Coastal wetland ecosystems play critical roles in mitigating climate change by sequestering substantial amounts of carbon in vegetation and sediments. The Laynhapuy Indigenous Protected Area, northern Australia, includes culturally significant floodplains that support diverse coastal wetlands. The Yirralka Rangers and Yolŋu Traditional Owners who manage this region have identified invasive ungulates as a key threat to wetlands. Paperbark forests, with species known to Yolŋu as raŋan ( Melaleuca viridiflora ) and nämbarra ( Melaleuca cajuputi ), have experienced ungulate damage combined with dieback due to saltwater intrusion. Sedgelands, dominated by culturally significant räkay ( Eleocharis dulcis ), suffer annual soil and vegetation damage caused by invasive pigs ( Sus scrofa ) and buffalo ( Bubalus bubalis ). The Rangers and Macquarie University scientists established an ungulate exclusion fenced plot array in 2018 across a supratidal paperbark forest and sedgeland on the Gurrumuru floodplain. To assess carbon cycle impacts, belowground carbon stocks in sediments and biomass were quantified, along with greenhouse gas (GHG) emissions across the plot array. Our findings revealed fourfold higher GHG emissions (combined CO 2 and CH 4 ) in locations damaged by invasive ungulates compared to undamaged sites in the early dry season. Belowground biomass increased by 21%–104% within exclusion plots compared with damaged plots. No significant differences in soil organic carbon (SOC) and total nitrogen (TN) stocks or rates of litter decomposition were found between damaged and undamaged plots. This study contributes to potential carbon crediting methods focused on reducing feral ungulate impacts to wetlands, that could help fund coastal floodplain wetland management.

The morphological characteristics of catchments are key controls on how flow is routed through catchments and the spatial and temporal dynamics of floods, therefore influencing the shape of hydrographs at any location. Here, we developed a hydro-morphic catchment classification to understand the extent to which various catchment characteristics act as controls on flood behaviour. The catchment characteristics include: size (as measured by gauge position in catchment and valley confinement at the gauge site), shape (elongation ratio and form factor), topography (catchment relief and longitudinal slope), and drainage network structure (drainage density). A total of 2452 high flow (near bankfull) and overbank flood hydrographs from rivers in 17 coastal catchments of New South Wales (NSW), Australia were used. Cluster analysis on hydrograph shape metrics of kurtosis, skewness, and rate-of-rise was performed to identify classes of hydrographs and their median shape. Three statistically distinct clusters were delineated for both high flows and overbank floods, and categorised as flashy, intermediate, and broad. Topographic characteristics of catchments (i.e., relief and longitudinal slope) were commonly among the dominant controls for all high flow and overbank flood hydrographs, excluding broad overbank floods. Drainage network structure (i.e., drainage density) also controlled flashy and intermediate high flows, and intermediate and broad overbank floods, while catchment size (i.e., gauge position in the network) influenced broad high flows. Catchment shape (i.e., elongation ratio) influenced broad overbank floods, and is a dominant control on flashy high flows, and intermediate and broad overbank floods. Overall, topographic controls were more useful for differentiating the hydrological behaviour of high flows relative to overbank floods. Understanding the relative control of different catchment morphometric characteristics on flow and flood behaviour can be used to identify the aspects of flood behaviour that are set by imposed controls and cannot therefore be realistically manipulated in management. A hydro-morphic classification can also be used in the design and calibration of hydrological models, tailoring their use to hydro-morphic catchment class.

