Great Barrier Reef Water Quality Research Articles

Modelling buoyancy-driven vertical movement of Trichodesmium application in the Great Barrier Reef

Trichodesmium cells aggregate and form single trichomes or larger colonies and possess strong intracellular gas vesicles that generate strong positive buoyancy and facilitate the vertical migration of colonies. Trichodesmium is proposed to be an important source of nitrogen in the Great Barrier Reef (GBR) with implications for nutrient cycling and eutrophication. To understand the dynamics of Trichodesmium in the GBR ecosystem, reliable model predictions of Trichodesmium growth, nitrogen fixation and distribution are required. The sinking rates of Trichodesmium colonies have been reported to be dependent on the shape and size of colonies, and the orientation of colonies in seawater. Therefore, to better simulate the vertical movement of Trichodesmium in the GBR, and subsequent biogeochemical dynamics, the Trichodesmium processes in the eReefs biogeochemical model was modified by applying the form resistance factor to the sinking velocities of tuft-shaped Trichodesmium colonies. Our model results compare well with observations from the Australian Institute of Marine Science Marine Monitoring Program sensor network sites and capture the emergent patterns of phytoplankton size spectrum observed in nature. The modified model formulations improve the physiological realism of the Trichodesmium growth submodel of the eReefs marine biogeochemical models, and can help to improve the understanding of Trichodesmium dynamics for effective GBR water quality management.

The effect of catchment load reductions on water quality in the crown-of-thorn starfish outbreak initiation zone

Crown-of-Thorns Starfish (CoTS) population outbreaks contribute to coral cover decline on Indo-Pacific reefs. On the Great Barrier Reef (GBR), enhanced catchment nutrient loads are hypothesised to increase phytoplankton food for CoTS larvae in the outbreak initiation zone. This study examines whether catchment load reductions will improve water quality in this zone during the larval period. We defined the i) initiation zone's spatial extent; ii) larval stage's temporal extent; and iii) water quality thresholds related to larval food, from published information. We applied these to model simulations, developed to quantify the effect of catchment load reductions on GBR water quality (Baird et al., 2021), and found a consistently weak response of chlorophyll-a, total organic nitrogen and large zooplankton concentrations in the initiation zone. Model results indicate marine and atmospheric forcing are more likely to control the planktonic biomass in this zone, even during major flooding events purported to precede CoTS outbreaks.

Meteorological Satellite Observations Reveal Diurnal Exceedance of Water Quality Guideline Thresholds in the Coastal Great Barrier Reef

The Great Barrier Reef (GBR) is a marine protected area subject to natural and anthropogenic disturbances. Water quality is critical for the health and protecting resilience of GBR coral ecosystems against the synergistic and cumulative pressures of tropical cyclones, marine heat waves, and outbreaks of crown-of-thorns starfish. The concentration of Total Suspended Solids (TSS) is a key water quality parameter measured at multiple spatio-temporal scales from in situ probes to satellite observations. High TSS concentrations can adversely impact coral and seagrasses on the inshore GBR. We present diurnal TSS derived from Himawari-8 Geostationary satellite observations at 10 min frequency and demonstrate its applicability for improved monitoring of GBR water quality. Diurnal TSS obtained from Himawari-8 observations were compared to TSS computed from in situ bio-optical measurements at the Lucinda Jetty Coastal Observatory (LJCO). The coastal waters at LJCO experience diurnal variability of TSS (~7 mg L−1), where magnitude peaks followed the slack tides, and the largest diurnal changes were associated with freshwater discharge residuals from the wet season. Exceedance maps revealed that TSS is above guideline thresholds in the open coastal and mid-shelf waters for ~60% of the valid monthly observations, including during dry season months.

EReefs modelling suggests Trichodesmium may be a major nitrogen source in the Great Barrier Reef

