Burdekin River Research Articles

The effectiveness of alluvial gully remediation in Great Barrier Reef catchments

This study presents data from a large-scale Before After Control Impact (BACI) design field experiment that measured the sediment reduction achieved by remediating large alluvial gullies. The study was carried out on Bonnie Doon Creek on the lower Burdekin River, in Queensland Australia. Prior to remediation, the four large alluvial gully complexes (active area of ∼17ha) were conservatively estimated to be delivering 5800 ± 1500 t of fine sediment (<20 μm) per year (20 year average). The experiment demonstrated that the average remediation effectiveness across 10 different treatments was a 96%–99% reduction in fine sediment yield (or an annualised reduction of ∼5500t). High resolution lidar DEM of Difference (DoD) derived sediment yields in the unremediated gullies were found to be, on average, 58% lower than yields derived from monitored suspended sediment concentration (SSC) data, albeit with some uncertainty. These data support the notion that even high resolution (0.1m) lidar DoD yields are missing erosion driven by rainfall driven downwearing across all internal gully surfaces that is below the limit of detection (LOD) of the lidar. The results highlight that the greatest uncertainty in predicting the sediment abatement from gully remediation is associated with the determination of the baseline sediment yield of each gully. Future research effort should be focused on improving our understanding of baseline (multi-decadal) sediment yields, and monitored (annual) yields in different types of unremediated gullies. This is dependent on developing a detailed understanding of how these gullies evolve through time, and what the processes are that drive ongoing gully growth.

The use of temporary, permeable structures in the lower burdekin river: A novel approach to river-level management

A review of in-channel structures finds a wide range of purposes, including enhancement of the storage capacity of rivers to improve water supply reliability and/or flood protection, and various other hydro-ecological, water quality, geomechanical and sediment transport functions. The installation of in-channel structures is typically intended to be permanent, or at least semi-permanent. The purpose of this note is to document the novel use of temporary in-channel structures in the lower reaches of the Burdekin River, within the Australian dry tropics. Their application reduces freshwater discharge to the sea during low-flow periods thereby enhancing the sustainability of irrigated agriculture within the Lower Burdekin Delta. Temporary structures are constructed in the Burdekin River to enhance the reliability of pumping stations by raising the river level locally and preventing sea water from reaching extraction points. The structures are designed to restrict river flow only partially during low-flow periods and to wash away during high-flow events, which provides several benefits, including the passage of riverine fauna and reduced river siltation. The long-term utilisation (1950s to present) of temporary structures in the Burdekin River is testament to their successful implementation, which may offer benefits over permanent structures for other dry-tropical regions.

Environmental DNA analysis confirms extant populations of the cryptic Irwin\u2019s turtle within its historical range

BackgroundApproximately 50% of freshwater turtles worldwide are currently threatened by habitat loss, rural development and altered stream flows. Paradoxically, reptiles are understudied organisms, with many species lacking basic geographic distribution and abundance data. The iconic Irwin’s turtle, Elseya irwini, belongs to a unique group of Australian endemic freshwater turtles capable of cloacal respiration. Water resource development, increased presence of saltwater crocodiles and its cryptic behaviour, have made sampling for Irwin’s turtle in parts of its range problematic, resulting in no confirmed detections across much of its known range for > 25 years. Here, we used environmental DNA (eDNA) analysis for E. irwini detection along its historical and contemporary distribution in the Burdekin, Bowen and Broken River catchments and tributaries. Five replicate water samples were collected at 37 sites across those three river catchments. Environmental DNA was extracted using a glycogen-aided precipitation method and screened for the presence of E. irwini through an eDNA assay targeting a 127 base pair-long fragment of the NADH dehydrogenase 4 (ND4) mitochondrial gene.ResultsElseya irwini eDNA was detected at sites within its historic distribution in the lower Burdekin River, where the species had not been formally recorded for > 25 years, indicating the species still inhabits the lower Burdekin area. We also found higher levels of E. iriwni eDNA within its contemporary distribution in the Bowen and Broken Rivers, matching the prevailing scientific view that these areas host larger populations of E. irwini.ConclusionsThis study constitutes the first scientific evidence of E. irwini presence in the lower Burdekin since the original type specimens were collected as part of its formal description, shortly after the construction of the Burdekin Falls Dam. From the higher percentage of positive detections in the upper reaches of the Broken River (Urannah Creek), we conclude that this area constitutes the core habitat area for the species. Our field protocol comprises a user-friendly, time-effective sampling method. Finally, due to safety risks associated with traditional turtle sampling methods in the Burdekin River (e.g., estuarine crocodiles) we propose eDNA sampling as the most pragmatic detection method available for E. irwini.

