, and secondary consumers along a gradient of freshwater to SLR impacted wetlands. Field-based primary producer and consumer biomass and fatty acid data along the salinity gradient will be compared to microcosm and mesocosm results to assess whether experimental outcomes can be extrapolated to forecast the potential effects of SLR on real-world wetland communities of the wet-dry tropics of Australia.