*Complete author list for each abstract can be found with the abstract.
Teresa Balser, Univ of Wisconsin-Madison, 1525 Observatory Dr., Dept of Soil Science, Madison, WI 53706
The issue of whether soil will act as a net carbon source or sink in response to climate warming is currently a matter of intense interest in global change policy and research communities Because global soil organic carbon concentration is greater than twice that of the atmosphere, even small changes in flux can have a significant impact on atmospheric CO2. In particular, the sensitivity of recalcitrant (‘older') carbon to temperature is a critical parameter for predicting the role of soil as a feedback agent in climate warming. While there is a reasonable level of agreement that younger (labile) C will generally display a predictable pattern of response to temperature (e.g. it has a Q10 of approximately 2.4 and increasing rate of mass loss as temperature rises), the dynamics of older carbon largely remain a mystery. The sensitivity of recalcitrant C to rising temperature has been predicted to increase, or remain invariant. This variability is likely due to the web of interacting factors that influence carbon stability in soil. As litter transforms to ‘soil organic matter', and then ages to stable (humic) forms it becomes increasingly chemically altered and associated with soil minerals. Further, litter of differing chemical quality will vary in its transformation, as will the availability of organisms to degrade it. As a result, temperature sensitivity of older carbon is not a simple function of enzyme response, but instead is the product of a complex suite of interactions among the varying temperature responses of competing processes such as activation energy, altered substrate diffusion, mineral sorption or occlusion, historical carbon input and land use, and acclimation of the decomposer community. To date, studies including or focusing on more than one of these factors at a time are rare, and consequently, results of existing studies often appear idiosyncratic or surprising. If we desire a predictive understanding of the potential of soil to feedback to climate warming, it will be necessary to increase our understanding of the factors controlling the temperature sensitivity of recalcitrant carbon, and advance our conceptual as well as quantitative models beyond the biologically simplistic assumptions embedded in current temperature sensitivity approximations. And although soil mineralogy does play an important role in control, and dissolved organic species are an important loss vector, ultimately an understanding of carbon cycling in soil must be predicated upon an understanding of microbial ecophysiological responses (adaptive responses to environmental change). It is no longer sufficient to assume that microorganisms are passive catalysts whose enzymatic abilities and behaviors are environmentally determined (i.e. it is no longer sufficient to assume that “everything is everywhere and the environment selects”). We now have both the awareness and the tools necessary to question this assumption and move toward a more sophisticated treatment of microbial behavior and temperature sensitivity in our ecosystem and global models. In this talk, we synthesize a set of experiments investigating the compositional and functional response of soil microorganisms to temperature, and present a conceptual model for microbial control over recalcitrant soil carbon temperature sensitivity. We propose that the microbial community will respond in two primary ways to increased temperature: 1) in the short-term, activity will change as extant enzymes are affected, and labile carbon is depleted; and 2) in the longer term, there will be a change community composition, potentially resulting in changing carbon use as microbial degradation ‘potential' shifts. We investigate the consequences of these two types of change for loss of older carbon from soil. We ask first, what is the impact of short-term changes in microbial behavior/activity? There is a growing body of work indicating that the size and quality of the carbon pool accessed by microorganisms changes as temperature changes. Models that define decomposition or respiration rate coefficients (k) as a function of temperature assume constant substrate pool size, and uniform substrate preference. However, the pool size of carbon substrate available to the microbial community can vary substantially with temperature. In addition, several researchers have found that not only does the size of the carbon pool accessed change with temperature, but microbial use of specific substrates also changes. We present results from longer-term studies of temperature change and carbon utilization to assess change in microbial community composition under altered climatic regimes.Owen Li, Univ of Wisconsin, Environmental Chemistry & Technology, 1525 Observatory Dr., Madison, WI 53706-1299, Kangwon Lee, Univ of Illinois at Urbana-Champaign, Natural Resources & Enviornmental Science, 1102 S. Goodwin, W-321 Turner Hall, Urbana, IL 61801, Joel Kostka, Florida State Univ, Oceanography, Tallahassee, FL 32306, Joseph W. Stucki, Univ of Illinois at Urbana -Champaign, W-321 Turner Hall 1102 South Goodwin Ave, Urbana, IL 61801, and William Bleam, Univ. of Wisconsin, Environmental Chemistry & Technology, 1525 Observatory Dr., Madison, WI 53706-1299.
