Microbial metabolism mediates interactions between dissolved organic matter and clay minerals in streamwater

Sorption of organic molecules to mineral surfaces is an important control upon the aquatic carbon (C) cycle. Organo-mineral interactions are known to regulate the transport and burial of C within inland waters, yet the mechanisms that underlie these processes are poorly constrained. Streamwater contains a complex and dynamic mix of dissolved organic compounds that coexists with a range of organic and inorganic particles and microorganisms. To test how microbial metabolism and organo-mineral complexation alter amino acid and organic carbon fluxes we experimented with 13C-labelled amino acids and two common clay minerals (kaolinite and montmorillonite). The addition of 13C-labelled amino acids stimulated increased microbial activity. Amino acids were preferentially mineralized by the microbial community, concomitant with the leaching of other (non-labelled) dissolved organic molecules that were removed from solution by clay-mediated processes. We propose that microbial processes mediate the formation of organo-mineral particles in streamwater, with potential implications for the biochemical composition of organic matter transported through and buried within fluvial environments.

Hydrobiogeochemical Interactions along “Flow Tubes” Controls: Watershed Scale Contaminant Flow and Transformation at the Oak Ridge IFRC

Geochemical,spectrographic, microbiological and hydrogeologic studies at the ORIFRC site indicate that groundwater transport in structured media may behave as a system of parallel flow tubes. These tubes are preferred flowpaths that enable contaminant transport parallel to bedding planes (strike) over distances of 1000s of meters. A significant flux of groundwater is focused within an interval defined by the interface between the competent bedrock and overlying highly-weathered saprolite, commonly referred to as the"transition zone." Characteristics of this transition zone are dense fractures and the relative absence of weathering products (e.g. clays)results in a significantly higher permeability compared to both the overlying clay-saprolite and underlying bedrock. Several stratabound low seismic velocity zones located below the transition zone were identified during geophysics studies and were also determined to be fractured high permeability preferred contaminant transport pathways during subsequent drilling activities. XANES analysis of precipitates collected from these deeper flow zones indicate 95% or more of the U deposited is U(VI). Linear combination fitting of the EXAFS data shows that precipitates are ~51±5% U(VI)-carbonate-like phase (e.g., liebigite) and ~49±5% U(VI) associated with an iron oxide phase; inclusion of a third component in the fit suggests that up to 15% of the U(VI) may be associated with a phosphate phase or OH- phase (e.g.,schoepite). Although precipitates with similar U(VI)-carbonate and/or phosphate associations were identified in the transition zone pathways,there were also U(VI) complexes adsorbed to mineral surfaces that would tend to be more readily mobilized. Groundwater in the different flow tubes has been determined to consist of different water quality types that vary with the solid phase encountered (e.g., clays, carbonates, clastics) as contaminants migrate along the flow paths. This lateral and vertical variability in geochemistry, particularly pH, has a significant impact on microbiological community composition and activity. Ribosomal RNA gene analyses coupled with physiological and genomic analyses suggest that bacteria from the genus Rhodanobacter(a diverse population of denitrifiers that are moderately acid tolerant) have a high relative abundance in the acidic source zone at the ORIFRC site.Watershed-scale analysis across different flow paths/tubes revealed strong negative correlation between pH and the absolute and relative abundance of Rhodanobacter. Recent studies also confirmed that the ORIFRC site hosts a diverse fungal community, with significant differences observed between acidic (pH <5) and circumneutral (>5) wells. The lack of nitrous oxide reduction capability in fungi, and the detection of denitrification potential in slurry microcosms suggest that fungi may have aheretofore under appreciated role in biogeochemical transformations, with implications forsite remediation and greenhouse gas emissions. Further research is needed to determine if these organisms can influence U(VI) mobility either directly through immobilization or indirectly through the depletion of nitrate.In conclusion, additional studies are required to quantify the processes (e.g., solid phase reactions, recharge, diffusion, microbial interactions) that are occurring along the groundwater flow tubes identified at the ORIFRC so predictive models can be parameterized and used to assess long-term contaminant fate and transport and remedial options.

