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A Scale-Dependent Approach to Study Pollution Control Processes in Wetland Soils Using Three Different Techniques
Abstract
The Elbe River, Germany, has received heavy metals and arsenic from the discharge of urban industrial, and agricultural effluent. During periods of inundation, these contaminants were transported with water into floodplain ecosystems, where they settled and accumulated predominantly in depressions and low-lying terraces. Markedly elevated arsenic concentration in soil solution during floods exceeded the inspection value of 10 μg L−1 of the German soil protection ordinance. Highly variable hydrological conditions in floodplains can affect the dynamics of pollutants. The study of processes controlling the dynamics of pollutants is challenging because the results are required to answer both scientific and practical questions regarding protection of groundwater and plants, sustainable management of floodplains or explain the fate of environmentally harmful substances.Our experiments in small groundwater lysimeter and biogeochemical microcosms tended to yield similar results regarding the functional relationships among the investigated site parameters. But the results of the field experiments, carried out at a floodplain site of the middle course of the Elbe River, Germany, are often characterized by complex and varying factors. Whereas arsenic tended to be mobilized during flooding due to decreasing redox potential (EH), chromium showed the opposite trend, with peak concentrations at the highest EH values. Our approach at three different spatiotemporally scale levels, ranging from 23 days (microcosms) to two-and-a-half years (field soil hydrological facility) allows us to overcome process interferences observed in field studies.
... The distribution of PTMs including Cr and Pb between the liquid and solid phase of floodplain soils and their release dynamics is mainly affected by soil properties and by changes of redox potential (E H ), soil pH, and metal carriers such as iron (Fe), manganese (Mn), dissolved organic carbon (DOC), and sulfate (SO 4 2À ) (Rinklebe et al., 2016a,b;Rupp et al., 2010;Schulz-Zunkel et al., 2015;Shaheen et al., 2013;Shaheen et al., 2014aShaheen et al., , 2016. A proper understanding of the geochemistry of Cr and Pb in floodplain soils is limited particularly under dynamic reducing-oxidizing conditions. ...
... Thus, this system allows for mechanistic experiments aiming at exploring underlying geochemical processes under fully controlled conditions. This system was successfully employed in previous studies (Anti c-Mladenovi c et al., 2011;Frohne et al., 2011Frohne et al., , 2014Frohne et al., , 2015Rupp et al., 2010;Rinklebe et al., 2016a,b;Shaheen et al., 2014c;Shaheen et al., 2016). Technical details are provided by Yu and Rinklebe (2011) and experimental specifics in Supplemental 2. ...
... Taking into account the contents of Fe and Mn oxides, it is plausible that oxidation of Cr 3þ to Cr(VI) could have occurred. Conversely, Fe 2þ reduces Cr(VI), which induces Cr precipitation with Fe oxides (Fendorf, 1995;Rupp et al., 2010;Shaheen et al., 2014a). This might be the case during flooding periods (reducing and acidic conditions in our experiment), which could lead to a decrease of Cr in the oxide fractions (F5 and F6) and an increase of Cr into the soil solution (Table 1; Fig. 3). ...
... The solubility of TEs under flooding conditions is controlled by E H and pH, dissolved organic carbon (DOC), iron (Fe)-manganese (Mn) oxides, and sulfate (SO 4 2− ) Rupp et al., 2010;Shaheen et al., in press). Thus, we hypothesized that different flood-dry-cycles in floodplain soils may affect the dynamics of the redox-dependent pollutants As, Cr, Mo and V due to changes of E H /pHvalues, DOC, Fe, Mn and SO 4 2− . ...
... However, this was in soil slurry by using an automated biogeochemical microcosm system on a laboratory scale. Rupp et al. (2010) have examined the solubility of As and Cr under different water levels within a short period. Nevertheless, little is known about the behavior of Mo and V in floodplain soils. ...
... Under reduced and acidic soil conditions the OM will decomposed which leads to the release of DOC and the attached As, Cr, Mo into the pore water (e.g. Evans and Barabash, 2010;Grybos et al., 2007;Rupp et al., 2010). However, the relation between Mo and DOC was stronger compared to As and Cr. ...
We hypothesize that the dynamics of water soluble arsenic (As), chromium (Cr), molybdenum (Mo), and vanadium (V) in soils might be controlled by the period of flooding due to changes of redox potential (EH), pH, and carriers of metals such as dissolved organic carbon (DOC), iron (Fe), manganese (Mn) and sulfate (SO42 −). Therefore, we aimed to assess the impact of different flood–dry-cycles on the temporal dynamics of pore water concentrations of As, Cr, Mo and V as affected by changes of soil EH/pH and dynamics of DOC, Fe, Mn and SO42 − in a contaminated floodplain soil collected at the Elbe River (Germany). For this purpose a specific groundwater lysimeter technique with two separate lysimeters which served as replicates was used. The groundwater level inside the lysimeters was controlled to simulate different flood–dry-cycles sequentially as follows: the long term (LT) includes 94 days of flooding followed by similar drying term. The short term (ST) comprises 21 days flooding followed by a similar drying term and was repeated six times. The entire experimental period (LT_ST) was about 450 days. The presented data are mean values of both lysimeters.
... ) (Rinklebe and Du Laing, 2011; Rupp et al., 2010; Shaheen et al., in press ). Thus, we hypothesized that different flood–dry-cycles in floodplain soils may affect the dynamics of the redoxdependent pollutants As, Cr, Mo and V due to changes of E H /pH-values, DOC, Fe, Mn and SO 4 2− ...
... nduced mobilization and immobilization processes of these elements in contaminated and slightly acidic floodplain soils are still rare. Frohne et al. (2011) have studied the impact of soil E H on metal mobilization and biomethylation of As. However, this was in soil slurry by using an automated biogeochemical microcosm system on a laboratory scale. Rupp et al. (2010) have examined the solubility of As and Cr under different water levels within a short period. Nevertheless, little is known about the behavior of Mo and V in floodplain soils. In particular, the impact of long and short term flood–dry-cycles on the dynamics of soluble As, Cr, Mo and V and their determining factors in acidic contaminated ...
... Under reduced and acidic soil conditions the OM will decomposed which leads to the release of DOC and the attached As, Cr, Mo into the pore water (e.g. Evans and Barabash, 2010; Grybos et al., 2007; Rupp et al., 2010). However, the relation between Mo and DOC was stronger compared to As and Cr. ...
... Especially at sites with strong periodic changes in soil moisture, redox processes act as key factor for temporal variations in the dissolved phase of metals and metalloids . Hence, pore waters in floodplain soils can underlie natural fluctuations of bioavailable pollutants during seasonal changes of hydrological conditions (van Griethusen et al. 2005) or episodic flood and low water events (Rupp et al. 2010). Extent and consequences of redox changes hereby depend on the continuity, frequency and intensity of inundation (Du Laing et al. 2007), as well as on the specific properties of the affected substrate (Schwartz et al. 2003). ...
... In sampling site ''Fr'' as well as in profile ''Fb2,'' a higher seasonal variability of groundwater levels and redox conditions induces stronger seasonal variations of these elements. Significant correlations between eH and DOC contents, as reported by Rupp et al. (2010), were not found in middle or deeper soil zones. ...
The effects of changing soil moisture conditions and oxidation–reduction (redox) processes on dissolved fractions of arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) were studied in floodplain soils in the Lower Lahn Valley (Germany). Multiple weirs and locks affect the groundwater levels in the adjacent river banks by modifying the river’s discharge rate. Redox conditions act as a key factor for sorption and desorption processes and are strongly regulated by groundwater levels. Hence, floodplain soils situated up- and downstream of impounded river segments were characterized by various contents of their mobile heavy metal fraction. To quantify the variations of the dissolved heavy metal concentrations during seasonal and periodic fluctuations of the groundwater levels, a 2-year field study was conducted. The results indicated that higher seasonal changes of river discharge downstream of a weir caused higher amplitudes of groundwater levels, redox changes and variations in dissolved As, Fe and Mn in soil depths (50–60 cm) with a strong groundwater influence. Upstream of a weir, higher dissolved concentrations and more smooth variations of As, Fe and Mn dominated within the same depths. A high rise of capillary waters within the same study site caused significant enrichments of dissolved Cd and Zn in the middle (25–35 cm) of the soil profile. The comparison of floodplain soils along the Lahn River showed how the stream regulations influence heavy metal concentrations of soil pore waters, which may in turn influence the quality of the river water.
... The intensity of soil reduction can be rapidly characterized by soil oxidation-reduction (redox) potential (E H ), which allows for the prediction of the mobilization of various nutrients and PTEs in soils and sediments (e.g., Yu et al., 2007;DeLaune and Seo, 2011;Shaheen et al., 2016). The mobilization of PTEs under different wetting and drying conditions is controlled by E H and pH, dissolved organic carbon (DOC), iron (Fe)manganese (Mn) oxides, and sulphate (SO 4 2-) Rupp et al., 2010;Shaheen et al., 2014b,c;Rinklebe et al., 2016a,b;Shaheen et al., 2016). Thus, according to the state-of-the-art of soil science in wetlands, we hypothesized that different wetting and drying conditions in wetland soils and sediments may affect the mobilization of the redox-dependent pollutants due to changes of E H /pH-values, DOC, Fe, Mn and SO 4 2-. ...
... The Fe/Mn oxide-bound Pb and Zn would be released during reductive dissolution of Fe/Mn oxides in reducing conditions (Guo et al., 2014). Therefore, reductive dissolution of Fe/Mn oxides might be the major cause for Pb and Zn mobilization in the moderately reducing conditions in the fish farm sediments, which is the most accepted mechanism for high Pb and Zn mobilization under wetting conditions in these sediments (Frohne et al., 2011;Rupp et al., 2010;Shaheen et al., 2014b). Those findings suggest that the chemistry of both Fe and Mn might important for the mobilization of soluble Zn in the fish farms sediments. ...
Heavy metal contamination of soils has been a long-standing environmental problem in many parts of the world, and poses enormous threats to ecosystem and human health. Spatial distribution and mobilization of heavy metals in wetlands is crucial to assessing environmental risks from contaminated soils and sediments. In this study, the spatial variability of total and mobile concentrations of copper (Cu), iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn) in soils and sediments of three different wetland soils and sediments in north of the Nile Delta, Egypt were assessed. Furthermore, the impact of wetting and drying conditions on the total and mobilization of the metals in the different wetlands were investigated. Soil and sediment samples were collected under dry and wet conditions from three different wetland ecosystems i.e., rice paddy soils (RS), fish farms sediments (FFS), and Burullus Lake sediments (BLS). Total (Aqua regia) and mobile (ammonium bicarbonate–diethylenetriaminepentaacetic acid) concentrations of the metals were extracted. Geo-statistical analytical technique (ArcGIS 10) was used to interpolate data for mapping spatial variability of the metals in the studied area.
The soils were alkaline and poor in organic carbon content. The texture of the RS and FFS was dominated by silt and clay, while the BLS was characterized by a relatively high content of sand followed by silt, and clay respectively. The total metal concentrations (mg kg-1) ranged from 4.0 to 76.5 for Cu, 3100.0 to 80350.0 for Fe, 86.8 to 1107.0 for Mn, 0.2 to 3.8 for Pb, and from 14.3 to 140.0 for Zn. The concentrations (mg kg-1) of mobile Cu, Fe, Mn, Pb, and Zn varied from 0.2 to 16.0, 8.0 to 123.1, 0.3 to 4.8, 0.2 to 3.8, and from 0.04 to 4.5, respectively. Mobilization of Cu decreased significantly under wetting/reducing conditions in in the three wetlands probably caused by sulfide precipitation and as a result of the reduction of Cu2+ to Cu1+. Mobilization of Fe and Mn significantly increased under wetting conditions in the three wetlands, which might be explained by reduction of Fe-Mn (hydr)oxides to soluble Fe2+ and Mn2+. Mobilization of Pb and Zn showed an inconsistent trend under drying and wetting conditions in the wetlands. Our findings suggest that the wetland types and flood-dry conditions affect metal mobilization in the soils and sediments. These results are an aid to provide information’s aiming to develop a reliable risk assessment and the sustainable management of those wetland ecosystems.
... More technical details of the system are provided in Yu and Rinklebe (2011). This system was successfully employed in previous studies for the determination of the dynamics of PTEs (Frohne et al., , 2014(Frohne et al., , 2015Rinklebe et al., 2016a,b;Rupp et al., 2010;Shaheen et al., 2014a). In addition, this system was used for the investigation of trace gases (Yu et al., 2007), for the quantification of mercury emissions , and mercury methylation (Frohne et al., 2012). ...
... The Fe/Mn oxide-bound As would be released during reductive dissolution of Fe/Mn oxides in reducing conditions (Guo et al., 2014). Therefore, reductive dissolution of Fe/Mn oxides was the major cause for As mobilization in the moderately reducing conditions, which is the most accepted mechanism for high As groundwater in Southeast Asia (Guo et al., 2014;Islam et al., 2004) and in soil solution Rupp et al., 2010;Shaheen et al., 2014b). Recently, Ying et al. (2013) found that As(III) oxidation by birnessite is appreciable in the presence of O 2 only; oxidation of As(III) to As(V) by Mn-oxides under anaerobic conditions might appear as a result of microbially mediated Mn(IV/III) reduction. ...
... However, it should also be kept in mind that the results of this study carried out under laboratory conditions might be different from field conditions. According to Du Laing et al. (2009b) and Rupp et al. (2010), the effects of soil water changes on metal availability were less pronounced in field conditions than in controlled greenhouse conditions. This difference might be attributable to three factors: firstly, the more distinct variation in the redox potential in controlled conditions; secondly, the sieved and air-dried soils used in the laboratory might result in different changes in available metal fractions compared to natural undisturbed soils; and thirdly, differences in soil sampling and sample processing may lead to different effects on soil biological properties which in turn influence metal availability (Du Laing et al. 2009b). ...
... This difference might be attributable to three factors: firstly, the more distinct variation in the redox potential in controlled conditions; secondly, the sieved and air-dried soils used in the laboratory might result in different changes in available metal fractions compared to natural undisturbed soils; and thirdly, differences in soil sampling and sample processing may lead to different effects on soil biological properties which in turn influence metal availability (Du Laing et al. 2009b). Although less pronounced effects in field conditions, the same factors control metal mobility induced by soil water variations in greenhouse and field conditions (Du Laing et al. 2009b), and the changing trend of metal availability is also similar in laboratory and field conditions (Rennert et al. 2010;Rupp et al. 2010). ...
Purpose Variation in soil moisture content can change metal availability. However, the effects of soil drying during wetting-drying cycles on metal availability have been little investigated. Metal availability to an imposed sink can be assessed by the diffusive gradients in thin film (DGT) technique. The purpose of this study was therefore to investigate the effects of the soil drying processes and previous soil moisture contents on metal availability using DGT. Materials and methods Two metal-polluted agricultural soils with contrasting pH (one acid and one calcareous) were collected from agricultural fields and were repeatedly phytoextracted with a Zn/Cd hyperaccumulator. Both soils, with and without phytoextraction, were subjected to two soil drying processes, i.e. drying from flooded conditions to 50 % maximum water holding capacity (WHC) and drying from 100 to 30 % WHC. Changes in metal availability induced by changing soil water moisture were examined using DGT. Results and discussion In acid soils, the availability of cadmium (Cd), zinc (Zn) and nickel (Ni) (but not copper) increased with drying from saturation to 50 % WHC. Drying soil from 100 to 30 % WHC had weak or no significant effects on available metals. Availabilities of Cd, Ni and Zn correlated well with available Al for both drying conditions. In calcareous soil, a decreasing trend of metal availability with soil drying from saturation to 50 % WHC or from 100 to 30 % WHC was found. Soils were also subjected to different wetting-drying cycles prior to drying. In acid soil, available copper (Cu) was correlated with dissolved organic carbon (DOC). Available Cd, Ni and Zn were correlated with available Al and increased with soil wetting-drying cycles in phytoextracted soil, but not in non-remediated soil. In calcareous soil, available Cu and Ni were correlated well with DOC and were higher with long dry periods. However, available Cd and Zn were lower in soils dried from the cycle of saturation to 50 % WHC. Conclusions The results indicate that soil water regimes can be manipulated to alleviate soil metal availability, but they must be tailored to individual metals and different soil types, and soil moisture content before drying should be considered when dried soils are used for evaluation of metal availability.
... The restricted diffusion of oxygen in flooded soil, coupled with the oxygen consumption by soil organisms, creates a reducing environment in which the pH gradually approaches neutrality and the soil Eh decreases accordingly [13,43]. As the Eh value decreases, Cr(VI) can undergo reduction to Cr(III) in the presence of various reductants, including organic matter, Fe(II) and sulfide [44][45][46][47]. Concurrently, the concentration of Cr(VI) in the AWD treatment exhibited fluctuations corresponding to changes in soil Eh. ...
Indoor incubation experiment was conducted under flooding (FD), 100% field capacity (100% FC), and alternating wetting and drying (AWD) conditions for 90 days using Guangdong (GD) and Jiangxi (JX) paddy soils spiked with hexavalent chromium [Cr(VI)]. The chromium speciation and availability were investigated usingsequential extraction, diethylene triamine pentaacetic acid (DTPA) leaching, and alkali solution extraction methods. The concentrations of Cr(VI), acid-extractable Cr and DTPA-Cr were reduced by 72%–89%, 48%–81%, and 42%–98%, respectively, at 90 d compared with 1 d. The sequence for acid-extractable Cr and DTPA-Cr concentrations was 100% FC>AWD>FD. While, it was AWD>100% FC>FD for Cr(VI) concentrations. Acid-extractable Cr, DTPA-Cr, and Cr(VI) concentrations in JX soil were higher compared with GD soil. The changes of DTPA-Cr concentrations were well fitted by Elovich kinetic model. These findings revealed water management and aging greatly affected chromium speciation and availability, having potential implications for sustainable agriculture and human health.
... That is, redox conditions are well defined and reproducible, and can be rapidly changed. In addition, the impact of E H can be investigated independently from other soil parameters (Rinklebe et al., 2016;Rupp et al., 2010). Thus, a total of 30 serum bottles were placed in a horizontal shaker and shake with a speed of 220 rpm min − 1 at 25 • C in the dark. ...
... From the variation of Eh value in this study, the Eh in the BA and BE presented a trend of decreasing firstly to about −300 mV in 42 days and then increasing slightly to −100 mV. The trend of Eh suggested that the system was gradually changing to a reducing state and then benefiting from the conversion of Cr(VI) to stable Cr(III) [6,52]. This is a promising and developing technology for the future to realize the efficient bioremediation of Cr(VI) [6,53]. ...
Unchecked releases of industrial waste, including chromium smelting slag (CSS), have resulted in disastrous effects on the environment for human use. Considering the problems of environment, efficiency, and sustainability, the present research was designed to evaluate the potential feasibility of Cr(VI) bioremediation by different strategies of natural attenuation (NA), bioaugmentation (BA), biostimulation (BS), and bioenhancement (BE). Results showed the BE was the best strategy for Cr(VI) removal and reached 86.2% in 84 days, followed by the BA, BS, and NA. The variation of Eh values indicated all systems translated the oxidation state into reduction continuously except for NA and BS during the bioremediation process. After bioremediation, the Tessier sequential extraction analyzed in the BE showed stable chromium levels up to 97%, followed by BA (89~93%), BS (75~78%), and NA (68%), respectively. Moreover, High-throughput sequencing was also used to assist in revealing the differences in microbial community structure between the different strategies. Stenotrophomonas, Ochrobactrum, and Azomonas, as the bioremediation microbes, were enriched in the BE in comparison with the others. This provided a new enhancement strategy for bioremediation microbes colonized in a new environment to achieve sustainable removal of Cr(VI).
... The Eh-value of the soil may be the most influential aspect regarding the biochemical behavior of metals in soil, particularly the ones with varying oxidation states like Cr (Van den Berg et al., 1994). Hazardous Cr(VI) may be converted to less harmful Cr(III) in soils that are subjected to deteriorating conditions, which then results in the precipitation and immobilization of Cr(III) (Rupp et al., 2010;Xiao et al., 2015). This procedure is utilized as a crucial phase in the management of soils that are polluted with Cr (Pettine, 2000). ...
Chromium (Cr) is released into the environment through anthropogenic activities and has gained significant attention in the recent decade as environmental pollution. Its contamination has adverse effects on human health and the environment e.g. decreases soil fertility, alters microbial activity, and reduces plant growth. It can occur in different oxidation states, with Cr(VI) being the most toxic form. Cr contamination is a significant environmental and health issue, and phytoremediation offers a promising technology for remediating Cr-contaminated soils. Globally, over 400 hyperaccumulator plant species from 45 families have been identified which have the potential to remediate Cr-contaminated soils through phytoremediation. Phytoremediation can be achieved through various mechanisms, such as phytoextraction, phytovolatilization, phytodegradation, phytostabilization, phytostimulation, and rhizofiltration. Understanding the sources and impacts of Cr contamination, as well as the factors affecting Cr uptake in plants and remediation techniques such as phytoremediation and mechanisms behind it, is crucial for the development of effective phytoremediation strategies. Overall, phytoremediation offers a cost-effective and sustainable solution to the problem of Cr pollution. Further research is needed to identify plant species that are more efficient at accumulating Cr and to optimize phytoremediation methods for specific environmental conditions. With continued research and development, phytoremediation has the potential to become a widely adopted technique for the remediation of heavy metal-contaminated soils.
... These findings have substantial implications for management and remediation of abandoned mine spoils. More specifically, encouraging aerobic conditions shall mitigate As release and its potential loss from the studied mine field, and thus mitigating the associated environmental and human health risks.. Beckers et al., 2019;El-Naggar et al., 2018;Pigna et al., 2009;Rinklebe and Shaheen, 2017;Rupp et al., 2010;Wang et al., 2021;Wolersdorfer, 2008;Yu et al., 2007. CRediT authorship contribution statement Bernd Marschner: Supervision. ...
Arsenic (As) redox-induced mobilisation and speciation in polluted gold mine sites in tropical climates largely remains unknown. Here, we investigated the impact of changes in soil redox potential (EH) (-54 mV to +429 mV) on mobilisation of As and its dominant species in an abandoned spoil (total As = 4,283 mg/kg) using an automated biogeochemical microcosm set-up. Arsenic mobilisation increased (85-137 mg/L) at moderately reducing conditions (-54 mV to + 200 mV)), while its reduced (6-35 mg/L) under oxic conditions (+200 to +400 mV). This indicates the high risk of As potential loss under reducing conditions. The mobilisation of As was governed by the redox chemistry of Fe. XANES analysis showed that sorbed-As(V)-goethite, sorbed-As(III)-ferrihydrite, scorodite and arsenopyrite were the predominant As species in the mine spoil. As(V) dominated at oxic conditions and As(III) predominated at moderately reducing conditions, which may be attributed to either inability of arsenate bacteria to reduce As or incomplete reduction. Lower Fe/As molar ratios during moderately reducing conditions show that the mine spoil may migrate As to watercourses during flooding, which may increase the hazardous effects of this toxic element. Therefore, encouraging aerobic conditions may mitigate As release and potential loss from the mine field.
... To date, several studies have suggested that the transformation of Cd fractions is greatly affected by soil properties [12][13][14][15]. For example, Yu et al. [16] confirmed that the addition of humic acid can effectively reduce the mobility and bioaccessibility of Cd in soil. ...
Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.
... Chromium speciation is highly regulated by redox potential of the soil as chromium exhibits various oxidation states (Xiao et al. 2015). Reduced soil condition promotes conversion of hexavalent chromium in less toxic trivalent form (Rupp et al. 2010). Neutral to alkaline pH of soil can store Cr(VI) if it contains high oxygen level. ...
Heavy metal contamination in the environment has been considered as an important threat to the life in recent days. ChromiumChromium contamination is also listed among the potential threat to the human and animals as well as plants. Chromium is a ubiquitous metal having three main oxidation states viz., Cr2+, Cr3+ and Cr6+. Among these, divalent form is unstable. Chromium and its particulates are excreted into the environment from different industries like tanneriesTanneries, textiles, ore miningMining, printing-photographic houses, dyeingDyeing factories, electroplating workshops and medical industries. Hexavalent chromiumHexavalent chromiumhaving carcinogenicCarcinogenic potentiality is considered to be the most toxic form because it can readily cross the biomembrane of organisms. Chromium can contaminate soilSoil, groundwaterGroundwater and surface water. To render the contaminated resource reusable, chromium must be removed physically or by using the techniques of bioremediationBioremediation. BioremediationBioremediation has been considered as the future of waste management technologies for sustainable development. The process includes the involvement of plants and microbesMicrobes that are capable of absorbing, degrading and removing contaminated chromium from the environment. Usually, the process can be practiced both Ex situex situ and In situin situ taking the advantage of natural homeostasis mechanism of environment. Among these two, in situ practice is cheaper and environment friendly.
... Furthermore, there are indications that the DOC concentration in the soil solution depends on the redox potential (E H ) of the soil. As a result of lysimeter and field experiments, we have found that DOC increased with decreasing E H [92]. ...
As a result of global climate change, heavy rainfall events and dry periods are increasingly occurring in Germany, with consequences for the water and solute balance of soils to be expected. The effects of climate change on nitrogen and carbon leaching were investigated using 21 non-weighable manually filled lysimeters of the UFZ lysimeter facility Falkenberg, which have been managed since 1991 according to the principles of the best management practices and organic farming. Based on a 29-year dataset (precipitation, evaporation, leachate, nitrate and dissolved organic carbon concentrations), the lysimeter years 1995/96, 2018/19, and 2003/04 were identified as extremely dry years. Under the climatic conditions in northeastern Germany, seepage fluxes were disrupted in these dry years. The reoccurrence of seepage was associated with exceptionally high nitrogen concentrations and leaching losses, which exceeded the current drinking water limits by many times and may result in a significant risk to water quality. In contrast, increased DOC leaching losses occurred primarily as a result of increased seepage fluxes.
... This MC system has been proven to be an efficient tool to study the redox-induced behaviors of trace elements including As in different soils (e.g., Frohne et al., 2011;Shaheen et al., 2014;El-Naggar et al., 2019;). A previous study proved that the results collected in the MC experiment are comparable to those in the field (Rupp et al., 2010). In the current study, each glass bottle was filled with 210 g of pre-incubated soils (Sections 2.3) and 1,680 mL of tap water (soil: water = 1: 8, w/v). ...
Iron (Fe)-modified biochar, a renewable amendment that synthetizes the functions of biochar and Fe materials, demonstrates a potential to remediate arsenic (As)-contaminated soils. However, the effectiveness of Fe-based biochar to immobilize As in paddy soils under varying redox conditions (Eh) has not been quantified. We tested the capability of the raw (RBC) and Fe-impregnated (FeBC) biochars to immobilize As in a paddy soil under various Eh conditions (from -400 to +300 mV) using a biogeochemical microcosm system. In the control, As was mobilized (686.2–1,535.8 μg L⁻¹) under reducing conditions and immobilized (61.6–71.1 μg L⁻¹) under oxidizing conditions. Application of FeBC immobilized As at Eh < 0 mV by 32-81% compared to the control, due to the transformation of As-bound Fe (hydro)oxides (e.g., ferrihydrite) and the formation of complexes (e.g., ternary As-Fe-DOC). Application of RBC immobilized As at Eh < -100 mV by 61-41% compared to the control, due to its porous structure and oxygen-containing functional groups. Mobilized As at Eh > +200 mV was caused by the increase of pH after RBC application. Amendment of the Fe-modified biochar can be a suitable approach for alleviating the environmental risk of As under reducing conditions in paddy soils.
... For the investigation of element and ion concentration changes in pore water, lysimeter studies can be used, which allows element monitoring in soil columns of intact soil structure, as well as a close monitoring of various related parameters such as the Eh (Meissner, Rupp, & Haselow, 2020;Rupp, Meissner, & Leinweber, 2018;Rupp, Rinklebe, Bolze & Meissner, 2010;Shaheen, Rinklebe, Rupp, & Meissner, 2014). Usually, leachate of whole soil columns has been investigated (Andersson, Bergström, Ulén, Djodijic, & Kirchmann, 2015;Siddique, Robinson, & Alloway, 2000), and studies analyzing pore water from different soil depths have most often been done with suction cups or suction plates (Koch, Kahle, & Lennartz, 2019;Siemens & Kaupenjohann, 2002). ...
For arable soils, it is not clear whether closing a controlled drainage system leads to P mobilization due to water table rise and associated changes in redox‐induced biogeochemical processes. Therefore, we investigated P mobilization at different redox conditions using three spring barley (Hordeum vulgare L.) cropped lysimeters filled with monoliths of arable northeastern German soil profiles. Pore water samples were collected weekly from three different depths, and dissolved (<0.45 μm) element concentrations of total C, P, Al, Fe, Mn, Ca, Mg, and K, as well as inorganic and organic C (DIC and DOC) and P (Pi and Po), SO4²⁻–S, and NO2⁻–N and NO3⁻–N were determined. The total P concentration in pore water collected from a given lysimeter at a given time was 1.8 mg P L⁻1 maximum. Organic P concentrations in subsoil solutions were positively correlated with Fe concentrations. Grain yield of spring barley ranged between 5.6 and 6.5 Mg ha⁻1, and total biomass P uptake was negatively correlated with the stable P stocks of the soil profiles. Results suggest that reductive conditions in subsoils led to dissolution of pedogenic Fe‐(oxy)hydroxides and release of Po compounds, the latter of which were more important for biomass P uptake than P released from stable P compounds. Overall, closing the drainage at the field site could represent a moderate P mobilization risk, which would probably be lower compared with a P mobilization risk caused by a heavy rainfall event.
... Soil water conditions can not only affect the pH, but also change the redox conditions of the soil, thereby affecting the oxidation and reduction processes of Cr (Kozuh et al., 2000;Xiao et al., 2015). When a paddy field is flooded, reduced conditions lead to the reduction of highly mobile Cr(VI) species into less mobile Cr(III), thereby reducing the uptake of Cr by rice plants (Rupp et al., 2010;Xiao et al., 2015). In contrast, compared with flooding irrigation, appropriate field drying, such as alternating wetting and drying, leads to dynamic changes in the soil redox potential (Eh), which may enhance the Cr uptake in rice plants (Brookshaw et al., 2014;Somenahally et al., 2011;UdDin et al., 2015). ...
Chromium (Cr) pollution in soil is a global problem owing to its wide industrial use. The mobility, toxicity, and crop uptake of Cr depends on its valence state. Cr(VI) is highly mobile and toxic whereas Cr(III) is generally considered immobile and less toxic. We performed a pot experiment to investigate the combined effects of rice straw-derived biochar and water management on transformation of Cr and its uptake by rice in contaminated soils. The main plots had water management treatments of alternating wetting and drying (AWD) and continuous flooding (CF), and the subplots had three levels of straw biochar (0, 5, and 10 g kg⁻¹). The results showed that water management and the addition of biochar had a significant effect on the dynamics of soil redox potential (Eh), pH, dissolved organic carbon (DOC), and Fe(II) concentration. As these parameters are important factors affecting Cr transformation in paddy soils, the dynamics of the Cr(III) and Cr(VI) concentrations were clearly different under different treatments. The highest reduction of Cr(VI) was observed in the treatment with CF water management in combination with 10 g kg⁻¹ of biochar amendment, which resulted in a 62% reduction of Cr(VI) to Cr(III) in soil. The alterations in the oxidation state of Cr greatly affected its accumulation in the rice grains. The CF combined with 10 g kg⁻¹ of biochar treatment, caused the Cr concentration in rice grains to be 66.2% lower compared with that of the unamended control under AWD water management. Possibly owing to the reduction in phytotoxic effects of Cr(VI), the combined treatment showed an improvement in rice grain weight. In conclusion, the combination of 10 g kg⁻¹ of biochar amendment and CF water management may potentially be used in Cr-contaminated soil to mitigate the impacts of Cr contamination on rice production.
... It remains questionable if the strong sorption is determined by a high binding capacity of the sediments or by high proportions of largely immobile Cr(III), as reported for sediments under reducing conditions (Masscheleyn et al., 1992). In the latter case, more oxic conditions, during a longer duration of sediment exposure, should slightly favor the mobilization of more mobile Cr(VI) (Rupp et al., 2010). However, this was not observed in the pore water of the Klingenberg Reservoir. ...
Dam draining can impact dissolved heavy metal concentrations in discharge water. • Amounts of downstream transported metals vary temporally and element-specifically. • Redox changes after emptying affect heavy metal pore water concentrations. • Pore water chemistry before emptying influences the metal export to surface water. The draining of a dam is a relatively rare event, however, it can have severe consequences for a watercourse connected to that reservoir. In order to understand the effects of the draining on the mobility of pollutants stored in the bottom sediments, the concentrations of heavy metals and arsenic were measured in pore water, river water, and sediments sampled from three emptied reservoirs in Germany. Two of these sites were analyzed immediately after the draining, while the third reservoir was studied one and a half years after the complete discharge of the stored water. Heavy metal and arsenic concentrations within the sediments varied among the studied dams as a result of different geological characteristics and the degree of anthropogenic impacts. Based on the analysis of pore water samples, the concentrations of heavy metals and arsenic were not significantly altered shortly after the draining. However, increased concentrations of As, Fe, Cd, Ni, and Zn were measured in pore water samples after a longer duration of sediment exposure, which altered the redox conditions and sediment properties. The changes in Cu, Cr, Mn, and Pb concentrations in pore water samples were less pronounced. As a result of the pore water drainage increased dissolved heavy metal concentrations were found in the discharge water immediately after draining. At the third site, which had been emptied for one and a half years, only for Mn, a concentration increase was detected in the reservoir discharge water, which emphasizes the strong temporal dynamic of the mobilization of the analyzed elements.
