Terrestrial pollutant runoff to the Great Barrier Reef: An update of issues, priorities and management responses

The Great Barrier Reef (GBR) is a World Heritage Area and contains extensive areas of coral reef, seagrass meadows and fisheries resources. From adjacent catchments, numerous rivers discharge pollutants from agricultural, urban, mining and industrial activity. Pollutant sources have been identified and include suspended sediment from erosion in cattle grazing areas; nitrate from fertiliser application on crop lands; and herbicides from various land uses. The fate and effects of these pollutants in the receiving marine environment are relatively well understood. The Australian and Queensland Governments responded to the concerns of pollution of the GBR from catchment runoff with a plan to address this issue in 2003 (Reef Plan; updated 2009), incentive-based voluntary management initiatives in 2007 (Reef Rescue) and a State regulatory approach in 2009, the Reef Protection Package. This paper reviews new research relevant to the catchment to GBR continuum and evaluates the appropriateness of current management responses.     

Assessment of chemical water types and their spatial variation using multi-stage cluster analysis, Queensland, Australia

A multivariate assessment has been adapted to the classification of a large, irregular dataset of approximately 34,000 surface water samples accumulated over more than 30 years. A two-stage K-means clustering method was designed to analyse chemical data in the form of percentages of major ions (Na, Mg, Ca, Cl, HCO₃ and SO₄); the first stage of clustering produced 347 groups, which were then re-clustered to generate the final nine water types. The analysis enabled the definition of provinces of water composition and highlighted natural processes influencing the surface water chemistry. On a statewide basis, sodium is the dominant cation and around 50% at all stream flows, while proportions of calcium and magnesium are about equal. Chloride and bicarbonate constitute the bulk of anions present, while sulfate occurs occasionally and tends to be localised. On a global basis, Queensland surface waters are relatively high in sodium, chloride and magnesium, and low in calcium and sulfate. It was also found that the geographical location has a greater impact on major ion ratios than does the stage of stream flow.

The regional chemical trends are consistent with geology and climate. Streams in northeast Queensland, with short, steep catchments and high rainfall, yield low salinity, sodium-dominated water; this is also the case for sandy southern coastal catchments. Both also reflect an oceanic influence. The proportions of sodium and chloride decrease westward; streams draining the western side of the Great Dividing Range or flowing into the Gulf of Carpentaria have low salinity but relatively hard water. Streams in western Queensland are higher in calcium and bicarbonate. In the large catchments flowing from Queensland into central Australia, the water composition is highly variable, commonly with elevated sulfate. Also in Queensland, there are several other clearly definable water provinces such as the high magnesium waters of basaltic areas.

The findings of this study confirm that the application of such analytical methods can provide a useful assessment of controls over water composition and support management at regional level; the approach used is shown and are applicable to large, disparate datasets.     

Reactive trace element enrichment in a highly modified, tidally inundated acid sulfate soil wetland: East Trinity, Australia

This study examines the abundance of trace elements in surface sediments of a former acid sulfate soil (ASS) wetland subjected to marine tidal inundation. Sediment properties of this highly modified study site are compared with those of an adjacent unmodified, intertidal mangrove forest. Whilst some trace elements (Al, Cd, Mn, Ni and Zn) were clearly depleted due to mobilisation and leaching in the previous oxic-acidic phase, other trace elements (As and Cr) displayed significant enrichment in the tidally inundated ASS. Many trace elements were strongly associated with the reactive Fe and acid volatile sulfide (AVS) fractions, suggesting that trace elements may be adsorbed to abundant reactive Fe phases or sequestered as sulfide minerals. These findings provide an important understanding of the fate and mobility of reactive iron, AVS and trace elements during tidal remediation of a formerly acidified Great Barrier Reef (GBR) catchment.     

