The contribution of stone cover to biological activity in the Negev desert,Israel

Ancient valley agriculture in the northern Negev highlands was based on the principle of directed collection of water and eroded material from the slopes and their consequent flow towards the valleys. The stones on these slopes were therefore removed and/or collected into piles known as ‘grape mounds’. The aim of this study was to understand the contribution of stone cover and slope‐facing to biological activity in soil. Soil samples from a depth of 0–5 mm from the soil surface were collected during the study period (December 1994–March 1996) from northern and southern hill slopes, from under limestones and between stones. Soil moisture, organic matter, chlorophyll‐a and soil respiration were determined. The results obtained in field and laboratory studies demonstrated differences between the northern and southern slopes. The stone cover on the northern slope made up 33 per cent and in the southern slope 23 per cent, stone size ranging from 15–50 cm² and 15–35 cm², respectively. Soil moisture content varied from 12 per cent in December 1994 on both slopes to one‐quarter of the initial value during the dry period. Organic matter content reached a maximal level of 14 per cent and 16 per cent on the northern and southern slopes, respectively. Values of chlorophyll‐a on both the northern and southern slopes were 0.38 μg g⁻¹ dry soil during the wet season, decreasing to 0.05 μg g⁻¹ dry soil during the dry period. Soil samples from under the stones on both slopes produced high levels of CO₂, ranging between 50 and 100 μg CO₂ g;⁻¹ dry soil h⁻¹, whereas in the control samples the levels ranged between 30 and 70 μg CO₂ g⁻¹ dry soil h⁻¹. In conclusion, the stone cover apparently plays an important role in the maintenance of biological activity through its contribution to slope biotope stability. Copyright © 2001 John Wiley & Sons, Ltd.     

USE OF FORMERLY PLOWED LAND IN NEW ENGLAND TO MONITOR THE VERTICAL DISTRIBUTION OF LEAD,ZINC AND COPPER IN MINERAL SOIL

In this study, we used once-plowed lands that have returned to forest for over 50 years to study the vertical distribution of meteorologically-deposited lead. These mineral soils were an essentially homogeneous 20 cm-thick layer when last plowed. As such, they were effectively a “clean slate” upon which pollutants deposited since the last plowing can be measured without the confounding aspects of well-developed natural soil horizons and the spatial heterogeneity of native forest soils. The concentration and amount of lead as well as copper and zinc, biologically active metals, were measured at five sites in New England. In the mineral soil, copper content ranged from 25 mg cm depth^-1 m^-2 at 0–2 cm depth to 37 mg cm depth^-1 m^-2 at 6–8 cm depth, but showed no consistent pattern with depth at all sites. Zinc concentrations and amounts increased with depth in the mineral soil to 14 μg g^-1 and 167 mg cm depth^-1 m^-2, respectively. In contrast, lead showed a decrease with depth from 350 mg cm depth^-1 m^-2 at 0–2 cm depth to 102–108 mg cm depth^-1 m^-2 between 10 and 20 cm depth. At all five sites, decreases in lead concentration with depth were correlated with decreases in the amount of organic mater. Amounts of total lead deposited since the abandonment from plowing have been estimated at 1.4 g m^-2 in rural sites. Thirty-five percent of this presumably anthropogenically-derived lead was in the forest floor; the remaining 65% was in the upper mineral soil.     

太湖地区水稻土中的β-葡糖苷酶活性

The electrical conductivity （EC） of 1：5 soil-water extract （EC1：5） was studied utilizing path coefficient analysis. The study focused on revealing the main chemical factors contributing to EC of soil extracts and their relative importance. Results showed that the most important factors influencing the EC1：5 of coastal salt-affected soils were the concentration of salt in 1：5 soil-water extract （So）, Cl^-, and the sodium adsorption ratio （SAR）, while effects of pH, CO3^2-, HCO3^, soluble sodium percentage （SSP）, and sodium dianion ratio （SDR） were very weak. Though the direct path coefficients between EC1：5 and SO4^2- , Ca^2＋, Mg^2＋, K^＋, or Na^＋ were not high, influence of other chemical factors caused the coefficients to increase, making the summation of their direct and indirect path coefficients relatively high. Evidences showed that multiple regression relations between EC1：5 and most of the primary factors （So, Cl^-, and SAR） had sound reliability and very good accuracy.     

