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Changes in sulfate (SO

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

Mineral specific surface area (SSA) increases as primary minerals weather and restructure into secondary phyllosilicate, oxide, and oxyhydroxide minerals. SSA is a measurable property that captures cumulative effects of many physical and chemical weathering processes in a single measurement and has meaningful implications for many soil processes, including water-holding capacity and nutrient availability. Here we report our measurements of SSA and mineralogy of two 21 m deep SSA profiles at two landscape positions, in which the emergence of a very small mass percent (

Mercury is a ubiquitous pollutant that accumulates in peatlands, an ecosystem highly sensitive to climate change. We examined the effects of increasing temperature and elevated atmospheric carbon dioxide (CO2) on the concentration of total mercury (THg) in peatland soil and porewater. This research was performed at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, an ecosystem-scale manipulation in an ombrotrophic bog in northern Minnesota, USA, which includes five temperature levels (above- and below-ground warming), with ambient or enhanced CO2 concentration. The effect of temperature on THgporewater concentration was dependent on depth but overall, increasing temperature led to increased THgporewater concentrations. The ratio of THgpeat to THgporewater decreased, indicating that THg moved from the peat into porewater under warmer conditions. Increased temperature resulted in decreased water table height, and as the water table dropped, increased THgporewater concentrations were observed, as well as decreased THgpeat concentration. The effect of elevated CO2 on THg concentrations in peat and porewater was less clear but in the top portion of the depth profile (0 cm to -40 cm), a negative correlation between elevated CO2 and THgpeat and a positive correlation between elevated CO2 and THgporewater concentration was observed. Our findings indicate with projected climate change, we may see enhanced concentrations of mercury in peatland porewaters that are available for export to surface waters, with potential implications for bioaccumulation in downstream aquatic communities.

The uppermost portion of the peat profile, an area of active diagenetic processes, is exceedingly important for understanding peatland dynamics and the diagenesis and geochemistry of atmospherically-deposited materials. We investigated high resolution carbon (C) accrual and peat decomposition rates at two Sphagnum-rich ombrotrophic bogs and one fen in northern Minnesota, USA by analyzing 1 cm increments from 30 cm thick intact frozen blocks of peat soil. We conducted radiocarbon analysis of Sphagnum cellulose to determine peat age and net C accumulation at each depth interval. Calibrated peat ages were determined using CALIBomb and a compilation of calibration datasets for the pre-bomb period. We fit data with a negative exponential accumulation model and used model-derived parameters to estimate net primary productivity (NPP) and a peat decomposition rate constant k. FTIR spectroscopy and C:N were used to derive humification indices and to chemically characterize the peat. NPP ranged from 180 to 266 g C m−2 year−1, k ranged from 0.015 to 0.019 year−1. Net C accumulation rates ranged from 112 to 174 g C m−2 year−1 at 25 years and 70 to 113 g C m−2 year−1 at 50 years. Mass loss was up to 55% during the first 50 years of peat accumulation. Decomposition is greater at depth in the bogs—where 25 cm of peat correspond to 55 years of peat accumulation—than in the fen, where peat age is approximately 25 years at 25 cm depth. Information on fine-scale variations in peat mass decomposition and loss across ombrotrophic bogs and a fen help interpret other diagenetic processes in peatlands.

In mountainous landscapes, rates of soil morphological and biogeochemical change during secondary forest succession (SFS) can vary widely with elevation due to gradients in water, energy, and mineral weathering status. Improved understanding of how elevation mediates the response of soils to SFS is critical not only for reducing the uncertainty of soil maps in complex terrain, but also for predicting the edaphic effects of SFS under future climatic conditions. Focusing on volcanic ash soils in Veracruz, Mexico, we sought to 1) quantify how elevation mediates the dynamics of soil organic carbon (SOC) and geochemistry during SFS and 2) disentangle the soil-forming processes responsible for altitudinal trends. We characterized 16 soil profiles (0-100 cm depth) at various stages of SFS after pasture abandonment at the lower and upper altitudinal limits of the cloud forest ecosystem (1350-1550 and 2050-2220 m) using a broad suite of analytical techniques. Elevation strongly affected the depth distributions of all measured inorganic elements and enhanced the rate of accumulation of biocycled elements (e.g., P, K, Ca, S, Mn) during SFS. Notwithstanding altitudinal differences in C inputs (namely, forest floor recovery rates), profile-level SOC composition and dynamics were more sensitive to mineral weathering status than to SFS stage or elevation per se. Differentiation of soil mineralogy and SOC dynamics contributed to variation of physical properties, consistent with local ‘folk’ soil taxonomy. Ongoing work addresses the interplay of climate, geology, and redistribution processes in determining the mineralogical properties and, ultimately, SOC dynamics of volcanic ash soils. Our findings underscore the importance of considering the complex environmental contingency of soil recovery rates during SFS.

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 () 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 on 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.

In upland soils in humid climates, mineral stabilization of organic matter (OM) on millennial scales is often driven by the abundance of poorly crystalline, metastable chemical weathering products....

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.