Blooms of the cyanobacterium Lyngbya majuscula in coastal Queensland, Australia: disparate sites, common factors

During the last decade there has been a significant rise in observations of blooms of the toxic cyanobacterium Lyngbya majuscula along the east coast of Queensland, Australia. Whether the increase in cyanobacterial abundance is a biological indicator of widespread water quality degradation or also a function of other environmental change is unknown. A bioassay approach was used to assesses the potential for runoff from various land uses to stimulate productivity of L. majuscula. In Moreton Bay, L. majuscula productivity was significantly (p<0.05) stimulated by soil extracts, which were high in phosphorus, iron and organic carbon. Productivity of L. majuscula from the Great Barrier Reef was also significantly (p<0.05) elevated by iron and phosphorus rich extracts, in this case seabird guano adjacent to the bloom site. Hence, it is possible that other L. majuscula blooms are a result of similar stimulating factors (iron, phosphorus and organic carbon), delivered through different mechanisms.     

Circulation in the Great Barrier Reef Lagoon using numerical tracers and in situ data

Numerical hydrodynamic models of the northeastern Queensland shelf, forced by regional winds and modelled boundary currents in the northern Coral Sea, are used to provide improved estimates of general flow trajectories and water residence times within the Great Barrier Reef (GBR) shelf system. Model performance was checked against a limited set of current metre records obtained at Lark Reef (16°S) and the Ribbon Reefs (15.5°S). Estimates of water parcel trajectories are derived from a series of numerical tracer experiments, with daily releases of neutrally buoyant, un-reactive particles at 320 sites along the coast between Cape York (10.7°S) and Hervey Bay (25°S). Flow trajectories and residence times for tracer particles introduced to the GBR lagoon in the southern—ca. 22°S, central—19°S, and northern reef—14°S are emphasised. For purposes of the analysis, the year was divided into two seasons based on mean alongshore current direction. Most coastal sourced tracers entering the central GBR lagoon between 16° and 20°S during the northward-current season (January–August) primarily encounter the outer-shelf reef matrix after exiting the lagoon at its northern “head” (nominally 16°S), after 50–150 days. Up to 70% of tracer particles entering in the southward-current season (August–December) eventually crossed the lagoon to the outer-shelf reef matrix, with median crossing times between 20 and 330 days. During favourable wind conditions, tracers introduced at the coast may move rapidly across the lagoon into the reef matrix. The tracer experiments indicate that most coastal-sourced tracers entering the GBR lagoon remain near the coast for extended periods of time, moving north and south in a coastal band. Residence times for conservative tracer particles (and implied residence times for water-borne materials) within the GBR shelf system ranged from ca. 1 month to 1 year—time frames that are very long relative to development times of planktonic larvae and cycling times for nutrient materials in the water column, implying they are transformed long before reaching the outer reef matrix.     

Large-scale pesticide monitoring across Great Barrier Reef catchments--Paddock to Reef Integrated Monitoring, Modelling and Reporting Program

The transport and potential toxicity of pesticides in Queensland (QLD) catchments from agricultural areas is a key concern for the Great Barrier Reef (GBR). In 2009, a pesticide monitoring program was established as part of the Australian and QLD Governments' Reef Plan (2009). Samples were collected at eight End of System sites (above the tidal zone) and three sub-catchment sites. At least two pesticides were detected at every site including insecticides, fungicides, herbicides, and the Reef Plan's (2009) five priority photosystem II (PSII) herbicides (diuron, atrazine, hexazinone, tebuthiuron and ametryn). Diuron, atrazine and metolachlor exceeded Australian and New Zealand water quality guideline trigger values (TVs) at eight sites. Accounting for PSII herbicide mixtures increased the estimated toxicity and led to larger exceedances of the TVs at more sites. This study demonstrates the widespread contamination of pesticides, particularly PSII herbicides, across the GBR catchment area which discharges to the GBR.     

