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USGS2015

Soil nutrient budgets following projected corn stover harvest for biofuel production in the conterminous United States

Increasing demand for food and biofuel feedstocks may substantially affect soil nutrient budgets, especially in the United States where there is great potential for corn ( Zea mays L) stover as a biofuel feedstock. This study was designed to evaluate impacts of projected stover harvest scenarios on budgets of soil nitrogen (N), phosphorus (P), and potassium (K) currently and in the future across the conterminous United States. The required and removed N, P, and K amounts under each scenario were estimated on the basis of both their average contents in grain and stover and from an empirical model. Our analyses indicate a small depletion of soil N (−4 ± 35 kg ha −1 ) and K (−6 ± 36 kg ha −1 ) and a moderate surplus of P (37 ± 21 kg ha −1 ) currently on the national average, but with a noticeable variation from state to state. After harvesting both grain and projected stover, the deficits of soil N, P, and K were estimated at 114–127, 26–27, and 36–53 kg ha −1 yr −1 , respectively, in 2006–2010; 131–173, 29–32, and 41–96 kg ha −1 yr −1 , respectively, in 2020; and 161–207, 35–39, and 51–111 kg ha −1 yr −1 , respectively, in 2050. This study indicates that the harvestable stover amount derived from the minimum stover requirement for maintaining soil organic carbon level scenarios under current fertilization rates can be sustainable for soil nutrient supply and corn production at present, but the deficit of P and K at the national scale would become larger in the future.

GCB Bioenergy↗

USGS2006

Soil-atmospheric exchange of CO2, CH4, and N2O in three subtropical forest ecosystems in southern China

The magnitude, temporal, and spatial patterns of soil-atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil-atmospheric CO2, CH4, and N2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean ?? SD) were 7.7 ?? 4.6MgCO2-Cha-1 yr-1, 3.2 ?? 1.2 kg N2ONha-1 yr-1, and 3.4 ?? 0.9 kgCH4-Cha-1 yr-1, respectively. The climate was warm and wet from April through September 2003 (the hot-humid season) and became cool and dry from October 2003 through March 2004 (the cool-dry season). The seasonality of soil CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O emission rates were often observed in the hot-humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO2 and N2O emissions and CH4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO2 effluxes by 17-44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer. ?? 2006 Blackwell Publishing Ltd.

Global Change Biology↗

USGS2006

Importance of recent shifts in soil thermal dynamics on growing season length, productivity, and carbon sequestration in terrestrial high-latitude ecosystems

In terrestrial high-latitude regions, observations indicate recent changes in snow cover, permafrost, and soil freeze-thaw transitions due to climate change. These modifications may result in temporal shifts in the growing season and the associated rates of terrestrial productivity. Changes in productivity will influence the ability of these ecosystems to sequester atmospheric CO2. We use the terrestrial ecosystem model (TEM), which simulates the soil thermal regime, in addition to terrestrial carbon (C), nitrogen and water dynamics, to explore these issues over the years 1960-2100 in extratropical regions (30-90??N). Our model simulations show decreases in snow cover and permafrost stability from 1960 to 2100. Decreases in snow cover agree well with National Oceanic and Atmospheric Administration satellite observations collected between the years 1972 and 2000, with Pearson rank correlation coefficients between 0.58 and 0.65. Model analyses also indicate a trend towards an earlier thaw date of frozen soils and the onset of the growing season in the spring by approximately 2-4 days from 1988 to 2000. Between 1988 and 2000, satellite records yield a slightly stronger trend in thaw and the onset of the growing season, averaging between 5 and 8 days earlier. In both, the TEM simulations and satellite records, trends in day of freeze in the autumn are weaker, such that overall increases in growing season length are due primarily to earlier thaw. Although regions with the longest snow cover duration displayed the greatest increase in growing season length, these regions maintained smaller increases in productivity and heterotrophic respiration than those regions with shorter duration of snow cover and less of an increase in growing season length. Concurrent with increases in growing season length, we found a reduction in soil C and increases in vegetation C, with greatest losses of soil C occurring in those areas with more vegetation, but simulations also suggest that this trend could reverse in the future. Our results reveal noteworthy changes in snow, permafrost, growing season length, productivity, and net C uptake, indicating that prediction of terrestrial C dynamics from one decade to the next will require that large-scale models adequately take into account the corresponding changes in soil thermal regimes. ?? 2006 Blackwell Publishing Ltd.

