共查询到20条相似文献,搜索用时 46 毫秒
1.
Soil salinity and sodicity are environmental problems in the shrimp farming areas of the Cai Nuoc district, Ca Mau province,
Vietnam. In 2000, farmers in the district switched en masse from rice cropping to shrimp culture. Due to recent failure in
shrimp farming, many farmers wish to revert to a rotational system with rice in the wet season and shrimps in the dry season.
So far, all their attempts to grow rice have failed. To assess soil salinity and sodicity, 25 boreholes in shrimp ponds were
analysed in four consecutive seasons from 2002 to 2004. The results showed that soil salinity was quite serious (mean ECe 29.25 dS m−1), particularly in the dry season (mean ECe 33.44 dS m−1). In the wet season, significant amounts of salts still remained in the soil (mean ECe 24.65 dS m−1) and the highest soil salinity levels were found near the sea. Soil sodicity is also a problem in the district (exchangeable
sodium percentage range 9.63–72.07%). Sodicity is mainly a phenomenon of topsoils and of soils near the sea. Both soil salinity
and sodicity are regulated by seasonal rainfall patterns. They could together result in disastrous soil degradation in the
Cai Nuoc district. 相似文献
2.
Sudip Jyoti Sahu Bibhash Nath Sharmi Roy Biswapati Mandal Debashis Chatterjee 《Environmental Earth Sciences》2012,65(3):813-821
Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long-term detrimental
effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable
and fruits, are used for human consumption. Therefore, an understanding of the leaching behavior of As in surface soils is
of high importance, because such behavior may increase the bioavailability of As in the soil horizon. In this study, we have
investigated the role of phosphate ions in leaching and bioavailability of As in the soil horizon, where drinking groundwater
contains elevated levels of As (≥50 μg/L). Soil and groundwater samples were characterized in the laboratory and measured
for physical and chemical constituents. The soils are generally neutral to slightly alkaline in character (pH range 7.5–8.1)
with low to moderate levels of free Fe2O3, Al2O3, CaCO3, organic carbon, and clay content. The measured electrical conductivity (mean 599 μS/cm) of the soils demonstrates their
non-saline nature. The Eh values (range −37 to −151 mV) of the groundwater indicate anoxic condition with low to moderate
levels of bicarbonate (range 100–630 mg/L) and phosphate (range 0.002–4.0 mg/L). The arsenic content (range 50–690 μg/L; mean
321 μg/L) in groundwater has exceeded both WHO recommended guideline values (10 μg/L) and the National safe drinking water
limit (50 μg/L). Regression analyses demonstrate that the bioavailability of As in the soil horizon is mainly controlled by
the composition of free Fe2O3 and CaCO3 content of the soils. However, application of P could increase bioavailability of As in the soil horizon and become available
to plants for uptake. 相似文献
3.
CO<Subscript>2</Subscript> absorption by alkaline soils and its implication to the global carbon cycle 总被引:2,自引:0,他引:2
Motivated by the rapid increase in atmospheric CO2 due to human activities since the Industrial Revolution, and the climate changes it produced, the world’s concerned scientific
community has made a huge effort to investigate the global carbon cycle. However, the results reveal that the global CO2 budget cannot be balanced, unless a “missing sink” is invoked. Although numerous studies claimed to find the “missing sink”,
none of those claims has been widely accepted. This current study showed that alkaline soil on land are absorbing CO2 at a rate of 0.3–3.0 μmol m−2 s−1 with an inorganic, non-biological process. The intensity of this CO2 absorption is determined by the salinity, alkalinity, temperature and water content of the saline/alkaline soils, which are
widely distributed on land. Further studies revealed that high salinity or alkalinity positively affected the CO2 absorbing intensity, while high temperature and water content had a negative effect on the CO2 absorbing intensity of these soils. This inorganic, non-biological process of CO2 absorption by alkaline soils might have significant implications to the global carbon budget accounting. 相似文献
4.
