Graham B Jones

ENCORE: The effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions

Coral reef degradation resulting from nutrient enrichment of coastal waters is of increasing global concern. Although effects of nutrients on coral reef organisms have been demonstrated in the laboratory, there is little direct evidence of nutrient effects on coral reef biota in situ. The ENCORE experiment investigated responses of coral reef organisms and processes to controlled additions of dissolved inorganic nitrogen (N) and/or phosphorus (P) on an offshore reef (One Tree Island) at the southern end of the Great Barrier Reef, Australia. A multi-disciplinary team assessed a variety of factors focusing on nutrient dynamics and biotic responses. A controlled and replicated experiment was conducted over two years using twelve small patch reefs ponded at low tide by a coral rim. Treatments included three control reefs (no nutrient addition) and three + N reefs (NH4Cl added), three + P reefs (KH2PO4 added), and three + N + P reefs. Nutrients were added as pulses at each low tide (ca twice per day) by remotely operated units. There were two phases of nutrient additions. During the initial, low-loading phase of the experiment nutrient pulses (mean dose = 11.5 microM NH4+; 2.3 microM PO4(-3)) rapidly declined, reaching near-background levels (mean = 0.9 microM NH4+; 0.5 microM PO4(-3)) within 2-3 h. A variety of biotic processes, assessed over a year during this initial nutrient loading phase, were not significantly affected, with the exception of coral reproduction, which was affected in all nutrient treatments. In Acropora longicyathus and A. aspera, fewer successfully developed embryos were formed, and in A. longicyathus fertilization rates and lipid levels decreased. In the second, high-loading, phase of ENCORE an increased nutrient dosage (mean dose = 36.2 microM NH4+; 5.1 microM PO4(-3)) declining to means of 11.3 microM NH4+ and 2.4 microM PO4(-3) at the end of low tide) was used for a further year, and a variety of significant biotic responses occurred. Encrusting algae incorporated virtually none of the added nutrients. Organisms containing endosymbiotic zooxanthellae (corals and giant clams) assimilated dissolved nutrients rapidly and were responsive to added nutrients. Coral mortality, not detected during the initial low-loading phase, became evident with increased nutrient dosage, particularly in Pocillopora damicornis. Nitrogen additions stunted coral growth, and phosphorus additions had a variable effect. Coral calcification rate and linear extension increased in the presence of added phosphorus but skeletal density was reduced, making corals more susceptible to breakage. Settlement of all coral larvae was reduced in nitrogen treatments, yet settlement of larvae from brooded species was enhanced in phosphorus treatments. Recruitment of stomatopods, benthic crustaceans living in coral rubble, was reduced in nitrogen and nitrogen plus phosphorus treatments. Grazing rates and reproductive effort of various fish species were not affected by the nutrient treatments. Microbial nitrogen transformations in sediments were responsive to nutrient loading with nitrogen fixation significantly increased in phosphorus treatments and denitrification increased in all treatments to which nitrogen had been added. Rates of bioerosion and grazing showed no significant effects of added nutrients. ENCORE has shown that reef organisms and processes investigated in situ were impacted by elevated nutrients. Impacts were dependent on dose level, whether nitrogen and/or phosphorus were elevated and were often species-specific. The impacts were generally sub-lethal and subtle and the treated reefs at the end of the experiment were visually similar to control reefs. Rapid nutrient uptake indicates that nutrient concentrations alone are not adequate to assess nutrient condition of reefs. Sensitive and quantifiable biological indicators need to be developed for coral reef ecosystems. The potential bioindicators identified in ENCORE should be tested in future research on coral reef/nutrient interactions. Synergistic and cumulative effects of elevated nutrients and other environmental parameters, comparative studies of intact vs. disturbed reefs, offshore vs. inshore reefs, or the ability of a nutrient-stressed reef to respond to natural disturbances require elucidation. An expanded understanding of coral reef responses to anthropogenic impacts is necessary, particularly regarding the subtle, sub-lethal effects detected in the ENCORE studies.