Global Change Biology↗

USGS2005

Aquifer sensitivity to pesticide leaching: Testing a soils and hydrogeologic index method

For years, researchers have sought index and other methods to predict aquifer sensitivity and vulnerability to nonpoint pesticide contamination. In 1995, an index method and map were developed to define aquifer sensitivity to pesticide leaching based on a combination of soil and hydrogeologic factors. The soil factor incorporated three soil properties: hydraulic conductivity, amount of organic matter within individual soil layers, and drainage class. These properties were obtained from a digital soil association map. The hydrogeologic factor was depth to uppermost aquifer material. To test this index method, a shallow ground water monitoring well network was designed, installed, and sampled in Illinois. The monitoring wells had a median depth of 7.6 m and were located adjacent to corn and soybean fields where the only known sources of pesticides were those used in normal agricultural production. From September 1998 through February 2001, 159 monitoring wells were sampled for 14 pesticides but no pesticide metabolites. Samples were collected and analyzed to assess the distribution of pesticide occurrence across three units of aquifer sensitivity. Pesticides were detected in 18% of all samples and nearly uniformly from samples from the three units of aquifer sensitivity. The new index method did not predict pesticide occurrence because occurrence was not dependent on the combined soil and hydrogeologic factors. However, pesticide occurrence was dependent on the tested hydrogeologic factor and was three times higher in areas where the depth to the uppermost aquifer was <6 m than in areas where the depth to the uppermost aquifer was 6 to <15 m. Copyright ?? 2005 National Ground Water Association.

Ground Water Monitoring and Remediation↗

USGS2007

Simulation and mapping of soil-water conditions in the Great Plains

Soil-water conditions provide valuable insight into the hydrologic system in an area. A soil-water balance quantitatively summarizes soil-water conditions and is based on climatic, soil, and vegetation characteristics that vary spatially and temporally. Soil-water balances in the Great Plains of the central United States were simulated for 1951-1980. Results of the simulations were mean annual estimates of infiltration, runoff, actual evapotranspiration, potential recharge, and consumptive water and irrigation requirements at 152 climatic data stations. A method was developed using a geographic information system to integrate and map the simulation results on the basis of spatially variable climatic, soil, and vegetation characteristics. As an example, simulated mean annual potential recharge was mapped. Mean annual potential-recharge rates ranged from less than 0.5 inch in much of the north-central and southwestern Great Plains to more than 10 inches in parts of eastern Texas and southwestern Arkansas.

Water Resources Bulletin↗

USGS2024

Nontarget effects of pre-emergent herbicides and a bioherbicide on soil resources, processes, and communities

Community-type conversions, such as replacement of perennials by exotic annual grasses in semiarid desert communities, are occurring due to plant invasions that often create positive plant–soil feedbacks, which favor invaders and make restoration of native perennials difficult. Exotic annual grass control measures, such as pre-emergent herbicides, can also alter soil ecosystems directly or indirectly (i.e. via the plant community), yet there are few studies on the topic in natural, non-cropped landscapes. We asked how spray treatments applied to soil post-fire with the intention of inhibiting invasive annual grasses (such as Bromus tectorum L.) and releasing existing native perennial grasses affected soil resources, a microbial process, and invertebrates in three climatically varied sagebrush steppe sites. Spray treatments included chemical herbicides (imazapic and rimsulfuron) that strongly affected plant communities and a bioherbicide ( Pseudomonas fluorescens strain D7) that did not. Chemical herbicides increased soil mineral nitrogen in proportion to their negative effects on plant cover for 2 years after treatments in all sites and increased soil water and net N mineralization (measured at one site) but did not affect total carbon, nitrogen, or organic matter. Invertebrate responses to herbicides varied by site, and invertebrates increased with chemical herbicides at the highest, wettest site. We show that herbicide treatments can exacerbate pulses of mineral nutrients, which previous studies have shown can weaken ecosystem resistance to invasion. Thus, restoration strategies that increase the likelihood that desired plants can capture mineralized nutrients after herbicide application will likely be more successful.