Vertical Distribution and Fate of Trace Metals and Persistent Organic Pollutants in Sediments of the Seine and Marne Rivers (France)

Trace metals: Cd, Cu, Cr, Ni, Pb and Zn and persistent organicpollutants: polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) were investigated in a fraction ofsediments characterized by a granulometry < 200 μm. Coresfrom 17 to 54 cm depth, were collected at two sites of theSeine river upstream (Port à l'Anglais) and downstream (Saint-Cloud) from Paris and at one site of the Marne river (Saint-Maurice). Marne river sediments displayed higher Cu andPb levels than those of the Seine river. Except for Cd and Cr,contents did not vary notably in the Seine river sediments.Metal contents, except Pb, were significantly correlated withthe sediment fraction which granulometry is < 50 μm,particularly at Port à l'Anglais (p < 0.001). Correlationcoefficients between Cr, Cu, Ni and Zn contents and clayfractions of the cores ranged from 0.85 to 0.99 at both sitesof the Seine river. PCB levels varied widely, ranging from 27to 689 μg kg^-1 and were highly correlated with bothsediment fraction < 50μm and particulate organic carbon(POC) ratio. PAH levels ranged from 2.30 to 41.3 μg g^-1 and displayed the highest values close to dams; theyshowed no correlations with sediment fraction < 50 μm and POC.     

Patterns of trace metal concentration and acidity in montane forest soils of the northeastern United States

Forest floor and mineral soil samples were collected from subalpine spruce-fir forests at 1000 m above mean sea level on 19 mountains in the northeastern United States to assess patterns in trace metal concentrations, acidity, and organic matter content. The regional average concentrations of Pb, Cu, and Zn in the forest floor were 72.3 (2.9 s.e.) μg g^?1, 8.5 (0.7) μg g^?1, and 46.9 (2.0) μg g^?1, respectively. The regional average concentrations of Pb, Cu, and Zn in the mineral soil were 13.4 (0.8) μg g^?1, and 18.2 (1.2) μg g^?1, respectively. The regional average pH values of the forest floor and mineral soil were 3.99 (0.03), and 4.35 (0.03), respectively. The Green Mountains had the highest concentrations of Pb (105.7 μg g^?1), and Cu (22.7 μg g^?1), in the forest floor. They also had the highest concentrations of Cu (18.0 μg g^?1), in the mineral soil. Site aspect did not significantly influence any of the values. Concentrations of Pb were lower than concentrations reported earlier in this decade at similar sites while concentrations of Cu and Zn remained the same. We believe that these lower Pb concentrations reflect real changes in forest Pb levels that have occurred in recent years.     

Soil lead concentrations in residential Minnesota as measured by ICP-AES

A total of 2454 samples were collected to evaluate the degree, extent, and distribution of Pb contaminated soil in Minnesota. Samples were collected primarily at locations where susceptible populations were concentrated. Soil Pb concentrations in chilldren's play areas, urban gardens, and at open sites were generally below 100 μg g ^?1 when Pb painted structures were absent. Street side and yard soils typically had Pb concentrations between 10 to 300 μg g^?1, with samples collected near major highways or Pb painted structures exhibiting greater values. The most severely contaminated soils were found in localized areas around the foundations of private residences, where concentrations up to 20 136 μg g^?1 were detected. Exterior Pb based house paint is the major Pb source in these soils, and its presence greatly influences the distribution of contaminated soil in individual yards. Contamination attributable to autoemissions is less concentrated but more widespread than contamination from paint. A higher proportion of soils exceeding 1000 wg g^?1 Pb was found in large cities than elsewhere. However, a sufficient number were detected in small cities and rural areas to confirm that high soil Pb levels are not exclusively an urban phenomenon. By examining the degree, extent, and distribution of Pb contaminated soils in Minnesota, this study provides information useful in guiding response actions to reduce children's exposure to Pb by this pathway.     

Lead-organic matter interactions in a mollisol

Samples from the surface layer (0–15 cm) of a cultivated Typic Haplaquoll, collected in the fall of 1975 from field plots amended with variable amounts of Pb in the spring of 1969 and with ground corn cobs in 1973 and 1974 (22.4 tons ha^?1), were analyzed for organic N, total Pb, exchangeable- and soluble-Pb, specifically-adsorbed Pb, and organically-bound Pb. Highly-significant correlations were obtained between organic N and soil Pb concentrations, from which it was concluded that the applied Pb resulted in small increases in the organic matter content of the soil. The most probable mechanism was believed to be through the formation of biologically-resistant Pb-organic matter complexes. At low amounts of soil Pb (20–30 μg g^?1 range), approximately 30% of the soil Pb occurred in organic linkages but the proportion increased steadily up to 400 μg g^?1 and gradually leveled off thereafter. The conclusion was reached that progressive contamination of the test soil by exogenous Pb additions, such as from automobile exhaust near traffic highways, would have little effect on plant available forms until soil Pb concentrations reached about 100 μg g^?1, following which the concentration in the soil solution would be related to and controlled by the size of the organic pool.     

Soil Aggregate and Organic Carbon Stability under Different Land Uses in the North China Plain

Soil aggregates and organic matter are considered to be important indicators of soil quality. The objective of this study was to determine land-use effects on the distribution of soil organic carbon (SOC) associated with aggregate-size fractions. Bulk soil samples were collected from incremental soil depths (0–10, 10–20 20–40, 40–70, and 70–100 cm) under three land-use types: fruit tree orchards established in 1987, cropland, and forage field. Soil samples collected from these plots were analyzed for aggregate stability after wet sieving into four aggregate-size classes (>2000, 250–2000, 53–250, and <53 μm), and the concentration of SOC was determined in each size fraction. Cropland and forage field soils were significantly more alkaline than the fruit tree soil. Bulk densities were greater in cropland and forage field (1.40–1.52 g cm^?3) than in fruit tree orchards (1.33–1.37 g cm^?3). The total weight of soil aggregates varied in the order of forage field > cropland > fruit tree orchard. Aggregate stability was greater in cropland and forage field than under fruit tree orchards. Soil organic C decreased with increasing soil depth but was greater under fruit tree orchards than others and was mainly concentrated in the topsoil layer (0–20 cm). Sieved fraction (<53 μm) had a greater SOC concentration, regardless of soil depth or land use. Our data supported the hypothesis that perennial vegetation (fruit tree orchard) and the proportion of aggregates with diameter <53 μm are suitable indicators of SOC accumulation and may therefore have a greater potential for SOC sequestration than the cropland.     

Variability and relationships between Pb,Cu, and Zn concentrations in soil solutions and forest floor leachates at heavily polluted sites

Seasonal variability of Cu, Pb, and Zn concentrations in litter leachates and soil solutions was examined in an afforested zone surrounding a copper smelter in SW Poland. Litter leachates (with zero‐tension lysimeters) and soil solutions (with MacroRhizon suction‐cup samplers, installed at a depth of 25–30 cm) were collected monthly at three sites differing in contamination levels in the years 2009 and 2010 (total Cu: 2380, 439, and 200 mg kg^–1, respectively). Concentrations of Cu in the litter leachate were correlated with dissolved organic C (DOC), whereas Zn and Pb were mainly related to leachate pH. Metal concentrations in the soil solution were weakly influenced by their total content in soils and the monthly fluctuations reached 300, 600, and 700% for Cu, Pb, and Zn, respectively. Metal concentrations in soil solutions (Cu 110–460 μg L^–1; Zn 20–1190 μg L^–1; Pb 0.5–36 μg L^–1) were correlated with their contents in the litter leachates. Chemical speciation, using Visual Minteq 3.0, proved organically‐complexed forms even though the correlations between metal concentrations and soil solution pH and DOC were statistically insignificant. The flux of organically‐complexed metals from contaminated forest floors is believed to be a direct and crucial factor affecting the actual heavy metal concentrations and their forms in the soil solutions of the upper mineral soil horizons.     