... In extreme cases even Fe(II)-containing minerals may be crystallized as a result of such reduction, as revealed in studies concerning waterlogged soils and aquatic sediments (Rothe et al., 2016). Subsequently, the solubility of TEs under flooding conditions is controlled by the redox potential (E H ), pH, the presence of electron carriers such as dissolved organic carbon (DOC), and the chemical behavior of Fe, Mn, and sulphur (S) (Rupp et al., 2010;Shaheen et al., 2014a;Rinklebe et al., 2016b,c,d;Shaheen et al., 2016;Rinklebe and Shaheen, 2017). Flooding conditions and the prevailing E H could in turn affect uptake and translocation of essential elements and contaminants by plants (Kashiwagi et al., 2009;Zimmer et al., 2011;Ye et al., 2012). ...
Trace elements (TEs) are deposited to soils mainly due to anthropogenic activities and pose a significant threat to human health. In this review we aimed at (a) discussing the phytoavailability of TEs as affected by various soil parameters, and by plant defense mechanisms related to uptake and translocation; (b) examining soil and plant indices related to TE phytoavailability; (c) clarifying the challenges and problems related to phytoremediation; and (d) exploring the often encountered discrepancies of lower-than-expected TE toxicity. We particularly discussed the soil-to-plant availability index (transfer coefficient, TC), because it encompasses all soil and plant factors related to TE phytoavailability. As for soil, we explored the effect of pH, redox potential, clay and organic matter contents, as well as aging of added elements. The latter is a key factor in interpreting the observed lower-than-expected toxicity to plants in real field conditions. This is because the discrepancy is very often generated by growth experiments that expose plants to TEs directly from TE-laden solutions or by studies that spike soils with TEs only days or weeks before planting. Also, the behavior of TEs depends on the nature and quantity of TEs. As for plant, TE absorption or exclusion is highly related to species-specific defense mechanisms developed by plants so that they are exposed to TE-induced stress. These mechanisms address TE exposure by operating both outside and inside the plant body; outside with the assistance of root exudates, and the rhizosphere microflora, and inside with selective translocation and storage processes. The absorption/exclusion behavior of plants also depends on root activities and related soil chemical processes which are highly localized within a spatial scale of a few mm from roots. Novel techniques for the imaging of TE biogeochemistry at the root-soil interface are therefore addressed and their explanatory power is demonstrated. Such plant behavior greatly affects phytoremediation, a process which also depends on the maximal TE uptake capacity of plants, especially of hyperaccumulators. However, phytoremediation also greatly depends on plant biomass yield, an important factor in determining the time required to complete the procedure. In conclusion, soil factors, as well as plant- and TE- related issues, may create discrepancies in TE phytoavailability and phytoremediation that need to be thoroughly understood and addressed.
... Soil Eh can be the dominating factor affecting biochemical behavior of metals especially those having various oxidation states (such as Cr) in soil (van den Berg et al., 1994). Reduced soil conditions cause conversion of toxic Cr (VI) into less toxic Cr (III), as well as immobilization and precipitation of Cr (III) (Rupp et al., 2010;Xiao et al., 2015). This process is being used as a key step in treatment of Cr-contaminated soils (Pettine, 2000). ...
Chromium (Cr) is a potentially toxic heavy metal which does not have any essential metabolic function in plants. Various past and recent studies highlight the biogeochemistry of Cr in the soil-plant system. This review traces a plausible link among Cr speciation, bioavailability, phytouptake, phytotoxicity and detoxification based on available data, especially published from 2010 to 2016. Chromium occurs in different chemical forms (primarily as chromite (Cr(III)) and chromate (Cr(VI)) in soil which vary markedly in term of their biogeochemical behavior. Chromium behavior in soil, its soil-plant transfer and accumulation in different plant parts vary with its chemical form, plant type and soil physico-chemical properties. Soil microbial community plays a key role in governing Cr speciation and behavior in soil. Chromium does not have any specific transporter for its uptake by plants and it primarily enters the plants through specific and non-specific channels of essential ions. Chromium accumulates predominantly in plant root tissues with very limited translocation to shoots. Inside plants, Cr provokes numerous deleterious effects to several physiological, morphological, and biochemical processes. Chromium induces phytotoxicity by interfering plant growth, nutrient uptake and photosynthesis, inducing enhanced generation of reactive oxygen species, causing lipid peroxidation and altering the antioxidant activities. Plants tolerate Cr toxicity via various defense mechanisms such as complexation by organic ligands, compartmentation into the vacuole, and scavenging ROS via antioxidative enzymes. Consumption of Cr-contaminated-food can cause human health risks by inducing severe clinical conditions. Therefore, there is a dire need to monitor biogeochemical behavior of Cr in soil-plant system.
... Agricultural soils worldwide reveal often high levels of HMs primarily due to anthropogenic activities (Bolan et al., 2014). The HMs in agricultural soils can be translocated to food crops and cause serious concerns associated with food safety (Shaheen and Rinklebe, 2015), and they can undergo several transformations, which are highly contingent on the biochemical and physical conditions, including soil pH, redox potential (Eh), soil texture, organic matter (OM) content, mineralogy, and microbial activities (Rupp et al., 2010;Shaheen et al., 2013). Consequently, the bioavailability of these HMs depends on the total HMs content, the stability of geochemical fractions, and dynamic soil biochemical properties. ...
... variations (Shaheen et al�, 2014a,b)� The solubility of PTEs under flooding conditions is controlled by redox potential (E H ), pH, and carriers of metals such as dissolved organic carbon (DOC), Fe, Mn, and SO 4 2− (Du Laing et al�, 2009;Rupp et al�, 2010;Rinklebe and Du Laing, 2011;Shaheen et al�, 2014a,b,c;Rinklebe et al�, 2016a,b;Shaheen et al�, 2016)� The PTEs can be redistributed into different geochemical fractions, released from the soil to soil solution, and transferred to the ecosystem and food chain, thereby posing a hazard to human and environmental health (Du Laing et al�, 2009;Shaheen et al�, 2014aShaheen et al�, ,b, 2015aSchulz-Zunkel et al�, 2015;Shaheen et al�, 2016)� ...
Temporary flooded soils around the world are often polluted by potentially toxic elements (PTEs). Wetlands are characterized by a highly dynamic and variable hydrological regime, which have considerable impacts on the mobilization and bioavailability of metals. Studies on factors controlling dynamics of PTEs in soils is challenging because the obtained results should elucidate the underlying processes and allow to explain their fate in the environment. Knowledge about the fate of PTEs in the ecosystem are required to answer both scientific and practical questions regarding protection of groundwater and plants, sustainable management of soils or explain the pathways of environmental harmful substances. Dynamics of redox-sensitive processes is of large importance for flooded soils as the location of the oxic–anoxic interface is subject to change due to fluctuating water table levels. Dynamics and release of PTEs in temporary flooded flood soils is determined by a complex of effects as metal concentrations, EH, pH, adsorption/desorption processes, the presence of Fe-Mn oxides, SOM, and total sulfur (Du Laing et al., 2009; DeLaune and Seo, 2011).
In many investigations, a significant concentration of the total Cd in flooded soils was observed in the mobile fraction, while the total Cu, Co, Cr, Ni, V, and Zn concentrations were dominated by less available fractions and large portions were assigned to fractions interpreted as Mn- and Fe-sorbed metals or to the residual fraction. This suggests that the potential mobility and bioavailability of many PTEs probably decline in the following order: Cd > Pb > Zn > Cu> Cr > Ni, suggesting greater mobility of Cd which mean that Cd in these soils is easily accumulated by plants through the root system, the concentration of Cd in the paddy soils could be a concern to human health (Zimmer et al., 2011; Jalali and Hemati, 2013; Rinklebe and Shaheen, 2014; Shaheen and Rinklebe, 2014; Shaheen et al., 2015a).
The dynamics of PTEs depend on the inundation periods and the reducing-oxidizing conditions. Therefore, the release of PTEs under different flood-dry cycles might be increased which might create potential environmental risks in using metal-enriched soils in temporary flooded agricultural systems (Du Laing et al., 2009; Rupp et al., 2010; DeLaune and Seo, 2011 Frohne et al., 2011; 2014; 2015; Shaheen et al., 2014a,b,c; ; Rinklebe et al., 2016a,b). In particular, numerous findings suggest that release of PTEs from temporally flooded soils should be considered due to increased mobility and the potential environmental risks in using metal-enriched soils in flooded agricultural systems (Shaheen et al., 2014a,b,c; Rinklebe and Shaheen, 2014).
Flooding conditions affect the availability of nutrients and PTEs to plants. Several plant species showed lower Cd, Cu, and Zn uptake in reduced soils (Gambrell and Patrick, 1989; Gambrell, 1994). As this evidence suggests that flooding and subsequently reduction of contaminated soils may result in lower environmental bioavailability, it may constitute a valid management option for polluted soils. This means that permanent or temporarily anoxic soils that characterize wetlands help to create conditions for immobilization of PTEs in the highly reduced sulfite or metallic form (Gambrell, 1994). However, other type of plants play an important role in metal removal via filtration, adsorption, and cation exchange, and through plant induced chemical changes in the rhizosphere (Dunbabin and Bowmer, 1992; Carbonell et al., 1998; Wright and Otte, 1999). There are evidences that some of wetland plants can accumulate PTEs in their tissues (Zayed et al., 1998; Vesk et al., 1999; Stoltz and Greger, 2002; Ye et al., 2001; Ye et al., 1997a,b; Shaheen and Rinklebe, 2015a). This means that these type of plants might be successfully used for phytoremediation of PTEs contaminated temporary waterlogged conditions (Stoltz and Greger, 2002; Overesch et al., 2007; Zimmer et al., 2009; Shaheen and Rinklebe, 2015a).
Rice had been considered as a particular crop that had high PTEs especially Cd uptake with depletion of Zn/Fe in its grain (Chaney et al., 2004; Gong and Pan, 2006; Reeves and Chaney, 2008). Consequently, Cd translocation and accumulation in the grain and aerial plant parts of rice could jeopardize of food safety in regions with metal-contaminated rice fields (Kashiwagi et al., 2009; Choppala et al., 2014). Thus, the development of adequate remediation approaches of those contaminated sites leading to reduce the release of metals under reducing conditions in floodplain ecosystems should be a challenge for the near future aiming to minimize the potential risk to humans and to the environment. Various organic and inorganic soil amendments were used to reduce the solubility, phytoavailability of PTEs by rice plants (Ok et al., 2011a,b; Bain et al., 2013; Lee et al., 2013). This is important since contaminated flooded areas are extended overall the world. Therefore, certain trials should to be done by law to conduct an appropriate risk assessment and to implement practical actions to eliminate (or reduce) these environmental problems in floodplain ecosystems.
... Thus, it is possible to study the effect of E H almost independent from other parameters. Recently this system was described in detail by Yu and Rinklebe (2011) and successfully used in previous studies for the investigation of trace gases (Yu et al., 2007), for the quantification of mercury emissions , and for the determination of the dynamics of trace metals (Rupp et al., 2010;Frohne et al., 2011). The current study was conducted in four independent trials for each soil. ...
An automated biogeochemical microcosm system allowing controlled variation
of redox potential (EH) in soil suspensions was used to assess the
effect of various factors on the mobility of mercury (Hg) as well as on the
methylation of Hg in two contaminated floodplain soils with different Hg
concentrations (approximately 5 mg Hg kg−1 and
>30 mg Hg kg–1). The experiment was conducted under stepwise variation from reducing
(approximately −350 mV at pH 5) to oxidizing conditions (approximately
600 mV at pH 5). Results of phospholipid fatty acids (PLFA) analysis indicate
the occurrence of sulfate reducing bacteria (SRB) such as Desulfobacter species (10Me16:0,
cy17:0, 10Me18:0, cy19:0) or Desulfovibrio species (18:2ω6,9), which are considered
to promote Hg methylation. The products of the methylation process are
lipophilic, highly toxic methyl mercury species such as the monomethyl
mercury ion [MeHg+], which is named as MeHg here. The ln(MeHg/Hgt)
ratio is assumed to reflect the net production of monomethyl mercury
normalized to total dissolved Hg (Hgt) concentration. This ratio
increases with rising dissolved organic carbon (DOC) to Hgt ratio
(ln(DOC/Hgt) ratio) (R2 = 0.39, p
... The Elbe River is one of the most polluted major rivers of Europe. Many investigations into the flood events and soil pollution involving this river have been conducted (Ockenfeld et al. 2005, Krüger et al. 2006, Schulz-Zunkel and Krueger 2009, Rupp et al. 2010, Zimmer et al. 2011, Baborowski et al. 2012, Zachmann et al. 2013. The Elbe River is an example of a catchment with old industrial and mine sites, which have caused polluted or contaminated river sediments. ...
Floodplain soils at the Elbe River are frequently polluted by heavy metals. Metal enrichments are linked to the composition of the floodplain's plant community. Various studies have shown that soil characteristics, floodplain geomorphology and other factors may influence plant physiology and have demonstrated an overlapping of heavy metal pollution and growing conditions such as water and nutrient supply. The goal of this study was to assess and separate the current heavy metal contamination of the floodplain vegetation from other parameters using spectrometric laboratory measurements. A standardized pot experiment with floodplain vegetation in differently contaminated soils provided the basis for measurements. Various vegetation indices and spectral methods were used to normalize the spectral curve of the vegetation and to investigate the potential of different methods for separating plant stress in floodplain vegetation. The results of this study show the influence of heavy metals on the spectral characteristics of the focal plants. From eleven tested methods, five showed a significant correlation (R² > 0.6) to heavy metal content. Most methods with a significant correlation to heavy metal also showed a high correlation (R² > 0.5) to other investigated parameters such as chlorophyll content and nutrient content. Only the developed method (band depth at continuum removal spectra at 1725 nm (CR1725)) showed a significant relationship to the heavy metal load (R² = 0.644) and not to other parameters, and can therefore be used as basis for further work in field studies in the context of heavy metal stress in floodplain plants.
... This system allows one to measure the E H , pH, and temperature in each MC every ten minutes, thereby allowing one to mechanistically conduct experiments aimed at exploring underlying geochemical processes under fully controlled conditions. This system has been utilized in previous studies to determine the dynamics of trace metal(loid)s (Anti c-Mladenovi c et al., 2011; Rupp et al., 2010;Frohne et al., 2011Frohne et al., , 2014Frohne et al., , 2015Shaheen et al., 2014a;Rinklebe et al., 2016a,b,c). More technical details of the system are provided in Yu and Rinklebe (2011) and experimental specifics are presented in Supplemental 3. ...
... An automated biogeochemical microcosm system was exploited to simulate flooding of the contaminated soil (CS) and contaminated soil + biochar (CS + BC) in laboratory. This system was successfully employed in previous studies (Antić -Mladenović et al., 2011;Rupp et al., 2010;Frohne et al., 2011Frohne et al., , 2014Frohne et al., , 2015Shaheen et al., 2014a). Technical details are provided in Yu and Rinklebe (2011) and experimental specifics in Supplemental 1. ...
Biochar (BC) can be used to remediate soils contaminated with potential toxic elements (PTEs). However, the efficiency of BC to immobilize PTEs in highly contaminated floodplain soils under dynamic redox conditions has not been studied up to date. Thus, we have i) quantified the impact of pre-definite redox conditions on the release dynamics of dissolved aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) in a highly contaminated soil (CS) (non-treated) and in the same soil treated with BC (CS+BC), and ii) assessed the efficacy of BC to reduce the concentrations of PTEs in soil solution under dynamic redox conditions using an automated biogeochemical microcosm apparatus. The impact of redox potential (EH), pH, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), iron (Fe), manganese (Mn), and sulfate (SO42-) on dynamics of PTEs was also determined. The EH was lowered to +68 mV and afterwards increased stepwise to +535 mV. Significant negative correlation between EH and pH in CS and CS+BC was detected. The systematic increase of EH along with decrease of pH favors the mobilization of PTEs in CS and CS+BC. The addition of BC seems to have little effect on redox processes because pattern of EH/pH and release dynamics of PTEs was basically similar in CS and CS+BC. However, concentrations of dissolved Al, As, Cd, Cu, Fe, Mn, Ni, and Zn were considerably lower in CS+BC than in CS which demonstrates that BC is able to decrease concentrations of PTEs even under dynamic redox conditions.
... Nevertheless, similar studies should be conducted with further serpentine soils from various sites world-wide to verify the detected dynamics and processes. Additionally, research at various scales including field conditions (e.g., Rupp et al., 2010), combined with plants response is recommended in future. ...
... PC3 is divided into eigenvectors with positive (Cu, Mo, Sb, Pb, and As) and negative (Al, Cr, Mn, Ni, Zn, Fe, and Cd) coefficients. The elution mechanisms in tsunami deposits are complex and depend on various physical factors such as pH, cation exchange capacity (CEC) redox potential (Rinklebr and Du, 2011;Du et al., 2009), and the concentration of heavy metals (Rupp et al., 2010). The concentrations of heavy metals in the tsunami deposits are most likely governed by sorption and desorption processes with different soil constituents. ...
