Great Barrier Reef Catchment Research Articles

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.

Social marketing’s role in improving water quality on the Great Barrier Reef

Purpose The purpose of this paper is to focus on the implications of claimed detrimental impacts for the agricultural activity of the Great Barrier Reef (GBR) ecosystem health in Queensland, Australia. The authors discuss the complex interaction of factors that have contributed to the decline in reef ecosystems and the challenges presented by multiple industries operating within the GBR catchment area. The authors then discuss measures employed to address agricultural run-off, claimed to be a significant factor in declining reef water quality. Design/methodology/approach Surveys of land managers were undertaken in partnership with two of the six natural resource management (NRM) organizations operating in areas adjacent to the GBR identified as having very high risk of natural and anthropogenic runoff. The sample population was obtained from a membership database within the two regions. Participants include land managers from the both regions who engaged in sugar cane production (Region 1 and Region 2, included in this paper) and cattle production (Region 2, to be reported later). Quantitative and qualitative data were analyzed including open-ended responses. Findings A large-scale study of land managers reveals several reasons for the lack of success at reducing agricultural run-off. The authors discuss the rationale for a move to a theory-grounded social marketing approach to encouraging land manager behavior change, highlighting barriers, and potential enablers of sustained behavior change. Originality/value This study is first of its kind that discusses the behavior of land managers in the GBR catchment area and highlights facilitators and impediments of land managers’ behavior change toward GBR protection actions.

Managing threats and restoring wetlands within catchments of the Great Barrier Reef, Australia

Abstract The catchments of the Great Barrier Reef (GBR) in Australia include more than one million ha of wetlands, which help to sustain the health and resilience of the reef. This article reviews the status, values, and threats of wetlands in the GBR catchments, as well as the management, protection, and challenges and opportunities for their restoration and rehabilitation. At present, wetlands in the GBR catchments have low rates of area loss and are generally well protected; however, they face major management challenges owing to the intensive land use of the catchments, especially for grazing, agriculture, horticulture, and mining. Major threats to these wetlands include water pollution, invasive species, changes in hydrology, and increasing temperature and salinity resulting from climate change. In recent years wetlands have been considered primarily for their role in improving water quality to ameliorate contaminated terrestrial run‐off to the GBR, with little attention given to their intrinsic value and other ecosystem services. Financial opportunities for wetland restoration in addition to government‐funded schemes include water pollution offsets, payment for ecosystem services, and nitrogen markets. Wetlands need to be protected, managed, and restored for the ecosystem services that they provide to the GBR, but also for their intrinsic value as significant features of coastal landscapes.

Do outcome or input risks limit adoption of environmental projects: Rehabilitating gullies in Great Barrier Reef catchments

A key challenge in agri-environmental policy is to encourage agricultural producers to adopt better management practices to reduce adverse environmental impacts. Research attention around has focused on the underlying drivers of landholder actions and decisions, the costs and returns of improving management practices, and the effects of different policy mechanisms to achieve change. One potential barrier to changing management practices are the risks that agricultural producers may perceive to exist. Outcome risks relate to the possibility that a management change may not achieve environmental goals or anticipated production increases, while input risks relate to the possibility that the costs of management change turn out to be much higher than expected. These risks lead to perceptions of winners' curse, where producers are reluctant to adopt better management practices in case costs are higher and returns are lower than expected. In this paper we test the extent to which the willingness to implement environmental improvements are limited by conservation outcome risks or input risks, using a choice experiment in workshops with landholders. Our case study involved projects to reduce gully erosion and subsequent sediment run-off which it attributed to inshore reef health decline in catchments adjacent to the Great Barrier Reef.

Putting uncertainty under the cultural lens of Traditional Owners from the Great Barrier Reef Catchments

Indigenous peoples in Australia, and globally, are situated in an unusual context of both significant vulnerability and unique resilience to climate change which influence their perceptions of climate risk and uncertainty. Their vulnerability to climate change arises in part from their contexts of living in many of the harshest and isolated environments. Their resilience originates from their accumulated knowledge of specific environments over millennia, mediated through sui generis cultural institutions. Our results illustrate that indigenous groups primarily perceive uncertainties related to volition of actors and institutions. When they are involved in climate adaptation planning in ways that mobilise their cultural institutions and knowledge, they can safely manage these uncertainties through their agency to determine and control key risks. We demonstrate that climate justice approaches can be strengthened for indigenous peoples by applying a linked vulnerability-resilience analytical framework. This enables stronger consideration of how unique cultural institutions and knowledge, which are not available to all vulnerable groups, affect indigenous perceptions of uncertainty in climate adaptation planning. We use this analytical approach in a case study with Yuibera and Koinmerburra Traditional Owner groups within the Great Barrier Reef Catchment. We conclude that a specific focus on sui generis indigenous knowledge and cultural institutions as a source of resilience can strengthen climate justice approaches and work more effectively with indigenous peoples in climate change contexts.