Restoration Ecology↗

USGS2015

Climate change and physical disturbance manipulations result in distinct biological soil crust communities

Biological soil crusts (biocrusts) colonize plant interspaces in many drylands and are critical to soil nutrient cycling. Multiple climate change and land use factors have been shown to detrimentally impact biocrusts on a macroscopic (i.e., visual) scale. However, the impact of these perturbations on the bacterial components of the biocrusts remain poorly understood. We employed multiple long-term field experiments to assess the impacts of chronic physical (foot trampling) and climatic changes (2 °C soil warming, altered summer precipitation (wetting), and combined warming and wetting) on biocrust bacterial biomass, composition, and metabolic profile. The biocrust bacterial communities adopted distinct states based on the mechanism of disturbance. Chronic trampling decreased biomass and caused small community compositional change. Soil warming had little effect on biocrust biomass or composition, while wetting resulted in an increase in cyanobacterial biomass and altered bacterial composition. Warming combined with wetting dramatically altered bacterial composition and decreased cyanobacteria abundance. Shotgun metagenomic sequencing identified four functional gene categories that differed in relative abundance among the manipulations, suggesting that climate and land use changes affected soil bacterial functional potential. This study illustrates that different types of biocrust disturbance damage biocrusts in macroscopically similar ways, but they differentially impact the resident soil bacterial communities and the community functional profile can differ depending on the disturbance type. Therefore, the nature of the perturbation and the microbial response are important considerations for management and restoration of drylands.

Utah↗

USGS1997

Bacterial oxidation of methyl bromide in fumigated agricultural soils

The oxidation of [ 14 C]methyl bromide ([ 14 C]MeBr) to 14 CO 2 was measured in field experiments with soils collected from two strawberry plots fumigated with mixtures of MeBr and chloropicrin (CCl 3 NO 2 ). Although these fumigants are considered potent biocides, we found that the highest rates of MeBr oxidation occurred 1 to 2 days after injection when the fields were tarped, rather than before or several days after injection. No oxidation of MeBr occurred in heat-killed soils, indicating that microbes were the causative agents of the oxidation. Degradation of MeBr by chemical and/or biological processes accounted for 20 to 50% of the loss of MeBr during fumigation, with evasion to the atmosphere inferred to comprise the remainder. In laboratory incubations, complete removal of [ 14 C]MeBr occurred within a few days, with 47 to 67% of the added MeBr oxidized to 14 CO 2 and the remainder of counts associated with the solid phase. Chloropicrin inhibited the oxidation of MeBr, implying that use of this substance constrains the extent of microbial degradation of MeBr during fumigation. Oxidation was by direct bacterial attack of MeBr and not of methanol, a product of the chemical hydrolysis of MeBr. Neither nitrifying nor methane-oxidizing bacteria were sufficiently active in these soils to account for the observed oxidation of MeBr, nor could the microbial degradation of MeBr be linked to cooxidation with exogenously supplied electron donors. However, repeated addition of MeBr to live soils resulted in higher rates of its removal, suggesting that soil bacteria used MeBr as an electron donor for growth. To support this interpretation, we isolated a gram-negative, aerobic bacterium from these soils which grew with MeBr as a sole source of carbon and energy.

California↗

USGS1995

Effect of timber harvest on soil carbon storage at Blodgett Experimental Forest, California

Four plots from a mixed conifer forest were similarly cleared, burned, and replanted at various times over 17 years; a plot logged 79 years before sampling was used as a control. The plots had similar slope (2 to 15%, midslope position), aspect (south to southeast), and soil type (Holland series: mesic Haploxeralf; a Gray Brown Luvisol in the Canadian classification system). Twenty sites at each plot were sampled volumetrically by horizon to 20 cm below the organic–mineral soil boundary. Samples were analyzed for bulk density, organic C, and total N. There was an initial loss (15%) of organic C from the soil within 1 to 7 years, likely the result of oxidation (burning and decomposition) and erosion. For 17 years of forest regrowth, the soil continued to lose C (another 15%), probably owing to decomposition of slash material and possibly erosion, despite the slight accumulation of new litter and roots. After 80 years of regrowth, rates of carbon accumulation exceeded rates of loss, but carbon storage had declined and was not likely to recover to preharvest levels. Timber harvest and site preparation dramatically altered soil C and N distribution, in which C/N ratios after site preparation were initially high throughout the upper 20 cm. Subsequently, C/N ratios became lower with depth and with recovery age. Although stocks of C and N varied considerably among the plots and did not change consistently as a function of recovery age, the C/N ratios did vary systematically with recovery age. We hypothesize that the amount of C ultimately stored in the soil at steady state depends largely on N reserves and potentials, which appear to vary with erosion, intensity of burning, and site treatment.

California↗

USGS2022

Metal dispersion and mobility in soils from the Lik Zn-Pb-Ag massive sulphide deposit, NW Alaska: Environmental and exploration implications

The Lik deposit in northern Alaska is a largely unexposed shale-hosted Zn-Pb-Ag massive sulphide deposit that is underlain by continuous permafrost. Residual soils overlying the mineralized zone have element enrichments that are two to six times greater than baseline values. The most prominent elements are Ag, Mo, P, Se, Sr, V by total 4-acid digestion and Tl by a weak partial digestion (Enzyme Leach or EL) because they show multi-point anomalies that extend across the entire mineralized zone, concentration ranges are 0.5-2.6 ppm Ag, 4-26 ppm Mo, 0.1-0.3% P, 3-22 ppm Se, 90-230 ppm Sr, 170-406 ppm V, and 1.6-30 ppb Tl. Lead, Sb, and Hg are also anomalous (up to 178 ppm, 30 ppm, and 1.9 ppm, respectively), but all are characterized by single point anomalies directly over the mineralized zone, with only slightly elevated concentrations over the lower mineralized section. Zinc (total) has a consistent baseline response of 200 ppm, but it is not elevated in soils overlying the mineralized zone. However, Zn by EL shows a distinct single-point anomaly over the ore zone that suggests it was highly mobile and partly adsorbed on oxides or other secondary phases during weathering. In situ analyses (by laser ablation ICP-MS) of pyrite and sphalerite from drill core suggest that sphalerite is the primary residence for Ag, Cd, and Hg in addition to Zn, and pyrite contains As, Fe, Sb, and Tl. The level and degree of oxidation, and the proportion of reacting pyrite and carbonate minerals are two factors that affected the mobility and transport of metals. In oxidizing conditions, Zn is highly mobile relative to Hg and Ag, perhaps explaining the decoupling of Zn from the other sphalerite-hosted elements in the soils. Soils are acidic (to 3.9 pH) directly over the deposit due to the presence of acid-producing pyrite, but acid-neutralizing carbonate away from the mineralized zone yield soils that are near neutral. The soils therefore formed in a complex system involving oxidation and weathering (mechanical and chemical) of sulphide minerals, dissolution of carbonate minerals, and precipitation of iron and manganese oxide minerals.

Geochemistry: Exploration, Environment, Analysis↗

USGS2001

A model for nematode locomotion in soil

Locomotion of nematodes in soil is important for both practical and theoretical reasons. We constructed a model for rate of locomotion. The first model component is a simple simulation of nematode movement among finite cells by both random and directed behaviours. Optimisation procedures were used to fit the simulation output to data from published experiments on movement along columns of soil or washed sand, and thus to estimate the values of the model's movement coefficients. The coefficients then provided an objective means to compare rates of locomotion among studies done under different experimental conditions. The second component of the model is an equation to predict the movement coefficients as a function of controlling factors that have been addressed experimentally: soil texture, bulk density, water potential, temperature, trophic group of nematode, presence of an attractant or physical gradient and the duration of the experiment. Parameters of the equation were estimated by optimisation to achieve a good fit to the estimated movement coefficients. Bulk density, which has been reported in a minority of published studies, is predicted to have an important effect on rate of locomotion, at least in fine-textured soils. Soil sieving, which appears to be a universal practice in laboratory studies of nematode movement, is predicted to negatively affect locomotion. Slower movement in finer textured soils would be expected to increase isolation among local populations, and thus to promote species richness. Future additions to the model that might improve its utility include representing heterogeneity within populations in rate of movement, development of gradients of chemical attractants, trade-offs between random and directed components of movement, species differences in optimal temperature and water potential, and interactions among factors controlling locomotion.

Nematology↗

USGS2002

Relations between soil moisture and satellite vegetation indices in the U.S. Corn Belt

Satellite-derived vegetation indices extracted over locations representative of midwestern U.S. cropland and forest for the period 1990–94 are analyzed to determine the sensitivity of the indices to neutron probe soil moisture measurements of the Illinois Climate Network (ICN). The deseasoned (i.e., departures from multiyear mean annual cycle) soil moisture measurements are shown to be weakly correlated with the deseasoned full resolution (1 km × 1 km) normalized difference vegetation index (NDVI) and fractional vegetation cover (FVC) data over both land cover types. The association, measured by the Pearson-moment-correlation coefficient, is stronger over forest than over cropland during the growing season (April–September). The correlations improve successively when the NDVI and FVC pixel data are aggregated to 3 km × 3 km, 5 km × 5 km, and 7 km × 7 km areas. The improved correlations are partly explained by the reduction in satellite navigation errors as spatial aggregation occurs, as well as the apparent scale dependence of the NDVI–soil moisture association. Similarly, stronger relations are obtained with soil moisture data that are lagged by up to 8 weeks with respect to the vegetation indices, implying that soil moisture may be a useful predictor of warm season satellite-derived vegetation conditions. This study suggests that a “long-term” memory of several weeks is present in the near-surface hydrological characteristics, especially soil water content, of the Midwest Corn Belt. The memory is integrated into the satellite vegetation indices and may be useful for predicting crop yield estimates and surface temperature anomalies.

Journal of Hydrometeorology↗

USGS2016

Migratory bird habitat in relation to tile drainage and poorly drained hydrologic soil groups

The Prairie Pothole Region (PPR) is home to more than 50% of the migratory waterfowl in North America. Although the PPR provides an abundance of temporary and permanent wetlands for nesting and feeding, increases in commodity prices and agricultural drainage practices have led to a trend of wetland drainage. The Northern Shoveler is a migratory dabbling duck species that uses wetland habitats and cultivated croplands in the PPR. Richland County in North Dakota and Roberts County in South Dakota have an abundance of wetlands and croplands and were chosen as the study areas for this research to assess the wetland size and cultivated cropland in relation to hydrologic soil groups for the Northern Shoveler habitat. This study used geographic information system data to analyze Northern Shoveler habitats in association with Natural Resource Conservation Service soil data. Habitats, which are spatially associated with certain hydrologic soil groups, may be at risk of artificial drainage installations because of their proximity to cultivated croplands and soil lacking in natural drainage that may become wet or inundated. Findings indicate that most wetlands that are part of Northern Shoveler habitats were within or adjacent to cultivated croplands. The results also revealed soil hydrologic groups with high runoff potential and low water transmission rates account for most of the soil within the Northern Shoveler‘s wetland and cropland habitats. Habitats near agriculture with high runoff potential are likely to be drained and this has the potential of reducing Northern Shoveler habitat.

Conference Paper↗

USGS2008

Distribution of glacial deposits, soils, and permafrost in Taylor Valley, Antarctica

We provide a map of lower and central Taylor Valley, Antarctica, that shows deposits from Taylor Glacier, local alpine glaciers, and grounded ice in the Ross Embayment. From our electronic database, which includes 153 sites from the coast 50 km upvalley to Pearse Valley, we show the distribution of permafrost type and soil subgroups according to Soil Taxonomy. Soils in eastern Taylor Valley are of late Pleistocene age, cryoturbated due to the presence of ground ice or ice-cemented permafrost within 70 cm of the surface, and classified as Glacic and Typic Haploturbels. In central Taylor Valley, soils are dominantly Typic Anhyorthels of mid-Pleistocene age that have dry-frozen permafrost within the upper 70 cm. Salt-enriched soils (Salic Anhyorthels and Petrosalic Anhyorthels) are of limited extent in Taylor Valley and occur primarily on drifts of early Pleistocene and Pliocene age. Soils are less developed in Taylor Valley than in nearby Wright Valley, because of lesser salt input from atmospheric deposition and salt weathering. Ice-cemented permafrost is ubiquitous on Ross Sea, pre-Ross Sea, and Bonney drifts that occur within 28 km of the McMurdo coast. In contrast, dry-frozen permafrost is prevalent on older (???115 ky) surfaces to the west. ?? 2008 Regents of the University of Colorado.

