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USGS2002

Effects of vertebrate herbivores on soil processes, plant biomass, litter accumulation and soil elevation changes in a coastal marsh

1 Submergence of coastal wetlands in Louisiana is currently rapid and widespread. A number of factors contribute to this loss of habitat, including the activities of herbivores. The objective of this study was to examine the effects of large mammals, predominantly nutria and wild boar, on processes controlling soil elevation in coastal marshes. 2 Effects of herbivores on soil and vegetation were assessed by the use of paired fenced and unfenced plots over two successive growing seasons. Above‐ground biomass, litter production, changes in soil elevation, vertical soil accretion, shallow subsidence, below‐ground production of roots and rhizomes, the thickness of the root zone, soil bulk density, and soil organic matter were measured. 3 Above‐ground biomass, below‐ground production, soil elevation and the expansion of the root zone decreased due to herbivore activity. Litter production, the rate of soil surface accretion and shallow soil subsidence were all higher in grazed compared to ungrazed plots, while soil organic matter and bulk density did not differ significantly between treatments. 4 The results indicate that herbivores can have a negative effect on soil building processes, primarily by reducing below‐ground production and expansion of the root zone. Where natural rates of mineral sediment deposition are high, coastal marshes are expected to persist, despite herbivore activities. However, where sediment inputs are substantially less, herbivores may lead to destruction of habitat.

Louisiana↗

USGS2011

Assessment of soil-gas, soil, and water contamination at the former hospital landfill, Fort Gordon, Georgia, 2009-2010

Soil gas, soil, and water were assessed for organic and inorganic constituents at the former hospital landfill located in a 75-acre study area near the Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia, from April to September 2010. Passive soil-gas samplers were analyzed to evaluate organic constituents in the hyporheic zone of a creek adjacent to the landfill and soil gas within the estimated boundaries of the former landfill. Soil and water samples were analyzed to evaluate inorganic constituents in soil samples, and organic and inorganic constituents in the surface water of a creek adjacent to the landfill, respectively. This assessment was conducted to provide environmental constituent data to Fort Gordon pursuant to requirements of the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. Results from the hyporheic-zone assessment in the unnamed tributary adjacent to the study area indicated that total petroleum hydrocarbons and octane were the most frequently detected organic compounds in groundwater beneath the creek bed. The highest concentrations for these compounds were detected in the upstream samplers of the hyporheic-zone study area. The effort to delineate landfill activity in the study area focused on the western 14 acres of the 75-acre study area where the hyporheic-zone study identified the highest concentrations of organic compounds. This also is the part of the study area where a debris field also was identified in the southern part of the 14 acres. The southern part of this 14-acre study area, including the debris field, is steeper and not as heavily wooded, compared to the central and northern parts. Fifty-two soil-gas samplers were used for the July 2010 soil-gas survey in the 14-acre study area and mostly detected total petroleum hydrocarbons, and gasoline and diesel compounds. The highest soil-gas masses for total petroleum hydrocarbons, diesel compounds, and the only valid detection of perchloroethene were in the southern part of the study area to the west of the debris field. However, all other detections of total petroleum hydrocarbons greater than 10 micrograms and diesel greater than 0.04 micrograms, and all detections of the combined mass of benzene, toluene, ethylbenzene, and xylene were found down slope from the debris field in the central and northern parts of the study area. Five soil-gas samplers were deployed and recovered from September 16 to 22, 2010, and were analyzed for organic compounds classified as chemical agents or explosives. Chloroacetophenones (a tear gas component) were the only compounds detected above a method detection level and were detected at the same location as the highest total petroleum hydrocarbons and diesel detections in the southern part of the 14-acre study area. Composite soil samples collected at five locations were analyzed for 35 inorganic constituents. None of the inorganic constituents exceeded the regional screening levels. One surface-water sample collected in the western end of the hyporheic-zone study area had a trichlorofluoromethane concentration above the laboratory reporting level and estimated concentrations of chloroform, fluoranthene, and isophorone below laboratory reporting levels.

Georgia↗

USGS2014

Soil-plant-microbial relations in hydrothermally altered soils of Northern California

Soils developed on relict hydrothermally altered soils throughout the Western USA present unique opportunities to study the role of geology on above and belowground biotic activity and composition. Soil and vegetation samples were taken at three unaltered andesite and three hydrothermally altered (acid-sulfate) sites located in and around Lassen VolcanicNational Park in northeastern California. In addition, three different types of disturbed areas (clearcut, thinned, and pipeline) were sampled in acid-sulfate altered sites. Soils were sampled (0–15 cm) in mid-summer 2010 from both under-canopy and between-canopy areas within each of the sites. Soils were analyzed for numerous physical and chemical properties along with soil enzyme assays, C and N mineralization potential, microbial biomass-C and C-substrate utilization. Field vegetation measurements consisted of canopy cover by life form (tree, shrub, forb, and grass), tree and shrub density, and above-ground net primary productivity of the understory. Overall, parameters at the clearcut sites were more similar to the unaltered sites, while parameters at the thinned and pipeline sites were more similar to the altered sites. We employed principal components analysis (PCA) to develop two soil quality indices (SQI) to help quantify the differences among the sites: one based on the correlation between soil parameters and canopy cover, and the second based on six sub-indices. Soil quality indices developed in these systems could provide a means for monitoring and identifying key relations between the vegetation, soils, and microorganisms.

California↗

USGS2015

Incorporating microbial dormancy dynamics into soil decomposition models to improve quantification of soil carbon dynamics of northern temperate forests

Soil carbon dynamics of terrestrial ecosystems play a significant role in the global carbon cycle. Microbial-based decomposition models have seen much growth recently for quantifying this role, yet dormancy as a common strategy used by microorganisms has not usually been represented and tested in these models against field observations. Here we developed an explicit microbial-enzyme decomposition model and examined model performance with and without representation of microbial dormancy at six temperate forest sites of different forest types. We then extrapolated the model to global temperate forest ecosystems to investigate biogeochemical controls on soil heterotrophic respiration and microbial dormancy dynamics at different temporal-spatial scales. The dormancy model consistently produced better match with field-observed heterotrophic soil CO 2 efflux ( R H ) than the no dormancy model. Our regional modeling results further indicated that models with dormancy were able to produce more realistic magnitude of microbial biomass (<2% of soil organic carbon) and soil R H (7.5 ± 2.4 Pg C yr −1 ). Spatial correlation analysis showed that soil organic carbon content was the dominating factor (correlation coefficient = 0.4–0.6) in the simulated spatial pattern of soil R H with both models. In contrast to strong temporal and local controls of soil temperature and moisture on microbial dormancy, our modeling results showed that soil carbon-to-nitrogen ratio (C:N) was a major regulating factor at regional scales (correlation coefficient = −0.43 to −0.58), indicating scale-dependent biogeochemical controls on microbial dynamics. Our findings suggest that incorporating microbial dormancy could improve the realism of microbial-based decomposition models and enhance the integration of soil experiments and mechanistically based modeling.

Journal of Geophysical Research G: Biogeosciences↗

USGS2017

Rates of soil development from four soil chronosequences in the southern Great Basin

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes. ?? 1991.

Quaternary Research↗

USGS2021

Biocrust and the soil surface: Influence of climate, disturbance, and biocrust recovery on soil surface roughness

Biocrust communities promote soil surface roughness, a key functional characteristic for soil ecology. However, the spatial scales at which biocrust communities contribute to surface roughness are not well understood. To refine our understanding of the spatial dynamics between biocrust and soil surface roughness, we used mm-resolution terrestrial LiDAR to measure micro-topographic roughness at seven sub-meter, 3-dimensional kernels (spatial scales) for undisturbed and disturbed biocrusts within the cool Great Basin and the hot Chihuahuan Deserts of western North America. This multi-scalar approach applied within the different desert regions allowed us to explore two objectives: 1) assess the relative importance of climate and disturbance on biocrust roughness, and 2) evaluate how soil surface roughness evolves with biocrust recovery. For objective 1, we found that undisturbed cool desert biocrust was up to three times rougher than hot desert biocrust. Much of the difference in roughness between the two desert biocrust communities appeared to be from climate or other regional factors. However, positive correlations between roughness and biocrust indicators, including soil chlorophyll-a and the field-based Level of Development (LOD) index, suggested that differences in roughness at spatial scales ≤ 10 cm are directly related to biocrust development. Mechanical disturbance aimed at removing biocrust resulted in significant reductions in roughness and removed much of the observed differences in roughness between cool and hot desert soils. We evaluated biocrust recovery within the cool desert study area two years after mechanical disturbance and found that the disturbed soil increased in roughness up-to 300%. The increased surface roughness at spatial scales ≤ 10 cm were positively correlated with increased aggregate stability and indicators of biocrust reestablishment. We found that topographic change area was also an important contributor to roughness at all spatial scales, particularly at spatial scales ≥ 20 cm where it was the most important factor evaluated. These results provide insight into how biocrust interacts with other biophysical processes to influence soil surface roughness and how soil surfaces evolve at time scales relevant to soil restoration activities.