Organo-mineral complexation alters carbon and nitrogen cycling in stream microbial assemblages

Inland waters are of global biogeochemical importance receiving carbon inputs of ~ 4.8 Pg C y^-1. Of this 12 % is buried, 18 % transported to the oceans, and 70 % supports aquatic secondary production. However, the mechanisms that determine the fate of organic matter (OM) in these systems are poorly defined. One important aspect is the formation of organo-mineral complexes in aquatic systems and their potential as a route for OM transport and burial vs. their use potential as organic carbon (C) and nitrogen (N) sources. Organo-mineral particles form by sorption of dissolved OM to freshly eroded mineral surfaces and may contribute to ecosystem-scale particulate OM fluxes. We tested the availability of mineral-sorbed OM as a C & N source for streamwater microbial assemblages and streambed biofilms. Organo-mineral particles were constructed in vitro by sorption of ¹³C:¹⁵N-labelled amino acids to hydrated kaolin particles, and microbial degradation of these particles compared with equivalent doses of ¹³C:¹⁵N-labelled free amino acids. Experiments were conducted in 120 ml mesocosms over 7 days using biofilms and streamwater sampled from the Oberer Seebach stream (Austria), tracing assimilation and mineralization of ¹³C and ¹⁵N labels from mineral-sorbed and dissolved amino acids.Here we present data on the effects of organo-mineral sorption upon amino acid mineralization and its C:N stoichiometry. Organo-mineral sorption had a significant effect upon microbial activity, restricting C and N mineralization by both the biofilm and streamwater treatments. Distinct differences in community response were observed, with both dissolved and mineral-stabilized amino acids playing an enhanced role in the metabolism of the streamwater microbial community. Mineral-sorption of amino acids differentially affected C & N mineralization and reduced the C:N ratio of the dissolved amino acid pool. The present study demonstrates that organo-mineral complexes restrict microbial degradation of OM and may, consequently, alter the carbon and nitrogen cycling dynamics within aquatic ecosystems.

Fate of organo-mineral particles in streams: Microbial degradation by streamwater & biofilm assemblages

Inland waters are of global biogeochemical importance. They receive carbon inputs of ~ 4.8 Pg C/ y of which, 12 % is buried, 18 % transported to the oceans, and 70 % supports aquatic secondary production. However, the mechanisms that determine the fate of organic matter (OM) in these systems are poorly defined. One aspect of this is the formation of organo-mineral complexes in aquatic systems and their potential as a route for OM transport and burial vs. their use as carbon (C) and nitrogen (N) sources within aquatic systems. Organo-mineral particles form by sorption of dissolved OM to freshly eroded mineral surfaces and may contribute to ecosystem-scale particulate OM fluxes. We experimentally tested the availability of mineral-sorbed OM as a C & N source for streamwater microbial assemblages and streambed biofilms. Organo-mineral particles were constructed in vitro by sorption of ¹³C:¹⁵N-labelled amino acids to hydrated kaolin particles, and microbial degradation of these particles compared with equivalent doses of ¹³C:¹⁵N-labelled free amino acids. Experiments were conducted in 120 ml mesocosms over 7 days using biofilms and water sampled from the Oberer Seebach stream (Austria). Each incubation experienced a 16:8 light:dark regime, with metabolism monitored via changes in oxygen concentrations between photoperiods. The relative fate of the organo-mineral particles was quantified by tracing the mineralization of the ¹³C and ¹⁵N labels and their incorporation into microbial biomass. Here we present the initial results of ¹³C-label mineralization, incorporation and retention within dissolved organic carbon pool. The results indicate that 514 (± 219) μmol/ mmol of the ¹³:¹⁵N labeled free amino acids were mineralized over the 7-day incubations. By contrast, 186 (± 97) μmol/ mmol of the mineral-sorbed amino acids were mineralized over a similar period. Thus, organo-mineral complexation reduced amino acid mineralization by ~ 60 %, with no differences observed between the streamwater and biofilm assemblages. Throughout the incubations, biofilms were observed to leach dissolved organic carbon (DOC). However, within the streamwater assemblage the presence of both organo-mineral particles and kaolin particles was associated with significant DOC removal (-1.7 % and -7.5 % respectively). Consequently, the study demonstrates that mineral and organo-mineral particles can limit the availability of DOC in aquatic systems, providing nucleation sites for flocculation and fresh mineral surfaces, which facilitate OM-sorption. The formation of these organo-mineral particles subsequently restricts microbial OM degradation, potentially altering the transport and facilitating the burial of OM within streams.

