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Cyanobacteria and other microbes are important moderators of biogeochemical processes in semi-arid floodplain wetlands with varying inundation regimes. Inundation is a key environmental driver for floodplain biological communities. Little is known about the effect of historical inundation frequency on the spatial abundance of floodplain–wetland Cyanobacteria and other microbes. In this study, soil samples were collected at two locations with a gradient of low-to-high inundation frequency in the Macquarie Marshes, south-east Australia. We used high-throughput sequencing to estimate the proportional abundance of the soil Cyanobacteria and other dominant microbes, targeting the bacterial 16S rRNA gene. Of the microbes recovered, Cyanobacteria constituted proportionally a minor component, relative to other dominant phyla like Proteobacteria and Actinobacteria. Linear regression (generalised least-squares) models accounting for spatial autocorrelation showed that historical inundation frequency had no significant effect on the proportional abundance of Cyanobacteria at both wetlands studied. However, inundation frequency had a significant positive effect on the proportional abundance of Proteobacteria and a significant negative effect on the proportional abundance of Actinobacteria. Cyanobacteria seem to occupy a different hydrological niche from Proteobacteria and Actinobacteria in semi-arid floodplain wetlands, suggesting taxon-dependent response of floodplain microbial communities to varying inundation regimes and associated soil conditions in those environments.

Fires are a common occurrence in Australian terrestrial ecosystems. A large fire occurred in January 2013 within and adjacent to the Warrumbungle National Park, near Coonabarabran in NSW, burning over 560 km2 of the park and surrounding region (the Wambelong fire). The Wambelong fire affected Dunphy Lake, the only lake in the park. In this study, we assessed the post-fire aquatic animal community of the lake in March and September 2014. At the times of sampling the lake was largely dry and had only small isolated pools. We found 53 invertebrate taxa including the larvae of the dragonfly Austrogynacantha heterogena and one vertebrate species (larvae of the frog Litoria rubella) in the pool-water samples. Artificial inundation of the lake sediment samples under laboratory conditions led to the emergence of 31 taxa, totalling 62 taxa in the lake overall. Most taxa found in the lake are opportunistic and characteristic of those in still-water bodies. Dunphy Lake seems to be highly resilient in sustai...

Freshwater calanoid copepods develop abundant populations in lentic water bodies such as lakes, reservoirs and lagoons. In this study, we examined the potential habitat value of edges in lotic systems such as creeks and rivers where waters tend to stagnate, providing lentic-like environments. We examined a total of 353 edge samples collected from 321 sites across the state of New South Wales, Australia, with latitudes in the range 28.3–37.4°S and elevations in the range 2–1834 m above sea level. Of the total samples examined, calanoid copepods were found in 94 samples, with the frequency of occurrences of species decreasing in the order: Boeckella fluvialis Henry, B. triarticulata (Thomson), Gladioferens spinosus Henry, G. pectinatus (Brady), B. major Searle, B. minuta Sars, and Calamoecia lucasi Brady. The probability of occurrence of the calanoid copepods was related negatively to both latitude (as absolute values) and elevation, based on logistic regression models. We conclude that the edges of many lotic systems provide additional habitats for some species of freshwater calanoid copepods, with constraints on their distributions along latitudinal and elevational gradients.

The devastating bushfires of the 2019–20 summer are arguably the most costly natural disaster in Australian recorded history. What is little known is that these fires severely affected the temperate highland peat swamps on sandstone (THPSS), a form of upland wetland that occurs in the water supply catchments of Sydney in the Greater Blue Mountains World Heritage Area and National Park. During the fires, 59% of THPSS was burnt and 72% of those by a high severity burn. Upland swamps at Newnes were the most affected, with 96% of swamps burnt and 84% of these experiencing a very high burn severity. We present an analysis of the spatial extent and severity of the bushfire on the THPSS and discuss some of the likely consequences on their geomorphological, hydrological and ecological structure, function and recovery potential.

