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We examined the composition and spatial correlation of sulfur and mercury pools in peatland soil profiles by measuring sulfur speciation by 1s X-ray absorption near-edge structure spectrocopy and mercury concentrations by cold vapor atomic fluorescence spectroscopy. Also investigated were the methylation/demethylation rate constants and the presence of hgcAB genes with depth. Methylmercury (MeHg) concentration and organic disulfide were spatially correlated and had a significant positive correlation (p< 0.05). This finding is consistent with these species being products of dissimilatory sulfate reduction. Conversely, a significant negative correlation between organic monosulfides and MeHg was observed, which is consistent with a reduction in Hg(II) bioavailability via complexation reactions. Finally, a significant positive correlation between ester sulfate and instantaneous methylation rate constants was observed, which is consistent with ester sulfate being a substrate for mercury methylation via dissimilatory sulfate reduction. Our findings point to the importance of organic sulfur species in mercury methylation processes, as substrates and products, as well as potential inhibitors of Hg(II) bioavailability. For a peatland system with sub-μmol L–1porewater concentrations of sulfate and hydrogen sulfide, our findings indicate that the solid-phase sulfur pools, which have a much larger sulfur concentration range, may be accessible to microbial activity or exchanging with the porewater.

Biogeochemical processes in northern peatland ecosystems are influenced by seasonal temperature fluctuations that are changing with the climate. Methylmercury (MeHg), commonly produced in peatlands, affects downstream waters; therefore, it is important to understand how temperature transitions affect mercury (Hg) dynamics. We investigated how the freeze–thaw cycle influences belowground peat pore water total Hg (THg), MeHg, and dissolved organic carbon (DOC). Four large, intact peat columns were removed from an ombrotrophic peat bog and experimentally frozen and thawed. Pore water was sampled across seven depths in the peat columns during the freeze–thaw cycle and analyzed for THg, MeHg, and DOC concentrations. Freezing results showed increased concentrations of THg below the ice layers and limited change in MeHg concentrations. During thawing, THg concentrations significantly increased, whereas MeHg concentrations decreased. Limited bromide movement and depth decreases in THg and DOC concentrations were associated with increased bulk density and degree of humification in the peat. The experiment demonstrates the effects of the freeze–thaw cycle on Hg concentrations in northern peatlands. Changes to freeze–thaw cycles with climate change may exacerbate Hg cycling and transport processes in peatland environments.

Wildland fire can alter mercury (Hg) cycling on land and in adjacent aquatic environments. In addition to enhancing local atmospheric Hg redeposition, fire can influence terrestrial movement of Hg and other elements into lakes via runoff from burned upland soil. However, the impact of fire on water quality and the accumulation of Hg in fish remain equivocal. We investigated the effects of fire—specifically, a low‐severity prescribed fire and moderate‐severity wildfire—on young‐of‐the‐year yellow perch (Perca flavescens) and lake chemistry in a small remote watershed in the Boundary Waters Canoe Area Wilderness in northeastern Minnesota. We used a paired watershed approach: the fire‐affected watershed was compared with an adjacent, unimpacted (reference) watershed. Prior to fire, upland organic horizons in the two study watersheds contained 1549 μg Hg m−2on average. Despite a 19% decrease in upland organic horizon Hg stocks due to the moderate severity wildfire fire, fish Hg accumulation and lake productivity were not affected by fire in subsequent years. Instead, climate and lake water levels were the strongest predictors of lake chemistry and fish responses in our study lakes over 9 yr. Our results suggest that low‐ to moderate‐severity wildland fire does not alter lake productivity or Hg accumulation in young‐of‐the‐year yellow perch in these small, shallow lakes in the northern deciduous and boreal forest region. The study investigated wildland fire impact on fish mercury and lake chemistry.A paired watershed approach was used in the investigation.Wildland fire decreased upland organic soil carbon and mercury stocks.There was no impact of wildland fire on fish mercury or lake productivity.Lake chemistry and fish mercury varied with climate and lake water levels.