R. E. Masto L. C. Ram P. R. Shandilya S. Sinha J. George V. A. Selvi 《Environmental Earth Sciences》2011,64(4):1107-1115
Coal handling, crushing, washing, and other processes of coal beneficiation liberate coal particulate matter, which would
ultimately contaminate the nearby soils. In this study, an attempt was made to determine the status of soil bio-indicators
in the surroundings of a coal beneficiation plant, (in relation to a control site). The coal beneficiation plant is located
at Sudamudih, and the control site is 5 km away from the contaminated site, which is located in the colony of Central Institute
of Mining and Fuel Research Institute, Digwadih, Dhanbad. In order to estimate the impact of coal deposition on soil biochemical
characteristics and to identify the most sensitive indicator, soil samples were taken from the contaminated and the control
sites, and analyzed for soil organic carbon (SOC), soil N, soil basal respiration (BSR), substrate-induced respiration (SIR),
and soil enzymes like dehydrogenase (DHA), catalase (CAT), phenol oxidase (PHE), and peroxidase (PER). Coal deposition on
soils improved the SOC from 10.65 to 50.17 g kg−1, CAT from 418.1 to 804.11 μg H2O2 g−1 h−1, BSR from 8.5 to 36.15 mg CO2–C kg−1 day−1, and SIR from 24.3 to 117.14 mg CO2–C kg−1 day−1. Soils receiving coal particles exhibited significant decrease in DHA (36.6 to 4.22 μg TPF g−1 h−1), PHE (0.031 to 0.017 μM g−1 h−1), PER (0.153 to 0.006 μM g−1 h−1), and soil N (55.82 to 26.18 kg ha−1). Coal depositions significantly (P < 0.01) decreased the DHA to 8.8 times, PHE to 1.8 times, and PER to 25.5 times, but increased the SOC to 4.71 times, CAT
to 1.9 times, SIR to 4.82 times, and BSR to 4.22 times. Based on principal component analysis and sensitivity test, soil peroxidase
(an enzyme that plays a vital role in the degradation of the aromatic organic compounds) is found to be the most important
indicator that could be considered as biomarkers for coal-contaminated soils. 相似文献
5.
The aim of this interdisciplinary study is to examine a component of the hydrological cycle in Galapagos by characterizing
soil properties. Nine soil profiles were sampled on two islands. Their physical and hydrodynamic properties were analyzed,
along with their mineralogical composition. Two groups of soils were identified, with major differences between them. The
first group consists of soils located in the highlands (>350 m a.s.l.), characterized by low hydraulic conductivity (<10−5 m s−1) and low porosity (<25%). These soils are thick (several meters) and homogeneous without coarse components. Their clay fraction
is considerable and dominated by gibbsite. The second group includes soils located in the low parts of the islands (<300 m
a.s.l.). These soils are characterized by high hydraulic conductivity (>10−3 m s−1) and high porosity (>35%). The structure of these soils is heterogeneous and includes coarse materials. The physical properties
of the soils are in good agreement with the variations of the rainfall according to the elevation, which appears as the main
factor controlling the soil development. The clayey alteration products constrain soils physical and hydrodynamic properties
by reducing the porosity and consequently the permeability and also by increasing water retention. 相似文献
6.
In Lake Cuicocha watershed, a young caldera lake, soils consist of volcanic deposits with a high SiO2 and Al2O3 content; these andisols are in an early stage of development; and in drainage water from the watershed, aluminium concentrations
reach 15.0 μmol L−1. Total aluminium concentrations in Lake Cuicocha water raises up to 7.2 μmol L−1, with nearly 70% occurring as filterable Al at neutral to weak alkaline conditions. Al polymerization to gelatinous aggregates
of a few hundred micrometres in diameter as well as the occurrence of Al microcrystals like gibbsite as an ageing product
of gelatinous Al polymers was noted in the lake water. The gelatinous Al leads to the formation of larger aggregates resulting
in flocs of bacteria, algae, microorganisms and detritus. 相似文献
7.
Man-Il Kim Nam-Won Kim Il-Moon Chung Gyo-Cheol Jeong 《Environmental Earth Sciences》2010,60(6):1153-1164
A dielectric measurement device called a frequency domain reflectometry (FDR) has been designed and constructed for the dielectric
measurement of unsaturated soil consisting of a volumetric soil water content of about 0.1, 0.2, and 0.3 m3/m3 with different soil porosity around 0.40–0.45, respectively. The dielectric constant is measured in the frequency range 1 GHz.
Soil calibration tests and tracer injection tests on standard sand and river sand are carried out in the laboratory. FDR measurement
probes at different soil depths allow volumetric soil water content and dielectric constant measurements. The tracer concentration
in the pore water is monitored by determining the dielectric constant, from the soil impedance. From the relationship between
volumetric soil water content and dielectric constant, the specific calibration equations for the unsaturated soils were derived,
and one can easily estimate the volumetric soil water content from the response of the measured dielectric constant for the
soils. In the study of dielectric mixture models using α-value of 0.5 which is dielectric geometric factor, the effective porosity for the soils was computed to a range of 87–92%
compared with the soil porosity. 相似文献
8.
In this study, we examined the movement of potassium (K) in columns of contaminated calcareous soils by sheep manure and ethylene
diamine tetraacetic acid (EDTA). Glass tubes, 4.9 cm in diameter and 40 cm in length, were packed with contaminated soils.
The resulting 20-cm long column of soil had a bulk density of 1.3–1.4 g cm−3. Columns were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl2, and sheep manure extract solutions. The amounts of K leached varied considerably between different soils (sandy loam and
loamy sand) and leaching solutions. The amount leached with EDTA solution, varied from 7.2 to 66.7% of the extractable K when
20 pore volumes had passed through the column. The breakthrough curves of K in the EDTA and CaCl2 were approximately similar, indicating they have similar ability to displace K from these contaminated calcareous soils.
Thus, among leaching solutions application of EDTA and CaCl2 on contaminated soils might enhance the mobility of K and large amounts of K will be leached. 相似文献
9.
Zongqiang Chang Qi Feng Jianhua Si Yonghong Su Haiyang Xi Jianlin Li 《Environmental Geology》2009,58(3):483-490
Field experiments on the CO2 flux of alpine meadow soil in the Qilian Mountain were conducted along the elevation gradient during the growing season of
2004 and 2005. The soil CO2 flux was measured using the Li-6400-09 soil respiration chamber attached to the Li-6400 portable photosynthesis system. The
effects of water and heat and roots on the soil CO2 flux were statistically analyzed. The results show that soil CO2 flux along the elevation gradient gradually decreases. The soil CO2 flux was low at night, with lowest value occurring between 0200 and 0600 hours, started to rise rapidly during 0700–0830
hours, and then descend during 1600–1830 hours. The peak CO2 efflux appears during 1100–1600 hours. The diurnal average of soil CO2 efflux was between 0.56 ± 0.32 and 2.53 ± 0.76 μmol m−2 s−1. Seasonally, soil CO2 fluxes are relatively high in summer and autumn and low in spring and winter. The soil CO2 efflux, from the highest to the lowest in the ranking order, occurred in July and August (4.736 μmol m−2 s−1), June and September, and May and October, respectively. The soil CO2 efflux during the growing season is positively correlated with soil temperature, root biomass and soil water content. 相似文献
10.
Soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation
and infiltration processes but little is known about them on karst hillslopes. The objectives of this paper were to investigate
the change in soil stable infiltration rate (q
s) and near-saturated hydraulic conductivity (K
ns) in different slope positions and to understand their relationship with rock fragment content and soil texture within the
topsoil in subtropical karst regions of southwest China. Tension infiltrometers (20 cm in diameter) were used to measure q
s and K
ns at pressure head of −20 mm on hillslopes 1 (a disintegrated landslide failure) and 2 (an avalanche slope). The change of
q
s and K
ns was great and they mostly had a moderate variability with coefficient of variations (CV) between 0.1 and 1.0 in the different
slope positions. On average, q
s ranged from 0.43 to 4.25 mm/min and K
ns varied from 0.75 to 11.00 mm/min. These rates exceed those of most natural rainfall events, confirming that overland flow
is rare on karst hillslopes. From bottom to top, q
s and K
ns had a decrease–increase–decrease trend due to the presence of large rock outcrops (>2 m in height) on hillslope 1 but had
an increasing trend on hillslope 2 with less complex landform. They tended to increase with increase in total rock fragment
content (5–250 mm) within the topsoil as well as slope gradient on both hillslopes. Pearson correlation analysis suggested
that higher coarse pebble (20–75 mm), cobble (75–250 mm), and sand (2–0.05 mm) contents as well as total rock fragment content
could significantly facilitate water infiltration into soils, but higher clay (<0.002 mm) content could restrict water movement.
This result indicated that rock fragment, sand, and clay contents may remarkably affect water flow in the topsoil layers,
and should be considered in hydrological modeling on karst hillslopes in subtropical regions. 相似文献
11.
Questions concerning the influence of soil type and crop cover on the fate and transport of nitrate (NO3−) were examined. During a growing season, soils derived from glacial material underlying either corn or soybeans were sampled
for levels of NO3− within the pore water. Measured levels of NO3− ranged from below detection limit to 14.9 g NO3− per kilogram of soil (g/kg). In fields with the same crop cover, the silty-clayey soil exhibited a greater decrease in NO3− levels with depth than the sandier soil. Crop uptake of NO3− occurs within the root zone; however, the type of crop cover did not have a direct impact on the fate or transport during
the growing season. The soils underlying soybeans had an increase in NO3− levels following harvest, suggesting that the decomposition of the soybean roots contributed to the net gain of NO3− in the shallow soil. For all of the soil types, conditions below 100 cm are conducive for microbial denitrification, with
both a high water saturation level (>60%) and moderate organic carbon content (1–2%). At depths below 100 cm, temporal differences
in NO3− levels of over a magnitude, up to a 95% reduction, were recorded in the soil units as the growing season progressed. Physical
properties that control the transport of NO3− or denitrification have a larger influence on NO3− levels than crop type.
相似文献
Eric W. PetersonEmail: |
12.
Selenomethionine (SeM) is an organic toxicant that is present in seleniferous environments. No kinetic data is yet available
regarding SeM reactions in coal mine environments, where selenium (Se) toxicity is a potential concern. A kinetic study was
conducted on two reclaimed coal mine soils (Typic Torriorthents) from Wyoming having sandy and clayey textures. Four levels
of SeM treatments (0, 50, 100 μM, and plant amendment from the mine vegetation) were reacted with the soils for 4, 7, 14,
28, 42, 56, and 84 days to characterize the kinetic behavior of overall SeM disappearance from soil solutions. Detection of
SeM in soil solutions at the control level (0 μM SeM) indicated occurrence of indigenous SeM in the soils. In the plant-amended
soil solutions, much greater concentrations of SeM were observed as compared with the soil-only systems. This indicated the
plant material was a more potential source of SeM than the mine soils. A time-dependent loss in solution SeM concentrations
was observed for both soils under 0, 50, 100 μM SeM treatments. For the soil-plant mixtures, the solution SeM concentration
increased initially, reached a maximum after 14 days, and then decreased thereafter. In the plant-amended soil solutions,
SeM concentrations at all time intervals were higher for the sandy as compared to the clayey soil. At 50 and 100 μM SeM treatments,
the solution pH was linearly related to the percentages of SeM disappeared from the solutions; greater percentage of SeM was
removed from solutions at comparatively lower pH levels, which was ≥90% at pH 7.7 for both soils. Solution SeM concentrations
decreased exponentially with time following first-order kinetic reactions. Under all applications (except for the control),
C
0 (SeM concentration at t=0) values for the sandy soil were greater than those determined for the clayey soil, indicating higher solution SeM availability
for the former and more SeM retention by the latter at t=0. Comparison of C
0 in controls (0 μM SeM addition) suggested greater indigenous SeM in the clayey soil. For both soils, C
0 values under different treatments followed the order, (soil+100 μM)>(soil+50 μM)>(soil+0 μM). The specific reaction rate
constants (K
r) of SeM for both soils were similar (0.031 and 0.029 day–1 for sandy and clayey soils, respectively); low K
r values indicated that SeM loss from our reclaimed coal mine soil solutions would follow rather slow kinetics. The half-life
(t
0.5) of SeM varied from 15 to 55 days depending on treatment level. The knowledge obtained from this study should contribute
in developing time-based Se reclamation strategies in coal mine environments.
Received: 18 September 1995 · Accepted: 28 December 1995 相似文献
13.
Sivajini Gilchrist Alexander E. Gates Matthew Gorring Evert Jan Elzinga 《Environmental Earth Sciences》2011,63(5):1029-1041
Organic material in metal contaminated soils around an abandoned magnetite mine–smelter complex in the critical Highlands
watershed protects the groundwater and surface water from contamination. Metals in these waters were consistently below local
and national water standards. Two groups of soil types cover the area: (1) Group A disturbed metal-rich soils, and (2) Group
B undisturbed organic soils. Chromium and nickel were more elevated than other metals with Cr more widespread than Ni. In
Group A, Cr correlated strongly with sesquioxides in the lower horizons (Fe2O3: r = 0.74, p < 0.025; Al2O3: r = 0.92, p < 0.005). In Group B, Cr correlated strongly (r = 0.96, p < 0.005) with soil organic matter (SOM) in the O-horizons. Ni–Cr (Group A: 52 and 70% in O- and lower horizons, respectively;
Group B: ~100% in both horizons) and V–Cr correlations (78% only in Group A lower horizons) suggest similar retention mechanisms
for these elements. Average soil
\textpH\textCaCl2 {\text{pH}}_{{{\text{CaCl}}_{2} }} for both groups ranged between 3.65 and 5.91, suggesting that soil acidity is determined by organic acids and solubility
of Al3+ releasing H+ ions. SOM and sesquioxides contribute significantly to creating naturally occurring filtration systems, removing metals,
and protecting water quality. High Ca, Fe, and Ti in Group A soils suggest slag and ash were mixed into the soils. Some low-Cr
sources include magnetite, slag, and ash (100, 100 and 200 mg/kg, respectively). Constant ZrO
2
:TiO
2
ratios in the lower soils indicate soil formation from breakdown of underlying tailing rocks, contributing Cr to these layers. 相似文献
14.
Evaluation of phosphorus leaching from contaminated calcareous soils due to the application of sheep manure and ethylenediamine tetraacetic acid 总被引:1,自引:0,他引:1
Organic amendment application to heavy metal contaminated soils may contribute to leaching of phosphorus (P). The objectives
of this study were to determine the influence of sheep manure and ethylenediamine tetraacetic acid (EDTA) on the P leaching
from a wide range of calcareous contaminated soils. Glass tubes, 4.9 cm diameter, and 40 cm long, were packed with contaminated
soil. The resulting 20 cm long column of soils had bulk density of 1.3–1.4 g cm−3. The columns were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl2 or sheep manure extract (SME) solutions. The breakthrough curves for P were different and the amounts of P leached varied
considerably between different soils and leaching solutions. The amounts leached with SME were less than the amount added
through the SME, indicating that some P was retained by the soil, mainly due to preliminary sorption of organic ligands on
to the soil with the creation of new sorbing surfaces. The amount leached with EDTA solution varied from 9.9 to 46.3% of the
extractable P when 15 pore volumes had passed through the column. Low amounts of P were leached by 0.01 M CaCl2, which is likely to be due to the high concentration of soluble Ca used in the solution. Thus, among leaching solutions the
application of EDTA and SME on contaminated calcareous soils might enhance the mobility of P and large amounts of P will be
leached, leading to contamination of ground and surface waters. 相似文献
15.
Orhan Dengiz H. Huseyin Ozaytekin Gokhan Cayci Abdullah Baran 《Environmental Geology》2009,56(6):1057-1063
The objective of this research was to investigate the morphology, genesis and classification of organic soils formed on depression
and flat land around Lake Yenicaga, west-central Turkey. Formation of the area has been influenced by tectonic and karst
processes. This peatland is important in this area due to its extensive use as a horticultural plant growth medium resulting
from positive physical and chemical properties. Organic soils in the study area were formed in nutrient-rich conditions and
it is classified as typical basin peat. Four representative pedons were excavated in the study area based on extensive observations
performed with random grid method using an auger. Samples were taken from horizons in each profile for laboratory analyses.
Organic matter contents ranged from 12.5 to 91.5% across all four pedons. Fiber contents were between 4.3 and 91.5%, and N ranged from 0.56 to 2.19%. Cation exchange capacity ranged from 37 to 222 cmol kg−1, bulk density from 0.09 to 0.78 g cm−3, lime from 0.15 to 2.62%. The pH and ECe values ranged from 5.38 to 7.92 and 0.50 to 3.80 dS m−1, respectively. Sand, silt and clay contents of the organic soils ranged between 0.75–3.92, 40.70–74.77 and 24.15–57.30%,
respectively. Differences in organic soils were found to depend on the environment, botanical origins, decomposition degrees,
and groundwater composition. The organic soils of the research area were classified in the typic, hemic and hydric subgroups
of Medifibrists (Soil Taxonomy 1999). 相似文献
16.
Displacement studies on leaching of potassium (K+) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and
25 cm long). Pulses of K+ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl2) at a rate of 18 mm h−1. The movement of K+ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM
CaCl2. The Ca2+ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K+ was displaced with the distilled water, K+ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow
and lack of K+ sorption. The application of gypsum and CaCl2 in the reclamation of sodic soils would be expected to leach K+ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca2+ concentration can also lead to leaching of K+ from soil. Average effluent concentration of K+ during leaching period was 30.2 and 28.6 mg l−1 for the gypsum and CaCl2 treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation
(12 mg K+ l−1). 相似文献
17.
Cui Hua Huang Xian Xue Tao Wang Roberto De Mascellis Giacomo Mele Quan Gang You Fei Peng Anna Tedeschi 《Environmental Earth Sciences》2011,63(4):701-708
Due to the lack of freshwater, highly saline groundwater was the main irrigation source in the last few decades in the Minqin
Basin, which is in northwest China. The study evaluates the effects of salt accumulation on the soil physical–chemicals properties.
Undisturbed and disturbed soil samples were taken from the experiment site, which was irrigated with saline water at a concentration
of 0.8, 2 and 5 g L−1 (coded later as C08, C2 and C5). Undisturbed soil samples, at depths of 0–45 and 45–60 cm were taken to determine the water retention curve (WRC). Moreover,
in the same place, another set of undisturbed soil samples were taken to determine the porosity and pore-size distribution
(PoSD). From the WRC, the water-holding capacity of the soil was estimated. Disturbed soil samples at depths of 0–20, 0–45,
45–60 and 80–100 cm were taken to determine the index of aggregates stability in water (IC). The electrical conductivity of
the saturated paste (ECe) was determined at depths of 0–30, 30–60 and 60–90 cm, during the irrigation season on C08, C2 and C5 treatments. The results show that the total porosity and the index of aggregates stability in water decrease with the increasing
salinity of irrigation water, and the ECe increases with the increasing salinity of irrigation water especially in the surface soil. The water-holding capacity (WHC)
of soil also increases with the increasing salinity of irrigation water. 相似文献
18.