New Mexico, Utah↗

USGS2017

Contaminant gradients in trees: Directional tree coring reveals boundaries of soil and soil-gas contamination with potential applications in vapor intrusion assessment

Contaminated sites pose ecological and human-health risks through exposure to contaminated soil and groundwater. Whereas we can readily locate, monitor, and track contaminants in groundwater, it is harder to perform these tasks in the vadose zone. In this study, tree-core samples were collected at a Superfund site to determine if the sample-collection location around a particular tree could reveal the subsurface location, or direction, of soil and soil-gas contaminant plumes. Contaminant-centroid vectors were calculated from tree-core data to reveal contaminant distributions in directional tree samples at a higher resolution, and vectors were correlated with soil-gas characterization collected using conventional methods. Results clearly demonstrated that directional tree coring around tree trunks can indicate gradients in soil and soil-gas contaminant plumes, and the strength of the correlations were directly proportionate to the magnitude of tree-core concentration gradients (spearman’s coefficient of -0.61 and -0.55 in soil and tree-core gradients, respectively). Linear regression indicates agreement between the concentration-centroid vectors is significantly affected by in-planta and soil concentration gradients and when concentration centroids in soil are closer to trees. Given the existing link between soil-gas and vapor intrusion, this study also indicates that directional tree coring might be applicable in vapor intrusion assessment.

Missouri↗

USGS2002

Sorption of vapors of some organic liquids on soil humic acid and its relation to partitioning of organic compounds in soil organic matter

Vapor sorption of water, ethanol, benzene, hexane, carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, and 1,2-dibromoethane on (Sanhedron) soil humic acid has been determined at room temperature. Isotherms for all organic liquids are highly linear over a wide range of relative pressure, characteristic of the partitioning (dissolution) of the organic compounds in soil humic acid. Polar liquids exhibit markedly greater sorption capacities on soil humic acid than relatively nonpolar liquids, in keeping with the polar nature of the soil humic acid as a partition medium. The limiting sorption (partition) capacities of relatively non-polar liquids are remarkably similar when expressed in terms of volumes per unit weight of soil humic acid. The soil humic acid is found to be about half as effective as soil organic matter in sorption of relatively nonpolar organic compounds. The nearly constant limiting sorption capacity for nonpolar organic liquids with soil humic acid on a volume-to-weight basis and its efficiency in sorption relative to soil organic matter provide a basis for predicting the approximate sorption (partition) coefficients of similar compounds in uptake by soil in aqueous systems.

Environmental Science & Technology↗

USGS2006

Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska

The influence of discontinuous permafrost on ground-fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four-way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground-fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5cm depth was about 0.5??C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems. ?? 2006 Blackwell Publishing Ltd.

Global Change Biology↗

USGS2011

Assessment of soil-gas, seep, and soil contamination at the North Range Road Landfill, Fort Gordon, Georgia, 2008-2009

