Refining fine sediment source identification through integration of spatial modelling, concentration monitoring and source tracing: A case study in the Great Barrier Reef catchments

Excess fine sediment delivery is a major contributor to the declining health of the Great Barrier Reef and identifying the dominant source areas of fine sediment has been critical to prioritising erosion remediation programs. The Bowen River catchment within the Burdekin Basin has been recognised as a major contributor and hence received considerable research investment over the last two decades. This study adopts a novel approach to integrate three independently derived sediment budgets produced from a catchment scale sediment budget model (Dynamic SedNet), targeted tributary water quality monitoring and geochemical sediment source tracing to refine and map the sediment source zones within the Bowen catchment. A four year study of water quality monitoring combined with modelled discharge estimates and geochemical source tracing both identified that the Little Bowen River and Rosella Creek were the largest sources of sediment in the Bowen River catchment. Both data sets contradicted initial synoptic sediment budget model predictions due to inadequate representation of hillslope and gully erosion. Recent improvements in model inputs have resulted in predictions that are consistent with the field data and are of finer resolution within the identified source areas. Priorities for further investigation of erosion processes are also revealed. Examining the benefits and limitations of each method indicates that these are complimentary methods which can effectively be used as multiple lines of evidence. An integrated dataset such as this provides a higher level of certainty in the prediction of fine sediment sources than a single line of evidence dataset or model. The use of high quality, integrated datasets to inform catchment management prioritisation will provide greater confidence for decision makers when investing in catchment management

2017 Scientific Consensus Statement: land use impacts on the Great Barrier Reef water quality and ecosystem condition, Chapter 2: sources of sediment, nutrients, pesticides and other pollutants to the Great Barrier Reef

This chapter provides an up-to-date review of the state of knowledge relating to the source of sediment and nutrients as well as pesticides and other pollutants delivered to the Great Barrier Reef from adjacent catchments. The strengths and limitations of the various datasets are also discussed. Collectively, sediment, nutrients, pesticides and other pollutants (e.g. petroleum hydrocarbons, pharmaceuticals) are described as ‘pollutants’. This chapter is focused on defining the major source areas of these pollutants across the Great Barrier Reef, how these sources have varied in space and time, the major processes (e.g. hillslope, gully and streambank erosion) delivering these pollutants, their relative loads to the Great Barrier Reef and a summary of the main drivers in terms of land use, land condition and agricultural practices. Plot- and paddock-scale studies, including the effectiveness of remediation approaches, are summarised in Chapter 4. Acknowledging that all forms of data used to estimate pollutant loads to the Great Barrier Reef have constraints and limitations, this review uses a ‘multiple lines of evidence’ approach and draws on data from three main sources. These include the Queensland Government load monitoring data, the latest Queensland Government whole of Great Barrier Reef Source Catchments modelling results (which underpin the Report Card 2015) as well as a summary of the numerous individual research projects and synthesis reports published over the last four years. Data and information are included that was published, publicly available and that had undergone a peer review process. In a few cases, grey literature (e.g. consulting reports) and journal publications currently in review are included. A synthesis of the broad findings of this chapter are outlined below and in Table 1. A detailed description of what has changed since the last Scientific Consensus Statement is provided in Table 20

Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration

Abstract: Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world’s largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change

The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review

publisher: Elsevier articletitle: The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review journaltitle: Earth-Science Reviews articlelink: http://dx.doi.org/10.1016/j.earscirev.2017.04.009 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved

The implications of regional variations in rainfall for reconstructing rainfall patterns using tree rings

Haines, HA ORCiD: 0000-0003-0019-4151Copyright © 2017 John Wiley & Sons, Ltd. In Australia, multidecadal periods of floods and droughts have major economic consequences. Due to the short duration of Australian instrumental precipitation records, it is difficult to determine the patterns of these multidecadal periods. Proxy records can be used to create long-term rainfall reconstructions for regions that are lacking instrumental data. However, the spatial extent over which single-site proxy records can be applied is poorly understood. Southeast Queensland (SEQ) is an area where tree rings can be used to reconstruct long-term rainfall patterns, but their regional representation is unknown. In this study, the spatial variability in rainfall across SEQ is investigated from 1908 to 2007 using 140 instrumental rainfall stations. Pearson correlation analysis between stations is used to create groups at the r = 0.80, 0.85, and 0.90 correlation levels, and then annual deviations from the mean are determined. These patterns indicate that rainfall is not uniform across SEQ but can be broken into 2 main spatially consistent groups. Each of these groups is broken down into several subgroups with higher correlation levels. Long-term streamflow records are found to be correlated to rainfall patterns local to the streamflow stations, indicating that analysis of extreme events should consider spatial precipitation variability. Finally, the only currently available proxy rainfall reconstruction for the region, a 140-year Toona ciliata tree ring width record from Lamington National Park, is compared to rainfall groups at different correlation levels across all of SEQ. The correlation between the reconstruction and the rainfall station groupings is best for the groups within which the tree-ring record is spatially located, and this correlation improves as rainfall group correlation increases. Correlation is nearly nonexistent for groupings located at a distance from the tree-ring site. These results demonstrate the importance of assessing the spatial variability of precipitation so that the spatial applicability of proxy records can be assessed.Associated Grant Code:LP12020009