An exploratory study of potential As and Pb contamination by atmospheric deposition in two urban vegetable gardens in Rome,Italy

Purpose

A preliminary study was carried out in Rome (Italy) to assess the potential role of atmospheric deposition in trace element contamination in urban vegetable gardens relative to human health risk from crop consumption.

Materials and methods

Two sites were selected on the basis of previously known contamination issues. Atmospheric deposition, parent material, soils properties affecting trace element mobility, and various anthropogenic inputs were considered. Soil samples were taken at depth from two points in each garden, within 5 cm of sampled crops. Inputs and crops were sampled and analysed for As and Pb content. A rain and dust gauge was set up in each garden for the duration of 93 days (late spring to late summer) for atmospheric deposition sampling.

Results and discussion

Atmospheric deposition influx was high at both sites (2.22 and 2.32 As and 2.67 and 3.42 Pb μg m^?3 day^?1). Soil pH was between 6.70 and 7.57 and texture varied from loamy sand to clay loam (3.4 to 31.9 % clay content). CEC ranged between 21.6 and 54.2 meq/100 g within rooting depth, rising almost commensurately with soil organic carbon (SOC) content (1.87–8.37 %). Somewhat high total soil Pb content (80.8–522.7 ppm) contrasted with negligible exchangeability and crop content (<0.01 ppm). Total soil As (17.0–32.0 ppm) corresponded with exchangeable and crop As for one site in one of the gardens. Leaves evinced high As accumulation levels (16.0–41.2 ppm) in all crops. High amounts of atmospheric Pb combined with negligible amounts of extractable Pb and Pb plant tissue content point to particulate inhalation and ingestion as a main health threat in the case of Pb. In contrast, food intake seems to be of greater concern relative to high As contamination. Greater soil As solubility may be explanatory, but the mostly low amounts of extractable As and the high atmospheric As suggest an airborne route being playing an important role.

Conclusions

Preliminary results suggest that research on trace element contamination in urban gardens should consider atmospheric deposition as a major contributing source.

     

Fluoride in bones of small rodents living in areas with different pollution levels

Bone fluoride concentration was measured in field voles (Microtus agrestis) trapped throughout a year at a moderately polluted site 1 km south of an Al reduction plant at Holyhead, Anglesey. Fluoride values ranged from 300 to 4800 μg g^?1, with a mean of 2074 μg g^?1 and increased with age as judged by dried eye-lens weight and body weight. At a heavily polluted site about 250 m from the pot-room of the reduction plant field voles had bone fluoride concentrations which ranged from 910 to 11000 μg g^?1 with a mean of 7148 μg g^?1. Wood mice (Apodemus sylvaticus) at this same location had a mean bone fluoride concentration of 8430 μg g^?1 and ranged from 1800 to 17 200 μg g^?1. The difference in mean bone fluoride concentration between these two species at this location was not significant (P > 0.1). A sample of field voles from presumed unpolluted sites in other parts of Britain had bone fluoride concentrations which ranged from 23 to 540 μg g^?1 with a mean of 168 jig g^?1. There was a high positive correlation (r > 0.97) between fluoride concentrations in different parts of field vole skeletons. There was no correlation between bone fluoride concentration in field voles and their femur diameters (r < 0.2).     

Effects of Distance and Depth on Total and Bioaccessible Lead Concentrations in Soils from Two Farmhouses in Beltsville,Maryland

Movement of soil lead (Pb) has been studied, but Pb bioaccessiblity as a function of distance and depth from houses with histories of lead paint use needs to be investigated. This study investigated the effect of distance and depth on total and bioaccessible Pb near two houses with histories of lead paint use. Soil samples were collected at four distances and four depths. Total and bioaccessible Pb were extracted using 1 N ammonia nitrate and 0.4 m glycine, respectively. Bioaccessible Pb ranged from 27 to 886 mg kg^?1 and from 187 to 4796 mg kg^?1 for houses 1 and 2, respectively. Total and bioaccessible Pb concentrations were greatest at the 0.5 m distance and 2.5 cm depth for both houses. Percentage of total Pb that was bioaccessible at lower horizons was greater than or equal to that of the surface soil. Soil Pb reduction with increasing distance and depth makes it amenable to soil remediation.     