Tsunami deposits accumulated on the Tohoku coastal area in Japan due to the impact of the Tohoku-oki earthquake. In the study reported in this paper, we applied principal component analysis (PCA) and cluster analysis (CA) to determine the concentrations of heavy metals in tsunami deposits that had been diluted with water or digested using 1 M HCl. The results suggest that the environmental risk is relatively low, evidenced by the following geometric mean concentrations: Pb, 16 mg kg(-1) and 0.003 ml L(-1); As, 1.8 mg kg(-1) and 0.004 ml L(-1); and Cd, 0.17 mg kg(-1) and 0.0001 ml L(-1). CA was performed after outliers were excluded using PCA. The analysis grouped the concentrations of heavy metals for leaching in water and acid. For the acid case, the first cluster contained Ni, Fe, Cd, Cu, Al, Cr, Zn, and Mn; while the second contained Pb, Sb, As, and Mo. For water, the first cluster contained Ni, Fe, Al, and Cr; and the second cluster contained Mo, Sb, As, Cu, Zn, Pb, and Mn. Statistical analysis revealed that the typical toxic elements, As, Pb, and Cd have steady correlations for acid leaching but are relatively sparse for water leaching. Pb and As from the tsunami deposits seemed to reveal a kind of redox elution mechanism using 1 M HCl.
... Soil microcosms are ideal experimental set-ups for simulating environmental conditions and its influence on soils in the laboratory (Patrick et al., 1973). It also allows for E H /pH changes as well for collecting samples under simulated conditions and has been successfully used in previous studies (Yu et al., 2007;Rinklebe et al., 2010;Rupp et al., 2010;Frohne et al., 2011Frohne et al., , 2012Frohne et al., , 2014. We chose soils from three different hydro-geomorphological units (depression, levee, and plateau) which are typical and representative for floodplains in terms of soil properties, degree of pollution, flooding frequency, and habitat characteristics. ...
... An automated biogeochemical microcosm system was exploited to simulate flooding of the contaminated soil (CS) and contaminated soil + biochar (CS + BC) in laboratory. This system was successfully employed in previous studies (Antić -Mladenović et al., 2011;Rupp et al., 2010;Frohne et al., 2011Frohne et al., , 2014Frohne et al., , 2015Shaheen et al., 2014a). Technical details are provided in Yu and Rinklebe (2011) and experimental specifics in Supplemental 1. ...
Biochar (BC) can be used to remediate soils contaminated with potential toxic elements (PTEs). However, the efficiency of BC to immobilize PTEs in highly contaminated floodplain soils under dynamic redox conditions has not been studied up to date. Thus, we have (i) quantified the impact of pre-definite redox conditions on the release dynamics of dissolved aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) in a highly contaminated soil (CS) (non-treated) and in the same soil treated with 10gkg(-1) biochar based material (CS+BC), and (ii) assessed the efficacy of the material to reduce the concentrations of PTEs in soil solution under dynamic redox conditions using an automated biogeochemical microcosm apparatus. The impact of redox potential (EH), pH, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), iron (Fe), manganese (Mn), and sulfate (SO4(2-)) on dynamics of PTEs was also determined. The EH was lowered to +68mV and afterwards increased stepwise to +535mV. Significant negative correlation between EH and pH in CS and CS+BC was detected. The systematic increase of EH along with decrease of pH favors the mobilization of PTEs in CS and CS+BC. The material addition seems to have little effect on redox processes because pattern of EH/pH and release dynamics of PTEs was basically similar in CS and CS+BC. However, concentrations of dissolved PTEs were considerably lower in CS+BC than in CS which demonstrates that BC is able to decrease concentrations of dissolved PTEs even under dynamic redox conditions.
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... On the other hand, Cr(VI) peaks in AWD treatments were observed during rice maturity stage after long drainage periods at soil Eh values above 100 mV. According to the literature (Rupp et al., 2010), reduced conditions result in the reduction of Cr(VI) into Cr (III) and the immobilization of chromates due to decreasing redox potential (Eh). Du Laing et al. (2009) also reported that soils tend to undergo a series of sequential redox reactions when the redox status of the soil changes from aerobic to anaerobic conditions during flooding. ...
... Organic matter transformation, precipitation/dissolution, complexation, and adsorption/desorption were important processes; overlapping of those processes should also be considered. Nevertheless, a verification of the detected dynamics and processes at various scales including field conditions is recommended in the future (e.g., Rupp et al. 2010). Additionally, similar studies should be conducted with further serpentine soils from various sites world-wide. ...
Purpose Serpentine soils exist in many regions around the world; they are naturally enriched with nickel (Ni). An adequate understanding of soil processes determining Ni solubility is a special need particularly since less research has been addressed to Ni behavior under dynamic and controlled redox conditions. Our aim was (1) to character-ize the properties of a serpentine soil and (2) to determine the impact of predefined redox windows on the mobility and dynamics of Ni in a serpentine soil. Material and methods A soil with high geogenic Ni concentrations from Serbia was incubated using an auto-mated biogeochemical microcosm system. Redox windows were created from reducing to oxidizing conditions in predefined steps of approximately 100 mV. Three micro-cosms were used as replicates; redox potential (E H) and pH were automatically monitored every 10 min. The samples were centrifuged, and the supernatants were immediately filtered under N 2 atmosphere and analyzed for soluble Ni, iron (Fe), manganese (Mn), dissolved organic carbon (DOC), and sulfate (SO 4 2−). X-ray diffraction was per-formed to assess mineral composition of the soil grain-size fractions. Nickel binding forms in the bulk soil were determined by the sequential extraction according to Tessier et al. (1979). Results and discussion Total Ni concentration in the bulk soil was 550 mg kg −1 . Quartz, chlorite, serpentine minerals, and secondary minerals were the prevalent minerals. The residual fraction contained the most Ni (91.3%). Nickel percentages of the fractions: Fe/Mn oxides, organic matter, carbonate, and exchangeable were low. Soluble Ni concen-trations varied in the range 77–166 μg L −1 , showing a linear decrease with increasing E H . Soluble Ni was positive correlated with Fe, Mn, and DOC and inversely correlated with SO 4 2− . Dissolution and precipitation of Fe/Mn oxides, organic matter transformations, and adsorption on solids are important processes controlling the Ni solubility during redox change. Nickel concentrations at definite redox windows were in the same order of magnitude as the exchangeable Ni determined by the sequential extraction procedure. Conclusions Our study demonstrates that considerable amounts of Ni can be mobilized during low E H despite a high Ni retention capacity of the soil. The sequential extraction might provide a reliable estimation of the potential mobile Ni under dynamic redox alterations. The interactions of DOC, pH, Fe, and Mn (hydr)oxides are controlling the dynamics of soluble Ni under changing E H conditions. It is important to verify the detected dynamics at various scales and in other serpentine soils in the future.
... In conclusion, our results might be an aid to answer scientific and practical questions regarding the suitability and efficiency of several emerging and low cost soil amendments and the bioenergy crop rapeseed for phytostabilization of Cd and Pb in contaminated wetlands around the globe. Nevertheless, a verification of the results gained on different scales (Rupp et al., 2010) is recommended in future. ...
... We took nine soil suspension samples during the experiment at defined EH levels. Figure 1.6 Soil microcosm set-up (adapted from: Rupp et al. 2010) ...
... Dynamics of redoxsensitive processes is of large importance for flooded soils as the location of the oxiceanoxic interface is subject to change due to fluctuating water table levels (Du Laing et al., 2009a). Dynamics and release of PTMs in floodplain soils is determined by a complex of effects as metal concentrations, redox potential (E H ), pH, adsorption/desorption processes, the presence of iron (Fe) and manganese (Mn) oxides, organic matter (OM), and total sulfur (S t ) Rupp et al., 2010). ...
We aimed to assess the dynamics of pore water concentrations of Cd, Co, Cu, Ni, Zn and their controlling factors (EH, pH, DOC, Fe, Mn, and SO42-) in a contaminated floodplain soil under different flood-dry-cycles. Two parallel undisturbed groundwater lysimeters (mean values presented) were used for long term (LT; 94 days) and short term (ST; 21 days) flood-dry-cycles. Reducing conditions under LT lead to low EH and pH, while DOC, Co, Fe, Mn, and Ni increased. Cadmium, Cu, Zn, and SO42- increased under oxidizing conditions during ST. Cobalt and Ni revealed a similar behavior which seem to governed by EH/pH, Mn, Fe, and DOC. Cadmium, Cu, and Zn reveal a similar fate; their dynamics were affected by EH/pH, DOC, and SO42-. Our findings suggest that a release of Cd, Cu, Co, Fe, Mn, Ni, and Zn under different flood-dry-cycles can assumed what might create potential environmental risks in using metal-enriched floodplain soils.
... A combined experimental/modeling approach could also be a reliable means to develop indicators to monitor the success of river restoration. We also need studies that combine different spatial scales from the catchment scale to the molecular level as proposed by Rupp et al. (2010). Apart from these temporal and spatial aspects, cross-disciplinary approaches should be fostered in order to tackle most of the discussed research challenges, as has been shown successfully in some of the papers of this special issue. ...
... Furthermore, the effect of E H can be studied independent from other soil parameters. This system was successfully employed in previous studies for the investigation of trace gases (Yu et al., 2007), for the quantification of mercury emissions , mercury methylation (Frohne et al., 2012), and for the determination of the dynamics of trace metals (Rupp et al., 2010;Frohne et al., 2011). More technical details of the system are provided in Yu and Rinklebe (2011). ...
Biogeochemical Factors Governing Co, Ni, Se, and V Dynamics in Periodically Flooded Egyptian North Nile Delta Rice Soils
Abstract
The mobility of water soluble cobalt (Co), nickel (Ni), selenium (Se), and vanadium (V) was determined in fluvial and lacustrine soils used for rice (Oryza sativa L.) production in the northern portion of the Egyptian Nile Delta. The impact of redox potential (EH), soil pH, dissolved organic carbon (DOC), dissolved aromatic carbon compounds (DAC), iron (Fe), manganese (Mn), and sulfate (SO42-) on the dynamics of the studied metals was quantified in soil suspensions using an automated biogeochemical microcosm apparatus. The experiment was conducted stepwise from reducing (-307 mV) to oxidizing (+564 mV) soil conditions. We found a significantly positive correlation between soil EH and pH in both soils. Concentrations of Co, Ni, Se, DOC, Fe, and Mn were higher under reducing conditions than under oxidizing conditions. This suggests that the changes of EH/pH, Fe, Mn, and DOC might be linked to the dynamics of Co, Ni, and Se in both soils. The specific UV absorbance (SUVA) and concentrations of V were higher under oxidizing conditions than under reducing conditions especially in the fluvial soil. This result implies that release of aromatic carbon compounds might be related to release of V in this soil. Our findings suggest that a release of Co, Ni, Se, and V in temporally flooded rice soils should be considered due to increased mobility and the potential environmental risks including food security in using metal-enriched soils for flooded agricultural systems.
Key Words: Redox potential (EH); dissolved organic carbon (DOC); Specific UV absorbance (SUVA), Trace elements; Wetland soils
... Furthermore, the effect of E H can be studied independent from other soil parameters. This system was successfully employed in previous studies for the investigation of trace gases (Yu et al., 2007), for the quantification of mercury emissions , mercury methylation (Frohne et al., 2012), and for the determination of the dynamics of trace metals (Rupp et al., 2010;Frohne et al., 2011). More technical details of the system are provided in Yu and Rinklebe (2011). ...
The mobility of water soluble cobalt (Co), nickel (Ni), selenium (Se), and vanadium (V) was determined in fluvial and lacustrine soils used for rice (Oryza sativa L.) production in the northern portion of the Egyptian Nile Delta. The impact of redox potential (EH), soil pH, dissolved organic carbon (DOC), dissolved aromatic carbon compounds (DAC), iron (Fe), manganese (Mn), and sulfate (SO42-) on the dynamics of the studied metals was quantified in soil suspensions using an automated biogeochemical microcosm apparatus. The experiment was conducted stepwise from reducing (-307 mV) to oxidizing (+564 mV) soil conditions. We found a significantly positive correlation between soil EH and pH in both soils. Concentrations of Co, Ni, Se, DOC, Fe, and Mn were higher under reducing conditions than under oxidizing conditions. This suggests that the changes of EH/pH, Fe, Mn, and DOC might be linked to the dynamics of Co, Ni, and Se in both soils. The specific UV absorbance (SUVA) and concentrations of V were higher under oxidizing conditions than under reducing conditions especially in the fluvial soil. This result implies that release of aromatic carbon compounds might be related to release of V in this soil. Our findings suggest that a release of Co, Ni, Se, and V in temporally flooded rice soils should be considered due to increased mobility and the potential environmental risks including food security in using metal-enriched soils for flooded agricultural systems.
Chromium (Cr) accumulating in soil caused serious pollution to cultivated land. At present, nano zero-valent iron (nZVI) is considered to be a promising remediation material for Cr-contaminated soil. However, the nZVI impact on the behavior of Cr in the soil-rice system under high natural geological background value remains unknown. We studied the effects of nZVI on the migration and transformation of Cr in paddy soil-rice by pot experiment. Three different doses of nZVI (0, 0.001 % and 0.1 % (w/w)) treatments and one dose of 0.1 % (w/w) nZVI treatment without plant rice were set up. Under continuous flooding conditions, nZVI significantly increased rice biomass compared with the control. At the same time, nZVI significantly promoted the reduction of Fe in the soil, increased the concentration of oxalate Fe and bioavailable Cr, then facilitated the absorption of Cr in rice roots and the transportation to the aboveground part. In addition, the enrichment of Fe(III)-reducing bacteria and sulfate-reducing bacteria in soil provided electron donors for Cr oxidation, which helps to form bioavailable Cr that is easily absorbed by plants. The results of this study can provide scientific basis and technical support for the remediation of Cr -polluted paddy soil with high geological background.
Efficient and sustainable technologies for cleaning up of hexavalent chromium (Cr(VI)) contaminated soil are under urgent demand. In this study, chemical reduction and biostimulation were combined to remediate contaminated soil with a high concentration of hexavalent Cr(VI) to compensate for the shortcomings of single-treatment technology. The Cr(VI) concentration, Cr speciation, and bacterial diversity of the contaminated soil were measured after combined remediation with ferrous sulfate (FeSO4) and different electron donors. The changes in various indexes in the soil after microbial death were also studied. The results indicated that the optimal reduction rate of Cr(VI) was as high as 95.20% when 10% FeSO4 was combined with lactic acid. The water-soluble fraction of Cr with the highest toxicity in the soil was almost completely converted into other stable fractions. Stabilization experiments proved that Cr(III) in the remediated soil did not revert to Cr(VI) after microorganism death, and had a good stabilization effect. The bacterial diversity results indicated that Acinetobacter spp. and Pseudomonas spp. were the dominant species during the biostimulation process and might be involved in the reduction of Cr(VI).
Soil degradation is an exceedance of the capacity and resiliency of soil for providing functions and ecosystem services. It is a complex ongoing phenomenon threatening humans’ livelihoods and our future on earth. Knowledge gain can help to find solutions for monitoring, preventing and combating soil degradation. In this chapter we address the essence, causes, extent, features and implications of various types of chemical and biological soil degradation. The aspects of chemical degradation, such as pollution, acidification, salinization, nutrient depletion and eutrophication are characterized shortly; for biological degradation, harm to soil microbiota and biodiversity, and soil organic matter depletion are considered. Progress in monitoring and modelling or forecasting these types of degradation is also shown. Soils of drylands, the Arctic and all man-made soils are hotspots of chemical and biological degradation. As chemical and biological degradation processes in the microscale are lingering and interacting, they need better awareness and monitoring approaches. Highly developed laboratory methods of soil chemical and biological analyses are existing, but screening methods that work under field conditions are comparatively rare. Biological soil degradation needs further evidence-based research and high-precision data for understanding and combating processes. Crucial questions such as calculation of carbon sequestration potential of agricultural soils and assessment of desertification processes should be better explored to bridge science-policy gaps.
de In Industriegesellschaften verteilen sich Schwermetalle vor allem als metallhaltige (Fein‐)Stäube durch Bergbau, Erzverarbeitung sowie durch Korrosion und Abnutzung von Produkten und Ausbringung von metallhaltigen organischen und anorganischen Dünge‐ und Pflanzenschutzmitteln in der Landwirtschaft. Dieses Umweltproblem wurde in den 1970er Jahren erkannt und seither untersucht. Einzige Möglichkeiten zum langfristigen Schutz der Böden vor schädlichen Belastungen bestehen in der Reduzierung der Emissionen und Direkteinträge. Dazu wurden zahlreiche internationale Konventionen und nationale Gesetze erlassen, auf die in diesem Beitrag eingegangen wird. Da die Schwermetallbelastung der Böden trotz erheblicher Reduktion der Emissionen auch heute noch weiter schleichend ansteigt, sollten lokale und regionale Kontrollen und Risikobewertungen den Eintrag potenziell toxischer Metalle in die Nahrungskette verhindern.