Trichodesmium can fix nitrogen that is later released into the water column. This process may be a major source of ‘new’ nitrogen in the Great Barrier Reef (GBR), but to date this contribution is poorly resolved. We have estimated the seasonal, spatial and annual contributions of Trichodesmium to the annual nitrogen budget of the GBR using the eReefs marine models. Models were run for the interval December 2010 to November 2012. During this period La Niña conditions produced record rainfalls and widespread flooding of GBR catchments. Model outputs suggest nitrogen fixation by Trichodesmium in the GBR (which covers about 348,000 km2) contributes approximately 0.5 MT/yr, exceeding the total average annual riverine nitrogen loads (0.05–0.08 MT/yr). Nitrogen fixation loads are exceeded by riverine loads only if the comparison is restricted to inshore waters and during the wet season. The river pollution is likely to have impacts in freshwater wetlands, mangroves, seagrasses and in-shore coral reefs; while Trichodesmium blooms are likely to be less intense but more widespread and affect offshore coral reefs and other oceanic ecosystems. Phosphorus and iron are suggested to be potential drivers of Trichodesmium growth and nitrogen fixation. This result is provisional but reinforces the need for more detailed assessment and reliable quantification of the annual nitrogen contribution from nitrogen fixation in the GBR and other coastal waters. Such advances will improve understandings of the role of terrestrial nitrogen loads in the GBR and of terrestrial phosphorus and iron loads which can modulate Trichodesmium abundance. These findings will help to broaden the focus of water quality management programmes and support management to improve GBR water quality.

A benthic light index of water quality in the Great Barrier Reef, Australia

Good water quality is essential to the health of marine ecosystems, yet current metrics used to track water quality in the Great Barrier Reef are not strongly tied to ecological outcomes. There is a need for a better water quality index (WQI). Benthic irradiance, the amount of light reaching the seafloor, is critical for coral and seagrass health and is strongly affected by water quality. It therefore represents a strong candidate for use as a water quality indicator. Here, we introduce a new index based on remote sensing benthic light (bPAR) from ocean color. Resulting bPAR index timeseries, based on the extent to which the observed bPAR fell short of the locally- and seasonally-specific optimum, showed strong spatial and temporal variability, which was consistent with the dynamics that govern changes in water clarity in the Great Barrier Reef. Our new index is ecologically relevant, responsive to changes in light availability and provides a robust metric that may complement current Great Barrier Reef water quality metrics.

Impact of catchment-derived nutrients and sediments on marine water quality on the Great Barrier Reef: An application of the eReefs marine modelling system

Water quality of the Great Barrier Reef (GBR) is determined by a range of natural and anthropogenic drivers that are resolved in the eReefs coupled hydrodynamic - biogeochemical marine model forced by a process-based catchment model, GBR Dynamic SedNet. Model simulations presented here quantify the impact of anthropogenic catchment loads of sediments and nutrients on a range of marine water quality variables. Simulations of 2011–2018 show that reduction of anthropogenic catchment loads results in improved water quality, especially within river plumes. Within the 16 resolved river plumes, anthropogenic loads increased chlorophyll concentration by 0.10 (0.02–0.25) mg Chl m−3. Reductions of anthropogenic loads following proposed Reef 2050 Water Quality Improvement Plan targets reduced chlorophyll concentration in the plumes by 0.04 (0.01–0.10) mg Chl m−3. Our simulations demonstrate the impact of anthropogenic loads on GBR water quality and quantify the benefits of improved catchment management.

Solutes in runoff under simulated rainfall on fertilised sugarcane (Saccharum sp.) beds: Measurements and results

Wet Tropics region is ranked as the highest relative risk to Great Barrier Reef water quality with improved nitrogen management as priority. Sugarcane is a major crop in Wet Tropics and contributes 84 % of estimated anthropogenic dissolved inorganic nitrogen (DIN). Experiments were undertaken using a rainfall simulator (rate ≈ 90 mm h−1, depth 48–67 mm) to measure solute amounts lost in runoff from raised beds planted with sugarcane on bare soil. Eighteen experimental plots, were constructed with a thin metal walls. Runoff was collected from 18 plots (1 m wide x 1.7 m long), plots were covered with shelters between simulations. Six plots had surface-applied fertiliser, six plots buried (subsurface) fertiliser in a band at 50–150 mm depth along the middle of plots, and a further six plots received no fertiliser. Fertiliser (Nitrophoska® Special) was applied at an equivalent rate of 46 kg-N ha−1 (ammonium at 19 kg-N ha−1 and nitrate at 27 kg-N ha−1), 20 kg-P ha−1 phosphate, 54 kg-K ha−1 potassium and 31 kg-S ha−1 sulfate.Two plots from each fertiliser treatment rained upon 7, 20 and 55 days after fertiliser was applied (DAF). Two fertilised treatment plots were re-rained upon on 20 and 55 DAF and another two fertilised plots were re-rained upon a third time on 55 DAF.No effect on runoff volume occurred when all treatments are included in analysis. On plots with repeated rainfall simulations, time to commencement of runoff decreased from rainfall simulation 1–2, no further decrease occurred.Runoff nitrogen load was dominated by particulate nitrogen with: > 75 % for all fertiliser treatments and > 90 % for no fertiliser treatment. DIN concentration was dominated by nitrate and nitrite (NOx-N) except for the first rainfall simulation on surface-applied fertiliser plots. Ammonia comprised more of the DIN in surface compared to subsurface treatment.Evaporative concentration resulted in no difference in NOx-N load between fertiliser treatments. Subsurface fertiliser placement did reduce ammonium concentration by 74 % and 90 % compared to surface applied fertiliser.Phosphorus in runoff was dominated by particulate phosphorus being > 95 %. Subsurface application of fertiliser reduced phosphorus load in runoff from 0.9 to 0.14 kg ha−1. Eighty-one% of applied surface sulfate was lost in runoff compared to 20 % of subsurface-applied fertiliser.Results highlighted the importance of particulate nitrogen and phosphorus in runoff and suggested that evaporative concentration of nitrogen can occur at the surface between rainfall events.

