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This article considers exchangeable potassium levels in the floodplain soils of the Amur River. The accumulation of exchangeable potassium in these soils was found to be largely determined by their age and weathering extent. In the young and highly weathered soils, the content of exchangeable potassium was lower than in the middle-aged soils. In the humus-accumulating horizon, it was 100–400 mg/kg and 200 mg/kg in the Upper and Middle Amur River, respectively. As for the mineral horizons, it ranged from 20 mg/kg in the young alluvial soils to 150 mg/kg in the residual-floodplain rusty soils. Interestingly, a significant increase in exchangeable potassium was observed for the coniferous-birch forests of the Upper Amur River (reaching an average of 400 mg/kg), but not for the oak forests in the Middle Amur River. Due to the asymmetry of the rate and ratio of zonal processes in the floodplain soils of the Upper and Middle Amur River, the residual-alluvial soils turned out to be sharply differentiated by the exchangeable potassium profiles. On average, the brown soils (Fluvic Cambisols) of the Upper Amur River contained up to 350 mg/kg of exchangeable potassium. The Fluvic Cambisols of the Middle Amur River had the lowest content of exchangeable potassium as compared to other studied soils.

PAHs are one of the most toxic organic compounds classes which is obligatory controlled all over the world. There is a luck of studies devoted to the PAHs levels and sources identification in the south of Russia. The features of the PAHs accumulation and spatial distribution in hydromorphic soils (Fluvisol) were studied on the example of the soils of the Don River delta floodplain landscapes. It has been shown that changes in the PAHs content in soils depended on the type and intensity of the emission source. A factor analysis and multivariate linear regression analysis were carried out to determine the features of the spatial distribution for individual PAH compounds, considering the properties of soils and typical differences in the emission source. The most polluted areas in the studied area located along the transit line of the long-distance tankers, where the content of the most toxic high molecular PAHs compounds reached 8862 ng g−1. As a result of regression analysis, a relationship was established between the PAHs accumulation rate with the content of silt (particles less than 0.001 mm in size) and Ca2+ and Mg2+ exchangeable cations in the soil (at p-level < 0.0001). Differences in individual PAH content for medium and heavy loamy Fluvisol and depend on the influence of different types of pollution sources. [ABSTRACT FROM AUTHOR]

Heavy metals transported by rivers are deposited in sediments and floodplains, and floodplain soils act as both sinks and sources of these metals. The Innerste River is contaminated by historical metal ore mining, processing, and smelting in the Harz Mountains (Germany). Our study compared the uptake of lead (Pb) and zinc (Zn) in wild blackberries (Rubus fruticosus L. agg.) growing within and outside the Innerste floodplain in a downstream area. The potential of blackberries as bioindicators and for phytoremediation of soils polluted by Pb and Zn was assessed based on bioconcentration factors (BCF) and the intra-plant mobility of the two metals based on translocation (TF) factors.Concentrations of Pb and Zn were significantly higher in soils and blackberry plants from the Innerste floodplain compared to adjacent non-flooded area, while soil pH and organic matter content did not differ significantly between the two zones. Mean concentrations (mg/kg d.w.) of Pb (1457.2) and Zn (1365.2) in the regularly flooded soils far exceeded the precautionary limits of the German Federal Soil Protection and Contaminated Sites Ordinance. Concentrations of both heavy metals in blackberry roots and leaves increased with their levels in soil. Except for BCFRoot Pb, BCFs and TFs decreased exponentially with increasing heavy metal concentration in soil and roots, respectively. This indicates that the uptake of Pb and Zn by R. fruticosus and their translocation within the plant are reduced at higher soil levels of both heavy metals. BCF < 1 were determined for both heavy metals and a TF < 1 for Pb. Only blackberries growing outside the floodplain showed a TF > 1 for Zn.Our results indicate that blackberries can be used as bioindicators of soil contamination by Pb and Zn. Regarding their uptake characteristics, blackberries constitute excluders rather than accumulators, and are thus unsuited for phytoremediation.

Metal contamination, especially in river floodplain soils, can have detrimental effects on human health. Much research has been conducted to describe the distribution patterns of metals and the factors involved in these patterns. However, most studies focus on the distribution of individual metals in soils, not on the co-occurrence of metals, and on a selection of metals associated with anthropogenic sources known to have especially severe effects; this had led to a lack of knowledge about many other metals with potentially harmful effects. Therefore, this study aimed to identify the multi-metal distribution patterns of 38 metals in the Sacramento River floodplain and find their controlling factors. We found 484 significant correlations between metal distributions. Less commonly studied metals, such as gallium, lanthanum, scandium, and vanadium, had more than 25 correlations each. In total, 13 individual metal patterns described the spatial distribution of 22 metals. Three multi-metal patterns were extracted, explaining 86.9% of the spatial variation of the individual patterns. The most important factors were the distance to specific streams due to emission and transport processes in their watersheds, and local soil properties. We conclude that multi-metal distribution patterns hold more information than individual metal patterns, contributing to the gathering of information about less commonly sampled metals and allowing more specific source identification. [ABSTRACT FROM AUTHOR]