Benthic diatoms as indicators of herbicide toxicity in rivers – A new SPEcies At Risk (SPEARherbicides) index

Benthic diatom communities are used widely as indicators of river health due to their rapid response to changes in water quality. The ability for diatom-based indices to detect eutrophication has been well documented; however, an index designed specifically to detect herbicide impacts is yet to be established. This is required as herbicide contamination of rivers is common in agricultural regions and poses a potential threat to aquatic ecosystems. This study developed a new biomonitoring index (SPEARherbicides) using benthic diatom communities to detect the toxic impacts of herbicides in rivers, and tested it across 14 rivers in the Great Barrier Reef catchment area, Australia. The new index uses diatom species traits to classify diatoms as either sensitive or tolerant to herbicides and calculates the fraction of sensitive taxa within a sample. The SPEARherbicides index showed a decline in herbicide sensitive diatoms with increasing herbicide toxicity of the sites. The impacts of herbicide toxicity on the diatom community were only apparent after the wet season when aqueous herbicide concentrations typically peak and diatoms were able to recover during the dry season when herbicide concentrations were lower. SPEARherbicides values had a negative relationship with the percentage of grazing and cropping in catchments but had a positive relationship with the percentage of conservation in catchments. SPEARherbicides also had a negative relationship with co-occurring potential stressors such as nutrients and total suspended solids.

Invertebrate responses to land use in tropical streams: discrimination of impacts enhanced by analysis of discrete areas

We identified influences of land-use disturbances on invertebrate assemblages in streams draining eight areas of the Great Barrier Reef catchment in tropical Australia (~15.7–22°S), a region of high biodiversity. We used distance-based linear modelling (DistLM) to analyse assemblage data (103 taxa), richness and the SIGNAL2 taxon sensitivity index. DistLM of assemblages explained ~40% of variation across all samples and 7–54% of variation in individual areas. DistLM of richness and SIGNAL2 explained respectively 19–81 and 26–95% of variation. Explanatory variables were land use (especially cropping and grazing v. forest), riparian width, instream habitat, climate (drier south) and water quality (conductivity greater in south). Local impacts of activities such as mining were evident in models of individual areas. A detailed comparison of streams with contrasting riparian management demonstrated a 25% loss of richness, but no change in SIGNAL2 score. Accounting for local environmental gradients and using measures appropriate to the type of disturbance improved identification of impacts, and could form a framework for future regional monitoring of stream ecological condition. The impacts identified may be mitigated by remediation such as riparian rehabilitation, although management at catchment scales is required to be effective.

A novel approach of combining isotopic and geochemical signatures to differentiate the sources of sediments and particulate nutrients from different land uses

Determining the source of sediments and associated nutrients from terrestrial to aquatic environments is critical for managing the detrimental impacts of soil erosion and loss of nutrients from terrestrial into aquatic environment. However, tracing the source of particulate nutrients from different land uses has not been adequately carried out due to methodological difficulties in separating sources, particularly in the Great Barrier Reef (GBR) catchment. The objective of this study was to develop a method to differentiate the sources of particulate nutrients from soils collected from different land uses (combination of beef and dairy grazing, sugarcane, forest and banana) using both geochemical and isotopic signatures. In order to select a discriminative group of signatures, all soil samples collected from each of the land use areas were fractionated to <63 μm size fraction and were analysed for both isotopic (δ13C, δ15N) and acid extractable geochemical properties (e.g. Zn, Pt and S). Considering the fact that the outcome of tracing models often depends on the type and robustness of the methods used, here we have employed a stable isotope mixing model (SIAR) to evaluate if the suite of selected elements could be used to estimate the relative contribution of different sources for a series of five virtually created sediment mixtures. For the five groups of virtual sediments, the SIAR model provided close estimates to the contribution values of sediment sources with the Mean Absolute Error (MAE) varying from 0.30 to 2.88%. Results from this study show for the first time that the combined use of isotopic and geochemical signatures enable the SIAR model to provide an accurate estimation of source apportionment where a variety of land uses needs to be investigated and shows promise as a valuable new sediment and particulate nutrient tracing tool.