The reduction and re-oxidation of the iron-rich smectite mineral nontronite causes changes in short-range structure discernible by polarized extended x-ray absorption fine structure (EXAFS) spectroscopy. Reduction causes shifts that indicate internuclear distance changes and a broadening in the overall EXAFS spectrum caused by increased structural disorder. Re-oxidation in air restores the nontronite EXAFS spectrum but not to its original state. Non-reversible structural changes occur mainly during the first reduction cycle; peak width and intensity after a second redox cycle resemble values observed after the first reduction cycle. No differences appear in the polarized EXAFS spectra of nontronite samples reduced by Shewanella oneidensis when compared to samples reduced by sodium dithionite. We also evaluate the iron-migration hypothesis that predicts a significant redistribution of octahedral iron during nontronite reduction. Our polarized EXAFS data and analysis fails to support this hypothesis and proposes a different structural model for ferrous nontronite.Previous studies show iron L-edge XANES is very sensitive to spin state, crystal field strength and symmetry. Our results demonstrate iron reduction changes the intensity but not the position of two peaks dominating x-ray absorption at the L3-edge. The intensity ratio of these two peaks is linearly correlated with the iron oxidation state in the clay, permitting us quantify the Fe(II)/Fe(III) ratio using Fe L3-edge XANES spectroscopy.
Juan Gao and Joel A. Pedersen, Univ of Wisconsin, Dept of Soil Science, 1525 Observatory Drive, Madison, WI 53706.
Sulfonamide antimicrobial agents are widely used in human medicine and animal husbandry. They enter soil environments through effluent irrigation and application of manure and sewage biosolids as soil amendments. The primary concern with introducing antimicrobial agents into soil and water environments is the spread of antibiotic resistance in response to increased selective pressure, potentially leading to proliferation of resistant pathogens. The interaction of sulfonamide antimicrobials with soil constituents influences their mobility and bioavailability. Mineral clay and humic substance are two important components in soil, which are usually associated with each other. In this study, we examined the sorption and desorption of sulfamethazine to three reference smectite montmorillonites (Ca-SWy-2, Ca-SAz-1 and Ca-SWa-1) with humic acid coatings (Elloit Soil humic acid, Summit Hill humic acid) at humic acid to clay ratios of 1:5, 1:50 and 1:100. Batch sorption experiments were conducted in 5 mM CaCl2 for 7 days and the solid to liquid ratio was 5 mg/mL. The desorption of sulfamethazine from humic-clay complexes was investigated using a single decant-refill procedure for 2 days equilibrium, the ratio of sulfamethazine-free solution to total solution was 0.95. Both sorption and desorption isotherms well fit by the Freundlich Model. Sorption of sulfamethazine to humic-clay complexes was non-linear (n < 1, p < 0.05) over the investigated concentration range. Increased humic acid loading enhanced sulfonamide sorption and slightly decreased isotherm linearity. Desorption hysteresis was observed and was higher at lower humic acid loadings. Apparent competitive sorption with another sulfonamide (sulfapyridine) was observed for clays with high humic acid loadings.