The shape characteristics of flow hydrographs hold essential information for understanding, monitoring and assessing changes in flow and flood hydrology at reach and catchment scales. However, the analysis of individual hydrographs is time consuming, making the analysis of hundreds or thousands of them unachievable. A method or protocol is needed to ensure that the datasets being generated, and the metrics produced, have been consistently derived and validated. In this lab protocol, we present workflows in Python for extracting flow hydrographs with any available temporal resolution from any Open Access or publicly available gauging station records. The workflow identifies morphologically-defined flow and flood types (i.e. in-channel fresh, high flow and overbank flood) and uses them to classify hydrographs. It then calculates several at-a-station and upstream-to-downstream hydrograph shape metrics including kurtosis, skewness, peak hydrograph stage, peak arrival time, rate-of-rise, peak-to-peak travel time, flood wave celerity, flood peak attenuation, and flood wave attenuation index. Some metrics require GIS-derived data, such as catchment area and upstream-to-downstream channel distance between gauges. The output dataset provides quantified hydrograph shape metrics which can be used to track changes in flow and flood hydrographs over time, or to characterise the flow and flood hydrology of catchments and regions. The workflows are flexible enough to allow for additional hydrograph shape indicators to be added or swapped out, or to use a different hydrograph classification method that suits local conditions. The protocol could be considered a change detection tool to identify where changes in hydrology are occurring and where to target more sophisticated modelling exercises to explain the changes detected. We demonstrate the workflow using 117 Open Access gauging station records that are available for coastal rivers of New South Wales (NSW), Australia.

Waterborne contaminants pose a significant risk to water quality and plant health in agricultural systems. This is particularly the case for relatively small-scale but intensive agricultural operations such as plant production nurseries that often rely on recycled irrigation water. The increasing global demand for plants requires improved water quality and more certainty around water availability, which may be difficult to predict and deliver due to variable and changing climate regimes. Production nurseries are moving to adopt best management practices that recycle water; however, the risks associated with waterborne contaminants of various types, including nutrients, pesticides, plant pathogens, micro-plastics, and toxic metals, are not well understood. We review and synthesise the physical and biogeochemical factors that contribute to waterborne contaminant risk, and the main types of contaminants that are likely to require management, at plant production nurseries. Catchment characteristics (i.e., topography, land use), hydroclimatic factors (i.e., storms, floods, droughts), and landscape hydrological and sediment connectivity influence surface runoff, sediment transport, and associated contaminant transfer and storage. High hydrological connectivity can increase the risk of contaminant transport from the surrounding landscape to nurseries, with potential negative impacts to water quality in reservoirs and in turn plant health. High connectivity may also increase the risk of contaminants (e.g., sediment, pesticides, and phytopathogens) being transferred from nursery farms into downstream waterways, with consequences for aquatic ecosystems. Like all intensive agricultural operations, nurseries need to consider sources of irrigation water, water treatment and management strategies, and catchment and hydroclimatic factors, to mitigate the spread of contaminants and reduce their impacts on both plant production and the surrounding environment. Further research is needed to quantify contaminant loads and transfer pathways in these agricultural systems, and to better understand the threshold levels of contaminants that adversely affect plant health and which may result in devastating economic losses.

Some previous assessments of dryland river resilience have focused on potential future adjustments to river flow regimes but consideration of the associated adjustments to river geomorphology (e.g. natural channel-floodplain structures) that may also influence riverine ecology or human land use is less common. How can we close this conceptual and practical gap to help enhance river management decision making? Here, we focus on Southern Hemisphere case studies where aerial image interpretations, field investigations, palaeohydrological calculations and geochronology have enabled reconstructions of dryland river responses to changing Holocene hydroclimates. We examine how knowledge of these river responses may provide important insights for improved conceptual definition and practical application of resilience thinking in dryland fluvial geomorphology and cognate disciplines. In particular, we: (1) demonstrate the range of past – and possible future – dryland river responses under changing boundary conditions and forcings; (2) highlight the significance of distinguishing between dryland 'river behaviour' and dryland 'river change' when considering resilience; (3) stress the importance of identifying proximity to quantified geomorphic thresholds to help distinguish between 'river behaviour' and potential 'river change'; and (4) identify key conceptual and data gaps that need to be addressed to ensure better uptake of these insights in research and management.

The largest pyramid field in Egypt is clustered along a narrow desert strip, yet no convincing explanation as to why these pyramids are concentrated in this specific locality has been given so far. Here we use radar satellite imagery, in conjunction with geophysical data and deep soil coring, to investigate the subsurface structure and sedimentology in the Nile Valley next to these pyramids. We identify segments of a major extinct Nile branch, which we name The Ahramat Branch, running at the foothills of the Western Desert Plateau, where the majority of the pyramids lie. Many of the pyramids, dating to the Old and Middle Kingdoms, have causeways that lead to the branch and terminate with Valley Temples which may have acted as river harbors along it in the past. We suggest that The Ahramat Branch played a role in the monuments' construction and that it was simultaneously active and used as a transportation waterway for workmen and building materials to the pyramids' sites. The pyramids of the Western desert in Egypt were built alongside a now extinct branch of the Nile River named as the Ahramat Branch and identified using a combination of radar satellite imagery, geophysical data and deep soil coring.