Soil fertility breakdown in a subtropical South African vertisol site used as a home garden

Soil samples were taken at three depths (0–10, 10–20, 20–30 cm) from an old home garden site, subtropical South Africa (KwaZulu Natal Province), exhibiting symptoms of soil fertility breakdown, and from a new garden site, used formerly as extensive grassland. The aims of our study were to investigate (1) whether soil fertility breakdown is reflected by soil biological indices and (2) whether these indices provide information for improving the situation. The bulk density was significantly larger at the old garden site, with an average of 1.25 g cm^-3 in comparison to 1.04 g cm^-3 at the new garden site. Also the soil pH was significantly higher at the old garden site, with an average of 5.6 in comparison to 4.0 at the new garden site. Soil organic C and all soil microbial indices declined markedly with depth. If the concentrations were converted to the total amounts stored per hectare at 0- to 30-cm depth, soil organic C was only 10% greater (18.9 versus 17.2 t) at the new garden site, but microbial biomass C was 110% (1,680 vs 790 kg) and ergosterol even 220% greater (5.1 vs 1.6 kg). The microbial biomass C to soil organic C ratio ranged from 0.25% to 1.10%, declined markedly with depth and was almost twice as high at the new garden site. The metabolic quotient qCO₂ revealed strong depth-specific variations of between 18 and 38 mg CO₂-C day^-1 g^-1 microbial biomass C at the old garden site on a two to three times higher level than at the new garden site. Soil micro-organisms are much more strongly affected by compaction than by acidification at the present two sites. Whether land use practices led to the increase in bulk density at the old garden site or to the decrease in soil pH at the new garden site is still not fully understood. For these reasons, it is very difficult to recommend a feasible melioration plan.     

Forms of trace metals from inorganic sources in soils and amounts found in spring barley

Barley (Hordeum vulgare L.) was grown on a sandy soil given different doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite) in a pot experiment conducted in a greenhouse. The element compounds were added to the soil in amounts equivalent to the following levels of the metals: Cd 5, 10, 50 μq ^?1; Cu and Pb 50, 100, 500 μg g^?1; Zn 150, 300, 1500 μg g^?1. Sequential extraction was used for partition these metals into five operationally-defined fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The residue was the most abundant fraction in the untreated soil for all the metals studied (43 to 61% of the total contents). The concentration of exchangeable Cd (0.2 μg g^?1), Cu (0.01 μg g^?1), Pb (0.1 μg g^?1), and Zn (1.4 μg g^?1) were relatively low in the untreated soil but increased markedly in the treated soils for Cd (up to 31 μg g^?1) and Zn (up to 83 μg g^?1), whereas only small changes were observed for Cu and Pb. The pot experiment showed a significant increase in the Cd and Zn contents of barley grown on the treated soils, but only small changes in Cu and Pb concentrations.     

Heavy metals in street and house dust in Bahrain

A total of 106 street and household dusts have been sampled throughout Bahrain and analyzed for Pb, Zn, Cd, Ni and Cr using the atomic absorption spectrophotometric method. The sampling sites were divided into seven categories, including the control site. Results showed that dust samples contained significant levels of the metals studied compared with the control values. The mean values for Pb, Zn, Cd, Ni and Cr in street dust were 697.2, 151.8, 72.0, 125.6 and 144.4 μg g^?1 respectively, whereas for household dust they were 360.0, 64.4, 37.0, 110.2 and 144.7 μg g^?1. These values suggest that motor vehicles form a major source of these metals in dust samples. The values of heavy metals in dust samples in this study were compared with values found in other investigations in various countries. With respect to Ni, elevated concentration could be attributed to smoke from the burning of Kuwait oil fields. Also correlations between metal levels in dust samples for all the metals were investigated. Our results show that heavy metal levels in various sites in Bahrain are similar, which indicate that Bahrain can be considered as one big urban center with high population and traffic density.     

