Predicting the response of coastal wetlands of Southeastern Australia to sea-level rise

Coastal saltmarsh is an endangered ecological community in New South Wales and sea-level rise has been listed as a key threatening process. Over the previous five decades moderate rates of sea-level rise have coincided with the invasion of saltmarsh by mangrove. Surface elevation tables (SETs) were installed in 12 coastal wetlands in Southeastern Australia to establish elevation and accretion trajectories for comparisons with mangrove encroachment of saltmarsh and sea-level rise. SETs confirmed that the elevational response of wetlands is more complex than accretion alone and elevation changes may also be attributed to below-ground processes that alter the soil volume such as subsidence/compaction, groundwater volume fluctuations, and below-ground biomass changes. A simple modelling approach was employed to establish a relationship between the observed rate of mangrove encroachment of saltmarsh and relative sea-level rise, which incorporates the eustatic component of sea-level rise and changes in the marsh elevation. Increasing access to high resolution digital elevation models will enhance our capacity to predict the response of coastal wetlands to sea-level rise. Long-term datasets of elevation dynamics and improved understanding of the feedback mechanisms influencing marsh elevations will further enhance our modelling capacity

Coastal saltmarsh vulnerability to climate change in SE Australia

Coastal saltmarsh has been listed as an Endangered Ecological Community in New South Wales. Recent research has highlighted the importance of coastal saltmarsh as a source of nutrition for fish, a nocturnal feeding habitat for microbats, and a roosting habitat for several species of migratory shorebirds. Since European colonisation, coastal saltmarsh has been reclaimed for agricultural, residential and industrial use, and the past five decades has seen a consistent replacement of saltmarsh by mangrove throughout SE Australia. Analysis of data from the network of Surface Elevation Tables in NSW and Victoria has demonstrated a link between the replacement of saltmarsh by mangrove and relative sea-level rise. However, this is not the only potential climate change impact, given the strong inverse relationship between saltmarsh diversity and temperature in Australia. Saltmarsh species diversity increases with latitude, with temperature explaining more than 80 percent of variability in saltmarsh species numbers between bioregions. A southward translation of climatic zones in Australia would pose significant challenges to the preservation of saltmarsh diversity at a continental scale

Variation in seagrass biomass estimates in low and high density settings: implications for the selection of sample size

Few seagrass biomass monitoring studies have considered the adequacy of monitoring intensity in their design. Power analysis is now widely used in ecological monitoring to determine sample size (replication) and the power (probability of not making a Type II error) of the monitoring design to detect change (effect size). We investigated seasonal variation of above-ground biomass of Zostera species at Woolooware Bay, Botany Bay, NSW and Ukerebagh Channel, Tweed River, NSW to show that seagrass biomass varies significantly between sites and seasonally. By conducting preliminary power analysis at each study site we found that our sampling design would only detect 70% change at Woolooware Bay, while \u3c10% change would be detected at Ukerebagh Channel with the same intensity of sampling. We demonstrate the potential efficiency of harvesting as a means of estimating biomass in high biomass situations, where percentage cover may provide less discrimination between sampling sites

Vegetation changes in Hexham Swamp, Hunter River, New South Wales, since the construction of floodgates in 1971

Hexham Swamp (32° 52’ S, 151° 41’ E), the largest wetland on the floodplain of the lower Hunter River, New South Wales (ca. 2500 ha in area), historically supported extensive areas of estuarine wetlands. Substantial vegetation changes have occurred following the 1971 construction of floodgates on the main creek draining the swamp. Previous areas of mangroves have been reduced from180 ha to 11 ha, and saltmarsh from 681 ha to 58 ha. Phragmites australis reedswamp has expanded from 170 ha to 1005 ha. Much of the mangrove loss (ca. 130 ha) was a result of clearing, and the remainder has gradually died off. The factors contributing to the dieback are likely to be a combination of drying of the soil, and, at times, waterlogging. Field sampling indicates that a reduction in soil salinity has been an important factor initiating successional change from saltmarsh to Phragmites reedswamp. The data also suggest that increased waterlogging has been an important factor in vegetation change. The initial effect of the floodgates was expected to have been a drying of the swamp, followed over time by an increasing wetness(floodgates and associated drainage are generally intended to reduce the flooding of wetlands). The apparently paradoxical result is likely to have resulted from occlusion of drainage lines by sediment and reeds

Sedimentation, elevation and marsh evolution in a southeastern Australian estuary during changing climatic conditions