Carrie A.M. Laboski (1), Emily G. Sneller (1), and Sarah K. Marshall (2). (1) Univ of Wisconsin-Madison, Dept of Soil Science, 1525 Observatory Dr., Madison, WI 53706, (2) USDA-ARS, Pasture Systems & Watershed Management Research Unit, Building 3702 Curtin Road, University Park, PA 16802
Fully understanding how soil test P level many change with manure application is important agronomically when one is trying to supply a portion or all of a crop's Phosphorus (P) needs with manure. It is also important environmentally as many nutrient management regulations are based in part on soil test P levels and P balancing/budgeting. Previous research has shown that the availability of manure P may vary with manure source meaning that not all manures will change soil test P by the same amount. This study was conducted to assess the effect of various manure application rates on P availability from dairy slurry, swine slurry, and potassium phosphate. An incubation study was conducted using two soils collected in Michigan: a Colwood loam and an Oshtemo sandy loam. The initial Bray 1-P soil test level were 15 and 11 mg kg -1 for the Colwood and Oshtemo soils, respectively. Dairy slurry, swine slurry, and potassium phosphate (KH 2PO 4) were applied to 50 g of each soil in triplicate. The rates of total P applied were 0, 10, 25, 50, 100, and 150 mg kg -1 for all sources with the exception that dairy slurry was not applied at the 150 mg kg -1 rate and swine slurry was not applied at the 10 mg kg -1 rate. These rates were chosen because they represent the range of application rates that might commonly be applied on farms, though the highest rate for each slurry is excessively high. The dairy slurry contained 530 mg L -1 of total P with 79 % as inorganic P. The swine slurry contained 1254 mg L -1 of total P with 88 % as total P. Treated soils were incubated at 20 C for 6 weeks at a moisture equivalent to 50 % of field capacity of each soil. At the end of the incubation, soils were air dried, sieved, and analyzed for Bray 1-P. The relative availability (RA) of manure P was calculated as the change in soil test P when manure was applied divided by the change in soil test P when potassium phosphate was applied. This was done for each total P application rate. As the rate of total P applied increased, the soil test level increased for all P sources on all soils. However, the rate of change in the soil test level varied between P sources for a given amount of total P applied. The RA of dairy slurry compared to potassium phosphate was 0.71 and 0.79 for Colwood and Oshtemo soil, respectively, when averaged over all rates of P applied. The RA of swine slurry was 0.88 and 0.95 for Colwood and Oshtemo soil, respectively, when averaged over all rates of P applied. When each P application rate is looked at individually, the RA of swine slurry on the Colwood soil increases with P application rate, while the RA of dairy slurry in not affect by P application rate. On the Oshtemo soil, both slurries have an increase in RA with the first two or three rates with no further increase at higher rates. This data shows that the RA of manure P to increase soil test levels compared to inorganic P varies with animal species. The average RA of manure P in similar to the inorganic P content of the manure. However, when individual P application rates are studied, RA changes with application rate, suggesting that the inorganic P content of manure alone is not the sole factor controlling the RA. Other research using these same manures and soils, show that for swine slurry there is preferential sorption of organic P. Thus, as more total P is applied in swine slurry, there may be a greater availability of the inorganic P because of the preferential sorption of the increasing quantities of organic P. In the previous study, preferential sorption of organic P in dairy slurry was not seen, and may explain why there were no real differences in RA at the different P rates for the Colwood soil. Research in the area of manure P availability should take into account application rate factors for different animal species that are typical of the range in rates actually applied in the field. Several past laboratory studies like this have used total P application rates around 100 mg kg -1, which for many manure sources produces a very high field application rate that may not be typical or allowable under nutrient management regulations. Research on manure P availability should continue to ensure a strong database from which practical recommendations may be made to sustain crop production and the environment.
Chao Liang, Guang Cheng, and Teresa Balser. Univ of Wisconsin-Madison, 1525 Observatory Dr., Dept of Soil Science, Madison, WI 53706
Although the carbon in their biomass is only a small fraction of the soil total, microorganisms can drive carbon stabilization by their intense activity and relatively short-term turnover. Application of modern techniques indicates a far greater role for incorporation of microbial biomass into soil stable carbon pools (via microbial byproducts and senesced microbial biomass) than previously believed. However, the microbial role in soil carbon dynamics is poorly understood. PhosphoLipid Fatty Acid (PLFA) and Amino Sugars (AS) are, separately, suitable as biomarkers for soil microbial living biomass and microbial necromass (including minor living cells). In addition, we can find conversion factors from both cell membrane PLFA, and cell wall AS to actual microbial biomass. In this research, we define carbon transformation as a function of three microbial states: living biomass, necromass, and removed from the microbial regime. We propose using absorbing Markov Chain for describing the dynamics of soil carbon transformation among the three states. Using the transition matrix in absorbing Markov Chain system, we could predict the situation after fixed steps and calculate expected number of steps to absorption. This can tell us how initial carbon will be distributed among the three states after the specific time, and also how long it will take for the entire initial carbon to move out of the microbial processing regime. This Markov Chain portrayal is a unique approach that will substantially increase our understanding of microbial role in carbon dynamics in soils.
Birl Lowery, Phillip E. Speth, and Keith A. Kelling. Department of Soil Science, University of Wisconsin-Madison, 1525 Observatory Drive, Madison, WI 53706-1299
Late growing season development of hydrophobic properties of sandy soils has resulted in preferential flow of water and excessive nitrate leaching with potato production on sand plains of Wisconsin, USA. Groundwater in these sand plains is within several meters of the soil surface. The problem of nitrate leaching is serious with respect to the environment as nitrate has been linked to the dead zone in the Gulf of Mexico. Under potato production in Wisconsin, nitrogen is band-applied to the shoulder of the row in an effort to reduce nitrate leaching as this is a location where it is believed that less water infiltrates. However, we discovered that in sandy soils with potato production the center of the row, where most of the potato plant roots are located, becomes hydrophobic midway through the growing season causing preferential flow of water through the shoulders of the row resulting in excessive nitrate leaching. Following this discovery a wetting agent was applied to the center of the potato row resulting in an increase in soil water content in the center of the row by as much as 50% following irrigation or rainfall events. This increase in water content continued throughout the growing season although the surfactant was only applied at planting or at the time of plant emergence. By improving water use efficiency there was as much as 35% reduction in the peak soil nitrate nitrogen concentration at 1-m depth. In general there were greater yields and greater reductions of nitrate leaching when the surfactant was applied at plant emergence compared to applications at planting. Surfactant treated plots had greater yield in 2003 and similar yield in 2004 and 2005 as the control.
J. Mark Powell (1) , Ellen Taylor-Powell (2), Richard Klemme (2), Timm Johnson (3), Larry Bruss (4), and Tom Misselbrook (5). (1) USDA-ARS, US Dairy Forage Research Center, 1925 Linden Drive West, Madison, WI 53706, (2) Univ of Wisconsin Cooperative Extension, Lake Street, Madison, WI 53706, (3) Wisconsin Dept Ag. Trade and Consumer Protection, Madison, WI 53701, (4) Wisconsin Department of Natural Resources, Madison, WI 53711, (5) Institute for Grasslands and Environmental Research, North Wyke, Okehampton, Devon, United Kingdom
Partnerships are key to understanding and solving complex issues facing agriculture. Yet, policy makers, agricultural research and extension, agribusiness and producers often have different interests and mandates, and therefore different approaches to the development and implementation of technologies that enhance farm profitability and environmental performance. All stakeholders need a common understanding of the real and perceived risks of alternative policies and technologies, and their compatibility with existing production practices. To respond to this need, the “Partnership in Understanding and Abating Ammonia Emissions from Wisconsin Dairy Farms” was created in March 2004 among research, extension, policy and producer groups. The “logic model” was used to provide an organizational framework that focused discussion and understanding, to identify the inputs, activities and outputs of each partner, and to create an action plan and a process for achieving agreed upon desired outcomes. Two logic models were created. The overall partnership logic model showed the role of each stakeholder and how they interrelate and contribute to the achievement of the ultimate goal, reduction in ammonia emissions. This overall logic model helped facilitate discussion, understanding and direction among the partners. It has been considered a roadmap that highlights and communicates the end destination and routes for getting there. The component research logic model was developed as a research planning exercise. It depicts in more detail the activities and outcomes for the research component, which feeds into the overall partnership (overall partnership logic model). The research logic model included activities such as field trials to evaluate tradeoffs between ammonia emissions and nitrate leaching when manure is land-applied. In summary, the logic model framework helped the partnership focus initial activities and initiated a process of planning future work. It helped us understand the nature of our partnership and the value of working collaboratively. It helped us focus on and articulate an ultimate end goal, and identify the contributions of each partner in achieving that desired end result. It has given us a one-page pictorial representation that shows the intended flow of action from investments (inputs) to activities and outputs to short, medium and long-term outcomes.
Mafmudije Selimi (1), Teresa Balser (2), Douglas I. Rouse (1), and Ann MacGuidwin (1). Univ of Wisconsin - Madison, (1) Dept of Plant Pathology, 1630 Linden Dr., Madison, WI 53706 and (2) Dept. of Soil Science, 1525 Observatory Drive, Madison, WI 53706.