Spatial distribution of dimethylsulfide and dimethylsulfoniopropionate in the Australasian sector of the Southern Ocean

During 1991–1995, seven voyages were made to the Southern Ocean to determine the distribution of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in seawater and air in the Australasian sector (60°E to 165°E). Measurements of DMSP in sea ice were also made. During the summer months the Subtropical Convergence (STC) and Antarctic Convergence (AC) were identified as important source regions of these sulfur compounds. In the Seasonal Ice zone (SIZ) there were marked longitudinal differences possibly reflecting higher productivity and the extent of the sea ice in this region. Levels of DMSP in sea ice cores were consistent with this regional difference. High and variable concentrations of DMSP also occurred in the Subantarctic Zone (SAZ) (45°-53°S), decreasing to lower levels around 64°S, close to the Antarctic Divergence (AD). Upwelling of deep water around the AD is suggested to have been responsible for the low biological activity and low DMSP levels. While there was generally a good relationship between DMSPp and biomass, there was a marked difference in the DMSPp:chlorophyll a ratio between regions, and between years. DMSP was generally negatively correlated with dissolved nitrate, however, it was unclear if the level of nitrate directly affected DMSP production. DMSw levels were highest in the mixed layer, with lower, yet detectable, levels in the deeper ocean. DMSw was occasionally elevated in Antarctic Bottom Water (AABW), suggesting that ice shelf water transports this substance to deeper waters. DMSP was not found above detection limits below the mixed layer, but some evidence was found that DMSP may be transported to deeper waters, close to the Antarctic continent.

DMS and DMSP in mucus ropes, coral mucus, surface films and sediment pore waters from coral reefs in the Great Barrier Reef

Concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP), two sulphur compounds that are involved in the formation of clouds, were measured for mucus ropes, coral mucus, surface films and sediment pore waters collected from three coral reefs in the Great Barrier Reef, Australia. The concentrations of DMS (61–18 665 nm) and DMSP (1978–54 381 nm) measured in mucus rope samples are the highest yet reported in the marine environment. The values exceed concentrations of DMS and DMSP reported from highly productive polar waters and sea ice algal communities. Concentrations of DMSP in coral mucus ranged from 1226 to 25 443 nm, with mucus from Acropora formosa containing the highest levels of DMSP. Dimethylsulphide and DMSP in surface microlayer samples from three coral reefs were two to four times subsurface (0.5 m) concentrations. In coral-reef sediment pore waters, concentrations of DMS and DMSP were substantially higher than water-column concentrations, suggesting that coral sediments may be a significant source of these two compounds to reef waters. Overall, the results strongly suggest that coral reefs in the Great Barrier Reef are significant sources of these two sulphur substances.

Dimethyl sulfide in the Southern Ocean: Seasonality and flux

The first flux estimate of dimethyl sulfide (DMS) from the Australian sector of the Southern Ocean (63°E to 162°E) has been calculated from seven voyages, which span spring and summer seasons from 1991 to 1995. Increases in seawater DMS and its precursor, dimethyl sulfoniopropionate (DMSP) generally occurred in Southern Ocean surface waters during the transition from spring to summer. DMS flux from the Subantarctic Zone (SAZ), Antarctic Zone (AZ), and Seasonal Ice Zone (SIZ) ranged from 1.7 to 49 μmol/m2/d with a mean value of 9.4 μmol/m2d. These flux calculations are believed to be underestimates, and do not include potential contributions from sea ice. Very high levels of DMSP in sea ice suggest that the SIZ may be a source of DMS to the atmosphere. The different types of vertical DMSP profiles found in sea ice possibly reflect the type of algal assemblage present and the age of the sea ice. Without considering contributions of DMS from sea ice, the overall Southern Ocean DMS emission estimate from this work was 139 Gmol S/yr. The emission estimate for the Antarctic region alone (AZ and SIZ) was 85 Gmol S/yr. This represents 17% of the global emission estimate, from 6% of the ocean surface area. This emission estimate is almost double that of an earlier estimate by Berresheim [1987] of 48 Gmol S/yr, and is likely to be higher when the amount released from the sea ice surrounding Antarctica is more accurately characterized.

