Phosphorus losses from two representative small catchments in the Mediterranean part of Spain

Purpose

Information about phosphorus (P) losses from agricultural catchments in Mediterranean environments is scarce. In this work, P losses in overland flow from two representative small Mediterranean catchments, one dominated by Alfisols and the other by Vertisols, were studied.

Materials and methods

At the lowest level of each catchment, overland flow was measured and several runoff samples taken in each runoff event during two growing seasons (2001–2002 and 2002–2003). After centrifugation, total P in sediments and total and molybdate reactive P in supernatant were determined. Different chemical extraction methods were used to quantify the forms of P in soils and sediments.

Results and discussion

Total P losses in the studied catchments ranged between 0.5 and 3.2 kg ha^?1 year^?1, losses higher than 2 kg P ha^?1 being observed in one event. Phosphorus was mainly lost in the sediments, the ratio of total dissolved P to particulate P being higher in the Alfisol than in the Vertisol catchment. Phosphorus concentration in sediments from the Vertisol catchment was similar to that in the source soils, whereas sediments in the Alfisol catchment had 2.1 times more inorganic P and 9 times more organic P (OP) than the source soils. In the latter catchment, there was an enrichment in the more labile inorganic P forms in the sediments relative to the source soils, which corresponds to a relative enrichment in iron (Fe) oxides by a factor of 2.4. Alfisols had lower TP contents and exhibited lower erosion rates than Vertisols in the studied period but they posed a greater environmental risk than the latter soils because their sediments were richer in P and had a higher proportion of P in forms bound to the Fe oxides compared to the source soils—these P forms can be easily released with the onset of reducing conditions at the bottom of waterbodies.

Conclusions

A study of the P enrichment ratios and the dominant P forms in eroded sediments is therefore necessary to predict the impact of P losses from soils on the ecological quality of waterbodies.     

Quantification of seasonal sediment and phosphorus transport dynamics in an agricultural watershed using radiometric fingerprinting techniques

Purpose

Phosphorus (P) is a limiting nutrient for most US Midwestern aquatic systems and, therefore, increases of P, through point or non-point sources (NPS) of pollution such as agriculture, causes eutrophication. Identifying specific NPS contributions (e.g., upland vs. stream channels) for sediments and P is difficult due to the distributed nature of the pollution. Therefore, studies which link the spatial and temporal aspects of sediment and P transport in these systems can help better characterize the extent of NPS pollution.

Materials and methods

Our study used fingerprinting techniques to determine sources of sediments in an agricultural watershed (the North Fork of the Pheasant Branch watershed; 12.4 km² area) in Wisconsin, USA, during the spring, summer, and fall seasons of 2009. The primary sources considered were uplands (cultivated fields), stream bank, and streambed. The model used fallout radionuclides, ¹³⁷Cs, and ²¹⁰Pb_xs, along with total P to determine primary sediment sources. A shorter-lived fallout radioisotope, ⁷Be, was used to determine the sediment age and percent new sediments in streambed and suspended sediment samples (via the ⁷Be/²¹⁰Pb_xs ratio).

Results and discussion

Upland areas were the primary source of suspended sediments in the stream channels followed by stream banks. The sediment age and percent new sediment for the streambed and suspended sediments showed that the channel contained and transported newer (or more recently tagged with ⁷Be) sediments in the spring season (9–131 days sediment age), while relatively old sediments (165–318 days) were moving through the channel system during the fall season.

Conclusions

Upland areas are the major contributors to in-stream suspended sediments in this watershed. Sediment resuspension in stream channels could play an important role during the later part of the year. Best management practices should be targeted in the upland areas to reduce the export of sediments and sediment-bound P from agricultural watersheds.     

Organic carbon mineralization responses to temperature increases in subtropical paddy soils

Purpose

Understanding organic carbon mineralization and its temperature response in subtropical paddy soils is important for the regional carbon balance. There is a growing interest in factors controlling soil organic carbon (SOC) mineralization because of the potential for climate change. This study aims to test the hypothesis that soil clay content impedes SOC mineralization in subtropical paddy soils.

Materials and methods

A 160-day laboratory incubation at temperatures from 10 to 30 °C and 90% water content was conducted to examine the dynamics of SOC mineralization and its temperature response in three subtropical paddy soils with different clay contents (sandy loam, clay loam, and silty clay soils). A three-pool SOC model (active, slow, and resistant) was used to fit SOC mineralization.

