dissolution

marine methane oxidation coupled to sulfate respiration

21 November 2012 in news

A very interesting article published in Nature this month:

nature 11656 figure 4.2 Milucka, J., Ferdelman, T.G., Polerecky, L., Franzke, D., Wegener, G., Schmid, M., Lieberwirth, I., Wagner, M., Widdel, F., Kuypers, M.M.M. Zero-valent sulphur is a key intermediate in marine methane oxidation. Nature, advance online publication, http://dx.doi.org/10.1038/nature11656

The research described in the article shows that marine methane oxidation coupled to sulfate respiration can be performed by a single microorganism, a member of the ancient kingdom of the Archaea, and does not need to be carried out in collaboration with a bacterium, as previously thought.

In our articles on sulfur geochemistry in sediments, we always refer to sulfate reduction being performed by bacteria – the currently accepted view. It would certainly be interesting to find out whether Milucka et al.’s findings apply to sulfate reduction in other contexts.

Tags: biogeochemistry, geochemistry, news, ocean, sediment Comments Off

by Andrew Rate

what’s expected of graduate students

15 November 2012 in Research group information, useful

This isn’t a post with general advice to postgraduates, but an idea of what is expected of you, and what you can expect, if you join this group as a graduate research student.

The post has been moved to the page ‘expectations‘ – click here to read it.

spacer

Tags: PhD, postgraduate, research skills Comments Off

by Andrew Rate

listening skills for scientists

13 November 2012 in opinion

So, I’m sitting in a symposium (as I type, as it happens) and an esteemed Professor of Soil Chemistry has just finished an interesting talk which addresses the future of soil science in the context of food security and environmental protection.

He made some (valid, I thought) comments about scientists needing to communicate with non-scientists, and about the need for visionary scientific leadership.

The follow up comments and questions were interesting. A younger scientist bemoaned the lack of ability of the general public to understand science, so how could he possibly communicate his work to them? Of course,in doing so he was missing the point that this was the point.

Someone else piped up with something they had heard – a second-hand opinion that we leave the decisions about science to teenagers, as their decisions affect university enrolments which [presumably] flow on in terms of funding to University science departments. Interesting, but slightly off-topic Another audience member, not listening to (or simply launching from) this comment, wanted everyone to know the we need to promote science to primary-school-aged children, rather than teenagers. True? – yes. Soap-boxing? – definitely.

This seemed to be the prompt for another person to dispute the need for good scientific leadership, by re-hashing the idea that scientific leadership needs to include stakeholders such as industry and so on. Again, a worthy (if tired) idea, but demonstrating, once again, that the commenter didn’t listen to the original speaker, who was talking about internal leadership to inspire a team and be an organisation’s advocate – quite a different idea.

Unfortunately science, by its very nature, is somewhat combative and critical (one only needs to consider peer review of publications and research proposals). So perhaps we find it hard to just listen, and hard not to resist the urge to promote our point of view (no matter how valid that may be). Diversion in conversation is one thing; occasionally it’s self-promotion in disguise.

So, just imagine how science could be different if we did just listen to one another?

Tags: communication, conference, opinion, rant, symposium Comments Off

by Andrew Rate

Two new articles from this research group – October 2012

2 October 2012 in news, Research group information

XinProfile

Du , X., Rate, A.W. and Gee, M.A.M. 2012. Redistribution and mobilization of titanium, zirconium and thorium in an intensely weathered lateritic profile in Western Australia. Chemical Geology, 330-331, 101–115 http://dx.doi.org/10.1016/j.chemgeo.2012.08.030.