Pedogenesis produces fine-grained magnetic minerals that record important information about the ambient climatic conditions present during soil formation. Yet, differentiating the compounding effects of non-climate soil forming factors is a nontrivial challenge that must be overcome to establish soil magnetism as a trusted paleoenvironmental tool. Here, we isolate the influence of vegetation by investigating magnetic properties of soils developing under uniform climate, topography, and parent material but changing vegetation along the forest-prairie ecotone in NW Minnesota. Greater absolute magnetic enhancement in prairie soils is related to some combination of increased production of pedogenic magnetite in prairie soils, increased deposition of detrital magnetite in prairies from eolian processes, or increased dissolution of fine-grained magnetite in forest soils due to increased soil moisture and lower pH. Yet, grain-size specific magnetic properties associated with pedogenesis, for example relative frequency dependence of susceptibility and the ratio of anhysteretic to isothermal remanent magnetization, are insensitive to changing vegetation. Further, quantitative unmixing methods support a fraction of fine-grained pedogenic magnetite that is highly consistent. Together, our findings support climate as a primary control on magnetite production in soils, while demonstrating how careful decomposition of bulk magnetic properties is necessary for proper interpretation of environmental magnetic data.

Identifying what determines fish mercury (Hg) bioaccumulation remains a key scientific challenge. While there has been substantial research on spatial variation in fish Hg bioaccumulation, the factors that influence temporal fluctuations in fish Hg have received less attention to date. In this study, we built upon a growing body of research investigating young-of-the-year (YOY) yellow perch Hg bioaccumulation and investigated annual fluctuations in YOY yellow perch Hg in six lakes in northeastern Minnesota over eight years. After accounting for spatial variation between the study lakes, we used model averaging to identify the lake physiochemical and climate factors that best explain temporal variation in fish biomass and fish Hg. Fish biomass of YOY yellow perch had a positive relationship with chlorophyll-α and total Kjeldahl nitrogen and a negative relationship with dissolved iron and dissolved oxygen. There was a positive relationship between annual variation in yellow perch Hg concentration and annual variation in lake total suspended solids, dissolved Fe and pH. Additionally, there was a negative relationship between fish Hg concentration and lake total Kjeldahl nitrogen and growing degree days. Together, our results suggest that annual variation in allochthonous inputs from the watershed, in-lake processes, and climate variables can explain temporal patterns in Hg bioaccumulation and growth biodilution is an important process controlling yellow perch Hg concentrations.

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 () 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 on 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.

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A sequential extraction technique for compartmentalizing mercury (Hg) in leaves was developed based on a water extraction of Hg from the leaf surface followed by a solvent extraction of the cuticle. The bulk of leaf Hg was found in the tissue compartment (90-96%) with lesser amounts in the surface and cuticle compartments. Total leaf concentrations of Hg varied among species and was most closely correlated with the number of stomates per sample, supporting the hypothesis that stomatal uptake of atmospheric Hg (most likely Hg(0)) is a potential uptake pathway. Mercury concentrations in leaves were monitored from emergence to senescence and showed a strong positive correlation with leaf age. Leaves accumulated Hg throughout the growing season; the highest uptake rates coincided with periods of high photosynthetic activity. Concentrations of Hg in leaf tissue increased steadily throughout the season, but no such trends were observed for surficial or cuticular accumulation. Factors affecting the variability of Hg in leaves were analyzed to improve protocols for the potential use of leaves as passive monitors of atmospheric Hg. Results show that total leaf Hg concentrations are affected by leaf age and leaf placement in the crown.

Invasive earthworms perturb natural forest ecosystems that initially developed without them, mainly by consuming the forest floor (an organic rich surficial soil horizon) and by mixing the upper parts of the soil. The fate of mercury (Hg) formerly contained in the forest floor is largely unknown. We used two mass balance approaches (simple mass balance and geochemical mass balance) to quantitatively assess the impact of exotic earthworms on Hg cycling in forest soils and the fate of Hg formerly contained in the forest floor. Two sets of soils, collected in 2009 and 2014 from an earthworm invasion transect in north central Minnesota, were analyzed in this study. We observed a substantial loss of Hg from the soil system following earthworm invasion. Mass balance calculations showed that 35 to 65 % of the forest floor Hg was retained in the underlying mineral soil with the remainder unaccounted. The most likely explanation for the loss of forest floor Hg from the system is microbially induced volatilization of Hg by soil microbes and possibly by earthworm gut microbes during consumption of the forest floor. Our calculations suggest that exotic earthworms can substantially perturb mercury cycling in the topsoil. Forest floor Hg may accumulate within worm biomass; however, this process can account for only a small fraction (1 to 3 %) of the lost Hg. Additionally, we calculated the mass balance of organic carbon (C) due to Hg’s high affinity for organic matter and found that a portion of the organic carbon also appears to be lost from the soil system.