Accuracy of mixing models in predicting sediment source contributions

International audienceDetermining the source of sediment using geochemical properties is now a widely used approach in catchment management. However the outcome of these studies often depends on the type of model used to determine the relative contribution from difference sources. Here we test the accuracy and robustness of four widely used sediment mixing models using artificial mixtures of three well-distinguished geologic sources. Sub-samples from these three sources were mixed to create four groups of samples, each consisting of five samples, with known source contributions, 20 samples in total. The source contributions to the individual and groups of artificial sediment mixtures were calculated using each of the four mixing models: Modified Hughes, Modified Collins, Landwehr and Distribution models. Unlike Modified Collins and Landwehr models which use calculated values from each tracer property of individual sources (e.g. mean and standard deviation), Hughes model uses the measured fingerprint property of replicated samples from each source and Distribution model incorporate distribution of tracers and correlation between tracer properties for sediment samples and sources. For the 20 individual sample mixtures the Distribution model provided the closest estimates to the known sediment source contribution values (Mean Absolute Error (MAE) = 10.8%, and standard error (SE) = 0.9%). The Modified Hughes (MAE = 13.5%, SE = 1.1%), Landwehr (MAE = 19%, SE = 1.7) and Collins models (MAE = 29%, SE = 2.1%) were the next accurate models, respectively. For the groups of the samples the Modified Hughes was the most robust source contribution predictor with 5.4% error. The Distribution model (MAE = 6.1%) and Landwehr model (MAE = 7.8%) were the second and third accurate models. Collins model with MAE of 28.3% was a significantly weaker source contribution predictor than the three other models. This study demonstrates the dependence of source attribution on model selection. The study highlight the need to test mixing model using known source and mixture samples prior to applying them to field samples. The results indicate that the Distribution and Modified Hughes models provided the most accurate source attributions using geochemical fingerprint properties

At least 17,000 years of coexistence: Modern humans and megafauna at the Willandra Lakes, South-Eastern Australia

It has been argued that globally the extinction of many species of megafauna appears to coincide with the dispersal of modern humans, however, with the refinement of age ranges on megafauna specimens it has been revealed that many extinctions are in fact time-transgressive. This appears to be the case in Europe and Asia, and probably also the Americas. The argument over what mechanism was responsible for megafauna extinction in Australia, however, remains heavily contested. This contribution investigates the age of a single articulated megafauna specimen of Zygomaturus trilobus from the Willandra Lakes. The Willandra is unique in that it is the only Australian landscape with evidence for a) continual occupation by Aboriginal people from 50,000 years ago and b) the presence of megafauna. As people have occupied the Willandra since the period of initial colonisation, establishing the age range of this specimen provides a good test to determine if people drove megafauna into extinction soon after their arrival, or whether megafauna and people co-existed for a long period of time. Two independent dating techniques show that the fossil has a maximum age range based on OSL of 33.3-36.7kya and a minimum age range based on U-series at 32.4 +/- 0.5kya. This specimen represents the youngest example of extinct megafauna reliably dated in Australia. Regardless of whether one accepts a short (47.5kya) or long (55kya) chronology for Aboriginal occupation of Australia, it would now appear that the second largest marsupial to ever exist was still present for a considerable time after the first arrival of Aboriginal people

Optical dating of Holocene sediments from a variety of geomorphic settings using single grains of quartz

This paper presents an improved method for the optical dating of Holocene sediments from a variety of geomorphic settings. We have measured the equivalent dose (D-e) in individual grains of quartz, using green laser light for optical stimulation, and have simulated the D-e distributions for multiple-grain 'synthetic' aliquots using the single-grain data. For 12 samples of known (independent) age, we show that application of a 'minimum age model' to the single-grain and 'small' (10-grain) aliquot D-e data provides the most accurate estimate of the burial dose for nine of the samples examined (3 aeolian, 5 fluvial, and I marine). The weighted mean D-e (as obtained using the 'central age model') gives rise to burial age overestimates of up to a factor of 10 for these nine samples, whether single grains, small aliquots, or 'large' (100-grain) aliquots are used. For the other three samples (two aeolian and one fluvial), application of either the minimum age model or the central age model to the single-grain, small aliquot, and large aliquot D-e data yields burial ages in accord with the independent age control. We infer that these three samples were well bleached at the time of deposition. These results show that heterogeneous bleaching of the optical dating signal is commonplace in nature, and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition. We also show that grains sensitive to infrared (IR) stimulation can give rise to low D-e values, which will result in significant underestimation of the burial dose and, hence, of the age of deposition. We demonstrate that use of a modified single-aliquot regenerative-dose protocol incorporating IR stimulation prior to green light stimulation deals effectively with contamination by IR-sensitive grains. We conclude that application of the modified protocol to single grains or small aliquots of quartz, using the lowest D-e population to estimate the burial dose, is the best means of obtaining reliable ages for Holocene sediments from a wide range of depositional environments.No Full Tex

Sediment fingerprinting in fluvial systems: review of tracers, sediment sources and mixing models

International audienceSuspended sediments in fluvial systems originate from a myriad of diffuse and point sources, with the relative contribution from each source varying over time and space. The process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended material. This review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling, and critically compares biogeochemical and physical tracers used in fingerprinting studies. Implications of applying different mixing models to the same source data are explored using data from 41 catchments across Europe, Africa, Australia, Asia, and North and South America. The application of seven commonly used mixing models to two case studies from the US (North Fork Broad River watershed) and France (Bléone watershed) with local and global (genetic algorithm) optimization methods identified all outputs remained in the acceptable range of error defined by the original authors. We propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins (using correction factors) and Hughes (relying on iterations involving all data, and not only their mean values) models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems