Sewage sludge as organic ameliorant for revegetation of fine bauxite refining residue

The rise in aluminium demand in the world has significantly increased the generation of bauxite residue which occupies huge areas of land worldwide. Direct revegetation of residue storage areas has been unsuccessful because of the high alkalinity and salinity, and poor nutrient contents of the fine residue (red mud). This paper describes glasshouse and field experiments evaluating the potential use of sewage sludge as an organic ameliorant for gypsum amended red mud. The growth of Agropyron elongatum in red mud receiving gypsum (0 and 38.5 t ha⁻¹) and sewage sludge (0, 38.5 and 77 t ha⁻¹) amendment was assessed in a glasshouse study. Leachate and soil analyses revealed that gypsum was effective in reducing the pH, EC and ESP of red mud, while sewage sludge gave additional reductions in EC, Na and ESP. No evidence of any significant increases in heavy metal contents were observed in the leachates following sewage sludge amendment. However, soil Al contents were more available in red mud receiving only sewage sludge treatment. Sewage sludge amendment significantly increased dry weight yield and provided sufficient nutrients for plant growth except K which was marginal. No heavy metal accumulation was observed in Agropyron. Following that, a field experiment was performed having red mud amended with sewage sludge (38.5, 77 and 154 t ha⁻¹) and gypsum (38.5 and 77 t ha⁻¹) to evaluate their effects on soil physical properties of red mud. Sewage sludge significantly reduced soil bulk density (25%) and particle density (9%) and increased the total porosity of red mud (8%). Hydraulic conductivity also increased from 1.5 to 23 × 10⁻⁵ m s⁻¹. Plant cover percentage and dry weight yield of Agropyron increased with an increase in gypsum and sewage sludge amendment. The results confirm that sewage sludge is effective in improving both soil structure and nutrient status of gypsum amended red mud. The use of sewage sludge for red mud revegetation provides not just an option for sludge disposal, but also a cost effective revegetation strategy for bauxite refining industry.     

Plant growth and uptake of mineral elements at an oily sludge landfarming site in Kuwait

Oily sludge landfarmed in Kuwait soil contains higher concentrations of certain elements than that of the untreated of, soil, e.g. S, Cu, Cr, Zn, Pb, Ni, Mo and V. The growth and elemental content of three different plants grown on a sandy soil previously treated with different concentrations of oily sludge were studied. Tested plants differed in their response to landfarmed oily sludge; ryegrass was the least affected followed by oats, then barley. Uptake of elements differed both qualitatively and quantitatively between test plants. In barley, Zn increased in plants cultivated in soil treated with oily sludge, whereas other metal concentrations were reduced or not affected, namely, Cu, Pb, Ni, V. The uptake of P was greater in plants grown on treated soil compared with those on untreated soil, whereas Na, Ca, K, were either reduced or unaffected. In oats, Zn, Ni, Cu, Pb, V, were not significantly changed. Uptakes of K, Ca, P, and Na in plants from treated soil were higher than that of the control. In ryegrass, heavy metal concentrations were either reduced or remained the same as that of the control. In all cases, concentrations of essential heavy metals and other true elements under investigation were still lower than the levels considered to be sufficient for micronutrients. Thus, the oily sludge was a source of certain micro-nutrients which were deficient in the sandy soil. Further, it appears that uptake and distribution of elements in plant tissues were both highly variable according to the plant, species, and the soil characteristics.     

Phytoremediation of aged petroleum sludge: effect of irrigation techniques and scheduling

The use of higher plants to accelerate the remediation of petroleum contaminants in soil is limited by, among other factors, rooting depth and the delivery of nutrients to the microsites at which remediation occurs. The objective of this study was to test methods of enhancing root growth and remediation in the subsurface of a contaminated petroleum sludge. The phytoremediation of highly contaminated petroleum sludge (total petroleum hydrocarbons >35 g kg(-1) was tested in the greenhouse as a function of the frequency and the depth of irrigation and fertilization. Water and dissolved plant nutrients were added to the soil surface or at a depth of 30 cm, either daily or weekly. Equivalent quantities of water and nutrients were added in all cases. Daily irrigation at a depth of 30 cm invoked greater root growth and enhanced contaminant degradation relative to all other treatments. In the absence of plants, residual concentrations of petroleum hydrocarbons after 7 mo were higher than with plants. The presence of plant roots clearly improved the physical structure of the soil and increased microbial populations. Thus, the plant roots in conjunction with daily additions of soluble N and P appeared to enhance oxygen transport to greater depths in the soil, stimulate petroleum-degrading microorganisms, and provide microbial access to soil micropores. Subsurface irrigation with frequent, small amounts of water and nutrients could significantly accelerate phytoremediation of field soils contaminated with petroleum hydrocarbons.     

Impact of intensive market gardening on the nutrient status of hydromorphic soil in the Ojo area of Lagos metropolis,Nigeria

Summary This study evaluates the impact of intensive market gardening on the nutrient status of hydromorphic soil in the Ojo area of Lagos metropolis. Following 15–20 years of continuous market gardening, the organic matter content of the 0–10 cm layer of the hydromorphic soil has been reduced to 75 percent of the level found in a swamp forest soil used as a control. The extent of the organic matter decline in the cultivated soil is slight compared with the degree of organic matter diminution in well-drained soil used for shifting or continuous cultivation. This is due to the low degree of humus mineralisation in water-logged soil and the application of organic manure.In spite of regular application of both organic and inorganic fertilisers, the levels of exchangeable calcium, magnesium, potassium and sodium are lower in the 0–10 cm and 10–20 cm layers of the intensively cultivated hydromorphic soil used for market gardening than in the swamp forest control areas. The mean level of extractable manganese is lower in the 10–20 cm layer of the cultivated soil. These differences are due to nutrient immobilisation and removal in harvested vegetables, and to nutrient loss from the market gardening plots through erosion. There is, however, a build-up of available phosphorus in the surface layer of the market garden soil due to the application of inorganic phosphate fertilisers.The levels of mineral nutrients in the surface layers of the cultivated soil are within the optimal ranges for most arable crops, suggesting that the soil is not impoverished. This is due to the judicious application of both organic and inorganic fertilisers, and is indicative of the fact that hydromorphic soils can support continuous cultivation under proper management.Dr A.O. Aweto is a Senior Lecturer in the Department of Geography, and Mr G.M. Ogurie was until recently a geography student in the same department.     

Role of Alternative Electron Acceptors (AEA) to control methane flux from waterlogged paddy fields: Case studies in the southern part of West Bengal, India

The rice fields, depleted of O₂, contain large amount of moisture and organic substrates to provide an ideal anaerobic environment for methanogenesis and are one of the principal anthropogenic sources of methane. In order to mitigate this emission Alternative Electron Acceptors (AEA) were altered in the soil. The experiments were carried out in four seasons at the site of Balarampur, near Baruipur, South 24 Parganas, West Bengal, namely September–December, 2005 (Cultivar: Sundari), February–May, 2006 (Cultivar: Sundari), September–December, 2006 and February–May, 2007 (Cultivar: Swarna-Pankaj). The seasonal average methane flux (Fe treated), for the cultivar type “Sundari” (season: September–December, 2005), is 4.41 t ha⁻¹, as compared to the value of 6.40 t ha⁻¹ for the untreated soil. Similarly for February–May, 2006, the seasonal average methane flux (Fe treated) is 5.52 t ha⁻¹, whereas the untreated flux is 5.69 t ha⁻¹. In the third and fourth seasons we had two treatments with Ammonium Thiosulphate and Ferric Hydroxide. The seasonal average methane flux (treatment: Ammonium Thiosulphate) is 4.35 t ha⁻¹ and 5.41 t ha⁻¹ respectively, whereas for the ferric hydroxide treated soil it is 4.35 t ha⁻¹ and 6.14 t ha⁻¹ respectively. The properties related to the nutrient quality of the harvested paddy seeds supplement these results.     

含油污泥无害化处理及综合利用的途径

原油脱水以及油田和炼油厂的污水处理系统会排出大量的含油污泥,从环境保护角度出发,必须进行无害化处理或综合利用。处理含油污泥的方法很多,有固化处理法、土地耕作法、回收污油法、固液分离处理及综合利用等方法。较为详细地叙述了各种方法的原理、特点及适用情况等,这些方法各有利弊。今后还应进一步加强含油污泥性质与特征的基础性研究,积极寻求多种利用途径,彻底解决含油污泥污染问题     

Soil and plant characteristics of landfill sites near Merseyside,England

An ecological survey of the plant and soil characteristics was carried out on three landfill sites near Merseyside, England. It was discovered that bare ground at two of the landfill areas had high levels of methane contained in the soil air (Sefton Meadows landfill: 6–8% at 35 cm and 16–35% at 65 cm below soil surface; Coalgate Lane landfill: 1–24% at 35 cm and 39–45% at 40 cm below soils surface), causing the appearance of dark grey reduced regions in the soil, a phenomenon similar to flooded soil. The wellvegetated areas at the two sites had lower levels of methane (under 7%).In areas relatively free of methane, the concentrations of mineralized N and NO₃ ^– had significant correlations with the dry weights of vegetation (r = 0.71 withp<0.01;r=0.61 withp<0.02 accordingly), indicating the necessity of applying available nitrogen fertilizer.     

Organic carbon diminution and estimates of carbon dioxide release from plantation soil

Summary This paper evaluates the rates of organic carbon diminution in the soil under monospecific tree plantations of teak, gmelina, rubber, oil palm, cashew and coffee. The differences between the organic carbon status of their soils and soil under nearby natural rain forest vegetation are compared. Annual rates of organic carbon decrease for the 0–10 cm soil layer, varied from 82.1 kg ha^–1 for cashew to 316.7 kg ha^–1 for oil palm. The tree plantations appear to release more carbon dioxide from the soil into the atmosphere than the natural forest. They therefore, appear to have the potential of contributing towards global warming — a threat they are supposed to mitigate.     

含油污泥薄层干燥特性及动力学模型分析

采用薄层干燥方式进行含油污泥热干燥的研究,引入薄层干燥模型对含油污泥干燥过程进行模拟,结果表明,Midilli模型比其他模型更适合含油污泥的薄层干燥分析。应用Fick扩散模型,得到80～140℃条件下含油污泥干燥的有效扩散系数变化范围为1.08×10-10～4.22×10-10 m2/s,其值随着温度升高而增大。根据Arrhenius经验公式建立温度与扩散系数的关系,得到含油污泥干燥时水分扩散的活化能为27.26kJ/mol。     

Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe

We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant–soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May–October) grazing by yearling heifers at heavy (60–75% utilization) and light (20–35% utilization) stocking rates, and nongrazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C₄ grass blue grama (Bouteloua gracilis), whereas excluding livestock grazing increased the production of C₃ grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha^–1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha^–1 higher in total soil C (0–90 cm) than the nongrazed treatment, with 68% (16.3 Mg ha^–1) attributable to higher SIC, and 32% (7.5 Mg ha^–1) to higher SOC. These results emphasize the importance in semiarid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant–soil C and in evaluations of the impacts of grazing management on C sequestration.     

Assessment of Lead Exposure in Thohoyandou, South Africa

Lead levels in different environmental media (soil, grass leaves, water, ceramics, pencil, paint, crayons and cosmetics) were determined to assess the major sources of lead exposure in Thohoyandou, South Africa. Soil and plant leaves were used as indicators of Pb pollution from vehicle exhaust emissions. After digestion with concentrated acids (HNO₃, HCl and HClO₄) Pb concentrations were determined in triplicate using a flame atomic absorption spectrometer. The mean Pb concentrations at the kerb of selected busy roads were 205.5 ± 90, 273.0 ± 90 and 312.8 ± 81 μg g⁻¹ and 154.7 ± 67, 182.9 ± 76 and 240.6 ± 66 μg g⁻¹ for soil and plant leaves (dry weight) respectively. These concentrations were substantially higher than the values found on soils 50 m away from the roads (97.4 ± 11 μg g⁻¹). Pb concentrations in plants collected further away from the road (50 m) were substantially lower (71.8 ± 9.0 μg g⁻¹). The observed levels on soil are lower than the UK critical value of 500 μg g⁻¹ for gardens and allotments; and 2000 μg g⁻¹ for parks and open space as well as the Canadian values for agricultural (375 μg g⁻¹), residential (500 μg g⁻¹ and industrial (1000 μg g⁻¹). From these data it was clear that Pb concentrations in soil samples were substantially higher than the levels obtained for plant leaves. The Pb levels in green crayons, blue crayons, pencils (from China & Germany), were 10650 ± 75.2, 8200 ± 52.4, 1160 ± 50.2, 79 ± 10.1 μg g⁻¹ for the inner contents; and 4870 ± 58.1, 5650 ± 55.5, 1950 ± 46.6, 60 ± 12.9 μg g⁻¹ for the outer surface paint respectively. The ceramics showed Pb levels of 630 ± 50.3 μg g⁻¹ (saucer) and 560 ± 32.2 μg g⁻¹ (cup), while the inner contents and outer surface paint showed 480 ± 32.4 and 318 ± 21.2 μg g⁻¹ of Pb respectively. Early morning tap water flush gave a Pb level of 20.6 ± 5.6 μg Pb l⁻¹. This value is higher than the WHO and FDA maximum permissible concentrations of 10 μg l⁻¹ and 15 μg l⁻¹ respectively.     

Water-quality effects of a mechanized subsurface-banding technique for applying poultry litter to perennial grassland

Poultry litter is known to be an excellent organic fertilizer, but the common practice of spreading litter on the surface of pastures has raised serious water-quality concerns and may limit potential benefits of litter applications. Because surface-applied litter is completely exposed to the atmosphere, runoff can transport nutrients into nearby streams and lakes, and much of the ammonium nitrogen volatilizes before it can enter the soil. Our previous research showed that a manual knifing technique to apply dry litter under a perennial pasture surface effectively prevented about 90% of nutrient loss with runoff from surface-applied litter, and tended to increase forage yield. However, this technique (known as subsurface banding) cannot become a practical management option for producers until it is mechanized. To begin that process, we tested an experimental single-shank, tractor-drawn implement designed to apply poultry litter in subsurface bands. Our objective was to compare this mechanized subsurface-banding method against conventional surface application to determine effects on nutrient loss with runoff from a perennial grassland treated with dry poultry litter. Early in the growing season, broiler litter was applied (6.7 dry-weight Mg ha⁻¹) to each plot (except three control plots) using one of two application methods: surface broadcast manually or subsurface banded using the tractor-drawn implement. Simulated rainfall (5 cm h⁻¹) generated 20 min of runoff from each plot for volume and analytical measurements. Results showed that subsurface-banded litter increased forage yield while decreasing nutrient (e.g. N and P) loss in runoff by at least 90% compared to surface-broadcast litter.     

Nutrient transport through a Vegetative Filter Strip with subsurface drainage

The transport of nutrients and soil sediments in runoff has been recognized as a noteworthy environmental issue. Vegetative Filter Strips (VFS) have been used as one of the best management practices (BMPs) for retaining nutrients and sediments from surface runoff, thus preventing the pollutants from reaching receiving waters. However, the effectiveness of a VFS when combined with a subsurface drainage system has not been investigated previously. This study was undertaken to monitor the retention and transport of nutrients within a VFS that had a subsurface drainage system installed at a depth of 1.2 m below the soil surface. Nutrient concentrations of NO₃-N (Nitrate Nitrogen), PO₄⁻ (Orthophosphorus), and TP (Total Phosphorus) were measured in surface water samples (entering and leaving the VFS), and subsurface outflow. Soil samples were collected and analyzed for plant available Phosphorus (Bray P1) and NO₃-N concentrations. Results showed that PO₄⁻, NO₃-N, and TP concentrations decreased in surface flow through the VFS. Many surface outflow water samples from the VFS showed concentration reductions of as much as 75% for PO₄⁻ and 70% for TP. For subsurface outflow water samples through the drainage system, concentrations of PO₄⁻ and TP decreased but NO₃-N concentrations increased in comparison to concentrations in surface inflow samples. Soil samples that were collected from various depths in the VFS showed a minimal buildup of nutrients in the top soil profile but indicated a gradual buildup of nutrients at the depth of the subsurface drain. Results demonstrate that although a VFS can be very effective in reducing runoff and nutrients from surface flow, the presence of a subsurface drain underneath the VFS may not be environmentally beneficial. Such a combination may increase NO₃-N transport from the VFS, thus invalidating the purpose of the BMP.     

Sludge-grown algae for culturing aquatic organisms: Part I. Algal growth in sludge extracts

This project is aimed at studying the feasibility of using sewage sludge to prepare culture media for microalgae (Chlorella-HKBU) and the use of the sludge-grown algae as a feed for some aquatic organisms. Part I of the project included results on preparing sludge extracts and their use on algal culture. By comparing two culturing techniques, aeration and shaking, it was noted that both lag and log phases were shortened in the aeration system. A subsequent experiment noted that algal growth subject to aeration rates of 1.0 and 1.5 liters/min had similar lag and log phases. In addition, both aeration rates had a significantly higher (P < 0.05) final cell density than that of 0.5 liters/min. A detailed study on the variation of growth conditions on the algal growth was done. The results indicated that pH values of all the cultures declined below 5 at day 12. The removal rates of ammonia N ranged from 62% to 70%. The sludge-grown algae contained a rather substantial amount of heavy metals (µg/g): Zn 289–581, Cu 443–682, Ni 310–963, Mn 96–126, Cr 25–118, and Fe 438–653. This implied that the rather high levels of heavy metals may impose adverse effects on higher trophic organisms.     

Screening analysis of volatile organic contaminants in commercial inorganic coagulants used for drinking water treatment

A method for quality screening is suggested to detect volatile impurities in inorganic coagulants that are used for drinking water treatment. Static headspace gas chromatography with mass spectrometry detection (HS–GCMS) is sensitive and selective to detect volatiles in low concentrations. This study has discovered that volatile organic impurities are detectable in ferric and aluminium-based coagulants which are used for drinking water treatment. For ferric chloride, 2-propanol was detected at a level of 17–24 μg ml⁻¹, acetone at 0.7–1.7 μg ml⁻¹, 1,1,1-trichloroacetone at 0.02–0.04 μg ml⁻¹, trichloromethane at 0.01–0.02 μg ml⁻¹ and toluene at 0.01–0.12 μg ml⁻¹. For ferric chloride sulfate, acetone was detected at a level of 0.12 μg ml⁻¹, 1,1,1-trichloroacetone at 0.06–0.08 μg ml⁻¹, trichloromethane at 0.13–0.23 μg ml⁻¹, bromodichloromethane at 0.04–0.06 μg ml⁻¹ and dibromochloromethane at 0.04–0.05 μg ml⁻¹. For aluminium hydroxide chloride, only trichloromethane was detectable, but below the method detection limits (MDL). Although the concentrations of these impurities in commercial coagulants are low, this observation is important and should have impact on water industries for them to pay attention to the chemicals they are using for drinking water production.     

Utilization of pulp and paper industrial wastes to remove heavy metals from metal finishing wastewater

Two pulp and paper industrial wastes, lime mud (LM) and recovery boiler ash (RB), have low moisture contents, low heavy metal contaminations and contain various carbonate compounds which contribute to a high pH. Metal finishing wastewater (MF-WW) has a low pH, high levels of TDS and high contaminations from Cr, Cu, Pb and Zn. The heavy metals from MF-WW were removed by sorption and precipitation mechanisms. LM gave better results in removing heavy metals from MF-WW than RB. At a reaction time of 45 min, the maximum removal efficiencies for Cr (93%) and Cu (99%) were obtained at 110 g L⁻¹ of LM, but at 80 g L⁻¹ for Pb (96%) and Zn (99%). Treatment with LM gives a higher sludge volume than with RB. However, the leachability of heavy metals from LM is lower. Leachability of heavy metals in the sediment for all selected treatment conditions is within government standards.     