Adoption of agricultural management for Great Barrier Reef water quality improvement in heterogeneous farming communities

There is growing recognition that coastal water quality is interdependent with agricultural management in coastal catchments. Economic-incentive-based instruments can be used to internalize the negative externalities from coastal water pollution. Bio-physical and socio-economic heterogeneity across farms is expected to be an important factor in explaining differing rates of adoption of management practices. This paper hypothesises that: i) different types of farmers are likely to respond differently to incentive payments that promote the adoption of management practices for Great Barrier Reef water quality improvement, and ii) if policy makers account for heterogeneity, cost-effectiveness of incentive payments will increase. Results show that if government paid farmers 100% of the transition costs of moving from their current practices to improved practices, and given current technologies, water quality improvement for the case-study region would be approximately 56% (measured as a reduction of dissolved organic nitrogen at the end of river). Total costs for the region would be almost AU$ 30 M over the planning horizon of one cropping cycle of 6 years. Results furthermore show that as the policy seeks more ambitious land-use changes, from common practice to improved practice to aspirational practice, the public cost of incentive payments increase at an exponential rate. Larger farms make the shift sooner as they are able to offset fixed investments against increased revenues over greater areas.

Water Quality and River Plume Monitoring in the Great Barrier Reef: An Overview of Methods Based on Ocean Colour Satellite Data

A strong driver of water quality change in the Great Barrier Reef (GBR) is the pulsed or intermittent nature of terrestrial inputs into the GBR lagoon, including delivery of increased loads of sediments, nutrients, and toxicants via flood river plumes (hereafter river plumes) during the wet season. Cumulative pressures from extreme weather with a high frequency of large scale flooding in recent years has been linked to the large scale reported decline in the health of inshore seagrass systems and coral reefs in the central areas of the GBR, with concerns for the recovery potential of these impacted ecosystems. Management authorities currently rely on remotely-sensed (RS) and in situ data for water quality monitoring to guide their assessment of water quality conditions in the GBR. The use of remotely-sensed satellite products provides a quantitative and accessible tool for scientists and managers. These products, coupled with in situ data, and more recently modelled data, are valuable for quantifying the influence of river plumes on seagrass and coral reef habitat in the GBR. This article reviews recent remote sensing techniques developed to monitor river plumes and water quality in the GBR. We also discuss emerging research that integrates hydrodynamic models with remote sensing and in situ data, enabling us to explore impacts of different catchment management strategies on GBR water quality.

A Paddock to reef monitoring and modelling framework for the Great Barrier Reef: Paddock and catchment component

Targets for improvements in water quality entering the Great Barrier Reef (GBR) have been set through the Reef Water Quality Protection Plan (Reef Plan). To measure and report on progress towards the targets set a program has been established that combines monitoring and modelling at paddock through to catchment and reef scales; the Paddock to Reef Integrated Monitoring, Modelling and Reporting Program (Paddock to Reef Program). This program aims to provide evidence of links between land management activities, water quality and reef health. Five lines of evidence are used: the effectiveness of management practices to improve water quality; the prevalence of management practice adoption and change in catchment indicators; long-term monitoring of catchment water quality; paddock & catchment modelling to provide a relative assessment of progress towards meeting targets; and finally marine monitoring of GBR water quality and reef ecosystem health. This paper outlines the first four lines of evidence.