Acid-base status of soils in groundwater discharge zones — relation to surface water acidification

Critical load calculations have suggested that groundwater at depth of 2 m in Sweden is very sensitive to acid load. As environmental isotope studies have shown that most of the runoff in streams has passed through the soil, there is a risk in the near future of accelerated acidification of surface waters.

To assess the importance of the last soil horizon of contact before discharge, the upper 0–0.2m of soils in seven discharge zones were analysed for pools of base cations, acidity and base saturation. The sites were about 3–4 m² in size and selected from two catchments exposed to different levels of acid deposition.

The soils in the seven sites had high concentrations of exchangeable base cations and consequently high base saturation. The high correlation (r² = 0.74) between base saturation in the soils of the discharge zones and mean pH of the runoff waters suggested that the discharge zone is important for surface water acidification. The high pool of exchangeable base cations will buffer initially against the acid load. As the cation exchange capacity (meq dm⁻³) and base saturation were lower in the sites from the catchment receiving lower deposition, these streams may be more vulnerable to acidification in the near future. The high concentration of base cations in non-exchangeable fractions may also buffer against acidification as it is likely that some of these pools will become exchangeable with time.     

The Effect of the Great Barrier Reef on the Propagation of the 2007 Solomon Islands Tsunami Recorded in Northeastern Australia

The effect of offshore coral reefs on the impact from a tsunami remains controversial. For example, field surveys after the 2004 Indian Ocean tsunami indicate that the energy of the tsunami was reduced by natural coral reef barriers in Sri Lanka, but there was no indication that coral reefs off Banda Aceh, Indonesia had any effect on the tsunami. In this paper, we investigate whether the Great Barrier Reef (GBR) offshore Queensland, Australia, may have weakened the tsunami impact from the 2007 Solomon Islands earthquake. The fault slip distribution of the 2007 Solomon Islands earthquake was firstly obtained by teleseismic inversion. The tsunami was then propagated to shallow water just offshore the coast by solving the linear shallow water equations using a staggered grid finite-difference method. We used a relatively high resolution (approximately 250 m) bathymetric grid for the region just off the coast containing the reef. The tsunami waveforms recorded at tide gauge stations along the Australian coast were then compared to the results from the tsunami simulation when using both the realistic 250 m resolution bathymetry and with two grids having fictitious bathymetry: One in which the the GBR has been replaced by a smooth interpolation from depths outside the GBR to the coast (the “No GBR” grid), and one in which the GBR has been replaced by a flat plane at a depth equal to the mean water depth of the GBR (the “Average GBR” grid). From the comparison between the synthetic waveforms both with and without the Great Barrier Reef, we found that the Great Barrier Reef significantly weakened the tsunami impact. According to our model, the coral reefs delayed the tsunami arrival time by 5–10 minutes, decreased the amplitude of the first tsunami pulse to half or less, and lengthened the period of the tsunami.     

Estimates of sediment and nutrient loads in 10 major catchments draining to the Great Barrier Reef during 2006-2009

The Great Barrier Reef (GBR) catchment area has been monitored simultaneously for sediment and nutrient exports from 10 priority catchments discharging into the GBR lagoon between 2006 and 2009. This allows GBR catchment-wide exports to be estimated and spatially compared within a discrete time-frame. Elevated levels of sediment and nutrient exports were recorded in all monitored catchments as compared to pre-European estimates, but vary around previous estimates of mean annual loads. During the period of monitoring, the Burdekin and Fitzroy catchments contributed the highest sediment and nutrient exports, however when loads were normalised for area, these catchments produced the lowest unit yields. In contrast, the highest yields were produced in the wetter and proportionately more intensively cultivated Johnstone, O'Connell, and Pioneer catchments particularly for dissolved nitrogens. This assessment offers the necessary scientific foundation for future monitoring, assessment, and management of sediment and nutrient loads entering the GBR.     