Mangrove and salt marsh vertical accretion and surface elevation change was measured at Kooragang Island within the Ramsar-listed Lower Hunter estuarine wetlands in New South Wales, Australia, using surface elevation tables and marker horizons over a ten-year period. We surveyed mangrove, salt marsh and a zone of mangrove encroachment into salt marsh. The period of analysis was dominated by El Niño (drought) climatic conditions, though included a series of east coast low pressure systems and associated storms over the central coast of NSW in June 2007. The storms may have initially caused scouring of sediments in the mangrove zone, followed by significant accretion within both the mangrove and salt marsh during the six months following the storms, with most of this accretion corresponding to spring tides several months after the storms. These accretion events were not accompanied by an equivalent elevation change, and robust elevation trends over the study period in mangrove and salt marsh indicate that the storms may have had little impact on the longer-term elevation dynamics within both the mangrove and salt marsh at Kooragang Island. Elevation dynamics in these zones appear to be regulated by vertical accretion over longer time periods and modulated by hydrology at shorter temporal scales. Elevation declined in the mangrove encroachment zone despite continued vertical accretion and we propose that this discrepancy may be associated with expansion of tidal creeks near the zone of mangrove encroachment or loss of salt marsh vegetation. This pattern of encroachment is consistent with observations from sites throughout the region and may be related to climatic perturbations (El Niño Southern Oscillation) rather than directly attributed to the storms

Contrasting diversity patterns of breeding Anatidae in the Northern and Southern Hemispheres

For sustaining ecosystem functions and services, environmental conservation strategies increasingly target to maintain the multiple facets of biodiversity, such as functional diversity (FD) and phylogenetic diversity (PD), not just taxonomic diversity (TD). However, spatial mismatches among these components of biodiversity can impose challenges for conservation decisions. Hence, understanding the drivers of biodiversity is critical. Here, we investigated the global distribution patterns of TD, FD, and PD of breeding Anatidae. Using null models, we clarified the relative importance of mechanisms that influence Anatidae community. We also developed random forest models to evaluate the effects of environmental variables on the Anatidae TD, FD, and PD. Our results showed that geographical variation in Anatidae diversity is hemispheric rather than latitudinal. In the species-rich Northern Hemisphere (NH), the three diversity indices decreased with latitude within the tropical zone of the NH, but increased in the temperate zone reaching a peak at 44.5-70.0 degrees N, where functional and phylogenetic clustering was a predominant feature. In the Southern Hemisphere (SH), Anatidae diversity increased poleward and a tendency to overdispersion was common. In NH, productivity seasonality and temperature in the coldest quarter were the most important variables. Productivity seasonality was also the most influential predictor of SH Anatidae diversity, along with peak productivity. These findings suggested that seasonality and productivity, both consistent with the energy-diversity hypothesis, interact with the varying histories to shape the contrasting hemispheric patterns of Anatidae diversity. Phylogenetic diversity (PD) and FD underdispersion, widespread across the species-rich, seasonally productive mid-to-high latitudes of the NH, reflects a rapid evolutionary radiation and resorting associated with Pleistocene cycles of glaciation. The SH continents (and southern Asia) are characterized by a widespread tendency toward PD and FD overdispersion, with their generally species-poor communities comprising proportionately more older lineages in thermally more stable but less predictably productive environments

Australian forested wetlands under climate change:Collapse or proliferation?

Climatically driven perturbations (e.g. intense drought, fire, sea surface temperature rise) can bring ecosystems that are already stressed by long-term climate change and other anthropogenic impacts to a point of collapse. Recent reviews of the responses of Australian ecosystems to climate change and associated stressors have suggested widespread ecosystem collapse is occurring across multiple biomes. Two commonly cited case studies concern forested wetland ecosystems: mangrove forest dieback in northern Australia (2015-16) and riverine forest dieback in the south-east of the continent (2002-09). We present an alternative interpretation that emphasises the dominant signal of climate change effects, rather than the interdecadal signal of climate variability that drives wetland forest dynamics. For both the south-east Australian riverine forests and mangroves of northern Australia, aerial extent remains greater after dieback than in the early 1990s. We interpret dieback and defoliation in both systems as a dry phase response and provide evidence of a current and near-future climate change trajectory of increased areal extent and cover (i.e. tree colonisation and range infilling). In both case studies, climate change-driven increases in tree cover and extent are occurring at the expense of wetland grasslands and the important ecosystem functions they support