Soil gas, seeps, and soil were assessed for contaminants at the North Range Road Landfill at Fort Gordon, Georgia, from October 2008 to September 2009. The assessment included delineating organic contaminants present in soil-gas samples beneath the area estimated to be the landfill and in water samples collected from three seeps at the base of the landfill. Inorganic contaminants were determined in three seep samples and in soil samples. This assessment was conducted to provide environmental contamination data to Fort Gordon pursuant to requirements for the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. All soil-gas samples collected contained total petroleum hydrocarbons above the method detection level. The highest total petroleum hydrocarbon mass detected was nearly 50 micrograms (μg) in a soil-gas sample from one of the three seeps. The highest BTEX mass detected was 0.83 μg in a soil-gas sample collected near the same seep. Some soil-gas samples had perchloroethylene (known as PCE) mass greater than the method detection level of 0.01 microgram. The highest PCE mass detected was 0.73 μg, and PCE mass was detected in soil gas in areas upgradient of the seeps and indicates that the seep contamination may be related to previous waste-disposal activities upgradient of the seeps No organic or semivolatile compounds in the seep samples were detected above their respective maximum contaminant levels established in the U.S. Environmental Protection Agency National Primary Drinking Water Standards. PCE was detected in water from all three seeps at concentrations between 0.85 and 0.95 microgram per liter. Trimethylsilanol was detected in water collected from all three seeps and may be related to the degradation of silicone-based materials commonly disposed of in landfills. Inorganic concentrations in water samples from one seep did not exceed any maximum contaminant levels in the National Secondary Drinking Water Standards. In water from one seep, however, iron was detected at 865 micrograms per liter, which exceeds the maximum contaminant level for iron in the Secondary Drinking Water Standard, and in water from the other seep, iron and manganese were detected at 492,000 and 10,700 micrograms per liter, repectively, both of which exceed the respective maximum contaminant levels for the Secondary Drinking Water Standard. Water from one of the seeps had concentrations of cadmium, copper, and zinc that exceed Georgia standards for in-stream water quality, and concentrations of arsenic and lead that exceed their respective maximum contaminant levels for the Primary Drinking Water Standards. Inorganic concentrations in all four soil samples did not exceed regional screening levels established by the U.S. Environmental Protection Agency. Barium concentrations, however, were two to three times higher than the background concentrations reported in similar Coastal Plain sediments of South Carolina.

Open-File Report↗

USGS2011

Assessment of soil-gas and soil contamination at the South Prong Creek Disposal Area, Fort Gordon, Georgia, 2009-2010

Soil gas and soil were assessed for contaminants at the South Prong Creek Disposal Area at Fort Gordon, Georgia, from October 2009 to September 2010. The assessment included identifying and delineating organic contaminants present in soil-gas and inorganic contaminants present in soil samples collected from the area estimated to be the South Prong Creek Disposal Area, including two seeps and the hyporheic zone. This assessment was conducted to provide environmental contamination data to Fort Gordon personnel pursuant to requirements for the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. All soil-gas samplers in the two seeps and the hyporheic zone contained total petroleum hydrocarbons above the method detection level. The highest total petroleum hydrocarbon concentration detected from the two seeps was 54.23 micrograms per liter, and the highest concentration in the hyporheic zone was 344.41 micrograms per liter. The soil-gas samplers within the boundary of the South Prong Creek Disposal Area and along the unnamed road contained total petroleum hydrocarbon mass above the method detection level. The highest total petroleum hydrocarbon mass detected was 147.09 micrograms in a soil-gas sampler near the middle of the unnamed road that traverses the South Prong Creek Disposal Area. The highest undecane mass detected was 4.48 micrograms near the location of the highest total petroleum hydrocarbon mass. Some soil-gas samplers detected undecane mass greater than the method detection level of 0.04 micrograms, with the highest detection of toluene mass of 109.72 micrograms in the same location as the highest total petroleum hydrocarbon mass. Soil-gas samplers installed in areas of high contaminant mass had no detections of explosives and chemical agents above their respective method detection levels. Inorganic concentrations in five soil samples did not exceed regional screening levels established by the U.S. Environmental Protection Agency. Barium concentrations, however, were up to four times higher than the background concentrations reported in similar Coastal Plain sediments of South Carolina.

Open-File Report↗

USGS2011

Assessment of soil-gas and soil contamination at the Old Metal Workshop Hog Farm Area, Fort Gordon, Georgia, 2009-2010

Soil gas and soil were assessed for contaminants at the Old Metal Workshop Hog Farm Area at Fort Gordon, Georgia, from October 2009 to September 2010. The assessment included delineating organic contaminants present in soil-gas and inorganic contaminants present in soil samples collected from the area estimated to be the Old Metal Workshop Hog Farm Area. This assessment was conducted to provide environmental contamination data to Fort Gordon personnel pursuant to requirements for the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. All soil-gas samplers contained total petroleum hydrocarbons above the method detection level. The highest total petroleum hydrocarbon mass detected was 121.32 micrograms in a soil-gas sampler from the western corner of the Old Metal Workshop Hog Farm Area along Sawmill Road. The highest undecane mass detected was 73.28 micrograms at the same location as the highest total petroleum hydrocarbon mass. Some soil-gas samplers detected toluene mass greater than the method detection level of 0.02 microgram; the highest detection of toluene mass was 0.07 microgram. Some soil-gas samplers were installed in areas of high-contaminant mass to assess for explosives and chemical agents. Explosives or chemical agents were not detected above their respective method detection levels for all soil-gas samplers installed. Inorganic concentrations in five soil samples collected did not exceed regional screening levels established by the U.S. Environmental Protection Agency. Barium concentrations, however, were up to eight times higher than the background concentrations reported in similar Coastal Plain sediments of South Carolina.