Many carbon dioxide (CO2) emission-reduction strategies currently under consideration rely on terrestrial carbon (C) sequestration to offset substantial proportions of CO2 emissions. We estimated C sequestration rates and potential land areas for a diverse array of land-cover changes in the Upper Midwest of the US, a “best case” region for this study because of its relatively modest CO2 emissions and the large areas of cropland potentially available for conversion. We then developed scenarios that apply some of the most widespread mitigation strategies to the region: the first, which aimed to offset 29% of regional CO2 emissions, required the unrealistic loss of two-thirds of working cropland; the second, which estimated the emission offset attainable by conversion of 10% of harvested croplands (5.8% of the US total), resulted in

The primary objective of this research is to investigate relationships between mercury in upland soil, lake water and fish tissue and explore the cause for the observed spatial variation of THg in age one yellow perch (Perca flavescens) for ten lakes within the Superior National Forest. Spatial relationships between yellow perch THg tissue concentration and a total of 45 watershed and water chemistry parameters were evaluated for two separate years: 2005 and 2006. Results show agreement with other studies where watershed area, lake water pH, nutrient levels (specifically dissolved NO(3)(-)-N) and dissolved iron are important factors controlling and/or predicting fish THg level. Exceeding all was the strong dependence of yellow perch THg level on soil A-horizon THg and, in particular, soil O-horizon THg concentrations (Spearman rho=0.81). Soil B-horizon THg concentration was significantly correlated (Pearson r=0.75) with lake water THg concentration. Lakes surrounded by a greater percentage of shrub wetlands (peatlands) had higher fish tissue THg levels, thus it is highly possible that these wetlands are main locations for mercury methylation. Stepwise regression was used to develop empirical models for the purpose of predicting the spatial variation in yellow perch THg over the studied region. The 2005 regression model demonstrates it is possible to obtain good prediction (up to 60% variance description) of resident yellow perch THg level using upland soil O-horizon THg as the only independent variable. The 2006 model shows even greater prediction (r(2)=0.73, with an overall 10 ng/g [tissue, wet weight] margin of error), using lake water dissolved iron and watershed area as the only model independent variables. The developed regression models in this study can help with interpreting THg concentrations in low trophic level fish species for untested lakes of the greater Superior National Forest and surrounding Boreal ecosystem.

Particulate Hg (pHg) is a component of smoke from biomass burning and has the potential for local redeposition. Throughfall (precipitation collected beneath a conifer or deciduous canopy) and open precipitation samples were collected pre- and postfire in 2005 and 2006 using passive precipitation collectors across the Superior National Forest, located in northern Minnesota, USA. Samples were collected approximately every two weeks and analyzed for total Hg (THg) and methyl Hg (MeHg). THg concentrations increased significantly postfire in conifer throughfall (> 4x increase), open precipitation (2.5x), and when all canopy types were considered (2.9x). MeHg concentrations also increased after fire regardless of the covertype (conifer throughfall: 10x increase; open precipitation: 3.5x increase; deciduous throughfall: 1.7x increase; all canopy types analyzed together: 8x increase). Total Hg deposition increased significantly under conifer cover (3.8x). Methyl Hg deposition increased significantly after fire when all canopy types were analyzed together (4.6x) and in conifer throughfall (5.9x). Canopy type influenced the magnitude of postfire THg and MeHg increase and the duration of elevated MeHg levels. Particulate Hg present in forest fire smoke represents a short-term source of increased Hg in the atmosphere that is available for local redeposition during and following fire.

Mercury is a highly toxic heavy metal and the ability of the neurotoxin methylmercury to biomagnify in the food chain is a serious concern for both public and environmental health globally. Because thousands of tons of mercury are released into the environment each year, remediation strategies are urgently needed and prompted this study. To facilitate remediation of both organic and inorganic forms of mercury, Escherichia coli was engineered to harbor a subset of genes (merRTPAB) from the mercury resistance operon. Protein products of the mer operon enable transport of mercury into the cell, cleavage of organic C-Hg bonds, and subsequent reduction of ionic mercury to the less toxic elemental form, Hg(0). E. coli containing merRTPAB was then encapsulated in silica beads resulting in a biological-based filtration material. Performing encapsulation in aerated mineral oil yielded silica beads that were smooth, spherical, and similar in diameter. Following encapsulation, E. coli containing merRTPAB retained the ability to degrade methylmercury and performed similarly to non-encapsulated cells. Due to the versatility of both the engineered mercury resistant strain and silica bead technology, this study provides a strong foundation for use of the resulting biological-based filtration material for methylmercury remediation.

Sediments from Lake Pepin on the Mississippi River, southeastern Minnesota, are used as provenance tracers to assess variations in hydrology and sediment-transport during the middle Holocene. Three rivers contribute sediment to Lake Pepin, and each catchment is characterized by a distinctly different geologic terrain. The geochemical fingerprint for each drainage basin was determined from the elemental composition of heavy minerals in the silt-sized fraction of modern sediment samples. Down-core elemental abundances were compared with these fingerprints by use of a chemical-mass-balance model that apportions sediment to the source areas. We observed a decreased contribution from the Minnesota River during the interval ~6700–5500 14C yr BP, which we attribute to decreased discharge of the Minnesota River, likely controlled by a combination of precipitation, snow melt, and groundwater input to the river. This hydrologic condition coincides with the mid-Holocene prairie period recorded by fossil pollen data. The occurrence of this feature in a proxy record for hydrologic variations supports the hypothesis that the mid-Holocene prairie period reflects drier conditions than before or after in midwestern North America.