Arctic, Antarctic, and Alpine Research↗

USGS2005

Forms and accumulation of soil P in natural and recently restored peatlands - Upper Klamath Lake, Oregon, USA

Forms, amounts, and accumulation of soil phosphorus (P) were measured in natural and recently restored marshes surrounding Upper Klamath Lake located in south-central Oregon, USA to determine rates of P accumulation in natural marshes and to assess changes in P pools caused by long-term drainage in recently restored marshes. Soil cores were collected from three natural marshes and radiometrically dated to determine recent (l37Cs-based) and long-term (210Pb-based) rates of peat accretion and P accumulation. A second set of soil cores collected from the three natural marshes and from three recently restored marshes was analyzed using a modification of the Hedley procedure to determine the forms and amounts of soil P. Total P in the recently restored marshes (222 to 311 ??g cm-3) was 2-3 times greater than in the natural marshes (103 to 117 ??g cm-3), primarily due to greater bulk density caused by soil subsidence, a consequence of long-term marsh drainage. Occluded Fe- and Al-bound Pi, calcium-bound Pi and residual P were 4 times, 22 times, and 5 times greater, respectively, in the recently restored marshes. More than 67% of the P pool in both the natural and recently restored marshes was present in recalcitrant forms (humic-acid P o and residual P) that provide long-term P storage in peat. Phosphorus accumulation in the natural marshes averaged 0.45 g m-2 yr-1 (137Cs) and 0.40 g m-2 yr-1 (210Pb), providing a benchmark for optimizing P sequestration in the recently restored marshes. Effective P sequestration in the recently restored marshes, however, will depend on re-establishing equilibrium between the P-enriched soils and the P concentration of floodwaters and a hydrologie regime similar to the natural marshes. ?? 2005, The Society of Wetland Scientists.

Wetlands↗

USGS2014

Ecological site-based assessments of wind and water erosion: informing accelerated soil erosion management in rangelands

Accelerated soil erosion occurs when anthropogenic processes modify soil, vegetation or climatic conditions causing erosion rates at a location to exceed their natural variability. Identifying where and when accelerated erosion occurs is a critical first step toward its effective management. Here we explore how erosion assessments structured in the context of ecological sites (a land classification based on soils, landscape setting and ecological potential) and their vegetation states (plant assemblages that may change due to management) can inform systems for reducing accelerated soil erosion in rangelands. We evaluated aeolian horizontal sediment flux and fluvial sediment erosion rates for five ecological sites in southern New Mexico, USA, using monitoring data and rangeland-specific wind and water erosion models. Across the ecological sites, plots in shrub-encroached and shrub-dominated vegetation states were consistently susceptible to aeolian sediment flux and fluvial sediment erosion. Both processes were found to be highly variable for grassland and grass-succulent states across the ecological sites at the plot scale (0.25 Ha). We identify vegetation thresholds that define cover levels below which rapid (exponential) increases in aeolian sediment flux and fluvial sediment erosion occur across the ecological sites and vegetation states. Aeolian sediment flux and fluvial erosion in the study area can be effectively controlled when bare ground cover is <20% of a site or the cover of canopy interspaces >100 cm in length is less than ~35%. Land use and management activities that alter cover levels such that they cross thresholds, and/or drive vegetation state changes, may increase the susceptibility of areas to erosion. Land use impacts that are constrained within the range of natural variability should not result in accelerated soil erosion. Evaluating land condition against the erosion thresholds identified here will enable identification of areas susceptible to accelerated soil erosion and the development of practical management solutions.