Results and discussion

Total CO₂ evolved during incubation following the order of clay loam > silty clay > sandy loam. The temperature response coefficients (Q ₁₀) were 1.92?±?0.39, 2.36?±?0.22, and 2.10?±?0.70, respectively, for the sandy loam soil, clay loam soil, and silty clay soil. But the soil clay content followed the order of silty clay > clay loam > sandy loam. The sandy loam soil neither released larger amounts of CO₂ nor showed higher temperature sensitivity, as expected, even though it contains lower soil clay content among the three soils. It seems that soil clay content did not have a dominant effect which results in the difference in SOC mineralization and its temperature response in the selected three paddy soils. However, dissolved organic carbon (DOC; representing substrate availability) had a great effect. The size of the active C pool ranged from 0.11 to 3.55% of initial SOC, and it increased with increasing temperature. The silty clay soil had the smallest active C pool (1.40%) and the largest Q ₁₀ value (6.33) in the active C pool as compared with the other two soils. The mineralizable SOC protected in the silty clay soil, therefore, had even greater temperature sensitivity than the other two soils that had less SOC stabilization.

Conclusions

Our study suggests that SOC mineralization and its temperature response in subtropical paddy soils were probably not dominantly controlled by soil clay content, but the substrate availability (represented as DOC) and the specific stabilization mechanisms of SOC may have great effects.     

Quantifying effects of primary parameters on adsorption–desorption of atrazine in soils

Purpose

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of atrazine in soils. Equilibrium batch experiments were carried out to investigate the adsorption–desorption characteristics of atrazine. The objectives of this study were to (1) determine and quantify the main soil parameters governing atrazine adsorption and desorption phenomena; (2) find the correlativity between the identified soil parameters; and (3) investigate the universal desorption hysteresis traits.

Materials and methods

Fifteen soils with contrasting physico-chemical characteristics were collected from 11 provinces in eastern China. The equilibrium time was 24 h both for adsorption and desorption experiments. Atrazine was detected by Waters 2695/UV HPLC.

Results and discussion

Adsorption isotherms of atrazine could be well described by the Freundlich equation (r?≥?0.994, p?<?0.01). The total organic carbon (TOC) was the first independent variable that described 53.0 % of the total variability of K _f, followed by the pH (9.9 %), and the clay (4.0 %) and silt (1.2 %) contents, separately; while the primary soil properties that affect desorption parameters included the TOC, pH, free Fe₂O₃ (Fe_d) and the sand content, with the biggest contribution achieved by the TOC (ranged from 48.5–78.1 %). The results showed that when the content ratio of clay to TOC (RCO) was less than 40, the atrazine adsorption was largely influenced by the organic matrix, while when the RCO was greater than 40, they were vital affected by the clay content.

Conclusions

Adsorption–desorption isotherms of atrazine in soils were nonlinear. The content of TOC, clay, and iron oxides, as well as the pH value were the key soil parameters affecting the adsorption–desorption of atrazine in soil, among which the RCO especially exhibited relevance. Additionally, the desorption hysteresis existed for atrazine retention in all 15 tested soils, and the hysteretic effect enhanced with the increasing time for desorption. This would be ascribed to the heterogeneity physical–chemical properties of these soils.     

A combined hydraulic and toxicological approach to assess re-suspended sediments during simulated flood events. Part I–multiple biomarkers in rainbow trout

Purpose

One of the central issues related to global changes in weather is the increasing occurrence of flood events that can result in the re-suspension of contaminated sediments in rivers. Here, we report on a proof-of-concept study combining hydraulic engineering and ecotoxicology in a new interdisciplinary approach to assess the toxicity of re-suspended polluted sediments after a simulated flood event.

Materials and methods

Rainbow trout (Oncorhynchus mykiss) were exposed for 5 days under simulated flood conditions in an annular flume with artificial sediments that were spiked with a mixture of polycyclic aromatic hydrocarbons (PAH) at environmentally relevant concentrations. Specifically, the objective of this study was to bridge the gap between the physical re-suspension of pollutants and resulting toxicological impacts on aquatic organisms. A suite of different molecular, biochemical and histological markers was used to test the hypothesis that re-suspension of sediments can lead to re-mobilization of PAHs and subsequently to effects on aquatic organisms.

