Papers by Ibrahim Elmetri
Marine Ecology Progress Series, 2004
Significant acetylene reduction and therefore N 2 fixation was observed for Lyngbya majuscula onl... more Significant acetylene reduction and therefore N 2 fixation was observed for Lyngbya majuscula only during dark periods, which suggests that oxygenic photosynthesis and N 2 fixation are incompatible processes for this species. Results from a series of batch and continuous-flow-culture reactor studies showed that the specific growth rate and N 2 fixation rate of L. majuscula increased with phosphate (P-PO 4 ) concentration up to a maximum value and thereafter remained constant. The P-PO 4 concentrations corresponding to the maximum N 2 fixation and maximum growth rates werẽ 0.27 and ~0.18 µM respectively and these values are denoted as the saturation values for N 2 fixation and growth respectively. Regular monitoring studies in Moreton Bay, Queensland, show that concentrations of P-PO 4 generally exceed these saturation values over a large portion of the Bay and therefore, the growth of the bloom-forming L. majuscula is potentially maximised throughout much of the Bay by the elevated P-PO 4 concentrations. Results from other studies suggest that the elevated P-PO 4 concentrations in the Bay can be largely attributed to discharges from waste-water treatment plants (WWTPs), and thus it is proposed that the control of the growth of L. majuscula in Moreton Bay will require a significant reduction in the P load from the WWTP discharges. If the current strategy of N load reduction for these discharges is maintained in the absence of substantial P load reduction, it is hypothesised that the growth of L. majuscula and other diazotrophs in Moreton Bay will increase in the future.
Marine Ecology Progress Series, 1999
ABSTRACT Studies in the Great Barrier Reef Lagoon (GBRL) show that Trichodesmium (Oscillatoria) s... more ABSTRACT Studies in the Great Barrier Reef Lagoon (GBRL) show that Trichodesmium (Oscillatoria) spp. fix significant amounts of atmospheric nitrogen and that the loads of 'new' nitrogen introduced by Trichodesmium spp. are at least of the same order as those entering via riverine discharge. The elevated growth of other genera of phytoplankton and hence eutrophication in some sections of the GBRL could now be largely driven by the in situ production of this 'new' nitrogen. Trichodesmium is more prolific in the Central GBRL than in the Northern GBRL and there is evidence that the concentrations of Trichodesmium spp, have increased since the 1928-29 Great Barrier Reef Expedition to Low Isles. It is hypothesised that this increase has resulted from increases in river borne nutrients that would promote N fixation (e.g. phosphorus, iron and dissolved organic matter). It is estimated that the loads of such nutrients have increased several fold since the development of the coastal catchments of Queensland.
Hydrobiologia, 2005
Cultures of Trichodesmium from the Northern and Southern Great Barrier Reef Lagoon (GBRL) have be... more Cultures of Trichodesmium from the Northern and Southern Great Barrier Reef Lagoon (GBRL) have been established in enriched seawater and artificial seawater media. Some cultures have been maintained with active growth for over 6 years. Actively growing cultures in an artificial seawater medium containing organic phosphorus (glycerophosphate) as the principal source of phosphorus have also been established. Key factors that contributed to the successful establishment of cultures were firstly, the seed samples were collected from depth, secondly, samples were thoroughly washed and thirdly, incubations were conducted under relatively low light intensities (PAR~40-50 lmol quanta m )2 s )1 ). N 2 fixation rates of the cultured Trichodesmium were found to be similar to those measured in the GBRL. Specific growth rates of the cultures during the exponential growth phase in all enriched media were in the range 0.2-0.3 day )1 and growth during this phase was characterised by individual trichomes (filaments) or small aggregations of two to three trichomes. Characteristic bundle formation tended to occur following the exponential growth phase, which suggests that the bundle formation was induced by a lack of a necessary nutrient e.g. Fe.
Hydrobiologia, 2007
The relative importance of the additions of iron (Fe), phosphorus (P) and the chelating agent EDT... more The relative importance of the additions of iron (Fe), phosphorus (P) and the chelating agent EDTA in promoting the growth of Lyngbya majuscula in waters collected from the NW region of Moreton Bay was investigated using a series of continuous-flow growth studies. In addition, the possible impact of sewage/waste-water treatment plant (WWTP) discharges on the growth of L. majuscula was investigated in a series of batch and semi-continuous-flow growth studies. A preliminary study on the potential of phytoplankton growth in the receiving waters to affect the productivity of L. majuscula was also conducted. The results from the continuous-flow growth studies show that the growth rates of L. majuscula in the NW Moreton Bay waters were stimulated by the addition of EDTA alone but were not stimulated by the addition of P. The additions of P + EDTA, FeEDTA and P + FeEDTA did not result in higher growth rates than those obtained by the addition of EDTA alone. These results demonstrate that the productivity of L. majuscula in the NW Moreton Bay waters was not limited by P and that the addition of Fe did not affect the productivity. The stimulation effect of EDTA could be due to various reasons but we hypothesise that the principal reason for the stimulation is that EDTA increases the bioavailability of non-labile Fe species already present in the water. The results of the batch and semi-continuous-flow growth studies show that diluted (100:1) WWTP discharge water and the receiving waters impacted by WWTP discharges supported significant growth of L. majuscula and that the addition of EDTA to those waters increased the growth potential of L. majuscula. Also the growth of phytoplankton in a sample of the receiving waters impacted by WWTP discharges significantly reduced the growth rate of L. majuscula but the addition of EDTA restored the growth rate to near its maximum value. These results suggest that phytoplankton growth (and probably that of the associated bacterioplankton) could reduce the bioavailability of trace chemical factors needed for the growth of L. majuscula in Moreton Bay and in particular, could reduce the bioavailability of Fe. Overall the results support the hypothesis that growth of L. majuscula in Moreton Bay is often limited by the bioavailability of Fe and the principal reason for this is the lack of supply of suitable organic ligands/chelators, not the lack of Fe per se.