Different factors related to mercury concentration in sediments and zooplankton of 73 Canadian Lakes

Surficial sediments were sampled with a light-weight gravity corer at 175 sites in 73 Ontario and Québec lakes and Zooplankton was collected with a 225 μm mesh size net in 24 lakes. Hg concentrations in surficial sediments (0–2 cm) ranged from 3 to 267 ng g^?1 dry weight with a mean of 80 ng g^?1 dry weight for all sites. A regression model including organic content of sediments and the ratio of the catchment area/lake surface explained 60% of the variation in sediments Hg concentrations. Hg in Zooplankton ranged from about 25 to 377 ng g^?1 dw with a mean of 108 ng g^?1 dw and was weakly correlated with catchment area, primary productivity and TOC. Our data indicate that an important fraction of Hg originates from the catchments, but do not show a clear west-east regional gradient for Hg concentrations in surficial sediments or in zooplankton.     

ACCUMULATION OF SULPHUR IN AND ON SCOTS PINE NEEDLES IN THE SUBARCTIC

Total S concentrations of Scots pine (Pinus sylvestris L.) needles studied in the Finnish subarctic (66–70°N, 24–30°E) in 1990/1992 ranged from 573 to 1153 μg g^-1. Levels were found to be ≈ 900 μg g^-1 (i.e. 1.3–1.8 times the ‘normal’ level of 500–700 μg g^-1) in areas where the long-term ambient SO₂ concentration was ≈ 2–5 μg m^-3, particulate SO₄ ^2- ≈ μg m^-3 and total S deposition ≈ 0.5 g m^-2. A statistically significant increase in needle total S concentrations was found towards the east, i.e. towards the smelters of the Kola Peninsula in Russia, which emit SO₂. The increase in needle total S concentrations to over 900 μg g^-1 close to the Russian border is thought to result mainly from exposure to high short-term SO₂ concentrations. The results also suggest that wintertime S deposition may have an impact on the needle total S content. It is suggested that the UNECE long-term critical level of 15 μg SO₂ m^-3 for forestry in boreal and high mountain climates in Europe is too high for the pine forests in the extreme north, where the proportion of dry-deposited S may be 60–80%.     

Dynamics of microbial biomass in Cambisols under a three year succession fallow in North Eastern Saxony

The response of microbial biomass carbon (C_mic), nitrogen (N_mic), basal respiration, and the metabolic quotient to 3 years of a natural succession fallow were studied in a field experiment on sandy soil in Northeast Saxony/Germany from 1996 to 1998. Soil samples were taken from Eutric Cambisol and Mollic Cambisol every six weeks during the vegetation period at soil depths of 0—10 and 10—30 cm. The C_mic content in the topsoils increased with time of succession in both soil types. This trend was more distinct in the Mollic Cambisol (70.7 μg g^—1 in June 1996 to 270.9 μg g^—1 in October 1998 at 0—10 cm) than in the Eutric Cambisol (69.7 μg g^—1 in June 1996 to 175.0 μg g^—1 in October 1998 at 0—10 cm). By contrast, the N_mic content slightly decreased in the Eutric Cambisol from 18.9 μg g^—1 to 17.7 μg g^—1 during the same time period. In the Mollic Cambisol, the N_mic increased from 18.8 μg g^—1 in spring 1996 to 35.5 μg g^—1 in fall 1998, however to a lower extent than the C_mic. Subsequently, the (C:N)_mic ratio increased from 4.3 to 5.8 at soil depth of 0—10 cm and from 3.5 to 6.5 at 10—30 cm during the 3‐year‐study at the Eutric Cambisol. In the Mollic Cambisol, the enhancement of (C:N)_mic ratio was more pronounced (i.e. from 4.3 to 6.7 at 0—10 cm and from 3.5 to 7.2 at 10—30 cm). Most likely this results from a shift in microbial populations towards a dominance of soil fungi. The already low basal respiration of, on average, 0.26 mg CO₂ g^—1 (24h)^—1 (0—10 cm) in June 1996 decreased with time of succession fallow to 0.15 and 0.22 mg CO₂ g^—1 (24h)^—1 in October 1998 in the Eutric and the Mollic Cambisol, respectively. Thus, the metabolic quotient as an indicator for the efficiency of organic matter turnover in soil was very low in both soils. During the summer months, the metabolic quotients reached minimum levels of ≤ 0.1 μg CO₂ C (g C_mic)^—1 h^—1, probably because of low soil moisture contents. Correlation analyses revealed close relationships between N_mic and total N, N_mic and water content, and N_mic and pH values. These relationships became even more pronounced with the time period of natural succession. For the samples from fall 1998, highly significant correlations were determined between N_mic and total N (coefficients were r_s = 0.91^***), N_mic and water content (r_s = 0.91^***), and N_mic and pH value (r_s = 0.76^***). The values for all biological parameters studied were larger in the Mollic than in the Eutric Cambisol. This indicates higher turnover rates of different C and N fractions in the Mollic Cambisol. In general, set aside of formerly agricultural managed sandy soils resulted in greater C_mic : N_mic ratios and thus, in a change in the microbiological community structure as well as in reduced C and N turnover rates (i.e. low metabolic quotient) under the climatic conditions of the East German lowlands.     