Changes in sulfate (SO42–) deposition have been linked to changes in mercury (Hg) methylation in peatlands and water quality in freshwater catchments. There is little empirical evidence, however, of how quickly methyl-Hg (MeHg, a bioaccumulative neurotoxin) export from catchments might change with declining SO42–deposition. Here, we present responses in total Hg (THg), MeHg, total organic carbon, pH, and SO42–export from a peatland-dominated catchment as a function of changing SO42–deposition in a long-term (1998–2011), whole-ecosystem, control-impact experiment. Annual SO42–deposition to half of a 2-ha peatland was experimentally increased 6-fold over natural levels and then returned to ambient levels in two phases. Sulfate additions led to a 5-fold increase in monthly flow-weighted MeHg concentrations and yields relative to a reference catchment. Once SO42–additions ceased, MeHg concentrations in the outflow streamwater returned to pre-SO42–addition levels within 2 years. The decline in streamwater MeHg was proportional to the change in the peatland area no longer receiving experimental SO42–inputs. Importantly, net demethylation and increased sorption to peat hastened the return of MeHg to baseline levels beyond purely hydrological flushing. Overall, we present clear empirical evidence of rapid and proportionate declines in MeHg export from a peatland-dominated catchment when SO42–deposition declines.

The Virtual Museum of Minerals and Molecules (VMMM) is a web-based resource presenting interactive, 3-D, research-grade molecular models of more than 150 minerals and molecules of interest to chemical, earth, plant, and environmental sciences. User interactivity with the 3-D display allows models to be rotated, zoomed, and specific regions of interest to be highlighted. The VMMM has been online since 1998 and currently serves 100 000 to 250 000 unique visitors annually from two mirror sites. In concept, it is a blend of a static bricks-and-mortar physical museum with wings, galleries, and displays with dynamic 3-D first-person video games. This museum is virtual not only in the sense that it exists in electronic format but also because the molecular size of the objects makes them colorless and imperceptibly small. To date, molecular visualization has been enabled in browsers using a proprietary third-party plug-in; compatibility with diverse platforms and browsers has been reduced over past years and recourse to open-source, molecular visualization Java applets may be required to avoid technological obsolescence.

Energy generation from biomass is an environmentally sound alternative to other energy producing technologies. Pilot studies have indicated that alfalfa (Medicago sativaL.) is a suitable feedstock for energy generation via the gasification process. The resulting ash is a potential liming agent and a source of plant nutrients. A growth chamber study was conducted with three soils to evaluate the potential use of this ash as a soil amendment. Corn (Zea maysL.) received 13 treatments: control, K and/or P fertilizer, seven ash rates (0.6 to 14.6 g ash kg−1soil), and one ash rate with K or P fertilizer. Soil pH increased with ash application on all soils. Ash application increased ammonium acetate‐exchangeable K, Ca, and Mg, and Olsen P in soil and decreased DTPA‐extractable soil Fe, Mn, Ni, and Pb. Averaged across the three soils, slopes of the cations recovered in plant and soil vs. cations applied in the ash were 0.48, 0.21, and 0.22 of total ash K, Ca, and Mg, respectively (r2> 0.97). Ash significantly increased plant K and Mo, and decreased Mg, Mn, and Zn concentration. Tissue P concentrations were not affected by ash, but increased with P fertilizer. Phosphorus fertilizer increased plant dry mass (DM), but K fertilizer did not, thus K did not limit yield. Alfalfa stem gasification ash is a potential liming agent, a source of K, and would not lead to excessive accumulation of trace elements in soil or plants when applied at rates based on lime or K need.