Summary Many plants disperse their seeds in waterbodies via hydrochoric transport. Despite a growing body of research into hydrochory, little is known about the fundamental seed traits that determine floatation ability or hydrochoric transport behaviour more generally. Seeds are transported in fluvial systems in one of three phases: surface transport, within the flow or incorporated in bedload. Seeds are often categorised as buoyant or non-buoyant based on density, with little consideration of the morphological traits that determine how long seeds spend in each transport phase. We investigated the seed traits that best predict time spent floating under laboratory conditions, using sixty species of riparian plants from south-eastern Australia. We measured and calculated key physical attributes (length, width, volume, surface area, mass, density, sphericity, roundness and shape category) and categorised seeds according to their primary dispersal modes (water/wind, vertebrate, adhesion, ants and unassisted). We used Cox's proportional hazards modelling to reveal that seed density and volume : surface area ratio were the physical traits that best predicted time spent floating. Volume : surface area ratio represents both seed size and shape, as it increases with size and sphericity. Our results showed that denser, larger and/or more spherical seeds (i.e. higher volume : surface area ratio) were poor floaters. They are therefore more likely to be transported in subsurface flow or as bedload. We combined our data with geomorphic models of sediment transport in flow to develop a biophysical process model of how hydrological forces and seed physical traits determine hydrochorous seed transport behaviour in rivers. The model describes how surface tension, buoyancy and flow velocity act on seed density and volume : surface area ratio to characterise time spent floating. We extrapolate from our data to conceptualise how these traits predict transitions between surface, subsurface and bedload transport. Hydrochoric seed transport behaviour and deposition are both threshold-driven and multidirectional. Our process model is likely to be applicable across a range of different seed types in a range of rivers. It substantially increases our understanding of hydrochoric processes in rivers, lakes and lotic wetlands and will help illuminate the links between seed traits, hydrochoric transport and patterns of riparian vegetation and species composition.

Floodplain wetlands in semi-arid regions have intricate channel-floodplain networks with highly variable and unpredictable wet and dry phases related to changes in hydrology and geomorphology. We tested the hypothesis that the presence of different hydro-geomorphic habitats in those systems drives structural and functional differences in aquatic communities. To test this hypothesis, we examined the densities and species composition (structural variables), and primary productivity and respiration (functional variables) of plankton communities, and water chemistry in three spatially explicit channel, floodout and lagoon habitat types inundated by environmental water releases in the Macquarie Marshes, semi-arid Australia. Significant differences were recorded among the community-level structural and functional variables among the three habitats. Greater densities of phytoplankton, zooplankton and planktonic bacteria were observed in a hydrologically isolated floodplain lagoon. The lagoon habitat also had greater primary productivity of phytoplankton and planktonic respiration compared with the channel and floodout. Our results suggest that water release to meet environmental flow requirements can be an important driver of planktonic diversity and functional responses in semi-arid wetland systems by inundating diverse, hydro-geomorphically distinct habitats.

Gross primary productivity (GPP) of phytoplankton and planktonic respiration (PR) (i.e., planktonic metabolism) are critical pathways for carbon transformation in many aquatic ecosystems. In inland floodplain wetlands with variable inundation regimes, quantitative measurements of GPP and PR are rare and their relationships with wetland environmental conditions are largely unknown. We measured PR and the GPP of phytoplankton using light and dark biological oxygen demand bottles in open waters of channel and non-channel floodplain habitats of inland floodplain wetlands of southeast Australia that had been inundated by environmental water. Overall, GPP varied from 3.7 to 405.5 mg C m−3 h−1 (mean ± standard error: 89.4 ± 9.2 mg C m−3 h−1, n = 81), PR from 1.5 to 251.6 mg C m−3 h−1 (43.2 ± 5.6 mg C m−3 h−1, n = 81), and GPP/PR from 0.2 to 15.6 (3.0 ± 0.3, n = 81). In terms of wetland environmental conditions, total nitrogen (TN) ranged from 682.0 to 14,700.0 mg m−3 (mean ± standard error: 2,643.0 ± 241.6 mg m−3, n = 81), total phosphorus (TP) from 48.0 to 1,405.0 mg m−3 (316.8 ± 31.4 mg m−3, n = 81), and dissolved organic carbon (DOC) from 1.9 to 46.3 g m−3 (22.0 ± 1.6 g m−3, n = 81). Using ordinary least-squares multiple regression analyses, the rates of GPP and PR, and their ratio (GPP/PR) were modeled as a function of TN, TP, and DOC that had been measured concomitantly. The “best” models predicted GPP and GPP/PR ratio in channel habitats as a function of DOC; and GPP, PR, and GPP/PR in non-channel floodplain habitats as a function of TN and/or TP. The models explained between 46 and 74 % of the variance in channel habitats and between 17 and 87 % of the variance in non-channel floodplain habitats. Net autotrophy (mean GPP/PR 3.0) of planktonic metabolism in our work supports the prevailing view that wetlands are a net sink for carbon dioxide. We propose a nutrient-DOC framework, combined with hydrological and geomorphological delineations, to better predict and understand the planktonic metabolism in inland floodplain wetlands.

