Enrichment of potentially toxic elements in the fine fraction of soils from Iraq and Kuwait

Journal of Soils and Sediments - The fine fraction of soils in arid and semi-arid regions can be readily suspended into the atmosphere by winds and transported long distances, carrying potentially...     

Distribution of some elements in soils of the Barada River bank in Syria

Abstract

The distribution of zinc (Zn), copper (Cu), lead (Pb), and arsenic (As) in a soil of the Barada River bank in eastern Damascus, Syria, was studied. The results showed a normal distribution of these elements with some anomalies. The mineralogical and physical studies did not reveal any changes, indicating that elemental anomalies were man made.     

Elements in water,suspended particulate matter and sediments of the Sava River

Purpose

River ecosystems are under pressure from several different stressors. Among these, inorganic pollutants contribute to multiple stressor situations and the overall degradation of the ecological status of the aquatic environments. The main sources of pollution include different industrial activities, untreated effluents from municipal waste waters and intensive agriculture. In the present study, water, suspended particulate matter (SPM) and sediments of the Sava River were studied in order to assess the pollution status of this river system.

Materials and methods

Sampling was performed during the first sampling campaign of the EU 7th FW funded GLOBAQUA project in September 2014, at 18 selected sampling sites along the Sava River. In 2014, floods predominated from spring to fall. Water samples were collected to determine the total element concentrations, the dissolved (0.45 μm) fraction and element concentrations in SPM. In order to assure comparative results with other river basins, the fraction below 63 μm was analysed in sediments. The extent of pollution was estimated by determination of the total element concentrations and by the identification of the most hazardous highly mobile element fractions (extraction 0.11 mol L^?1 acetic acid) and anthropogenic inputs of elements to sediments (normalization to aluminium (Al) concentration). Concentrations of selected elements were determined by inductively coupled plasma mass spectrometry (ICP-MS).

Results and discussion

Since during sampling campaign the water level was extremely high, water samples contained high amounts of SPM (in general between 80 and 100 mg L^?1). The data of chemical analysis revealed that concentrations of elements in water, SPM and sediments in general increase along the Sava River from its origin to the confluence with the Danube River. Elevated concentrations of chromium (Cr) and nickel (Ni) in SPM and sediments were observed at industrially exposed sites. Concentrations of Cr and Ni in sediments were up to 320 and 250 mg kg^?1, respectively. Nevertheless, these elements were present in sparingly soluble forms and hence did not represent an environmental threat. Phosphorus (P) was found in elevated concentrations (up to 1500 mg kg^?1) at regions with intensive agricultural activities and cities with dense population.

Conclusions

With respect to element concentrations, the pollution of the Sava River is similar to other moderately polluted European rivers. The data from the present study are beneficial for the water management authorities and can contribute to sustainable utilization, management and protection of the Sava River water resources.

     

Distinguishing between natural and anthropogenic sources for potentially toxic elements in urban soils of Talcahuano,Chile

Purpose

The objectives of this study were (1) to determine the concentrations and background concentrations of Ba, Co, Cr, Mn, and Ni in the urban soils of Talcahuano (Chile); (2) assess the level of contamination in the urban soils based on different pollution indexes; and (3) to identify natural or anthropogenic sources in order to obtain a spatial distribution of the pollutants.

Material and methods

A total of 420 samples were collected from the study area as follows: 140 topsoil samples (TS) (0–10 cm), 140 subsoil samples (SS) (10–20 cm), and 140 deep soil samples (DS) (150 cm). The soils were characterized, and the concentrations of Ba, Co, Cr, Mn, and Ni were analyzed by atomic absorption photospectrometry following aqua regia digestion. Correlations and principal component analysis combined with spatial analysis were implemented in order to distinguish the sources and their classification as geogenic or anthropogenic. Several simple and robust statistical methods were applied to datasets in order to explore their potential in the evaluation of a useful and robust background values. The degree of contamination along with the geoaccumulation index, enrichment factor, and contamination factor were also evaluated.

Results and discussion

The median concentrations obtained for various elements includes Ba 461 mg kg^?1, Co 82.7 mg kg^?1, Cr 134 mg kg^?1, Mn 311 mg kg^?1, and Ni 56.1 mg kg^?1. In general, the concentrations of Ba, Co, Cr, Mn, and Ni decrease with depth. Correlations and principal component analysis suggest that Cr, Mn, and Ni are contributed by external sources. The spatial distribution of Cr, Mn, and Ni in TS displays a spatial pattern extending along industrial environments and emission sources.