Soil microbial activity in opencast coal mine restorations

Abstract. A number of restored areas, a soil store and undisturbed areas on opencast coal mine sites, all of similar soil type, were sampled. The microbiological activity (dehydrogenase assay), nitrogen mineralization and nitrifying potentials and physico-chemical characteristics of the soils were determined. Dehydrogenase activities ranged from 140 to 580 μg TPF g^-1 24 h^-1 in undisturbed control soils, whereas the disturbed soils had activities of 10 to 220 μg g^-1 24 h^-1, with the smallest activities being recorded in the stored and most recently reinstated soil, indicating that disturbance has depressed microbial activity. Nitrogen mineralization potential was significantly affected by disturbance, with a value of 18 to 26 μg inorganic N g^-1 21 d^-1 in the soil store and 38 μg^-1 21 d^-1 in a soil reinstated for six months, although the values were less than this in soils reinstated for up to six years. Nitrifying potential was not significantly less in the stored soils, being within the range of 60 to 135 μg nitrate N formed g^-1 soil 21 d^-1, which was similar to that found in the undisturbed control soil. The water-holding capacity was less in the stored soil than the undisturbed controls, and was significantly less in soil reinstated for 1.5 to 2.5 years, being only 65% of the undisturbed value (0.66 g water g^-1 soil). Ammonium content of the soil store was one hundred fold larger in the soil store than in the controls (0.6 to 1.7 μg ammonium N g^-1). The carbon contents in the control soils ranged from 4.5 to 7.2%, whereas the stored and reinstated soils had generally less amounts ranging from 1.6 to 5.8%. There was a significant and positive correlation between water-holding capacity and nitrifying potential. The implications for long-term restoration are discussed.     

Conservation of mineral nitrogen in restored soils at opencast coal mine sites: I. Results from field studies of nitrogen transformations following restoration

One of the characteristics of soils located within the cores of stockpile storage mounds at opencast mine sites is their accumulation of ammonium-nitrogen. Two areas of restored land were constructed from soil stockpiled for 3 years; one consisted of mound-surface (‘aerobic zone’) soil, and the other of deeply buried (‘anaerobic zone’) soil. In that constructed from mound-surface soil, concentrations of both ammonium- and nitrate-nitrogen remained fairly stable throughout the first 6 months of restoration at about 12–20 μg g^?1, but in the site constructed from deeply buried soil, concentrations of ammonium-N decreased from an initial high of 160 to 14 μg N g^?1 soil after 14 weeks, and increased again to 42 μg N g^?1 soil by week 29. In contrast, concentrations of nitrate-nitrogen at the latter site increased from an initial 9 μg to a maximum recorded level of 77 μg N g^?1 soil by week 14, before subsiding to 9 μg N g^?1 soil by week 29. Nitrate was considered to have been lost from the restored soils by a combination of leaching and denitrification, as no vegetation was established at these sites. After a short-term stimulation following restoration, soil microbial biomass levels remained fairly constant, though soils (up to 3 years after restoration) were characterized by a very small ratio of biomass C: organic C.