Towards ecologically relevant targets for river pollutant loads to the Great Barrier Reef

Degradation of coastal ecosystems in the Great Barrier Reef (GBR), Australia, has been linked with a decline in water quality from land-based runoff. This paper examines the reduction in current end-of-catchment loads required for total suspended solids (TSS) and dissolved inorganic nitrogen (DIN) to achieve GBR water quality guidelines. Based on first-order estimates of sustainable pollutant loads, current TSS and DIN loads would need to be reduced by approximately 7000ktons/y (41%) and 6000tons/y (38%), respectively. Next, these estimated reductions for TSS and DIN are compared with Reef Plan targets for anthropogenic sediment (−20% by 2020) and nitrogen (−50% by 2013) loads. If successful, these targets will accomplish approximately 40% of TSS and 92% of DIN load reductions required to achieve sustainable loads to the GBR lagoon. These first-order estimates elucidate the need to establish ecologically relevant targets for river pollutant loads to the GBR for management and policy.

New Regionalism and Planning for Water Quality Improvement in the Great Barrier Reef, Australia

AbstractNew regionalism encompasses a diversity of approaches to address regional planning problems. Within Australia, the Great Barrier Reef Water Quality Protection Plan was developed to enhance water quality within the World Heritage‐listed Great Barrier Reef, and the plan gave responsibility to regional, natural resource management bodies to undertake several actions. This paper evaluates these initiatives in the light of the emerging theory of new regionalism and highlights six main lessons: up‐scaling of the catchment approach to a reef‐wide approach is essential in order to improve water quality, but must be complemented by cross‐regional collaboration; new governance and institutional arrangements and strengthened partnerships must be effectively integrated; culture and history are important in determining the most effective management approaches; pilot projects must move to comprehensive and strategic implementation; science is important but needs to incorporate other branches of knowledge; and economic incentives are important in encouraging the implementation of best practices, but delivery needs to be flexible. We conclude that the new regional approach is appropriate for addressing complex, multi‐scale problems such as water quality, and has incorporated several key principles of new regionalism, but that the process must move quickly to a higher level of commitment and application.

Agricultural lands are hot-spots for annual runoff polluting the southern Great Barrier Reef lagoon

The world’s largest coral reef ecosystem, the Great Barrier Reef (GBR), continues to be degraded from land-based pollution. Information about the source of pollutants is critical for catchment management to improve GBR water quality. We report here on an 11-year source to sea study of pollutant delivery in runoff from the Fitzroy River Basin (FRB), the largest GBR catchment. An innovative technique that relates land use to pollutant generation is presented. Study results indicate that maximum pollutant concentrations at basin and sub-catchment scales are closely related to the percentage area of croplands receiving heavy rain. However, grazing lands contribute the majority of the long-term average annual load of most common pollutants. Findings suggest improved land management targets, rather than water quality targets should be implemented to reduce GBR pollution. This study provides a substantial contribution to the knowledge base for the targeted management of pollution ‘hot-spots’ to improve GBR water quality.

Target setting for pollutant discharge management of rivers in the Great Barrier Reef catchment area

Water Quality Improvement Plans (WQIPs) are being developed for individual river basins on the Great Barrier Reef (GBR) catchment associated with the GBR Water Quality Protection Plan. Within each WQIP, marine ecosystem targets are linked to end-of-river pollutant (suspended sediments, nutrients and pesticides) load targets and to farm level management practice targets. The targets are linked through quantitative models; e.g. one model connects GBR chlorophyll concentrations (marine target) to end-of-river nitrate loads, a second connects the end-of-river nitrate loads to fertiliser management targets in the catchment, whereas a third model links fertiliser application to nitrate loss at the farm scale. The difficulties of applying these linked models to derive credible and practical management targets are great, given the high degree of uncertainty in each model. Our understanding of the generation of suspended sediments, nutrients and pesticides in catchments and the relationship to on-farm management, the transport of these materials to the ocean, their transport in coastal waters and their effects on marine ecosystems is incomplete. The challenge is to produce estimates from the models, with known levels of uncertainty, but robust enough for management purposes. Case studies from the Tully–Murray basin and the Burdekin basin in north Queensland are discussed.

Catchment management and health of coastal ecosystems: synthesis and future research

Globally, many coastal ecosystems are threatened by a decline in water quality from land-based runoff. However, dynamic and complex biophysical and socioeconomic interdependencies often hamper the reversal of this decline in water quality. This Special Issue illustrates an integrated approach to address deteriorating water quality from land-based runoff in the Tully basin to the Great Barrier Reef (GBR), Australia. Nitrate was identified as the key pollutant, and was mainly derived from sugarcane and banana farms. To achieve GBR water quality targets for chlorophyll a, the dissolved inorganic nitrogen (DIN) load needs to be reduced by at least 80%. Modelling shows that financially beneficial changes to management of sugarcane results in a 50% reduction in DIN load. However, larger reductions would come at a significant cost. An adaptive approach is proposed as a framework to assess (i) the efficacy of implementing the recommended management practices, and (ii) progress against set targets. Quantification of linkages between catchment management and coastal ecosystem health will help inform management strategies based on ecosystem performance measures. Verification of the efficacy of existing and exploration of innovative management strategies, as well as spatial and temporal prioritisation of their implementation, remain critical to achieve coastal ecosystem rehabilitation, including water quality improvement.

Assessment of the Water Quality and Ecosystem Health of the Great Barrier Reef (Australia): Conceptual Models

Run-off containing increased concentrations of sediment, nutrients, and pesticides from land-based anthropogenic activities is a significant influence on water quality and the ecologic conditions of nearshore areas of the Great Barrier Reef World Heritage Area, Australia. The potential and actual impacts of increased pollutant concentrations range from bioaccumulation of contaminants and decreased photosynthetic capacity to major shifts in community structure and health of mangrove, coral reef, and seagrass ecosystems. A detailed conceptual model underpins and illustrates the links between the main anthropogenic pressures or threats (dry-land cattle grazing and intensive sugar cane cropping) and the production of key contaminants or stressors of Great Barrier Reef water quality. The conceptual model also includes longer-term threats to Great Barrier Reef water quality and ecosystem health, such as global climate change, that will potentially confound direct model interrelationships. The model recognises that system-specific attributes, such as monsoonal wind direction, rainfall intensity, and flood plume residence times, will act as system filters to modify the effects of any water-quality system stressor. The model also summarises key ecosystem responses in ecosystem health that can be monitored through indicators at catchment, riverine, and marine scales. Selected indicators include riverine and marine water quality, inshore coral reef and seagrass status, and biota pollutant burdens. These indicators have been adopted as components of a long-term monitoring program to enable assessment of the effectiveness of change in catchment-management practices in improving Great Barrier Reef (and adjacent catchment) water quality under the Queensland and Australian Governments' Reef Water Quality Protection Plan.

Great News for the Great Barrier Reef: Tully River Water Quality

A prerequisite for meaningful environmental legislation is that it be based upon an adequate scientific understanding of the natural system to which it is applied. In 2003, the Australian Commonwealth and Queensland State governments introduced a Reef Water Quality Protection Plan, which aimed to “improve” water quality in river catchments adjacent to the Great Barrier Reef (GBR) and in nearby coastal waters. The Plan was introduced in the absence of any substantive evidence for regional degradation of GBR water quality. This paper reviews the available data regarding nutrient contents in the Tully River, north Queensland, which is cited as the best (available) evidence for human-related changes in nutrient export from (GBR) catchments [1]. It is shown that the claim of human-related nutrient enrichment in the Tully River, and regionally, is without substance. No detectable trends in GBR water quality have occurred since systematic measurements were first started in the 1980s. Environmental policies that are based on mischievous claims of chimerical damage to the Great Barrier Reef damage the reputation of science as a tool for disinterested analysis, and provoke widespread cynicism in the community regarding the integrity of contemporary environmental politics.

Policy options for Great Barrier Reef water quality

Ecological Management & RestorationVolume 6, Issue 2 p. 134-136 Policy options for Great Barrier Reef water quality Ben Jacobsen, Ben JacobsenSearch for more papers by this author Ben Jacobsen, Ben JacobsenSearch for more papers by this author First published: 30 June 2005 https://doi.org/10.1111/j.1442-8903.2005.230-2.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume6, Issue2August 2005Pages 134-136 RelatedInformation

Adaptive management and its role in managing Great Barrier Reef water quality

Adaptive management is the pathway to effective conservation, use and management of Australia’s coastal catchments and waterways. While the concepts of adaptive management are not new, applications involving both assessment and management responses are indeed limited at the national and regional scales. This paper outlines the components of a systematic framework for linking scientific knowledge, existing tools, planning approaches and participatory processes to achieve healthy regional partnerships between community, industry, government agencies and science providers to overcome institutional barriers and uncoordinated monitoring. The framework developed by the Coastal CRC ( www.coastal.crc.org.au/amf/amf_index.htm) is hierarchical in the way it displays information to allow associated frameworks to be integrated, and represents a construct in which processes, information, decision tools and outcomes are brought together in a structured and transparent way for adaptive catchment and coastal management. This paper proposes how an adaptive management approach could be used to benefit the implementation of the Reef Water Quality Protection Plan (RWQPP).