Metabolism of mineral-sorbed organic matter depends upon microbial lifestyle in fluvial ecosystems

In fluvial ecosystems mineral erosion, carbon (C) and nitrogen (N) fluxes are linked via organo-mineral complexation, where dissolved organic molecules bind to mineral surfaces. Biofilms and suspended aggregates represent major aquatic microbial lifestyles whose relative importance changes predictably through fluvial networks. We tested how organo-mineral sorption affects aquatic microbial metabolism, using organo-mineral particles containing a mix of ¹³C, ¹⁵N-labelled amino acids. We traced ¹³C and ¹⁵N retention within biofilm and suspended aggregate biomass and its mineralisation. Organo-mineral complexation restricted C and N retention within biofilms and aggregates and also their mineralisation. This reduced the efficiency with which biofilms mineralise C and N by 30 % and 6 %. By contrast, organo-minerals reduced the C and N mineralisation efficiency of suspended aggregates by 41 % and 93 %. Our findings show how organo-mineral complexation affects microbial C:N stoichiometry, potentially altering the biogeochemical fate of C and N within fluvial ecosystems.

Physico-geochemical and mineral composition of neem tree soils and relation to organic properties

The Neem tree, the oil of which has a long history of pesticide, fertilizer and medicinal use in India, has been studied extensively for its organic compounds. Here we present a physical, mineralogical and geochemical database resulting from the analyses of two Neem soil profiles (epipedons) in India. Neem tree derivatives are used in the manufacture of a variety of products, from anti-bacterial drugs and insecticides to fertilizers and animal feeds. A preliminary geochemical and mineralogical analysis of Neem soils is made to explore the potential for chemical links between Neem tree derivatives and soils. Physical soil characteristics, including colour, texture and clay mineralogy, suggest the two pedons formed under different hydrological regimes, and hence, are products of different leaching environments, one well-drained site, the other poorly drained. Geochemically, the two Neem soils exhibit similarities, with elevated concentrations of Th and rare earth elements. These elements are of interest because of their association with phosphates, especially monazite and apatite, and the potential link to fertilizer derivatives. Higher concentrations of trace elements in the soils may be linked to nutritional derivatives and to cell growth in the Neem tree.

Physicochemical and mineralogical characteristics of soil/saprolite cores from a field research site, Tennessee

Site characterization is an essential initial step in determining the feasibility of remedial alternatives at hazardous waste sites. Physicochemical and mineralogical characterization of U-contaminated soils in deeply weathered saprolite at Area 2 of the DOE Field Research Center (FRC) site, Oak Ridge, TN, was accomplished to examine the feasibility of bioremediation. Concentrations of U in soil–saprolite (up to 291 mg kg–1 in oxalate-extractable Uo) were closely related to low pH (ca. 4–5), high effective cation exchange capacity without Ca (64.7–83.2 cmolc kg–1), amorphous Mn content (up to 9910 mg kg–1), and the decreased presence of relative clay mineral contents in the bulk samples (i.e., illite 2.5–12 wt. %, average 32 wt. %). The pH of the fill material ranged from 7.0 to 10.5, whereas the pH of the saprolite ranged from 4.5 to 8. Uranium concentration was highest (about 300 mg kg–1) at around 6 m below land surface near the saprolite–fill interface. The pH of ground water at Area 2 tended to be between 6 and 7 with U concentrations of about 0.9 to 1.7 mg L–1. These site specific characteristics of Area 2, which has lower U and nitrate contamination levels and more neutral ground water pH compared with FRC Areas 1 and 3 (ca. 5.5 and

Casting of Self-Compacting Concrete

Increased productivity and improved working environment have had high priority in the development of concrete construction over the last decade. Development of a material not needing vibration for compaction—i.e. selfcompacting concrete (SCC)—has successfully met the challenge and is now increasingly being used in routine practice. The key to the improvement of fresh concrete performance has been nanoscale tailoring of molecules for surface active admixtures, as well as improved understanding of particle packing and of the role of mineral surfaces in cementitious matrixes. Fundamental studies of rheological behaviour of cementitious particle suspensions were soon expanded to extensive innovation programmes incorporating applied research, site experiments, instrumented full scale applications supporting technology, standards and guides, information efforts as well as training programmes. The major impact of the introduction of SCC is connected to the production process. The choice and handling of constituents are modified as well as mix design, batching, mixing and transporting. The productivity is drastically improved through elimination of vibration compaction and process reorganisation. The working environment is significantly enhanced through avoidance of vibration induced damages, reduced noise and improved safety. Additionally, the technology is improving performance in terms of hardened material properties like surface quality, strength and durability.

Control of biofilm growth through photodynamic treatments combined with chemical inhibitors: in vitro evaluation methods

The rock/atmosphere interface is inhabited by a complex microbial community including bacteria, algae and fungi. These communities are prominent biodeterioration agents and remarkably influence the status of stone monuments and buildings. Deeper comprehension of natural biodeterioration processes on stone surfaces has brought about a concept of complex microbial communities referred to as "subaerial biofilms". The practical implications of biofilm formation are that control strategies must be devised both for testing the susceptibility of the organisms within the biofilm and treating the established biofilm. Model multi-species biofilms associated with mineral surfaces that are frequently refractory to conventional treatment have been used as test targets. A combination of scanning microscopy with image analysis was applied along with traditional cultivation methods and fluorescent activity stains. Such a polyphasic approach allowed a comprehensive quantitative evaluation of the biofilm status and development. Effective treatment strategies incorporating chemical and physical agents have been demonstrated to prevent biofilm growth in vitro. Model biofilm growth on inorganic support was significantly reduced by a combination of PDT and biocides

Do spectral gamma ray data really reflect humid-arid palaeoclimates? A test from the Palaeogene Interbasaltic weathered horizons at the Giant’s Causeway, N.Ireland

Since 1999, the rapid, inexpensive and non-destructive use of Th/K and Th/U ratios from spectral gamma ray measurements have been used as a proxy for changes in palaeo-hinterland weathering. This model is tested here by analysis of in situ palaeoweathering horizons where clay mineral contents are well-known. A residual palaeoweathered horizon of Palaeogene laterite (developed on basalt) has been logged at 14 locations across N. Ireland using spectral gamma ray detectors. The results are compared to published elemental and mineralogical data. While the model of K and U loss during the early stages of weathering to smectite and kaolinite is supported, the formation (during progressively more advanced weathering) of gibbsite and iron oxides has reversed the predicted pattern and caused U and Th retention in the weathering profile. The severity (duration, humidity) of weathering and palaeoweathering may be estimated using Th/K ratios as a proxy. The use of Th/U ratios is more problematic should detrital gibbsite (or similar clays) or iron oxides be detected. Mineralogical analysis is needed in order to evaluate the hosts for K, U and Th: nonetheless, the spectral gamma ray machine offers a real-time, inexpensive and effective tool for the preliminary or conjunctive assessment of degrees of weathering or palaeoweathering.

Microscopic Mechanism and Kinetics of Ice Formation at Complex Interfaces: Zooming in on Kaolinite

Most ice in nature forms because of impurities which boost the exceedingly low nucleation rate of pure supercooled water. However, the microscopic details of ice nucleation on these substances remain largely unknown. Here, we have unraveled the molecular mechanism and the kinetics of ice formation on kaolinite, a clay mineral playing a key role in climate science. We find that the formation of ice at strong supercooling in the presence of this clay is about 20 orders of magnitude faster than homogeneous freezing. The critical nucleus is substantially smaller than that found for homogeneous nucleation and, in contrast to the predictions of classical nucleation theory (CNT), it has a strong two-dimensional character. Nonetheless, we show that CNT describes correctly the formation of ice at this complex interface. Kaolinite also promotes the exclusive nucleation of hexagonal ice, as opposed to homogeneous freezing where a mixture of cubic and hexagonal polytypes is observed.