The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of
nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km2), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion,
hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values
of δ15N [N2] ranged from −1 to 0.28‰ in the epilimnion, −1.5 to 1.25‰ in the hypolimnion, −1.8 to 12.2‰ in the benthic boundary layer
and −0.7 to 3.5‰ in sediment pore waters. Values of δ15N [N2] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification.
Increases in 15N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen
concentrations <6.3 μM) and may be related to abundant ammonium substrate (up to 275 μM) to support denitrification. Nitrate
concentrations increased up to 36 μM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor
besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides
and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium
in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ15N [N2] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of
Lake Ngapouri. The changes in δ15N [N2] values indicate the potential use of isotope ratios to identify and quantify potential chemo-nitrification/denitrification
in the water column and sediment pore waters of lakes. 相似文献
19.
Large tank experiment on nitrate fate and transport: the role of permeability distribution 总被引:2,自引:1,他引:1
M. Mastrocicco N. Colombani S. Palpacelli G. Castaldelli 《Environmental Earth Sciences》2011,63(5):903-914
A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted
within a large tank (4 × 8 × 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m3), used to fill the tank, were excavated from an unconfined alluvial aquifer near Ferrara (Northern Italy); the field site
was connected to a pit lake located in a former agricultural field. To evaluate spatial heterogeneity, the tank’s filling
material was characterized via slug tests and grain-size distribution analysis. The investigated sediments were characterized
by a large spectrum of textures and a heterogeneous hydraulic conductivity (k) field. Initial tank pore water composition exhibited high concentration of nitrate (NO3
−) sulfate (SO4
2−) calcium (Ca2+), and magnesium (Mg2+), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO3
− and SO4
2− was heterogeneous and not related to the finer grain-size content (<63 μm). The tank’s material was flushed with purified
tap water for 800 days in steady-state conditions; out flowing water was regularly sampled to monitor the migration rate of
fertilizer by-products. Complete removal of NO3
− and SO4
2− took 500 and 600 days, respectively. Results emphasized organic substrate availability and spatial heterogeneities as the
most important constraints to denitrification and nitrogen removal, which increase the time required to achieve remediation
targets. Finally, the obtained clean-up time was compared with a previous column experiment filled with the same sediments. 相似文献
20.
Claire M. C. Rambeau Denis Baize Nicolas Saby Virginie Matera Thierry Adatte Karl B. Föllmi 《Environmental Earth Sciences》2010,61(8):1573-1585
Cadmium (Cd) is a highly toxic element and its presence in the environment needs to be closely monitored. Recent systematic
surveys in French soils have revealed the existence of areas in eastern and central France, which show systematically high
cadmium concentrations. It has been suggested that at least part of these anomalous levels are of natural origin. For the
Lower Burgundy area in particular, a direct heritage from the Jurassic limestone bedrock is highly suspected. This potential
relationship has been studied in several localities around Avallon and this study reports new evidence for a direct link between
anomalously elevated cadmium contents of Bajocian and Oxfordian limestone and high cadmium concentrations in deriving soils.
Soils in this area show cadmium concentrations generally above the average national population values, with contents frequently
higher than the ‘upper whisker’ value of 0.8 μg g−1 determined by statistical evaluation. In parallel, limestone rocks studied in the same area exhibit cadmium concentrations
frequently exceeding the mean value of 0.030–0.065 μg g−1 previously given for similar rocks by one order of magnitude, with a maximum of 2.6 μg g−1. Mean ratios between the cadmium concentrations of limestone bedrock and deriving soils (Cdsoil/Cdrock), calculated for different areas, range from 4.6 to 5.7. Calculations based on the analyses of both soils from a restricted
area and fragments of bedrock sampled in the immediate vicinity of high-concentration soils are around 5.5–5.7. Cdsoil/Cdrock is useful in determining the potential of soils in Lower Burgundy to reflect and exacerbate the high concentrations of cadmium
present in parent bedrocks. 相似文献