Coral record of increased sediment flux to the inner Great Barrier Reef of Australia since European Settlement

Research School of Earth Sciences, Australian National University, Canberra 0200, Australia.
Nature (Impact Factor: 42.35). 03/2003; 421(6924):727-30. DOI: 10.1038/nature01361
Source: PubMed

ABSTRACT The effect of European settlement on water quality in the Great Barrier Reef of Australia is a long-standing and controversial issue. Erosion and sediment transport in river catchments in this region have increased substantially since European settlement, but the magnitude of these changes remains uncertain. Here we report analyses of Ba/Ca ratios in long-lived Porites coral from Havannah Reef--a site on the inner Great Barrier Reef that is influenced by flood plumes from the Burdekin river--to establish a record of sediment fluxes from about 1750 to 1998. We find that, in the early part of the record, suspended sediment from river floods reached the inner reef area only occasionally, whereas after about 1870--following the beginning of European settlement--a five- to tenfold increase in the delivery of sediments is recorded with the highest fluxes occurring during the drought-breaking floods. We conclude that, since European settlement, land-use practices such as clearing and overstocking have led to major degradation of the semi-arid river catchments, resulting in substantially increased sediment loads entering the inner Great Barrier Reef.

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    • "Terrestrial runoff alters water quality in four ways: by introducing (1) inorganic nutrients and (2) particulate organic matter, (3) by reducing light owing to turbidity, and (4) by sediment deposition (e.g., Fortes 2000; Fabricius 2005). Human activity has generally increased sediment loading on coral reefs (e.g., McCulloch et al. 2003) and often results in chronic sediment stress to coral reef ecosystems (e.g., Jokiel et al. 2004; Cooper et al. 2007; Erftmeijer et al. 2012; DeMartini et al. 2013). Predicting effects of (Acevedo et al. 1989; Jokiel et al. 2014), or acclimatization to (Anthony and Larcombe 2002; Mallela and Perry 2007; Perry et al. 2012), chronic sediment stress is predicated on determining relationships between physical factors and physiological responses. "
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    ABSTRACT: Sediment has been shown to be a major stressor to coral reefs globally. Although many researchers have tested the impact of sedimentation on coral reef ecosystems in both the laboratory and the field and some have mea- sured the impact of suspended sediment on the photosynthetic response of corals, there has yet to be a detailed investigation on how properties of the sediment itself can affect light availability for photosynthesis. We show that finer-grained and darker-colored sediment at higher suspended-sediment concentrations attenuates photosynthetically active radiation (PAR) significantly more than coarser, lighter-colored sediment at lower concentrations and provide PAR attenuation coefficients for various grain sizes, colors, and suspended-sediment concentrations that are needed for biophysical modeling. Because finer-grained sediment particles settle more slowly and are more susceptible to resuspension, they remain in the water column longer, thus causing greater net impact by reducing light essential for photosynthesis over a greater duration. This indicates that coral reef monitoring studies investigating sediment impacts should concentrate on measuring fine- grained lateritic and volcanic soils, as opposed to coarser- grained siliceous and carbonate sediment. Similarly, coastal restoration efforts and engineering solutions ad- dressing long-term coral reef ecosystem health should focus on preferentially retaining those fine-grained soils rather than coarse silt and sand particles.
    Coral Reefs 05/2015; 34(3):967-975. DOI:10.1007/s00338-015-1268-0 · 3.62 Impact Factor
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    • "Coral reefs in the inshore area of the Great Barrier Reef, Australia (GBR), are situated in naturally turbid waters, as fine terrigenoclastic sediment is continuously resuspended by prevailing south-easterly winds and tidal currents (Larcombe et al. 1995, 2001; Wolanski et al. 2005; Orpin and Ridd 2012). In addition, suspended solids, nutrients, pesticide residues and other contaminants are delivered by catchment runoff during seasonal flooding of adjacent rivers (Devlin and Brodie 2005; Devlin and Schaffelke 2009; Brodie et al. 2010) and reach the inshore reefs (McCulloch et al. 2003; Jupiter et al. 2008; Kennedy et al. 2012; Bainbridge et al. 2012; Devlin et al. 2012). Since European colonisation, the loads of sediment, total nitrogen and total phosphorus transported to the coastal GBR as runoff are estimated to have increased by factors of 5.5, 5.7 and 8.9, respectively (Kroon et al. 2012). "
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    ABSTRACT: A five-year period (2002–2006) of below-median rainfall followed by a six-year period (2007–2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll-a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February–April), while TSS was elevated for four months, extending into the dry season (March–June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes.
    Coral Reefs 08/2014; 33(4). DOI:10.1007/s00338-014-1201-y · 3.62 Impact Factor
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    • "However, it is currently unknown whether adverse effects of salinity on coral reefs have become more frequent or extensive with alteration of freshwater flow regimes to tropical coastal waters. Cores of reef sediment and corals have indicated both increases (McCulloch et al., 2003) and decreases (Hungspreugs et al., 2002) in terrestrial sediment fluxes to coral reefs since the 1900s. Increases in sediment fluxes can result in smothering of coral reef organisms due to the settling of suspended sediment (sedimentation ), as well as in reduced light availability for photosynthesis due to turbidity caused by suspended sediment in the water column (Fabricius, 2011). "
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    ABSTRACT: The continuing degradation of coral reefs has serious consequences for the provision of ecosystem goods and services to local and regional communities. While climate change is considered the most serious risk to coral reefs, agricultural pollution threatens approximately 25% of the total global reef area with further increases in sediment and nutrient fluxes projected over the next 50 years. Here, we aim to inform coral reef management using insights learned from management examples that were successful in reducing agricultural pollution to coastal ecosystems. We identify multiple examples reporting reduced fluxes of sediment and nutrients at end-of-river, and associated declines in nutrient concentrations and algal biomass in receiving coastal waters. Based on the insights obtained, we recommend that future protection of coral reef ecosystems demands policy focused on desired ecosystem outcomes, targeted regulatory approaches, up-scaling of watershed management, and long-term maintenance of scientifically robust monitoring programs linked with adaptive management.
    Marine Pollution Bulletin 08/2014; 85(1). DOI:10.1016/j.marpolbul.2014.06.003 · 2.79 Impact Factor
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