Results and discussion

The micronucleus frequency was significantly 4.3-fold elevated after exposure. There was no significant indication of Aryl hydrocarbon receptor signaling (no EROD induction or increased CYP1A protein content, only slight induction of CYP1A gene expression). Biliary metabolite concentration was the most sensitive marker of PAH exposure. Results for other biomarkers (glutathione-S-transferase, catalase and lipid peroxidation) were inconclusive.

Conclusions

In combination with chemical analyses of suspended matter, the presented approach will be used to improve understanding of the re-mobilization of pollutants from sediments in support of environmental risk assessment.     

Assessment of the stability of chromium in remedied soils by Pannonibacter phragmitetus BB and its risk to groundwater

Purpose

Acid rain can accelerate the acidification of the chromium-contaminated soils, resulting in chromium releasing into soil solution and causing ecological risk. The current study aims to investigate the release of chromium in the remedied soils by Pannonibacter phragmitetus BB under the simulated acid rain leaching and to assess its risk to groundwater.

Materials and methods

P. phragmitetus BB was utilized to remedy the Cr(VI)-contaminated soils at two levels (80 and 1,276 mg kg^?1) by the column leaching experiment, and the chemical remediation with ferrous sulfate was used as a control. The remedied soils by P. phragmitetus BB and ferrous sulfate were leached under the simulated acid rain to evaluate the release of chromium. Furthermore, the risk of chromium release from the remedied soils to the groundwater was assessed by a fuzzy comprehensive evaluation method.

Results and discussion

The average concentrations of water-soluble Cr(VI) in the remedied soils by P. phragmitetus BB were reduced to less than 5.0 mg kg^?1. Under leaching situation with the simulated acid rain, the release of total chromium and Cr(VI) from the remedied soils by P. phragmitetus BB and ferrous sulfate declined rapidly with the extended leaching time. However, the release amounts of total chromium and Cr(VI) from the remedied soil by P. phragmitetus BB more efficiently deceased as compared with that by ferrous sulfate remediation. Carbonate-bounded, exchangeable, and organics-bonded chromium were the major chromium-releasing sources under the simulated rain leaching. After microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate, the risk grades of the remedied soils to groundwater declined from classes 11 to 5 and 6, respectively.

Conclusions

The risks of the remedied soils by both microbial remediation with P. phragmitetus BB and chemical remediation with ferrous sulfate to groundwater effectively decreased and microbial remediation more significantly declined the chromium risk to groundwater than chemical remediation.     

Clay amendment to sandy soil—effect of clay concentration and ped size on nutrient dynamics after residue addition

Purpose

Crop growth on sandy soils can be increased by claying. In modified sandy soils, the added clay is in the form of peds ranging in size from millimetres to centimetres creating a highly non-uniform matrix where ped size could influence nutrient availability and organic C binding. The aim of the study was to determine the effect of clay addition rate and ped size in residue amended sandy soil on soil respiration, nutrient availability and organic C retention.

Materials and methods

In this study, clay peds of 1, 2 or 3 mm size derived from a clay-rich Vertosol (73 % clay) were added to a sandy soil (3 % clay) at clay addition rates of 10 and 20 % w/w. After the addition of ground faba bean residue (C/N 37) at 10 g kg^?1, the soils were incubated for 45 days at 80 % of water-holding capacity.

Results and discussion

Clay addition had no consistent effect on cumulative respiration, but reduced NH₄ ⁺ availability with a greater reduction at 20 % compared to 10 % clay and with 1 and 2 mm compared to 3 mm peds. Sandy soil with clay peds had a greater maximum NH₄ ⁺ and P sorption capacity than sandy soil alone, and sorption capacity was higher at 20 % compared to 10 % clay addition and greater with 1 mm compared to 3 mm peds. Retrieval of clay peds at the end of the experiment showed ped breakdown during the experiment but also the formation of larger peds. Compared to the <53 μm fraction added at the start of the experiment, the total organic carbon (TOC) content of the <53 μm fraction was increased up to nearly two fold, particularly in the smaller peds (1 and 2 mm).

Conclusions

When sandy soils are amended with clay, N availability and organic C binding depend on both clay addition rate and ped size.

     

Fractionation of Cd and Zn in Cd-contaminated soils amended by sugarcane waste products from an ethanol production plant

Purpose

Sugarcane waste products (boiler ash, filter cake, and vinasse) from an ethanol production plant were used as soil amendments by adding 3 % (w/w) in single and/or in combination, with a research focus towards stabilization of cadmium (Cd) and zinc (Zn) in contaminated soils. The objective of this laboratory study was to evaluate the effects of adding these sugarcane waste products on bioavailability of Cd and Zn over time (aging) in Cd- and Zn-contaminated agricultural soils of Thailand.

Materials and methods

Two agricultural contaminated soils of low (<3 mg kg^?1) and high (10–15 mg kg^?1) Cd concentrations were collected from Tak Province, Northwest Thailand. Fourteen treatments were sampled at 2-week intervals for 84 days for metal bioavailability using BCR extraction procedures (proposed by The Standards, Measurements and Testing Programme of the European Union, SM&T) that determined exchangeable (BCR1), reducible (BCR2), oxidizable (BCR3), and residual (BCR4) fractions, and total concentration was determined using aqua regia digestion and microwave digestion.

Results and discussion

Cd was potentially bioavailable, predominantly in exchangeable (BCR1) and reducible (BCR2) fractions, while the higher contribution of Zn was more prevalent in refractory fractions (BCR2 and BCR4). Aging had an influence on fractionation of Cd and Zn, most notably in the first two fractions (BCR1 and BCR2) of BCR sequential extraction, which resulted in reduction of exchangeable Cd during the first few weeks of incubation (T?=?0 to 28 days). At the end of pot experiment, the exchangeable Cd fraction in the low Cd (LCdS) soil was reduced from 2.3 to 4.7 % and 9.4 to 39.9 % in low and high Cd (HCdS)-contaminated soils, respectively, as compared to nonamended soils.

Conclusions

The observed reduction in exchangeable Cd (BCR1) in the amended soils at the 3 % (w/w) application rate, the low total metal concentrations, and the significant amount of essential plant nutrients (N, P, and K) within these waste products highlight the benefits of amending metal-rich soils with them.     

Changes in nutrient pools,microbial biomass and microbial activity in soils after transit through the gut of three endogeic earthworm species of the genus Postandrilus Qui and Bouché, 1998

Purpose

Endogeic earthworms play a significant role in biogeochemical cycles due to the large amount of soil they ingest, and because after transit through their guts, casts usually show differences in nutrient contents and microbial populations with bulk soil. Here, we studied how three endogeic earthworm species, Postandrilus majorcanus, Postandrilus sapkarevi and Postandrilus palmensis, inhabiting soils in Majorca island (Balearic Islands, W Mediterranean), modify nutrient pools and microbial communities of soil.

Materials and methods

To do this, we analysed C, N and P pools, microbial biomass (phospholipid fatty acids, PLFA) and microbial activity (fluorescein diacetate hydrolysis, FDA) in paired samples of bulk soil and fresh casts.

Results and discussion

The mineral and organic N contents were generally enhanced in casts produced by all three earthworm species. However, inorganic P and organic C contents were only higher in P. sapkarevi (32 %, only P) and P. majorcanus casts (100 % for both soil nutrient pools) than in bulk soil. Bacterial and fungal biomass were only higher than in bulk soil in P. majorcanus casts (65 and 100 %, respectively), but without effects on microbial activity, that was lower in P. palmensis casts (26 %). Earthworm gut transit strongly influenced the soil microbial community structure, resulting in differences between casts and soils.

Conclusions

The increased nutrient mineralization (6-, 1.3- and 1.4-fold for N, C and P, respectively) in casts produced by these earthworm species is of particular importance because of the amount of casts released and the seasonal variations in earthworm activity, which may favour plant growth.     

Application of the Weng’s ratio for the identification of Zn, Cu, and Pb contamination in soils and sediments

Purpose

This work explores the application of the use of Zn, Cu, and Pb relative contents as a new type of normalization method for geochemical properties of soils and sediments in an Atlantic Basin (Anllóns River, NW Spain). The method is based on the conservative behavior of these elements, which exhibit a certain concentration ratio that remains stable as long as there are no human disturbances.

Materials and methods

The average relative contents of Zn, Cu, and Pb were calculated by dividing the concentration of each metal in soils or sediments, in the <63-μm fraction, by the sum of Zn, Cu, and Pb, expressed as a percentage. The evaluation of the sum of the average relative concentrations of Zn, Cu, and Pb (Ri), together with three standard deviations for each element, namely, Ri ± 3Si, allows a hexagon to be constructed, represented in ternary diagrams of Zn:Cu:Pb. Following the method proposed by Weng et al. (Environ Geol 45:79–85, 2003), those samples falling outside the hexagon must be considered outliers.