This work was carried out to study the content and distribution of available for plants phosphorus in different types of floodplain soils along five catenas located in the upper and the middle Amur. It was found that the available for plants phosphorus forms in the soils of floodplains are influenced by the following factors: the structure of the river system, the type of floodplain, the type of vegetation cover, and soil-forming processes. During the long-term transportation of alluvium along the river bed, its hydrogenic weathering occurs with the release of phosphorus into river waters. In the absence of tributaries serving as additional sources of alluvium, the phosphorus content decreases downstream. More intense floodplain and alluvial processes in small floodplains provide renewal of the soil profile and replenishment of phosphorus reserves. In the soils under the birch forest, there is a significant accumulation of phosphorus, in comparison with the soils under meadow vegetation. The development of gley processes leads to active mobilization of phosphorus, but the long-term exposure leads to the depletion of its total reserves. The illimerization processes, initiated and developing when the floodplain hydrological regime of alluvial soils is changed to another one, promote the migration of iron oxides and phosphorus, adsorbed by the former, beyond the soil profile. To summarize, the average content of available for plants phosphorus, depending on the type of soil, decreases downstream from 300–100 mg/kg in the upper Amur to 170–20 mg/kg in the middle Amur. Available for plants of phosphorus are best provided in primitive alluvial layered soils, while in residual floodplain brunezems the lowest content is recorded.

Modeling metal sorption in soils is of great importance to predict the fate of heavy metals and to assess the actual risk driven from pollution. The present study focuses on adsorption of HM ions on two types of hydromorphic soils, including calcaric fluvisols loamic and calcaric fluvic arenosols. The individual and competitive adsorption behaviors of Cu and Zn on soils and soil constituents are evaluated comprehensively. It is established that the sorption processes were best described with the Langmuir model. The results suggest that the calcaric fluvic arenosols are more vulnerable to heavy metal input compared to fluvisols loamic. In all cases, Cu had a higher range of values of the adsorption process parameters relative to Zn. The Zn is likely to be the most critical environmental factor in such soils since it exhibited a decreased sorption under competitive conditions. The retention mechanisms of HM in hydromorphic soils are considered. Based on theoretical calculations of ion activity in soil solutions using solubility diagrams of Cu and Zn compounds, the possibility of precipitation of Cu hydroxide and Zn carbonate in the studied soils is shown. Direct physical methods of nondestructive testing (XAFS and XRD) are applied to experimentally prove the formation of these HM compounds on the surface of montmorillonite, the dominant mineral in hydromorphic soils, and calcite. Thus, the combination of both physicochemical methods and direct physical methods can provide a large amount of real information about the mechanisms of HM retain with solid phases. [ABSTRACT FROM AUTHOR]

Nitrate pollution in aquatic ecosystems is still a major problem in Germany. There is a great potential to permanently remove nitrate from aquatic systems through denitrification as a relevant ecosystem function. However, the controlling factors and the dimension of the denitrification potential are still not fully understood due to the high complexity of the process. This study presents the combined assessment of potential soil denitrification rates, physical and chemical soil parameters, and hydrological parameters from six floodplains of four large German rivers, namely the Rhine, the Elbe, the Weser, and the Main. Based on multivariate statistics, results show that the denitrification potential of soil was almost solely controlled by soil pH. The lab assays showed mean soil denitrification potentials of 6.4–11.4 mg N m−2 h−1 (pH < 7) and 23.0–30.5 mg N m−2 h−1 (pH > 7). We contend that when upscaling these estimates to annual rates of potential denitrification, the duration of average inundation should be incorporated, as this accounts for water saturation and nutrient supply − the major controlling variables for denitrification. Results provide evidence that the denitrification potential can only be fully exploited in frequently inundated floodplains. Thus, despite favorable soil conditions for denitrification, floodplains that have suffered from anthropogenic impacts, lose their importance in nitrate removal for the river system. We conclude that pH and lateral hydrological connectivity are likely to be key factors that should be considered when estimating denitrification as an ecosystem function.