Abstract: The mobility of titanium, zirconium and thorium, elements commonly considered insoluble during supergene weathering, is still not well understood, especially in intensely weathered regolith. Thus, an intensely weathered lateritic profile (JG) developed on meta-granitoids in Jarrahdale, Western Australia, was investigated. The mobility of Ti, Zr and Th has been assessed at both mineral assemblage and profile scales and the mode of occurrence has been investigated through the combined use of geochemical data from bulk regolith, particle size fractions and sequential extractions, with in situ data determined by electron probe micro-analyzer and synchrotron X-ray powder diffraction. Neoformed poorly crystalline phases containing trace to minor amounts of Zr, Ce and Th unassociated with silicates or phosphates were identified on the walls of Al/Fe-rich pores in the ferruginous duricrust. This implies that some mobilization and redistribution of Zr and Th occurs within a sample scale. Breakdown of primary thorite and rare earth element rich fluorocarbonates is thought to be the source for Zr and Th in the neoformed phases rather than zircon. Thus, the mineral hosts of Zr, Ti and Th in the parent rock and their relative susceptibility to weathering are the fundamental controls on subsequent mobility during initial weathering. Trace amounts of Th in secondary phases, such as rhabdophane and florencite, show translocation of Th at the mineral scale, while strong partitioning of Th into gravel rather than matrix reflects redistribution of Th at the profile scale. The absence of primary sphene from the regolith and the presence of partially dissolved ilmenite and rutile grains in the ferruginous mottled zone suggest mobilization and translocation of Ti at a mineral assemblage scale. Furthermore, the fluctuation of Ti/Zr in the ferruginous zone is in contrast to the consistency of Zr/Hf throughout the profile in general (within the range of parent meta-granitoid). This suggests that Ti and Zr fractionate from each other and partition between gravel and matrix during extreme weathering and advanced lateritization. This study demonstrates that Ti, Zr and Th are mobile at a variety of scales, an important consideration that is often overlooked when calculating element mass flux in intensely weathered regolith.

Drain sampling Morgan, B., Rate, A.W. and Burton, E.D. 2012. Trace element reactivity in FeS-rich estuarine sediments: influence of formation environment and acid sulfate soil drainage. Science of the Total Environment, accepted 27 August 2012. http://dx.doi.org/10.1016/j.scitotenv.2012.08.088

Abstract: Iron monosulfides (FeS) precipitate during benthic mineralisation of organic C and are well known to have a strong influence on trace element bioavailability in sediments. In this study we investigate the reactivity of trace elements (As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Zn) in sediments containing abundant and persistent FeS stores, collected from a south-western Australian estuarine system. Our objective was to explore the influence of sediment formation conditions on trace element reactivity by investigating sediments collected from different environments, including estuarine, riverine and acid sulfate soil influenced sites, within a single estuarine system. In general, we found a higher degree of reactivity (defined by 1 mol/L HCl extractions) for Cd, Mn, Pb and Zn, compared with a lower reactivity of As, Co, Cr, Cu, Mo and Ni. Moderate to strong correlations (R² > 0.4, P < 0.05) were observed between AVS and reactive Cd, Co, Mn, Mo, Ni, Pb and Zn within many of the formation environments. In contrast, correlations between AVS and As, Cr and Cu were generally poor (not significant, R² < 0.4, P > 0.05). Based on their reactivity and correlations with AVS, it appears that interactions (sorption, co-precipitation) between FeS and Cd, Mn, Pb and Zn in many of the sediments from this study are probable. Our data also demonstrate that drainage from acid sulfate soils (ASS) can be a source of trace elements at specific sites. A principal components analysis of our reactive (1 mol/L HCl extractable) trace element data clearly distinguished sites receiving ASS drainage from the other non-impacted sites, by a high contribution from Fe–Co–Mn–Ni along the first principal axis, and contributions from higher S–As/lower reactive Pb along the second axis. This demonstrates that trace element reactivity in sediments may provide a geochemical signature for sites receiving ASS drainage.

Tags: geochemistry, journal article, papers, PhD, postgraduate, regolith, research, sediment Comments Off

by Andrew Rate

three theses

6 September 2012 in news, Research group information

Our groups is getting smaller! Three excellent PhD theses have been submitted this year:

…and no, this is not a mini-Martin Luther copycat attempt…

	Bree Morgan “Sulfur geochemistry as a driver of trace metal, rare earth element and nutrient cycles in eutrophic estuarine sediment”
	Talitha Santini “Chemical and mineralogical aspects of soil formation in bauxite residue”
	Xin Du “Occurrence and behaviour of rare earth and associated elements in lateritic regolith profiles, Western Australia”

All of these people are extraordinarily capable and talented scientists, and it’s been a pleasure and privilege working with them. We’re sad to see them go (all interstate or overseas, for now).

Tags: geochemistry, postgraduate, research, student, thesis Comments Off

by Andrew Rate

Two new articles from our group

20 July 2012 in Research group information

Lucas, A.R., Rate, A.W., Zhang, H., Salmon, S.U. and Radford, N.W. 2012. Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters.Analytical Chemistry 84, 6994–7000. doi: 10.1021/ac301003g

Abstract:
Gold is a precious metal that exists in most soils, sediments and natural waters at extremely low concentrations (< 1 μg/kg). The diffusive gradients in thin films (DGT) technique, used extensively for measuring trace metal concentrations in soils, sediments and waters, has potential for geochemical exploration for gold, but it has not been developed for this metal. This work investigates the possibility of measuring labile gold using DGT by introducing a new binding layer based on activated carbon. The performance of this new technique was assessed using gold (III) chloride in solution by: 1) determining the diffusion coefficient of gold (III) in hydrogels; 2) determining the uptake of gold (III) chloride by the new activated carbon binding layer; 3) determining an elution methodology for the binding layer and evaluating its efficiency; 4) assessing the capacity of the activated carbon binding layer to adsorb gold; 5) determining the effect of pH and ionic strength (as NaCl) on performance, and; 6) assessing the new binding layer’s selectivity for gold. It was found that the diffusion coefficient of gold (III) increased as solution pH decreased. The diffusion coefficient also increased at high ionic strength (≥ 0.1M NaCl). Accounting for these phenomena, the DGT technique behaved predictably under all tested conditions. The technique can potentially be used as a geochemical exploration tool for gold in soils and in aqueous environments, with method detection limits as low as 0.9 ng/L for a 7-day deployment.

Morgan, B., Rate, A.W. and Burton, E.D. 2012. Water chemistry and nutrient release during the resuspension of FeS-rich sediment in a eutrophic estuarine system. Science of the Total Environment, 432, 47-56. doi:10.1016/j.scitotenv.2012.05.065

Abstract:
The objective of this study was to investigate the impact of resuspending FeS-rich benthic sediment on estuarine water chemistry. To address this objective, we conducted (1) a series of laboratory-based sediment resuspension experiments and (2) also monitored changes in surface water composition during field-based sediment resuspension events that were caused by dredging activities in the Peel–Harvey Estuary, Western Australia. Our laboratory resuspension experiments showed that the resuspension of FeS-rich sediments rapidly deoxygenated estuarine water. In contrast, dredging activities in the field did not noticeably lower O₂ concentrations in adjacent surface water. Additionally, while FeS oxidation in the laboratory resuspensions caused measurable decreases in pH, the field pH was unaffected by the dredging event and dissolved trace metal concentrations remained very low throughout the monitoring period. Dissolved ammonium (NH₄⁺) and inorganic phosphorus (PO₄–P) were released into the water column during the resuspension of sediments in both the field and laboratory. Following its initial release, PO₄–P was rapidly removed from solution in the laboratory-based (< 1 h) and field-based (< 100 m from sediment disposal point) investigations. In comparison to PO₄–P, NH₄⁺ release was observed to be more prolonged over the 2-week period of the laboratory resuspension experiments. However, our field-based observations revealed that elevated NH₄⁺ concentrations were localised to < 100 m from the sediment disposal point. This study demonstrates that alongside the emphasis on acidification, deoxygenation and metal release during FeS resuspension, it is important to consider the possibility of nutrient release from disturbed sediments in eutrophic estuaries.

Tags: DGT, geochemistry, journal article, papers, PhD, sediment Comments Off

by Andrew Rate

NZ Submarine Volcano Grows at Astonishing Rate

23 May 2012 in news, Uncategorized

Monowai Seamount image This is very cool, not least because of the New Zealand connections in our group…

The Monowai seamount, which lies at the intersection of the Pacific and Indo-Australian tectonic plates at the Tonga-Kermadec subduction zone, underwent one of the fastest episodes of volcano growth documented on Earth.

It added about 8.75 million cubic metres of rock to its summit – a volume equal to 3500 Olympic-size swimming pools – in just five days. [read more at Stuff.co.nz].

Tags: environment, geology, hydrothermal, New Zealand Comments Off

by Andrew Rate

New article in Chemical Geology

26 March 2012 in news, Research group information

Another new article from our group, one forming part of Bree Morgan’s PhD thesis:

Morgan, B., Rate, A.W., Burton, E.D., Smirk, M. 2012. Enrichment and fractionation of rare earth elements in FeS- and organic-rich estuarine sediments receiving acid sulfate soil drainage. Chemical Geology doi:10.1016/j.chemgeo.2012.03.012.

Abstract

An understanding of processes controlling the behaviour of rare earth elements (REEs) within estuarine sediments is essential for the effective use of REEs as tracers of environmental conditions. This study investigates the enrichment and fractionation of REEs in sediments with abundant iron monosulfides (FeS, measured as acid-volatile sulfide, median = 156 μmol/g) and organic carbon (median = 3.2 mmol/g). We examined sediments collected from a eutrophic estuary in Western Australia, which comprised several sedimentary environments, including sites receiving drainage from acid sulfate soils (ASS). In general, sediment-bound REEs were highly soluble in HCl, with 1 mol/L HCl extractable REE concentrations amounting to > 80% of corresponding total concentrations in approximately 70% of samples. A mid-REE (MREE) enrichment was consistently apparent in all sediment samples, with a median MREE enrichment value of 1.30 (range = 1.13 – 1.50) for the total REE concentrations and 1.44 (range = 1.17 – 1.26) in the 1 mol/L HCl extractions. Also, a Ce anomaly was consistently observed in the sediments examined here, with a median value of 1.11 (range = 0.79 – 1.58) for the total REE concentrations and 1.19 (range = 1.04 – 1.71) in the 1 mol/L HCl extracts. In general, a minor depletion of heavy-REEs (HREEs) relative to light-REEs (LREEs) was also apparent in many of the sediments (Yb/La < 1). This fractionation trend, in addition to a strong positive correlation between the MREE enrichments and Yb/La ratios, is consistent with sediment organic matter acting as a REE host phase. Abundant sedimentary FeS was also hypothesised to have influenced REE behaviour in the field, based on the high proportion of total REEs extracted by 1 mol/L HCl, as well as strong correlations between total REE concentrations and both total Fe and total S in the sediments examined here. However, in our laboratory experiment we found that REEs exhibit little (or no) short-term sorptive affinity for FeS, implying that if any FeS-REE interactions were occurring, this must involve mechanisms other than rapid sorption to pre-existing FeS. Sites receiving ASS drainage were unique in displaying (1) a strong relative enrichment of total REE concentrations in comparison to non-impacted sites, and (2) a significant positive correlation between the magnitude of the positive Ce anomalies and the magnitude of MREE enrichment. This observation demonstrates the utility of REEs as tracers of anthropogenic influences (especially the influence of ASS drainage) in FeS- and organic–rich estuarine sediments.

Highlights► REE dynamics in FeS- and organic C- rich estuarine sediments are poorly investigated. ► REE enrichments were observed in sediments receiving acid sulfate soil drainage. ► Sediment-bound REEs were highly soluble in 1 M HCl extractions. ► REE fractionation was consistent with a role of organic C in sediment REE retention. ► No conclusive evidence to show FeS retains REEs in estuarine sediments

Tags: geochemistry, papers, postgraduate, sediment Comments Off

by Andrew Rate