Geochemical Assessment of Iron and Vanadium Relationships in Oxic Soil Environments

Geochemical assessment has become a cost-effective and highly accurate tool for estimating metal contamination, especially in those cases where the level of contamination is not considered severe. Difficulties frequently arise in attempting to discriminate between pristine metal concentrations and low-level environmental impacts. As an example, Vanadium contamination is frequently associated with coal and petroleum bi-products; however, air and water contamination pathways are also possible. The purpose of this investigation was to characterize the V and Fe concentration relationship among a wide variety of soil types and to formulate an estimate of the pristine V concentrations in these soils. If a linear relationship may be established between Fe and V, then geochemical analysis of impacted soils may discriminate between V as a natural background component and anthropogenic V. Forty-six moderately well-drained to well-drained soil profiles having cambic, argillic or calcic soil horizons were characterized for Fe and V using an aqua-regia digestion to determine if these soils exhibited a one-to-one correspondence between V and Fe. Such a correspondence was authenticated for the majority of these soils and may be used to discriminate between natural and anthropogenic V. The presence of argillic, calcic or fragipan horizons did not reduce the one-to-one correspondence between V and Fe, suggesting that these soil processes did not selectively partition either V or Fe. The method needs to be further evaluated for soils having anoxic soil conditions, lithologic discontinuities and other specific pedogenic processes.     

Vertical Distribution of Lead and Mercury in the Wetland Argialbolls of the Sanjiang Plain in Northeastern China

The wetland Argialbolls pedon was chosen to investigate the effects of pedogenic processes and anthropogenic activities on the vertical distribution of lead and mercury concentration and to assess the potential use of soil as an archive of atmospheric Pb and Hg pollution. The soil was sampled from 5 cm from the surface to a depth of 90 cm at two locations in the Sanjiang Plain in northeastern China. The soil was analyzed for pH, soil organic matter (SOM), Fe, Mn, and Al. The results indicate that the SOM concentration gradually decreased with depth, while Fe and Mn were reductively leached from the upper horizons and accumulated significantly in the lower argillic horizons. Atmospheric Pb and Hg deposition and their redistribution during the pedogenic process led to a unique vertical distribution in the wetland Argialbolls. Overall, Pb was leached from the upper horizons and then accumulated in the lower argillic horizons. However, the Hg concentration decreased with depth, following the SOM distribution. The Pb concentration was significantly correlated to the Fe and Mn concentrations in the Argialbolls profiles, while the Hg concentration was significantly correlated with SOM. Post-depositional mobility along the wetland Argialbolls profile is higher for Pb and low for Hg. Therefore, the Argialbolls profile does not provide an accurate reconstruction of atmospheric Pb deposition, but might provide an accurate reconstruction of net atmospheric Hg deposition.     

Multi-proxy paleosol evidence for middle and late Triassic climate trends in eastern Utah

Prior investigations suggest that alluvial lowlands of Pangea in the southwestern U.S.A. during the middle to late Triassic experienced an arid to semiarid climate with significant seasonality. Our investigation finds evidence for a global pluvial episode from paleosols in the middle to late Triassic section of eastern Utah. Multi-proxy paleosol evidence is used to quantify rainfall amounts, ambient temperatures and atmospheric CO₂ concentrations and infer associated plant formations related to ecosystem persistence. Rainfall estimates are derived from geochemical molecular weathering ratios; temperature and atmospheric CO₂ levels from stable oxygen and carbon isotopes of pedogenic carbonate, respectively; and ecosystem reconstruction by a combination of climate indexes and paleosol characteristics. Eight pedotypes were identified and include poorly drained aquic Entisols (Fisher), well-drained non-aquic Entisols (Salt Valley), calcic Aridisols (Castle Valley), calcic Inceptisols (Moab), cambic (Ute) and calcic (La Sal) Vertisols, dystric Inceptisols (Kokopeli), and argillic Alfisols (Slickrock). The middle Triassic Moenkopi Formation (Anisian) was dominated by Castle Valley paleosols with mean annual rainfall between 300 and 400 mm and mean annual temperature between 13 and 23 °C (mesic to hyperthermic). Based on these climate indexes and root traces, the associated plant formation was most likely desert shrub or dry woodland. The lower Chinle Formation (Carnian) contains a succession of Ute and La Sal paleosols that changed up-section to Kokopeli, Fisher and Slickrock paleosols. In accordance with geochemical and isotopic signatures from these pedotypes, rainfall amounts initially increased to between 700 and 900 mm, and then to between 1300 and 1400 mm. Temperatures estimated from the La Sal paleosol are approximately 18 °C (thermic) at this time. The lower Chinle marks a transition from dry woodland to open forest that appears to correlate with the formation of the Petrified Forest Member in Arizona. The upper Chinle Formation (Carnian-Norian) reveals a return to semiarid to subhumid conditions and the formation of Castle Valley, Moab and Salt Valley paleosols, all of which appear to have supported desert shrub or dry woodlands. Rainfall amounts decreased to between 400 and 600 mm with temperatures eventually increasing to 29 °C (hyperthermic). Using the paleosol isotopic barometer, atmospheric CO₂ estimates generally correlate with other proxy for the Triassic. The well-developed Alfisols and noncalcareous Inceptisols identified during the Carnian of the lower Chinle correlate with a previously identified global pluvial episode based on sedimentological and marine isotopic evidence, possibly in response to rifting of Pangea. It should not be assumed that the middle to late Triassic in continental alluvial lowlands supported a uniform, semiarid to arid climate, with strong seasonality.     

Using Lanthanum,Neodymium, and Thorium as Conservative Indexing Elements to Indicate Soil Lead Deposition

A critical need exists for data evaluation protocols to determine if heavy metal deposition has impacted soil or sediment. For routine reconnaissance these protocols need to be analytically precise and affordable, two issues lacking in many regions. We employed a low-cost, commercially available aqua regia digestion procedure and developed a simple protocol for isolating pristine soil horizons and conservative indexing elements to compare to more Pb impacted soil horizons. Strongly Pb impacted soil horizons are easy to ascertain; however, moderately to slightly Pb impacted soils are more problematic to identify because of the natural Pb variation in soils. Using the harmonic mean of the soil concentrations of Lanthanum (La) and Neodymium (Nd) and also the soil concentrations of Thorium (Th) as conservative indexing elements, we were able to discriminate pristine soils from slightly to moderately Pb impacted soils. Ro values are estimators of elemental gain and loss, with Ro values greater than unity implying Pb addition, providing the comparative loss of other elements or biocycling are substantial contributing factors. All pedons known to have received Pb from atmospheric addition exhibited Ro values appreciably greater than unity, whereas soils known to be not impact or at most minimally impacted showed Ro values near unity. Commercially available and relative low cost aqua regia digestion analysis provided the analytical data for Pb, Fe, La, Nd and Th.     

A procedure for securing large and undisturbed soil cores for field simulation studies

Summary Dynamic load is a technique which can be used to secure large pedons successfully in duplex profiles with massive clay B horizons. Data show that soil profiles obtained by this method have minimum change in soil physical properties including structure and compaction. The work reported here is part of that submitted as a requirement for the Ph. D. at the University of New England by the senior author.     

Tree Species Effects on Soil Organic Matter Dynamics: The Role of Soil Cation Composition

Abstract We studied the influence of tree species on soil carbon and nitrogen (N) dynamics in a common garden of replicated monocultures of fourteen angiosperm and gymnosperm, broadleaf and needleleaf species in southwestern Poland. We hypothesized that species would influence soil organic matter (SOM) decomposition primarily via effects on biogeochemical recalcitrance, with species having tissues with high lignin concentrations retarding rates of decomposition in the O and A horizons. Additionally, because prior work demonstrated substantial divergence in foliar and soil base cation concentrations and soil pH among species, we hypothesized that species would influence chemical stabilization of SOM via cation bridging to mineral surfaces in the A-horizon. Our hypotheses were only partially supported: SOM decomposition and microbial biomass were unrelated to plant tissue lignin concentrations, but in the mineral horizon, were significantly negatively related to the percentage of the cation exchange complex (CEC) occupied by polyvalent acidic (hydrolyzing) cations (Al and Fe), likely because these cations stabilize SOM via cation bridging and flocculation and/or because of inhibitory effects of Al or low pH on decomposers. Percent CEC occupied by exchangeable Al and Fe was in turn related to both soil clay content (a parent material characteristic) and root Ca concentrations (a species characteristic). In contrast, species influenced soil N dynamics largely via variation in tissue N concentration. In both laboratory and in situ assays, species having high-N roots exhibited faster rates of net N mineralization and nitrification. Nitrification:mineralization ratios were greater, though, under species with high exchangeable soil Ca²⁺. Our results indicate that tree species contribute to variation in SOM dynamics, even in the mineral soil horizons. To our knowledge the influence of tree species on SOM decomposition via cation biogeochemistry has not been demonstrated previously, but could be important in other poorly buffered systems dominated by tree species that differ in cation nutrition or that are influenced by acidic deposition.     

Sorption of dissolved organic matter by mineral soils of the Siberian forest tundra

Because of low net production in arctic and subarctic surface water, dissolved organic matter (DOM) discharged from terrestrial settings plays an important role for carbon and nitrogen dynamics in arctic aquatic systems. Sorption, typically controlling the export of DOM from soil, may be influenced by the permafrost regime. To confirm the potential sorptive control on the release of DOM from permafrost soils in central northern Siberia, we examined the sorption of DOM by mineral soils of Gelisols and Inceptisols with varying depth of the active layer. Water‐soluble organic matter in the O horizons of the Gelisols was less (338 and 407 mg C kg^?1) and comprised more dissolved organic carbon (DOC) in the hydrophobic fraction (HoDOC) (63% and 70%) than in the O horizons of the Inceptisols (686 and 706 mg C kg^?1, 45% and 48% HoDOC). All A and B horizons from Gelisols sorbed DOC strongly, with a preference for HoDOC. Almost all horizons of the Inceptisols showed a weaker sorption of DOC than those of the Gelisols. The C horizons of the Inceptisols, having a weak overall DOC sorption, sorbed C in the hydrophilic fraction (HiDOC) stronger than HoDOC. The reason for the poor overall sorption and also the preferential sorption of HiDOC is likely the high pH (pH>7.0) of the C horizons and the smaller concentrations of iron oxides. For all soils, the sorption of HoDOC related positively to oxalate‐ and dithionite–citrate‐extractable iron. The A horizons released large amounts of DOC with 46–80% of HiDOC. The released DOC was significantly (r=0.78, P<0.05) correlated with the contents of soil organic carbon. From these results, we assume that large concentrations of DOM comprising large shares of HiDOC can pass mineral soils where the active layer is thin (i.e. in Gelisols), and enter streams. Soils with deep active layer (i.e. Inceptisols), may release little DOM because of more frequent infiltration of DOM into their thick mineral horizons despite their smaller contents of reactive, poorly crystalline minerals. The results obtained for the Inceptisols are in agreement with the situation observed for streams connecting to Yenisei at lower latitudes than 65°50′ with continuous to discontinuous permafrost. The smaller sorption of DOM by the Gelisols is in agreement with the larger DOM concentrations in more northern catchments. However, the Gelisols preferentially retained the HoDOC which dominates the DOC in streams towards north. This discrepancy can be explained by additional seepage water from the organic horizons that is discharged into streams without intensive contact with the mineral soil.     

Effect of submergence on availability of certain plant nutrients in three Ultisol catenas

Soil samples from surface and sub-surface horizons in the well-drained and poorly-drained members of three soil catenas were incubated under submergence or at field capacity to study the effects of these incubation conditions and prior natural drainage on the solubility of four plant micro-nutrients. Iron, Mn, Zn and Cu were extracted by water using a 11 water:soil ratio. The four micronutrient metals were also extracted by DTPA solutions buffered at either pH 5.3 or pH 7.3 to compare the effectiveness of these two extractants under these incubation conditions with acid soils. Generally the extractability of the nutrients was much affected by the horizon (A, E or B) with A horizons having the greatest amounts of all nutrients and undergoing greater changes in water- and DTPA-extractability during incubation. Soil drainage class (wellvs. poorly drained) had few effects. Incubation moisture regime had major effects on water extractable Fe and Mn with lesser effects on Zn and Cu. Submerged soils generally had the greatest levels of water extractable nutrients, though rice uptake did not reflect this. DTPA at pH 5.3 extracted 2 to 3 times as much Fe, Mn, Zn and Cu as did DTPA at pH 7.3 and about 50 to 100 times as much as did water. Correlations between DTPA extractable nutrients and rice uptake were significant only for Fe and Cu and declined during incubation. The changes in all variables during incubation were complex, being related to soil properties such as organic matter content, pH and mineralogy as well as to incubation conditions.     

The relation between spruce monoculture and incipient podzolisation in ochreous brown earths of the Belgian Ardennes

Summary The effects of coniferous monoculture on the distribution of C, Fe and Al in the upper horizons of brown ochreous earths of the Belgian Ardennes were investigated by comparing 5 soil profiles developed under an 80 year old spruce stand with another 5 profiles developed under a climactic broad-leaved forest (beechwood).Organic carbon, Fe and Al were extracted with 0.1N NaOH/Na-tetraborate solution buffered at pH 9.7: recent studies have shown that this extraction is particularly appropriate for the detection of incipient podzolisation in brown earths-brown podzolic soils intergrades.Even if most of the classic podzolisation indexes fail to illustrate differences, nevertheless our results show that fulvic acids and organo-ferric complexes are present in significantly greater amounts in the upper part of the cambic (B)₁ horizon of the soils developed under conifers. Moreover, this podzolic tendancy is confirmed by the weathering patterns of the clay minerals in the A₁(B) horizons developed under spruces, i.e. a more pronouced weathering of chloritic layers than those observed in the beechwood soil, with a correlative genesis of more abundant smectite-like minerals. One may therefore conclude that the change in the humus type (moder to mor) after the planting of spruce trees, has been sufficient, within the local climatic and edaphic context, to promote incipient podzolisation.     

Quantification and Comparison of Soil Elements in the Tibetan Plateau Kaschin-Beck Disease Area

The prevalence rate of Kaschin-Beck disease (KBD) in most parts of China is currently decreasing, but the disease is still active and severe on the Tibetan Plateau. Soil samples including the surface layer (0–20 cm) and the subsurface layer (20–40 cm) in the cultivated and natural soil profiles were collected, and the mechanical composite and total concentration of arsenic, cobalt, copper, iron, mercury, manganese, molybdenum, selenium, and zinc were determined. Concentrations of arsenic, iron, manganese, copper, and selenium in the surface soil were lower than those in the subsurface soil. The same was true of physical clay in the soil profiles. However, there were no significant differences between the different soil layers. The concentrations of selenium, molybdenum, and mercury were somewhat lower compared with the average concentrations of soils in China. Deficiencies of molybdenum and selenium both play a critical role in occurrence of KBD, but whether or not soil mercury at a low level contributes to KBD is still unclear. A correlation analysis of soil elements showed that there is a positive correlation between iron, cobalt, and manganese due to their similar chemical characteristics. Selenium concentrations in soil as well as the physical clay and iron descend with the deterioration of KBD, but mercury concentrations in soil ascend with the aggravation of the disease. The results show that selenium deficiencies greatly influence the disease, and a deficiency of molybdenum is likely another important factor in inducing KBD. Moreover, determining whether low levels of soil mercury contribute to KBD should be investigated in the future.     

Nitrogen dynamics of a boreal black spruce wildfire chronosequence

This study examined the nitrogen (N) dynamics of a black spruce (Picea mariana (Mill.) BSP)-dominated chronosequence in Manitoba, Canada. The seven sites studied each contained separate well- and poorly drained stands, originated from stand-killing wildfires, and were between 3 and 151 years old. Our goals were to (i) measure total N concentration ([N]) of all biomass components and major soil horizons; (ii) compare N content and select vegetation N cycle processes among the stands; and (iii) examine relationships between ecosystem C and N cycling for these stands. Vegetation [N] varied significantly by tissue type, species, soil drainage, and stand age; woody debris [N] increased with decay state and decreased with debris size. Soil [N] declined with horizon depth but did not vary with stand age. Total (live + dead) biomass N content ranged from 18.4 to 99.7 g N m⁻² in the well-drained stands and 37.8–154.6 g N m⁻² in the poorly drained stands. Mean soil N content (380.6 g N m⁻²) was unaffected by stand age. Annual vegetation N requirement (5.9 and 8.4 g N m⁻² yr⁻¹ in the middle-aged well- and poorly drained stands, respectively) was dominated by trees and fine roots in the well-drained stands, and bryophytes in the poorly drained stands. Fraction N retranslocated was significantly higher in deciduous than evergreen tree species, and in older than younger stands. Nitrogen use efficiency (NUE) was significantly lower in bryophytes than in trees, and in deciduous than in evergreen trees. Tree NUE increased with stand age, but overall stand NUE was roughly constant (∼ ∼150 g g⁻¹ N) across the entire chronosequence.     

