Floodplain Soils Research Articles

Machine-learning-based prediction and key factor identification of the organic carbon in riverine floodplain soils with intensive agricultural practices

Machine-learning-based prediction and key factor identification of the organic carbon in riverine floodplain soils with intensive agricultural practices

Meanders as a scaling motif for understanding of floodplain soil microbiome and biogeochemical potential at the watershed scale

BackgroundBiogeochemical exports from watersheds are modulated by the activity of microorganisms that function over micron scales. Here, we tested the hypothesis that meander-bound regions share a core microbiome and exhibit patterns of metabolic potential that broadly predict biogeochemical processes in floodplain soils along a river corridor.ResultsWe intensively sampled the microbiomes of floodplain soils located in the upper, middle, and lower reaches of the East River, Colorado. Despite the very high microbial diversity and complexity of the soils, we reconstructed 248 quality draft genomes representative of subspecies. Approximately one third of these bacterial subspecies was detected across all three locations at similar abundance levels, and ~ 15% of species were detected in two consecutive years. Within the meander-bound floodplains, we did not detect systematic patterns of gene abundance based on sampling position relative to the river. However, across meanders, we identified a core floodplain microbiome that is enriched in capacities for aerobic respiration, aerobic CO oxidation, and thiosulfate oxidation with the formation of elemental sulfur. Given this, we conducted a transcriptomic analysis of the middle floodplain. In contrast to predictions made based on the prominence of gene inventories, the most highly transcribed genes were relatively rare amoCAB and nxrAB (for nitrification) genes, followed by genes involved in methanol and formate oxidation, and nitrogen and CO2 fixation. Within all three meanders, low soil organic carbon correlated with high activity of genes involved in methanol, formate, sulfide, hydrogen, and ammonia oxidation, nitrite oxidoreduction, and nitrate and nitrite reduction. Overall, the results emphasize the importance of sulfur, one-carbon and nitrogen compound metabolism in soils of the riparian corridor.ConclusionsThe disparity between the scale of a microbial cell and the scale of a watershed currently limits the development of genomically informed predictive models describing watershed biogeochemical function. Meander-bound floodplains appear to serve as scaling motifs that predict aggregate capacities for biogeochemical transformations, providing a foundation for incorporating riparian soil microbiomes in watershed models. Widely represented genetic capacities did not predict in situ activity at one time point, but rather they define a reservoir of biogeochemical potential available as conditions change.AU1kaDmL5ojSw8dBEKS2i-Video abstract

Morphological Features of Soils in the Yelshanka River Floodplain Under Conditions of Urbotechnopedogenesis

The river system on the territory of Volgograd is represented by eight small rivers. Currently, in the territory of Volgograd there is an active inclusion of valley and floodplain landscapes in the urban area. Under conditions of the anthropogenic impact, the normal regime of valley and floodplain landscapes is disturbed. As a result of changes in the hydrological regime of floodplains and valleys, various morphological transformations of soil cover occur, such as the formation of specific iron and carbonate new formations, etc. As a result of economic activities, modern alluvial soils and sediments are often buried under the thickness of the anthropogenic material. The relevance of the study is due to the high recreational value of valley and floodplain landscapes. The authors analyze 6 soil profiles set up in different parts of the Yelshanka river floodplain. The description of soil sections was performed with the use of the Field Qualifier of Soils of Russia. Soil profiles were named in accordance with the Russian Soil Classification and Diagnosis (2004) and the Field Qualifier of Soils of Russia (2008). In Volgograd, as in most cities in Russia and abroad, the study of soils of floodplain landscapes is not systematic, and in some cases is limited to a certain area of research. The purpose of the work was to monitor the morphological state of the floodplain soil cover of the Yelshanka River in order to determine the degree of soils transformation in the area as a result of urbotechnopedogenesis. The studies conducted at the site allow considering that the urban soils of recreational areas are a consequence of the combined effect of zonal natural and climatic and urbanogenic factors of soil formation. Studies of soils of floodplain landscapes in the urban environment make it possible to monitor the state of natural landscapes and their transformation in conditions of urbotechnopedogenesis, as well as the development of the ecological framework of the city.

Porewater Lead Concentrations Limited by Particulate Organic Matter Coupled With Ephemeral Iron(III) and Sulfide Phases during Redox Cycles Within Contaminated Floodplain Soils.