Agricultural and industrial pollution release large amounts of heavy metals into the atmosphere, surface water, soil, and plants. The protection and restoration of soils and water contaminated with heavy metals generate a great need to develop efficient adsorbents for these pollutants. This study reports the adsorption of Pb(II) and Hg(II) by two reference montmorillonites, Wyoming (SWy-2) and Arizona (SAz-1), that were pretreated with various natural organic cations containing different functional groups (L-carnitine, L-cysteine ethyl ester, L-cystine dimethyl ester, and thiamine cations) and with synthetic, nonfunctionalized organic cations (hexadecyltrimethylammonium [HDTMA] and phenyltrimethylammonium [PTMA] cations). Most of the organoclays adsorbed less Pb(II) than the untreated montmorillonites, with the exception of the L-carnitine-treated montmorillonites. The carboxyl functional group on L-carnitine was apparently effective for complexing Pb. In contrast, Hg(II) adsorption was greatly increased by several of the organic cation pretreatments. Sulfur-containing organic functional groups enhanced Hg(II) adsorption. The synthetic organic cations PTMA and HDTMA suppressed adsorption of Pb(II) and Hg(II) because these organic cations competed with the metals for adsorption sites on the day surfaces and lack organic functional groups capable of interacting with the heavy metals. These findings are consistent with prior understanding of organic functional group-metal complexation reactions but go further by demonstrating that organoclays can be selectively functionalized with natural organic cations to enhance their affinity for heavy metals., This work was partially supported by the MCYT Project REN2001-1700-CO2-01/TECNO and by Junta de Andalucía through Research Group RNM124. M.C-G. gratefully acknowledges the Spanish Ministry of Education and Culture for her F.P.U. fellowship.

Methylmercury cation (CH3Hg+) is known to have a strong affinity for organic matter in soil, sedimentary, and aquatic environments. The objective of this study is to determine the dominant ligands binding CH3Hg+ in humic acids by evaluating several CH3Hg+-ligand complexation models, using mercury LIII-edge extended X-ray absorption fine structure (EXAFS). The model CH3Hg+ binding ligands examined in this study include thiol (-SH), hydrogen polysulfide (-SSH or -SSSH), sulfide (-S-), disulfide (-SS-), carboxyl (-COOH), and amine (-NH2). Based on the atomic geometry around mercury in each model structure, we distinguished CH3Hg+-binding ligands in two different humic acids (soil and aquatic). We observed CH3Hg+ preferentially binds to thiol ligands. After saturating reactive thiol ligands, the majority of CH3Hg+ binds to carboxyl ligands rather than to amine or other reduced sulfur ligands than thiol. We found no evidence of significant CH3Hg+-sulfide/disulfide or CH3Hg+-hydrogen polysulfide complexes in any samples. When CH3Hg+ binds to a humic ligand, the C-Hg bond in CH3Hg+ remains intact. Some heavy atoms are proximately coordinated around the mercury atom in the sample containing the highest CH3Hg+ levels used in this study.

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.

Reconstruction of soil weathering is one of the more difficult problems for palaeoecologists interested in landscape-scale environmental changes. Here we use scanning electron microscopy and energy dispersive x-ray analysis (SEM/EDS) to study the pitting of feldspars in soils and lake sediments at two sites in the Great Lakes region, USA. A semi-quantitative feldspar weathering index (FWI) allows description of the weathering status for large numbers of individual grains, and reveals differences among soil horizons and strata of lake sediment as well as between the two sites. Feldspars in upper soil horizons generally have greater FWI than those in lower horizons, but analyses also suggest considerable weathering in the soil C horizon at the site with more rapid water infiltration. At one site, the FWI of upper soil horizons and surface lake sediment are similar, implying that lake sediments have the potential to record changes in soil over time. However, differ ences between upper soil horizons and surface sediment at the other site highlight the need to examine more sites and more profiles within sites to better relate catchment and sediment characteristics. We interpret increases in the FWI over time within lake sediments as evidence of progressive weathering of soils and conclude that the sites had different histories of soil development. However, the complexities of sediment deposition in lakes and the paucity of information relating FWI to soil characteristics prevent straightforward reconstruction of soil development. Variability within each record appears tied to initial grain chemistry, depo sitional environment, changes in lake level and progressive degradation of grains. As more information relating micromorphology to soil characteristics becomes available, this technique should become a more useful complement to chemical studies of lake sediment.

Surface–atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface–air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two 1-week measurement periods, and was longer in duration than previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 190.5 (evolution) and –91.7 ng m −2 h −1 (deposition) with an average evolution of 9.67 ng m −2 h −1 . The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.