Results and discussion

Results obtained confimed the conservative behavior between the relative contents of Zn, Cu, and Pb in surficial samples (soils, bed, and suspended sediments). Only sediment cores displayed nonconservative behavior, showing a marked Pb enrichment, with respect to the surficial samples. When Zn, Cu, and Pb relative contents were plotted in ternary diagrams, outliers were best classified when the hexagon was drawn with standard deviations of samples from the study area. The hexagon drawn with an international database of soils and sediments showed a poorer classification of outliers.

Conclusions

The results showed that total Zn, Cu, and Pb relative contents may be employed to investigate anthropogenic disturbances of these elements in soils and sediments of the Anllóns River Basin, thus corroborating that this type of normalization may be employed as a tool to assess outliers in a contaminated area.     

Multiproxy investigation of a Holocene sedimentary sequence near Ferrara (Italy): clues on the physiographic evolution of the eastern Padanian Plain

Purpose

This paper investigates soils and sediments from the eastern Padanian Plain (northern Italy) in order to delineate the physiographic evolution of the area.

Materials and methods

We present new geochemical, mineralogical and textural analyses of alluvial sediments collected from a 13-m-deep section located a few kilometres south of Ferrara. The chronology of the related depositional events is provided from ¹⁴C dating of tree trunks buried at depths of ca. 9 m and organic matter from the underlying horizons.

Results and discussion

The data indicate that (1) the upper part of the sequence (down to depths of 9 m) includes sediments characterized by low nickel–chromium (Ni–Cr) concentrations ascribed to the alluvial deposits of the river Reno, deposited in the last 400 years; (2) buried soils (depths of 9–10.5 m) developed on Ni–Cr-rich sediments related to the river Po; and (3) the deeper facies (depths of 10.5–13 m) are CaCO₃-free and characterized by higher amounts of organic carbon, sulphur and arsenic, reflecting episodic lacustrine/marsh environments. These wetlands probably developed in the area during the Iron and Roman ages, persisting up to the Middle Ages.

Conclusions

The data provide a contribution to the understanding of the evolution of the river network during the last 3,000 years and provide insights on the related paleohydrological framework that can be useful for geographical and historical reconstructions of the area. Results highlight the importance of investigating alluvial sediments to elucidate (1) fluctuations of environmental conditions and (2) anthropogenic impacts on the natural landscape.     

Linking Ni and Cr concentrations to soil mineralogy: does it help to assess metal contamination when the natural background is high?

Purpose

In soils from serpentinitic areas the natural background of Ni and Cr is so high that the assessment of contamination by comparing metal concentrations with some fixed thresholds may give unreliable results. We therefore sought a quantitative relation between serpentines and Ni and Cr concentrations in uncontaminated soils, evaluated if the approach may help in establishing a baseline, and discussed if additional anthropogenic inputs of Ni and Cr can be realistically individuated in these areas.

Materials and methods

We analysed the total, acid-extractable and exchangeable concentrations of Ni and the total and acid-extractable concentrations of Cr in 66 soil horizons, belonging to 19 poorly developed and uncontaminated Alpine soils. The soils had different amounts of serpentines, depending on the abundance of these minerals in the parent material. We calculated an index of abundance of serpentines in the clay fraction by XRD and related total metal contents to the mineralogical index. We then tested the regressions on potentially contaminated soils, developed on the alluvial plain of the same watershed.

Results and discussion

We found extremely high total concentrations of Ni (up to 1,887 mg kg^–1) and Cr (up to 2,218 mg kg^–1) in the uncontaminated soils, but only a small proportion was extractable. Total Ni and Cr contents were significantly related to serpentine abundance (r ²?=?0.86 and 0.74, respectively). The regressions indicated that even small amounts of serpentines induced metal contents above 200 mg kg^–1, and the 95% confidence limits were 75 and 111 mg kg^–1 of Ni and Cr, respectively. When the regressions were tested on the potentially contaminated soils, a good estimate was obtained for Cr, while the Ni concentration was overestimated, probably because of some leaching of this element.

Conclusions

The concentrations of Ni and Cr that can be expected in soils because of the presence of small amounts of serpentines are comparable to the amounts accumulated in the soil because of diffuse contamination and potentially contaminated soils had metal concentrations falling in the range expected from the presence of natural sources. Only in the case of very severe contamination events, the identification of anthropogenic sources adding to the natural background would be feasible.     