The binding of Hg2+in organic matter of soils and waters controls the transport and transformations of Hg in terrestrial and aquatic ecosystems. We developed a competitive complexation method using the strong complexation of Hg2+by Br−for determining the Hg2+binding strength in organic soils at native and elevated Hg concentrations. The distribution coefficients determined in KBr suspensions for sorption of native Hg2+to soil organic carbon (SOC) (KSOC) are in the range of 1022to 1023. The KSOCsignificantly decreased with increased additions of Hg2+and with decreasing pH. Using data for reduced organic S concentrations determined by x‐ray absorption near‐edge structure spectroscopy (XANES), we calculated surface complex formation constants on the order of 1032for a model site having acidity constants of mercaptoacetic acid. This value is in fair agreement with the tabulated value of 10345for Hg2+binding in mercaptoacetic acid. At native Hg concentrations, formation constants and KSOCvalues were similar for different types of soil organic matter along transects from uplands into wetlands, despite varying concentrations of Hg and reduced organic S. Our adsorption data are consistent with the conclusions from our previous extended x‐ray absorption fine structure spectroscopy (EXAFS) study that in a humic acid and soil, Hg2+ions bond in two‐fold coordination involving one reduced S and one O or N.

The chemical composition of the soil solution provides useful information on the feasibility of amending agricultural land with municipal and industrial waste, because the soil solution is the medium for most soil chemical reactions, the mobile phase in soils, and the medium for mineral absorption by plant roots. The soil solutions studied in this research were from plots in a 4‐yr field experiment conducted to evaluate the effects of the trace metals and P in sewage‐sludge incinerator ash. Treatments compared ash with equivalent P rates from triple‐superphosphate fertilizer and a control receiving no P application. Ash and phosphate fertilizer were applied annually at rates of 35, 70, and 140 kg citrate‐soluble P ha−1. Cumulative ash applications during 4 yr amounted to 3.6, 7.2, and 14.4 Mg ash ha−1. Soil solutions were obtained by centrifugation‐immiscible liquid displacement using a fluorocarbon displacing agent. Following chemical analysis, a chemical speciation model was used to determine possible solubility‐controlling minerals for trace metals and P, and correlations between solution composition and plant uptake were analyzed. Ash increased soil solution pH, Cd, and Zn, but had no significant effect on solution concentrations of other trace metals. Ash increased soil solution P and S, but P increases were less than those from equivalent citrate‐soluble P rates of phosphate fertilizer. Soil solution Ba appeared to be in equilibrium with barite (BaSO4). Solubility data did not indicate that any discrete mineral phases controlled Cd, Zn, Cu, Ni, Ph, or P solubility. Soil solution P concentration was strongly correlated (r= 0.92) with P accumulation in sweet corn (Zea maysL.) plants, but solution trace metal concentrations were either weakly correlated (r= 0.49 for Zn and 0.36 for Cd) or not signilicantly correlated (r= 0.09 for Ni and −0.25 for Cu) with plant accumulation.

Dyes are often used as tracers of water and solute flow in soil. However, there has been little published research on the effects of flow velocity on the relative movement of dye and wetting fronts. Recently, the FD&C Blue no. 1 dye has been used as a tracer of preferential water flow paths in soils, and has attractive properties suggesting it will be used increasingly in the future. The objective of this study was to characterize the effects of flow velocity on the adsorption characteristics of the FD&C Blue no. 1. We performed a series of laboratory experiments on the characterization of the equilibrium adsorption isotherm as well as the effect of flow velocity on adsorption characteristics of the FD&C Blue no. 1 in three horizons of Verndale sandy loam (coarse‐loamy over sandy, mixed, frigid Udic Argiboroll). Batch equilibration (24 h) measurements resulted in linearized Freundlich distribution coefficients (Kd) of 4.33, 23.95, and 4.59 L kg−1for the Ap, Bt, and C horizons, respectively. Neither organic C nor clay content differences accounted for the variation between horizons. Leaching experiments with a 1 g L−1dye solution and repacked soil columns containing either Ap, Bt, or C horizon material showed that the dye was retarded relative to the wetting front, and that the extent of retardation was inversely related to the time period during which dye solution was applied. Therefore, this dye (and perhaps others) should not be used to make inferences about the movement of water or other solutes until the effect of the application rate is evaluated for the flow conditions in the system(s) of interest.