Two geochemical techniques from soil mineralogy were used with lake sediment to reconstruct soil development in the catchments of two lakes—one on outwash and the other on till—in the Great Lakes region. A sodium pyrophosphate extraction provides information about leaching of exchangeable and organically complexed cations from terrestrial sources, while an acidified ammonium oxalate extraction removes mineral materials without well-developed crystalline structure that are indicative of podzolization. More evidence of pedogenesis is preserved in sediment of the lake on outwash—likely a result of greater retention of material within the soil profile in the catchment on till. This difference between the records suggests that excessively well-drained (leaky) catchments may provide better records of soil development than those with higher water-holding capacity. Evidence of acidification and podzolization appeared first at the lake on till and 4500 years later at the lake on outwash. Both records reveal a late Holocene intensification of weathering that coincided with a regional climatic change to greater moisture availability. The variability in weathering rates observed presents a more complex picture of weathering than the simple exponential functions often assumed in chronosequence studies. Use of lake sediment records provides better temporal resolution of significant events in soil formation than could be achieved using a chronosequence approach.

The hydrologic cyvling of total Hg (HgT) and organic C (OC) was studies for a 1-yr period in a northern Minnesota forested watershed, consisting of an upland surrounding a bog peatland with a narrow lagg at their interface. Throughfall and sternflow contributed twice as much HgT as seven times as much OC to the forested watershed than atmospheric deposition in a nearby opening. Fluxes in upland runoff accounted for 16% of the HgT and 8% of the OC inputs to the lagg and were dominated by interflow transport. Bog runoff accounted for 57% of the HgT and 83% of the OC inputs to the lagg. For an annual cycle, upland soils were sinks for both HgT and OC, while bog soils were sinks for HgT but sources of OC. Fluxes to the lagg accounted for 184% of the HgT and 87% of the OC transported from the watershed outlet. We speculate that HgT was lost in the lagg by both volatilization and soil accumulation. Total Hg and dissolved organic C (DOC) are positively related in both throughfall and stemflow, with stemflow showing the strongest relationships. In the soil system, HgT-DOC relationships deteriorate and HgT-particulate organic C (POC) relationships dominate. Water residence time in contact with OC appears to be important in determining the relationships between HgT and OC. At the stream outlet, our data suggest that ~70% of the HgT transported from the watershed is associated with POC, while 30% is associated with DOC.

Sediment samples were collected from three known sources contributing to a depositional basin of the Upper Mississippi River, USA. The heavy silt fraction (2–63 μm, density >2.95) isolated from the sediments was analyzed for 42 elements by inductively coupled plasma-mass spectrophotometry (ICP-MS) to give signature profiles characteristic of each source catchment. Known proportions of heavy silt fractions from each source were mixed and the composite samples analyzed in the same way. The proportions of components in the composite samples were compared to their apportionments calculated statistically using the US Environmental Protection Agency (USEPA) chemical mass balance (CMB) air quality receptor model. This showed that the CMB technique can apportion sediments to their catchment sources reliably. The technique was then applied to dated sediments of Lake Pepin, in the Upper Mississippi basin, to apportion them to their contributing catchments. The results show that almost all the recent sediments deposited in the basin originated in the Minnesota River catchment, and that the sediment load increased over time as anthropogenic impacts increased. This technique could be used elsewhere to determine sediment provenance and identify changes in sediment sources over time.

Electricity generation from biomass is becoming a more environmentally sound option than nonrenewable fuels. Pilot studies have demonstrated that alfalfa (Medicago sativa L.) stems are a suitable feedstock for energy generation via gasification. Developing beneficial uses for ash produced as a bypro

Electricity generation from biomass is an attractive option from an environmental perspective. Pilot studies have indicated that alfalfa (Medicago sativa L.) stems are suitable feedstock for energy generation via gasification. Detailed information on chemical characteristics of the ash generated from gasification of alfalfa stem is required to develop environmentally and economically sound ash management strategies. Alfalfa fly and bottom ashes were characterized with respect to chemical properties that are important in developing ash management practices with emphasis on beneficial utilization as a soil amendment. Mean concentrations of total C, K, Ca, and Cl were 424, 120, 85, and 26 g kg{sup {minus}1}, respectively, in fly ash. In bottom ash, the mean concentrations of C, K, and Ca, were 63, 61, and 193 g kg{sup {minus}1}. Concentrations of total Pb, As, Cd, Co, and Se were below detection limits in both ash types. Naphthalene ranged from 6.2 to 74 mg kg{sup {minus}1}, but concentrations of many other polyaromatic hydrocarbons were low or below mg kg{sup {minus}1} detection limits. Available K and P in fly ash were 90 to 120 and 8 to 10 g kg{sup {minus}1}, respectively. Mean CaCO{sub 3} equivalent value of fly ash was 400 g kg{sup {minus}1}, itsmore » electrical conductivity (EC) and pH were 127 dS m{sup {minus}1} and 11.5, respectively. These results suggest that when managed properly, gasified alfalfa ash could potentially be utilized as a beneficial soil amendment with few potential environmental concerns.« less

The binding of Hg{sup 2+} in organic matter of soils and waters controls the transport and transformations of Hg in terrestrial and aquatic ecosystems. The authors developed a competitive complexation method using the strong complexation of Hg{sup 2+} by Br{sup {minus}} for determining the Hg{sup 2+} binding strength in organic soils at native and elevated Hg concentrations. The distribution coefficients determined in KBr suspensions for sorption of native HG{sup 2+} to soil organic carbon (SOC) (K{sub soc}) are in the range of 10{sup 22} to 10{sup 23}. The K{sub soc} significantly decreased with increased additions of Hg{sup 2+} and with decreasing pH. Using data for reduced organic S concentrations determined by x-ray absorption near-edge structure spectroscopy (XANES), the authors calculated surface complex formation constants on the order of 10{sup 32} for a model site having acidity constants of mercaptoacetic acid. This value is in fair agreement with the tabulated value of 10{sup 345} for Hg{sup 2+} binding in mercaptoacetic acid. At native Hg concentrations, formation constants and K{sub soc} values were similar for different types of soil organic matter along transects from uplands into wetlands, despite varying concentration of Hg and reduced organic S. Their adsorption data are consistent withmore » the conclusions from their previous extended x-ray absorption fine structure spectroscopy (EXAFS) study that in a humic acid and soil, Hg{sup 2+} ions bond in two-fold coordination involving one reduced S and one O or N.« less

This contribution presents an assessment of the modern and historic fluxes of sediments exiting the Mississippi, St. Croix, and Minnesota watersheds and entering Lake Pepin, a natural riverine lake on the Upper Mississippi River. A Chemical Mass Balance receptor model and elemental signatures for sediments in Lake Pepin and the rivers draining its three principal catchment areas were used to apportion sediments in the lake to their source watersheds. The apportionment data, estimated trapping efficiency of the lake, and watershed basin areas were used to calculate sediment fluxes and erosion rates for each basin on a decadal basis. The relative apportionment of sediments from the Minnesota River watershed increased since European settlement of the region circa 1830 from 83 to 87% for the upper, 83 to 90% for the middle, and 78 to 87% for the lower reaches of the lake. Sediment loading to the whole lake shows a 12-fold increase from historic levels in the mass of Minnesota River-derived sediments. The amount of sediment currently supplied by this river is more than seven times the amount supplied by the headwater-Mississippi and St. Croix Rivers combined. Sediment contributions from these two combined watersheds have risen sevenfold since settlement. The causes of these increases are attributable to intensive agricultural production, especially within the Minnesota River basin. Watershed alterations have resulted in a decrease in wetlands, riparian zones, and native prairie and an increase in acreage artificially drained by sub-surface tile lines and surface ditching.

Inputs, outputs, and pool sizes of total mercury (Hg) were measured in a forested 10 ha,watershed consisting of a 7 ha hardwood-dominated upland surrounding a 3 ha coniferdominated peatland. Hydrologic inputs via throughfall and stemflow, 13 +/- 0.4/ug m-2 yr-1 over the entire watershed, were about double precipitation inputs in the open and were significantly higher in the peatland than in the upland (19.6 vs. 9.8/ug m-2 yr-1). Inputs of Hg via litterfall were 12.3 +/- 0.7/ug m-2 yr-1,/sup> , not different in the peatland and upland (11.7 vs. 12.5 ug m-2 yr-1). Hydrologic outputs via streamflowwere 2.8 +/- 0.3/ug m-2 yr-1 and the contribution from the peatland was higher despite its smaller area. The sum of Hg inputs were less than that in the overstory trees, 33+/-3 ug m-2 above-ground, and much less than either that in the upland soil, 5250+/-520ug m-2, or in the peat, 3900+/-100ug m-2 in the upper 50cm. The annual flux of Hg measured in streamflow and the calculated annual accumulation in the peatland are consistent with values reported by others. A sink for Hg of about 20ug m-2 yr-1 apparently exists in the upland, and could be due to either or both storage in the soil or volatilization.

A model of topographic influence on the regional transport and accumulation of loess in sparsely vegetated landscapes is proposed, based on the critical role played by saltating eolian sand in the entrainment and long-distance transport of finer-grained suspended dust. In this model, long-term accumulation of loess occurs mainly downwind of topographic obstacles that limit eolian transport of sand, and associated re-entrainment of dust. Regional and local patterns of distribution of late Wisconsinan loess in parts of the Upper Mississippi River basin are closely related to the distribution of topographic obstacles to sand transport. These cases of topographic influence occur in a region where evidence exists for sparse tundra-like vegetation during the deposition of loess in the late Wisconsinan. Similar topographic effects may not be evident further south in the Missouri and Mississippi River basins because vegetation density was generally sufficient to prevent the movement of eolian sand out of source valleys. Thus, topographic obstacles and dense vegetation may have similar effects on loess distribution under different environmental conditions.