Conclusions

The estimated background values determined with the iterative 2σ-technique includes 536 mg kg^?1 for Ba, 95.9 mg kg^?1 for Co, 208 mg kg^?1 for Cr, 464 mg kg^?1 for Mn, and 90.5 mg kg^?1 for Ni. The geochemical index, enrichment factor, and the contamination factor register a moderate to considerable contamination in some soil samples.

     

The content of chemical elements in alluvial soils and bottom sediments of the Urkan River (the Amur River basin)

The distribution patterns of the chemical elements in the bottom sediments and alluvial soils of the Urkan River valley (one of the largest tributaries of the Zeya River, a tributary of the Amur River) have been examined. It is shown that the concentrations of the chemical elements in the bottom sediments generally correspond to those in the bedrocks composing the river catchment and in the upper part of the continental earth’s crust, though the accumulation of most of the elements in the bottom sediments is somewhat lower. The composition of the microelements in the alluvial soils is mainly determined by the composition of the microelements in the bottom sediments. The alluvial soils are somewhat enriched in Mn, Zn, Co, and Cu, which is related to the biological accumulation of these elements entering the trophic chains.     

Temporal denitrification patterns in different horizons of two riparian soils

The dynamics of biological denitrification in riparian soil is still poorly understood. We studied the spring‐time pattern of denitrifying enzyme activity (DEA) and the rate of denitrification (DNT) in two hydromorphic riparian soils, one a mollic Gleysol and the other a terric Histosol. The average DEA ranged from 73 to 1232 ng N g^?1 hour^?1, and DNT ranged from 4 to 36 ng N g^?1 hour^?1. Both DEA and DNT diminished with increasing depth in both soil types. This decrease corresponded to a decrease in total and K₂SO₄‐extractable organic carbon and K₂SO₄‐extractable mineral nitrogen. The DEA and DNT differed in their dynamics. The former had no evident pattern in subsurface horizons but increased with temperature at the end of spring in surface and structural horizons. The DNT diminished as the soil dried in the mollic Gleysol when the water table fell. In the terric Histosol, the water table was still too high at the end of spring to affect the DNT. The results suggest that the vertical pattern of denitrification is related to that of organic carbon content. This organic carbon content determines biological activity and the supply of carbon and nitrous oxides. In biologically active horizons temperature drives the dynamics of DEA, whereas soil moisture drives the dynamics of DNT. Our results show the importance of the dynamic soil–water relationship in controlling denitrification within the riparian zone.     

Spatial distribution and solubilization characteristics of metal(loid)s in riparian soils within reservoirs along the middle Jinsha River

Journal of Soils and Sediments - The construction of large dams submerges riparian soils within reservoirs. However, little is known about the influence of water submergence on metal(loid)...     

Reservoir riparian zone characteristics in the Upper Tennessee River Valley

Impoundments in the upper Tennessee River Basin have inundated historic river riparian and mesic valley slope habitats. Fifteen major Tennessee Valley Authority (TVA) reservoirs, upstream of Chattanooga TN, have effected 50,000 ha of modern reservoir riparian zones on formerly mesic terrain. These zones were defined here as winter mudflats between winter pool shores and summer pool shores and summer riparian habitats with diminishing soil saturation from summer shores up to flood zone boundaries. Watts Bar (WB), the largest of these 15 projects in terms of area, was chosen for background and field analyses of the consequential reservoir riparian processes and expressions. WB, at the median age of areal TVA reservoirs, was closed in 1942. Transects were taken in the WB summer riparian forest after consideration of topoedaphics, species composition, and the level of contemporary disturbance. Regional bottomland forests were compared. Coefficients of species similarity showed 70% compositional similarity. The basal area (BA) density of WB summer riparian forests was not similar as was composition in regional bottomland stands. Four (of twelve) subjectively selected WB transect BA densities were compared nonparametrically and were the same (90% confidence) as other bottomland stands of like chronology. Overall however, WB stands averaged 19.6 m²/ha BA to 30.0 + for regional comparisons. Stocking was low, but measured litterfall was relatively high, resulting in similar biomass productivity corrected on a unit area basis. The winter mudflats showed expanding development of phenologically distinct herbaceous and graminoid communities under a five to six month drawdown exposure regime. Thermal modifications from the winter pool heat sink were determined to alter the mudflat microenvironment. A recent shortening of the drawdown period has interrupted the adapted life history strategy of the counter-seasonal plants, and seed maturity has been restricted. Erosion of the summer shore has been increasing the extent of the mudflats at the expense of the hydrologically influenced summer riparian habitat foreslope. The discernable trend of summer riparian stand succession over mesic expression will be limited by the height and hydric avoidance occasioned by an abrupt slope to mesic, unsaturated profile, conditions. Approximations of biomass production potential pre- and post impoundment have shown a 12∶1 diminution from historic carbon detention, on a seasonal basis, within normal pool shore boundaries. Further approximations comparing the WB summer riparian forest carbon retention and detention to historic forest compartments highlighted the importance of a relatively copious, non-lignified, litterfall in the seasonally available carbon budget.     