The complex task of determining the inundation requirements of large floodplain wetlands is often simplified through the use of representative, umbrella or flagship species. This subset of species is targeted based on the assumption that their collective inundation requirements serve as a surrogate for the broader suite of species found within the wetland. We tested the application of representative species commonly used in wetland and water management planning in the Murray-Darling Basin. In a review of the water requirements of 155 plants and animals, we collated information on preferred inundation timing, duration, depth, rate of rise and fall, and inter-flood period for 115 species. We then used cluster analysis to determine the extent to which ten commonly used representative species corresponded in inundation requirements to the broader suite of species. We found that the habitat surrogates of river red gum, black box, spike rush, coolibah, water couch, lignum and marsh club-rush represented only one third of species at a 60% level of similarity in inundation requirements, due mainly to the lower inundation return period and duration required by the habitat surrogates. The addition of faunal representative species facilitated the inclusion of a broader range of requirements, though primarily amongst related taxa. We recommend the inclusion of several additional indicator species to more adequately cover the inundation requirements of large wetland ecosystems.

Paleoecological responses to coupled geomorphic and hydrological changes have rarely been studied using a multiproxy approach in freshwater floodplain wetlands of semiarid Australia. The Macquarie Marshes are a large, multi-channelled and morphodynamic floodplain wetland system in the lowland interior of the Murray-Darling Basin, southeastern Australia. Evidence from historical maps, aerial photographs, geomorphology and sedimentology indicate that avulsion in the southern Macquarie Marshes caused the formation of a major new channel (Monkeygar Creek) and the abandonment of a reach of the Macquarie River in the last 200 years. Paleobiological samples from near-uniform sediment cores were studied to determine the environmental changes related to this avulsion, as well as associated floodplain evolution and hydrological changes in the adjoining flood-reliant wetlands. Fifteen macrophyte taxa, seven charophyte taxa, 28 diatom taxa and 18 aquatic invertebrate taxa were identified in sediments from the termina...

In the context of static conservation reserves, dynamic fluvial processes and patterns of river channel and floodplain change are problematic for environmental management. Floodplain wetlands that evolve by erosion and sedimentation experience changes in the location and extent of channels and wetlands regardless of conservation reserve boundaries. We describe historical channel and floodplain change in an Australian wetland of international ecological significance, the southern Macquarie Marshes, and synthesise the role of avulsion in wetlands that move laterally on the broader floodplain. Avulsion has shifted the foci of flooding and areas of aquatic habitat in the system over the last century. By ~1925, active wetlands surrounding the Old Macquarie River and the original conservation area contracted around Monkeygar Creek within the present nature reserve, and the boundary of this reserve has changed little since the 1940s. Ecological changes associated with continued wetland desiccation in the reserve triggered a recent Ramsar Article 3.2 notification for the Macquarie Marshes, prompting management responses from government agencies. Fluvial morphodynamics and their impacts on wetland ecology should be specifically recognised and integrated with adaptive management plans to combine new findings with lessons learned from previous intervention strategies for the long-term ecological sustainability of floodplain wetlands.

Floodplain wetlands of the Murray-Darling Basin provide critical habitat for numerous species of flora and fauna, yet the ecology of these wetlands is threatened by a range of environmental issues. This book addresses the urgent need for an improved ecohydrological understanding of the biota of Australian freshwater wetlands. It synthesises key water and habitat requirements for 35 species of plants, 48 species of waterbirds, 17 native and four introduced species of fish, 15 species of frogs, and 16 species of crustaceans and molluscs found in floodplain wetlands of the Murray-Darling Basin. Each species profile includes: the influence of water regimes on the survival, health and condition of the species; key stimuli for reproduction and germination; habitat and dietary preferences; as well as major knowledge gaps for the species. Floodplain Wetland Biota in the Murray-Darling Basin also provides an overview of the likely impacts of hydrological change on wetland ecosystems and biota, in the context of climate change and variability, with implications for environmental management. This important book provides an essential baseline for further education, scientific research and management of floodplain wetland biota in the Murray-Darling Basin.