Acute drivers influence recent inshore Great Barrier Reef dynamics.

Understanding the dynamics of habitat-forming organisms is fundamental to managing natural ecosystems. Most studies of coral reef dynamics have focused on clear-water systems though corals inhabit many turbid regions. Here, we illustrate the key drivers of an inshore coral reef ecosystem using 10 years of biological, environmental, and disturbance data. Tropical cyclones, crown-of-thorns starfish, and coral bleaching are recognized as the major drivers of coral loss at mid- and offshore reefs along the Great Barrier Reef (GBR). In comparison, little is known about what drives temporal trends at inshore reefs closer to major anthropogenic stress. We assessed coral cover dynamics using state-space models within six major inshore GBR catchments. An overall decline was detected in nearly half (46%) of the 15 reefs at two depths (30 sites), while the rest exhibited fluctuating (23%), static (17%), or positive (13%) trends. Inshore reefs responded similarly to their offshore counterparts, where contemporary trends were predominantly influenced by acute disturbance events. Storms emerged as the major driver affecting the inshore GBR, with the effects of other drivers such as disease, juvenile coral density, and macroalgal and turf per cent cover varying from one catchment to another. Flooding was also associated with negative trends in live coral cover in two southern catchments, but the mechanism remains unclear as it is not reflected in available metrics of water quality and may act through indirect pathways.

Characterisation of spatial variability in water quality in the Great Barrier Reef catchments using multivariate statistical analysis

Water quality monitoring is important to assess changes in inland and coastal water quality. The focus of this study was to improve understanding of the spatial component of spatial-temporal water quality dynamics, particularly the spatial variability in water quality and the association between this spatial variability and catchment characteristics. A dataset of nine water quality constituents collected from 32 monitoring sites over a 11-year period (2006–2016), across the Great Barrier Reef catchments (Queensland, Australia), were evaluated by multivariate techniques. Two clusters were identified, which were strongly associated with catchment characteristics. A two-step Principal Component Analysis/Factor Analysis revealed four groupings of constituents with similar spatial pattern and allowed the key catchment characteristics affecting water quality to be determined. These findings provide a more nuanced view of spatial variations in water quality compared with previous understanding and an improved basis for water quality management to protect nearshore marine ecosystem.

Targeting for pollutant reductions in the Great Barrier Reef river catchments

The declining health of the Great Barrier Reef (GBR) from poor water quality has increased the urgency for pollutant reductions at the same time that available financial resources and knowledge regarding the most appropriate interventions are limited. Prioritisation of water quality interventions in the Great Barrier Reef catchments is the process of identifying which land based actions can achieve the largest environmental benefits at the lowest cost. For prioritisation to be effective a focus is required on the outcomes of pollution reduction activities as compared to the inputs. In this paper we set out a framework for prioritising actions to improve water quality into the Great Barrier Reef, as well as providing a case study analysis using 47 individual river basins across the six large scale catchments, three pollutants and two industries. The results identify the most cost-effective options for water quality improvements aligning to locations of medium risk to reef health. The outcomes of the analysis highlight the importance of seeking pollutant reductions where the most effective outcome can be achieved rather than simply targeting an industry or a catchment.

Simulated fate of catchment-derived sediment on the Great Barrier Reef shelf

Numerical experiments using a 3D model of fine sediment transport in the Great Barrier Reef region indicate deposition of the bulk mass of catchment sediments from river plumes within a few tens of kilometres from river mouths. A very fine fraction of easily resuspended catchment sediment has a capacity to propagate over much greater distances reaching out into the mid-shelf and outer-shelf regions. The model suggests such particles, instrumental to the development of low density flocs in the marine environment, can play a critical role in altering optical properties of water masses over the shelf during wet years. The mid-term (4 year) impact of Great Barrier Reef catchments on the probability of suspended sediment concentration exceeding the ecologically significant trigger value of 2 mg/L is confined to inshore regions adjacent to river mouth locations.