Sediment source analysis in the Linganore Creek watershed, Maryland, USA, using the sediment fingerprinting approach: 2008 to 2010

Purpose

Fine-grained sediment is an important pollutant in streams and estuaries, including the Chesapeake Bay in the USA. The objective of this study was to determine the sources of fine-grained sediment using the sediment fingerprinting approach in the Linganore Creek watershed, a tributary to the Chesapeake Bay.

Materials and methods

The sediment fingerprinting approach was used in the agricultural and forested, 147-km² Linganore Creek watershed, Maryland from 1 August 2008 to 31 December 2010 to determine the relative percentage contribution from different potential sources of fine-grained sediment. Fine-grained suspended sediment samples (<63 μm) were collected during storm events in Linganore Creek using an automatic sampler and manual isokinetic samplers. Source samples were collected from 40 stream bank sites, 24 agricultural (cropland and pasture) sites, and 19 forested sites. Suspended sediment and source samples were analyzed for elements and stable isotopes.

Results and discussion

Results of sediment fingerprinting for 194 samples collected in 36 separate storm events indicate that stream banks contributed 53% of the annual fine-grained suspended sediment load, agriculture contributed 44%, and forests contributed 3%. Peak flows and sediment loads of the storms correlate to stream bank erosion. The highest peak flows occurred in the winter and, along with freeze–thaw activity, contributed to winter months showing the highest rate of stream bank erosion. Peak flow was negatively correlated to sediment sources from agricultural lands which had the greatest contribution in non-winter months. Caution should be observed when trying to interpret the relation between sediment sources and individual storms using the sediment fingerprinting approach. Because the sediment fingerprinting results from individual storms may not include the temporal aspects of the sourced sediment, sediment that is in storage from previous events, remobilized and sampled during the current event, will reflect previous storm characteristics. Stream bank sediment is delivered directly to the channel during an event, whereas the delivery of upland sediment to the stream is lower due to storage on hillslopes and/or in channels, sediment from stream banks are more likely to be related to the characteristics of the sampled storm event.

Conclusions

Stream banks and agricultural lands are both important sources of fine-grained sediment in the Linganore Creek watershed. Peak flows and sediment loads for the 36 storms show a significant relation to sediment sources from stream bank erosion. Attempting to link upland sediment sources to flow and seasonal characteristics is difficult since much of the upland sediment eroded in an event goes into storage. By averaging sediment sources over several storms, it may be possible to determine not only the sediment sources that are directly contributed during the current event but also sediment from previous events that was in storage and remobilized.     

Metal removal from and microbial property improvement of a multiple heavy metals contaminated soil by phytoextraction with a cadmium hyperaccumulator Sedum alfredii H.

Purpose

Effects of phytoextraction by Sedum alfredii H., a native cadmium hyperaccumulator, on metal removal from and microbial property improvement of a multiple heavy metals contaminated soil were studied under greenhouse conditions.

Materials and methods

A rhizobox experiment with an ancient silver-mining ecotype of S. alfredii natively growing in Zhejiang Province, China, was conducted for remediation of a multiple heavy metals contaminated soil. The rhizobox was designed combining the root-shaking method for the separation of rhizospheric vs near-rhizospheric soils and prestratifying method for separation of sublayers rhizospheric soils (0–10 mm from the root) and bulk soil (>10 mm from the root). Soil and plant samplings were carried out after 3 and 6 months of plant growth.

Results and discussion

Cadmium (Cd), zinc (Zn), and lead (Pb) concentrations in shoots were 440.6, 11,893, and 91.2 mg kg^?1 after 6 months growth, and Cd, Zn, and Pb removed in the shoots were 0.862, 25.20, and 0.117 mg/plant. Microbial biomass C, basal respiration, urease, acid phosphatase, and invertase activities of the rhizospheric soils were significantly higher than that of unplanted soils after 6 months growth. Microbial biomass carbon (MBC) of 0–2 mm and basal respiration (BR) rate of 0–8 mm sublayer rhizospheric soils were significantly higher than that of bulk soil after 6 months growth. So were the three enzyme activities of 0–4 mm sublayer rhizospheric soils. BR rate and urease were significantly negatively correlated with soluble Cd, so were MBC, acid phosphatase, and intervase activities with soluble Zn, MBC, BR rate, and three enzyme activities with soluble Pb.