Potentially toxic elements in urban soil catenas of W-Mo (Zakamensk,Russia) and Cu-Mo (Erdenet,Mongolia) mining areas

Purpose

The aim of this study was to characterize the conditions of the lateral migration of potentially toxic elements (PTEs) and to identify the zones of their accumulation in soil catenas of ore-mining landscapes in the cities of Zakamensk (Buryat Republic, Russia) and Erdenet (Mongolia) which are situated in the basin of the Selenga River.

Materials and methods

Eight soil catenas across the river valley with 31 pits in Zakamensk area and five catenas with 15 pits in Erdenet area were studied. Soil samples were collected in four landscape–geochemical positions: autonomous, on tops of the hills; trans-eluvial, on slopes of river valleys; trans-accumulative, at the footslopes; and superaqual, on the river floodplains. The total contents of 16 PTEs in the 148 samples were determined by mass spectrometry and by atomic emission spectrometry with inductively coupled plasma.

Results and discussion

It is found that the chemical composition of undisturbed soils is greatly affected by the widespread distribution of volcanic rocks enriched with W, Mo, Cd, Bi, and Sr in Zakamensk and with V, Co, Sr, and As in Erdenet. The difference between geochemical positions is relatively small. Under the influence of technogenic loads in the cities, the concentrations of PTE change along soil catenas increases by an order of magnitude. For chalcophile elements—Mo, Bi, Pb, Sb, and Cu in Zakamensk and Cu, Zn, Mo, Cd, Sn, and W in Erdenet—the type of their lateral distribution in the soil catenas changes because of the intense migration from the tailings and facilities with water and air flows. The accumulation of PTEs takes place on the chemisorptive (V, Co, Ba, As, Cr, and Ni), gley (Mo and Sb), organomineral (Sn), and alkaline (Sr and W) lateral geochemical barriers (LGBs) confined to subordinate positions. The artificial technological LGBs are formed due to the increased content of sand derived from the tailings by water erosion in Zakamensk and the input of silt particles windblown from the technogenic sources in Erdenet. This causes the rise in the concentrations of major ore elements (Mo, W, and Cu) and the accompanying elements (Pb, Bi, As, Sr, Cr, and Ni).

Conclusions

The results of soil–geochemical studies using the catenary approach and concept of LGBs made it possible to understand the main features of migration and fixation of PTEs in soils of the mining centers. They indicate the formation of a system of LGBs with intensive accumulation of major ore elements and associated ones in the subordinate landscapes of Zakamensk and Erdenet.

     

Microbial community structure in restored riparian soils of the Canadian prairie pothole region

In the Prairie Pothole Region (PPR) of Canada, wetlands once utilized for agricultural purposes are restored through the placement of a ditch plug to return them to their pre-existing hydrological state. The overall objective of this research was to assess differences in riparian soil microbial community structure between reference wetlands, those which had never been utilized for agricultural purposes, and restored wetlands, of varying times since restoration. Soil samples (0-6 cm) were taken from 15 reference and 28 restored wetlands. The soil microbial community was characterized using phospholipid fatty acid (PLFA) analysis. Data were analyzed using non-metric multidimensional scaling, multivariate regression trees (MRT) and indicator species analysis. The microbial community of younger restored soils (1-3 and 4-6 yrs) differed significantly from the reference soils, with reference soils having higher microbial biomass, evenness, and diversity. Richness showed an increasing trend with time since restoration. Results from the MRT underlined the importance of climatic factors, specifically precipitation - potential evapotranspiration (P-PE) in explaining the variation found in the microbial community. More specifically, drier sites had strong indicator species values associated with PLFAs of actinomycetal origin and fungal origin. Within the wetter sites, it was found that the older restored sites (7-11 yrs) and reference sites had strong indicator species values associated with PLFAs of Gram negative and fungal origin. The similarities in microbial community composition and biomass of the older restored sites (7-11 yrs) and the reference sites indicate that this component of the wetland ecosystems begins to recover within this time period.     