Open-File Report↗

USGS2011

Assessment of soil-gas and soil contamination at the Patterson Anti-Tank Range, Fort Gordon, Georgia, 2009-2010

Soil gas and soil were assessed for contaminants at the Patterson Anti-Tank Range at Fort Gordon, Georgia, from October 2009 to September 2010. The assessment included identifying and delineating organic contaminants present in soil-gas samplers from the area estimated to be the Patterson Anti-Tank Range and in the hyporheic zone and floodplain of Brier Creek. This assessment was conducted to provide environmental contamination data to Fort Gordon personnel pursuant to requirements for the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. Soil-gas samplers in the hyporheic zone and floodplain of Brier Creek contained total petroleum hydrocarbons, benzene, octane, and pentadecane concentrations above method detection levels. All soil-gas samplers within the boundary of the Patterson Anti-Tank Range contained total petroleum hydrocarbons above the method detection level. The highest total petroleum hydrocarbon mass detected was 147.09 micrograms in a soil-gas sampler located near the middle of the site and near the remnants of a manmade earthen mound and trench. The highest toluene mass detected was 1.04 micrograms and was located in the center of the Patterson Anti-Tank Range and coincides with a manmade earthen mound. Some soil-gas samplers installed detected undecane masses greater than the method detection level of 0.04 microgram, with the highest detection of soil-gas undecane mass of 58.64 micrograms collected along the southern boundary of the site. Some soil-gas samplers were installed in areas of high-contaminant mass to assess for explosives and chemical agents. Explosives or chemical agents were not detected above their respective method detection levels for all soil-gas samplers installed.

Open-File Report↗

USGS2005

Using soil redistribution to understand soil organic carbon redistribution and budgets

Patterns of soil organic carbon (SOC) vary across the landscape leading to uncertainties in SOC budgets, especially for agricultural areas where water, wind, and tillage erosion redistribute soil and SOC. This study determined SOC patterns related to soil redistribution in small agricultural fields. Soil redistribution patterns were determined using the fallout caesium-137 technique in agricultural fields in Maryland and Iowa, USA. In two Iowa fields, SOC ranged from 0.5 to 5% whereas in the Maryland field the SOC ranged from 0.4 to 2.9%. Soil organic carbon was statistically significantly correlated with soil 137Cs inventories and soil erosion/deposition rates. Sites of soil erosion in Iowa and Maryland had significantly lower average concentrations of SOC (2.4% and 1.3%, respectively) than sites of soil deposition (3.4% and 1.6%, respectively). These studies show the impact of soil redistribution patterns, within a field or catchment, and aid in understanding SOC patterns and budgets.

Conference Paper↗

USGS2016

Assessment of trace element accumulation by earthworms in an orchard soil remediation study using soil amendments

This study assessed potential bioaccumulation of various trace elements in grasses and earthworms as a consequence of soil incorporation of organic amendments for in situ remediation of an orchard field soil contaminated with organochlorine and Pb pesticide residues. In this experiment, four organic amendments of differing total organic carbon content and quality (two types of composted manure, composted biosolids, and biochar) were added to a contaminated orchard field soil, planted with two types of grasses, and tested for their ability to reduce bioaccumulation of organochlorine pesticides and metals in earthworms. The experiment was carried out in 4-L soil microcosms in a controlled environment for 90 days. After 45 days of orchardgrass or perennial ryegrass growth, Lumbricus terrestris L. were introduced to the microcosms and exposed to the experimental soils for 45 days before the experiment was ended. Total trace element concentrations in the added organic amendments were below recommended safe levels and their phytoavailablity and earthworm availability remained low during a 90-day bioremediation study. At the end of the experiment, total tissue concentrations of Cu, Cd, Mn, Pb, and Zn in earthworms and grasses were below recommended safe levels. Total concentrations of Pb in test soil were similar to maximum background levels of Pb recorded in soils in the Eastern USA (100 mg kg −1 d.w.) because of previous application of orchard pesticides. Addition of aged dairy manure compost and presence of grasses was effective in reducing the accumulation of soil-derived Pb in earthworms, thus reducing the risk of soil Pb entry into wildlife food chains.