The release of phosphorus (P) and iron (Fe) from a melter slag filter in solutions of varying Eh ... more The release of phosphorus (P) and iron (Fe) from a melter slag filter in solutions of varying Eh and pH was examined. The filter had been removing P from waste stabilization pond effluent for several years. The study revealed that the highest P (95% of total P) and Fe (25% of total Fe) release from the slag occurred in the solution with the lowest Eh (-400 mV, relative to the standard hydrogen electrode, SHE) and lowest pH (4.9). Solutions with high pH (9.1) also proved favorable for P release (20 to 40% of total P) from the slag, at both reducing (-400 mV) and oxidizing (+300 mV) Eh. By contrast, solutions with pH 4.9 and 6.7 and oxidizing Eh (+300 mV) liberated the lowest P and Fe contents into the aqueous phase (<1% for both elements). The findings showed that Eh and pH are important parameters affecting P release from slag filters. At low Eh and low pH, P is released due to the dissolution of Fe oxides/oxyhydroxides, as supported by scanning electron microscopy (SEM)/energy dispersive spectrometry (EDS). At high pH, P is desorbed from negatively charged Fe oxide/oxyhydroxide surfaces. The results of this investigation are pertinentto the design and operation of melter slag filters that treat all forms of P-rich waters, such as wastewater, stormwater, and farm runoff. The study demonstrated that P retention by melter slag filters is optimal in water bodies characterized by near-neutral pH and oxidizing Eh because these conditions favor P adsorption onto Fe oxides/oxyhydroxides.
AMBIO, 2014
Long-term monitoring data show that hard coral cover on the Great Barrier Reef (GBR) has reduced ... more Long-term monitoring data show that hard coral cover on the Great Barrier Reef (GBR) has reduced by >70 % over the past century. Although authorities and many marine scientists were in denial for many years, it is now widely accepted that this reduction is largely attributable to the chronic state of eutrophication that exists throughout most of the GBR. Some reefs in the far northern GBR where the annual mean chlorophyll a (Chl a) is in the lower range of the proposed Eutrophication Threshold Concentration for Chl a (~0.2-0.3 mg m⁻³) show little or no evidence of degradation over the past century. However, the available evidence suggests that coral diseases and the crown-of-thorns starfish will proliferate in such waters and hence the mandated eutrophication Trigger values for Chl a (~0.4-0.45 mg m⁻³) will need to be decreased to ~0.2 mg m⁻³ for sustaining coral reef communities.
AMBIO: A Journal of the Human Environment, 2007
The results from the multimillion dollar Enrichment of Nutrients on Coral Reefs Experiment (ENCOR... more The results from the multimillion dollar Enrichment of Nutrients on Coral Reefs Experiment (ENCORE) on One Tree Island Reef (OTIR) suggest that increased nutrient loads to coral reefs will have little or no effect on the algal growth rates and, hence, on the associated effects that increased algal growth might have on the functioning and stability of coral reefs. However, a comparison of the concentrations of nutrients within the OTIR lagoon with the proposed nutrient threshold concentrations (NTC) for coral reefs suggests that all sites, including the control sites, were saturated with nutrients during ENCORE, and, hence, one would not expect to get any differences between treatments in the algal-growth related measurements. Thus, ENCORE results provide strong support for the proposed NTCs and support the ecological principle that algal productivity and, consequently, the functioning of coral reefs are sensitive to small changes in the background concentrations of nutrients. The principal conclusion of ENCORE, namely that the addition of nutrients did not cause the "pristine" OTIR to convert from coral communities to algal dominated reefs, is contrary to the fact that there was prolific macroalgal growth on the walls and crests of the experimental microatolls by the end of ENCORE.
Water Research, 2006
Active filters, which facilitate phosphorus (P) removal via precipitation and/or adsorption, offe... more Active filters, which facilitate phosphorus (P) removal via precipitation and/or adsorption, offer a promising 'appropriate technology' for upgrading small wastewater treatment systems. Research on active filters for P removal using steel slag material has been conducted in laboratories across the world, however, field experiments have been limited and long-term data is practically non-existent. This paper presents a decade of experience on P removal by active slag filters at a full-scale treatment plant. During 1993-1994 the filter removed 77% of the total phosphorus (TP), and over the first 5 years of the filter's operation it reduced the mean effluent TP concentration to 2.3 mg l À1 . However during the sixth year of operation P removal was significantly reduced. Over the 11 years of monitoring, 22.4 tonnes of TP was removed by the filter, 19.7 tonnes of this in the first 5-year period. It was determined that the slag material maintained its maximum removal potential until reaching a P-retention ratio of 1.23 kg TP per tonne of slag. This paper provides the first long-term field data for slag filters, and shows that they can provide P removal for a half a decade before filter replacement/rejuvenation is required.
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Papers by Ibrahim Elmetri