Paul M. Bertsch

Forest sources and pathways of organic matter transport to a blackwater stream: a hydrologic approach

Quantitative information regarding landscape sources and pathways of organic matter transport to streams is important for assessing impacts of terrestrial processes on aquatic ecosystems. We quantified organic C, a measure of organic matter, flowing from a blackwater stream draining a 12.6 km2 watershed on the upper Atlantic Coastal Plain in South Carolina, and utilized a hydrologic approach to partition this outflow between its various pathways from upland and wetland forest sources. Results of this study indicate that 28.9 tonnes C yr−1 were exported in stream flow, which was estimated to be 0.5% of the annual C input from forest detritus to the watershed. Upland forest, which covers 94% of the watershed area, contributed only 2.0 tonnes C yr−1 to stream flow, which amounted to 0.04% of detritus annually produced by the upland forest. Organic matter was transported from uplands to the stream almost entirely through groundwater. Apparently, upland soils are too sandy to support overland flow, and the sloping topography insufficiently extensive or steep enough to drive important quantities of interflow. Riparian wetland forest, which covers only 6% of the watershed area, contributed 26.9 tonnes C yr−1 to stream flow, amounting to about 10.2% of detritus annually produced by the wetland forest. Dissolved organic C leached from wetland soil accounted for 63% of all organic C entering the stream, and was transported chiefly in baseflow. These results indicate that upland detritus sources are effectively decoupled from the stream despite the sandy soils and quantitatively confirm that even small riparian wetland areas can have a dominant effect on the overall organic matter budget of a blackwater stream. In view of the recognized importance of dissolved organic matter in facilitating transport of other substances (e.g., cation nutrients, metals, and insoluble organic compounds), our results suggest that the potential for movement of these substances through wetland soils to streams in this region is high.

Evidence That the ZNT3 Protein Controls the Total Amount of Elemental Zinc in Synaptic Vesicles

The ZNT3 protein decorates the presynaptic vesicles of central neurons harboring vesicular zinc, and deletion of this protein removes staining for zinc. However, it has been unclear whether only histochemically reactive zinc is lacking or if, indeed, total elemental zinc is missing from neurons lacking the Slc30a3 gene, which encodes the ZNT3 protein. The limitations of conventional histochemical procedures have contributed to this enigma. However, a novel technique, microprobe synchrotron X-ray fluorescence, reveals that the normal 2- to 3-fold elevation of zinc concentration normally present in the hippocampal mossy fibers is absent in Slc30a3 knockout (ZNT3) mice. Thus, the ZNT3 protein evidently controls not only the “stainability” but also the actual mass of zinc in mossy-fiber synaptic vesicles. This work thus confirms the metal-transporting role of the ZNT3 protein in the brain.

Influence of sorbate-sorbent interactions on the crystallization kinetics of nickel- and lead-ferrihydrite coprecipitates

Abstract Metals sorbed to or coprecipitated with ferrihydrite can significantly inhibit transformation to more crystalline endproducts. We hypothesized that metals with a higher stability constant for a metal-ferrihydrite surface complex would retard the transformation process to a greater extent. To test this hypothesis, we examined the influence of Ni or Pb sorption on the kinetics of ferrihydrite crystallization to goethite/hematite. Reported surface stability constants for Ni and Pb sorbed to ferrihydrite are logK 1,int = 0.37 and 4.0, respectively (Dzombak and Morel, 1990) . The structural evolution of nickel- and lead-ferrihydrite coprecipitates was studied for various metal loadings during aging at pH 6 or 11 and 70°C. Results of aging studies demonstrated that the influence on transformation kinetics was not related to the magnitude of the stability constant of the Ni- or Pb-ferrihydrite surface complex. At pH 11, crystallization was retarded more significantly in the presence of Ni and rates decreased with increasing Ni/Pb surface loading. At pH 6, crystallization rates were accelerated in the presence of Pb, and this was also true for systems at the lowest Ni loading. However, crystallization rates in the presence of Ni were always slower relative to systems containing Pb. Characterization of crystalline iron (hydr)oxide endproducts by x-ray diffraction and high-resolution thermogravimetric analysis showed that hematite was formed to a greater extent than goethite in the presence of Ni. X-ray absorption fine structure spectroscopy suggested that the majority of sorbed Pb was present as an inner-sphere surface complex. The distribution of coprecipitated Ni or Pb on aged solids, as assessed via continuous dissolution with oxalic acid, suggested that a significant fraction of Ni was partitioned into the structure of a crystalline iron (hydr)oxide. In contrast, Pb desorption/dissolution behavior confirmed that this metal was primarily associated with surface sites or poorly ordered iron (hydr)oxide phases. The relative metal-specific influence on crystallization rate and endproduct, and the apparent Ni and Pb distribution in aged solids suggest that Pb forms a more kinetically labile sorption complex than Ni with iron (hydr)oxides.