Three methods of determining the extent of excess salt removal during alcohol washing of clays were compared. Clays (<2 µm) separated from Wyoming bentonite, halloysite, and a Fargo soil (fine, montmorillonitic, frigid Vertic Haplaquoll) were saturated with 0.5 MCaCl2or 1.0 MKCl. Excess salts were removed by eight consecutive washes with 95% ethanol. Vortex and ultrasonication mixing methods were also compared. After centrifugation, the supernatants were analyzed for excess salt by (i) the AgNO3‐Cl test, and by measuring (ii) electrical conductivity, and (iii) elemental concentrations. Elemental concentration and conductivity measurements indicated that substantial amounts of excess Ca and K (approximately 5 to 10% of CEC) remained in the clays when the AgNO3‐Cl test was first negative. Ultrasonication reduced the number of washings required to remove excess salt from clays when compared with vortex mixing. The results demonstrate that electrical conductivity is a rapid and reliable method of determining completion of excess salt removal.

The quantification of the relative mineralogical composition of clay mixtures by powder X-ray diffraction or chemical mass balance methods has been severely hampered by a lack of representative standards. The recent development of elemental mass balance models that do not require standards for all minerals in the mixture may help circumvent this problem. These methods, which are based on the numerical optimization of systems of non-linear equations using the Marquardt algorithm, show promise for mineral quantification. The objective of this study is to make a preliminary assessment of the accuracy of these methods and to compare them to linear models that require standards for all mineral phases. Methods 1 and 2 are based on weighted average solutions to simultaneous linear equations solved for single samples with known standards. Solutions were achieved by a matrix decomposition algorithm and the Marquardt algorithm, respectively. Methods 3 and 4 are based on a set of simultaneous non-linear equations with reduced non-linearity solved by least squares optimization based on the Marquardt algorithm for multiple samples. Illite and halloysite compositions were fixed in Method 3, only the halloysite composition was fixed in Method 4. All models yielded relative weight fractions of the three mineral components; additionally, Methods 3 and 4 yielded compositions of smectite, and smectite and illite, respectively. Ten clay mixtures with varying proportions of the <0.2 μm size fraction of three different reference clays (Wyoming bentonite, Fithian illite, and New Bedford halloysite) were prepared gravi-metrically and analyzed by inductively coupled plasma-atomic emission spectroscopy. Accuracy of the four methods was evaluated by comparing the known mineralogical compositions of the mixtures with those predicted by the models. Relative errors of 5 and 10% (randomly +/-) were imposed on the elemental composition of the smectite standard to simulate errors due to lack of good standards. Not surprisingly, the accuracy of Methods 1 and 2 decreased rapidly with increasing error. Because Methods 3 and 4 optimized for the smectite composition and only used it for an initial guess, they were unaffected by the level of introduced error. They accurately quantified the mineralogical compositions of the mixtures and the elemental compositions of smectite, and smectite and illite, respectively.

A study of Wisconsinan loess in part of southeastern Minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the Mississippi River. Two Wisconsinan loess units, the Peoria Loess and Roxana Silt, occur in the study area. Peoria Loess, 1-8 m thick, fines systematically eastward from an abrupt western border towardthe Mississippi. There are no apparent grain-size trends away from other adjacent rivers. Peoria Loess thickness generally decreases eastward, but is highly variable, probably because of differential erosion. Potential sources for this unit are pre-Wisconsinan sediments on the Iowan Erosion Surface immediately west of the border of thick loess and Wisconsinan glacial sources tens or hundreds of kilometers to the west. The underlying Roxana Silt, up to 1 m thick, occurs only near the Mississippi and fines away from that river. The Roxana Silt deposit could reflect aggradation of the Mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area. By contrast, transport of the Peoria Loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive, very sparsely vegetated surfaces west of the study area when the Peoria Loess accumulated.