Export of Acidity in Drainage Water from Acid Sulphate Soils

Disturbed acid sulphate soils are potent sources of acidity in coastal waterways. Monitoring studies of the drainage water for sites at East Trinity, Cairns and Pimpama, south-east Queensland indicate that considerable acidity is found in the drainage water from these sites. Hydrogen (H⁺), ferrous (Fe²⁺) and aluminium (Al) ions are the dominant acid cations involved. When drainage water is mixed with fresh or marine waters the effect of H⁺ on acidity generation is immediate. Aluminium can release acidity on hydrolysis, while the oxidation of Fe²⁺ to Fe³⁺ both acidifies and removes dissolved oxygen from the water. Strongly acidic waters with low levels of dissolved oxygen concentration are undesirable for most forms of aquatic life. Export of acidity from acid sulphate soil is likely to have a major effect on inshore fisheries and breeding grounds especially in periods of flood following drought or periods of low rainfall, where large volumes of acidity can be flushed/leached into sensitive aquatic/marine habitats. Impacts may include low dissolved oxygen, fish kills, epizootic ulceration syndrome and damage to oysters. During the processes of oxidation and hydrolysis, iron and aluminium flocs form, that can smother benthic communities. Heavy metals are found in the drainage water at elevated levels and may also be of concern for aquatic organisms. Chronic effects such as habitat degradation, mortality of marine worms, bivalves, invasion of acid tolerant species (both plant and animal) and avoidance of habitat have been documented elsewhere. These areas require further research.     

Inter-annual variability of wet season freshwater plume extent into the Great Barrier Reef lagoon based on satellite coastal ocean colour observations

Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the Great Barrier Reef (GBR) lagoon and connect the land with the receiving coastal and marine waters. Knowledge of the variability of the freshwater extent into the GBR lagoon is relevant for marine park management to develop strategies for improving ecosystem health and risk assessments. In this study, freshwater extent has been estimated for the entire GBR lagoon area from daily satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2010. To enable a reliable mapping of freshwater plumes we applied a physics-based coastal ocean colour algorithm, that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM), from which we used CDOM as a surrogate for salinity (S) for mapping the freshwater extent.     

The influence of a season of extreme wet weather events on exposure of the World Heritage Area Great Barrier Reef to pesticides

The 2010-2011 wet season was one of extreme weather for the State of Queensland, Australia. Major rivers adjacent to the Great Barrier Reef (GBR) were discharging at rates 1.5 to >3 times higher than their long term median. Exposure to photosystem II herbicides has been routinely monitored over a period of up to 5 years at 12 inshore GBR sites. The influence of this wet season on exposure to photosystem II herbicides was examined in the context of this long-term monitoring record and during flood plume events in specific regions. Median exposures expressed as diuron equivalent concentration were an average factor of 2.3 times higher but mostly not significantly different (p<0.05) to the median for the long-term monitoring record. The herbicides metolachlor and tebuthiuron were frequently detected in flood plume waters at concentrations that reached or exceeded relevant water quality guidelines (by up to 4.5 times).     

Health of the coral reefs at the US Navy Base,Guantánamo Bay,Cuba: A preliminary report based on isotopic records from gorgonians

Specimens of the gorgonian Plexaura homomalla were sampled from several areas along the fringing reefs fronting the United States Naval Base at Guantánamo Bay, Cuba. Sample coverage extended from apparently healthy reefs in oceanic waters to declining reefs located in the plume of the drainage from upper parts of Guantánamo Bay. Tentacle tips were excised, and trunk sections were cut and polished. Stable isotope ratios of nitrogen (δ¹⁵N) and carbon indicate a strong correlation of reef health with proximity to the plume of the river.     

The effect of Marmara (Izmit) Earthquake on the chemical oceanography of Izmit Bay,Turkey

After the Marmara (Izmit) Earthquake (magnitude 7.4) on 17 August 1999, chemical oceanographical characteristics of Izmit Bay were investigated in order to examine the possible effects of the refinery fire and uncontrolled entrance of domestic wastes to the surface waters. The dissolved oxygen (DO) content of the water column in August 1999 was the lowest value of all the measurement periods. It was found to be lower than the detection limit of the method (0.03 mgl(-1)) in the lower layer of eastern and central basins of the Bay, whereas the dissolved hydrogen sulfide (DHS) values were high, varying between 0.14 and 1.28 mgl(-1). The deficiency of DO and in turn formation of DHS were caused by the spreading petroleum from the refinery fire onto the sea surface and waste loads from the damaged municipal waste effluent system. The increasing organic/inorganic loads into the Bay stimulated the phytoplankton blooms which cause locally saturated DO concentrations in the eastern basin during autumn 1999. DO concentrations increased in lower layer waters during winter, whilst DHS formation disappeared when water originating from the Marmara Sea replenish the water column of Izmit Bay. However, DHS formation established again in August 2000.     

Reflectance spectral characterization and mineralogy of acid sulphate soil in subsurface using hypcrspectral data

Acid sulphate soil（ASS） is a kind of soil which is harmful to the environment.ASS is hard to efficiently assess efficiently in the subsurface,although it is detectable on the surface by remote sensing.This paper aims to explore a new way to rapidly assess ASS in the subsurface by introducing a proximal hyperspectral instrument,namely the HyloggerTM system which can rapidly scan soil cores and provide high resolution hyperspectral data.Some minerals in ASS,which usually act as indicators of the severity of ASS,such as iron oxides,hydroxides,and sulphates,as well as some clay minerals,such as kaolinite,have diagnostic spectral absorption features in the reflectance spectral range（400-2500 nm）.Soil cores were collected from a study area and hyperspectral data were acquired by HyloggerTM scanning.The main minerals related to ASS were characterized spectrally,and were subsequently identified and mapped in the soil cores based on their reflectance spectral characteristics.Traditional X-ray diffraction（XRD） and scanning electron microscope（SEM） were also applied to verify the results of the mineral identification.The main results of this study include the spectral characterisation of ASS and its main compositional minerals,as well as the distribution of these relevant minerals in different depth of cores.     

In the other 90%: phytoplankton responses to enhanced nutrient availability in the Great Barrier Reef Lagoon

Our view of how water quality effects ecosystems of the Great Barrier Reef (GBR) is largely framed by observed or expected responses of large benthic organisms (corals, algae, seagrasses) to enhanced levels of dissolved nutrients, sediments and other pollutants in reef waters. In the case of nutrients, however, benthic organisms and communities are largely responding to materials which have cycled through and been transformed by pelagic communities dominated by micro-algae (phytoplankton), protozoa, flagellates and bacteria. Because GBR waters are characterised by high ambient light intensities and water temperatures, inputs of nutrients from both internal and external sources are rapidly taken up and converted to organic matter in inter-reefal waters. Phytoplankton growth, pelagic grazing and remineralisation rates are very rapid. Dominant phytoplankton species in GBR waters have in situ growth rates which range from approximately 1 to several doublings per day. To a first approximation, phytoplankton communities and their constituent nutrient content turn over on a daily basis. Relative abundances of dissolved nutrient species strongly indicate N limitation of new biomass formation. Direct ((15)N) and indirect ((14)C) estimates of N demand by phytoplankton indicate dissolved inorganic N pools have turnover times on the order of hours to days. Turnover times for inorganic phosphorus in the water column range from hours to weeks. Because of the rapid assimilation of nutrients by plankton communities, biological responses in benthic communities to changed water quality are more likely driven (at several ecological levels) by organic matter derived from pelagic primary production than by dissolved nutrient stocks alone.     