Synchrotron X-Ray Techniques in Soil, Plant, and Environmental Research

Publisher Summary New generations of synchrotrons designed exclusively as X-ray sources have followed, and these powerful sources of X-rays have become important to a wide variety of scientific disciplines. The past five years have seen a growing number of applications of synchrotron-based techniques to problems in the soil and environmental sciences. Synchtron-based techniques have applications in many other areas of agricultural research as well. The chapter highlights some of the major applications in soil, plant, and environmental research. Many of these applications represent the first use of synchrotron-based techniques in particular agricultural disciplines. The chapter describes the ways in which synchrotrons work, describe the properties of synchrotron radiation, and explain the terminology associated with synchrotron-based research. Synchrotrons vary in their capabilities, so a general understanding of their differences will allow, in a general sense, to assess the suitability of a particular synchrotron for a specific experiment. Synchrotron light is extremely intense is emitted over a wide range of energies, is highly collimated and highly polarized, and has a pulsed time structure. The chapter reviews the applications of synchrotron-based techniques to soil, plant, and environmental research and suggests possible future applications. Some techniques are well established and widely used, e.g., X-ray absorption spectroscopy, X-ray diffraction, and the X-ray microprobe. Other techniques, such as Mossbauer and infrared spectroscopies, are still being developed and there is little or no literature on direct applications to soil, plant, or environmental research.

Chemistry and structure of colloids obtained by hydrolysis of Fe(III) in the presence of SiO4 ligands

Abstract Fe(III)–Si systems at various Si/Fe molar ratios and pH values were examined at the local and semi-local scale. The growth of Fe species is strongly dependent on the Si concentration: at Si/Fe 1, the predominance of edge linkages corresponds to a two dimensional growth. Si–O–Fe and Si–O–Si bonds are formed simultaneously from the lowest pH and the lowest Si/Fe. At low pH, silica domains of approximately 2 nm are detected within the samples having the highest Si/Fe ratios. The polymerization level of Si strongly decreases at high pH, whereas Fe polymerization is only moderately sensitive to pH variations. The high fractal dimension of these amorphous phases indicates dense aggregation. The evolution of the fractal dimension with pH is correlated with modifications of the Fe speciation.

Factors influencing uranium reduction and solubility in evaporation pond sediments

Evaporation ponds in the San Joaquin Valley (SJV), CA, USA that are used for the disposal of irrigation drainage waters, contain elevated levels of U that may be a threat to pond wildlife. The ponds support euryhaline algae, which become incorporated in the sediments as depositional organic matter (OM) — facilitating reducing conditions. Our earlier studies have shown that U in one SJV sediment was primarily present as the highly soluble U(VI) species (as opposed to the less soluble U(IV) species), despite the presence of volatile sulfides. In this research, we investigated the effects of native pond algae (Chlorella) and potential reducing agents on U redox chemistry of SJV pond sediments. San Joaquin Valley pond sediments were equilibrated with natural and synthetic pond inlet waters containing approximately 10 mg U(VI) L−1 to which reducing agents (acetate, sucrose, and alfalfa shoot) were added. The equilibrations were done under oxic (Chlorella only) and O2-limiting conditions (remaining treatments). Sediments were examined for changes in average U oxidation state by X-ray near-edge absorption structure (XANES) spectroscopy and U concentration by ICP-MS.For the alfalfa treatments, a 95 percent loss of U(VI) from solution, the presence of sulfides, and results from the XANES studies suggest U(VI) was reduced to U(IV). Upon exposure to air, the precipitated U was readily oxidized, suggesting the reduced U is susceptible to oxidation. Much less reduction of U(VI) was observed in the other 3 treatments and the solid phase was dominated by U(VI) as in the natural pond sediments. A second study was conducted with pond sediment-water suspensions to determine the effects of controlled PCO2 and low redox potential (Eh) on U solubility. These suspensions were equilibrated at 0.22 and 5.26 kPa PCO2 and allowed to “free-drift” from an oxidized to a reduced state. At high Eh and high PCO2, dissolved U concentrations were higher than in the low PCO2 systems due to greater complexation with CO3. Dissolved U concentrations decreased only under intense sulfate reducing conditions, even at low Eh conditions. It appears that U reduction occurred by chemical reduction via sulfide ion. Comparing the XANES data of the pond sediments with the laboratory-produced solids we conclude that biosorption by algae and bacteria is the dominant mechanism depositing U in the sediments. Even though there are organisms that can use U(VI) as a terminal electron acceptor, we found that sulfate reduction was preferred in these high-SO4 waters. Mixed oxidation state U-solids were preferentially formed in the pond sediments and in the lab except under intense SO4 reducing conditions.

Spectroscopic characterization of uranium in evaporation basin sediments

Evaporation ponds in the San Joaquin Valley (SJV), CA, used for the containment of irrigation drainage waters contain elevated levels of uranium (U) resulting from the extensive leaching by carbonate-rich irrigation waters of the local agricultural soils that contain low levels of naturally-occurring U. The SJV ponds are subjected to changes in redox chemistry with cycles of drying and flooding. Our past studies have shown that U in the SJV Pond 14 surface sediments is present as mostly the oxidized and soluble form, U(VI). However, we were uncertain whether the U in the soil was only present as a U oxide of mixed stoichiometry, such as U3O8(s) (pitchblende) or other species. Here we present characterization information, which includes wet chemical and in situ spectroscopic techniques (X-ray absorption near-edge structure (XANES) and low temperature time-resolved luminescence spectroscopies) for samples from two SJV Pond sediments. Surface sediments from SJV Pond 16 were characterized for average oxidation state of U with XANES spectroscopy. The fraction of U(VI) to U(IV) in the Pond 16 sediments decreased with depth with U(IV) being the dominant oxidation state in the 5 cm to 15 cm depth. Two luminescent U(VI) species were identified in the surface sediments from Pond 14; a U(VI)-tricarbonate phase and another phase likely comprised of U(VI)-hydroxide or hydroxycarbonate. The luminescent U(VI) population in the Pond 16 sediments is dominated by species with comparable spectral characteristics to the U(VI)-hydroxide or hydroxycarbonate species found in the Pond 14 sediments. The luminescence spectroscopic results were complemented by wet chemical U leaching methods, which involved the use of carbonate and sulfuric acid solutions and oxidizing solutions of peroxide, hypochlorite and Mn(IV). Leaching was shown to decrease the total U concentration in the sediments in all cases. However, results from luminescence studies of the residual fraction in the leached sediments suggest that there was no selectivity in the removal of the spectroscopically identifiable U(VI) species by acidic oxidizing, basic oxidizing or basic non-oxidizing solutions. A net increase in the emission intensity of the U(VI) luminescent species in most leached samples was consistent with conversion of U(IV) to U(VI), as a result of chemical oxidation and exposure to air during the leaching process. The wet chemical extractions and in situ spectroscopic techniques provided fundamental and basic knowledge about the fraction of U(IV) to U(VI), the speciation of luminescent U(VI), and the susceptibility of the sediment U species to leaching.

Application of Synchrotron X‐Ray Microbeam Spectroscopy to the Determination of Metal Distribution and Speciation in Biological Tissues

Abstract Resolving the distribution and speciation of metal(loid)s within biological environmental samples is essential for understanding bioavailability, trophic transfer, and environmental risk. We used synchrotron x‐ray microspectroscopy to analyze a range of samples that had been exposed to metal(loid) contamination. Microprobe x‐ray fluorescence elemental mapping (µSXRF) of decomposing rhizosphere microcosms consisting of Ni‐ and U‐contaminated soil planted with wheat (Triticum aestivum) showed the change in Ni and U distribution over a 27‐day period, with a progressive movement of U into decaying tissue. µSXRF maps showed the micrometer‐scale distribution of Ca, Mn, Fe, Ni, and U in roots of willow (Salix nigra L.) growing on a former radiological settling pond, with U located outside of the epidermis and Ni inside the cortex. X‐ray computed tomography (CMT) of woody tissue of this same affected willow showed that small points of high Ni fluorescence observed previously are actually a Ni‐rich substance contained within an individual xylem vessel. µSXRF and x‐ray absorption near‐edge spectroscopy (XANES) linked the elevated Se concentrations in sediments of a coal fly ash settling pond with oral deformities of bullfrog tadpoles (Rana catesbeiana). Se distribution was localized within the deformed mouthparts, and with an oxidation state of Se (−II) consistent with organo‐Se compounds, it suggests oral deformities are caused by incorporation of Se into proteins. The range of tissues analyzed in this study highlight the applicability of synchrotron X‐ray microspectroscopic techniques to biological tissues and the study of metal(loid) bioavailability. This paper was by special invitation as a contribution to a special issue of the journal entitled “Application of Spectroscopic Methods to Environmental Problems.” The special issue was organized by Professor Peter A. Tanner, Professor in the Department of Biology and Chemistry at City University of Hong Kong.

Ionic tracer movement through highly weathered sediments

A highly-weathered, sandy aquifer material from the Upper Coastal Plain region of the southeastern U.S.A. (Aiken, South Carolina) was used to determine the impact of ionic strength and solution composition on the determination of physical transport parameters using ionic tracers. The mineralogy of the clay fraction consisted primarily of kaolinite, goethite and mica. Repacked saturated columns (bulk density ∼ 1.5 g cm−3) were leached at a constant rate (∼ 0.25 cm min−1) with a given tracer solution. For comparison, tritium (∼ 200 pCi mL−1) was included in leachate of selected columns and several of the experiments were replicated in columns of acid-washed sand. Pore volume estimates based on tritium breakthrough were consistent with those calculated from the bulk density of the repacked matrix. In contrast, solute breakthrough for the sandy geologic material was dependent on concentration, as well as cation and anion type. At low ionic strenghts (0.0005–0.010 M) that are analogous to conditions that may be encountered ins field-scale transport experiments, neither the cation nor the anion acted conservatively, yielding systematically high estimates of column porosity or low estimates of flow velocity. At the higher ionic strengths (∼ 0.10 M), solute breakthrough was essentially conservative regardless of ionic composition. The impact of cation valence and concentration on Br− breakthrough was determined using MgBr2 and KBr solutions of varying concentrations (0.001–0.1 N). Bromide breakthrough was substantially delayed for concentrations below 0.10 M and was delayed to a greater extent in the presence of a divalent cation (Mg2+) than in the presence of a monovalent cation (K+). Failure to recognize these interactions in the field could lead to a false interpretation of Br displacement in terms of physical interactions, i.e. flow velocity, dispersivity, etc.

Sodium and chloride sorption by imogolite and allophanes

The surface excesses of Na and Cl on synthetic imogolite and allophanes with varying Al/Si molar ratios in 0.10 M and 0.01 M NaCl solutions were determined using 22Na and 36Cl as ion probes. The point of zero net charge (PZNC) values ranged from 4.1 to 8.4, increasing with the Al/Si molar ratio for the allophanes, and was highest for imogolite (Al/Si = 2.01). The PZNC values were significantly lower than the point of zero charge (PZC) values previously determined by microelectrophoresis for the same material, indicating that Na resided within the shear plane to a greater extent than Cl. The PZNC values of allophanes were lower than their PZSE values, indicating that permanent charge existed in allophanes, and increased as Al/Si decreased. Conversely, the PZNC of imogolite was higher than its point of zero salt effect (PZSE) determined by potentiometric titration. Adsorption of Cl on imogolite from 0.1 and 0.01 M NaCl solutions below pH 8.4 and of Na from 0.1 M NaCl solutions between pH 5 and 8.4 exceeded the proton charge determined by potentiometric titration. There was no direct evidence of permanent charge in imogolite and excess Cl adsorption could not be entirely explained by simultaneous intercalation of Na and Cl. Isomorphic substitution of Al in tetrahedral sites was shown to increase with decreasing Al/Si by 27Al high-resolution solid-state nuclear magnetic resonance (NMR) spectra of allophanes, and was absent in imogolite. The chemical shifts of Al(4) and Al(6) were similar in allophanes (63.0–64.7 ppm and 6.1–7.8 ppm, respectively) and the chemical shift of Al(6) was 9.4 in imogolite.