Impact of European settlement and land use changes on Great Barrier Reef river catchments reconstructed from long-term coral Ba/Ca records

The increase in sediment and nutrient loads entering the coastal waters of the Great Barrier Reef (GBR) and the associated degradation of water quality represents a major threat to coral reefs. Although the strengthening of preventative management strategies remains a priority, there is a general lack of terrestrial runoff baseline information with respect to the spatial and temporal severity of disturbances associated with ongoing European-style land use practices. Here we use new and existing high-resolution coral Ba/Ca and luminescence records from the central Cairns region to the southern GBR shelf to reconstruct sediment fluxes discharged into the GBR from before European settlement in the 1860s to the present-day. Since the commencement of European settlement in the 1860s we document a tripling of flood-plume suspended sediment loads delivered by the Burdekin River to the GBR lagoon relative to ‘natural’ pre-European baseline levels. We show that this is indicative of a much more extreme degradation of the river catchments than hitherto appreciated with intensified discharge events particularly from the central and southern catchments carrying higher sediment loads. More-over from the 1930s onwards the Burdekin River, the largest source of both sediment and freshwater to the GBR, has also exhibited a progressive northwards expansion of its flood plume. This, together with increased variability of freshwater inputs indicated by coral luminescence records, now shows that the inner GBR not only continues to be impacted by increasing sediment/nutrient loads but is also subject to higher intensity river discharge events due to the loss of ground cover causing increased overland runoff and erosion.

Dams and climate change accelerate channel avulsion and coastal erosion and threaten Ramsar-listed wetlands in the largest Great Barrier Reef watershed

• Dam-induced sand settling in the Burdekin River delta is raising the flood levels and threatening channel avulsion. • This trapping of sand in the Delta is starving the coast of sand and generating rapid coastal erosion. • Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. • This is threatening Ramsar-listed wetlands of international significance. • The connectivity of water and sediment between the various parts of river basin demonstrates the need to manage the river at the basin scale using ecohydrology principles. This study documents the impact of climate change and human activities on the Burdekin River delta and coast. The Burdekin River is located in the dry tropics with a seasonally and interannually highly variable discharge, controlled by occasional cyclones and the ENSO-dependent monsoon. Even though the peak discharge from cyclonic rainfall is decreased by a dam, large floods still occur during long-duration monsoon. While the dam traps much of the coarse sediment runoff, large amounts still reach the Delta originating from catchments downstream of the dam. The riverbed in the Delta has measurably risen in recent decades. In turn, this increases the flood levels and the threat of channel avulsion. Sand trapping by the dam and in the Delta is also starving the coast of sand, and this generates rapid coastal erosion along the 11 km long Cape Bowling Green peninsula. Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. The peninsula may breach soon. As the peninsula protects Ramsar-listed wetlands of international significance, its breaching is predicted to impact the fisheries that depend on the Cape (the black marlin billfish) and on the wetlands (mud crabs, barramundi and mangrove jacks), as well as shorebirds and waterbirds. These findings demonstrate the connectivity of water and sediment throughout the river basin and the coast, and the need for management at the basin scale using ecohydrology principles.

Enhancing whole-of-river conservation

We argue for improved conservation of freshwater ecosystems at catchment or eco-regional scales by explicit assignment of values to all river sections and wetlands, recognising current disturbance, and aiming for ‘no further harm’ to the commons. The need is indicated by the global deterioration of biodiversity and ecosystem services of rivers and wetlands, increasing demands on water and land resources, and climate change. Regional pressures include multiple jurisdictions, competing demands, piecemeal management, pollution and habitat impacts. Effective resource and conservation management needs to integrate multiple uses via governance of activities of stakeholders, recognising hydrogeomorphic, water quality and ecological properties of ecosystems. Complete ecological protection is impractical amidst water-resource and land-use development, but we suggest that all river reaches and wetlands be given a conservation rating based on habitat, biodiversity and connectivity values. We present a straightforward approach to spatial conservation rating of freshwaters, using hydrogeomorphic typology and assignment of conservation values on the basis of available information and expert elicitation. We illustrate the approach by using the large Burdekin River catchment in north-eastern Australia. This approach is complementary to more spatially focused conservation prioritisation and could greatly improve management for sustainability, reduce further decline in conservation values, and facilitate rehabilitation.

Anonychomyrma inclinata sp. nov. (Hymenoptera: Formicidae): description, biology and interaction with the endangered bulloak jewel butterfly, Hypochrysops piceatus Kerr, Macqueen &amp; Sands, 1969 (Lepidoptera: Lycaenidae)

AbstractThe ant Anonychomyrma inclinata sp. nov. is described. It is an arboreal species, nesting in hollows of living mature trees including Allocasuarina luehmannii, Angophora leiocarpa and various Eucalyptus species. Anonychomyrma inclinata can form colonies which are among the most populous recorded for an ant species in Australia, with over 10 000 workers and a total population of 170 000, including all castes. The ant forms extensive trails, forages for insects, collects nectar from a range of flowering plants including many mistletoes and collects honeydew from Hemiptera. The ant's distribution extends from northern inland New South Wales and south central inland Queensland, as far north‐east as Home Hill, on the Burdekin River. The ant is an obligate attendant of the immature stages of the endangered bulloak jewel butterfly, Hypochrysops piceatus Kerr, Macqueen &amp; Sands, 1969, and the southern population of the sapphire azure, Ogyris aenone Waterhouse, 1902. The distribution of A. inclinata is much wider than that currently known for H. piceatus, suggesting that suitable breeding sites may exist for this rare butterfly in areas not previously surveyed. While A. inclinata appears relatively widespread and is able to utilise a wide range of tree species, it is reliant, like H. piceatus, on mature live trees and so is subject to threats including vegetation clearance, timber‐getting, grazing, and increased drought and fire frequency. Due to its critical importance in the life cycle of H. piceatus, any action taken to conserve the butterfly must also consider the importance of preserving healthy populations of A. inclinata.

Connecting targets for catchment sediment loads to ecological outcomes for seagrass using multiple lines of evidence

Catchment impacts on downstream ecosystems are difficult to quantify, but important for setting management targets. Here we compared 12 years of monitoring data of seagrass area and biomass in Cleveland Bay, northeast Australia, with discharge and associated sediment loads from nearby rivers. Seagrass biomass and area exhibited different trajectories in response to river inputs. River discharge was a slightly better predictor of seagrass indicators than total suspended solid (TSS) loads, indicating that catchment effects on seagrass are not restricted to sediment. Linear relationships between Burdekin River TSS loads delivered over 1–4 years and seagrass condition in Cleveland Bay generated Ecologically Relevant Targets (ERT) for catchment sediment inputs. Our predicted ERTs were comparable to those previously estimated using mechanistic models. This study highlights the challenges of linking catchment inputs to condition of downstream ecosystems, and the importance of integrating a variety of metrics and approaches to increase confidence in ERTs.

First report of strong phosphine resistance in stored grain insects in a far northern tropical region of Australia, combining conventional and genetic diagnostics

Although phosphine resistance monitoring and management programs are well advanced in Australia, the tropical northern part of the continent has received little attention. To address this, grain storages were sampled in the Townsville region in the Burdekin river catchment area of northern Queensland, and insect populations were subjected to resistance testing. Sampling of storages including silos, food processing facilities and feedlots was carried out during July to August 2019 and February to March 2020. Of the several species collected, populations of two major pest species, Rhyzopertha dominica and Tribolium castaneum were subjected to phenotypic resistance and molecular screening using discriminating doses and gene specific DNA marker, respectively. Utilising phenotypic assay, of the 17 populations of R. dominica, 12 were diagnosed as weakly resistant and five as strongly resistant; whereas of the 34 populations of T. castaneum, two were found to be susceptible to phosphine, 15 were determined as weakly resistant and 17 as strongly resistant. The molecular diagnostics, however, determined rph2 alleles for strong resistance in some populations each of R. dominica and T. castaneum that were diagnosed as weakly resistant in the phenotypic assay. The most prevalent rph2 alleles were found to be P49S and K142E in R. dominica populations and P45S and G131S in T. castaneum populations. Our results highlight the need of more comprehensive study towards determining the level of pests and resistance risks in this region.