Transcriptomic, lipid, and histological profiles suggest changes in health in fish from a pesticide hot spot

Barramundi (Lates calcarifer) were collected at the beginning (1st sampling) and end (2nd sampling) of the wet season from Sandy Creek, an agriculturally impacted catchment in the Mackay Whitsundays region of the Great Barrier Reef catchment area, and from Repulse Creek, located approximately 100 km north in Conway National Park, to assess the impacts of pesticide exposure. Gill and liver histology, lipid class composition in muscle, and the hepatic transcriptome were examined. The first sample of Repulse Creek fish showed little tissue damage and low transcript levels of xenobiotic metabolism enzymes. Sandy Creek fish showed altered transcriptomic patterns, including those that regulate lipid metabolism, xenobiotic metabolism, and immune response; gross histological alterations including lipidosis; and differences in some lipid classes. The second sampling of Repulse Creek fish showed similar alterations in hepatic transcriptome and tissue structure as fish from Sandy Creek. These changes may indicate a decrease in health of pesticide exposed fish.

Contribution of individual rivers to Great Barrier Reef nitrogen exposure with implications for management prioritization

Dissolved inorganic nitrogen (DIN) runoff from Great Barrier Reef (GBR) catchments is a threat to coral reef health. Several initiatives address this threat, including the Australian Government's Reef 2050 Plan. However, environmental decision makers face an unsolved prioritization challenge: determining the exposure of reefs to DIN from individual rivers. Here, we use virtual river tracers embedded within a GBR-wide hydrodynamic model to resolve the spatial and temporal dynamics of 16 individual river plumes during three wet seasons (2011−2013). We then used in-situ DIN observations to calibrate tracer values, allowing us to estimate the contribution of each river to reef-scale DIN exposure during each season. Results indicate that the Burdekin, Fitzroy, Tully and Daintree rivers pose the greatest DIN exposure risk to coral reefs during the three seasons examined. Results were used to demonstrate a decision support framework that combines reef exposure risk with river dominance (threat diversity).

Indicators of phytoplankton response to particulate nutrient bioavailability in fresh and marine waters of the Great Barrier Reef

Sediments delivered to freshwater and marine environments can make important contributions to the aquatic bioavailable nutrient pool. In the Great Barrier Reef (GBR) catchments, particulate nutrients comprise an important fraction of the end of catchment loads; however, their contribution to the bioavailable nutrient pool is not well understood. This research determined which particulate nutrient parameters are the best indicators of the potential effect of fine sediment (<10 μm) on phytoplankton growth. Surface and subsurface sediments were lab-generated to cover a wide spectrum of particulate nutrient bioavailability from key soil types, land uses and erosion processes (hillslope and gully) in a wet and a dry tropics catchment of the GBR. Phytoplankton bioassays were used to assess freshwater and marine phytoplankton responses to sediments. The best indicators were selected by regressing measurements of phytoplankton growth against nutrient bioavailability parameters measured on the sediments. The selected indicator equations included organic carbon (C) pools for both fresh and marine water, highlighting the role of bacteria in mediating nutrient availability for phytoplankton. The equations also included various fractions of particulate nitrogen (N) (differentiating the adsorbed ammonium-N from the particulate organic N), and the ratios of C to N, which indicate the lability of the organic matter present in the sediment. Dissolved reactive phosphorus was also an important indicator in freshwater. The indicators performed better in assessing bioavailability potential than traditional methods to monitor particulate nutrients, e.g., particulate N and particulate phosphorus. Phytoplankton bioassays indicated that nutrients in sediment can promote phytoplankton growth, with nutrient bioavailability depending not only on sediment load, but also sediment characteristics associated with its parent soil. These characteristics vary with soil type, land use and erosion process. Findings will help prioritize erosion control to catchment areas which are most likely to contribute large amounts of bioavailable particulate nutrients to the GBR.

Assessing cost‐effectiveness when environmental benefits are bundled: agricultural water management in Great Barrier Reef catchments

Using economic analysis to prioritise improvements in environmental conditions is particularly difficult when multiple benefits are involved. This includes ‘bundling’ issues in agricultural pollution management, where a change in management action or farming systems generates multiple improvements, such as reductions in more than one pollutant. In this study, we conceptualise and compare two different approaches to analysing cost‐effectiveness when varying bundles of benefits are generated for a single project investment. Each approach requires data to be transformed in some way to allow the analysis to proceed. The index approach requires the transformation on the benefits side so that the effects of multiple pollutant changes can be combined into a measure for each project which can then be compared to costs. By comparison, the disaggregation approach requires the transformation on the costs side where costs for each project have to be apportioned across the different pollutants involved. The paper provides novel insights with an application to agricultural water quality improvements into the Great Barrier Reef in Australia, demonstrating that while both approaches are effective in prioritising projects by cost‐effectiveness, the disaggregation approach provides more insightful results and values that may be relevant for use as upper value guidelines in future project selection.