Correlations between the satellite-derived seasonal cycles of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice

The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50°S and 70°S, for the period (1997-2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50°S and 60°S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60°S. Marked interannual variability in CHL occurs south of 60°S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions (aerosol precursors) are being produced over the SIZ in spring (October-December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.

Influence of different water masses and biological activity on dimethylsulphide and dimethylsulphoniopropionate in the subantarctic zone of the Southern Ocean during ACE 1

Measurements of salinity, temperature, phytoplankton biomass and speciation, dissolved nitrate, dimethylsulfide (DMS) in seawater and air, and dimethylsulfoniopropionate (DMSP), were made in the subantarctic zone of the Southern Ocean from 40°-54°S, and 140°-153°E during the southern hemisphere marine First Aerosol Characterization Experiment (ACE 1). DMSP concentrations were highest in subtropical convergence zone (STCZ) waters, intermediate in subantarctic waters, and lowest in polar waters. DMSP appeared to decrease at frontal regions between these major water masses. In subantarctic waters, high levels of DMSP were generally associated with an increase in dinoflagellate biomass and low microzooplankton grazing rates. Lower DMSP concentrations occurred in polar waters when the diatom biomass and grazing rates were high. DMS levels measured on Southern Surveyor ranged from not detectable (nd) to 5.6 nM (mean 1.7 nM), with below average levels in subantarctic waters (mean 1.25 nM), and above average levels (mean = 1.93 nM) in polar waters. Pulses of DMS occurred as Southern Surveyor traveled south into polar waters, with a large pulse (mean = 2.3 nM) highlighted as the vessel traveled back into subantarctic waters (46°-47°S, 148°-151°E) in early December. By using the dissolved DMSP (DMSPd) to DMS ratio as an index of the bacterial conversion of DMSPd to DMS some evidence was found that, in polar waters, increased microzooplankton (MZP) grazing in diatom dominated waters, may lead to above average concentrations of DMS. This does not appear to be the case when the biomass was dominated by dinoflagellates in subantarctic waters.

Phosphate Removal from Aqueous Solutions using Neutralised Bauxite Refinery Residues (Bauxsol

Environmental Context.Eutrophication of freshwater and marine ecosystems is a global problem, which is frequently linked to high phosphorus concentrations. The present study investigated the use of Bauxsol™, a modified bauxite refinery residue, to remove dissolved phosphate from water, and has shown that it can be used as a cost-effective adsorbent for treating phosphate-contaminated waters. The results provide water and environmental managers with a new technique for decreasing the phosphate loads in water and wastewater. Environmental benefits include improved water quality, minimisation of excessive plant growth, including potentially toxic blue green algae, and the utilisation of an industrial residue for environmental remediation. Abstract.Phosphate (PO43–) removal by Bauxsol™, a neutralised bauxite refinery residue, was investigated as a function of time, pH, ionic strength, adsorbent dosage, competing ions, and initial phosphate concentration. The results of adsorption and desorption studies indicate that adsorption of PO43– by Bauxsol™ is based on a ligand-exchange mechanism, although the low reversibility pH-independent desorption observed in acid-treated Bauxsol™ indicates a dominance of chemisorption. It was shown that PO43– adsorption onto both Bauxsol™ and acid-treated Bauxsol™ followed a Langmuir isotherm model, with adsorption capacities of 0.21 and 0.48 mmol g−1 at pH 9.0 and 5.2 respectively. Adsorption of PO43– by Bauxsol™ increased with decreasing pH, with maximum adsorption efficiencies obtained at pH 5.2 ± 0.1 (the lowest pH investigated), higher Bauxsol™ to initial phosphate concentration ratios, and increased time. Studies of the effects of competing ions on the adsorption of PO43– by Bauxsol™ indicated that adsorption decreased in the presence of HCO3− ions, whereas SO42–and Cl− ions had little effect, and Ca2+ and Mg2+ ions increased adsorption. These findings suggest that Bauxsol™ could be used as an efficient low-cost adsorbent for treating phosphate-contaminated waters.