A four-year field experiment was conducted in Central Wisconsin to evaluate the effect of individual and combined cultural practices on Potato Early Dying – a disease complex caused by a synergistic interaction between a soilborne fungus Verticillium dahliae and a migratory endoparasitic nematode Pratylenchus penetrans. The cultural practices evaluated in this study were manure-straw based compost (0, 3 and 9 T/a), fallow, rye and soybean cover crops, and sanitation through the removal of infested plant material (+/-).The experiment consisted of a two-year rotation of potato and snap beans. Beginning with potatoes in 2001, compost was applied in early spring before planting, and vines were removed in late summer at the time of vine killing operations. In 2002, snap beans were planted as a short-season crop, harvested, and the cover crops were established in late July. This allowed us to examine interactions between compost and cover crops. We were able to evaluate the full factorial of compost, cover crops and vine removal on disease beginning in 2003. The identical experimental design was established adjacent to the first experiment beginning in 2002. Therefore, the first time we were able to observe the complete factorial of treatments on potatoes on this repeat of the experiment was in 2004. Bulk soil samples were taken in spring and fall of each year from both sides of the field for Verticillium analysis. Pratylenchus counts were obtained only from soil planted to potatoes. Since little is known about the ecological environment in which this interaction takes place, another objective of this study was to evaluate whether certain microbial community patterns could be associated with disease. A subset of the treatments was chosen based on their impact on disease and information in the literature pertaining to changes in community profiles. Therefore, we selected the compost treatments with/without vine removal, and the two controls – fumigation and continuous potatoes. Bulk soil samples were taken in spring and fall of each year where potatoes were planted, and in 2003 rhizosphere soil was obtained from plants in which stem sampling for Verticillium was done. Vine removal reduced Verticillium in both 2003 and 2004. Vine removal also had lower values for all levels of compost, and there was a combined effect of low compost and vine removal on Verticillium in 2004. Interestingly, while high compost treatments did the best job in maintaining yield, they also maintained the highest populations of Verticillium. Pratylenchus populations were highest in soybean treatments in 2003 and there was a combined effect of no compost and soybean on Pratylenchus populations in both 2002 and 2004. While soybean treatments had higher populations than rye or fallow in the compost treatments, these populations were significantly lower than the no compost treatments, thus indicating that compost had a mitigating effect on Pratylenchus populations. Principal components analysis distinguished each sampling date, with gram (-) and fungal lipids characterizing the first and second principle components respectively. Pairwise correlations of the principal components, and pathogen data indicated that gram (-) bacteria were negatively correlated with Verticillium in bulk soil and in the rhizosphere, while Pratylenchus was negatively correlated with fungi and gram (-) bacteria. Rhizosphere soil had greater absolute abundance of lipid biomass, gram (+), gram (-), and fungal lipids than bulk soil. The continuous potato control had lower absolute abundance of gram (+) bacteria, gram (-) bacteria, and fungal lipids in rhizosphere soil than compost and fumigation treatments. Subsequent analysis using canonical correspondence analysis and path analysis is planned in order to further investigate these relationships.
Krista Stensvold and Cynthia Stiles, Univ of Wisconsin, Dept of Soil Science, 1525 Observatory Drive, Madison, WI 53706.