Towards environmental management of water turbidity within open coastal waters of the Great Barrier Reef

Water turbidity and suspended sediment concentration (SSC) are commonly used as part of marine monitoring and water quality plans. Current management plans utilise threshold SSC values derived from mean-annual turbidity concentrations. Little published work documents typical ranges of turbidity for reefs within open coastal waters. Here, time-series turbidity measurements from 61 sites in the Great Barrier Reef (GBR) and Moreton Bay, Australia, are presented as turbidity exceedance curves and derivatives. This contributes to the understanding of turbidity and SSC in the context of environmental management in open-coastal reef environments. Exceedance results indicate strong spatial and temporal variability in water turbidity across inter/intraregional scales. The highest turbidity across 61 sites, at 50% exceedance (T₅₀) is 15.3 NTU and at 90% exceedance (T₉₀) 4.1 NTU. Mean/median turbidity comparisons show strong differences between the two, consistent with a strongly skewed turbidity regime. Results may contribute towards promoting refinement of water quality management protocols.     

Distribution and origin of biologically available phosphorus in the water of the Meiliang Bay in summer

The investigation and continuous monitoring with an innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) on the concentrations of biologically available phosphorus (BAP) were conducted in the Meiliang Bay of the Taihu Lake during summer in 2004. The results showed that the concentrations of dissolved (FeO-DP), particulate (FeO-PP) and total bioavailable phosphorus (FeO-P) had similar horizontal distribution. The BAP concentrations were the highest in those estuaries in the northern bay. With the decrease of the distance to the estuary or long shore, there was little difference between BAP concentrations in an open lake area. During the observation period, algal blooms occurred in most waters of the northern bay, which was reflected from the high concentrations of chlorophyll a (Chl-a). While they were not highest in the estuarine waters of those major rivers, this is the case for the BAP concentrations. The concentrations of Chl-a had a significantly positive correlation with those of bioavailable phosphorus in the open area of the Meiliang Bay. With the sediment resuspension induced by wind and wave, BAP concentrations increased in a short-term, indicating that the riverine P inputs mainly contribute to the concentrations of BAP in the estuarine water while internal P release was the major source of BAP in the open lake area. In the eutrophic shallow lake, the blooms of alga may cause pH increase and further result in internal P release. The above results showed that the new membrane of FeO/CAM can be used to monitor the concentrations of BAP and provide the scientific justifications for the control strategy of the lake eu-trophication.     

Mobilisation and transport of dissolved organic carbon and iron in peat catchments—Insights from the Lehstenbach stream in Germany using generalised additive models

During the last decades, increasing exports of both dissolved organic carbon (DOC) and iron were observed from peat catchments in North America and Europe with potential consequences for water quality of streamwater and carbon storages of soils. As mobilisation and transport processes of DOC and iron in peat catchments are only partly understood, the purpose of this study was to elucidate these processes in an intensively monitored and studied system. Specifically, it was hypothesised that dissimilatory iron reduction in riparian peatland soils mobilises DOC initially adsorbed to iron minerals. During stormflow conditions, both DOC and iron will be transported into the stream network. Ferrous iron may be reoxidised at redox interfaces on its way to the stream, and subsequently, ferric iron could be transported together with DOC as complexes. To test these hypotheses, generalised additive models (GAMs) were applied to 14 years of weekly time series of discharge and concentrations of selected solutes measured in a German headwater stream called Lehstenbach. This stream drains a 4.19‐km² forested mountain catchment; one third of which is covered by riparian peatland soils. We interpreted results of different types of GAM in the way that (a) iron reduction drove the mobilisation of DOC from peatland soils and that (b) both iron and DOC were transported as complexes after their joint mobilisation to and within the steam. It was speculated that low nitrate availability in the uppermost wetland soil layer, particularly during the growing season, promoted iron reduction and thus the mobilisation of DOC. However, the influence of nitrate on the DOC mobilisation remains relatively uncertain. This influence could be further investigated using methods similar to the GAM analysis conducted here for other catchments with long‐term data as well as detailed measurements of the relevant species in riparian wetland soils and the adjacent stream network.