The concentrations of 28 polychlorinated biphenyls (PCBs) were determined in soils collected at three depths from thirteen different sites along the floodplain of the lower reaches of the River Niger (LRRN) in Nigeria. The aim of the study was to provide data on the levels of contamination, sources of the contaminants, and risks to the ecosystem and humans. Soil samples were Soxhlet extracted with a solvent mixture of dichloromethane (DCM)/n-hexane and cleaned up on a column packed with Florisil and silica gel. The PCBs in the samples were quantified by gas chromatography-mass spectrometry. The Ʃ28 PCB concentrations in the floodplain soils varied between not detected (nd) and 11,151 ng g−1 for different sampling sites and depths. The PCB concentrations and homologue distribution patterns in soil profiles of the floodplain of the LRRN showed remarkable differences with respect to sites and depths. The results obtained were used to evaluate the ecological and human health risks, which indicated that there is a potential risk to organisms and humans from exposure to PCBs in these soil profiles. The source evaluation as determined by principal component analysis suggested that PCBs in these soil profiles came from burnt circuit boards, cable wires, use of paints, discharges from transformers, long-range migration, and deposition. [ABSTRACT FROM AUTHOR]

Radiocaesium and radiostrontium contamination in the 'soil – rhizosphere – plants (aerial parts)' system was monitored in the floodplain ecosystem of the Yenisei River in the near impact zone of the Krasnoyarsk Mining and Chemical Combine (MCC). The monitored system included soil, rhizosphere, and sedge vegetation on islands and the river's east bank. The 137Cs and 90Sr specific activities displayed intricate space and time patterns controlled by the river water level, including the time and duration of floods and their correlation with the sedge vegetation season. The specific activities of both radionuclides, especially 137Cs, were above the background in all years of observation, except in a few cases. The soil-to-plant transfer factor (TF) patterns showed continuous 137Cs and 90Sr influx into the system and annual variations in the shares of their bioavailable and fixed forms, especially for 90Sr. The 90Sr distribution in the 'soil – rhizosphere – plants' system observed in 2014–2016 provides evidence for possible local fallout. [ABSTRACT FROM AUTHOR]

Metal contamination, especially in river floodplain soils, can have detrimental effects on human health. Much research has been conducted to describe the distribution patterns of metals and the factors involved in these patterns. However, most studies focus on the distribution of individual metals in soils, not on the co-occurrence of metals, and on a selection of metals associated with anthropogenic sources known to have especially severe effects; this had led to a lack of knowledge about many other metals with potentially harmful effects. Therefore, this study aimed to identify the multi-metal distribution patterns of 38 metals in the Sacramento River floodplain and find their controlling factors. We found 484 significant correlations between metal distributions. Less commonly studied metals, such as gallium, lanthanum, scandium, and vanadium, had more than 25 correlations each. In total, 13 individual metal patterns described the spatial distribution of 22 metals. Three multi-metal patterns were extracted, explaining 86.9% of the spatial variation of the individual patterns. The most important factors were the distance to specific streams due to emission and transport processes in their watersheds, and local soil properties. We conclude that multi-metal distribution patterns hold more information than individual metal patterns, contributing to the gathering of information about less commonly sampled metals and allowing more specific source identification.

Understanding the behavior of colloidal phosphorus (P coll ) under anoxic conditions is pivotal for addressing soil phosphorus (P) mobilization and transport and its impact on nutrient cycling. Our study investigated P coll dynamics in acidic floodplain soil during a 30-day flooding event. The sudden oxic-to-anoxic shift led to a significant rise in pore-water P coll levels, which exceeded soluble P levels by more than 2.7-fold. Colloidal fractions transitioned from dispersed forms (<220 nm) to colloid-associated microaggregates (>220 nm), as confirmed by electron microscopy. The observed increase in colloidal sizes was paralleled by their heightened ability to form aggregates. Compared to sterile control conditions, anoxia prompted the transformation of initially dispersed colloids into larger particles through microbial activity. Curiously, the 16S rRNA and ITS microbial diversity analysis indicated that fungi were more strongly associated with anoxia-induced colloidal release than bacteria. These microbially induced shifts in P coll lead to its higher mobility and transport, with direct implications for P release from soil into floodwaters.

The Holocene paleoclimate of the Caucasus region is rather complex and not yet well understood: while existing studies are mainly based on pollen records from high‐altitude and humid lowland regions, no records are available from the semi‐humid to semi‐arid south‐eastern Caucasian lowlands. Therefore, this study investigated compound‐specific δ2H and δ13C isotopes of leaf wax biomarkers from Holocene floodplain soils in eastern Georgia. Our results show that the leaf wax δ2H signal from the paleosols mostly reflects changes in the moisture source and its isotopic composition. Depleted δ2H values before ~8 cal ka bp change towards enriched values after ~5 cal ka bp and become again depleted after ~1.6 cal ka bp. This trend could be caused by Holocene changes of the isotopic compositions of the Black and eastern Mediterranean Sea, and/or by varying contribution of both moisture sources linked with the North Atlantic Oscillation. The leaf wax δ13C signal from the paleosols directly indicates varying local water availability and drought stress. Depleted δ13C values before ~8 and after ~5 cal ka bp indicate wetter local conditions with higher water availability, whereas more enriched values during the middle Holocene (~8 until at least 5 cal ka bp) indicate drier conditions with increased drought stress. [ABSTRACT FROM AUTHOR]