Spatiotemporal variation of rare earth elements from river to reef continuum aids monitoring of terrigenous sources in the Great Barrier Reef

Degradation of inshore water quality associated with catchment modification is threatening global coral reef ecosystems. Coral trace element proxies are widely applied to document the magnitude and timing of historical changes in river runoff and other disturbances. However, conflicting interpretations of commonly used coral proxies (Ba/Ca, Y/Ca and Mn/Ca) complicate their application for examining historical changes in coastal water quality. The exploration of other coral trace element proxies (such as rare earth elements, REE) is limited in space and time, and to few coral genera. This study examined the dynamics of dissolved REE and yttrium (REEY) in the Fitzroy and Burdekin river tributaries and estuaries, Queensland, Australia. In addition, monthly-resolution long-term temporal records of Ba/Ca, Mn/Ca, Y/Ca and REEY proxies were investigated in two Porites and one Cyphastrea coral colonies from the central and southern Great Barrier Reef in order to test the reliability of these proxies to record the variability of river runoff and local anthropogenic disturbances. The results showed large scale removal of REEY (55–86%) in the low salinity mixing zones of both estuaries with significant fractionation of Nd-Yb and Y-Ho, confirming the ability of coral REEY to act as a terrestrial runoff proxy. Coralline Ba/Ca, Y/Ca and Mn/Ca records generally lack coherence with proximal discharge. However, temporal fluctuations of REEY proxies, irrespective of geographic location and coral genus, showed consistent behaviour relative to regional discharge with progressive increase of total REE/Ca and shale normalized Nd/Yb and decrease of Y/Ho during high-flow summer periods. The shifting baselines of REEY proxies in Cyphastrea grown in the turbid water setting of Rat Island effectively captured the timing of Gladstone Port dredging activities. Our findings suggest that shale normalized coral REEY distributions outperformed other commonly used trace element proxies and are robust indicators of changing inshore water quality. Longer-term records of coral REEY, even covering the period before European settlement from the 1850s, may provide a means to identify shifting baselines and evaluate and quantify the impacts of catchment alteration on coastal water quality and specific coral reef communities.

Shelf-edge delta and reef development on a mixed siliciclastic–carbonate margin, central Great Barrier Reef

ABSTRACT The Great Barrier Reef (GBR) is the world's largest extant mixed silicilastic–carbonate margin. Previous research on the Great Barrier Reef has suggested that the extensive barrier reef system may act as an impermeable barrier and limit the development of delta systems during lowstands, but sufficient geophysical data to support this hypothesis are lacking. We use dense sparker seismic and sub-bottom profiler data to better understand the structure of a large lobe-shaped feature (∼ 10 km × 10 km) on the shelf edge of the central GBR and the interactions between siliciclastic and carbonate sedimentary systems. Interpreted sparker seismic contains prograding clinoforms and suggest that the lobe-shaped feature was a river-dominated shelf-edge delta. A delta on the shelf edge implies that the presence of an exposed barrier reef was not a major impediment to deposition and that other adjacent lobe-shaped features are also deltaic deposits. The shelf-edge deltas were deposited onto a broad upper-slope terrace that allowed continued progradation and limited incision when sea level fell below the shelf edge. Delta foresets are commonly colonized by coral reefs, but the spatial and temporal relationship between reefs and some deltaic units remains unclear. The presence of multiple shelf-edge deltas that link to previously mapped Burdekin River paleo-channels indicates a complex history of sedimentation, with the Burdekin River delta migrating up to 100 km along the GBR margin during the late Quaternary. Regional bathymetric data suggest that large modern or recent shelf-edge deltas are rare on the GBR and that there was a broad range of sedimentary processes operating along the margin of the GBR during periods of low sea level.

Controls on channel deposits of highly variable rivers: Comparing hydrology and event deposits in the Burdekin River, Australia

AbstractDischarge event frequency, magnitude and duration all control river channel morphology and sedimentary architecture. Uncertainty persists as to whether alluvial deposits in the rock record are a time‐averaged amalgam from all discharge events, or a biased record of larger events. This paper investigates the controls on channel deposit character and subsurface stratigraphic architecture in a river with seasonal discharge and very high inter‐annual variability, the Burdekin River of north‐east Australia. In such rivers, most sediment movement is restricted to a few days each year and at other times little sediment moves. However, the maximum discharge magnitude does not directly correlate with the amount of morphological change and some big events do not produce large deposits. The Burdekin channel deposits consist of five main depositional elements: (i) unit bars; (ii) vegetation‐generated bars; (iii) gravel sheets and lags; (iv) antidune trains; and (v) sand sheets. The proportions of each depositional element preserved in the deposits depend on the history of successive large discharge events, their duration and the rate at which they wane. Events with similar peak magnitude but different rate of decline preserve different event deposits. The high intra‐annual and inter‐annual discharge variability and rapid rate of stage change make it likely that small to moderate‐scale bed morphology will be in disequilibrium with flow conditions most of the time. Consequently, dune and unit bar size and cross‐bed set thickness are not good indicators of event or channel size. Antidunes may be more useful as indicators of flow conditions at the time they formed. Rivers with very high coefficient of variance of maximum discharge, such as the Burdekin, form distinctive channel sediment bodies. However, the component parts are such that, if they are examined in isolation, they could lead to misleading interpretation of the nature of the depositional environment if conventional interpretations are used.

Effect of reduced grazing pressure on sediment and nutrient yields in savanna rangeland streams draining to the Great Barrier Reef

Excess sediment and nutrient yields from degraded rangelands have detrimental off-site ecological and on-site economic impacts, yet the effect of reduced grazing pressure on water quality is not fully understood. This study compares 15-year records of runoff, sediment and nutrient yields amongst three ephemeral headwater catchments (10.5–13.5 km2) with similar wet/dry tropical climate and landform characteristics, but contrasting cattle grazing pressure. The catchments are located within the Burdekin River basin which is the largest source of sediment and particulate nutrients to the Great Barrier Reef, Australia. Estimated mean annual total suspended sediment (TSS), total nitrogen (TN) and total phosphorus (TP) loads are: 0.6 t ha−1, 1.3 and 0.3 kg ha−1, respectively, in a catchment from which cattle were excluded over the study period (‘Main Creek’); 1.5 t ha−1, 1.4 and 0.4 kg ha−1, respectively, in a catchment where grazing pressure was reduced from approximately 25 to 13 cattle per km2 at the commencement of monitoring (‘Weany Creek’); and 1.4 t ha−1, 3.0 and 0.5 kg ha−1, respectively, in a catchment which maintained higher levels of grazing pressure (‘Wheel Creek’, approximately 25 head per km2). Higher annual sediment loads in the grazed catchments compared to the ungrazed catchment are likely due to degradation of soil water storage capacity, soil surface protection and gully erosion rates, but could also be influenced by differences in catchment geomorphic attributes (e.g., hydrological and sediment connectivity). Events with runoff >20 mm (16–25% of all events) generated 79–85% of the total runoff volume and 71–78% of the total TSS, TN, and TP loads. At the event timescale, there are not clear differences in runoff, sediment and nutrient loads among the catchments, attributed to variability in catchment conditions (e.g., antecedent soil moisture, rainfall intensity, vegetation) that occur within- and between events. It is concluded that recovery of degraded savanna rangelands following reduction in livestock grazing pressure takes decades and is strongly influenced by climate. Measuring water quality responses to land management change in variable climates requires nested spatial monitoring over long time scales that also includes factors that can influence the response (e.g., climate, soil properties, vegetation and land use).

Unit bar architecture in a highly‐variable fluvial discharge regime: Examples from the Burdekin River, Australia

AbstractUnit bars are relatively large bedforms that develop in rivers over a wide range of climatic regimes. Unit bars formed within the highly‐variable discharge Burdekin River in Queensland, Australia, were examined over three field campaigns between 2015 and 2017. These bars had complex internal structures, dominated by co‐sets of cross‐stratified and planar‐stratified sets. The cross‐stratified sets tended to down‐climb. The development of complex internal structures was primarily a result of three processes: (i) superimposed bedforms reworking the unit bar avalanche face; (ii) variable discharge triggering reactivation surfaces; and (iii) changes in bar growth direction induced by stage change. Internal structures varied along the length and across the width of unit bars. For the former, down‐climbing cross‐stratified sets tended to pass into single planar cross‐stratified deposits at the downstream end of emergent bars; such variation related to changes in fluvial conditions whilst bars were active. A hierarchy of six categories of fluvial unsteadiness is proposed, with these discussed in relation to their effects on unit bar (and dune) internal structure. Across‐deposit variation was caused by changes in superimposed bedform and bar character along bar crests; such changes related to the three‐dimensionality of the channel and bar geometry when bars were active. Variation in internal structure is likely to be more pronounced in unit bar deposits than in smaller bedform (for example, dune) deposits formed in the same river. This is because smaller bedforms are more easily washed out or modified by changing discharge conditions and their smaller dimensions restrict the variation in flow conditions that occur over their width. In regimes where unit bar deposits are well‐preserved, their architectural variability is a potential aid to their identification. This complex architecture also allows greater resolution in interpreting the conditions before and during bar initiation and development.

Linking hydrological connectivity to gully erosion in savanna rangelands tributary to the Great Barrier Reef using structure‐from‐motion photogrammetry

AbstractGully erosion is a major land management challenge globally and a particularly important issue in dry tropical savanna rangelands tributary to the Great Barrier Reef, Australia. This study investigated linkages between hillslope hydrological connectivity pathways and gully geomorphic change in the Burdekin River Basin. High‐resolution (0.1 m) topographic and land cover data derived from low‐cost aerial (via unmanned aircraft system) structure‐from‐motion with multiview stereo photogrammetry (SfM) were used to map fine‐scale connectivity patterns and quantify headcut retreat at the hillslope scale (~150,000 m2). Very high resolution (0.01 m) topographic models derived from ground‐based (via handheld digital camera) SfM were used to quantify the morphology and geomorphic change of several gully arms (300–700 m2) between 2016 and 2018. Median linear, areal, and volumetric headcut (n = 21) retreat rates were 0.2 m, 0.8 m2, and 0.3 m3 yr−1, respectively. At all study sites, the points where modelled hydrological flow lines intersected gullies corresponded to observed geomorphic change, enabling spatially explicit identification of gully extension pathways as a result of overland flow. Application of an index of connectivity demarcated parts of the hillslope most connected to the gully network. Bare areas, roads, and cattle trails were identified as important runoff source areas and hydrological conduits driving gully extension. Ground‐based SfM accurately reconstructed complex morphologic features including undercuts, overhangs, rills, and flutes, providing insights into within‐channel erosion processes. This study contributes to an improved understanding and modelling of hydrogeomorphic drivers of gully erosion in degraded savanna rangelands, ultimately benefiting gully management.

Assessing the relative impacts of land‐use change and river regulation on Burdekin River (Australia) floodplain wetlands

Abstract The Burdekin River floodplain wetlands are internationally important and act as a sink for sediments and nutrients that would otherwise enter the World Heritage‐listed Great Barrier Reef lagoon. The Burdekin River has the highest natural discharge of any Great Barrier Reef catchment and contributes the greatest mass of sediment to the reef. The river and its catchment have been substantially modified by land clearance, river regulation introduced in the 1960s, the construction of the Burdekin Falls Dam in 1987 and invasive aquatic plants. We hypothesised that the natural variability of Burdekin River discharge would render its wetland ecosystems resistant to human‐induced pressures. Diatoms were analysed from the sediments of two lower Burdekin River floodplain wetlands with contrasting regulation histories. Labatt Lagoon has a long history of flow alteration, whereas Swan's Lagoon has experienced limited regulation. Both wetlands experienced dramatic increases in sedimentation as a result of land clearance, yet the Swan's Lagoon diatom record indicates that the wetland's ecology remains within the range of natural variability. In contrast, Labatt Lagoon is markedly different from its pre‐settlement state. It is now permanent, having been ephemeral for more than 1000 years before European settlement. The conversion to artificial permanence facilitated aquatic plant invasion, resulting in more marked changes than widespread pastoralism. Modern diatom assemblages from 28 lower Burdekin River floodplain wetlands indicate that the contemporary flora of Swan's Lagoon is unusual. Most wetlands have similar assemblages to those in the Labatt Lagoon record in its present, altered state. It is possible, therefore, that the ecological shift registered in Labatt Lagoon is widespread. Diatom records highlight the striking impact that river regulation has had on the trajectory of the Burdekin floodplain wetlands. It is likely that wetland rehabilitation can be facilitated by the re‐introduction of a variable hydrological regime.

The development and evolution of the Burdekin River estuary freshwater plume during Cyclone Debbie (2017)

This paper investigates the plume morphology and dynamics prior to and after the landfall of Cyclone Debbie (2017). The heavy rainfall and flooding produced a large buoyant coastal current, which moved southward after the cyclone landfall then advected northward with the prevailing southerly wind. The plume is simulated using the eReef GBR1 1-km model and a passive tracer is used to identify the plume behaviour. Based on the concentration of river tracers from the Burdekin River, the plume had propagated over 100 km to the north 23 days after the cyclone landfall.Based on an Empirical Orthogonal Function (EOF) analysis, the cyclone-induced river discharge is found to be the major cause for surface salinity variation with a lag time equal to 17 h. The response of surface plume area to the river flow is about 40 h lag with correlation coefficient = 0.68 and according to the wind strength index, the plume was controlled by buoyancy on c1 but could be controlled by wind in the far field. Wind also plays a very important role. Under weak downwelling wind forcing lower than 0.1 Pa, the plume thickness is sensitive to river discharge and tides. With stronger downwelling wind forcing larger than 0.1 Pa vertical mixing is generated, the plume is restricted to the coast, and high river discharge can only affect the thickness of the plume, but not its width. After Cyclone Debbie made landfall, upwelling winds developed, and the freshwater plume reversed direction from northward to southward most likely due to the influence of the northerly wind as well as the ambient current and topography.

A critical evaluation of coral Ba/Ca, Mn/Ca and Y/Ca ratios as indicators of terrestrial input: New data from the Great Barrier Reef, Australia

Coral trace element proxies of terrestrial runoff are widely applied to document and quantify historical changes in river discharge, constituent loads and land disturbance. However, some studies show poor replication between trace element records where cores from multiple coral colonies have been analyzed. Conflicting interpretations also exist on the environmental variable the coral trace element proxy is recording. Indeed, few studies have examined trace element behavior in the estuarine mixing zone that influence the coral records and only limited data on river discharge and constituent loads are available to validate the proxy records of terrestrial runoff. This study examined the behavior of Barium (Ba), Manganese (Mn) and Yttrium (Y) in the Burdekin River estuarine mixing zone, north-eastern Australia during several flood events and investigated the ability of coral Ba/Ca, Mn/Ca and Y/Ca ratios to record the variability of measured Burdekin River discharge and suspended sediment loads along a transect of replicate coral cores (10 cores from 5 locations). The results show limited evidence for Ba desorption from suspended sediments in the estuarine mixing zone while considerable desorption of Mn over a wide salinity mixing gradient was evident. Y showed evidence of removal in the initial mixing zone of the estuary (0–5 PSU) but displayed a relatively flat pattern thereafter indicating that it was not diluted by seawater mixing. The coral trace element records generally showed poor agreement within sites and the Ba/Ca ratios in some corals did not respond to regional river discharge, although coral luminescent lines were present in all cores and were significantly correlated with each other and Burdekin River discharge. While it was difficult to disentangle the influence of Burdekin River discharge and suspended sediment loads on the coral Ba/Ca proxy, several lines of evidence point towards discharge as the major contributor to this proxy in this region. A combination of factors likely influence the coral Ba/Ca ratio including an as yet undetermined physiological mechanism possibly related to crystallography or species, distance of the coral to the river mouth, variability in river discharge (including both annual totals and peaks, and local influences), variability in sediment load, the behavior of trace elements in the estuarine mixing zone, the hydrodynamics of flood plumes in the marine environment and the water depth of the coral. While the coral Mn/Ca and Y/Ca ratios did not respond to Burdekin River discharge events, the considerable desorption of Mn and the elevated Y throughout the estuarine mixing zone shows some promise in their ability to record long-term changes in suspended sediment loading and large terrestrial disturbances. Future studies examining coral records of terrestrial runoff should examine trace element behavior in the river estuarine mixing zone of influence, establish a correlation between the trace element and river discharge (such as luminescent lines) and demonstrate replication between different coral colonies.

Bottomset Architecture Formed In the Troughs of Dunes and Unit Bars

Abstract Bottomsets are formed in the troughs of migrating bedforms. The flow and sediment dynamics downstream of bedforms differ, and consequently, the thickness, grain size, and internal structure of bottomsets vary greatly. A classification of the controls on bottomset formation is proposed related to two- and three-dimensional processes, flow and sediment unsteadiness, and pre-existing deposits. Structures and deposits created by flow and sediment unsteadiness as well as pre-existing deposits are also considered in relation to changes they can induce in subsequent trough processes. The classification is illustrated by observations from laboratory flumes, the modern Burdekin River (Australia), and the rock record (The Roaches Grit, England, and Hawkesbury Sandstone, Australia). In bottomset examples described in this paper, internal variability, both vertically and laterally, was much greater than that within the dominant foreset component. Complex compound structures were created by the interaction and predominance of different bottomset controls. This, combined with their high preservation potential, makes them a highly useful paleoenvironmental indicator. Bottomset variation (e.g., changes in the abundance of mud laterally) will influence the permeability heterogeneity of fluvial reservoir rocks. Bottomsets formed under relatively steady conditions are likely to be laterally extensive and have similar characteristics over their entire length. They may act as significant barriers to vertical flow. Conversely, bottomsets generated in unsteady regimes tend to be highly variable, potentially creating conduits between cross-bed sets aiding inter-set permeability.

Grazing impacts on gully dynamics indicate approaches for gully erosion control in northeast Australia

AbstractDrainage network extension in semi‐arid rangelands has contributed to a large increase in the amount of fine sediment delivered to the coastal lagoon of the Great Barrier Reef, but gully erosion rates and dynamics are poorly understood. This study monitored annual erosion, deposition and vegetation cover in six gullies for 13 years, in granite‐derived soils of the tropical Burdekin River basin. We also monitored a further 11 gullies in three nearby catchments for 4 years to investigate the effects of grazing intensity. Under livestock grazing, the long‐term fine sediment yield from the planform area of gullies was 6.1 t ha‐1 yr‐1. This was 7.3 times the catchment sediment yield, indicating that gullies were erosion hotspots within the catchment. It was estimated that gully erosion supplied between 29 and 44% of catchment sediment yield from 4.5% of catchment area, of which 85% was derived from gully wall erosion. Under long‐term livestock exclusion gully sediment yields were 77% lower than those of grazed gullies due to smaller gully extent, and lower erosion rates especially on gully walls. Gully wall erosion will continue to be a major landscape sediment source that is sensitive to grazing pressure, long after gully length and depth have stabilised. Wall erosion was generally lower at higher levels of wall vegetation cover, suggesting that yield could be reduced by increasing cover. Annual variations in gully head erosion and net sediment yield were strongly dependent on annual rainfall and runoff, suggesting that sediment yield would also be reduced if surface runoff could be reduced. Deposition occurred in the downstream valley segments of most gullies. This study concludes that reducing livestock grazing pressure within and around gullies in hillslope drainage lines is a primary method of gully erosion control, which could deliver substantial reductions in sediment yield. Copyright © 2018 John Wiley &amp; Sons, Ltd.