Conclusions

Harvesting shoots of S. alfredii could remove remarkable amounts of Cd, Zn, Pb, and lower water-soluble Cd, Zn, and Pb concentrations in the rhizospheric soils. MBC, BR rate, and enzyme activities of the metal polluted soil, especially the rhizospheric soils increased with phytoextraction process, which is attributed to the stimulation of soil microbes by planting as well as the decrease in soil-soluble metal concentration.     

Soluble components of sediments and their relation with dissolved arsenic in aquifers from the Hetao Basin,Inner Mongolia

Purpose

High groundwater arsenic (As) and salinity have been detected in aquifers of the Hetao Basin in Mongolia which have caused serious public health concerns. The objective of this study was to characterize the distributions of the soluble components in sediment in different lithologies and depths and to assess the relationship between soluble As in sediments and dissolved As in groundwater.

Materials and methods

One hundred and one sediment samples and 13 groundwater samples were collected from four boreholes at varied depths. In addition to total chemicals and mineralogical phases of sediments, the soluble components (including major ions and As, Fe, and Mn) in sediments and dissolved chemicals in groundwater were analyzed.

Results and discussion

Clay or silty clay had relatively higher EC values (189–805 μS cm^?1) than aquifer sands (approximately 92–261 μS cm^?1). The major soluble components were Na⁺, Ca²⁺, HCO₃ ^?, and SO₄ ^2?, which were more variable in clay samples than fine sand samples. Soluble As concentrations ranged between 2 and 950 μS cm^?1, and high contents generally occurred in clay sediments with high contents of soluble Fe and Mn. A comparison of chemicals between soluble components in sediments and dissolved species in groundwaters at matched depths showed that chemicals were preferentially partitioned into sediments at the mountain front and deep aquifers (>60 m), while partitioned into groundwater in the shallow aquifers (<60 m) of the flat plain. Arsenic was preferentially partitioned into groundwater in aquifers with relatively low dissolved SO₄ ^2?.

Conclusions

Groundwater components were mostly sourced from corresponding sediments. In clay sediments, As was desorbed from the surface sites along with other soluble components. Under reducing conditions, reduction of Fe oxides with high surface sites for As adsorption led to a weak association of As with other phases (such as carbonates), and therefore resulted in high dissolved As concentrations and low As partition between sediments and groundwater in deep aquifers.

     

Effects of iron-based amendments on soil structure: a lab experiment using soil micromorphology and image analysis of pores

Purpose

Recent trends in soil green and sustainable remediation require an increased attention on environmental effects. The physical consequences of remediation practices on soil structure are very rarely investigated.

Material and methods

A laboratory experiment was carried out by adding iron grit to a sand (S), a silt loam (L), and a clay (C) soil subjected to several wetting-drying cycles. The physical effects of the treatment on soil pore system were identified and quantified combining physical measurements on repacked samples with image analysis of pores on resin-impregnated soil blocks and micromorphological analysis on thin sections.

Results and discussion

A negligible reduction of total porosity (P) resulted in S, and a slight increase was observed in the L and C soils. However, an important impact on soil structure was identified in pore size range >10 μm for the L and C soils, with the formation of new pores related to the differential shrink-swell behavior between soil matrix and added iron grains. Different plasticity of these soils also played a role in planar pore formation.

Conclusions

Effects of the addition of iron grit on soil pore system are strongly dependent on soil physical properties. The performed experiment showed that iron-based amendments can improve soil structure in low-plastic shrink-swell soil increasing porosity in the range of transmission pores (50–500 μm). This study showed the high potential of soil micromorphology and pore image analysis in order to evaluate the environmental impact of soil remediation practices.     

Optimization of arsenic and pentachlorophenol removal from soil using an experimental design methodology

Purpose

In this study, a soil-washing process was investigated for arsenic (As) and pentachlorophenol (PCP) removal from polluted soils. This research first evaluates the use of chemical reagents (HCl, HNO₃, H₂SO₄, lactic acid, NaOH, KOH, Ca(OH)₂, and ethanol) for the leaching of As and PCP from polluted soils.

Materials and methods

A Box–Behnken experimental design was used to optimize the main operating parameters for soil washing. A laboratory-scale leaching process was applied to treat four soils polluted with both organic ([PCP] _i ?=?2.5–30 mg kg^?1) and inorganic ([As] _i ?=?50–250 mg kg^?1, [Cr] _i ?=?35–220 mg kg^?1, and [Cu] _i ?=?80–350 mg kg^?1) compounds.

