Shallow Soil Samples Research Articles

The Influence of Nitrate on Selenium in Irrigated Agricultural Groundwater Systems

Selenium (Se) contamination of groundwater is an environmental concern especially in areas where aquifer systems are underlain by Se-bearing geologic formations such as marine shale. This study examined the influence of nitrate (NO₃) on Se species in irrigated soil and groundwater systems and presents results from field and laboratory studies that further clarify this influence. Inhibition of selenate (SeO₄) reduction in the presence of NO₃ and the oxidation of reduced Se from shale by autotrophic denitrification were investigated. Groundwater sampling from piezometers near an alluvium-shale interface suggests that SeO₄ present in the groundwater was due in part to autotrophic denitrification. Laboratory shale oxidation batch studies indicate that autotrophic denitrification is a major driver in the release of SeO₄ and sulfate. Similar findings occurred for a shale oxidation flow-through column study, with 70 and 31% more reduced Se and S mass, respectively, removed from the shale material in the presence of NO₃ than in its absence. A final laboratory flow-through column test was performed with shallow soil samples to assess the inhibition of SeO₄ reduction in the presence of NO₃, with results suggesting that a concentration of NO₃ of approximately 5 mg L or greater will diminish the reduction of SeO₄. The inclusion of the fate and transport of NO₃ and dissolved oxygen is imperative when studying or simulating the fate and transport of Se species in soil and groundwater systems.

EVALUATION OF HYDROCARBON PROSPECTS USING SURFACE GEOCHEMICAL DATA WITH CONSTRAINTS FROM GEOLOGICAL AND GEOPHYSICAL OBSERVATIONS: SAURASHTRA BASIN, INDIA

The Saurashtra Basin in western India is considered to have significant hydrocarbon potential. However conventional exploration methods, particularly for Mesozoic prospects, have been hampered by the thick basalt cover. In this study, near‐surface geochemical methods are used to investigate the generation of thermogenic gaseous hydrocarbons in the basin. Shallow soil samples were collected from favourable locations identified by integrated geophysical and geochemical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons (methane through pentane) together with soil iodine concentrations were used as surface indicators of petroleum micro‐seepages. High concentrations of adsorbed thermogenic methane (C1= 518 ppb) and ethane plus higher hydrocarbons (ΣC2+= 977 ppb) along with iodine concentrations up to 68.5 ppm were observed. Total organic and inorganic carbon (TOC and TIC) measurements, fluorescence and X‐ray diffraction (XRD) studies showed that the near‐surface hydrocarbon occurrences were seepage related. Elevated hydrocarbon and iodine concentrations were coincident with dykes and lineaments in the study area, which probably served as conduits for the micro‐seepage of hydrocarbons.

Deep Soil Horizons: Contribution and Importance to Soil Carbon Pools and in Assessing Whole-Ecosystem Response to Management and Global Change

Abstract Most of the C in terrestrial ecosystems is found in the soil. Although C calculations indicate that soils are more important than plants as reservoirs of C, soil rarely receives the attention given aboveground ecosystem components when C budgets are calculated. When soil pools are quantified they are typically sampled to relatively shallow depths. Shallow soil sampling in research includes studies that estimate C and nutrient pools and studies assessing the response of terrestrial ecosystems (i.e., forests, grasslands, and agricultural fields) to management treatments. Although many soils have sola that are substantially deeper than 20 cm and C accumulates well below these depths in many soils, the majority of studies of soil C sample to depths of 20 cm or less, generally because of the difficulty and cost of sampling the soil profile deeper. Shallow soil sampling is often justified by assuming that deeper soil horizons are stable and will not change over time, although some medium- and long-term studies do not support this assumption. Shallow soil sampling can result in both a major underestimate of soil C present in the soil profile and an inability to adequately measure the impacts of both treatments for specific goals (i.e., tillage, fertilization, and vegetation management) or other changes (i.e., global change and atmospheric inputs) over time in whole-ecosystem studies. We assessed the potential of shallow soil sampling to underestimate C in the soil profile as well as to change the conclusions of studies of management treatments on soil C. Results showed that where soils were sampled to at least 80 cm or more depth 27-77% of mineral soil C was found >20 cm in depth. In addition, analysis of results for 105 different studies of N fertilization in forests and N fertilization or conversion to switchgrass in agricultural studies shows that deeper sampling can actually change the conclusions of results of some research studies of net C accumulation or loss. Researchers wishing to either quantify soil C pools or measure changes of soil C over time are cautioned to sample soil profiles as deeply as possible and not assume that deeper soil horizons are not a critical part of adequate ecosystem analysis.