Abstract
en Metal‐bearing fine‐dust from mining, processing of ores, corrosion and abrasion of metal products as well as application of metal‐bearing mineral fertilizers and pesticides in agriculture, causes pollution of soils with heavy metals. This environmental problem was realized researched since the 1970s. The only possibilities for soil protection against harmful pollution with heavy metals are the reduction of emissions and direct inputs. For this reason, international conventions and national laws were legislated, which are subject of this contribution. In spite of considerable efforts, the heavy metal pollution is stealthy increasing. Therefore, local and regional controls and risk assessments are necessary to prevent the uptake of potentially toxic metals into the food chain.
Short-term studies of wetlands show that wetlands scavenge pollutants, thereby mitigating the pollution of downstream water bodies. However, there are few long-term studies that demonstrate this effect. This study provides a wealth of data demonstrating that there is variable long-term mobility of metals and arsenic in wetland-lake systems. More than 900 samples were analyzed from 14 soil and sediment cores collected from six wetland-lake systems in the same floodplain. Cores were analyzed for a suite of trace elements (As, Co, Cu, Ni, Pb, Zn are reported in this paper), organic matter content, clay content, and water content. Sediment age was estimated using ²¹⁰Pb and ¹³⁷Cs data, facilitating comparison of element concentrations in contemporaneous wetland and lake sediments. In all six systems, sediment-laden water passes through the wetland before settling into the lake. In three of the systems, element concentrations were consistently higher in lake sediments, indicating a history of remobilization of wetland elements and subsequent deposition in lake sediments. Results in the other three lakes were variable, documenting unique long-term histories of element mobility and sequestration in otherwise similar systems.
In den 1970er Jahren war der Neckar einer der am stärksten mit Schwermetallen belasteten Flüsse Deutschlands. Seitdem hat sich die Sedimentgüte durch systematische Umweltschutzmaßnahmen stark verbessert. Die Sedimentbelastung der Moskva und der Oka in Russland ähnelte im Jahr 1993 der des Neckars in den 1970er Jahren. Die Sedimente dieser beiden Flüsse zeigten in der folgenden Probenahme verringerte Gehalte an Schwermetallen. Ziel dieser Arbeit ist es, die aktuelle Sedimentgüte dieser Flüsse zu bestimmen und die zeitlichenVeränderungen der Belastungen zu bewerten. Die aktuelle Sedimentgüte wurde anhand von systematischen Probenahmen am Neckar sowie an der Moskva und Oka bestimmt. Dazu wurden am Neckar 14 und an der Moskva und Oka 62 Sedimentproben entnommen. Die Ergebnisse dieser Probenahmen wurden mit den Ergebnissen früherer Probenahmen vergleichen. Mit Hilfe von Sedimentkernuntersuchungen wurde die zeitliche Veränderung der Einträge in die Sedimente erfasst. Die Sedimente der Moskva und Oka zeigten generell gegenüber dem geogen Background wenig erhöhte Schwermetallgehalte. An einzelnen Punkten lagen die Konzentrationen von Cadmium, Blei und Zink jedoch deutlich darüber. Cadmium erreichte einen Maximalwert von 22,2 mg/kg in der Feinkornfraktion des Sedimentes. Blei wurde in Konzentrationen von bis zu 3400 mg/kg gefunden. Im Neckar fanden sich keine signifikant erhöhten Gehalte an Schwermetallen. Die Phosphorgehalte waren in den Sedimenten aller drei Flüsse gering. Im Vergleich zu den Ergebnissen der vorherigen Probenahmen zeigten sich in den Sedimenten der Moskva und Oka generell eine Verringerung der Schwermetallgehalte. An einzelnen Punkten traten jedoch lokal eng begrenzte starke Belastungen auf. Die Schwermetallgehalte in den Sedimenten des Neckars haben sich nicht signifikant gegenüber den Konzentrationen, die im Jahr 1998 gefunden wurden, verändert. Im Neckar zeigt sich deutlich, dass die getroffenen Umweltschutzmaßnahmen nachhaltig zu einer Verbesserung der Sedimentgüte geführt haben. Ausgelöst durch den Zusammenbruch der Sowjetunion wurde in Russland die staatliche Industrie stillgelegt oder privatisiert. Die daraus resultierende Verbesserung der Sedimentgüte lässt sich durch die Daten der verschiedenen Probenahmen nachweisen. Die lokal begrenzten Belastungen sind ein neuer Einflussfaktor auf die Sedimentgüte der Moskva und Oka. Eine weitere Überwachung Sedimentgüte der Moskva und Oka wäre in Hinblick auf diese Entwicklung sinnvoll.
Purpose
The primary purpose of this study was to determine how flooding and draining cycles affect the redox chemistry of metal (hydr)oxides and organic matter in paddy soils and how the pH influences these processes. Our secondary purpose was to determine to what extent a geochemical thermodynamic equilibrium model can be used to predict the solubility of Mn and Fe during flooding and draining cycles in paddy soils.
Material and methods
We performed a carefully designed column experiment with two paddy soils with similar soil properties but contrasting pH. We monitored the redox potential (Eh) continuously and took soil solution samples regularly at four depths along the soil profile during two successive flooding and drainage cycles. To determine dominant mineral phases of Mn and Fe under equilibrium conditions, stability diagrams of Mn and Fe were constructed as a function of Eh and pH. Geochemical equilibrium model calculations were performed to identify Mn and Fe solubility-controlling minerals and to compare predicted total dissolved concentrations with their measured values.
Results and discussion
Flooding led to strong Eh gradients in the columns of both soils. In the acidic soil, pH increased with decreasing Eh and vice versa, whereas pH in the alkaline soil was buffered by CaCO3. In the acidic soil, Mn and Fe solubility increased during flooding due to reductive dissolution of their (hydr)oxides and decreased during drainage because of re-oxidation. In the alkaline soil, Mn and Fe solubility did not increase during flooding due to Mn(II) and Fe(II) precipitation as MnCO3, FeCO3, and FeS. The predicted levels of soluble Mn and Fe in the acidic soil were much higher than their measured values, but predictions and measurements were rather similar in the alkaline soil. This difference is likely due to kinetically limited reductive dissolution of Mn and Fe (hydr)oxides in the acidic soil. During flooding, the solubility of dissolved organic matter increased in both soils, probably because of reductive dissolution of Fe (hydr)oxides and the observed increase in pH.
Conclusions
Under alternating flooding and draining conditions, the pH greatly affected Mn and Fe solubility via influencing either reductive dissolution or carbonate formation. Comparison between measurements and geochemical equilibrium model predictions revealed that reductive dissolution of Mn and Fe (hydr)oxides was kinetically limited in the acidic soil. Therefore, when applying such models to systems with changing redox conditions, such rate-limiting reactions should be parameterized and implemented to enable more accurate predictions of Mn and Fe solubility.
Acid sulphate (AS) soils are most prevalent in the tropics, but the acidic discharge from cultivated AS soils also threatens water bodies under boreal conditions. Feasible options to reduce the acid load are needed. In this study, the groundwater of an AS field was monitored for 3.5years, and the efficiency of waterlogging in mitigating the environmental risks caused by acidic discharge was investigated in a 2.5-year experiment with 10 monolithic lysimeters taken from the same field. In order to unravel the transferability of the results from lysimeters to the field scale, the Al, Fe and S concentrations in discharge water from the lysimeters were compared with those in the groundwater of the AS field (pedon and field scale), and in pore water (pedon and horizon scale). In the waterlogged bare lysimeters (HWB), the Al, Fe and S concentrations in discharge waters were broadly similar to those measured in the groundwater and followed the changes in the pore water. In the waterlogged cropped (reed canary grass, Phalaris arundinacea) lysimeters (HWC), in contrast, the discharge waters were markedly higher in Fe and lower in Al than the groundwater in the field. This outcome was attributable to the reduction of Fe(3+) to the more soluble Fe(2+) and the reduction-induced increase in pH, which enhanced the formation of Al(3+) hydroxy species. Lowering of the water table (LWC) caused soil ripening, which resulted in increased saturated hydraulic conductivity and porosity and enhanced the oxidation of sulphidic materials and acid formation. The responses of Al, Fe and S in drainage waters from HWC and LWC lysimeters resembled previous findings in AS soils. Based on this and the similarity between dissolved element concentrations in the discharge water of HWB lysimeters and groundwater in the field, we conclude that our monolithic lysimeters yielded realistic results concerning the efficiency of various methods in mitigating environmental risks related to cultivated AS soils.
An increasing amount of information is being collected on the ecological and socio-economic value of goods and services provided by natural and semi-natural ecosystems. However, much of this information appears scattered throughout a disciplinary academic literature, unpublished government agency reports, and across the World Wide Web. In addition, data on ecosystem goods and services often appears at incompatible scales of analysis and is classified differently by different authors. In order to make comparative ecological economic analysis possible, a standardized framework for the comprehensive assessment of ecosystem functions, goods and services is needed. In response to this challenge, this paper presents a conceptual framework and typology for describing, classifying and valuing ecosystem functions, goods and services in a clear and consistent manner. In the following analysis, a classification is given for the fullest possible range of 23 ecosystem functions that provide a much larger number of goods and services. In the second part of the paper, a checklist and matrix is provided, linking these ecosystem functions to the main ecological, socio–cultural and economic valuation methods.
Presently, heavy metal pollution of our cultivable agricultural farmlands is
increasing and is often associated with anthropogenic sources. Wetlands contaminated with
detectable levels of metal toxicants and other trace macro-elements are frequently used for
growing vegetable crops. To assess the impact of floodwater on soil of floodplain wetland
of Cross River, soil samples were taken from uppermost 0-30 ern within designated thirty
square grids and analytical determinations of cobalt (Co), lead (Pb ), manganese (Mn), nickel
(Ni), vanadilllll (V) and copper (Cu) were carried out. The results show high accillllulat:ion
of Mn (40.22±2.79 Mg g-'), Pb (22.47±0.58 Mg g-'), Cu (16.17±7.93 Mg g-') and Ni
(17.24±4.12 Mg g-') from the wetland. The exploratory data analyses for each of the heavy
metals revealed that the concentrations of the metals in the floodplain ultisols were more
effectively influenced by environmental and anthropogenic attributes.
The influence of sediment redox potential and pH on As and Se speciation and solubility weas studied. Hyco Reservoir (North Carolina) sediments were equilibrated under controlled redox (500, 200, 0, and {minus}200 mV) and pH (5, natural, and 7.5) conditions. Redox potential and pH affected both speciation and solubility of As and Se. Under oxidized conditions As solubility was low and 87% of the As in solution was present as As(V). Upon reduction, As(III) became the major As species in solution, and As solubility increased. Total As in solution increased approximately 25 times upon reduction to {minus}200 mV. No organic arsenicals were detected. In contrast to As, Se solubility reached a maximum under highly oxidized (500 mV) conditions and decreased significantly upon reduction. Selenium (VI) was the predominant dissolved Se species present at 500 mV. At 200 and 0 mV, Se(IV) became the most stable oxidation state of Se. Under strongly reduced conditions ({minus}200 mV) oxidized Se species were no longer detectable and Se solubility was controlled by the formation of elemental Se and/or metal selenides. Biomethylation of Se was important under oxidized and moderately reduced conditions (500, 200, and 0 mV). More alkaline conditions (pH 7.5) resulted in both greater As and Se concentrations in solution. Dissolved As and Se increased up to 10 and 6 times, respectively, as compared to the more acidic equilibrations.
The oxidized and reduced layers in flooded soil were characterized by vertical distribution of the oxidation‐reduction (redox) potential and concentrations of manganous manganese, ferrous iron, sulfide, nitrate, and ammonium. Redox potential was measured with a special motor‐driven assembly which advanced a platinum electrode at a rate of 2 mm/hour through the flooded soil profile. Vertical distribution of reduced forms of manganese, iron, and sulfur and of nitrate and ammonium was determined by freezing and slicing the flooded soil into segments 1 or 2 mm thick. The apparent thickness of the oxidized layer was different when evaluated by the distribution of the various components in the profile, with the sulfide profile indicating the thickest oxidized zone, the manganese profile indicating the thinnest oxidized zone, and the iron profile showing an intermediate thickness. The thickness of the oxidized layer increased with duration of flooding.
The services of ecological systems and the natural capital stocksthat produce them are critical to the functioning of the
Earth’s life-support system. They contribute to human welfare, both directly and indirectly, and therefore represent
part of the total economic value of the planet.We have estimated the current economic value of 17 ecosystem services
for 16 biomes, based on published studies and a few original calculations. For the entire biosphere, the value (most of
which is outside the market) is estimated to be in the range of US33trillion per year. Because of the nature of the uncertainties, thismust be considered a minimum estimate. Global
gross national product total is around US$18 trillion per year.
Spatio-temporal variations of nitrogen, phosphorus and base cation concentrations in groundwater were related to the drastic change in hydrological conditions of the Rhine alluvial floodplain (Eastern France), which has been disconnected from the river by canalisation. The Groundwater chemistry was studied in two alluvial forests with contrasting hydrological conditions: one in a sector unflooded for 30 years, the second one in a sector still subject to flooding. Nutrient concentrations were measured at two levels, in the root zone (1.5 m depth) and in the gravel below the root layer (4.5 m depth). In the unflooded sector, the average nitrate concentration was significantly lower in the shallow groundwater (2.06 mg l−1 NO3−) than in the deeper layer (5.84 mg l−1NO3−). In contrast, in the flooded sector the nitrate concentrations in the shallow groundwater (5.02 mg l−1 NO3−) were not significantly different from those in the deep groundwater (3.98 mg l−1 NO3−). The concentration of phosphate was similar in shallow and deep groundwater in the unflooded sector (46 and 35 μg l−1, respectively) but significantly lower in the deep groundwater of the flooded sector (47 μg l−1), than in the shallow groundwater (58 μg l−1). The major elements (cations: Ca2+, Mg2+, Na+ and associated anions: HCO3−, SO4−2, Cl−) concentrations were significantly higher in the groundwaters than in the surface water. The results are discussed in terms of changes that accompanied suppression of floods, and processes that take place during the transfer of nutrients through the groundwater–soil–plant compartments. The reduction of groundwater fluctuations in the unflooded sector modified the transfer of nitrate by reducing the resolubilisation of locally produced nitrate, and/or denitrification. The transfer of phosphate was affected to a lesser extent, because of precipitation and adsorption. Base cation concentrations reflect exchange between groundwater and the calcareous gravel.
The services of ecological systems and the natural capital stocks that produce them are critical to the functioning of the Earth's life-support system. They contribute to human welfare, both directly and indirectly, and therefore represent part of the total economic value of the planet. We have estimated the current economic value of 17 ecosystem services for 18 biomes, based on published studies and a few original calculations. For the entire biosphere, the value (most of which in outside the market) in estimated to be in the range of US33 trillion per year. Because of the nature of the uncertainties, thin must be considered a minimum estimate. Global gross national product total is around US$18 trillion per year.
The embanked floodplains of the lower Rhine river in the Netherlands contain large amounts of heavy metals, which is a result of many years of deposition of contaminated overbank sediments. The metal pollution varies greatly between the various floodplain sections as well as in vertical direction within the floodplain soil profiles. The present contribution describes the key processes producing the spatial variability of the metal pollution in floodplain soils: (1) spatial patterns of the concentrations and deposition of Cd, Cu, Pb and Zn during a single flood, which have been determined from samples collected after a high-magnitude flood event; (2) the pollution trends of the lower Rhine over the past 150 years, which were reconstructed on the basis of metal concentrations in sediments from small ponds within the floodplain area. During the flood the largest metal depositions (0.03 g/m
2
Cd, 0.7 g/m
2
Cu, 1.1 g/m
2
Pb and 5.0 g/m
2
Zn for the Rhine) occurred along the natural levees, decreasing to about one third of these values at larger distance from the river. Deposition of heavy metals occurred since the end of the nineteenth century. Periods of maximum pollution occurred in the 1930s and 1960s, when Cu, Pb and Zn concentrations were about 6–10 times as high as background values.
The resulting metal distribution in the floodplain soil profiles is illustrated by means of typical examples. Maximum metal concentrations in floodplain soils vary from 30 to 130 mg/kg for Cu, from 70 to 490 mg/kg for Pb, and from 170 to 1450 mg/kg for Zn. The lowest metal pollution is found in the distal parts of floodplain sections with low flooding frequencies, where average sedimentation rates have been less than about 5 mm/a. The largest metal accumulations occur in low-lying floodplain sections where average sedimentation rates have been more than 10 mm/a.
We aimed to assess the presence and availability of arsenic (As) in intertidal marshes of the Scheldt estuary. Arsenic content was determined in soils sampled at 4 sampling depths in 11 marshes, together with other physicochemical characteristics. Subsequently, a greenhouse experiment was set up in which pore water arsenic (As) concentrations were measured 4 times in a 298-day period in 4 marsh soils at different sampling depths (10, 30, 60 and 90 cm) upon adjusting the water table level to 0, 40 and 80 cm below the surface of these soils. The As content in the soil varied significantly with sampling depth and location. Clay and organic matter seem to promote As accumulation in the upper soil layer (0-20 cm below the surface), whereas sulfide precipitation plays a significant role at higher sampling depths (20-100 cm below the surface). The As concentrations in the pore water of the greenhouse experiment often significantly exceeded the Flemish soil sanitation thresholds for groundwater. There were indications that As release is not only affected by the reductive dissolution of Fe/Mn oxides, but also by e.g. a direct reduction of As(V) to As(III). Below the water table, sulfide precipitation seems to lower As mobility when reducing conditions have been sufficiently established. Above the water table, sulfates and bicarbonates induce As release from the solid soil phase to the pore water.
Since 1994, water-quality constituents have been measured monthly in three adjacent Coastal Plain watersheds in southwestern Georgia. During 1994, rainfall was 650 mm above annual average and the highest flows on record were observed. From November 1998 through November 2000, 19 months had below average rainfall. Lowest flows on record were observed during the summer of 2000. The watersheds are human-dominated with row-crop agriculture and managed forestlands being the major land uses. However, one watershed (Chickasawhatchee Creek) had 10 to 13% less agriculture and greater wetland area, especially along the stream. Suspended particles, dissolved organic carbon, NH4-N, and soluble reactive phosphorus concentrations were greater during wet and flood periods compared with dry and drought periods for each stream. Regional hydrologic conditions had little effect on NO3-N or dissolved inorganic carbon. Chickasawhatchee Creek had significantly lower suspended sediment and NO3-N concentrations and greater organic and inorganic carbon concentrations, reflecting greater wetland area and stronger connection to a regional aquifer system. Even though substantial human land use occurred within all watersheds, water quality was generally good and can be attributed to low stream drainage density and relatively intact floodplain forests. Low drainage density minimizes surface run-off into streams. Floodplain forests reduce nonpoint-source pollutants through biological and physical absorption. In addition to preserving water quality, floodplain forests provide important ecological functions through the export of nutrients and organic carbon to streams. Extreme low flows may be disruptive to aquatic life due to both the lack of water and to the scarcity of biologically important materials originating from floodplain forests.
The sediment or fauna incubation experiment (SOFIE) is an experimental research tool that was developed to analyze concentrations and chemical speciation of heavy metals in pore waters of natural, undisturbed sediments or water-sediment interfaces over time, while simultaneously conducting exposure tests with sediment-dwelling organisms. In this way, concentrations of chemical species are directly linked to accumulation by biota. It is shown that discrete gradients of redox-sensitive metals and nutrients occur over very small intervals. These gradients differ from those of free metal ion activities. Speciation affects the uptake of metals by sediment-dwelling organisms, which, in their turn, have a significant effect on metal speciation. With reaction kinetics that differ per metal, uptake of metals by organisms from the water phase may be hindered (e.g., Cu, Zn) or promoted (e.g., Ni, As). Time-varying exposure concentrations of metals were incorporated in uptake and elimination models. Body concentrations of Cd, Cu, Ni, and Zn in the aquatic oligochaete Limnodrilus could best be described by the time-varying free ion concentration in the overlying water. Body concentrations of As and Pb were best described by sediment pore water concentrations. It is concluded that SOFIE provides the necessary experimental tool to support, in a mechanistic way, environmental risk assessments of contaminants.
Research was undertaken to determine the effects of pH and redox potential on heavy metal speciation and on the size distribution of the organo-metal complexes in the soluble fraction of sediment-water systems. A cation exchange technique was effective in separating free and complexed metal ions. Fe, Mn and Zn differed in the extent of complexation with soluble organic matter. Under reducing conditions approximately two thirds of the soluble Fe was in a complexed form that was not sorbed in passing through the cation exchange resin. Soluble Mn on the other hand, was almost completely ionic under reducing conditions, with only a trace amount passing through the resin column. Over 90 percent of the soluble Zn was complexed under reduced conditions, with only 9 percent sorbed onto the resin. The complexed Fe and Zn were bound to soluble organic matter particles with equivalent molecular weight greater than 25,000 while Mn passed through this size filter. There were marked differences in the size distribution of the various organo-metal complexes under different redox and pH conditions. The soluble Fe was associated with both the largest and smallest size ranges of soluble organic matter. The effect of pH was most evident in the smallest size range with much more complexed iron being present at low pHs. Mn, on the other hand, was associated with only the smallest size range under all pH and redox conditions, reflecting its ionic nature. The greater solubility and mobility of Mn probably accounts for it being depleted relative to iron in Gulf Coast sediments. Hg and Pb were associated with only the largest size soluble complexes and were little affected by pH and redox conditions.
Hintergrundwerte sind Konzentrationen von Stoffen in Umweltkompartimenten, die sich ohne anthropogene Einflüsse eingestellt haben und damit den natürlichen Zustand charakterisieren. Im Gegensatz zu Hintergrundwerten als eine eher wertneutrale, rein geochemische Bewertungsgrundlage sind die meisten Qualitätsanforderungen von Wertvorstellungen geprägt. Hintergrundwerte sind daher im allgemeinen eine geeignete Grundlage zur Feststellung eines Referenzzustandes und nur in Ausnahmefällen auch zur Festlegung von Zielvorgaben geeignet. Eine derartige Ausnahme betrifft Zielvorgaben für Schwermetalle zum Schutz der aquatischen Lebensgemeinschaften. Schudoma (1994) hat im Rahmen eines Auftrages des BLAK QZ (Bund/Länder-Arbeitskreises „Qualitätsziele“) herausgestellt, daß die NOEC-Werte (No Observation Effect Concentration) für empfindliche Arten der aquatischen Lebensgemeinschaften im Bereich der natürlichen Hintergrundkonzentrationen in Fließgewässern liegen und Zielvorgaben (90-Perzentilwerte) in Höhe des doppelten oberen Hintergrundwertes aufgestellt. Zielvorgaben — und damit im Fall der Schwermetalle auch Hintergrundwerte — können somit eine geeignete Grundlage für die chemische Klassifizierung der Schadstoffbelastung von Fließgewässern darstellen (Irmer 1997).
Publisher Summary
Humus is defined as being synonymous with soil organic matter, which in turn is the total organic matter in a soil exclusive of the biomass and undecayed material. Dissolved humus consists of the dissolved organic material (DOM) in soil, which influences the overall ecology and geochemistry of soil. This chapter focuses on the DOM's ecological role in the unsaturated zone, with the saturated zone and the surface aquatic ecosystems being peripherally considered. The relation of the DOM to other ecological components in soil is influenced by two types of fluxes. The first one is physical diffusion. The DOM diffuses over a concentration gradient. The second physical flux is convection, which is dependent on a gradient in the soil's water content as a result of precipitation. The dissolved humus is mobile and so it can be fully available theoretically. This mobility and availability is not constant; it can vary both over space and time. The potential ecological function and in situ availability of the dissolved humus are considered in the chapter so that one is able to understand and predict its environmental role.
This review deals with environmental origin, occurrence, episodes, and impact on human health of arsenic. Arsenic, a metalloid occurs naturally, being the 20th most abundant element in the earth's crust, and is a component of more than 245 minerals. These are mostly ores containing sulfide, along with copper, nickel, lead, cobalt, or other metals. Arsenic and its compounds are mobile in the environment. Weathering of rocks converts arsenic sulfides to arsenic trioxide, which enters the arsenic cycle as dust or by dissolution in rain, rivers, or groundwater. So, groundwater contamination by arsenic is a serious threat to mankind all over the world. It can also enter food chain causing wide spread distribution throughout the plant and animal kingdoms. However, fish, fruits, and vegetables primarily contain organic arsenic, less than 10% of the arsenic in these foods exists in the inorganic form, although the arsenic content of many foods (i.e. milk and dairy products, beef and pork, poultry, and cereals) is mainly inorganic, typically 65-75%. A few recent studies report 85-95% inorganic arsenic in rice and vegetables, which suggest more studies for standardisation. Humans are exposed to this toxic arsenic primarily from air, food, and water. Thousands and thousands of people are suffering from the toxic effects of arsenicals in many countries all over the world due to natural groundwater contamination as well as industrial effluent and drainage problems. Arsenic, being a normal component of human body is transported by the blood to different organs in the body, mainly in the form of MMA after ingestion. It causes a variety of adverse health effects to humans after acute and chronic exposures such as dermal changes (pigmentation, hyperkeratoses, and ulceration), respiratory, pulmonary, cardiovascular, gastrointestinal, hematological, hepatic, renal, neurological, developmental, reproductive, immunologic, genotoxic, mutagenetic, and carcinogenic effects. Key research studies are needed for improving arsenic risk assessment at low exposure levels urgently among all the arsenic research groups.
In order to enhance phytoremediation efficiency, we investigated the effects of dual inoculation
with ectomycorrhizal fungi and the ectomycorrhiza associated bacteria Micrococcus
luteus and Sphingomonas sp. on the growth and metal accumulation of willows (Salix
viminalis x caprea) on contaminated soil. The bacterial strains were previously collected
from sporocarps of ectomycorrhizal fungi. The bacteria increased plant growth and the
mycorrhizal dependency of willows colonized with the ectomycorrhizal fungus Hebeloma
crustuliniforme. The total cadmium (Cd) and zinc (Zn) accumulation in the shoot biomass
was increased after inoculation with the fungal strain Hebeloma crustuliniforme in
combination with Micrococcus luteus up to 53% and in combination with Sphingomonas
sp. up to 62%, respectively. The dual inoculation in combination with Laccaria laccata did
not increase the accumulation of Cd and Zn in the willows. We conclude that associated
bacteria can enhance the ectomyorrhiza formation and growth of willows and, thereby, the
Cd and Zn accumulation in the plant biomass. The results suggest that bacterial support of
root growth promoting ectomycorrhizal fungi may be a promising approach to improve the
remediation of metal-contaminated soils by using willows.
The rivers Saale and Elbe, including their catchment areas (Germany), have been heavily polluted by ore mining and other anthropogenic emission sources during the last centuries. Heavy metal contamination along the Elbe River floodplains can vary depending on location. In this study data on methyl mercury, mercury, and other heavy metal contents in three soil profiles from a representative site under the influence of the rivers Elbe and Saale are presented. The relationship of metal distribution to chemical and physical characteristics in the soil profiles is outlined. Methyl and total mercury were detected in extremely high concentrations in the soil profiles. Results showed that Zn, Cu, and Pb were elevated, above the reported levels considered as excessive in soils. Concentrations of Ni, Cd, and Se were not elevated, while other elements (Al, Na, K, Ca, Mg, Mn, and Fe) were at geological or background levels.The research was supported by National Science Foundation (Grant # INT 9901301).
Wetlands at the riverside of the UNESCO Biosphere Reserve “Central Elbe” are highly contaminated by heavy metals, especially mercury (Hg). The Hg-polluted Elbe floodplain soils turn out to be a source of gaseous mercury via Hg volatilization from soil into the atmosphere. A modified field sampling method was used to measure total gaseous mercury (TGM) volatilization from three different sites at the Elbe River. The modified setup had a reduced chamber size and contained an internal gas circulation system. An in-ground stainless steel cylinder minimizes Hg volatilization from adjacent soil air. Cold vapor atomic absorption spectrometry (CV-AAS) was used to determine TGM amalgamated on gold traps. Sampled TGM amounts ranged between 0.02 and 0.63 ng (absolute), whereas the calculated Hg fluxes varied from 2.0 to 63.3 ng m h. The modified system should allow measurements of Hg volatilization at various sites with a high spatial resolution, which should enable the study of interrelations between TGM emission and several key factors influencing Hg emission from floodplain soils at the Elbe River and other riverine ecosystems in the near future.
Research was undertaken to determine the effects of pH and redox potential on heavy metal speciation and on the size distribution of the organo-metal complexes in the soluble fraction of sediment-water systems. A cation exchange technique was effective in separating free and complexed metal ions. Fe, Mn and Zn differed in the extent of complexation with soluble organic matter. Under reducing conditions approximately two thirds of the soluble Fe was in a complexed form that was not sorbed in passing through the cation exchange resin. Soluble Mn on the other hand, was almost completely ionic under reducing conditions, with only a trace amount passing through the resin column. Over 90 percent of the soluble Zn was complexed under reduced conditions, with only 9 percent sorbed onto the resin. The complexed Fe and Zn were bound to soluble organic matter particles with equivalent molecular weight greater than 25,000 while Mn passed through this size filter. There were marked differences in the size distribution of the various organo-metal complexes under different redox and pH conditions. The soluble Fe was associated with both the largest and smallest size ranges of soluble organic matter. The effect of pH was most evident in the smallest size range with much more complexed iron being present at low pHs. Mn, on the other hand, was associated with only the smallest size range under all pH and redox conditions, reflecting its ionic nature. The greater solubility and mobility of Mn probably accounts for it being depleted relative to iron in Gulf Coast sediments. Hg and Pb were associated with only the largest size soluble complexes and were little affected by pH and redox conditions.
A simple system, utilizing laboratory pH meters and suitable meter relays, is described for controlling the redox potential and pH of flooded soils.
A series of vertical alluvial profiles from the upper River Severn floodplain at Welshpool ranging in age from Late Pleistocene to the present have been examined for their Ni, Cu, Zn, Cd, Ba and Pb concentrations. The floodplain deposits have been variably contaminated with heavy metals following extensive metalliferous mining in the upper catchment during the mid-19th century. The data are used to establish whether vertical increases in concentrations can be used to indicate a younging-upwards of the sediments. The data show that grain size and organic content do not influence heavy metal concentrations. Although some of the most recent alluvial profiles contain the highest levels of contamination, a great deal of variation exists, not only between the general vertical distribution of individual metals but also between the absolute values themselves. There was no consistent age-concentration relationship in the vertical profiles. Pb displays the least complex picture with predominantly increasing values towards the top of the alluvial profiles in the historically sedimented sites, indicating a younging-upwards. Rapid sedimentation and post-depositional processes such as leaching, particle translocation or the lateral migration of groundwaters enriched in heavy metals result in different vertical heavy metal distributions at superficially similar sites. It is recommended that sampling strategies for contaminated floodplain sediments utilise a multiple profile approach including the whole range of sediment types, ages and depositional forms that are known to exist at a study site.
In Untersuchungen mit einem Elektronenmikrostrahlanalysator (Mikrosonde) an Dünnschliffen von vier A‐Horizonten schleswigholsteinischer Marschen wurden die Gehalte von Konkretionen an 14 Haupt‐ (Ti, Fe, Mn, Si, Al, Ca) und Nebenelementen (P, S, Co, Ni, Cu, Zn, Cd, Pb) ermittelt. Nach dem Gehalt an Hauptelementen können folgende Konkretionstypen unterschieden werden: Ti‐Fe(‐Mn)‐Konkretionen (31–39% Ti; 18–29% Fe; 0,3–5,5% Mn), Fe(‐Mn)‐Konkretionen (31–58% Fe; ≤ 1,8% Mn), Fe‐Si(‐Mn)‐Konkretionen (6–28% Fe; 8–42% Si; ≤ 5% Mn) sowie Mn‐Fe‐ und Mn‐Fe‐Si‐Konkretionen (16–40% Mn; 2–9% Fe; 2–15% Si).
Die Entstehung der Ti‐Fe(‐Mn)‐Konkretionen ist wahrscheinlich durch eine Adsorption von Fe ²⁺ ‐Ionen unter reduzierenden Bedingungen auf den Oberflächen von Ti‐Mineralen und anschließende Fe ²⁺ ‐Oxidation zu Fe(III)‐Oxiden – möglicherweise unter Bildung von Pseudorutil – bedingt. Fe‐ und Mn‐reiche Konkretionen weisen z.T. Carbonate, Silicate und/oder SiO 2 (z.T. Bioopal) als Einschlüsse und wahrscheinliche Kerne der Konkretionsbildung auf. Durch die in A‐Horizonten von Marschen zeitweilig ablaufenden Redoxprozesse kommt es dabei zur Ausbildung von Konkretionen mit vorherrschender Fe‐ oder Mn‐Akkumulation.
Von den akzessorischen Elementen weisen die als Anionen vorliegenden Elemente Phosphor und Schwefel – wie auch Titan und Silicium – vor allem hohe Gehalte in Fe‐reichen Konkretionen auf (bis 54.000 mg P/kg; bis 4.200 mg S/kg). Dabei scheint eine Anionenkonkurrenz zwischen P, Si und wahrscheinlich auch Ti um die Bindungsposition in Fe‐reichen Konkretionen zu bestehen.
Von den Schwermetallen besitzt Blei die höchste Anreicherung (bis 12.000 mg/kg) in Fe(‐Mn)‐Konkretionen. Dagegen treten die höchsten Gehalte an Cobalt (bis 3.400 mg/kg), Nickel (bis 1.800 mg/kg), Zink (bis 13.200 mg/kg) und Cadmium (bis 1.000 mg/kg) in Mn‐reichen Konkretionen auf. Kupfer weist ebenfalls in einigen Konkretionen Anreicherungen auf (bis 1140 mg/kg); eine besondere Affinität zu einem bestimmten Konkretionstyp ist jedoch nicht feststellbar.
Relative to the two-step origin proposed by J. H. Moses and W. D. Michell for bauxite deposits of British Guiana and Surinam, results of studies of the chemistry of submerged soils are reported which support an alternative theory of subaqueous bauxitization. Formation is considered to have occurred at sea level, in a coastal swamp drained by an aquifer with submarine discharge.
Mercury fluxes between soil and atmosphere have often been determined by using dynamic flux chambers and micrometeorological methods to assess ecological risks. However, both systems are complex, stationary, and expensive impeding measurements of Hg emissions at various field sites.The mobile, easy to handle, and cost-effective field method to determine total gaseous mercury (TGM), according to [Böhme, F., Rinklebe, J., Stärk, H.-J., Wennrich, R., Mothes, S., Neue, H.-U., 2005. A simple field method to determine mercury volatilisation from soils. Environ. Sci. Pollut. Res. (ESPR), 12: 133–135] creates a drop in air pressure that enhance the Hg emission. We optimized the sampling set-up using an air circulation system resulting in a continuous air flow over the soil surface. Thus, a drop in air pressure can be avoided and the detected TGM emissions are closer to reality. Additional benefits are an in-ground cylinder which inhibits lateral flow of gaseous mercury and the reduced size of the glass socket facilitating handling.To test the suitability of the optimized method, TGM emissions have been quantified on a set of Hg-contaminated riverine soils. Compared with non-polluted soils, mean Hg fluxes were strongly increased (between 138 and 711ngm−2h−1) and showed high spatial heterogeneity. Due to impacts of multiple environmental conditions that affect TGM emissions, no significant correlations have been found between Hg stocks in bulk soils and Hg fluxes.
Three alternates utilized by facultative microorganisms when O2 becomes depleted are NO-3, Mn4+ compounds, and Fe3+ compounds. The sequence of reduction of these three redox systems were studied under controlled redox potential conditions. The results of this study showed that the oxidation and reduction of the three electron acceptors were sequential, with no overlap in the oxidation or reduction of the NO-3 and Mn systems and little overlap in the Mn and Fe systems. For all three redox systems, the critical redox potentials for the oxidized-to-reduced transition were approximately 50 mV lower than for the reduced-to-oxidized transition. -from Authors
Abbreviations: DOC, dissolved organic carbon; EH, redox potential; GC, gas chromatograph; OM, organic matter. Six soils used for rice (Oryza sativa L.) production were incubated using an automatic micro- cosm system. Production of trace gases (CO2, CH4, and N2O) and transformation of N, S, and metals (Fe and Mn) were studied in soil suspensions incubated from reducing to oxidiz- ing conditions. Results show that soil pH variation was inversely correlated to soil redox potential (EH) change (P < 0.01). Soil CO2 production exponentially increased with soil EH increase. In contrast, soil CH4 production and DOC showed an exponential decrease with soil EH increase. Without the presence of soil oxidants, methanogenesis occurred across the entire EH range, with probable H2-supported methanogenesis at higher soil EH conditions constituting up to 20% of total CH4 production. The CH4 compensation point, where CH4 concentration became constant due to equilibrium between CH4 production and con- sumption, exponentially decreased with soil EH increase. At pH 7, the critical EH above which soils consumed atmospheric CH4 varied among the soils, but was generally >400 mV. Signifi cant N2O production was observed between 200 and 500 mV. Nitrifi cation could also contribute to N2O production when EH is >500 mV, a possible critical EH for the initiation of nitrifi cation. The critical EH for substantial immobilization of Fe and Mn was estimated to be around 50 and 250 mV, respectively. The intermediate EH range (approximately −150 to 180 mV) provided optimum conditions for minimizing cumulative global warming poten- tial resulting from CO2, CH4, and N2O production in soils. Our results have implications in interpreting the overall benefi ts of soil C sequestration efforts.
Dissolved organic matter (DOM) in soils plays an important role in the biogeochemistry of carbon, nitrogen, and phosphorus, in pedogenesis, and in the transport of pollutants in soils. The aim of this review is to summarize the recent literature about controls on DOM concentrations and fluxes in soils. We focus on comparing results between laboratory and field investigations and on the differences between the dynamics of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP).
Both laboratory and field studies show that litter and humus are the most important DOM sources in soils. However, it is impossible to quantify the individual contributions of each of these sources to DOM release. In addition, it is not clear how changes in the pool sizes of litter or humus may affect DOM release. High microbial activity, high fungal abundance, and any conditions that enhance mineralization all promote high DOM concentrations. However, under field conditions, hydrologic variability in soil horizons with high carbon contents may be more important than biotic controls. In subsoil horizons with low carbon contents, DOM may be adsorbed strongly to mineral surfaces, resulting in low DOM concentrations in the soil solution. There are strong indications that microbial degradation of DOM also controls the fate of DOM in the soil.
Laboratory experiments on controls of DOM dynamics have often contradicted field observations, primarily because hydrology has not been taken into account. For example, laboratory findings on the effects of plant species (conifer vs. deciduous) on DOM release from forest floors and on the effects of substrate quality (e.g.: C/N ratio) or pH on DOC concentrations were often not confirmed in field studies. The high adsorption capacity of soil clay minerals and oxides for DOM shown in laboratory studies may not control the transport of DOM in soils in the field if macropore fluxes dominate under field conditions. Laboratory findings about the biodegradability of DOM also await verification under field conditions.
Studies that include DON and DOP dynamics in addition to DOC are few. The rate of release and the fate of DOC, DON, and DOP in soils may differ to a far greater extent than previously assumed. Controls established for DOC might thus be not valid for DON and DOP.
Despite intensive research in the last decade, our knowledge of the formation and fate of DOM in soils and its response to changing environmental conditions is still fragmented and often inconsistent. Predictions at the field scale are still very uncertain, and most of the information available today is the result of studies on temperate soils and forest ecosystems. Thus, future research on controls of DOM dynamics should be extended to soils under different land uses and in other climate zones. Emphasis should also be given to: (i) the effects of soil organic matter properties on the release of DOM (ii) environmental factors controlling DOM quantity and quality (iii) the assessment of biological versus physico-chemical controls on the release and retention of DOM in soils, and (iv) the differences between DOC, DON, and DOP. Finally, if our goal is to predict DOM concentrations and fluxes in soils, future research on the controls of DOM dynamics should have a strong focus on field studies.
The study of the distribution of various forms of Zn under fluctuating oxidation-reduction (redox) conditions is necessary to improve predictions of Zn solubility and bioavailability when Zn is added to soils with large quantites of organic C that oxidize over time. We conducted plant-soil interaction studies to determine the effect of redox potential in flooded and unflooded soils on the solubility and uptake of Zn by rice (Oryza sativa L., Calrose-76), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) in a growth chamber. Sequential extractions were used to fractionate Zn in biosolids-amended and unamended A horizon samples (25-cm depth) of three soil series of a typical toposequence from the Coastal Plain of Maryland: a Galestown loamy sand (Psammentic Hapludults), a Bertie silt loam (Typic Hapludults), and an Othello silt loam (Typic Endoaquults). Addition of organic C (as biosolids) increased the leaf dry matter yield, but not leaf tissue Zn concentration, compared with Zn-amended soil with no organic C addition. Flooding decreased leaf dry matter yield and Zn concentrations in the leaf tissue of all plants, especially in the organic waste-amended soils. Among the crops, rice had higher levels (P < 0.05) of Zn (7.4-34 μmol/g) than did wheat (0.3-4.3 μmol/g) and barley (1.2-6.1 μmol/g). Exchangeable Zn (25 to 48% of added Zn) extracted by Ca(NO3)2 was correlated with the concentration of leaf Zn of the three crops (r = 0.62, P < 0.05), whereas the fraction of nonexchangeable Zn (48 to 78% of added Zn) extracted by 100 m M NH2OH · HCL in 1 M HNO3 was negatively correlated with leaf Zn (r = -0.49, P < 0.05). Reduced soil conditions depressed exchangeable Zn and enhanced nonexchangeable Zn in all of the ponded soils, apparently the result of the enhancement of surface-induced hydrolysis of Zn caused by increases in pH after flooding. The addition of organic C increased the fraction of Zn in nonexchangeable forms in the flooded soils, whereas the Zn levels in nonexchangeable forms in the unflooded soils were not affected by the addition of organic C. Thus, Zn availability to the crops was more dependent on pH changes induced by flooding than on the addition of organic C.
ZINC is a dominant heavy metal found in many organic waste materials (Keller et al., 2002). It is an essential trace element for plant growth and human nutrition, but it can be toxic at high concentrations, depending on pH and organic C concentrations (Berti and Jacobs, 1996;Krebs et al., 1998;Norvell and Welch, 1993;Whatmuff, 2002). Zinc reacts with organic C by forming outer- and inner-sphere complexes, and in the presence of organic C, it may form different species with different binding sites. Organic C-Zn complexes can be coupled to adsorption reactions that may reduce Zn solubility. Increasing Zn sorption with increasing pH is thought to be caused by surface-induced hydrolysis of Zn on Fe(III) and Mn(III,IV)(hydr) oxides (Yoo and James, 2002). Zinc availability in soils is dependent on various chemical forms, particularly as it is affected by soil pH, because the different Zn fractions differ in their solubility (Cabral and Lefebvre,1998;Luo and Christie, 1998;Martinez and Motto, 2000;Shuman, 1999).
In flooded soils, the inverse relationship of pH and redox potential (pe) controls the solubility of Zn bound to oxides and hydroxides of Fe(III) and Mn(III,IV) via reduction, complexation, and reprecipitation if labile organic compounds are available as a source of electrons in organic waste-amended soils (Brennan and Lindsay, 1998). The reduced and solubilized Fe2+ and Mn2+ and the higher pH of acidic soils caused by flooding can be both beneficial and harmful to plant growth because the reduced condition can increase concentrations of Fe2+ and Mn2+ and the availability of P (deMello et al., 1998), but it can also lower Al3+ toxicity and decrease the solubility of Zn, thereby resulting in a decrease in Zn availability for plant uptake (Dutta et al., 1989;Sajwan and Lindsay, 1988).
There has been speculation regarding the observed decrease in Zn availability to plants in flooded soils. Dutta et al. (1989) reported that the decrease in availability of Zn in acidic to near-neutral soils upon flooding was caused by Zn precipitation as hydroxides, carbonates, and sulfide compounds and by co-precipitation with Fe2+. Reduced Fe2+ that is reoxidized and precipitated in Fe(III) minerals can have great capacity to adsorb Zn, thereby diminishing the free Zn2+ concentration in soil solutions (Mandal and Hazra, 1997). Paracrystalline sesquioxides, changed from crystalline oxides of Fe(III) by reduction and reoxidation in reduced and oxidized zones of flooded soils, were the major sink for applied Zn (Mandal et al., 1992;Singh and Abrol, 1986). Luo and Christie (1998) suggested that the Fe(III) and Mn(III, IV) oxide-bound fraction was an important control on the solubility and bioavailability of Zn in sludge-amended soils. Therefore, reduction of Fe(III) and Mn(III, IV)(hydr) oxides may modify the transformation of Zn to different chemical forms, and it may interfere directly with the uptake of Zn by plants as a result of higher concentrations of solubilized Fe2+ and Mn2+ in flooded and organic waste-amended soils.
Many researchers have investigated the effect of redox on Zn availability in soils (Chuan et al., 1996;Mandal et al., 1992;Sajwan and Lindsay, 1988), but much less is known about the effect of biosolids containing high levels of organic matter on redox conditions that affect the availability of Zn in organic waste-amended soils. Organic compounds of biosolids can complex Zn because of the properties of organic polyelectrolytes. Soil pH can alter the surface charges of adsorption sites and the charge of organic ligands by protonation and deprotonation. Because pH varies as a result of flooding, Zn adsorption is not only a function of the properties of the adsorption surface sites but also depends on the sign of the charge of complexed Zn species (Harter and Naidu, 1995). Fluctuating pH following flooding and draining cycles may affect Zn mobility with respect to bioavailability in the rhizosphere in organic waste-amended soils. Chuan et al. (1996) reported that the effect of pH was more significant than that of pe in controlling the solubility of heavy metals in a contaminated soil. In this study, we evaluate the effect of organic C on Zn solubility in the various chemical forms, and we examine the relationships between Zn fractions and plant uptake, especially as a function of pH and of redox status induced by flooding.
Most of the studies on the effects of redox by flooding on Zn availability address paddy rice production (Mandal et al., 1992;Pavanasasivam and Axley, 1980;Reddy and Patrick, 1977;Sajwan and Lindsay, 1988). In this study, rice, wheat, and barley having different tolerances to flooded soil were selected to compare responses in plant growth and Zn uptake according to variations in soil pe and pH. A topohydrosequence of soils from the Coastal Plain of Maryland was chosen because the drainage characteristics of soils in different landscape positions affect native organic C levels and sesquioxide soil properties pertinent to heavy metal sorption and phytoavailability. We selected biosolids to determine the effect of organic C addition because they contain high organic C levels and often contain variable levels of heavy metals. We used a sequential extraction scheme to differentiate the Zn recovered and to define operationally the bioavailability of Zn in biosolids-amended soils.
The objectives of this study were (i) to investigate the effects of flooding soil, with and without organic C added, on the distribution of different Zn fractions related to bioavailability of Zn; and (ii) to evaluate plant growth and Zn uptake according to variations in soil pe and pH and organic C.
Although the qualities of the river water and the sediments of the river Elbe have greatly improved over the past twenty years, both the suspended matter and the sediments are still contaminated with heavy metals and arsenic (HM). This contamination exceeds the action values specified in the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV). The status of floodplain soil contamination with HM along the entire German alluvial Elbe was investigated and evaluated, based on former research activities and recently performed analyses after the extreme flood event in August 2002 and the subsequent winter flooding. The section downstream of the river Mulde inflow was contaminated much higher than the upstream section. With the installation of permanently marked observation areas a tool for soil quality monitoring has been established for the future.Die hochwasserbedingte Belastung der Auen mit Schwermetallen und Arsen entlang der ElbeObgleich sich die Flusswasser- und Sedimentqualität der Elbe in den letzten 20 Jahren erheblich verbessert haben, sind die Schwebstoffe und schwebstoffbürtigen Sedimente immer noch hoch mit Schwermetallen belastet. Dies führt bei Bodenbildungen aus diesen Substraten häufig zur Überschreitung der in der Bundesbodenschutz- und Altlastenverordnung (BBodSchV) festgelegten Maßnahmewerte. Basierend auf früheren Untersuchungen und aktuellen Erhebungen während des extremen Hochwassers vom August 2002 und des folgenden Winterhochwassers wurde der gegenwärtige Belastungsstatus der Böden in den Überflutungsgebieten entlang der gesamten deutschen tidefreien Elbe ermittelt und bewertet. Dabei war der Flussabschnitt unterhalb der Muldemündung wesentlich höher als der oberhalb gelegene belastet. Durch die Anlage dauerhaft markierter Beobachtungsflächen wird es ermöglicht, in Zukunft Veränderungen des Stoffbestandes exakt zu erfassen.
As floodplain soils are often contaminated, we studied the release of trace metals from three topsoil horizons in column experiments
with variable flow interruptions and flow velocities, compared it with that in batch leaching tests and evaluated the column
data by inverse simulations. Only small proportions (<1%) of trace metals present in the neutral and humic soils were mobilised
by the batch leaching tests and the column experiments. Release of Cr, Cu, Ni and Zn in the column experiments was rate-limited,
as detected by increased concentrations after flow interruptions. A combination of linear equilibrium and non-equilibrium
isotherms reflected the Ni and Zn elution data, with Zn release being slower. Simulated values for initially bound metals
available for release are in the same order of magnitude as those determined by the batch leaching tests. However, the consistency
of both experimental approaches decreases with increasing rate limitation, as detected here for Zn.
The applicability of laboratory tests for the prediction of soil solution composition and concentrations of inorganic contaminants
is still under debate. Therefore, we carried out two batch-leaching tests differing in their liquid/solid ratios and column
experiments (saturated flow, two flow velocities, four flow interruptions ranging from 4h to 21days) with a contaminated
humic horizon (total contents: As, 196mgkg−1; Cd, 4mgkg−1; Cr, 202mgkg−1; Cu, 227mgkg−1; Ni, 64mgkg−1; Pb, 308mgkg−1; Zn, 1,176mgkg−1) from a Mollic Fluvisol near the rivers Elbe and Saale (Germany) and compared the aqueous contaminant concentrations with
those of soil solutions obtained in situ with ceramic suction cups on a monthly basis between 2002 and 2006. Contaminant release
in the field slightly depended on the water regime, pH, and redox potential and was characterized by partially high concentrations
(e.g., As, 47µgl−1; Cd, 136µgl−1; Ni, 328µgl−1; Zn, 8.68mgl−1), which exceeded the German inspection values. Metal concentrations obtained in batch-leaching tests partially fitted to
those determined in the soil solution and to those from the column experiments even irrespective of the varying liquid/solid
ratios. The column experiments yielded realistic concentrations of Cr, Cu, Ni, and Pb and their ranges. Furthermore, they
provided an insight into release kinetics and release processes as well as into potential contaminant release due to enforced
reducing conditions. As column experiments allow a larger temporal sampling resolution and enable quickly to manipulate experimental
conditions, they are a useful complement of soil solution monitoring.