Lead contamination in soils and sediments is a major threat to water quality. In surface and near-surface environments, Pb is not redox active; however, common Pb hosts, including Fe(III)-(hydr)oxides and sulfides, dissolve and precipitate as redox conditions change. Dissolution of Pb hosts may release Pb to porewater, leading to spikes in dissolved Pb concentrations and potential transport into surface or groundwater. Here, we examine the impacts of hydrologically coupled redox transitions on Pb partitioning in contaminated floodplain soils. We find that the affinity of Pb for particulate organic matter (POM), inclusive of mineral-associated organic matter, ensures that across redox transitions Pb is retained in the solid phase, despite host-phase (Fe(III)-(hydr)oxide and sulfide) dissolution. As seasonal hydrologic dynamics shift porewater redox conditions, Pb-bearing Fe(III)-(hydr)oxides (Pb-HFO) and sulfides (PbS) are dissolved and (re)precipitated. However, despite these shifts in redox conditions and associated host-phase transformations, Pb retention on POM, coupled with the formation of PbS and Pb-HFO, maintains dissolved Pb concentrations below 17 μg L-1. Importantly, the predominance of Pb adsorbed on POM alongside low dissolved Pb concentrations indicates that Pb released from HFO and PbS is retained by POM. Thus, despite host-phase dissolution during redox transitions, partitioning of Pb to the aqueous phase is minimal and, therefore, transport of dissolved Pb is unlikely.

Exchangeable form of potentially toxic elements in floodplain soils along the river-marine systems of Southern Russia

Large rivers and especially their deltaic parts and adjacent coastal zones are subjected to strong anthropogenic influence and are often considered as hotspots of environmental pollution. The Don River is one of the largest and most important rivers in the South of Russia. The Don River basin is a highly urbanized area with developed agriculture and industry which negatively affect water quality, aquatic ecosystems and soils. The main objectives of the proposed research were to determine the levels exchangeable form of PHEs in soils of various aquatic landscapes of the study area, as well as to reveal the relationships between the content of exchangeable PTEs and the physical–chemical properties of floodplain soils. The obtained results showed that soils of the Lower Don and Taganrog Bay coastal zone are rather contrast in terms of properties and metal contents, which indicates the variability of landscapes, natural and anthropogenic processes in the studied systems. High CV values for a number of metals such as Pb, Zn, Cd and Cr indirectly indicate strong anthropogenic influence on these environments. The group median values for extractable forms for most of the metals except for Cu and Ni were higher for urbanized areas. The results of PCA analysis showed that there are two association of metals in terms of geochemical behavior and sources. The first one included Cr-Zn-Pb-Cd, the elements of anthropogenic origin, the second Mn, Ni, and Cu, which are probably of mixed origin. The obtained results showed that the Lower Don and Taganrog Bay coastal zone is a diverse and complex system subjected to anthropogenic activities, which is pronounced in the enrichment of aquatic soils with a number of metals and higher proportions of exchangeable forms from different types of sources that likely can be of both local and whole basin scale.

Planktonic Metabolism and Microbial Carbon Substrate Utilization in Response to Inundation in Semi‐Arid Floodplain Wetlands

AbstractIn semi‐arid floodplain wetlands, planktonic metabolism, a balance of gross primary productivity of phytoplankton (GPP) and planktonic respiration (PR), may be affected by hydrology, geomorphology, carbon, and microbial communities. Understanding relationships between these factors helps develop effective water and land management plans for these wetlands. In this study, variations in planktonic metabolism and microbial carbon substrate utilization were investigated in the semi‐arid floodplain wetlands of the Macquarie Marshes, south‐eastern Australia, by comparing three geomorphologically distinct zones with different historical inundation frequencies (zones 1: moderate, 2: low, and 3: very low). Floodplain soil samples collected from each zone were inundated artificially in controlled laboratory conditions. GPP and PR were determined using biological oxygen demand methods. Biolog EcoPlates™ were used to assess microbial utilization of carbon substrate. Among the zones examined, zone 1 had the highest GPP and lowest PR, while zone 3 had the lowest GPP and highest PR. GPP/PR showed zones 1 and 2 autotrophic, and zone 3 heterotrophic. EcoPlates showed the highest and lowest microbial activity in zone 3 and zone 1 respectively, indicating a strong link between microbial carbon substrate utilization and PR for heterotrophy in the rarely inundated zone. Inundation of drier wetland zones may lead to a large pulse in PR, at least for a short period of time, potentially leading to anoxic water events. When making decisions for environmental water allocations, the antecedent hydro‐geomorphological and microbial condition of the targeted wetlands should be considered to help predict expected aquatic ecosystem responses.

Performance of vermicompost in zinc and boron nutrition for quality production of cabbage

The quality and efficacy of vermicompost are greatly influenced by the respective feeding materials as well as earthworm species used in vermicomposting. Consequently, the variable role of applied vermicompost is reflected in crop production. With a view to observe the efficacy of vermicompost produced from various sources in supplementing zinc and boron requirement for quality production of cabbage, a field study was conducted in Floodplain soil of Bangladesh. Six treatment combinations comprising of vermicompost from different sources, and different levels of zinc and boron from mineral fertilizers were tested in the study. The vermicompost used in different treatments were produced from different combinations of feeding materials (cowdung and poultry litter) and earthworm species (Eisenia fetida and Eudrilus eugeniae). A control treatment having no supplement of Zn and B was tested in the study. Higher measurements were recorded for most of the parameters studied, i.e., head diameter, marketable yield and total yield in the vermicompost treated plots than the solely mineral fertilizer treated plot. Except for P, the highest uptake of each of the elements by cabbage was observed due to the application of T3 treatment (VC-ECD @2.0 t ha-1 + 1.5 kg Zn ha-1 + 1.0 kg B ha-1). The findings of this research work indicate the additional benefit of using vermicompost over the mineral fertilizer in supplying zinc and boron for better production of cabbage.

Differentiation of the soil cover of the floodplain of the Middle-Amur Lowland in connection with the evolution of the relief forms

The article is based on a long-term study of floodplain soils of the Amur River valley within the north-eastern part of the Middle-Amur Lowland. The results of field work on the soil-geomorphological profile across the Slavyansky Island, located 200 km from Khabarovsk down the Amur River, are discussed. The study analyzes the occurrence of the island's floodplain soils on riolkas[1] and their properties, with an emphasis on morphology and lithological and particle-size composition. The features of soil formation on riolkas of different genesis – alluvial and aeolian – are shown. On sandy and sandy-loam deposits of alluvial riolkas (“meadow-forest” ridges) poorly developed sod gley soils are formed. On heavy loam and clay alluvium of the “meadow“ ridges, annually flooded by river waters, sod-meadow gley soils develop under the woodreed grass stand. Sand deposits of high aeolian riolkas are characterized by a homogeneous fine-grained structure without interlayers, signs of organic matter and with a significant amount of mica. They describe poorly developed sod-forest soils under high-trunk oak forests. The formation of texture-differentiated soils on all types of riolkas was not revealed. When the floodplain reaches the position of the first terrace above the floodplain, the differences in the lithological composition and particle-size distribution, soil texture, height above the water edge and the nature of vegetation on the inherited riolkas provide a multidirectional evolution of soil formation. At the same time, the development is taking place in accordance with the zonal types of soils (sod-forest, brown-earth, texture-differentiated – soil with a bleached horizon (podbel)). The last are mainly formed on clay-loam alluvium, which can overlay not only alluvial, but also some aeolian riolkas. [1]Riolkas are ancient, relatively high sand ridges (extended dunes) with plant cover found in Amur region (Russian Far East).

Implementation of the productivity potential of forage crops in the west of the Briansk region

In the non-black soil zone of Russia on sod-podzolic and floodplain soils, the adaptive properties of forage crops of the bluegrass family were assessed in terms of ecological stability and plasticity and the effect of mineral fertilizers on them according to the yield criterion. The analysis of changes in the yield of forage crops was carried out from 2009 to 2015. It was characterized by different weather conditions. As a result of the research, it was found that the environmental index varied over the years from –6.36 to 6.08. The highest adaptation coefficient was observed in Sudanese grass (1.37) and millet (1.33). The smallest yield variability was found in the cultivation of awnless brome (10.8%), millet (13.2%) and annual ryegrass (14.6%). The highest stress resistance was found in one-year ryegrass (–6.00) awnless brome (–6.20) and oats (–6.50) – the main forage crops in the study area. The minimum value of the yield range in contrasting conditions was set in millet (20.4) and awnless brome (22.0). The most stable crops in obtaining the harvest were two-source reed, annual ryegrass, Scleranthus, meadow fescue and Sudanese grass. Sudanese grass, millet and oats were the most responsive to changes in cultivation conditions. The most intense (bi = 2.40, and Sd 2 = 0.39) fodder crop in the western Briansk region is Sudan grass, while millet and oats are highly responsive in combination with low yield stability. The awnless brome reacts poorly to the improvement of external conditions, but has a fairly high yield stability. The use of mineral fertilizers increases the environmental index, adaptation, variability of the yield of forage crops, increases the gap between the maximum and minimum yield, and also enhances the stability and reduces the responsiveness of crops to environmental changes.

Assessment of iron-rich tailings via portable X-ray fluorescence spectrometry: the Mariana dam disaster, southeast Brazil.

On November 5, 2015, the Fundão dam collapsed and released > 60 million m3 of iron-rich mining sediments into the Doce river basin, covering >1000ha of floodplain soils across ~80km from the rupture. The characterization of alluvial mud covering and/or mixed with native soil is a priority for successful environmental rehabilitation. Portable X-ray fluorescence (pXRF) spectrometry was used to (1) assess the elemental composition of native soils and alluvial mud across impacted riparian areas; and 2) predict fertility properties of the mud and soils that are crucial for environmental rehabilitation and vegetation establishment (e.g., pH, available macro and micronutrients, cation exchange capacity, organic matter). Native soils and alluvial mud were sampled across impacted areas and analyzed via pXRF and conventional laboratory methods. Random forest (RF) regression was used to predict fertility properties using pXRF data for pooled soil and alluvial mud samples. Mud and native surrounding soils were clearly differentiated based on chemical properties determined via pXRF (mainly SiO2, Al2O3, Fe2O3, TiO2, and MnO). The pXRF data and RF models successfully predicted pH for pooled samples (R2 = 0.80). Moderate predictions were obtained for soil organic matter (R2 = 0.53) and cation exchange capacity (R2 = 0.54). Considering the extent of impacted area and efforts required for successful environmental rehabilitation, the pXRF spectrometer showed great potential for screening impacted areas. It can assess total elemental composition, differentiate alluvial mud from native soils, and reasonably predict related fertility properties in pooled heterogeneous substrates (native soil + mud + river sediments).

Оценка эколого-геохимического состояния аллювиальных почв пойм малых рек города Пермь

In the conditions of the city of Perm - a multidisciplinary industrial center of Russia, the regularities and quantitative characteristics of the redox and ecological-geochemical state of the soils of the floodplains of small rivers-tributaries of the Kama River within the Votkinsk reservoir are revealed. The regularities of the content, distribution and interrelation of potentially toxic chemical elements are established, the priority elements-pollutants, and their mobility in floodplain soils are determined. It was found that under the influence of heterogeneity of redox conditions, sorption, gley, and hydrogen sulfide geochemical barriers are formed in the soil profile. It was found that when hydrogenic pollution of urban alluvial soils occurs, natural-technogenic associations of chemical elements are formed in their profile, which differ from natural associations in the background soil. Elemental geochemical associations are characterized at different levels of technogenic load on the floodplains of small rivers. The relationship between the concentration of chemical elements and the value of the specific magnetic susceptibility in floodplain soils is determined. Keywords: REDOX STATE, HEAVY METALS, GEOCHEMICAL COEFFICIENTS, URBO-ALLUVIAL SOILS, CHEMOSEMS ON URBO-ALLUVIAL SOILS

Comparison of Cubist models for soil organic carbon prediction via portable XRF measured data

Soil organic carbon (SOC) tends to form complexes with most metallic ions within the soil system. Relatively few studies compare SOC predictions via portable X-ray fluorescence (pXRF) measured data coupled with the Cubist algorithm. The current study applied three different Cubist models to estimate SOC while using several pXRF measured data. Soil samples (n = 158) were collected from the Litavka floodplain area during two separate sampling campaigns in 2018. Thirteen pXRF data or predictors (K, Ca, Rb, Mn, Fe, As, Ba, Th, Pb, Sr, Ti, Zr, and Zn) were selected to develop the proposed models. Validation and comparison of the models applied the mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R2). The results revealed that Cubist 1, utilizing all the predictors yielded the best model outcome (MAE = 0.51%, RMSE = 0.68%, R2 = 0.78) followed by Cubist 2, using predictors with relatively high importance (VarImp. predictors) (MAE = 0.64%, RMSE = 0.82%, R2 = 0.68), and lastly Cubist 3 with predictors showing a significantly positive correlation (MAE = 0.69%, RMSE = 0.90%, R2 = 0.62). The Cubist 1 model was considered more promising for explaining the complex relationships between SOC and the pXRF data used. Moreover, for the estimation of SOC in temperate floodplain soils all the Cubist models gave an acceptable model. However, future research should focus on using other auxiliary data [e.g., soil properties, data from other sensors (e.g., FieldSpec)] as well as extend the study area to cover more soil types hence improve model robustness as well as parsimoniousness.

Anthropogenic records in a fluvial depositional system: The Odra River along The Czech-Polish border

Industrial revolution induced contamination of lowland rivers and floodplain soils with heavy metals worldwide. This pollution was particularly significant in former coal mining regions where hard coal was utilised in various industrial facilities like coke, iron and steel works. The upper Odra River draining Ostrava Coal District in Czech and Upper Silesia mining region in Poland is an example of such a European river with strong historical pollution followed by modern one originating from heavy industry in times of communistic industrialisation in both countries. In the presented studies we sought 19th and 20th century transboundary contamination of the upper Odra River waters recorded in floodplain soil by the most common potentially toxic elements, i.e. lead and zinc as well as by the presence of magnetic particles (spherules). We expected to reveal the general pattern of the Odra River floodplain soil contamination with risk elements which allow us to differentiate sediments of the industrial and pre-industrial era. We used robust regression and robust principal component analysis, using a log-ratio methodology of compositional data analysis, which is a fast and effective tool in assessing contamination levels. Significant increases in risk element concentrations were found downstream from the Ostrava–Bohumín agglomeration, and in some places they exceed the safety limits for agricultural soils in Poland. A comparison of sediments within and outside of the inter-embankment zone showed no systematic difference in their contamination levels suggesting that the sediments were probably contaminated before dike construction mainly since the half of 19th century.

Growth of willow energy plantations on the marginal lands of the Kyiv Polissia

Purpose. Investigation of the features of growth, development and productivity of energy willow varieties on peat-bog and alluvial sandy soils in the floodplains of the Kyiv Polissia rivers.
 Methods. Field, laboratory, analytical, and statistical.
 Results. It is advisable to use the variety ‘Zbruch’, to create willow energy plantations on the peat-swampy soils of the Kyiv Polissia. It is characterized by the highest yield of three-year biomass (9.84 t/ha), while in the ‘Ternopil’ cultivar the maximum was 3.29 t/ha and in the Salix triandra clone 2.68 t/ha. On alluvial sandy soil, the highest average height (194 ± 6.6 cm), with a productivity of two-year biomass of 3.15 t/ha had Swedish variety ‘Tordis’. In addition, relatively high productivity have Polish varietyes ‘082’ and ‘1047’ and the domestic variety ‘Ternopil’. The productivity of the latter after two years of growth on the sandy soil is 1.53–6.41 t/ha, and after three years on the peat soil only 1.74–3.29 t/ha. To increase the productivity of energy plantations of willow on fresh alluvial sandy soils, it is advisable to apply organic and mineral fertilizers, and on peat soils to apply deep plowing, to conduct proper control over the number of weeds, to use the density of planting cuttings about 20 000 plants ha and a 4-year biomass harvest cycle.
 Conclusions. It is established that in alluvial soils of floodplains of Kyiv Polissia rivers, fresh alluvial soils are more suitable for growing willow energy plantations than rich on organic substances moist peat-bog soils. ‘Tordis’, ‘082’, ‘1047’ and ‘Ternopil’ varieties are promising for growing on the sandy soils of the study area, and ‘Zbruch’ for peat soils. Considering the low fertility of the studied variants of marginal lands, in order to increase the efficiency of cultivation of energy biomass of willow on them, first of all, it is necessary to improve the water-physical properties of soils.