Trace Metals as Tracers of Dredging Activity in Cleveland Bay - Field and Laboratory Studies

This study has investigated in detail trace metal concentrations in Cleveland Bay in the central Great Barrier Reef and assessed the significant carrier phases of several metals during a simulated disturbance of sediments designed to investigate the effects of dredging. Organic, iron oxide and carbonate phases were shown to be important carrier phases for several trace metals. The application of an acid-leach technique to monitor labile or pollutant concentrations of copper, zinc, lead and nickel in sediments collected from coral reefs sampled before and after two dredging events in 1991 yielded useful information on the fate of dredged sediment. Trace metal contamination close inshore was attributed to port activities, sewage discharge and urbanization.

Carbon Capture and the Aluminium Industry: Preliminary Studies

Environmental Context. Carbon dioxide concentrations in the atmosphere are rising every year by 1.5–3.0 ppm and there is now a general acceptance that increased efforts must be made to reduce industrial sources of this greenhouse gas. Carbonation of red mud wastes produced by aluminium refineries has been carried out to study the capacity of these wastes to capture carbon dioxide. Removal is very rapid, with the added carbon dioxide recorded as a large increase in bicarbonate alkalinity. Although these results can only be considered preliminary, the experiments indicate that these wastes can potentially remove up to 15 million tonnes of carbon dioxide produced in Australia per annum. Furthermore, the carbonated waste can be used in other industrial processes to add further value to these waste materials. Abstract. Carbonation of raw red mud produced by aluminium refineries and a chemically and physically neutralized red mud (Bauxsol™) has been carried out to study the capacity of these wastes to capture carbon dioxide. After only 5 min of carbonation of raw red mud, total alkalinity dropped 85%. Hydroxide alkalinity was almost totally consumed, carbonate alkalinity dropped by 88%, and bicarbonate alkalinity increased to 728 mg L–1. After 24 min carbonation, the bicarbonate alkalinity reached its maximum value of 2377 mg L–1, and hydroxide and carbonate alkalinity were virtually absent. After 30 and 60 min carbonation, bicarbonate alkalinity started to decrease slightly as the pH of the slurry increased. After 5 min carbonation of Bauxsol™, total and bicarbonate alkalinity dropped 89% and 9%, respectively. After 20 min carbonation, bicarbonate alkalinity dropped another 11%, but after 30 min carbonation bicarbonate alkalinity increased 26% to levels found in the original Bauxsol material, and pH was stable. Based on these experiments, a calculation of the amount of carbon dioxide that could be removed annually at aluminium refineries in Australia is potentially 15 million tonnes, and suggests that further studies are necessary to maximize this carbon removal process. Furthermore, carbonation produces a product, which can potentially be used in other industrial and agricultural activities to remove toxic metals and nutrients.

The influence of coral reefs on atmospheric dimethylsulphide over the Great Barrier Reef, Coral Sea, Gulf of Papua and Solomon and Bismarck Seas

Marked regional differences in dissolved dimethylsulphide (DMS), atmospheric DMS and DMS flux were recorded during July 1997 through the northern Great Barrier Reef, Coral Sea, Gulf of Papua, Solomon and Bismarck Seas. Highest concentrations of dissolved DMS occurred in the Coral Sea, Gulf of Papua and Bismarck Sea, with lower concentrations in the Great Barrier Reef and Solomon Sea. Elevated levels of atmospheric DMS often occurred in south-easterly to southerly trade winds sampled in the region 18°32′–8°12′S to 145°–151°E, where the highest biomass of coral reefs occurred. Atmospheric DMS often increased in the day after low tides and was positively correlated with tidal height in the northern Great Barrier Reef (r = 0.91, P < 0.05). For tides less than 1.6 m, atmospheric DMS increased on the rising tide for the northern GBR and NW Coral Sea (r = 0.66; P < 0.05) and for the whole voyage (r = 0.25; P < 0.05). As coral reefs have been identified as significant sources of DMS, it is suggested that the daytime increase in atmospheric DMS over much of the study area was mainly a result of high winds and extremely low tides in July, which exposed the reefs during the day.