New Mexico↗

USGS2010

Micromorphology and stable-isotope geochemistry of historical pedogenic siderite formed in PAH-contaminated alluvial clay soils, Tennessee, U.S.A

Alluvial clay soil samples from six boreholes advanced to depths of 400-450 cm (top of limestone bedrock) from the Chattanooga Coke Plant (CCP) site were examined micromorphologically and geochemically in order to determine if pedogenic siderite (FeCO3) was present and whether siderite occurrence was related to organic contaminant distribution. Samples from shallow depths were generally more heavily contaminated with polycyclic aromatic hydrocarbons (PAHs) than those at greater depth. The upper 1 m in most boreholes consisted of mixtures of anthropogenically remolded clay soil fill containing coal clinker, cinder grains, and limestone gravel; most layers of coarse fill were impregnated with creosote and coal tar. Most undisturbed soil (below 1 m depth) consisted of highly structured clays exhibiting fine subangular blocky ped structures, as well as redox-related features. Pedogenic siderite was abundant in the upper 2 m of most cores and in demonstrably historical (< 100 years old) soil matrices. Two morphologies were identified: (1) sphaerosiderite crystal spherulites ranging from 10 to 200 um in diameter, and (2) coccoid siderite comprising grape-like "clusters" of crystals 5-20 ??n in diameter. The siderite, formed in both macropores and within fine-grained clay matrices, indicates development of localized anaerobic, low-Eh conditions, possibly due to microbial degradation of organic contaminants. Stable-isotope compositions of the siderite have ??13C values spanning over 25%o (+7 to - 18%o VPDB) indicating fractionation of DIC by multiple microbial metabolic pathways, but with relatively constant ??18O values from (-4.8 ?? 0.66%o VPDB) defining a meteoric sphaerosiderite line (MSL). Calculated isotope equilibrium water ??18O values from pedogenic siderites at the CCP site are from 1 to 5 per mil lighter than the groundwater ??18O values that we estimate for the site. If confirmed by field studies in progress, this observation might call for a reevaluation of low-temperature siderite-water 18O fractionations. Investigations at the CCP site thus provide valuable information on the geochemical conditions under which siderite can form in modern soils, and thus insight on controls on siderite formation in ancient soils. Copyright ?? 2010, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗

USGS2014

Soil resources influence vegetation and response to fire and fire-surrogate treatments in sagebrush-steppe ecosystems

Current paradigm suggests that spatial and temporal competition for resources limit an exotic invader, cheatgrass ( Bromus tectorum L.), which once established, alters fire regimes and can result in annual grass dominance in sagebrush steppe. Prescribed fire and fire surrogate treatments (mowing, tebuthiuron, and imazapic) are used to reduce woody fuels and increase resistance to exotic annuals, but may alter resource availability and inadvertently favor invasive species. We used four study sites within the Sagebrush Steppe Treatment Evaluation Project (SageSTEP) to evaluate 1) how vegetation and soil resources were affected by treatment, and 2) how soil resources influenced native herbaceous perennial and exotic annual grass cover before and following treatment. Treatments increased resin exchangeable NH4 + , NO3 − , H2PO4 − , and K + , with the largest increases caused by prescribed fire and prolonged by application of imazapic. Burning with imazapic application also increased the number of wet growing degree days. Tebuthiuron and imazapic reduced exotic annual grass cover, but imazapic also reduced herbaceous perennial cover when used with prescribed fire. Native perennial herbaceous species cover was higher where mean annual precipitation and soil water resources were relatively high. Exotic annual grass cover was higher where resin exchangeable H 2 PO 4 − was high and gaps between perennial plants were large. Prescribed fire, mowing, and tebuthiuron were successful at increasing perennial herbaceous cover, but the results were often ephemeral and inconsistent among sites. Locations with sandy soil, low mean annual precipitation, or low soil water holding capacity were more likely to experience increased exotic annual grass cover after treatment, and treatments that result in slow release of resources are needed on these sites. This is one of few studies that correlate abiotic variables to native and exotic species cover across a broad geographic setting, and that demonstrates how soil resources potentially influence the outcome of management treatments.

Rangeland Ecology and Management↗