A toposequence of 12 upland soil pedons within a first-order watershed in the southern Driftless Area of Wisconsin was studied to determine the influence of aspect on soil development. The pedons were located on summit, shoulder, backslope, and footslope positions on contrasting north and south aspects (1-20% slope). Physical, chemical, and mineralogical analyses of each profile were conducted to give complete characterizations of each profile. The southern Driftless Area landscape and soils have been subjected to both periglacial conditions during the Pleistocene and temperate climates during the Holocence. The soils of this soilscape are derived from late Pleistocene loess and dolomite residuum. The clay mineralogy at these sites reflects the contributions to these soils from late Pleistocene loess. Each pedon is made up of silty Ap and Bt horizons overlying a clay rich 2Bt horizon. Below the 2Bt is a fine sandy loam saprolite that has developed from the underlying dolostone bedrock. Differences in soil properties on contrasting slope aspects over a range of slope gradients are attributed to variations in energy inputs (radiant and gravitational) into the system over time. Percent increase of clay content in the subsurface horizon (2Bt), the zone of maximum accumulation, was significantly higher on south slopes (41.6%) than on north slopes (36.1%). Maximum accumulation of both iron and aluminum oxides occurred in conjunction with the zone of maximum clay accumulation and was greater on south slopes. Translocation processes were determined to be the dominant soil forming process in the soilscape and are thus assumed to be sensitive to variations in solar insolation on slopes of different aspects. South-facing slopes in the southern Driftless Area receive 51.5% more solar radiation than north-facing slopes at the winter solstice, the time of maximum difference. In addition to the amount of solar radiation received by each slope, the duration of which each slope is susceptible to pedogenic processes is also an important factor. South-facing slopes thaw earlier in the season than north-facing slopes and stay exposed later into the season. These early and late season periods of pedogenesis are especially crucial due to the lack of vegetation and increased amounts of precipitation common in this climate regime. The difference in duration of pedogenesis on each slope may only be minor factor annually but over pedogenic time has resulted in a noticeable difference in levels of development between slopes. Hillslope erosion processes were predictably sensitive to slope gradient. We used the thicknesses of individual horizons to tell us about the temporal differences in erosion rates in these polygenetic soils. Surface soils, formed from modern day pedogenic processes, show uniformity in thickness over the entire landscape while subsurface secondary argillic (2Bt) horizons that began forming during the early Pleistocene showed decreasing thickness with increasing slope gradient. This indicates that modern day erosional processes are not influenced by slope gradient on slopes <20% but that Pleistocene erosional rates were more sensitive to difference in slope gradient.
Cynthia Stiles, Univ of Wisconsin, Dept of Soil Science, 1525 Observatory Drive, Madison, WI 53706 and Elizabeth H. Gierlowski-Kordesch, Ohio Univ, Dept of Geological Sciences, 316 Clippinger Labs, Athens, OH 45701-2979.
Rifting during the opening of the Atlantic Ocean during the Triassic to Jurassic periods (from 250 to 175 Myr ago) produced rift valleys on both sides of the nascent Atlantic ocean. The Hartford Basin in Connecticut, U.S.A., contains sedimentary rocks that originally accumulated as sediments within one of these Triassic-Jurassic rift valleys. The sedimentary fill of this ancient valley reflects the source area materials from the surrounding highlands and contains paleosol sequences that contain imprints of the climate of the region. Detailed description of the paleosol horizons from three of the formations within this rift basin highlights the depositional paleoenvironments as well as the climatic influences on sedimentation and soil formation during the Triassic and Jurassic rifting event. The continental fill of the Hartford Basin contains four sedimentary formations with three basalt flows (all dated as approximately 200-202 Myr) separating them. These formations, the New Haven Arkose (NHA), the Shuttle Meadow Formation (SMF), the East Berlin Formation (EBF), and the Portland Formation (in order from youngest to oldest) are intercalated with the Talcott, Holyoke, and Hamden Basalts, respectively. The three lowermost formations are composed of breccias, conglomerates, sandstones, siltstones, mudrocks, and limestones. The paleosols are found within the massive mudrock facies. Analyses of sedimentation patterns and lithologies in the basin indicate that New Haven Arkose depositional sequences occurred under a more humid climate than for the Shuttle Meadow and East Berlin Formations. The morphology and geochemistry of several paleosols found within the sequences confirm this interpretation. The NHA paleosols, the earliest sequences, have very weak pedogenic development and poor aggregation – occurring as loose flakes with faint root traces along aggregate faces. There are no large root casts to indicate surface stability and boundaries in paleosols “horizons” are actually stacked fine-textured alluvial deposits. The bulk geochemistry of these paleosols indicates very little difference in pedogenically active elements such as Ca, K, P, and Mg from adjacent basalts. Zirconium contents are similar to basalt contents throughout the profiles. These paleosols can be classified as paleo-Inceptisols, formed in a wet pedogenic setting that limits pedogenesis. The SMF paleosols have stronger crumb-like aggregation at the uppermost portion of the sequences with very weak slickenside planes filled with secondary carbonates. The geochemistry of these paleosols, which can be discerned to occur in Vertisol-like paleo-gilgai with microhighs and microlows, show slight depletions of plant nutrient elements such as K and P relative to the NHA paleosols and parent basalt. These paleosols can be classified as Vertisol-like paleosols, because of their weak development in claystone to mudstone, but little pedogenesis, indicating that there is still a good deal of rainfall occurring with rare seasonal drying during paleosol formation. The EBF paleosols are interpreted to have formed in a much drier time period than either NHA or SMF paleosols, which is corroborated by the morphology of the paleosols. The presence of relatively pervasive cracks at the surface grading to significant slickensides at about 50-90 cm depth indicates that these are paleoVertisols. Upper crumb aggregation and gilgai microtopography had been truncated by basalt flows, but slickenside planes indicated direction of clay deformation. The geochemistry of the EBF paleosols – with lower total Ca, K, and P, elevated Ti at depth, and Zr contents concentrated in the upper portion of the sequences – indicates that these were soils formed in a drier climate with more seasonal precipitation and longer periods of pedogenic stability. Thus the tectonic/depositional model is supported by paleosol information in the Hartford Basin.