We determined the fluxes of total mecury (HgT), total organic carbon (TOC), and dissolved organic carbon (DOC) from five upland/peatland watersheds at the watershed outlet. The difference between TOC and DOC was defined as particulate OC (POC). Concentrations of HgT showed moderate to strong relationships with POC (R2 = 0.77) when all watersheds were grouped. Although POC only accounts for 10 to 20% of the OC transported, we estimate that it is associated with 52 to 80% of the HgT transported from the five watersheds. Total transport of HgT from the watersheds ranged from 0.70 to 2.82 ?gm-2yr-1. Watershed geometry and hydrology play important roles in determining the influence of OC on HgT transport in forested watersheds. Watershed properties such as peatland area have considerable promise as predictors for estimating HgT transport in streams draining forested watersheds in the Great Lakes States

Numerous studies have reported on preferential solute transport, giving evidence that preferential flow is widespread. However there has been little field documentation of the relative importance of different preferential transport mechanisms. This study used a dye tracer to examine the extent and relative importance of different preferential transport mechanisms in a glacial outwash-derived soil that is used extensively for high input agriculture in central Minnesota, USA (Verndale sandy loam: coarse loamy over sandy, mixed, frigid, Udic Argiborolls). Experimental treatments included three initial soil water contents (WET, MEDIUM, and DRY) and three dye solution application rates (FLOOD, SPRINKLER-High, and SPRINKLER-Low). Thirteen cm of FD&C Blue no. 1 (also known as Brilliant Blue FCF) food dye solution (200 g l−1) were applied to replicated 1 m×1 m plots in a recently tilled 5 year old alfalfa stand and to two additional plots with no history of alfalfa. Vertical soil profile faces were exposed at 10-cm increments across each plot. Extensive and deeper preferential dye movement occurred under FLOOD conditions regardless of initial soil moisture or recent vegetation history. The two SPRINKLER rates generally resulted in relatively shorter preferential flow paths (PFPs). Within-plot variability of dye patterns—including depth and number of PFPs—was very high. Most PFPs observed were associated with roots and decayed roots, or with patterns in the abruptness and topography of the boundary between the Ap and Bt horizons. Open burrows were uncommon, but contributed to extensive preferential flow in the two NO-ALFALFA plots. Our findings indicate that preferential transport is prevalent under the variety of application rate and soil moisture conditions evaluated, and that observable soil features appear to be initiators of the majority of the PFPs. Only a few (10 of 126) of the profiles excavated had preferential flow paths that were not associated with visible soil features. The observed high variability gives support to the idea that observations of spatial variability in pesticide transport studies is due to preferential transport. Our initial goal of elucidating the relationship between rate of application and the relative number and depth of PFPs was aimed at evaluating water flow patterns. However, subsequent research found that dye retardation was increased at slower application rates, indicating that the dye patterns we observed were due to both the rate and the pattern of water movement. As a result, we caution that our findings of generally deeper and more extensive preferential dye transport under the higher velocity FLOOD application rate do not necessarily indicate more extensive preferential water (or non-adsorbing solute) transport at this rate compared to the intermittent SPRINKLER rate. It is possible that our observations may be indicative of patterns in movement of adsorbed solutes such as pesticides, however this contention would require further research.

Inputs of mercury (Hg) and dissolved organic carbon (DOC) in throughfall and stemflow waters were measured for an upland/bog watershed in northern Minnesota, and were compared to the deposition in a nearby opening to determine the influence of tree canopies on Hg and DOC deposition. Twice as much Hg and seven times as much DOC was deposited in the forested watershed compared to the opening. Mass balance studies that are based on wet-only deposition in openings severely underestimate atmospheric deposition of Hg in forests. Conifer canopies are more efficient filters of airborne, particulates than are deciduous canopies as indicated by much higher Hg concentrations and total deposition in throughfall and stemflow waters under conifers. Significant positive relationships existed between Hg and DOC in both throughfall (36-57% of the variation) and stemflow waters (55-88% of the variation). Hg complexation by DOC appears to be related to the contact time between precipitation and carbon sources.

We conducted a simple observational experiment to test whether differences in Hg in tissue of red pine (Pinus resinosa Ait.) were related to soil or to atmospheric sources of Hg. We sampled two plantations in each of three areas, and within each plantation sampled two sites with different levels of soil Hg. Woody tissue Hg concentration differed by area, and differences in foliar concentrations, though not statistically significant, were ranked in the same order. Total mass of Hg in forest floor and mineral soil also differed by area, but with ranking opposite that of tissue. On an individual-tree basis, concentrations of Hg in 1994 needles (2-year old) were about twice those in 1995 needles (1-year old) (r = 0.77). Neither woody tissue Hg nor any measure of Hg in soil or forest floor were closely related to foliar levels and some relationships were inverse. We interpret the data to indicate that Hg in plant tissue is derived directly from the atmosphere, not the soil. Tissue concentration by area was closely related to the respective growing season length (1994 needles, r = 0.88; 1995 needles, r = 0.97; wood, r = 0.97), as was total mass of Hg in forest floor and surface mineral soil (r = – 0.80). Other climatic measures, such as growing degree days and actual evapotranspiration, had similar relationships. These relationships imply that both foliar uptake of Hg0 from the atmosphere and efflux of Hg from the soil system depend on biological activity.

Analysis of Hg(II) complexed by a soil humic acid (HA) using synchrotron-based X-ray absorption spectroscopy (XAS) revealed the importance of reduces sulfur functional groups (thiol (R-SH) and disulfide (R-SS-R)/disulfane (R-SSH)) in humic substances in the complexation of Hg(II). A two-coordinate binding environment with one oxygen atom and one sulfur atom at distances of 2.02 and 2.38 {angstrom}, respectively, was found in the first coordination shell of Hg(II) complexed by humic acid. Model calculations show that a second coordination sphere could contain one carbon atom and a second sulfur atom at 2.78 and 2.93 {angstrom}, respectively. This suggests that in addition to thiol S, disulfide/disulfane S may be involved with the complexation of Hg(II) in soil organic matter. The appearance of carbon atom in the second coordination shell suggests that one O-containing ligand such as carboxyl and phenol ligands rather than H{sub 2}O molecule is bound to the Hg(II). The involvement of oxygen ligand in addition to the reduced S ligands in the complexation of Hg(II) is due to the low density of reduced S ligands in humic substances. The XAS results from this experiment provided direct molecular level evidence for the preference of reduced S functional groups over oxygen ligandsmore » by Hg(II) in the complexation with humic substances.« less

Structural units in freshly tilled soil are mainly fragments derived from tillage. Fractal geometry is potentially useful to model this structure. This research was designed to test the applicability of fractal models for mass– and number–size distributions, and surface roughness of soil fragments produced by tillage; and evaluate relationships among parameters of these fractal models. Fragments were sampled from the soil surface of three soil management experiments on a Normania clay loam: (1) moldboard, chisel, and disc as primary tillage tools, (2) three sequences of primary and secondary tillage, and (3) three crops followed by one tillage sequence. Air-dried samples were sieved to obtain eight fragment–size fractions with average diameters, xm, ranging from 0.4 to 28.0 mm. The size fraction with xm=0.4 mm had different patterns of fragmentation and mass distribution and was not used to estimate fractal parameters. Mass–size relations from size fractions and individual fragments did not show evidence of a fractal distribution of mass; but soil management influenced the estimated mass of fragments of unit diameter, km. Two-dimensional roughness of fragment surfaces measured on thin sections was fractal with dimensions, Ds, between 1.02 and 1.18. Disc tillage produced the highest Ds among primary tillage tools. Fragment number–size distributions were fractal with the fragmentation fractal dimension, Df, between 2.14 and 3.19, and sensitive to management effects. The number of fragments of unit diameter, kf, was inversely related to km, but relationships of Df–kf and Df–Ds were not consistent with present fragmentation fractal models. Parameters, Df and kf were valuable for characterizing freshly tilled soils. More research is needed to understand links between Df, kf, and the geometrical configuration of a tilled layer.

Dyes are often used as tracers of water and solute flow in soil. However, there has been little published research on the effects of now 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 (K d ) of 4.33, 23.95, and 4.59 L kg -1 for 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 -1 dye 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.

Elevated levels of mercury in aquatic environments remote from industrial sources have been broadly attributed to long-range atmospheric transport and deposition of anthropogenic Hg. Evidence in support of this prevailing scientific viewglobal biogeochemical Hg models, sedimentary archives of historic Hg fluxes, and geographic trends in soil Hghave been challenged as being insuf ficiently rigorous to rule out the alternative explanation that natural geologic sources are the principal contributors of Hg in remote locations. In this review, we examine the weaknesses in interpretation and the choice of information that has been used to argue against atmospheric Hg contamination. Analytical advances in measuring trace levels of environmental Hg have greatly narrowed estimates of natural Hg fluxes, providing a clear measure of the relative magnitude of anthropogenic Hg emissions and deposition. Recent experimental results indicate that diagenetic processes cannot explain the mounting number of lake sediment an...

Fractal theory has been used to quantify morphological properties of pore systems in soil, but predictive capabilities of the derived fractal dimensions have remained largely untested. The objective of this study was to use morphologically derived fractal dimensions to predict an exponent N in a power law relation between saturated hydraulic conductivity, K sat , and porosity. A Kozeny-Carman equation was used to derive N as a function of two fractal dimensions (pore volume, D v , and pore surface roughness, D s ) and a connectivity parameter, α. The α parameter was used as α matching factor between fitted and calculated N values. Values of D v and D s characterizing pores in both undisturbed and packed soil were obtained from images with pixel sizes of 0.06 and 0.29 mm. Porosity was measured on the 0.29-mm pixel images, while K sat was measured in undisturbed cores and packed soil columns. Also, published data on porosity, K sat , and D v and D s from dye-stained patterns of four undisturbed soils were used. Lower coefficients of variation and lower absolute values of α were obtained with fractal dimensions from the 0.06-mm pixel images. Values of α were related to parameters from probability distributions of hydraulic radii as calculated from the 0.06-mm pixel images, and to the connectivity of pores as inferred from dye-stained patterns. Fractal characterization of pore structure proved useful for predictingN, but predictions would probably be improved by considering only flow-active pores in the calculation of a fractal dimension. Methods to obtain such fractal dimensions were suggested.