KeywordsWetland soil-Soil solution-Metals-Batch-leaching test-Column experiments-Soil contamination
The submerged aquatic plant Myriophyllum spicatum L. (Eurasian water milfoil) has been suggested as an efficient plant species for the treatment of metal-contaminated industrial wastewater. The process of metal removal by plants involves a combination of rapid sorption on the surface and slow accumulation and translocation in the biomass. This study focussed on the sorption/desorption characteristics of the surface of M. spicatum for Co, Cu, Ni and Zn. Batch sorption tests with mixed metal solutions covering a range of 0, 1, 5, 10, 50 and 100 mg l−1 of each metal, were performed. For Co, Ni and Zn, the sorption process was well described by the Langmuir model, whereas sorption of Cu was better described by the Freundlich model. The biomass showed the highest affinity for Cu and Zn. Langmuir sorption maxima of Co, Ni and Zn were 2.3, 3.0 and 6.8 mg g−1 DM, respectively. At the highest initial concentration of 100 mg l−1, a maximum of 29 mg g−1 DM of Cu was sorbed onto the surface of the biomass. Desorption by 0.1 M HCl did not fully recover the metals sorbed onto the surface and there was evidence of leaching from within the biomass. Recovery of heavy metals and regeneration of the biomass by washing with 0.1 M HCl was therefore not suggested as a viable strategy.
Kinetics and chemical fractionation procedures were used to quantify the effect of the sediment redox (Eh) condition on the behavior of As, Cd, Cr, and Zn in the bottom sediment collected from a Louisiana coastal site receiving produced water discharge. Sediment samples were incubated in microcosms in which Eh-pH conditions were controlled. Sediment was sequentially extracted to determine metals in various chemical fractions (water soluble, exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to insoluble organic and sulfides) and the chemical inactive fraction (mineral residue). Under oxidizing conditions, As, Zn, and Cr behavior was governed by redox chemistry of Fe(III) and Mn(IV) oxides. Cd transformations were controlled by both Fe(III) and Mn(IV) oxides and carbonates. Under a reducing condition, the behaviors of Zn and Cr were controlled primarily by insoluble large molecular humic material and sulfides; the behavior of Cd was controlled by carbonates. When sediment redox potential increased, the affinity between Fe(III) and Mn(IV) oxides and As, Cd, Cr, and Zn increased. When sediment redox potential decreased, the affinity between carbonates and Cd and Zn increased; the affinity between insoluble sulfides, large molecular humic matter and As, Cd, Cr, and Zn increased; the soluble Cd and Zn decreased; the soluble As and Cr remaine d constant. Results suggest reducing sediment conditions would reduce Cd and Zn toxicity. Under reducing or anaerobic conditions, the solibilization rate constants (mg kg−1 d−1) for As, Cr, Cd, and Zn bound to Fe(III) and Mn(IV) oxides were −0.88, −0.32, −0.01, and −6.5, respectively; the rate constants (mg kg−1 d−1) for dissolved Cd and Zn were −0.09 and −1.78, respectively.
Soil contamination by heavy metals could be caused by long-term storage of sewage sludge on the territory of most municipal wastewater treatment plants (WWTPs) worldwide. Different methods to deal with heavy metal pollution and rehabilitation can be applied, but they are costly. Phytoremediation is a method using plants in order to extract, sequester and/or detoxify pollutants such as heavy metals. Phytotechnologies are more advantageous economically, than other in situ and ex situ remedial approaches (they estimated to be at least 40% less costly) (ITRC, 2001).In this work the suitability of several plant species for phytoremediation under natural conditions was studied. Brassica napus, Medicago sativa, Zea mays, Triticum aestivum and Hordeum vulgare were grown in pots with sewage sludge from “Bezludivka” WWTP in Kharkiv, Ukraine and from Sindos WWTP in Thessaloniki, Greece.Plants in the experimental series were compared to those in the control samples (the same species grown in compost). In experimental series, shoot growth was less reduced in T. aestivum and H. vulgare than in the other plant species studied. M. sativa had the lowest germination rate. Generally B. napus and M. sativa, giving less biomass production than Z. mays and T. aestivum, were characterized by higher ability to accumulate heavy metals (Cd, Cu, Ni, Pb, Zn, Cr, As and Hg).
Pore-water concentration profiles provide insight into diagenetic processes taking place in aquatic sediments. Due to the high input of reactive organic matter and the relatively low availability of external oxidators, redox zones generally occur on a millimetre to centimetre scale in organic-rich freshwater sediments. Distinct peaks in dissolved trace metal concentrations measured immediately below the sediment—water interface, can be mainly attributed to degradation of organic matter. The resulting concentration gradients between the pore water and the water column indicate that upward fluxes of trace metals from the sediment may contribute to concentrations in the surface water. An excess of acid-volatile sulphide (AVS) over reactive metals (SEM) in the anoxic sediment layer is a strong indication that trace metals may be effectively scavenged by sulphides, thus reducing their pore-water concentrations. However, supersaturation of the pore water with respect to metal sulphides indicates intensive complexation of trace metals with dissolved organic compounds. Given the large vertical variation in redox potential with depth, mixed homogenized sediment samples (0–10 cm) are generally not suited for the assessment of potential toxicity of sediments with respect to trace metals. Temporal variation in pore-water chemistry reflects environmental and intrinsic changes. These may be related to fluctuation in temperature, the supply of degradable organic matter, microbiological activity in the sediment, diffusion of solutes, mixing and reaction rates. As a result of this variation in the intensities of biogeochemical processes, (bio)availability of trace metals may fluctuate considerably. Therefore, in dynamic depositional environments it is necessary to account for non-steady state to determine diffusive exchange between sediments and surface water, as well as potential toxicity of sediments with respect to trace metals.
A research project dealing with the phytoremediation of a soil polluted by pyrite cinders is currently running. The case study is represented by a polluted area located in an industrial site; since 2001, the site has been listed in the clean-up national priority list. Before the beginning of the in situ trials, two experiments in controlled conditions were carried out. The first pot experiments were performed growing Glycine max, Sorghum bicolor, Zea mays and Helianthus annuus on substrates polluted by different levels of pyrite cinders, containing As, Cd, Cu, Pb and Zn. In a second experiment, the possible influence of fertilization on the uptake of As and heavy metals by S. bicolor and H. annuus was observed.The potential of phytoextraction of crops was evaluated considering the plant biomass, the concentration of As and heavy metals in the plant tissues and also the bioconcentration factor (BCF) and the translocation factor (TF).In the most polluted substrate, S. bicolor appeared more efficient than H. annuus in the uptake of metals; the transport of the metals from roots towards stems and leaves was less efficient in S. bicolor.
Aggregating floodplain soil- and substrate-types allows a simple and practicable transfer of their properties, with little loss of information. Spatial distribution of floodplain soils along the Central Elbe River with increased concentrations of nutrients and heavy metals tend to be determinable and definable. Soils of the low-lying terraces (“Tschernitzen” consisting of floodplain silt and loam) and soils in depressions (“Gleye” consisting of floodplain clay and silt) have the largest concentrations of nutrients and pollutants because they reveal high humus content and fine mineral particles as a result of sedimentation through frequent or extended flooding periods with low flow-rates. Proper knowledge of the distribution of floodplain soil- and substrate-types allows predicting spatial distributions of concentrations of nutrients and pollutants, although high variability within soil types and transitions between them remains a challenge to be solved.
Ecological engineering was defined as the practice of joining the economy of society to the environment symbiotically by fitting technological design with ecological self design. The boundary of ecological engineering systems includes the ecosystems that self organize to fit with technology, whereas environmental engineering designs normally stop at the end of the pipe. For example, the coastal marsh wildlife sanctuary at Port Aransas, Texas, developed when municipal wastewaters were released on bare sands. The energy hierarchy concept provides principles for planning spatial and temporal organization that can be sustained. Techniques of ecological engineering are given with examples that include maintaining biodiversity with multiple seeding, experimental mesocosms, enclosed systems with people like Biosphere 2, wetland filtration of heavy metals, overgrowth and climax ecosystems, longitudinal succession, exotics, domestication of ecosystems, closing material cycles, and controlling water with vegetation reflectance.
The Rı́o Pilcomayo rises on the Cerro Rico de Potosı́ precious metal-polymetallic tin deposits of Bolivia, and flows in a southeasterly direction for ca. 600 km to Bolivia's southern border with Argentina. Mining of the Potosı́ deposits has occurred continuously since 1545, generating large quantities of waste materials in the headwater of the basin. In addition, a tailings dam breach at the Porco mine in 1996 released an estimated 235 000 m3 of tailings and fluid into the upper reaches of the Rı́o Pilaya, the largest tributary to the Pilcomayo.
Sampling along the River Lahn, a major tributary to the River Rhine that flows through an agrarian region of west-central Germany, reveals that heavy metal pollution occurs outside major industrial regions and mined landscapes. Along a 60-km reach of the river between Marburg and Wetzlar, mean concentrations of Cu, Pb and Zn at depths of 5 and 15 cm in four floodplain transects were greater than background levels. Concentrations declined sharply between 15 and 25 cm. Laterally, concentrations peaked at the bank top and in the near-channel zone of the floodplain. Beyond the near-channel zone (generally up to 100 m from the channel) concentrations were much less and fairly uniform to the valley wall. The clustering of metals close to the channel suggests that they are a fluvial rather than an eolian deposit. During floods of a moderate magnitude, sediments and attached metals are deposited soon after the river overtops its banks. Although the overall store of metals in the valley is less than that along the Rhine, near-channel metal concentrations are similar to those along rivers draining major industrial and mined areas.
Incl abstract and bibl. The aim of this study is to clarify the nature of teacher effectiveness and develop a measure for evaluating teacher effectiveness. The present study was conducted in two phases. In phase one, 148 undergraduate students were asked to identify qualities of effective teachers. In phase two items from existing instruments, intended to measure effective teaching, were combined with items generated from students in phase one to form a meta-inventory. The meta-inventory was administered to 266 undergraduate psychology students. Factor analysis revealed that teacher effectiveness is multi-dimensional in nature, comprising three factors; respect for students, ability to challenge students, organisation and presentation skills. In addition, the findings from the present study supported several teacher effectiveness dimensions evident in past research
"Broad rivers, slowly flowing through endless lowlands" is a famous phrase taken from Dutch poetry. 'Endless', indeed, are the changes to which lowland river floodplains will be subjected in the near future. More and longer inundations, restoration of floodplain forests, rehabilitation of the morphology, new legislation on the emission of pollutants, land abandonment in the river's hinterland... All these changes subsequently affect the deposition of sediments and associated heavy metals on lowland river floodplains. This book studies the key factors behind the process of floodplain deposition, describes the current deposition patterns and assesses how the suite of changes will affect both process and patterns.
Environmental pollution by mercury (Hg) is a considerable environmental problem world-wide. Due to the occurrence of Hg volatilization from their soils, floodplains can function as an important source of volatile Hg. Soil temperature and soil water content related to flood dynamics are considered as important factors affecting seasonal dynamics of total gaseous mercury (TGM) fluxes. We quantified seasonal variations of TGM fluxes and conducted a laboratory microcosm experiment to assess the effect of temperature and moisture on TGM fluxes in heavily polluted floodplain soils. Observed TGM emissions ranged from 10 to 850 ng m(-2) h(-1) and extremely exceeded the emissions of non-polluted sites. TGM emissions increased exponentially with raised air and soil temperatures in both field (R(2): 0.49-0.70) and laboratory (R(2): 0.99) experiments. Wet soil material showed higher TGM fluxes, whereas the role of soil water content was affected by sampling time during the microcosm experiments.
The current paper aims to check whether the factors affecting metal mobility in intertidal sediments and floodplain soils of the river Scheldt, as identified under controlled greenhouse conditions in previous studies, also play a similar role under variable field conditions. Moreover, we aimed to assess the importance of these factors as a function of sampling time and depth, with respect to the natural variations in water table levels. This field monitoring revealed that the mobility of metals in intertidal sediments of the Scheldt estuary indeed are affected by factors which were identified to affect the metal fate in the upper sediment layer in previous greenhouse experiments. However, the effects were often less pronounced under field conditions. This can be attributed to the lower sampling resolution, the occurrence of interactions between factors, the disturbance of microbial communities during setup of greenhouse experiments and the more moderate environmental conditions in the field, affecting microbial and enzymatic activities. At most of the sampled wetlands, the level of the water table fluctuated only slightly during fall, winter and spring, whereas it decreased substantially during summer, especially at the sites with more sandy sediments. The highest sulphide concentrations were found at the sites where the water table level never decreased considerably. These sulphides primarily suppress the availability of Cd, Cu, Ni and Zn. Organic complexation resulted in the mobilisation of Cu, Ni and Cr. The concentrations of Cd, Ni and Zn in the pore water were affected by Fe/Mn oxide reduction, whereas Cd and Zn concentrations appeared to be also affected by the salinity.
This paper reviews the factors affecting trace metal behaviour in estuarine and riverine floodplain soils and sediments. Spatial occurrence of processes affecting metal mobility and availability in floodplains are largely determined by the topography. At the oxic-anoxic interface and in the anoxic layers of floodplain soils, especially redox-sensitive processes occur, which mainly result in the inclusion of metals in precipitates or the dissolution of metal-containing precipitates. Kinetics of these processes are of great importance for these soils as the location of the oxic-anoxic interface is subject to change due to fluctuating water table levels. Other important processes and factors affecting metal mobility in floodplain soils are adsorption/desorption processes, salinity, the presence of organic matter, sulphur and carbonates, pH and plant growth. Many authors report highly significant correlations between cation exchange capacity, clay or organic matter contents and metal contents in floodplain soils. Iron and manganese (hydr)oxides were found to be the main carriers for Cd, Zn and Ni under oxic conditions, whereas the organic fraction was most important for Cu. The mobility and availability of metals in a floodplain soil can be significantly reduced by the formation of metal sulphide precipitates under anoxic conditions. Ascending salinity in the flood water promotes metal desorption from the floodplain soil in the absence of sulphides, hence increases total metal concentrations in the water column. The net effect of the presence of organic matter can either be a decrease or an increase in metal mobility, whereas the presence of carbonates in calcareous floodplain soils or sediments constitutes an effective buffer against a pH decrease. Moreover, carbonates may also directly precipitate metals. Plants can affect the metal mobility in floodplain soils by oxidising their rhizosphere, taking up metals, excreting exudates and stimulating the activity of microbial symbionts in the rhizosphere.
The wetland soils of the Mulde river in the industrial district of Bitterfeld-Wolfen (Germany) are highly contaminated with heavy metals and arsenic. We studied the mobility of accumulated heavy metals and arsenic and the influence of dissolved organic matter (DOM) on element mobility. Undisturbed soil cores were taken from five different sites to represent a wide range of heavy-metal contamination, soil properties and dissolved organic carbon (DOC) concentrations. The acid-soluble concentrations (mostly equal to the total content) were up to 1100 mg kg-1 for Zn, 800 mg kg-1 for Cr, 364 mg kg-1 for Cu, 265 mg kg-1 for As and 37 mg kg-1 for Hg, depending on the sampling site. Percolation experiments using small lysimeters with undisturbed topsoil cores illustrated a considerable mobilization of Zn, Cd, Cu, Cr and Hg, depending on soil properties. Up to 80 micrograms l-1 Cd, 8 mg 1-1 Zn, 130 micrograms l-1 Cr, 160 micrograms l-1 Cu and 7 micrograms l-1 Hg were detected in the soil percolates. Arsenic mobilization was low. The concentration of Cr, Hg, Cu and As in the soil percolates was positively correlated with DOM. Besides the element content (mobile or acid-soluble), soil pH and soil characteristics describing the soil potential for heavy-metal adsorption (clay, oxides, cation exchange capacity), the DOC concentration in the soil solution should be known to access the potential mobilization of Hg, Cr, Cu and As. In contrast, Cd and Zn mobilization depends on soil pH and mobile element content, but not on DOM. Additional studies on two soil profiles (down to 1.5 m) confirmed the translocation of heavy metals from the highly contaminated topsoil into deeper soil horizons and into the groundwater and the influence of DOM as revealed with the percolation experiment. Our results also showed that DOM is of minor importance on the mobilization of heavy metals in soils with a low soil pH (< 4.5).