Studies of the availability of toxic heavy elements in soils and sediments in the vicinity of a lead smelting site (Germany)

The lead smelting site near Clausthal-Zellerfeld (Harz Mountains, Germany) was in operation for 700 years. As a result of this long operating time, the soil and stream sediments in the vicinity of the site are highly contaminated due to airborne pollution and dumping of slags. The knowledge of bulk concentrations does not give sufficient information for an estimate of the hazard potential stored in the contaminated materials. Therefore, as a first step, the element speciation in the three sample populations was determined. As the extractability (availability) of the speciations varies significantly for the different elements, a second step was used to test for the availability. The investigations on the availabilities yield a very high hazard potential for lead, followed by Cu and Zn.     

Microbially available carbon in buried riparian soils in a glaciated landscape

Buried horizons and lenses in riparian soil profiles harbor large amounts of carbon relative to the surrounding soil horizons. Because these buried soil horizons, as well as deep surface horizons, frequently lie beneath the water table, their impact on nitrogen transport across the terrestrial–aquatic interface depends upon their frequency and spatial distribution, and upon the lability of associated organic matter. We collected samples of 51 soil horizons from 14 riparian zones Rhode Island, USA, where soil profiles are characterized by glacial outwash and alluvial deposits. These soil samples came from as deep as 2 m and ranged in carbon content from <1% to 44% in a buried O horizon 54–74 cm deep. We used these samples to: (1) determine the extent to which carbon in buried horizons, and deep surface horizons, is potentially microbially available; (2) identify spatial patterns of carbon mineralization associated with surface and buried horizons; and (3) evaluate likely relationships between soil horizon types, chemical characteristics and carbon mineralization. Carbon mineralization rates associated with buried horizons during anaerobic incubations ranged from 0.0001 to 0.0175 μmol C kg soil^?1 s^?1 and correlated positively with microbial biomass (R=0.89, P<0.0001, n=21). Excluding surface O horizons from the analysis, carbon mineralization varied systematically with horizon type (surface A, buried A, buried O, lenses, A/C, B, C) (P<0.05) but not with depth or depth x horizon interaction (overall R²=0.59, P<0.0005, n=47). In contrast to this result and to most published data sets, ¹³C-to-¹²C and ¹⁵N-to-¹⁴N ratios of organic matter declined with depth (¹³C?26.9 to ?29.3 per mil, ¹⁵N+5.6 to ?0.8 per mil). The absence of a relationship between horizon depth and C availability suggests that carbon availability in these buried horizons may be determined by the abundance and quality of organic matter at the time of horizon formation or burial, rather than by duration since burial, and implies that subsurface microbial activity is largely disconnected from surface ecosystems. Our results contribute to the emerging view that buried horizons harbor microbially available C in quantities relevant to ecosystem processes, and suggest that buried C-rich soil horizons need to be incorporated into assessments of the depth of the biologically active zone in near-stream subsurface soils.     

Trace elements in Bangladesh paddy soils

Abstract

A study was carried out to investigate the status of four micronutrients, iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn), and five other trace elements, cobalt (Co), chromium (Cr), nickel (Ni), lead (Pb), and strontium (Sr), in paddy soils of Bangladesh. Soil samples were digested by hydrofluoric acid (HF)‐nitric acid (HNO₃)‐perchloric acid (HClO₄) for determination of total contents of the nine elements, while DTPA, ASI and 0.1 Mhydrochloric acid (HC1) methods were used for determination of available Fe, Cu, Mn, and Zn. Total trace element contents were found to vary with physiography on which soils are distributed. In general, Ganges Tidal Floodplain soils had the highest content, whereas terrace soils had the lower content. Among the soil properties examined, clay content had a good relation with total trace element contents in the topsoil, except for Sr. Based on the variation with physiography or clay content, the nine trace elements could be grouped into six groups: Cu, Fe and Zn, Pb, Co and Cr and Ni, Mn, Sr. According to the extractable levels of four micronutrients, Bangladesh paddy soils had the medium to optimum amounts of Fe and Cu, but were deficient sporadically in Mn and extensively in Zn. It was indicated that paddy soils of Bangladesh are yet to be polluted with heavy metals.     