Results and discussion

Removals of 72–89, 43–62, 52–68, and 64–98 % were obtained for As, Cr, Cu, and PCP, respectively, using the optimized operating conditions ([NaOH]?=?1 N, [cocamidopropylbetaine] _i ?=?2 % w w^?1, t?=?2 h, T?=?80 °C, and PD?=?10 %).

Conclusions

The use of NaOH, in combination with the surfactant, is efficient in reducing both organic and inorganic pollutants from soils with different levels of contamination.     

Partitioning fine sediment loads in a headwater system with intensive agriculture

Purpose

This study was developed to improve understanding of the temporal variability of sediment delivery in a representative, intensively agricultural, headwater system of the U.S. Midwest by identifying the primary sediment source (i.e., uplands or channel banks) to the fine suspended sediment loads of three consecutive runoff events (with the third event being a flash flood) using naturally occurring radionuclides.

Materials and methods

Suspended sediment concentrations (C _s) from discrete and continuous sampling techniques agreed well despite differences in operating principles. The total sediment flux (Q _s) during each event was quantified over a 24-h period from the initiation of the rainfall using the following: (1) measured C _s and flow discharges (Q _w); (2) individual Q _w?CQ _s relationships for each event (herein called individual event relationships); and (3) a cumulative Q _w?CQ _s rating curve. The radionuclide tracers, beryllium-7 (⁷Be) and excess lead-210 (²¹⁰Pb_xs), were used with a simple two end-member mixing model to differentiate eroded upland surface soils and channel-derived sediments in the suspended loads of each event.

Results and discussion

Total load estimates from the measurement-based values and individual event relationships were similar, within 10?%, because they accounted for an observed non-linearity between C _s and Q _w (i.e., a clockwise hysteresis) during the events. The sediment rating curve assumed a linear relationship between C _s and Q _w and under-estimated the loads of the first two events while over-estimating the load of the flood event. The radionuclide partitioning quantified the proportion of eroded upland soils at 67?% for the first event, which was attributed to a ??first flush?? of readily available material from past events. For the subsequent and flood-event loads, 34?% and 21?% were respectively derived from the uplands, because less material was readily available for mobilization. Proportions are based on integrated samples for each event and are consistent with individual samples where available. During the flood event, stream bank mass failure was observed and bank erosion estimates from multiple methods compared favorably with the load results.

Conclusions

The radionuclide analysis showed decreasing proportions of eroded upland soils in the loads of the three successive events that was supported by observed clockwise hysteresis from source material exhaustion. Decreasing slopes observed in successive hysteresis plots for the events suggested that less material was readily available for mobilization following the first event flushing. The results of this study can assist watershed planners in identifying erosion-prone areas and determining optimal management strategies for sediment control.     

Spatial occurrence and geochemistry of soil salinity in Datong basin,northern China

Purpose

Soil quality assessment is tremendously important for agronomic and environmental concern. The objective of this study was to spatially evaluate soil salinity and its geochemistry at regional scale.

Materials and methods

A soil quality assessment study was conducted over a 1,000 km² field in Datong basin, northern China via collecting and determining 163 topsoil samples. A combined approach of statistical methods and hydrochemical tools was applied for a comprehensive analysis in this study.

Results and discussion

In the study area, the nonsaline lands (total dissolved solids (TDS) <0.08 %, Ca-HCO₃ type soils) that are located in the pluvial plains consist of coarse-medium sands and deep unsaturated zone (depth >10 m). The slightly (0.08 %?<?TDS?<?0.2 %, Ca-Na-HCO₃-NO₃ type soils) and the moderately (0.2 %?<?TDS?<?1 %, Ca-Na-SO₄ type soils) saline lands are located in the alluvial plains and the central basin composed of fine sediments like fine sands, loams and silts, and intermediately deep unsaturated zone (depth 2–10 m). By contrast, due to irrigation, the very (1 %?<?TDS?<?2 %) and the extremely (TDS >2 %) saline areas with Na-SO₄/Na-Cl type soils are locally found in some desolate lands comprised of silty clays and shallow unsaturated zone (depth <2 m) in the central basin.

Conclusions

As a result of water-rock/sediments interactions, effects of landscapes and anthropogenic activities, soil salinity is characterized by strong spatial variability in Datong. The new insights into the basin-scale distribution pattern of soil salinity in inland basins of silicate terrain under arid climatic conditions should be applicable in other similar regions of the world.