The location of the Meidum Pyramid on the Western Desert Plateau of Egypt, distant from the Nile River, suggests the presence of a nearby ancient river that was used as a logistical route for transporting construction materials and personnel to the site. Radar satellite data led to the discovery of two buried river courses bordering the pyramid structure. The termination of the pyramid’s causeway exactly at the bank of the eastern river course implies that this ancient channel was active concurrently at the time of the pyramid’s construction. Furthermore, given that the plateau, where the pyramid lies, is encircled by the two river channels, it is likely that this plateau was formerly an unstable river island that did not favor heavy structures. This study offers a potential explanation as to why the pyramid structure has partially collapsed and the site was abandoned.

Non-perennial rivers are valuable water resources that support millions of humans globally, as well as unique riparian ecosystems. In Australia, the Earth’s driest inhabited continent, over 70% of rivers are non-perennial due to a combination of ancient landscape, dry climates, highly variable rainfall regimes, and human interventions that have altered riverine environments. Here, we review Australian non-perennial river research incorporating geomorphology, hydrology, biogeochemistry, ecology, and Indigenous knowledges. The dominant research themes in Australia were drought, floods, salinity, dryland ecology, and water management. Future research will likely follow these themes but must address emerging threats to river systems due to climate change and other anthropogenic impacts. Four high level opportunities for future research are identified, namely: (1) integrating Indigenous and western scientific knowledge; (2) quantifying climate change impacts on hydrological and biological function; (3) clarifying the meaning and measurement of “restoration” of non-perennial systems; and (4) understanding the role of groundwater. These challenges will require inter- and multi-disciplinary efforts supported by technological advances. The evolving body of knowledge about Australian rivers provides a foundation for comparison with other dryland areas globally where recognition of the importance of non-perennial rivers is expanding.

Dryland alluvial rivers are naturally complex systems with a range of in-stream and floodplain geomorphic units that provide habitat for aquatic and terrestrial biota. These systems are increasingly threatened by accelerated rates of sedimentation leading to declines in geomorphic complexity, habitat quality, and ponding depth. The implications of sedimentation on waterholes, or deep pools, is of particular concern, as they provide critical refugia in arid environments. However, sources of sediment entering and infilling waterholes, and the flow-on effects for habitat and water quality, are not well understood. This study addresses the potential for sediment derived from alluvial floodplain gullies to influence geomorphic change in dryland rivers. Alluvial floodplain gullies are often overlooked in comparison to more widely documented hillslope, or colluvial, gullies. Alluvial gullying is a prevalent feature of the Barwon-Darling River, one of Australia's longest and most important waterways in the northern Murray-Darling Basin (MDB). The estimated volume of sediment derived from floodplain gullies is 168 million m(3), which far exceeds estimates used in past sediment budgets. Gully size and complexity varied from small, linear features to large, complex, branching gullies and the total number of gullies increased by similar to 40 % from the 1960s to 2000s. However, the more recent episodes of gullying (i.e., post 1960s) are limited to smaller gullies, which are likely to yield less sediment than the side walls of the older, larger, more complex gullies. Based on the average decline in maximum waterhole depth, similar to 19 million m(3) of sediment has accumulated in Barwon-Darling waterholes over the past 120 years (equivalent to similar to 158,000 m(3) a(-1)). A predictive relationship between gully volume and change in waterhole depth was expected, but not observed. Nevertheless, the role of alluvial floodplain gullies as a significant source of sediment should not be overlooked when assessing dryland river forms and processes. River management should consider the implications of changing sediment sources and in-stream loads, with associated changes in water quality and aquatic habitats, which influence river condition.

Natural flood management (NFM), a nature-based solution to flood mitigation where hydrological and biophysical processes are harnessed to reduce flow velocity, erosive energy and flood risk, is an emerging global theme of water and river management. The catastrophic 2021 and 2022 floods in eastern Australia are used to assess the hydrological properties of discrete events and to start an investigation of whether widespread changes in flood hydrology are occurring. We find that most coastal rivers in New South Wales (NSW) had a noticeable decrease in flood wave celerity (increase in flood travel time) when the 2021 and 2022 floods are contrasted with equivalent floods since the 1970s and that several also exhibit increases in flood peak attenuation. For some rivers, there is a coincident trend between these changing flood properties, riparian vegetation regrowth (regreening) and geomorphic recovery over the last +30 years. These may be the first signals that passive riparian management is counteracting some of the more severe hydrological effects of floods on these rivers and that some degree of NFM is possible. Lessons from this work are that there is an immediate opportunity to implement large-scale NFM in coastal catchments of NSW, but this will only occur if we re-examine current flood mitigation and adaption strategies and recognise and prioritise nature-based solutions that include space-to-flood and corridors of river recovery, as essential parts of the modern flood mitigation toolkit.

The character and behaviour of dryland rivers are driven by complex interactions between extrinsic and intrinsic controls. A long-term perspective is necessary to assess the sensitivity of dryland rivers to extrinsic forcing, such as hydroclimatic changes, and to contextualise the threshold channel responses. The semi-arid Mara River in northern Tanzania is the only perennial river in the UNESCO World Heritage Serengeti-Mara ecosystem and provides water resources for human and wildlife populations. Satellite imagery and discharge modelling were used to assess the valley-scale controls and hydrogeomorphic processes driving the morphological adjustments of the lower Mara River and its floodplain wetland. Both the modern and palaeochannels undergo downstream morphological and hydrological changes as they traverse the broad, alluvial floodplain. In response to marked downstream declines in discharge (from similar to 300 m(3).s(-1) to -45 m(3).s(-1)) and stream power (from similar to 40 W.m(-2) to -0.5 W.m(-2)), the modern channel exhibits a nonequilibrium river response resulting in downstream declines in channel size (from similar to 60 m to similar to 10 m wide) and eventual channel breakdown in the floodplain wetland. Palaeochannels in the unconfined reaches are typically larger with higher palaeodischarges than the modern channel. While some palaeochannels exhibit similar downstream trends to the modern channel, others may have maintained a continuous channel farther into the wetland. Comparison of the Mara River to other dryland river systems highlights the importance of valley setting and hydroclimate as long-term controls that influence geomorphic river response over time. The lower Mara River represents a nonequilibrium river response to declining discharges related to transmission losses that leads to channel bed aggradation and avulsion, constituting an inherent condition in many dryland alluvial rivers. An improved understanding of the interplay between intrinsic and extrinsic controls is important for the assessment of river character, behaviour, and floodplain wetland development, particularly under future projections of more variable or extreme climate conditions.

An understanding of river adjustment processes, previous landform changes, and sensitivity to flow regimes are prerequisites for predicting how rivers may respond to future climate change and anthropogenic disturbance. Geomorphic river sensitivity is an important concept that can be used to assess the capacity of adjustment for a river type and forecast river responses to hydroclimatic change over time. In this study, we use satellite imagery to characterise and quantify recent geomorphic river adjustment in a dryland river in East Africa, over the past 32 years (1988-2020). The natural or expected river behaviour (i.e., behavioural regime) and capacity for adjustment (i.e., valley confinement) are quantified to provide a measure of the reach-scale geomorphic sensitivity of the lower Mara River, Tanzania. Two behavioural river sensitivity classes are identified. The upper reach is classified as Passive sensitive, exhibiting a limited range of bend adjustments and low migration rates (0.89 m a-1) owing to valley confinement and capacity to recover from disturbance events. The middle reach is classified as Fragile and shows the greatest capacity to adjust in response to intrinsic fluxes. This reach is characterised by numerous lateral migration features and cut-offs (0.2/km) on the floodplain and exhibits the highest migration rates (1.39 m a-1). The lower reach is also categorised as Passive sensitive and undergoes bend and boundary adjustments within its behavioural regime and exhibits the lowest migration rates (0.63 m a-1). However, this reach appears to be operating close to a threshold state and if subjected to a threshold-breaching disturbance event it may 'switch' to a Fragile system where avulsions are dominant. The Mara River shows that geomorphic sensitivity is an important consideration in assessing system response to short-term variability and forecasting future river behaviour and will be key in guiding the management and rehabilitation efforts of other dryland wetlands under different land use and climate change scenarios.

Flood dynamics, and in particular the shape of flood hydrographs, are influenced by a mix of catchment morphometric characteristics. To identify different flood hydrograph shapes and the key catchment controls on them, we use a hydro-morphic catchment classification method. A total of 1,584 high flow (near bankfull) hydrographs and 868 overbank flood hydrographs from rivers in 17 coastal catchments of New South Wales (NSW), Australia are used.We find three hydrograph shape clusters for high flows and three for overbank floods. On average, across all clusters of high flows and overbank floods, elongation ration (Er) and catchment relief (Rh) are the dominant catchment controls on hydrograph shape, followed by drainage density (Dd), average longitudinal slope upstream of the gauge (Sl), and gauge position in the catchment (Gp). Overall, overbank flood hydrographs are influenced more by catchment-scale controls than high flow hydrographs where flow is confined to a channel.Ultimately, the proposed hydro-morphic classification of catchments could be used to understand the fundamental, imposed, catchment-scale controls on flood behaviour. It could also be used to better calibrate hydrologic models and assess the relative impacts of land use and climate change on catchment scale hydrological behaviour versus imposed controls.

Genetic sequencing as well as culture-based studies have revealed diverse aerobic and anaerobic microbes across a range of aquatic environments in floodplain wetlands. Hydrological conditions related to riverine inundation are a predominant factor determining the structure and function of soil bacterial communities in floodplain wetlands. Despite their complex mosaics of topography, landforms and aquatic habitats, some consistent response patterns are observed among soil bacterial communities with changing inundation patterns and history. Considering hydrological events and changes as a form of disturbance, Connell’s ‘intermediate disturbance hypothesis’ has been used to explain the observed bell-shaped response of soil microbial communities with varying hydrological conditions. Further application and testing of general ecological theories and hypotheses may help advance our understanding and predictive modelling capability for the dynamics of floodplain soil bacterial communities with changing hydrological conditions.

Since European colonisation, many coastal rivers of New South Wales (NSW) have been highly modified by channelisation, flow regulation, sediment mining, intensive grazing and agriculture, deforestation, and riparian vegetation and wood removal. Since the late 1980s, nearly 55% of these rivers have undergone a significant ‘re‐greening’ and geomorphic recovery with changes to instream and riparian roughness. However, little research has been undertaken to quantify if there have been any coeval changes in flow hydrology. Approximately 7000 flow hydrographs with one‐hour time‐steps from 117 gauges on 45 study rivers (17 of 20 coastal catchments of NSW) were used to assess changes to in‐channel and overbank hydrology over decadal timeframes. Hydrograph shape and attenuation characteristics for three morphologically defined flow stages were analysed: in‐channel fresh, high flow and overbank flood. Time‐series analysis was used to quantify changes in flow hydrology from the early‐20th century to present and identify trends occurring between known degradation phases (1910s–1940s and 1940s–1980s) and a recovery phase (1990s to present) for these rivers. Our findings indicate that, on average, and for some key examples, changes in flow hydrology are occurring. Flows are slowing and attenuating as indicated by decreases in flood wave celerity and hydrograph kurtosis, skewness and rate of rise and increases in peak‐to‐peak travel time, flood peak attenuation and flood wave attenuation index. The most significant changes have occurred since the 1980s with the most noticeable effects on the behaviour of high flows (around the bankfull stage). However, there is not a consistent direction change in these indicators in all places. We use these findings to categorise the flow mitigation signal of the study regions and catchments and discuss the implication for river and flood management.

Wetlands in semiarid regions are important systems that provide numerous ecosystem services in otherwise dry environments. Their functioning depends on the connected transfer of materials from source to sink which is determined by the degree of landscape connectivity. A combination of catchment characteristics, climatic variables and human activities are important factors driving landscape connectivity; however, wetland management rarely considers all these factors when conserving these systems. In this paper, we evaluate the landscape connectivity of the Mara River catchment in East Africa to understand the hydrogeomorphic processes driving material transfer to the floodplain wetlands. This semiarid catchment hosts the UNESCO World Heritage Serengeti-Mara ecosystem providing a unique opportunity to assess the influence of protected areas on wetlandcatchment connectivity patterns. We use the index of connectivity and Emerging Hot Spot analysis to assess the hillslope-channel connectivity and identify specific subcatchments which have contributed positively to the wetland's connectivity over time. The catchment-scale analysis highlights significant spatiotemporal variability in connectivity patterns and associated sediment dynamics. The results reflect that the Upper catchment is highly connected owing to the steep slopes and high rainfall and is likely responsible for the greatest sediment inputs into the fluvial network. Under greater future climatic and anthropogenic pressures, this region is expected to contribute increased sediment inputs into the river which will likely affect the geomorphic response of the downstream floodplain wetlands and may need to be prioritised for management. The protected areas are generally poorly connected due to intact vegetation and their local sediment contribution to the fluvial network is comparatively lower. Consideration of their placement in the catchment is important for managing these ecologically significant areas. Understanding the patterns and variability of hillslope-channel connectivity and the broader-scale landscape connections can help to identify and prioritise existing and emerging hotspots of change in large, semiarid catchments.

ecological, and social-ecological features, and as a result, they require carefully tailored research and management strategies.The surface or near-surface expression of water in these otherwise dry and climatically-variable environments (e

Background Increasing occurrence of megafires and wildfires is threatening the integrity of many natural systems and sustainability of the ecosystem services they provide. For example, the 2019–2020 Australian fires were one of the costliest natural disasters in the country’s recorded history. Aims This study aims to analyse the extent and severity of the fires on riparian systems across coastal catchments of New South Wales. We open a discussion about whether megafires and wildfires are creating novel riparian ecosystems and if prescribed and cultural burns should be used as a riparian vegetation management technique. Key results Of the 81 304 km of stream analysed, ~29% (23 266 km) were impacted by extreme or high-severity burning, with vegetation canopy completely consumed, or completely scorched and partially consumed. A further 21% (17 138 km) experienced moderate to low-severity burning, with partial canopy scorching or understorey burning. Such widespread, synchronous burning of riparian systems is unprecedented. Conclusion and implications Riparian management strategies must evolve to mitigate against future catastrophic fires that are becoming more frequent and severe under climate change. Research needs to establish the extent to which Australian riparian ecosystems are adapted to fire, the regimes and customs of cultural burning in these zones, and how to use such burning in riparian management.

Freshwater wetlands are a key component of the global carbon cycle. Wet–dry tropics wetlands function as wet-season carbon sinks and dry-season carbon sources with low aquatic metabolism controlled by predictably seasonal, yet magnitude-variable flow regimes and inundation patterns. However, these dynamics have not been adequately quantified in Australia’s relatively unmodified wet–dry tropics freshwater wetlands. A baseline understanding is required before analysis of land-use or climate change impacts on these aquatic ecosystems can occur. This study characterises geomorphology and sedimentology within a seasonally connected wet–dry tropics freshwater wetland system at Kings Plains, Queensland, Australia, and quantifies soil carbon stocks and wet- and dry-season aquatic metabolism. Soil carbon stocks derived from loss-on-ignition on samples to 1 m depth were 51.5 ± 7.8 kg C m −2 , higher than other wet–dry tropics wetlands globally, with potential for long-term retention at greater depths. Gross primary productivity of phytoplankton (GPP) and planktonic respiration (PR) measured through biological oxygen demand bottle experiments in the water column of sediment inundated under laboratory conditions show overall low GPP and PR in both wet- and dry-season samples (all wetland samples were heterotrophic with GPP/PR < 1). Despite the short-term dominance of aquatic respiration processes leading to net release of carbon in the water column under these conditions, there is appreciable long-term storage of carbon in sediment in the Kings Plains wetlands. This demonstrates the importance of wet–dry-tropics wetland systems as hotspots of carbon sequestration, locally, regionally and globally, and consideration should be given to their conservation and management in this context.