Catchment to Reef: water quality issues in the Great Barrier Reef Region--an overview of papers

Nitrate dynamics in groundwater under sugarcane in a wet-tropics catchment

The transport of nitrogen (N) to groundwater and surface water in the form of nitrate (NO₃^-), as a by-product of the application of N-rich fertilisers, has been studied extensively. Yet, in the catchments adjacent to the Great Barrier Reef (GBR) in tropical north Queensland, Australia, NO₃^- transport in groundwater is not regularly monitored. An assessment of groundwater chemistry in the Liverpool Creek catchment of Queensland's wet-tropics region was conducted by regular sampling and analysis of groundwater over 12 months, through wet and dry seasons. A distinct spatial variability in groundwater chemistry was observed; groundwater aquifers with very low dissolved oxygen (DO) and NO₃^- consistently displayed relatively higher concentrations of sulphate (SO₄^2-), sulphur (S^2-) and ferrous iron (Fe²⁺) and low concentrations of dissolved organic carbon (DOC) (<2 ppm). Combined with averaged measured redox potential (Eh) of <250 mV, this indicates certain regions of the catchment have conditions favourable for removal of NO₃^- via autotrophic denitrification (DN), while other groundwater aquifers retained NO₃^– concentrations just above the acceptable trigger limits defined in regional water quality guidelines. Observations indicate that the naturally heterogeneous structure of the coastal alluvium contributes to the distinct variability in groundwater chemistry over small distances, with NO₃^- concentrations influenced by a combination of DN, lateral shallow drainage and potential adsorption to clay surfaces within the alluvial sediments.

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.

A multi-omics based ecological analysis of coastal marine sediments from Gladstone, in Australia's Central Queensland, and Heron Island, a nearby fringing platform reef

The impact of anthropogenic factors arising from point and non-point pollution sources at a multi commodity marine port and its surrounding ecosystems were studied using sediment samples collected from a number of onshore (Gladstone Harbour and Facing Island) and offshore (Heron Island and Fitzroy Reefs) sites in Australia's Central Queensland. Sediment samples were analyzed for trace metals, organic carbon, polycyclic aromatic hydrocarbons (PAH), emerging chemicals of concern (ECC) and sterols. Similarly, the biological and biochemical interaction between the reef and its environment was analyzed by the multi-omic tools of next-generation sequencing characterization of the bacterial community and microbial community metabolic profiling. Overall, the trace elements were observed at the lower end of the Australian environmental guideline values at the offshore sites, while higher values were observed for the onshore locations Nickel and copper were observed above the high trigger value threshold at the onshore sites. The levels of PAH were below limits of detection across all sites. However, some of the ECC and sterols were observed at higher concentrations at both onshore and offshore locations, notably, the cholesterol family sterols and 17α-ethynylestradiol. Multi-omic analyses also indicated possible thermal and photo irradiation stressors on the bacterial communities at all the tested sites. The observed populations of γ-proteobacteria were found in combination with an increased pool of fatty acids that indicate fatty acid synthesis and utilisation of the intermediates of the shikimate pathways. This study demonstrates the value of applying a multi-omics approach for ecological assessments, in which a more detailed assessment of physical and chemical contaminants and their impact on the community bacterial biome is obtained.

On the occurrence of a widespread contamination by herbicides of coral reef biota in French Polynesia

Research has been conducted within the framework of the French Initiative for Coral Reefs (IFRECOR) to assess pesticide pollution levels in the coral reef trophic webs in French Polynesia. Unexpected widespread contamination by herbicides was found in algae, fishes and macro-invertebrates located at various levels of the reef trophic web. Concentrations in organisms investigated were for the majority below the lowest observable effect level and do not pose a dietary risk to native population who subsist on these fish. However, the widespread contamination may affect the reef ecosystem in the future as coral symbiotic algae, Symbidinium sp. (Dinophyta) are particularly sensitive to photosystem II herbicides, particularly the substituted urea and triazine derivatives.

A novel approach to model exposure of coastal-marine ecosystems to riverine flood plumes based on remote sensing techniques

Increased loads of land-based pollutants are a major threat to coastal-marine ecosystems. Identifying the affected marine areas and the scale of influence on ecosystems is critical to assess the impacts of degraded water quality and to inform planning for catchment management and marine conservation. Studies using remotely-sensed data have contributed to our understanding of the occurrence and influence of river plumes, and to our ability to assess exposure of marine ecosystems to land-based pollutants. However, refinement of plume modeling techniques is required to improve risk assessments. We developed a novel, complementary, approach to model exposure of coastal-marine ecosystems to land-based pollutants. We used supervised classification of MODIS-Aqua true-color satellite imagery to map the extent of plumes and to qualitatively assess the dispersal of pollutants in plumes. We used the Great Barrier Reef (GBR), the world's largest coral reef system, to test our approach. We combined frequency of plume occurrence with spatially distributed loads (based on a cost-distance function) to create maps of exposure to suspended sediment and dissolved inorganic nitrogen. We then compared annual exposure maps (2007-2011) to assess inter-annual variability in the exposure of coral reefs and seagrass beds to these pollutants. We found this method useful to map plumes and qualitatively assess exposure to land-based pollutants. We observed inter-annual variation in exposure of ecosystems to pollutants in the GBR, stressing the need to incorporate a temporal component into plume exposure/risk models. Our study contributes to our understanding of plume spatial-temporal dynamics of the GBR and offers a method that can also be applied to monitor exposure of coastal-marine ecosystems to plumes and explore their ecological influences.

