Leaching of depleted uranium in soil as determined by column experiments

The basic features of the leachability of depleted uranium (DU) projectiles in soil was investigated by using 12 projectiles (145–294 g DU) and 16 columns installed in an air-conditioned laboratory. Two soils widely distributed in Europe, a sandy-loamy cambisol and a silty-loamy luvisol, were filled into the columns (3.3 kg dry soil each). The effluents of all columns were collected weekly during the observation period of 1 year. In 648 samples, ²³⁵U and ²³⁸U were determined by inductively coupled plasma mass spectrometry. The leaching rates of ²³⁸U from natural uranium were in general about 0.01 μg week^-1 or smaller, while those of ²³⁸U from the DU munitions varied considerably and reached values of up to 100 μg week^-1, for the different columns. In total, about 0.3 μg natural uranium corresponding to 20 ppm of its inventory in the soil was leached during the observation period. From the projectiles, an average of about 50 μg DU were leached corresponding to 18 ppm of the corroded DU mass (about 1.6% of the mean initial DU mass of the projectiles). Assuming that corrosion and leaching continue as observed, the mobilisation of ²³⁸U from DU munitions will last, on an average, for thousands of years in the soils investigated, while the munitions themselves will have been corroded after a much shorter time. It is proposed to use, for the investigated soil types, the mean leaching rates of the six columns with projectiles for transport calculations of ²³⁸U to the groundwater and, thus, for a better risk assessment of the water-dependent uptake pathways of DU.     

Microbial Community Composition Near Depleted Uranium Impact Points

Military training activities can result in the deposition of depleted uranium (DU) into surface soils. Mechanisms of introduction include the generation of dust from firing and impact as well as the eventual corrosion of projectile fragments and unexploded ordnance. Microorganisms in surface soils have the potential to affect the transport of DU by direct binding of the metal to the cell surface, by altering near field soil chemistry that affects metal solubility, and by microbially influenced corrosion. We investigated the response (in terms of community composition) of a native soil microbiota to the presence of DU in an arid environment. Bacteria in soils outside of the test area were challenged in dilute media with “yellow cake” or U ₃ O ₈ . At concentrations of 200 to 20,000 mg L^{? 1} only species of Bacillus were identified. In situ characterizations (by PLFA analysis) of exposed site soils showed an enrichment in sulfate reducing bacterial (i17:1w7c up 39%) and Bacillus species (a15:0 up 35%) biomarkers. Three types of microbial communities were defined (as PLFA profiles) using exploratory statistics and related to three different levels of DU exposure. The community types were then statistically corresponded to site soil chemistry. Observed differences in site soil chemistry were attributed to munitions firing since enrichments (unexposed to exposed) were observed in the minerals magnesium (increase of ～ 18 mg kg^?1 ), potassium (increase of ～ 46 mg kg^?1 ) and sulfur (increase of ～ 12 mg kg^?1 ), all constituents of munitions residues. Increased concentrations of these minerals corresponded with a community type that was associated with an area of extensive DU round use.     

Investigations on the solubility of corrosion products on depleted uranium projectiles by simulated body fluids and the consequences on dose assessment

Ingestion and inhalation of corrosion products covering weathered penetrators made of depleted uranium (DU) represent potential radiological exposure pathways. In order to study the bioavailability of these corrosion products, their solubility was determined using simulated gastric and pulmonary juices. About 75 and 36% of the uranium in the corrosion products were found to be soluble in simulated gastric and pulmonary juices, respectively. The effective dose coefficient for adults after ingestion was calculated to be 0.61 μSv mg⁻¹ DU. This compares to an effective dose coefficient for an adult of 0.71 μSv mg⁻¹ for DU materials given by the World Health Organization (WHO). The effective dose coefficient for inhalation was calculated to be 3.7 × 10⁻⁶ Sv Bq⁻¹ for workers and 5.3 × 10⁻⁶ Sv Bq⁻¹ for members of the public, respectively, which is between those of particles of Types M and S as defined by the International Commission on Radiological Protection (ICRP). The speciation of the corrosion products was investigated by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mean oxidation state of uranium was found to be 4.6, which suggests that the uranium in the corrosion products consists of a mixture of U(IV) and U(VI) species.     