Vertical root distribution in relation to soil properties in New Jersey Pinelands forests

Vertical distribution of root density (length per unit soil volume) and abundance (length per unit ground surface area) to a depth of 1.5 m or to the depth of the water table and their relationships with soil properties and tree basal area were examined in 36 soil profiles of pine-oak and oak-pine forests of the New Jersey Pinelands. Soil morphology were almost uniform within the forest type and characterized by the presence of high coarse fragment contents in the C horizon in oak-pine uplands; by the spodic B horizon and water table in the C horizon in pine-oak lowlands; by the sandy soil throughout the profile in pine-oak uplands; and by the firm argillic B horizon in pine-oak plains. Root density decreased from ranges of 44423–133369 m m^-3 in the 0–5 cm depth in all the forest types to 1900–5593 m m^-3 in the 100–150 cm depth in all the forest types except in pine-oak lowlands. Total profile root density and abundance was in the order: oak-pine uplands>pine-oak lowlands>pine-oak uplands>pine-oak plains. Root density correlated positively with organic C, total N, water soluble P, exchangeable Ca, Mg, K, Al, Fe, and cation exchange capacity, and negatively with bulk density, coarse fraction content, and pH, whereas root abundance correlated positively with organic C, total N, water soluble P, exchangeable Ca, Mg, K, and Fe, and negatively with bulk density. No correlation existed between root density and abundance with tree basal area. Higher root density in the E horizon of oak-pine uplands as compared to the other forest types was associated with high nutrient content; higher root density in the C horizon of pine-oak lowlands was associated with a shallow water table beneath the horizon; and lower root densities in the B and C horizons of pine-oak plains were associated with the presence of a firm clay layer in the B horizon.     

Metal Transport and Bioavailability in Soil Contaminated with CCA-Treated Wood Leachates

A laboratory study was conducted to investigate metal transport and accumulation within soils contaminated with As, Cr, and Cu from CCA-treated wood leachates. New blocks of CCA-treated wood were leached using synthetic rainwater. Soil columns were constructed and filled with three different soils, including a sandy soil, an organic soil and a clay soil. The leachate was applied intermittently until 80 pore volumes were eluted through each column. Metal concentrations (Cu, Cr, and As) were measured in the leachate before passage through the columns as well as in each elutriate fraction collected. Chemical analysis was complemented with toxicity testing using Ceriodaphnia dubia, Selenastrum capricornutum, and MetPLATE?. Following application of 80 pore volumes of leachate, the columns were dissected and the profile of the metal concentrations within each column was determined. A comparison of the arsenic, chromium and copper leaching patterns found arsenic to be the most mobile, with copper the most retained in the soil columns (As < Cr < Cu). Transport patterns of As differed in the three soil types, with observed mobility highest in the sandy soil and lowest in the clay soil. The three metals accumulated in the top layer of soil. Arsenic posed the greatest risk when soil concentrations were compared to risk-based target levels. Although metals were detected in soil elutriates, no toxicity was detected in any of the soil column elutriates using any of the three toxicity assays.     

Depth-Related Changes in Community Structure of Culturable Mineral Weathering Bacteria and in Weathering Patterns Caused by Them along Two Contrasting Soil Profiles

Bacteria play important roles in mineral weathering and soil formation. However, few reports of mineral weathering bacteria inhabiting subsurfaces of soil profiles have been published, raising the question of whether the subsurface weathering bacteria are fundamentally distinct from those in surface communities. To address this question, we isolated and characterized mineral weathering bacteria from two contrasting soil profiles with respect to their role in the weathering pattern evolution, their place in the community structure, and their depth-related changes in these two soil profiles. The effectiveness and pattern of bacterial mineral weathering were different in the two profiles and among the horizons within the respective profiles. The abundance of highly effective mineral weathering bacteria in the Changshu profile was significantly greater in the deepest horizon than in the upper horizons, whereas in the Yanting profile it was significantly greater in the upper horizons than in the deeper horizons. Most of the mineral weathering bacteria from the upper horizons of the Changshu profile and from the deeper horizons of the Yanting profile significantly acidified the culture media in the mineral weathering process. The proportion of siderophore-producing bacteria in the Changshu profile was similar in all horizons except in the Bg2 horizon, whereas the proportion of siderophore-producing bacteria in the Yanting profile was higher in the upper horizons than in the deeper horizons. Both profiles existed in different highly depth-specific culturable mineral weathering community structures. The depth-related changes in culturable weathering communities were primarily attributable to minor bacterial groups rather than to a change in the major population structure.     

Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes

Non-native earthworms are a continued source of environmental change in the northeastern United States that may affect trace metals in the plant-soil system, with largely unknown effects. We assessed earthworm impacts on exchangeable and strong acid extractable (total) concentrations and pools of Al, Fe, Cu, Zn, Mo, Pb in non-point source polluted, forest soil horizons (Organic, A, and B) and foliar metals concentrations in young (<?3 years) Acer saccharum and Polystichum acrostichoides at four proximal forests in the Finger Lakes Region of New York. We observed decreasing total trace metal Organic horizon pools and increasing total trace metal A horizon concentrations as a function of increasing earthworm biomass. Earthworms had limited effects on exchangeable concentrations in A and B horizons and total metal concentrations in the B horizon. Foliar trace metal concentrations in Acer were better explained by earthworm biomass than soil concentrations but foliar concentrations for Polystichum were poorly predicted by both earthworm biomass and soil metal concentrations. Our results suggest that earthworms can affect trace metal uptake by some plants, but not by increasing soil trace metal exchangeability or from changing soil properties (pH, %SOM, or cation exchange capacity). Instead, non-native earthworms may indirectly alter understory plant uptake of trace metals.     

Some microbiological aspects of surface and buried soils on Mt. Kenya,East Africa

When numbers of microorganisms in profiles of surface and buried horizons on Mt. Kenya were estimated by dilution plate counting they were found to be consistently lower than those from other soils in different geographical regions as determined from the literature. The lower numbers are probably characteristic of the poorly weathered Inceptisols and Entisols usually found in the alpine zone.The A horizons of the soils studied contain proportionately fewer of the total numbers of organisms in the A, B and C horizons than observed in most soils. Estimates of organic matter were positively correlated with numbers of fungi and bacteria in the A horizons. However, other factors such as severe drought, high light intensity, low temperatures, diurnal frost heaving, low pH and paucity of clay minerals may be significant factors in suppressing the more luxuriant growth of microbial populations.Organic and inorganic horizons of buried soils sometimes exhibit higher counts of microorganisms than adjacent horizons of surface soils. However, the bacteria and fungi even in deeply buried paleosols exhibit characteristics of an unspecialized heterotrophic population. Among fungi the species were obviously the same as those isolated from one or more of the overlying horizons. Taken in conjunction with other evidence from the profiles it is concluded that the microorganisms were introduced and represent a transient or non-active population. Contamination of buried organic horizons may influence the estimated age as assessed by radiocarbon dating.     

Evaluating Hydroperiod Response in Restored Carolina Bay Wetlands Using Soil Physicochemical Properties

Carolina bays are shallow depression wetlands found in the southeastern United States that have been severely altered by human activity. The need to restore these complex and diverse systems is well established, but our limited understanding of wetland hydrologic processes in these systems hinders our ability to assess the effectiveness of bay restoration efforts. Carolina bays exhibit a wide range of moisture regimes from seasonally saturated to semipermanently inundated. Differing physicochemical properties of soils within bay interiors may control bay hydrology. However, previous efforts to establish relationships between soil characteristics and bay hydrology have been inconclusive. An assessment of soil and hydroperiod was initiated in 16 bays designated to be restored and 6 bays that were not restored (reference). Soil morphology was described, and permanent monitoring wells were installed at each site. Multiple regression analysis was used to determine relationships between the soil physicochemical characteristics and the bay hydroperiod for restored and reference bays in both pre‐ and postrestoration periods. A significant relationship (r²= 0.75, p= 0.02) between prerestoration hydroperiod and clay content in the argillic horizon (Bt) of the reference bays was observed. This relationship was then used to evaluate hydroperiod change in the restored bays from the postrestoration period. The relationship accurately identified sites that exhibited high prerestoration hydroperiods and did not need hydrologic restoration (n= 4) and effectively showed sites that exhibited substantial increases in hydroperiod due to the restoration activities (n= 7).     