Soil Sample Depth in Pasture Soils for Environmental Soil Phosphorus Testing

Phosphorus (P) in runoff from agricultural land is a major contributor to eutrophication of surface waters. This study investigated the relationship between dissolved P in surface runoff and soil-test P measured at different sample depths (0–2 and 0–10 cm). Soil at these depths was collected from 136 sites in southeast New South Wales, Australia, under pastoral agriculture, covering a wide range of soil types and land-use intensity, from native pasture to intensive dairying. Bicarbonate-extractable soil P concentrations at these two depths were curvilinearly related over a very wide range of P (r2 = 0.91). Small-plot rainfall simulations were conducted at 14 of these locations, for which the relationship between the sampling depths was even closer (r2 = 0.95). After dividing the soils into two groups based on parent material (basalt and nonbasalt), linear relationships were found between extractable soil P and runoff dissolved reactive P, with more of the variance being accounted for with the sedimentary soils (r2 = 0.89, 0–10 cm; 0.91, 0–2 cm) compared with basalt soils (r2 = 0.63; 0–10 cm; 0.57, 0–2 cm). The results suggest that agronomic soil P testing in pastoral soils (typically 0–10 cm depth) is sufficient for estimating the potential for losses of P in runoff and that there is no need to collect shallow soil samples especially for this purpose.

Study on Arsenic Contamination in Soil and Water in Five-selected Agro Ecological Zone (AEZ) of Bangladesh

A research was carried out at the five different Agro-Ecological Zones (AEZ) of Bangladesh, viz. Tista Meander Floodplain (FP), High Ganges FP, Low Ganges FP, Active Ganges FP and Gopalganj-Khulna Bills during January 2001 to January 2002. The objectives were to assess the arsenic (As) concentration in the soil and water as well as to test tube well water samples and examines whether these exceed the acceptable limit of As. Water of shallow tube wells (STW) and soil samples were collected from ten sites under five AEZs of Bangladesh. Considerable number of water samples showed high contents of arsenic, which ranged from 0.032 to 203.9 ?g/l. Out of 428 water samples, 155 were found unsafe (>10-<50 ?g/l) and 78 were toxic (>50 ?g/l) for drinking purpose. However, out of 2648 soil samples collected from different Upazilas, only 4 samples collected from Chargat showed toxic level (>20 ?g/kg).

Shallow Groundwater and Cultivated Soil Suitability Assessments with Respect to Heavy Metal Content in the Köprübaşı U Mineralization Area (Manisa, Turkey)

Shallow groundwater and cultivated soil samples were collected from the area within Köprübaşi U mineralization and analyzed to determine U and selected heavy metals (Fe, Mn, Cu, As, Pb, Zn, Cr, Co and Ba). After this, the suitability of the shallow groundwater and soil samples were evaluated for irrigation, livestock watering and agricultural use, respectively. One groundwater sample (4) showed Mn-concentration of 112.6, exceeding the FAO (Ayers and Westcot 1985) livestock drinking limit (50 microg/l). Nevertheless, the amount of heavy metals including Fe, Cu, As, Pb, Zn, Cr and Co in groundwater is not high for irrigation and livestock drinking water standards cited by the FAO (Ayers and Westcot 1985). On the other hand, all cultivated soil samples have higher uranium concentrations than the typical concentration of natural uranium in soil (ATSDR 1999). The majority of the cultivated soil samples showed higher concentrations than the values for heavy metals (Fe, Mn, Cu, As, Pb, Zn, Cr, Co, Ba) found in normal soils of the world (Connor and Shacklette 1975). However, according to G.L.C guidelines, these soils are classified as uncontaminated with Mn, Cu, Pb, Zn and Cr, slightly contaminated with Ba and As.

Microbial community response to a release of neat ethanol onto residual hydrocarbons in a pilot‐scale aquifer tank

The microbial community response to a neat ethanol release (E100, 76 l) onto residual hydrocarbons in sandy soil was evaluated in a continuous-flow 8 m(3) pilot-scale aquifer tank, simulating a release at a bulk fuel terminal. Microbial genotypic shifts were assessed using quantitative real-time PCR analysis. High ethanol concentrations in the capillary fringe at potentially toxic levels, exceeding 100,000 mg l(-1), were tolerated by the microbial community. The high biochemical oxygen demand exerted by ethanol rapidly induced anaerobic conditions, and both methane production (up to 1.2 mg l(-1)) and growth of putative methanogenic Archaea (up to 10(6) gene copies per g of soil) were observed in shallow groundwater and soil samples 75 cm down gradient from the source. Aerobic conditions returned after ethanol was flushed out of the system, approximately 45 days after the spill (less than 7.5 pore volumes flushed). Total Bacteria growth coincided with ethanol migration and availability, which was restricted to a relatively thin layer at the capillary fringe and water table interface. The concentrations of bacteria harbouring the aerobic catabolic genes dmpN (coding for phenol hydroxylase) and to dC1 (coding for toluene dioxygenase) increased (up to 100x) down gradient from the source, likely as a result of both fortuitous growth on ethanol and on aromatic hydrocarbons mobilized by ethanol. Growth of hydrocarbon degraders was corroborated by denaturing gradient gel electrophoresis analysis showing proliferation of Azospirillum and Brevundimonas spp., which are bacteria commonly associated with microaerophilic hydrocarbon degradation. Nevertheless, the relative abundance of hydrocarbon-specific degraders (as a fraction of total Bacteria) decreased as other bacteria grew to a higher extent. Overall, the observed growth of hydrocarbon degraders suggests a potential enhancement in aerobic natural attenuation in shallow aquifers after ethanol and its degradation by-products are degraded or flushed from sites impacted by ethanol-blended fuels.

The impact of a naturally occurring CO 2 gas vent on the shallow ecosystem and soil chemistry of a Mediterranean pasture (Latera, Italy)

Recent research into CO 2 geological storage has shown that it has potential to be a safe and effective way to rapidly decrease short-term anthropogenic CO 2 emissions. Despite this progress, stakeholders must be convinced that the scientific community has studied all possible scenarios, including a potential leak into the biosphere. To better understand the potential impact of such an event, a detailed geochemical and biological study was conducted during two different seasons on a naturally occurring gas vent located within a Mediterranean pasture ecosystem (Latera geothermal field, central Italy). Results from botanical, soil gas, and gas flux surveys, and from chemical and biological analyses of shallow soil samples (0–20 cm depth), show that a significant impact is only observed in the 6 m wide centre of the vent, where CO 2 flux rates exceed 2000–3000 g m −2 d −1. In this “vent core” there is no vegetation, pH is low (minimum 3.5), and small changes are observed in mineralogy and bulk chemistry. In addition, microbial activities and populations are regulated in this interval by near-anoxic conditions, and by elevated soil gas CO 2 (>95%) and trace reduced gases (CH 4, H 2S, and H 2). An approximately 20 m wide halo surrounding the core forms a transition zone, over which there is a gradual decrease in CO 2 concentrations, a rapid decrease in CO 2 fluxes, and the absence of reactive gas species. In this transition zone grasses dominate near the vent core, but these are progressively replaced by clover and a greater plant diversity moving away from the vent centre. Physical parameters (e.g. pH, bulk chemistry, mineralogy) and microbial systems also gradually return to background values across this transition zone. Results indicate that, even at this anomalous high-flux site, the effects of the gas vent are spatially limited and that the ecosystem appears to have adapted to the different conditions through species substitution or adaptation.

Estimation of Efficiency Lithogeochemical Surveys For Petroleum and Gas Prospecting

The paper describes application of litho geochemical surveys for petroleum and gas prospecting within direct detection of hydrocarbons escaping from subsurface accumulations and source beds ? most common technique. The geochemical data came from shallow probes soil samples and shallow probes of soil gas. The adsorbed soil gases were analyzed for methane, ethane, ethylene, propane, propylene, iso-butane and normal butane by gas chromatography using a Flame Ionization detector. Samples of soil were analyzed for number of elements using spectral analysis. Direct relationships between distribution of hydrocarbons and certain elements in the vicinity of oil and gas accumulations were discovered. Those elements form halos marking structures perspective for oil and gas (Ni, Co, Cr, Sc, Mo, Li, B). Presence of positive correlation between hydrocarbon halos and active elements anomalies lends to the deduction that hydrocarbons migrating from oil and gas reservoirs affect on distribution elements in overlapping layers. These elements can be used for detecting chemical changes in the soils and rocks associated with the oil and gas deposits. Important result of these studies litho geochemical sur- vey pretty accurate showed board of Orenburg Gas Con- densate Oilfield, which has very complicated geological structure. Main advantage of using the complex litho and athmo geochemical methods is make geochemical surveys cheaper. Litho geochemical studies could be used to find out main regularities of the surveyed area. To approve anomalies discovered by litho geochemical surveys athmo geochemical and over methods should be used.

Water content and porosity estimated from ground-penetrating radar and resistivity

Both ground-penetrating radar and the resistivity method have proven to be useful tools for exploring water content variations, since related parameters such as dielectric constant and the resistivity of rocks and sediments are highly dependent on moisture content. These methods were used independently to estimate volumetric water content in the unsaturated zone and porosity in the saturated zone in a 100-m sandy section. Two sample sites along the profile were also chosen for a shallow geophysical investigation and soil sampling, to enable the calibration and verification of the indirect geophysical methods. The grain distribution at these sites is dominated by medium-sized sand (0.25–0.5 mm). The water content was 6.9 vol.% and calculated porosities are 37% and 40% respectively. At each of these sites the mean water content values calculated from resistivity are within one percentage unit of measured water content while those calculated from ground-penetrating radar give higher values by as much as 2.9 percentage units. The water contents in the unsaturated zone in the section, estimated from resistivity and ground-penetrating radar, show very similar trends, although that deduced from ground-penetrating radar is generally somewhat larger, consistent with the results from the sample sites. The mean porosity values obtained from the two methods in the saturated zone are in good agreement.

Maximum Rates of Nitrate Removal in a Denitrification Wall

Denitrification walls are constructed by mixing a carbon source such as sawdust into soils through which ground water passes. These systems can reduce nitrate inputs to receiving waters by enhancing denitrification. Maximum rates of nitrate removal by denitrification need to be determined for design purposes. To determine maximum rates of nitrate removal we added excess nitrate (50 mg N L(-1)) to a trench up-gradient of a denitrification wall during a 9-d trial. Bromide (100 g L(-1)) was also added as a conservative tracer. Movement of nitrate and bromide was measured from shallow wells and soil samples were removed for measurements of denitrification, carbon availability, nitrate, and other microbial parameters. Rates of nitrate removal, determined from the ratio of NO3-N to Br and ground water flow, averaged 1.4 g N m(-3) of wall d(-1) and were markedly greater than denitrification rates determined using the acetylene block technique (average: 0.11 g N m(-3) of wall d(-1)). These nitrate removal rates were generally lower than reported in other denitrification walls. Denitrification rates increased when nitrate was added to the laboratory incubations, indicating that despite large nitrate inputs in the field, denitrification remained limited by nitrate. This limitation was partially attributed to nitrate predominantly moving through zones of greater hydraulic conductivity or in the mobile fraction of the ground water and slow diffusion to the immobile fraction where denitrifiers were active.

Soil – Plant Relations on Sandy Grassland in the Middle Vistula River Valley

Abstract The paper is on environmental condition of sandy grassland on alluvial deposits. The soil and phytosociological study ware conducted south of Warsaw in middle Vistula river valley. Listing of vascular plants and shallow soil sampling were made in order to answer the question of plant and soil relationship. Standard chemical determination directed on trophism were done in plant and soil material. The spatial distribution of chemical parameters of plants and soils is related to local microrelief and distance of Vistula river. The plants dominating the study prefer less fertile habitats. The soil is being enriched by water from the Vistula river. High carbon content is correlated with the presence of the Salix arenaria. The greater the share of vegetation not belonging to the grass family, the greater the carbon content. Potassium and phosphorus looks like to be the less plant-dependent elements. Its documents an initial stage of development of the Vistula river valley environment.

Fate of phosphorus applied in slurry and mineral fertilizer: accumulation in soil and release into surface runoff water

Phosphorus (P) accumulation on the soil surface and its effect on the concentration of dissolved orthophosphate P (PO4-P) in surface runoff water were studied after three years of surface application of slurry and mineral fertilizer to grass ley on a sandy soil, poor in P. The total amount of P applied was 107–143 kg ha−1>, of which 72–119 kg ha−1> was applied on the soil surface during two or three years without incorporation or mixing. The addition of slurry and mineral fertilizer resulted in an increase in inorganic P in the 0–5 cm but not the 5–25 cm soil layer, but organic P was not affected. The measured changes in inorganic P deviated only by 4–6 kg ha−1> from the values derived from inputs and outputs of P (crop uptake + losses in surface runoff and drainage water). The increase in inorganic-P was accompanied by increases in the degree of P saturation (DPS) and in P extracted with acid am monium acetate (PAc ), sodium bicarbonate (POlsen) and anion-exchange resin (PResin). In surface runoff, 10–18 months after the last surface application of P, the mean flow-weighted concentration of PO4-P was linearly increased with the values of DPS, PAc, POlson and PResin in the 0–5 cm soil layer. PO4-P was lowest (0.033 mg l−1> ) in the control plots and highest (0.62 mg l−1>) in the plot where 143 kg ha−1> P had been applied in slurry and fertilizer. On that plot, the corresponding values of DPS, PAc, POlson and PResin were 16%, 13 mg kg−1>, 85 mg kg−1> and 71 mg kg−1 , even within a few years, and multiply the P loading to surface runoff from the site. A very shallow soil sampling (< 5 cm) is needed to assess P loading potential in a soil where P has been surface-applied.

Surface Geochemical Hydrocarbon Signature of the Eastern Colorado and Western Kansas Morrow Formation

Meandering fluvial deposition, combined with valley-fill stratigraphic and combination traps, makes the Pennsylvanian Morrow Formation sandstones of eastern Colorado and western Kansas a very challenging exploration target. Surface geomicrobial analysis of shallow soil samples enhances and ranks geophysical and geological leads by identifying hydrocarbon microseepage patterns. Productive versus nonproductive Marrow traps are delineated by microbial prospecting which locates and measures concentrations of specific microbial populations associated with hydrocarbon gases leaking from buried reservoirs. We provide examples of microbial signature profiles over known production and prospect locations prior to drilling, including the Moore-Johnson state-line field.

Soil hydrocarbon geochemistry, a potential petroleum exploration tool in the Cooper Basin, Australia

The ethane, propane, butanes and pentanes concentrations of shallow soil samples collected in 1975 from 1070 sites over the Permian Cooper Basin have been analyzed. The samples were taken at a spacing of 300 m along two regional traverses; on a widely spaced irregular grid from above the known gas fields of Daralingie and Della; and above potential gas field areas. Geochemical anomalies appear to be associated with all the known fields traversed and with structures having petroleum potential either as anomalies directly above the gas fields or as halo anomalies. The most useful variables mapped are: (1) the sum of soil concentration of the four hydrocarbons (expressed in ppb of soil by weight), and (2) that sum divided by the percentage of acid-soluble material. Average and highest hydrocarbon concentrations measured respectively are ethane 0.59, 18.9; propane 0.34, 10.9; butanes 0.21, 4.6; pentanes 0.20, 3.8. The acid-soluble material averaged 4.2% with the highest value at 62.8% and moisture content at 60°C averaged 5.7% with a highest value of 25.7%. Some apparent anomalies are probably spurious. The soil geochemical prospecting method has a potential in petroleum exploration only if interpreted in conjunction with good structural and stratigraphic information.