The preparation of the rice coral Montipora capitata nubbins for application in coral-reef ecotoxicology

Securing adequate and appropriate source material for coral-reef ecotoxicology studies is a significant impediment to conducting various experiments supporting the goal of conserving coral-reef ecosystems. Collecting colonies from wild stocks may be counter to protecting coral reef populations. To address this issue the rice coral Montipora capitata was used to generate sufficient genetically identical nubbins for research purposes. Growth and survival rates of these laboratory-prepared M. capitata nubbins were studied over a period of 90 days. The resulting data support the conclusion that the laboratory-prepared M. capitata nubbins showed successful growth and survival rates and are the best solution to solve the source material issue for lab experimentation. This paper describes the laboratory method used for the preparation and maintenance of these M. capitata nubbins and discusses the benefits and difficulties of using these nubbins in ecotoxicity studies.

Additive pressures of elevated sea surface temperatures and herbicides on symbiont-bearing foraminifera

Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F'(m)), while elevated temperatures (>30 °C, only 2 °C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (F(v)/F(m)), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced F(v)/F(m) and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥ 1 µg L(-1)). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures.

Phytotoxicity induced in isolated zooxanthellae by herbicides extracted from Great Barrier Reef flood waters

To date there has been limited evidence anthropogenically sourced pollution from catchments reaching corals of the Great Barrier Reef (GBR). In this study, freshly isolated zooxanthellae were exposed to polar chemicals (chiefly herbicides) extracted from water samples collected in a flood plume in the GBR lagoon. Photosynthetic potential of the isolated zooxanthellae declined after exposure to concentrated extracts (10 times) from all but one of the sampling sites. Photosynthetic potential demonstrated a significant positive relationship with the concentration of diuron in the concentrated extracts and a significant inverse relationship with salinity measured at the sampling site. This study demonstrates that runoff from land based application of herbicides may reduce photosynthetic efficiency in corals of inshore reefs in the GBR. The ecological impacts of the chemicals in combination with other potential stressors on corals remain unclear.

Plutonium as a chronomarker in Australian and New Zealand sediments: a comparison with (137)Cs

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides (210)Pb and (137)Cs. The anthropogenic radionuclide, (137)Cs, originating from atmospheric nuclear weapons testing can provide an important "first appearance" horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with (210)Pb geochronology. However, while (137)Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of (137)Cs in the southern hemisphere was only 25% that of the north and the low activities of (137)Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low (137)Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator. This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding (137)Cs profiles and (210)Pb geochronologies. We find that Pu has significant advantages over (137)Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to (137)Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the (238)Pu/(239+240)Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over (137)Cs due to its enrichment in bottom sediment relative to (137)Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles.

The coral reef crisis: the critical importance of<350 ppm CO2

Temperature-induced mass coral bleaching causing mortality on a wide geographic scale started when atmospheric CO(2) levels exceeded approximately 320 ppm. When CO(2) levels reached approximately 340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events. Recovery was dependent on the vulnerability of individual reef areas and on the reef's previous history and resilience. At today's level of approximately 387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline. Mass bleaching will in future become annual, departing from the 4 to 7 years return-time of El Niño events. Bleaching will be exacerbated by the effects of degraded water-quality and increased severe weather events. In addition, the progressive onset of ocean acidification will cause reduction of coral growth and retardation of the growth of high magnesium calcite-secreting coralline algae. If CO(2) levels are allowed to reach 450 ppm (due to occur by 2030-2040 at the current rates), reefs will be in rapid and terminal decline world-wide from multiple synergies arising from mass bleaching, ocean acidification, and other environmental impacts. Damage to shallow reef communities will become extensive with consequent reduction of biodiversity followed by extinctions. Reefs will cease to be large-scale nursery grounds for fish and will cease to have most of their current value to humanity. There will be knock-on effects to ecosystems associated with reefs, and to other pelagic and benthic ecosystems. Should CO(2) levels reach 600 ppm reefs will be eroding geological structures with populations of surviving biota restricted to refuges. Domino effects will follow, affecting many other marine ecosystems. This is likely to have been the path of great mass extinctions of the past, adding to the case that anthropogenic CO(2) emissions could trigger the Earth's sixth mass extinction.