Cynthia Stiles and Krista Stensvold. Univ of Wisconsin - Madison, Dept of Soil Science, 1525 Observatory Dr, Madison, WI 53706-1299
Silicate replacement of dissolving carbonates is a significant soil formation process. Clay-rich soils formed on carbonatic bedrock (Terra Rosa) are presumed to be derived from a combination of dissolution and replacement, with varying amounts of materials originating mainly from the carbonate source. Windborne additions contribute significantly to soil formation in these settings. Congruent dissolution of the carbonatic material elevates pH and enrichs the soil solution at the weathering interface, inducing precipitation and strong aggregation of neoformed phyllosilicates and oxyhydroxide phases, derived from loess, to build argillic horizons from the interface upward. This augments normal “top-down” argilluviation happening in the upper loess-derived solum. Geochemical and micromorphological assessment of soils forming on dolomite-rich bedrock in the southern Driftless Area (sDA) of Wisconsin reveals a pattern of complex pedogenesis dominated by surficial additions/transformations of wind-blown materials (loess) and dolostone degradation. Total elemental compositional data show strong differentiation between the upper portion of these soils (quartz-rich silt loams) and underlying redder hued clay-rich subsoils (also called the Rountree Formation) abruptly contacting bedrock. The high clay contents of these subsoils (41-83%) suggests that the relatively high purity dolomite cannot be the sole parent material for sDA soils, but rather serve as a foundation for silicate replacement through geochemical accumulation zones with high pH and oxidizing Eh conditions. Conservative tracers in the soil profiles with depth indicate that both parent materials contributed to soil formation. In the deeper horizons, ‘dilution' of loess materials by selective translocation of Si and Al into dissolving carbonate matrix may have been as great as 95%, as Zr levels approach that of the bedrock parent and the assumption is made that the loess contains significantly greater amounts of Zr than the carbonates (up to 100x). Micromorphology supports this concept by showing pervasive intergranular clay intercalation between dolomite grains of the saprolite, suggesting replacement of calcite cements from the original bedrock by pedogenic clays (sandy loam horizons with clay component dominated by fine to very fine clays) derived from the overlying silty materials. The thick sub-surface clays derived from combined parent material processing indicate that they are the product of long-term inputs into the epikarst interface with subsequent dissolution over long episodes of weathering. Based on this observed geochemical and physical behavior, we propose a six-stage model for silicate replacement of carbonatic rock in humid environments with abundant available soil organic matter: 1) intergranular cements infiltrated and replaced by mixed Mn carbonates and oxyhydroxides; 2) pedogenic phyllosillicates (smectites and illites) replace Mn phases buffered by carbonate dissolution; 3) laminar phyllosilicate replacement with hydrated Fe phases along intergranular voids; 4) carbonate crystallite boundaries effected by acid hydrolysis and replaced by Mn/Fe phases and phyllosilicates; 5) intragranular replacement continues with some remaining carbonate within the crystallite boundary; and finally 6) complete dissolution and isovolumetric replacement by phyllosilicates and Fe oxyhydroxides. This creates stable and persistent argillic horizons built from alkaline bedrock degradation which differ from argillic horizons developed closer to the surface through organic acid dominated argilluviation. Generations of bedrock-derived and cumulative argillic horizons may occur in soil profiled and tend to have gradual to diffuse boundaries as they agglomerate into thick sequences.
Zhuo Zhang, Philip Helmke, and Cynthia Stiles. Univ of Wisconsin, Dept of Soil Science, 1525 Observatory Dr, Madison, WI 53706
A geochemical survey of the concentrations of about 50 elements in surface soils from Wisconsin, USA is currently being conducted as a state-funded ancillary effort of the USGS Geochemical Landscapes project. This data will be used to produce databases and GIS-based maps of elemental distributions for eventual public use. Analytical methods employed in the Wisconsin survey are NAA (neutron activation analysis), XRF (X-ray fluorescence), ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) and ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy). When undertaking a survey of this magnitude, questions arise as to the choice of sampling sites being truly representative of a larger landscape and how sampling designs can assist to alleviate this uncertainty. Most of Wisconsin has been glaciated repeatedly and is covered with tills that can be assigned to particular glacial intervals and movements. Till geochemistry may be more easily determined due to the homogenization of the materials during the glacier movements. However, the southwestern quadrant of the state [known as the Driftless Area (DA)] has escaped glaciation and has bedrock dominated topography underlying varying thicknesses of loess. A preliminary evaluation of statewide soils shows that while the concentrations of elements in the total soils show significant spatial variation, the concentrations of elements in the clay-size fraction (<2 micrometers) are relatively uniform, especially in soils from the glaciated areas. The variation in element concentrations in the total soils appears to be directly related to variations in quartz contents in the soils. The soils in the DA are much older than soils from recent (12 kyr old) glacially-derived till, outwash and lacustrine sediments, having formed from both loess deposits (which have been deposited and eroded most pervasively over the past 120 kyr, correspondent to glacial advances) and mixed dolostone/sandstone bedrock. The DA soils in Wisconsin occupy a two-story landscape with productive ridge and valley soils separated by steep and wooded shallow soil sideslopes and rockland. To investigate the variability caused by landscape variables, surface soils in a small watershed (about 15 km2) in the DA were intensively sampled and analyzed to determine the relationships between element concentrations in soils with soil series and position in the landscape. The common bedrock for this watershed is dominantly dolostone and sandstone, often disaggregated by periglacial effects of the last glacial maximum. Relationships between geochemical-element concentrations and geographical-soil characterization data, such as altitude and terrain curvature (profile and planform), were established. The associations between the soil properties used to generate soil mapping units and the element composition of soil were tested to determine the confidence of the geochemical uniformity within a soil series. Differences were evident in some parts of the watershed where loess-derived soils are thin over the residual (and much older) sub-soils, which have a much higher content of redox-sensitive and phyllosilicate-bound elements. These results can potentially aid the classification of soils as well as helping to fine-tune precision management plans for landscapes for agriculture or urban development. Reliable patterns of element compositions can serve as a useful tool to study soil formation processes and potential problems that might arise through disturbances. For example, hydrochemical transport processes increase the content of clay-size particles in the B horizon and tend to enhance the loss of cations by leaching. The total variance of major and trace element concentrations can clearly be viewed as related to spatial components within the watershed. The spatial variance patterns with respect to each element were achieved by statistical methods, such as ANOVA (analysis of variance) and PCA (principle component analysis).First, a discrete version of this cumulative variance as a function of increasing distance can be obtained by balanced ANOVA based on a hierarchical nested sampling design with different distances as subclasses or levels. Samples are grouped into several levels according to the distance between sample groups in the watershed. In addition, samples in other counties of Wisconsin are considered as the highest level to check the regional (or glaciation) effect on variance. Secondly, element concentrations were classified into several groups according to their variance pattern. For example, elements subject to variations in concentration due to waste disposal or localized mineral deposits have a large variance on a small scale and behave differently from major elements, which can be described mineralogically. Both ANOVA and PCA can be used for grouping purpose. With the support of geostatistics, these results can be expanded to the soils originating from the same geological processes, which are the southwest corner of Wisconsin and conterminous non-glaciated area in Minnesota.