The concentrations of the 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were determined in the floodplain soils of the lower parts of the River Niger, Nigeria in 2013 and 2014 after recent flood waters had receded completely into the river channels. The aim of the research was to provide data on the spatiotemporal changes in the contamination levels, compositional patterns, sources and human health risks linked with exposure to PAHs in these soils through non-dietary ingestion, inhalation and dermal contact pathways. The PAHs in the soil samples were extracted by ultrasonication with hexane/dichloromethane, followed by clean-up on a silica gel/alumina column, and gas chromatography-mass spectrometry was used for their separation, detection and quantification. The concentrations of the 16 PAHs varied from 812 to 10,700 µg kg−1 in 2013 after an extreme flooding event, and from 12.2 to 2630 µg kg−1 in 2014 after a natural flooding event. The benzo[a]pyrene (BaP) potency factors and incremental life cancer risks (ILCR) were used to evaluate the risks of human exposure to PAHs in these soils. The average total ILCR values obtained for 2014 (a year after the extreme flooding) indicated that there was a probability of 443 children and 308 adults in a population of one million equally exposed individuals at risk of developing cancer or cancer-related illnesses in their lifetime as opposed to 6450 children and 4480 adults in 2013 immediately after the extreme flooding event. This study has shown that flooding events can cause significant variations in pollutant concentrations of floodplain soils that markedly alter human health risks. [ABSTRACT FROM AUTHOR]

Lateral movements of soil organic C (SOC) influence Earth's C budgets by transporting organic C across landscapes and by modifying soil-profile fluxes of CO2. We extended a previously presented model (Soil Organic C Erosion Replacement and Oxidation, SOrCERO) and present SOrCERODe, a model with which we can project how erosion and subsequent deposition of eroded material can modify biosphere-atmosphere CO2 fluxes in watersheds. The model permits the user to quantify the degree to which eroding and depositional profiles experience a change in SOC oxidation and production as formerly deep horizons become increasingly shallow, and as depositional profiles are buried. To investigate the relative importance of erosion rate, evolving SOC depth distributions, and mineralization reactivity on modeled soil C fluxes, we examine two forests exhibiting distinct depth distributions of SOC content and reactivity, hydrologic regimes and land use. Model projections suggest that, at decadal to centennial timescales: (1) the quantity of SOC moving across a landscape depends on erosion rate and the degree to which SOC production and oxidation at the eroding profile are modified as deeper horizons become shallower, and determines the degree to which depositional profile SOC fluxes are modified; (2) erosional setting C sink strength increases with erosion rate, with some sink effects reaching more than 40% of original profile SOC content after 100 y of a relatively high erosion rate (i.e., 1 mm y−1); (3) even large amounts of deposited SOC may not promote a large depositional profile C sink even with large gains in autochthonous SOC post-deposition if oxidation of buried SOC is not limited; and (4) when modeled depositional settings receive a disproportionately large amount of SOC, simulations of strong C sink scenarios mimic observations of modest preservation of buried SOC and large SOC gains in surficial horizons, suggesting that C sink scenarios have merit in these forests. Our analyses illuminate the importance of cross-landscape linkages between upland and depositional environments for watershed-scale biosphere-atmosphere C fluxes, and emphasize the need for accurate representations and observations of time-varying depth distributions of SOC reactivity across evolving watersheds if we seek accurate projections of ecosystem C balances.

The paired Fluvisol and cereal samples in both the field screening and controlled experiments are reported to elucidate the soil–crop relationship for As, Cd, and Pb in relation to changing contamination levels. Significant varietal differences in plant uptake were observed for crop type (barley, triticale) and the harvested part of the crop (oat shoots and grain). When parametrizing the stepwise regression models, the inclusion of soil properties often improved the performance of soil–crop models but diverse critical soil parameters were retained in the model for individual metal(loid)s. The pH value was often a statistically significant variable for Cd uptake. For As and Pb, the more successful model fit was achieved using the indicators of quantity or quality of soil organic matter, but always with lower inherent model reliability compared to Cd. Further, a single correlation analysis was used to investigate the relationship between extractable metal concentrations in soil solution and their crop accumulation. For Cd, there were strong intercorrelations among single extractions, the NH4NO3 extraction stood out with perfect correlation with plant uptake in both experiments. For As and Pb, the CaCl2 and Na2EDTA solutions outperformed other single extractions and were the better choice for the assessment of depositional fluvial substrates.

Abstract Identifying floodplains with high rates of denitrification will help prioritize restoration projects for the removal of nitrogen. Currently, relationships of denitrification with hydrogeomorphic, physiographic, and climate (i.e. , largescale) characteristics of floodplains are relatively unknown, even though these characteristics have datasets (e.g. , geographic mapping tools) that are publicly available (or soon-to-become) that could be used to understand denitrification variability. Thus, we investigated control of denitrification by these largescale characteristics in eighteen nontidal floodplains of the Chesapeake Bay watershed (i.e. , at regional scale, >100 km, scale), using measurements or compiled data at the scales of the stream reach and respective catchment; floodplain soil and herbaceous vegetation (i.e. , local) characteristics were additionally investigated. Soil denitrification potentials were measured in May, July, and August using complementary acetylene-based techniques under an anoxic environment. Linear largescale predictors of denitrification potential measurements included stream nitrogen and phosphorus concentrations (+), channel width-to-depth ratio (+), floodplain sedimentation (+), forested (−) and urban (+) catchment land cover, and seasonal air temperature (−). Three predictors, catchment forested land cover (strongly related to agricultural land cover), catchment urban land cover, and floodplain sedimentation were related to the most number of denitrification potential measurements. Soil structure, soil nutrient concentrations, and herbaceous vegetation characteristics that were seasonally measured (with a few exceptions) were linear predictors of denitrification potentials in May and August, with nitrogen and carbon characteristics the most consistent (positive) predictors across measurements. Nutrient amendment assays further supported the importance of nitrogen and carbon controls. Using the local characteristics as statistical mediators in path analysis, greater non-forested catchment land cover indirectly increased denitrification through greater floodplain soil nitrate, total phosphorus, and herbaceous aboveground biomass. Additionally, greater floodplain sedimentation indirectly increased denitrification through greater soil pH, total phosphorus, and potential carbon mineralization. Due to the consistency of relationships across denitrification potential measurements along with path modeling results, hotspots of floodplain denitrification should be found in urban and agricultural catchments where river-floodplain hydrologic connectivity promotes sedimentation. Largescale predictors explained 43–57% of the variation in denitrification potentials and should be useful for prediction in floodplains. Siting restoration projects in watersheds for maximum nitrate removal using publicly available largescale datasets is both feasible and effective. Highlights • Land cover and floodplain sedimentation strong predictors of denitrification • Non-forested catchments with hydrologic connectivity should promote denitrification. • Largescale predictors linked to denitrification through local predictors • Largescale predictors explained 43–57% of the variation in denitrification. [ABSTRACT FROM AUTHOR]

ABSTRACT Although anthropogenic dark earth (ADE) is generally found in non-floodable land, it also occurs on floodplains but, there is no information about the chemical and physical characteristics of ADE in this environment. In this study, we propose to check the hypothesis that a Gleysol, classified as ADE, presents improved chemical and physical conditions than an adjacent soil, no anthropogenic. Thus, the objective of this study was to characterize the chemical and physical properties of the top layer of two ADE profiles in a Gleysol and compare them with an adjacent soil. Samples were taken from two areas classified as ADE in Bragança, Pará State, Brazil, at the "Jabuti" archaeological site, and from an adjacent non-anthropogenic site. Disturbed and undisturbed soil samples were collected at the soil depth of 0.05-0.10 m for chemical (pH, potential acidity, exchangeable cations, and soil organic carbon) and physical (soil particle size distribution, particles density, water retention curve, total porosity, microporosity, macroporosity, and bulk density) analysis. The two areas of ADE in a Gleysol, showed improved soil chemical properties compared to the adjacent soil, particularly in relation to phosphorus and calcium levels that contributed to higher cation exchange capacity which, in turn, was positively related to organic carbon content. Changes in soil physical properties were less noticeable but both areas of ADE presented higher water retention capacity, particularly at low tension. The improved conditions of the ADE soil under Gleysols shows that these areas are adequate for soil cultivation, especially with plants adapted to floodplain.

Denitrification in floodplain soils is one key process that determines the buffering capacity of riparian zones in terms of diffuse nitrate pollution. One widely used approach to measure the denitrification potential is the acetylene inhibition technique that requires fresh soil samples. We conducted experiments with air-dried soils using a time series analysis to determine the optimal rewetting period. Thus, air-dried soil samples from six different floodplain areas in Germany were rewetted for 1 to 13days to 100% water-filled pore space. We analyzed nitrogen accumulated as N2O in the top of anaerobic flasks with and without acetylene by gas chromatography after four hours of incubation. We observed an overall optimal rewetting of at least seven days for complete denitrification. We also saw the strong influence of pH and field capacity on the denitrification product ratio; in soils with pH < 7, we hardly assumed complete denitrification, whereas the treatments with pH > 7 achieved stable values after seven days of rewetting. This advanced method provides the opportunity to carry out campaigns with large soil sample sizes on the landscape scale, as samples can be stored dry until measurements are taken.

In a study of mineral soils in floodplains, shallow depressions, and dry valley heads of the Saale-Elster plateau in eastern Germany and along the lower Eger/Ohře river in Czechia, sixteen earthworm species were found. On the basis of these findings, areas of gray-brown podzolic soils can be differentiated from chernozem areas mainly by the occurrence in the former of the two species Proctodrilus antipai and P. tuberculatus. In a section of one floodplain in the gray-brown podzolic soil area, the distribution of these two earthworm species shows a vicariance situation, such that P. antipai is restricted to the outer edges of the floodplain while P. tuberculatus inhabits the parts close to the river. In the chernozem areas, on the other hand, P. antipai is the only one of the two species to occur, and is also found in those areas close to the river. P. tuberculatus disappears in the transitional zone between a floodplain where it occurs and a chernozem floodplain. The distribution of P. antipai ends where a floodplain inhabited by it graduates into one belonging to a large river with a high rate of flow. On the stretch of the Elbe near Mlékojedy, where the position of the confluence with the Ohře has migrated over time, the vicariant distribution of the two species within the soil profile was noted. Here P. antipai is found in the uppermost soil layer, while P. tuberculatus lives in the lower-lying mineral soil at the same location. This ecological vicariance appears to represent different stages of clay translocation in flood loam. The results show that P. tuberculatus is dependent on such clay translocation or lessivage, and where this soil-profile-influencing process cannot take place the species does not occur. Examples would be oligotrophic acid montane brown forest soils, eutrophic brown forest soils, and chernozems, as well as the floodplain soils derived from all three

For south ‘Wessex’, despite complexity evident on the ground, there is little research that directly links river channel form with historic economic development; that is, channel genesis and planforms are seldom discussed in relation to landscape development within valleys. Of specific interest are relationships linking channel topography, artificial cuts and floodplains with development associated with mills, water-meadows, artificial watercourses and gravel extraction. These are an outcome of a strong regional culture of economic development including water management. It is demonstrated that river planforms within the valleys determine the location of fixed assets and there is a strong relationship between soils and floodplain development. It is concluded that there is an intricate continuum between perceived ‘natural’ fluvial process and human-influenced environmental change, and that genetic interpretation of river channel forms presents a challenge for landscape historians. [ABSTRACT FROM AUTHOR]

The chemical fractionation of nine metals, Cd, Pb, Cr, Ni, Cu, Co, Ba, Mn and Zn, in soil profiles of the floodplain of the lower reaches of the River Niger in Nigeria, was investigated with a view to providing information on the forms, bioavailability and mobility of these metals in the soil profiles. The chemical forms of metals in the soil were determined by using the European Community Bureau of Reference (BCR) sequential chemical extraction method and the concentrations were measured by inductively coupled plasma-atomic emission spectrophotometry (ICP-AES). The results indicated that the residual and Fe-Mn oxide/hydroxide phases were the predominant forms of the metals in the soil profiles. The percentage of metals in the readily available and potentially available fractions followed the order: Pb > Ba > Cd > Ni > Co > Zn > Mn > Cu > Cr. Significant proportions of these metals were found in the potentially available phases, which indicate an increase in mobility and availability as a result of changes in the physicochemical characteristics (pH and Eh) of the soil following flooding events. [ABSTRACT FROM AUTHOR]

The mechanisms controlling soil succession in floodplains remain much less studied than in uplands due to the complexity that flooddriven erosion and sedimentation bring into soil development processes. The amount of organic matter and C generally grows with soil ageing and is controlled by multiple and interacting allogenic and autogenic factors, but to what extent the production of organic matter by in situ vegetation contributes to soil formation in floodplains remains unknown. The objective of this work was to explore the importance of autochthonous organic matter versus allochthonous organic matter in organic C accumulation of floodplain forest soils along a vegetation succession and hydrogeomorphic connectivity gradient. Physicochemical analyses of sediment collected after one single flood event in a large Mediterranean floodplain (Middle Ebro, a 9th order regulated river reach in NE Spain) were used to estimate the proportion of organic C found in the topsoil (first 10 cm) samples of young (50 yr) floodplain forests that had an allochthonous (i.e., % of organic C deposited by floods) or autochthonous (i.e., % of organic C produced in situ by vegetation) source. Results of this exploratory study showed that the accumulation of autochthonous organic C in the floodplain topsoil only occurred in floodplain forests older than 50 year-old, but even then, it was more than six-fold less abundant than that with an allochthonous origin. Moreover, a linear mixed effect model showed that, although autochthonous organic C accumulation was mainly explained by the forest structure, a small proportion of it was also controlled by an allogenic factor, the groundwater table depth. Then, groundwater table depth variations could be partly controlling autochthonous organic matter production and decomposition in this Mediterranean floodplain. Although flow regulation and embankment has dramatically limited the hydrogeomorphic dynamics of the river, allogenic overbank sedimentation during flood events still controls floodplain soil succession and organic C accumulation in the floodplain.

The fractionation and potential mobilization of As, Cr, Mo, and Se in four floodplain soil profiles collected along the Nile (Egypt) and Wupper (Germany) Rivers were assessed using the BCR sequential extraction procedure. The concentrations of total and the geochemical fractions (acid soluble (F1), reducible (F2), oxidizable (F3), and residual (F4) fraction) of the elements were determined. The Wupper soils had the highest total concentrations (mg kg −1 ) of As (378) and Cr (2,797) while the Nile soils contained the highest total Mo (12) and Se (42). The residual fraction of As, Cr, Mo, and Se was dominant in the Nile soils suggesting the geogenic source of the elements in these soils. The residual fraction of As and Mo and the oxidizable fraction of Cr and Se were dominant in the Wupper soils. Among the non-residual fractions (potential mobile fractions; PMF = ∑F1−F3), the oxidizable fraction was dominant for Cr, Mo, and Se in the Nile soils and for Mo in the Wupper soils, while the reducible fraction was dominant for As in both soils. The PMF of As, Cr, and Se was higher in the Wupper than in the Nile soils which might reflect the anthropogenic sources of these elements in the Wupper soils, while the opposite was the case for the PMF of Mo. The high PMF of Se (87%), Cr (87%), and As (21%) in the Wupper soils suggested that a release of these toxic elements may happen which increase the potential environmental risks in the anthropogenically polluted soils. [ABSTRACT FROM AUTHOR]

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the biogeochemical processes driving Si fractionation in these soils. Therefore, we applied for the first time a sequential Si extraction scheme to three floodplain soils (Mollic Fluvisols) to separate six Si fractions: mobile Si, adsorbed Si, Si bound to organic matter, Si included in pedogenic oxides and hydroxides, biogenic as well as minerogenic amorphous silica. Residual Si was calculated. The highest Si proportion apart from the residual fraction (Si bound in primary and secondary silicates) was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02–0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget (here periodic flooding with prolonged water saturation) on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous minerogenic as well as biogenic silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. These processes are more pronounced in floodplain than in terrestrial soils, thus implying different distributions of Si among soil fractions. [ABSTRACT FROM AUTHOR]

Measuring soil organic carbon (SOC) in riparian forest soils affected by floods is crucial for evaluating their concentration and distribution along hydrological gradients (longitudinal and transversal). Hydromorphological factors (e.g., sedimentation vs. erosion, size of floodplain, flood recurrence) may be the cause of major variations in the concentration of organic matter and SOC in soils and could have a direct impact on C levels in soil profiles. For this study, SOC concentrations were assessed in riparian soils collected along transects perpendicular to the riverbanks which cross through inundated and non-inundated zones. Other soil properties (e.g., acidity, nitrogen, texture, bulk density) that may affect the concentration of SOC were also considered. The main purpose of this study was to assess SOC concentrations in soils subjected to flooding with those outside the flood zones, and also measure various soil properties (in surface soils and at various depths ranging from 0 to 100 cm) for each selected area. Across the various areas, SOC shows marked differences in concentration and spatial distribution, with the lowest values found in mineral soils affected by successive floods (recurrence of 0-20 years). SOC at 0-20 cm in depth was significantly lower in active floodplains (Tukey HSD test), with average values of 2.29 ±1.64% compared to non-inundated soils (3.83 ±2.22%). The proportion of C stocks calculated in soils (inundated vs. non-inundated zones) was significantly different, with average values of 38.22 ±10.40 and 79.75 ±29.47 t·ha-1, respectively. Flood frequency appears to be a key factor in understanding the low SOC concentrations in floodplain soils subjected to high flood recurrence (0-20 years). [ABSTRACT FROM AUTHOR]

Studies about the mobilization of potentially toxic elements (PTEs) in deltaic soils can be challenging, provide critical information on assessing the potential risk and fate of these elements and for sustainable management of these soils. The impact of redox potential (E H ), pH, iron (Fe), manganese (Mn), sulfate (SO 4 2− ), chloride (Cl − ), aliphatic dissolved organic carbon (DOC), and aromatic dissolved organic carbon (DAC) on the mobilization of copper (Cu), selenium (Se), and zinc (Zn) was studied in two soils collected from the Nile and Mississippi Rivers deltaic plains focused on increasing our understanding of the fate of these toxic elements. Soils were exposed to a range of redox conditions stepwise from reducing to oxidizing soil conditions using an automated biogeochemical microcosm apparatus. Concentrations of DOC and Fe were high under reducing conditions as compared to oxidizing conditions in both soils. The proportion of DAC in relation to DOC in solution (aromaticity) was high in the Nile Delta soil (NDS) and low in the Mississippi Delta soil (MDS) under oxidizing conditions. Mobilization of Cu was low under reducing conditions in both soils which was likely caused by sulfide precipitation and as a result of reduction of Cu 2+ to Cu 1+ . Mobilization of Se was high under low E H in both soils. Release of Se was positively correlated with DOC, Fe, Mn, and SO 4 2− in the NDS, and with Fe in the MDS. Mobilization of Zn showed negative correlations with E H and pH in the NDS while these correlations were non-significant in the MDS. The release dynamics of dissolved Zn could be governed mainly by the chemistry of Fe and Mn in the NDS and by the chemistry of Mn in the MDS. Our findings suggest that a release of Se and Zn occurs under anaerobic conditions, while aerobic conditions favor the release of Cu in both soils. In conclusion, the release of Cu, Se, and Zn under different reducing and oxidizing conditions in deltaic wetland soils should be taken into account due to increased mobilization and the potential environmental risks associated with food security in utilizing these soils for flooded agricultural and fisheries systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

On the earthworm fauna (Oligochaeta: Lumbricidae), in particular the distribution of Proctodrilus, in the floodplains of the chernozem and gray-brown podzolic soil areas on both sides of the Ore Mts. In a study of mineral soils in floodplains, shallow depressions, and dry valley heads of the Saale-Elster plateau in eastern Germany and along the lower Eger/Ohře river in Czechia, sixteen earthworm species were found. On the basis of these findings, areas of gray-brown podzolic soils can be differentiated from chernozem areas mainly by the occurrence in the former of the two species Proctodrilus antipai and P. tuberculatus. In a section of one floodplain in the gray-brown podzolic soil area, the distribution of these two earthworm species shows a vicariance situation, such that P. antipai is restricted to the outer edges of the floodplain while P. tuberculatus inhabits the parts close to the river. In the chernozem areas, on the other hand, P. antipai is the only one of the two species to occur, and is also found in those areas close to the river. P. tuberculatus disappears in the transitional zone between a floodplain where it occurs and a chernozem floodplain. The distribution of P. antipai ends where a floodplain inhabited by it graduates into one belonging to a large river with a high rate of flow. On the stretch of the Elbe near Mlékojedy, where the position of the confluence with the Ohře has migrated over time, the vicariant distribution of the two species within the soil profile was noted. Here P. antipai is found in the uppermost soil layer, while P. tuberculatus lives in the lower-lying mineral soil at the same location. This ecological vicariance appears to represent different stages of clay translocation in flood loam. The results show that P. tuberculatus is dependent on such clay translocation or lessivage, and where this soil-profile-influencing process cannot take place the species does not occur. Examples would be oligotrophic acid montane brown forest soils, eutrophic brown forest soils, and chernozems, as well as the floodplain soils derived from all three. [ABSTRACT FROM AUTHOR]

River-floodplain ecosystems are long-term sinks for certain contaminants. Fluctuations between flooding and drying are major drivers of spatial and temporal changing biogeochemical processes within floodplain soils. Even small changes of the frequency, magnitude, and timing of drying and rewetting can episodically turn those ecosystems into a source for matter. To understand such changes we investigated the effects on top soils of three hydro-geomorphological units that are typical for floodplains: depression, levee, and plateau. They show distinct characteristics regarding soil type, trace element (TE) pollution level and hydrology. In the laboratory we used an automated biogeochemical microcosm set up to simulate oxidized–reduced cycles to monitor the effects of strong fluctuating redox potential ( E H ), on pH, iron (Fe), manganese (Mn), sulfur (S), nitrate (NO 3 ), dissolved organic carbon (DOC) and dissolved concentrations of arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) in the soil solution. The results indicated different responses regarding the course of E H /pH and different release patterns of TEs for each hydro-geomorphological unit separately. Both could be mainly allocated to their explicit spatial characteristics; due to differences in its buffer capacities and to the interaction between pH-value and microbial activity. In particular, we could demonstrate that a combination of several biogeochemical factors may influence TE release or retention in floodplain soils by means of generalized additive models (GAMs). Using those, Fe and S were identified as most important factors that determined the dynamics of TEs in all three studied soils; concentrations of As, Cu, Cr, Ni, and Zn increased with increasing Fe-concentrations whereas Cd, Cu, Cr, Ni, and Zn seem correspondingly to be dependent on S that went along with the course of the oxidized–reduced cycle. Still, several uncertainties between environmental changes and TE release from floodplain soils may exist. Thus, the fate of dissolved TEs in river-floodplain ecosystems needs to be taken under serious consideration since the ecotoxicology threat of them is of undisputed risk. [ABSTRACT FROM AUTHOR]