Earthworm functional groups are related to denitrifier activity in riparian soils

Riparian buffers, located in the transition zone between terrestrial and aquatic ecosystems, are a hotspot for nitrogen (N) removal through denitrification. Earthworms are abundant in riparian buffers and may enhance denitrification. This study investigated earthworm demographics of three earthworm functional groups (anecic, epigeic, and endogeic) and denitrifier activity in temporarily flooded and non-flooded riparian soils from April to October 2012 in southern Quebec, Canada. Nine earthworm species, mostly endogeic, were found in the temporarily flooded soil, while only six earthworm species were found in the non-flooded soil. On average, there were 11.7 times more earthworms with 12.4 times greater biomass (P<0.05) found in the temporarily flooded soil than in the non-flooded soil. The denitrification enzyme activity (DEA) was of similar magnitude in temporarily flooded and non-flooded soils, with temporal variation associated with rainfall patterns. Endogeic earthworm biomass was positively correlated (P<0.05) with DEA, while epigeic earthworm biomass was positively correlated (P<0.05) with 16S rRNA gene copies and nosZ gene copies from bacteria, indicating an association between earthworm functional groups and denitrifier activity in riparian soils. Stepwise multiple regressions showed that DEA in riparian soils could be predicted using soil moisture, inorganic N concentration, and earthworm functional groups, suggesting that endogeic and epigeic earthworms contributed to denitrifier activity in riparian soils.     

Biological and physical effects of non-native earthworms on nitrogen cycling in riparian soils

Global nitrogen cycling is being altered by anthropogenic disturbances including invasion by non-native species. European and Asian earthworms have invaded northern temperate forests in North America with dramatic consequences for litter thickness, forest floor plant diversity, and soil nitrogen cycling. Invasive earthworms present at the boundary of terrestrial and aquatic ecosystems (i.e., riparian zones) may alter the flux of nitrogen into adjacent aquatic ecosystems. We examined how nitrogen cycling in riparian soil responds to amendments of invasive earthworms or artificial earthworm burrows. In earthworm-free riparian plots (0.25 m²), we established treatments of invasive earthworms (60 g fresh mass·m⁻²), artificial burrows (120 m⁻²), or control plots and sampled the plots after 30 days. Before and after treatment application we measured major soil characteristics (water-filled pore space, organic matter, and pH), nitrogen pools (exchangeable NH₄⁺ and NO₃⁻), and nitrogen transformation rates (net N-mineralization, net nitrification, and denitrification). Exchangeable NH₄⁺ and NO₃⁻ changed through time but did not differ among treatments. Net N-mineralization and net nitrification rates did not change through time and were similar across all treatments. However, denitrification rates in plots with added earthworms were 4 times greater than rates in control and burrow-only plots, which represents a large rapid increase in gaseous nitrogen flux out of these riparian soils. For all response variables, artificial burrows responded similarly to control plots, suggesting that earthworm biological activity (i.e., feeding, excretion, and mucus production) rather than physical effects (i.e., burrowing and soil aeration) drove the changes in nitrogen cycling. Examination of soil nitrogen pool and flux measurements suggest that this increase in denitrification was coupled with NH₄⁺ consumption by nitrifying bacteria, but future studies are needed to confirm this hypothesis. We conclude that the activity of invasive earthworms in riparian zones can increase the flux of N out of riparian zones, but the hydrologic context of the riparian zone (e.g., pore-water residence time) ultimately controls whether denitrification or nitrate leaching is the dominant flux of N.     

Trace elements in tropical Asian paddy soils

Attempts were made to evaluate correlations of total trace elements with various soil characters in the hope that such correlations would allow prediction of the trace element status of paddy soils in Tropical Asia.

Among the 11 trace elements studied, Ni and Cr showed by far the highest correlation, followed by the pairs of V and Zn, Ni and Zn, and Cr and Zn.

High positive correlations of trace elements with soil characters were found for the following pairs: total Fe₂O³, and V and Zn, total K₂0 and Rb, total CaO and Sr, total TiO₂, and V, total Al₂0³ and Zn, 10 Å clay content and Rb, clay and V, and sand and Zr. Among the negative correlations, the highest was between total SiO₂ and V, followed by those between total SiO₂ and Zn and sand and Zn.

Soil material classes and inherent potentiality ratings previously established were found to have some value for the prediction of the status of certain trace elements in soil.