Feasibility of Phytoextraction to Clean Up Low-Level Uranium-Contaminated Soil

The potential to phytoextract uranium (U) from a sandy soil contaminated at low levels was tested in the greenhouse. Two soils were tested: a control soil (317 Bq ²³⁸U kg^-1) and the same soil washed with bicarbonate (69 Bq ²³⁸U kg^-1). Ryegrass (Lolium perenne cv. Melvina), Indian mustard (Brassica juncea cv. Vitasso), and Redroot Pigweed (Amarathus retroflexus) were used as test plants.

The annual removal of the soil activity with the biomass was less than 0.1%. The addition of citric acid (25 mmol kg^-1) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15000 kg ha^-1 and 10000 kg ha^-1, respectively, up to 3.5% and 4.6% of the soil activity could annually be removed with the biomass.

With a desired activity reduction level of 1.5 and 5 for the bicarbonate washed and control soil, respectively, it would take 10 to 50 years to attain the release limit.

A linear relationship between the plant ²³⁸U concentration and the ²³⁸U concentration in the soil solution of the control, bicarbonate-washed, or citric acid-treated soil points to the importance of the soil solution activity concentration in determining U uptake and hence to the importance of solubilising agents to increase plant uptake.

However, citric acid addition resulted in a decreased dry weight production (all plants tested) and crop regrowth (in case of ryegrass).     

Effect of Hydrogenase and Mixed Sulfate-Reducing Bacterial Populations on the Corrosion of Steel

The importance of hydrogenase activity to corrosion of steel was assessed by using mixed populations of sulfate-reducing bacteria isolated from corroded and noncorroded oil pipelines. Biofilms which developed on the steel studs contained detectable numbers of sulfate-reducing bacteria (10⁴ increasing to 10⁷/0.5 cm²). However, the biofilm with active hydrogenase activity (i.e., corrosion pipeline organisms), as measured by a semiquantitative commercial kit, was associated with a significantly higher corrosion rate (7.79 mm/year) relative to noncorrosive biofilm (0.48 mm/year) with 10⁵ sulfate-reducing bacteria per 0.5 cm² but no measurable hydrogenase activity. The importance of hydrogenase and the microbial sulfate-reducing bacterial population making up the biofilm are discussed relative to biocorrosion.     

氮肥配施生化抑制剂组合对黄泥田土壤氮素淋溶特征的影响

揭示尿素类肥料添加生化抑制剂组合后,在黄泥田土壤中硝态氮(NO~-_3-N)和铵态氮(NH~+_4-N)的淋溶损失规律。采用室内土柱淋溶培养试验,研究脲酶抑制剂N-丁基硫代磷酰三胺(NBPT)和硝化抑制剂2-氯-6-(三氯甲基)吡啶(CP)单独添加及配合施用对尿素和尿素硝铵(300 kg N/hm~2)中氮(N)素在土体中淋溶损失的影响。结果表明:尿素和尿素硝铵处理淋溶液中NH~+_4-N和NO~-_3-N浓度均呈先升后降的变化趋势,而出峰时间不一。NH~+_4-N和NO~-_3-N淋失量随着时间的延长,处理间差异逐渐变大。NBPT处理可以减缓尿素水解,有效抑制NH~+_4-N生成,延缓其出峰时间,减少NH~+_4-N流失;CP处理可以有效抑制NH~+_4-N向NO~-_3-N转化,减少NO~-_3-N流失。与单独添加NBPT和CP处理相比,两者配施对N素淋溶损失有明显的协同抑制效果在黄泥田土壤中,既能减缓尿素水解,保持土壤中较高NH~+_4-N含量,又能降低淋溶液中NO~-_3-N浓度。培养结束时(第72天),UAN处理中NO~-_3-N、NH~+_4-N、矿质态N淋失总量及硝化率较U处理高34.39%、5.32%、31.72%和15.71%。U+NBPT、U+CP和U+NBPT+CP处理较U处理分别显著降低NO~-_3-N淋失总量达15.58%、114.77%和73.45%;UAN+NBPT、UAN+CP和UAN+NBPT+CP处理较UAN处理分别显著降低达15.88%、54.87%和37.46%。不同处理NO~-_3-N淋失总量大小表现为:UAN UAN+NBPT U UAN+NBPT+CP U+NBPT UAN+CP U+NBPT+CP U+CP CK。在一定施肥量条件下,NBPT和CP单独施用或配施均可降低黄泥田土壤中NO~-_3-N累积淋失量。对各处理淋溶液中NO~-_3-N淋失量(y)随时间(x)的变化进行拟合,其中以线性方程(y=ax+b)的拟合度较高,且各抑制剂处理a、b值均存在明显差异。总体认为,在黄泥田土壤中施用CP及其与NBPT配施可以显著降低土壤NO~-_3-N淋溶损失,减少N素淋失风险,提高肥料利用率。     

Investigation of physicochemical form of uranium in sediment of brackish Lake Obuchi using sequential extraction procedure

The physicochemical form of uranium (²³⁸U) in the sediment of brackish Lake Obuchi was investigated using the standard procedures of sequential extraction. Approximately 60% to 70% of ²³⁸U was composed of the form bound to carbonates and iron (Fe)-manganese (Mn) oxides in silty sediments, whereas more than 50% of ²³⁸U existed in the minerals of sandy sediments. The proportions of ²³⁸U bound to carbonates in the sediments of brackish Lake Obuchi were larger than those in fresh-water lake sediments. Most of the uranium in the brackish lake sediment was considered to be mainly influenced by UO₂(CO₃)₃ ⁴⁻ in seawater, judging from the fact that the ²³⁴U/ ²³⁸U activity ratios (1.13 to 1.16) of silty sediments were very close to that of seawater (1.14). The high correlation found between the ²³⁸U concentration in the sediment and the amount of organic matter demonstrated that organic matter acts as a scavenger for ²³⁸U accumulation on the lake bottom. Received: July 2, 1999 / Accepted: May 25, 2000     

Effects of a catch crop on leaching of nitrogen from a sandy soil: Simulations and measurements

The effects of an undersown catch crop on the dynamics and leaching of nitrogen in cropping systems with spring cereals were investigated in southern Sweden. Field measurements of soil mineral nitrogen and nitrogen concentrations in drainage water were made for 4 years in a sandy soil. The experiment was performed on four tile-drained field plots sown with spring cereals. On two of the plots, Italian rye grass was undersown and ploughed down the following spring during three of the years. The other two plots were treated in a conventional way and served as controls. Soil nitrate levels were substantially reduced in the catch-crop treatment, but increased during the fourth year when no catch crop was grown. The differences between the treatments in soil nitrate were reflected in the nitrate concentrations measured in the drainage water. A mathematical model was used to simulate nitrogen dynamics in corresponding treatments. There was good agreement between measurements and simulations with regard to patterns of change in soil mineral nitrogen and nitrate concentrations in drainage water for each treatment. Simulated leaching of nitrate in the conventional treatment was 1.9–3.9 g N m^–2 y^–1 during the first three years while calculated leaching based on the measurements was 2.7–4.4 g N m^–2 y^–1. In the catch-crop treatment leaching of nitrate was reduced by 1.4–2.6 g m^–2 y^–1 according to the simulations and by 2.2–4.1 g m^–2 y^–1 according to calculations based on the measurements. Measurements showed that leaching of nitrogen compounds other than nitrate was hardly affected by the catch crop. In the simulations the ploughed-down catch crop resulted in temporary increases of the litter pool, a net increase of the humus pool and a reduced C-N ratio of the litter pool. Simulated net mineralization from the litter pool was substantially higher in the catch-crop treatment compared with the conventional treatment. In the fourth year, the yield of the main crop was 20–25% higher in the catch-crop treatment, and leaching was higher than in the conventional treatment.     

Brain accumulation of depleted uranium in rats following 3- or 6-month treatment with implanted depleted uranium pellets

Depleted uranium (DU) is used to reinforce armor shielding and increase penetrability of military munitions. Although the data are conflicting, DU has been invoked as a potential etiological factor in Gulf War syndrome. We examined regional brain DU accumulation following surgical implantation of metal pellets in male Sprague-Dawley rats for 3 or 6 mo. Prior to surgery, rats were randomly divided into five groups: Nonsurgical control (NS Control); 0 DU pellets/20 tantalum (Ta) pellets (Sham); 4 DU pellets/16 Ta pellets (Low); 10 DU pellets/10 Ta pellets (Medium); 20 DU pellets/0 Ta pellets (High). Rats were weighed weekly as a measure of general health, with no statistically significant differences observed among groups in either cohort. At the conclusion of the respective studies, animals were perfused with phosphate-buffered saline, pH 7.4, to prevent contamination of brain tissue with DU from blood. Brains were removed and dissected into six regions: cerebellum, brainstem (pons and medulla), midbrain, hippocampus, striatum, and cortex. The uranium content was measured in digested samples as its ²³⁸U isotope by high-resolution inductively coupled plasma-mass spectrometry. After 3 mo postimplantation, DU significantly accumulated in all brain regions except the hippocampus in animals receiving the highest dose of DU (p<0.05). By 6 mo, however, significant accumulation was measured only in the cortex, midbrain, and cerebellum (p<0.01). Our data suggest that DU implanted in peripheral tissues can preferentially accumulate in specific brain regions.     

不同缓控释肥对鲜食玉米产量、品质及氨挥发的影响

采用田间试验,设置不施氮对照(CK)、常规施肥(U)、增效尿素(DU)、包膜尿素(CU)、缓控释掺混尿素(CDU)共5个处理,研究了常规施肥(240 kg N·hm^-2)和不同缓控释肥料一次性减量施用(180 kg N·hm^-2)对鲜食玉米产量、品质与土壤无机氮变化和氨挥发的影响。结果表明: U处理氨挥发总量最高,追肥是产生氨挥发损失的重要因素;与U处理相比,DU、CU、CDU处理氨挥发减排78%～81%。收获后U处理80～100 cm土层硝态氮浓度最高,为51.6 mg·kg^-1,氮淋溶风险较高,而DU、CU、CDU处理同土层硝态氮含量均较低,降低了淋溶风险。与U处理相比,减氮25%的3个缓控释肥处理没有减产,并增加了籽粒维生素C、可溶性糖和蛋白质含量;缓控释肥处理之间,DU处理的氮肥农学效率和经济效益最高。综上,减量施用新型缓控释肥可以实现鲜食玉米稳产提质,显著降低氨挥发损失和硝态氮淋失风险。与成本较高的树脂包膜控释肥相比,双效抑制剂增效肥(DU)成本低、制作便捷,是鲜食玉米专用肥的较好选择。     

Fate of airborne nitrogen in heathland ecosystems: a 15N tracer study

In the present study, we analyze the fate of airborne nitrogen in heathland ecosystems (NW Germany) by means of a ¹⁵N tracer experiment. Our objective was to quantify N sequestration and N allocation patterns in an ecosystem that is naturally limited by N, but that has been exposed to airborne N inputs exceeding critical loads for more than 3 decades. We hypothesized that the system has a tendency towards N saturation, which should be indicated by low N sequestration and high N leaching. We analyzed ¹⁵N partitioning (aboveground biomass and soil horizons) and investigated ¹⁵N leaching over 2 years following a ¹⁵N tracer pulse addition. ¹⁵N tracer recovery was 90% and 76% in the first and second year, respectively. Contrary to our expectations, more than 99% of the tracer recovered was sequestered in the biomass and soil, while leaching losses were <0.05% after 2 years. Mosses were the most important short‐term sink for ¹⁵N (64% recovery in the first year), followed by the organic layer. In the second year, the moss layer developed from a sink to a source (23% losses), and soil compartments were the most important sink (gains of 11.2% in the second year). Low ¹⁵N recovery in the current year's shoots of Calluna vulgaris (<2%) indicated minor availability of ¹⁵N tracer sequestered in the organic layer. N partitioning patterns showed that the investigated heaths still have conservative N cycling, even after several decades of high N loads. This finding is mainly attributable to the high immobilization capacities for N of podzols in soil compartments. In the long term, the podzol A‐ and B‐horizons in particular may immobilize considerable amounts of incoming N. Since N compounds of these horizons are not readily bio‐available, podzols have a high potential to withdraw airborne N from the system's N cycle.     

The effects of acid deposition on the biogeochemical cycles of major nutrients in miniature red spruce ecosystems

As part of an experimental study of air pollution effects on tree growth and health, we combined process studies with an ecosystem approach to evaluate the effects of acidic deposition on soil acidification, nutrient cycling and proton fluxes in miniature red spruce ecosystems. Ninety red spruce saplings were transplanted into 1-m diameter pots containing reconstructed soil profiles and exposed to simulated acid rain treatments of pH 3.1, 4.1 and 5.1 for four consecutive growing seasons. All the principal fluxes of the major elements were measured. During the first year of treatments, the disturbance associated with the transplanting of the experimental trees masked any treatment effects by stimulating N mineralization rates and consequent high N0₃ ⁻ cation, and H⁺ flux through the soil profile. In subsequent years, leaching of base cations and labile Al was accelerated in the most intensive acid treatment and corresponding declines in soil pH and exchangeable pools of Ca and Mg and increases in exchangeable Al concentrations were observed in the organic horizon. Leaching of Ca²⁺ and Mg²⁺ also was significantly higher in the pH 4.1 than in the pH 5.1 treatment. Flux of Ca from foliage and soil was increased in response to strong acid loading and root uptake increased to compensate for foliar Ca losses. In contrast, K cycling was dominated by root uptake and internal cycling and was relatively insensitive to strong acid inputs. Cation leaching induced by acidic deposition was responsible for the majority of H⁺ flux in the pH 3.1 treatment in the organic soil horizon whereas root uptake accounted for most of the H⁺ flux in the pH 4.1 and 5.1 treatments. Although no measurable effects on tree nutrition or health were observed, base cation leaching was significantly accelerated by acidic deposition, even at levels below that observed in the eastern U.S., warranting continued concern about acid deposition effects on the soil base status of forested ecosystems.     

Assessment of Elevated Radionuclide Levels in Soils Associated with an Avian Colony in a High Arctic Environment

This article presents the results of an investigation into the occurrence of elevated levels of radionuclides in soils associated with a seabird colony in the Arctic. Soils and other materials were collected from a seabird colony (primarily composed of kittiwakes) in Kongsfjorden, located in the High Arctic archipelago of Svalbard. The samples were analyzed for a suite of gamma emitting natural and anthropogenic radionuclides, including ¹³⁷Cs and nuclides of the ²³⁸U and ²³²Th series, to establish the level of enrichment and the behavior of the radionuclides in the immediate area. The results indicate that soils near the colony exhibit enrichment factors of 8 for ¹³⁷Cs, 5 for ²³⁸U and 2 for ²²⁶Ra compared to the nuclide content of soils from the general area. The spatial patterns of the nuclides in the soil are consistent with enrichment of the soil via run-off draining from a large accumulation of fecal and nesting material that has developed at the base of the colony. ¹³⁷Cs ingress to the soil appears to have peaked at some point in the past as patterns of enrichment at the colony are different to those exhibited by ²³⁸U, which must be assumed to be a steady state contribution. The means of introduction of radionuclides to the colony remains unclear but the transfer of ¹³⁷Cs from the marine environment to the terrestrial environment via the food chain and deposition of feces is discussed.     

Spatial distributions and dose assessment of natural radionuclides in rocks and soils of some selected sites in southwestern Nigeria

The activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in rock and soil samples collected from Ondo and Ekiti States in southwestern Nigeria were measured by using gamma-ray spectrometer with a high-purity germanium (HPGe) detector. The mean activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in the rock were 25.53, 61.12, and 554.20 Bq kg^?1 respectively, while that of the soil were 8.27, 17.37, and 151.72 Bq kg^?1 respectively. Results showed that the activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K were higher in the rocks than the soils of the areas studied. To assess the radiological impact of some radionuclides on the population in the region, the annual effective dose equivalent (AEDE), annual gonadal equivalent dose (AGED), and excess lifetime cancer risk (ELCR) were calculated. The mean values of the indoor and outdoor AEDE, and AGED were 88.08 µSv y^?1, 352.34 µSv y^?1, and 508.40 mSv y^?1, respectively for the rock samples, and 25.31 µSv y^?1, 101.25 µSv y^?1, and 145.80 mSv y^?1 respectively for the soil samples. The mean values obtained for AEDE and AGED for the soil were below ICRP recommended limits of 1 and 300 mSv y^?1, respectively. AGED for the rocks was higher than the maximum permissible limit.     

不同施肥对雷竹林径流及渗漏水中氮形态流失的影响

雷竹经营过程中化肥的大量施用,是产区水体污染的主要原因之一,养分管理技术可有效控制面源污染。为了探明减量施肥和有机肥施用对雷竹不同氮形态流失的影响,2012年在浙江省临安市雷竹产区设置了4种施肥处理:对照(CK);常规施肥(CF);减量无机(DI);减量有机无机(DOI),试验于5月18日、9月7日、11月9日分别施用肥料总量的40%,30%和30%,施肥后均进行浅翻,深度5 cm左右。通过建立径流场和土壤渗漏水收集装置,同时在试验田附近布置量雨筒,观察2012年不同氮形态浓度及流失负荷随降雨量的动态变化。研究结果表明:不同施肥处理径流水硝态氮、水溶性有机氮(WSON)以及颗粒态氮的浓度分别在3.82-6.82 mg/L、0.89-1.85 mg/L和0.89-1.83 mg/L,其占总氮的百分比分别为60.9%-68.2%、16.0%-18.1%和15.1%-21.6%。不同施肥处理渗漏水中硝态氮、铵态氮及WSON的浓度分别在26.2-92.5 mg/L、0.50-6.42 mg/L和6.57-12.6 mg/L,其占总氮的百分比分别为75.8%-82.9%、1.50%-6.36%和11.2%-20.6%。不同施肥处理径流水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了46.9%和23.1%;不同施肥处理的渗漏水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了19.1%和52.1%,可见减量施肥和减量有机无机减少氮流失的效果显著。     

Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with 203Hg‐radiolabeled compounds

Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with ²⁰³Hg‐labeled HgCl₂ and CH₃HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl ²⁰³Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of ²⁰³Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.     

The small-scale pattern of seepage water nitrate concentration in an N saturated spruce forest is regulated by net N mineralization in the organic layer

Soil net nitrogen (N) mineralization and nitrification as well as gross nitrification rates were studied in a forest soil within a 30?×?18m homogeneous plot located in an N saturated mature spruce stand at the Höglwald Forest (Bavaria, Germany) in order to explain the small-scale variation in nitrate (NO₃ ^?) concentration in seepage water. Seepage water was sampled below the main rooting zone in 40cm depth with suction cups over two periods at 20 measuring spots respectively. The sampling spots were uniformly distributed over the plot for both sampling periods, and represented the whole concentration range of seepage water NO₃ ^?concentrations measured within a close mesh of 121 suction cups. At each measuring spot soil net N mineralization, gross and net nitrification, heterotrophic soil respiration, extractable soil ammonium (NH₄ ⁺) and NO₃ ^?, and additional physical and chemical soil parameters were measured in the organic layer and correlated with the NO₃ ^? concentrations in seepage water. Furthermore, the effects of environmental parameters on N conversion processes were evaluated using multiple linear regression analysis. We found that the small-scaled variations in seepage water NO₃ ^? concentration were related to similar small-scaled variations in key processes of microbial N turnover rates in the organic layer. Within this study net N mineralization in the organic layer could explain 51–59% of the corresponding small-scale variation of nitrate concentrations in seepage water below the main rooting zone using a multiple linear regression model with stepwise procedure. In addition, we found that small-scale patterns of N turnover in the organic layer were strongly influenced by water content in the organic layer and the dry mass of organic matter.     

Leaching of subterranean clover-derived N from a loam soil

The leaching of subterranean clover-derived N (¹⁵N) was investigated in a laboratory and a field experiment. In both experiments 30 cm i.d. ×50cm soil columns were used. In the laboratory experiment the clover material was buried in the soil in mesh bags, and leaching of clover-derived N was compared to leaching of added NH ₄ ⁺ −N and NO ₃ ⁻ −N over a period of 75 days at 20°C. During that time 75% of the clover-N was released from the mesh bags and 17% of the clover-N, 50% of the NH ₄ ⁺ −N and 70% of the NO ₃ ⁻ −N was leached through the soil column. In the field experiment 6 lysimeters and 7 control microplots were constructed. The clover material was buried in soil (to the soil of two control microplots within mesh bags) in October. During one year 2% of the added clover-N was leached. This was despite a release of 65% of the N from the mesh bag contents and despite a 26% loss of the clover-derived N in total from the controls.     

Do “hot moments” become hotter under climate change? Soil nitrogen dynamics from a climate manipulation experiment in a post-harvest forest

Whole-tree forest harvest can increase soil nitrous oxide (N₂O) effluxes and leaching of nitrogen (N) from soils. These altered N dynamics are often linked to harvesting effects on microclimate, suggesting that this “hot moment” for N cycling may become hotter with climate change. We hypothesized that increases in temperature and precipitation during this post-harvest period would increase availability of soil mineral N and soil-atmosphere N₂O efflux. To test this hypothesis we implemented a climate manipulation experiment after a forest harvest, and measured soil N₂O fluxes and inorganic N accumulating on ion exchange resins. Climate treatments were: control (A, ambient), heated (H, +2.5 °C), wetted (W, +23 % precipitation), and a two-factor treatment (H+W). For all treatments, the first year after harvest had highest N₂O efflux and resin N. Wetting significantly increased cumulative soil N₂O fluxes, but only when soils were not heated too. The cumulative soil-to-atmosphere N₂O efflux from W (5.8 mg N₂O–N m^?2) was significantly higher than A (?1.9 mg N₂O–N m^?2), but H+W (~0 mg N₂O–N m^?2) was similar to A. Regardless of wetting, heating increased resin N, but only on certain dates. Cumulative resin N was on average 125 % greater in the H plots than non-heated plots. Thus, changes in temperature and precipitation each impart distinct changes to the soil N cycle. Heating increased resin N regardless of water inputs, while wetting increasing N₂O but not when combined with heating. Our results suggest that climate change may exacerbate soil N losses from whole-tree harvest in the future, but the form and quantity of N loss will depend on how the future climate changes.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.