MANAGEMENT EFFECTS ON GROUND COVER CLUMPINESS: SCALING FROM FIELD TO SENTINEL-2 COVER ESTIMATES

Abstract. Significant progress has been made in the development of cover data and derived products based on remotely sensed fractional cover information and field data across Australia, and these cover data sets are now used for quantifying and monitoring grazing land condition. The availability of a dense time-series of nearly 30 years of cover data to describe the spatial and temporal patterns in landscape changes over time can help with monitoring the effectiveness of grazing land management practice change. With the advent of higher spatial resolution data, such as that provided by the Copernicus Sentinel 2 series of satellites, we can look beyond reporting purely on cover amount and more closely at the operational monitoring and reporting on spatial arrangement of cover and its links with land condition. We collected high spatial resolution cover transects at 20 cm intervals over the Wambiana grazing trials in the Burdekin catchment in Queensland, Australia. Spatial variance analysis was used to determine the cover autocorrelation at various support intervals. Coincident Sentinel-2 imagery was collected and processed over all the sites providing imagery to link with the field data. We show that the spatial arrangement and temporal dynamics of cover are important indicators of grazing land condition for both productivity and water quality outcomes. The metrics and products derived from this research will assist land managers to prioritize investment and practice change strategies for long term sustainability and improved water quality, particularly in the Great Barrier Reef catchments.

Avoiding Implementation Failure in Catchment Landscapes: A Case Study in Governance of the Great Barrier Reef.

Water quality outcomes affecting Australia's Great Barrier Reef (GBR) are governed by multi-level and multi-party decision-making that influences forested and agricultural landscapes. With international concern about the GBR's declining ecological health, this paper identifies and focuses on implementation failure (primarily at catchment scale) as a systemic risk within the overall GBR governance system. There has been limited integrated analysis of the full suite of governance subdomains that often envelop defined policies, programs and delivery activities that influence water quality in the GBR. We consider how the implementation of separate purpose-specific policies and programs at catchment scale operate against well-known, robust design concepts for integrated catchment governance. We find design concerns within ten important governance subdomains that operate within GBR catchments. At a whole-of-GBR scale, we find a weak policy focus on strengthening these delivery-oriented subdomains and on effort integration across these subdomains within catchments. These governance problems when combined may contribute to failure in the implementation of major national, state and local government policies focused on improving water quality in the GBR, a lesson relevant to landscapes globally.

Rainfall contributes ~ 30% of the dissolved inorganic nitrogen exported from a southern Great Barrier Reef river basin

A study was conducted to estimate how much of the annual load of dissolved inorganic nitrogen (DIN) from Great Barrier Reef (GBR) river basins could come from rainfall. Results suggest rainfall contributed ~37% of the average annual DIN load from the Fitzroy Basin over three wet seasons. Rainfall DIN contribution at plot to sub-catchment scale ranged from 5 to >100% for study sites in the Fitzroy and Pioneer Basins. An estimate using measured and modelled data indicates ~28% of the longer-term average annual DIN load from the entire GBR catchment may originate from rainfall. These estimates may affect current GBR management and water quality targets. Numerous studies predict increases in atmospheric nitrogen pollution from Asia via fossil fuel combustion and more frequent severe La Nina events via global warming. Future GBR rainfall chemistry data may be required for assessing catchment management outcomes and regional trends in atmospheric DIN deposition.

Setting ecologically relevant targets for river pollutant loads to meet marine water quality requirements for the Great Barrier Reef, Australia: A preliminary methodology and analysis

Loads of suspended sediment, nutrients and pesticides discharged to the Great Barrier Reef (GBR) have increased greatly due to agricultural and urban development of the GBR catchment. As a result, in association with climate change impacts, the ecosystems of the GBR have degraded greatly in recent decades, and the decline in ecosystem health continues. Improved agricultural management practices are now being funded to reverse the decline. However the quantum of reduction in contaminant loads from individual rivers needed to reverse the decline is not known. To estimate load reductions that would reverse the decline we developed what we term Ecologically Relevant Targets (ERTs). These targets are the load reductions of sediment, nutrients and pesticides needed such that GBR lagoonal waters meet the relevant water quality guidelines for the region. The methodology proposed for setting the ERTs is described and examples of ERTs set for the Burdekin Region of the GBR are given.