Maryland↗

USGS2015

Soil moisture response to experimentally altered snowmelt timing is mediated by soil, vegetation, and regional climate patterns

Soil moisture in seasonally snow-covered environments fluctuates seasonally between wet and dry states. Climate warming is advancing the onset of spring snowmelt and may lengthen the summer-dry state and ultimately cause drier soil conditions. The magnitude of either response may vary across elevation and vegetation types. We situated our study at the lower boundary of persistent snow cover and the upper boundary of subalpine forest with paired treatment blocks in aspen forest and open meadow. In treatments plots, we advanced snowmelt timing by an average of 14 days by adding dust to the snow surface during spring melt. We specifically wanted to know whether early snowmelt would increase the duration of the summer-dry period and cause soils to be drier in the early-snowmelt treatments compared with control plots. We found no difference in the onset of the summer-dry state and no significant differences in soil moisture between treatments. To better understand the reasons soil moisture did not respond to early snowmelt as expected, we examined the mediating influences of soil organic matter, texture, temperature, and the presence or absence of forest. In our study, late-spring precipitation may have moderated the effects of early snowmelt on soil moisture. We conclude that landscape characteristics, including soil, vegetation, and regional weather patterns, may supersede the effects of snowmelt timing in determining growing season soil moisture, and efforts to anticipate the impacts of climate change on seasonally snow-covered ecosystems should take into account these mediating factors.

Utah↗

USGS2006

Coupling chemical weathering with soil production across soil-mantled landscapes

Soil-covered upland landscapes constitute a critical part of the habitable world. Our understanding of how they evolve as a function of different climatic, tectonic and geological regimes is important across a wide range of disciplines and depends, in part, on understanding the links between chemical and physical weathering processes. Extensive previous work has shown that soil production rates decrease with increasing soil column thickness, but chemical weathering rates were not measured. Here we examine a granitic, soil-mantled hillslope at Point Reyes, California, where soil production rates were determined using in situ produced cosmogenic nuclides ( 10 Be and 26 Al), and we quantify the extent as well as the rates of chemical weathering of the saprolite from beneath soil from across the landscape. We collected saprolite samples from the base of soil pits and analysed them for abrasion pH as well as for major and trace elements by X-ray fluorescence spectroscopy, and for clay mineralogy by X-ray diffraction spectroscopy. Our results show for the first time that chemical weathering rates decrease with increasing soil thickness and account for 13 to 51 per cent of total denudation. We also show that spatial variation in chemical weathering appears to be topographically controlled: weathering rate decreases with slope across the divergent ridge and increases with upslope contributing area in the convergent swale. Furthermore, to determine the best measure for the extent of saprolite weathering, we compared four different chemical weathering indices – the Vogt ratio, the chemical index of alteration (CIA), Parker's index, and the silicon–aluminium ratio – with saprolite pH. Measurements of the CIA were the most closely correlated with saprolite pH, showing that weathering intensity decreases linearly with an increase in saprolite pH from 4·7 to almost 7. Data presented here are among the first to couple directly rates of soil production and chemical weathering with how topography is likely to control weathering at a hillslope scale.

Earth Surface Processes and Landforms↗

USGS2009

The organic contamination level based on the total soil mass is not a proper index of the soil contamination intensity

Concentrations of organic contaminants in common productive soils based on the total soil mass give a misleading account of actual contamination effects. This is attributed to the fact that productive soils are essentially water-saturated, with the result that the soil uptake of organic compounds occurs principally by partition into the soil organic matter (SOM). This report illustrates that the soil contamination intensity of a compound is governed by the concentration in the SOM (C om ) rather than by the concentration in whole soil (C s ). Supporting data consist of the measured levels and toxicities of many pesticides in soils of widely differing SOM contents and the related levels in in-situ crops that defy explanation by the C s values. This SOM-based index is timely needed for evaluating the contamination effects of food crops grown in different soils and for establishing a dependable priority ranking for intended remediation of numerous contamination sites.

Environmental Pollution↗