Methods of Improving the Awnless Brome Productivity in Yakutia

The article presents an author’s long term works results on the development of the agroecological technique for growing seeds and hay of awnless brome in permafrost floodplain soils on the Lena river middle reaches. The awnless brome Ammachaan and Kamalinskiy 14 varieties seeding rate and row space for cultivars are recommended. Varieties morphological changes in Oymakonya conditions are given. Recommended agroecological methods of cultivation provide guaranteed seed yield from 1.9 to 2.25 C/ha and hay yield up to 21-54 C/ha in conditions without irrigation and irrigation. It should be noted that the awnless brome Ammachaan and Kamalinskiy 14 varieties despite meteorological conditions during the research years showed excellent winter hardiness in the conditions of Central Yakutia, and the Pole of Cold of Yakutia (Oymyakonye). At the same time, it was conducted the agroecological assessment of the initial material (150 samples) in the Oymyakonye region. Mostly varieties from the world collection of VIR were presented. Also, the Yakut breeding hybrids and local populations from the Republic of Sakha (Yakutia) were tested. As a result of the research, the local samples were selected that exceed the Kamalinskiy 14 variety by selection indicators. It was determined the potential of awnless brome’ seeds and green mass formation using a wide-row method of sowing with 60 cm row space and a seeding rate of three million pieces per one hectare. The conducted researches have shown that the Kamalinskiy 14 variety are well-prepared to the winter grazing of horses in Yakutia.

Changes in selected physico-chemical properties of floodplain soils in three different land-use types after flooding

This article provides information on selected physico-chemical properties, including soil colour, texture, electrical conductivity, pH<sub>H</sub>2O, pH<sub>CaCl</sub>2, content of total carbon and Q<sub>4/6</sub> quotient, of the topsoil and subsoil of former flood sediments at three diverse vegetation plots in a floodplain and in two reference plots unaffected by floods, and changes of some soil properties caused by a new subsequent flood. Aggradation of flood sediments in the area was controlled both by local terrain morphology and vegetation type cover. Differences in the properties of sediments in the individual plot types were caused by the different production of litter, root biomass and carbon cycling before the new flood. Vertical distributions and inventories of <sup>137</sup>Cs in soils revealed the position and proportion of modern sediments in soil profiles, man-made filling of former erosion grooves and ploughing depths. The new flood of a lower hydrological power aggraded a thin layer of organo-clay sediment on the soil surface but showed minor effects on the investigated soil properties. The lowest dry bulk density and highest total porosity values were found in the topsoil of woody and grassy plots after the flood implying no substantial break down of soil aggregates by the flood. The highest dry bulk density values in the subsoil of fields indicated soil compaction from agricultural machinery. No increased soil salinity was found after the flood. The flood did not significantly affect the pH<sub>H</sub>2O of the topsoil and subsoil; however, a significant increase in pH<sub>CaCl</sub>2 was found for the topsoil of grassy plots and for all topsoil samples from the park. No significant increases in total carbon (C<sub>tot</sub>) contents were found in topsoils of any plot types after the flood in spite of an accumulation of thin organo-clay material on the soil surface after the flood. However, significant increases in C<sub>tot</sub> in subsoils of all plot types indicate the vertical migration of colloidal and dissolved organic carbon in soils during the flood. C<sub>tot</sub> contents positively correlated with electrical conductivity values and negative correlated with pH values. The relatively minor changes in soil physico-chemical properties found after the flood can be explained by the short duration and small dynamic power of the flood, and the timing of sampling when the flood had receded and soil aeration was already being restored.

Soil Protection in Floodplains—A Review

Soils in floodplains and riparian zones provide important ecosystem functions and services. These ecosystems belong to the most threatened ecosystems worldwide. Therefore, the management of floodplains has changed from river control to the restoration of rivers and floodplains. However, restoration activities can also negatively impact soils in these areas. Thus, a detailed knowledge of the soils is needed to prevent detrimental soil changes. The aim of this review is therefore to assess the kind and extent of soil information used in research on floodplains and riparian zones. This article is based on a quantitative literature search. Soil information of 100 research articles was collected. Soil properties were divided into physical, chemical, biological, and detailed soil classification. Some kind of soil information like classification is used in 97 articles, but often there is no complete description of the soils and only single parameters are described. Physical soil properties are mentioned in 76 articles, chemical soil properties in 56 articles, biological soil properties in 21 articles, and a detailed soil classification is provided in 32 articles. It is recommended to integrate at least a minimum data set on soil information in all research conducted in floodplains and riparian zones. This minimum data set comprises soil types, coarse fragments, texture and structure of the soil, bulk density, pH, soil organic matter, water content, rooting depth, and calcium carbonate content. Additionally, the nutrient and/or pollution status might be a useful parameter.

Does soil organic matter in mollic horizons of central/east European floodplain soils have common chemical features?

Soils on riverine floodplains in temperate climate may be characterized by a mollic epipedon, i.e. by dark colour, enhanced content of soil organic matter (SOM), high ‘base’ saturation and developed structure in the topsoil. We studied 124 soil samples from ten central/east European countries to investigate whether SOM in mollic horizons has similar chemical features. We determined carbon contents with a thermal-gradient method to differentiate SOM with varying thermal stability, and carbonates. We characterized SOM by diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. According to the World Reference Base for Soil Resources, 102 of the samples fulfilled all criteria of a mollic horizon. Mollic features were not restricted to the uppermost horizon but also detected in buried former surface horizons. Soil colour was mostly the criterion to exclude non-mollic samples. Mollic and adjacent non-mollic horizons contained thermostable SOM, indicating SOM stabilized by interaction with minerals or as black carbon (BC), to very similar extent, up to 20.4% of total soil organic carbon (SOC). However, the correlation between the contents of thermostable SOC and total SOC, the SOC:N ratios of the thermostable fraction, and the smaller extent of metal complexation of carboxyl groups, pointed to a larger contribution of BC to SOM of mollic samples than to SOM in non-mollic samples. Thus, like in mollic horizons in Chernozems and Phaeozems not affected by fluviatile dynamics, SOM in mollic horizons of floodplain soils seemed to consist of SOM affected by natural or anthropogenic fires, constituting a common chemical feature of SOM. Thus, BC may contribute to soil colour and SOM stability in mollic horizons of floodplain soils. However, apart from BC contribution, SOM in mollic horizons of floodplain soils may have further pathways of formation and development, as SOM may be inherited from deposited material or form/transform by degradative or constructive processes.

Prediction of Spatial Distribution of Organic Carbon in Lower Brahmaputra Active Floodplain Soils of Bangladesh

Soil acts as a large reservoir of Organic Carbon (OC) but the amount varies significantly with space and time. Thus, soil analysis and interpretation of spatial variability of Soil Organic Carbon (SOC) are keys to site-specific management. The study aimed to characterize the spatial variability of SOC in an active floodplain. Soil samples were collected in three major landform categories (natural levee, back slope, marsh land) from the lower Brahmaputra River floodplain and then analyzed for SOC measurement in the laboratory. The measured data were then analyzed for spatial variability interpretation using descriptive statistics and geo-statistical analysis. The study found that the amount of SOC varies with landform variation, soil texture and distance between sample points. The topsoil of marsh land has the highest (1.41%), back slope holds a moderate amount (1.15%) and the natural levee has the lowest (0.75%) amount of SOC. The amount of clay particles at the top layer was found to be positively correlated to the SOC whereas in the same layer of sand and silt showed a negative correlation. The geo-statistical analysis illustrated the nugget effect. Low (<1%) SOC is commonly found in the agricultural soils of Bangladesh which was corroborated in this study; moderate (1.1%) SOC was found in the floodplain. This study aimed to provide an insight into spatial variability to assist in predicting SOC in the active floodplain; consequently, the interpretation of spatial variability analysis can be implemented for site specific management strategies and to calculate carbon stock in floodplain soils.
 The Dhaka University Journal of Earth and Environmental Sciences, Vol. 8(2), 2019, P 33-40

Heavy metal distribution in particle size fractions of floodplain soils from Dongchuan, Yunnan Province, Southwest China.

The heavy metal pollution level in soils is heavily affected by the soil particle size distribution. However, the heavy metal loss during particle size extraction and the effect of calcite on the heavy metals removal in terms of the particle size are unclear. In this study, the distribution of heavy metals (Cu, Cd, Cr, Co, Ni, Zn, Pb, U, and V) was determined in five particle fractions (> 2, 2-0.25, 0.25-0.02, 0.02-0.002, and < 0.002 mm) of two soil and one sediment samples collected from the floodplain of Dongchuan, Yunnan Province, Southwest China. The sampled floodplain soils were mainly composed of gravel and sand fractions (> 97%). The concentrations of all nine heavy metals in the sampled soils and sediment increase significantly with decreasing particle sizes. The maximal loss rate of Cd and Cu reaches 54% and 8.6%, respectively, which should be considered in the process of particle size fraction extraction in soils. The removal amount and removal rate of heavy metals in solution by pure calcite ranks in the order of Pb2+ > Cu2+ > Cr6+, while the removal rate of Pb (93.13%) is much higher than that of Cu (24.56%) and Cr (10.71%), which increase with the calcite particle size decreasing. The stabilization of carbonate minerals in soils is crucial for heavy metal pollution control in floodplain soils with high carbonate concentrations in Dongchuan, China.