Environmental hazards of arsenic associated with black shales: a review on geochemistry, enrichment and leaching mechanism

Black shales are high organic matter-rich dark coloured mudstones those are often deposited during ??oceanic anoxia events??. Most of the black shale horizons are rich in arsenic far above their average crustal abundance and are susceptible to weathering eventually leaching high As contents to the surrounding environment causing As enrichment in soil and water which adversely affect the living beings. Numerous arsenic contaminations are being reported from black shale hosted areas globally, hence, making extremely crucial to understand the processes of enrichment, leaching and broader prospective of environmental hazards. Few studies have shown arsenic concentrations as high as 6,000?mg/kg within black shales causing groundwater enrichment up to hundreds mg/L. Arsenic is commonly attached to sulphide mineral structure and partly to organic matter and clay contents during deposition and diagenetic processes. Majority of sulphide bound arsenic becomes available to oxidative dissolution processes in presence of atmospheric oxygen and water which is further triggered by certain microbial community such as Acidophilus ferrooxidans hence, enhancing arsenic release. Physical weathering processes carry the arsenic-rich shale constituents to the depositional site where it is dissolved subsequently. Chemical diffusion and mechanical transport are two prime processes transporting arsenic from black shale horizons to the water bodies or soil columns, while air pollutions are caused by combustions of organic matter-rich coaly shales.     

Use of Arsenic Contaminated Irrigation Water for Lettuce Cropping: Effects on Soil, Groundwater, and Vegetal

The present study investigated the effects of using arsenic (As) contaminated irrigation water in Lactuca sativa L. cropping. Two different arsenic concentrations, i.e., 25 and 85 μg L⁻¹ and two different soils, i.e., sandy and clay loam, were taken into account. We determined the arsenic mobility in the different soil fractions, its amount in groundwater, and the phytotoxicity and genotoxicity. Nuclear magnetic resonance (NMR) and inductively coupled plasma (ICP) were used to assess the lettuce metabolic profile changes and the arsenic uptake by the plant, respectively, as a function of the various conditions studied, i.e., As content and type of soil. Data indicated that at both concentrations in sandy soil, arsenic is in part quickly leached and thus present in groundwater and in part absorbed by the vegetable, being therefore readily available for assimilation by consumption. NMR results reported a large modification of the metabolic pattern, which was depending on the pollutant amount. In clay loam soil, the groundwater had a low As content with respect to sandy soil, and NMR and ICP performed on the lettuce did not reveal severe changes related to As, most likely because the metalloid is bound to the colloidal fraction.     

Site disturbance effects on a clay soil under radiata pine

Timber harvesting of forested lands can cause impacts which reduce the long-term productivity of the soil. This study examined long-term effects of timber harvesting on soil morphology, soil solutions and clay mineral stability. A disturbance study established in 1981 an Ultisol located in the North Island of New Zealand was examined in 1990. Disturbance treatments were installed following cable logging of radiata pine (Pinus radiata D. Don); treatments consisted of no disturbance (UN), O horizon removed (OR), and O and A horizons removed with compaction of the Bt1/A horizon (OARHC). The morphology of the A and Bt1/A horizons of the OR treatment showed little difference from the UN treatment. Soil solutions were collected using centrifugation and soil mineralogy determined. Soil solutions of the O horizon had nutrient concentrations that were approximately 10 times greater than that of the mineral horizons, indicating that nutrient availability would be reduced by reduced by removal of this horizon during harvesting. Soil solutions of the Bt1/A horizon showed substantially lower nutrient concentrations in the OARHC treatment compared to the UN and OR treatment, at 9-years after treatment. Stability diagrams of soil solutions for clay minerals of the soil showed that smectite was unstable and weatherable with the highest disturbance treatment, but was stable in the no and low disturbance treatment. No disturbance effects were evident in the stability of iron minerals. Results suggest that this soil is capable of returning to pre-disturbance conditions well-within a rotation period when disturbance is limited, but that recovery with the highest disturbance treatment could take substantially longer. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.