Denitrification potential in relation to lithology in five headwater riparian zones

The influence of riparian zone lithology on nitrate dynamics is poorly understood. We investigated vertical variations in potential denitrification activity in relation to the lithology and stratigraphy of five headwater riparian zones on glacial till and outwash landscapes in southern Ontario, Canada. Conductive coarse sand and gravel layers occurred in four of the five riparian areas. These layers were thin and did not extend to the field-riparian perimeter in some riparian zones, which limited their role as conduits for ground water flow. We found widespread organic-rich layers at depths ranging from 40 to 300 cm that resulted from natural floodplain processes and the burial of surface soils by rapid valley-bottom sedimentation after European settlement. The organic matter content of these layers varied considerably from 2 to 5% (relic channel deposit) to 5 to 21% (buried soils) and 30 to 62% (buried peat). Denitrification potential (DNP) was measured by the acetylene block method in sediment slurries amended with nitrate. The highest DNP rates were usually found in the top 0- to 15-cm surface soil layer in all riparian zones. However, a steep decline in DNP with depth was often absent and high DNP activity occurred in the deep organic-rich layers. Water table variations in 2000-2002 indicated that ground water only interacted frequently with riparian surface soils between late March and May, whereas subsurface organic layers that sustain considerable DNP were below the water table for most of the year. These results suggest that riparian zones with organic deposits at depth may effectively remove nitrate from ground water even when the water table does not interact with organic-rich surface soil horizons.     

Treatment and reuse of sewage sludge

Sewage sludge was treated using composting, fixed-bed and stirred anaerobic digesters. The treatment performance in terms of the physico chemical parameters, bacterial indicators and pathogenic forms were assessed. In addition, the biogas production rate was recorded in the case of anaerobic digesters. Composting of the sewage sludge increased its total solids from 39 to 93% after 6 weeks, while the reduction in organic matter was 40% and the total nitrogen and phosphorus contents increased by 22 and 30%, respectively. Complete removal of salmonellae and faecal coliforms occurred, so that the composted sludge could be used as a soil conditioner and fertilizer. The results of the anaerobic treatment indicated that an organic load of 4.8kg COD m–3 per day achieved the best operating conditions for either the stirred or fixed-bed digester. The mean percentage removals of COD, BOD, faecal coliforms, faecal streptococci and the biogas production rate for the stirred digester were 53, 53, 24 and 29% and 259 L kg–1 COD per day, respectively. The corresponding mean percentage removals and production rate for the experiments with a fixed-bed digester were 61, 62, 33 and 35% and 328 L kg–1 COD per day, respectively. Improvements in the BOD and faecal coliform reductions and the gas production rate of 17, 38 and 21%, respectively, were achieved due to the presence of media (Berl saddles) in the fixed-bed digester. The microbial content of the anaerobically treated sludge is too high to be used as a fertilizer, while that of the composted sludge is low enough for such use.     

Utilization of waste product (tamarind seeds) for the removal of Cr(VI) from aqueous solutions: Equilibrium, kinetics, and regeneration studies

In the present study, an adsorbent was prepared from tamarind seeds and used after activation for the removal of Cr(VI) from aqueous solutions. The tamarind seeds were activated by treating them with concentrated sulfuric acid (98% w/w) at a temperature of 150 °C. The adsorption of Cr(VI) was found to be maximum at low values of initial pH in the range of 1–3. The adsorption process of Cr(VI) was tested with Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Tempkin, Dubinin–Radushkevich and Generalized isotherm models. Application of the Langmuir isotherm to the system yielded a maximum adsorption capacity of 29.7 mg/g at an equilibrium pH value ranging from 1.12 to 1.46. The adsorption process followed second-order kinetics and the corresponding rate constants obtained were 2.605 × 10⁻³, 0.818 × 10⁻³, 0.557 × 10⁻³ and 0.811 × 10⁻³ g/mg min⁻¹ for 50, 200, 300 and 400 mg/L of initial Cr(VI) concentration, respectively. The regenerated activated tamarind seeds showed more than 95% Cr(VI) removal of that obtained using the fresh activated tamarind seeds. A feasible solution is proposed for the disposal of the contaminants (acid and base solutions) containing high concentrations of Cr(VI) obtained during the regeneration (desorption) process.     

Changes in Soil Properties After Establishment of Artemisia halodendron and Caragana microphylla on Shifting Sand Dunes in Semiarid Horqin Sandy Land, Northern China

In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0–5 cm and 5–20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0–5-cm topsoil in both C. microphylla and A. halodendron. At the 5–20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla.