Rare earth and other trace and major elemental distribution in a pedogenic calcrete profile (Slimene,NE Tunisia)

A calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of NE Tunisia (semi-arid climate) was studied with the aim to investigate the behavior of the chemical elements (rare earth elements—REE—and other trace and major elements) during the processes associated with calcrete formation, particularly dissolution and precipitation of carbonates in the vadose zone. The profile shows a vertical sequence, with clear zonations from the surface downwards: a reddish soil at the land surface, a nodular horizon, a laminar-structured level, and the consolidated old dune. Chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and X-ray diffraction (bulk samples and < 2 μm fraction). Detailed studies of iron speciation and iron minerals were done by Mössbauer spectroscopy. Microfauna, mineralogical and chemical variations in the Slimene weathering profile point to a long term aerial exposure of the old dune in a semi-arid carbonated environment leading to the development of a pedogenic calcrete profile. The mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium. Secondary carbonates overgrow primary ones and precipitate as coating or concretions below. Minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs. Phyllosilicates decrease while calcite and K-feldspars increase with depth. Kaolinite was the only clay mineral found in the old dune. Illite and chlorite were also found in all samples with calcrete. Authigenic smectite formation occurs above the laminar-structured calcrete due to restricted drainage conditions. The most significant chemical variations associated with the calcrete formation are (i) enrichment of Co, U, Br, and REE in calcrete; (ii) depletion of middle REE in the upper levels, particularly Eu, and enrichment of middle REE and heavy REE in calcrete; and (iii) Hf, Zr, Cr, Th, Cs, Ta, Ga, Rb, and K appear to be retained in the upper levels, where calcite has been dissolved. Here iron is more reduced. Fe³⁺ occurs in iron oxides (goethite and hematite), and clay minerals. The ratio goethite/hematite appears to increase down the profile; and Fe²⁺ is mainly present in clay minerals.     

The Role of Soil Mineralogical Characteristics in Sustainable Soil Fertility Management: A Case Study of Some Tropical Alfisols in Nigeria

The pedogenic horizons of nine profile pits dug across three toposequences were studied to determine the soil mineralogical characteristics and its implications on sustainable management of the fertility of some tropical Alfisols in Nigeria. Results showed that the epipedon which were predominantly ochric had textures that ranged from sand to sandy loam, while the subsurface (B/Bt) horizons had sandy clay loam to sandy clay texture and were gravelly (31.79–83.04%). The soil reaction ranged from strongly acid to neutral (pH 5.10 to 7.05). Calcium and magnesium dominated the exchange sites and accounted for about 75% of the exchangeable bases. Illite/mica and kaolinite were the dominant minerals in the clay fractions, while quartz, mica, and feldspars dominated the fine sand and silt fractions of the soils. While the presence of illite and mica could be important for potassium nutrition in these soils, kaolinite and oxides of iron could also cause phosphorus fixation.     

Evaluation of ferrolysis in soil formation

The concept of ferrolysis as defined in the 1970s by Brinkman and co‐workers is mentioned in the recent literature as a dominant process to explain clay disintegration, interlayering of clay minerals, and strong texture contrast of duplex soils, in which bleaching and mottling are predominant features. Ferrolysis is based on biochemical reduction of free iron(III) oxides to Fe²⁺ and re‐oxidation of Fe²⁺ during alternating reducing and oxidizing conditions in the soil. The acidity produced during the oxidation is assumed to release cations from silicates which results in the destruction of clay minerals. A detailed analysis of data from chemical analyses, laboratory experiments, and mineralogical and micromorphological investigations, which have been considered to sustain the ferrolysis theory, has been carried out. Some soils in Belgium and France, which have been considered to be formed mainly by ferrolysis, show strong textural contrast or albeluvic features. It has been shown that the development of these soils is due to clay translocation rather than to clay destruction by ferrolysis. Fine quartz and chlorite, assumed to be secondary minerals formed during ferrolysis, are more likely formed by disintegration of larger quartz and chlorite particles.     

Specific Features of Profile Distribution and Crystallochemistry of Phyllosilicates in Soils of the Cisbaikal Forest-Steppe

The mineralogical composition of agrogray, dark gray, and agro-dark gray soils (Luvic Greyzemic Retic Phaeozems); agro-dark gray residual-calcareous soils (Calcaric Cambic Phaeozems); clay-illuvial agrochernozems (Luvic Chernic Phaeozems); and agrochernozems with migrational–mycelial carbonates (Haplic Chernozems) developed in the forest-steppe of Central Siberia within the Irkutsk Depression has been studied. The clay (<1 μm) fraction separated from these soils consists of mixed-layer minerals with alternating layers of hydromica, smectite, vermiculite, and chlorite; the proportions between them change within the soil profiles. The clay fraction also contains hydromicas, kaolinite, chlorite, and some admixture of the fine-dispersed quartz. Each type of the soils is characterized by its own distribution pattern of clay material with specific alternation of layers in the mixed-layer formations. Mixed-layer minerals of the chlorite–vermiculite type predominate in the upper horizons of texture-differentiated soils. Down the soil profile, the content of mixed-layer mica–smectitic minerals increases. In the clay fraction of arable dark gray-humus soils with residual carbonates, the distribution of the clay fraction and major mineral phases in the soil profile is relatively even. An increased content of well-crystallized kaolinite is typical of these soils. The parent material of agrochernozems has a layered character: the upper horizons are generally depleted of clay, and the middle-profile and lower horizons are characterized by the considerable kaolinite content. In general, the clay material of soils of the Tulun–Irkutsk forest-steppe differs considerably from the clay material of foreststeppe soils developed from loesslike and mantle loams in the European part of Russia. In particular, this difference is seen in the proportions between major mineral phases and between biotitic and muscovitic components, as well as in the degree of crystallinity and behavior of kaolinite and chlorite.     

Clay minerals of red-yellow soils derived from pleistocene sediments in Japan

Red-Yellow soils are widely developed on terraces and hilly lands in the south-western half of Japan. They do not show any evidence of bleaching in the lower part of the A horizon, and are characterized by an extremely strong acid reaction, and a very low base-status⁹⁾. There are few studies on clay mineralogy of Red-Yellow soils in Japan. Egawa et al⁴⁾. have reported on clay mineralogy of soils derived from the Pleistocene and the Tertiary sediments most of which may be regarded as Red-Yellow soils. Matsui and Katô¹⁰⁾ have described clay minerals of Red-Yellow soils derived from the Pleistocene sediment in the environs of Shinjobara, Shizuoka Prefecture. These investigations indicated that clay minerals of Red-Yellow soils derived from the Pleistocene sediments consisted mainly of kaolin minerals, whereas those of Red-Yell ow soils derived from the Tertiary sediments were of the kaolin-illite association.     

Zur Verwendung von Gesteinsmehlen in der Landwirtschaft. II. Wirkung von Gesteinsmehlen als Bodenverbesserungsmittel

The use of rock powders in agriculture. II. Efficiency of rock powders for soil amelioration Five rock powders with different chemical and mineralogical characteristics were investigated in order to test their suitability for agricultural soil amelioration. The highest cation exchange capacity (CEC) was determined for the powder of smectite rich volcanic ash. Carbonate rock powders showed highest values for acid neutralization capacity (ANC). Silicate rock powders (granite, basalt) showed the lowest values for both investigated parameters. After some decades, a yearly application per hectare of 1000 kg of rock powder consisting of clay minerals or carbonates could at best successfully improve extreme poor soils, e.g. sandy soils with low humus content, by raising the CEC or the ANC. Rock powders rich in silicium, e.g. of granite, are not suitable to improve soils significantly.     

我国北亚热带白浆化土壤矿物学特性的研究

本文对北亚热带地区七个白浆化土壤的原生矿物和次生矿物的特性进行了研究。重，轻矿物含量表明土壤继承了母质的特性，粘淀层与漂白层的母质沉积是间断的，前者风化强度大于后者。石英颗粒表现特征显示漂白层物来来源于黄土物质再堆积，粘土矿物以水云母为主，其结晶度较差，氧化铁类型以针铁矿和赤铁矿为主，也有非晶质氧化铁和硅酸盐中的Ｆｅ＾２＋，其形成条件与现代化成土条件一致。     

Chemical and mineralogical properties of sandy and loamy-sandy ochreous brown earths in relation to incipient podzolization in a brown earth—podzol evolutive sequence

Chemical and mineralogical properties of ochreous brown earths have been studied with particular reference to: (1) the distribution within the profiles of Fe and Al compounds; (2) the occurrence of smectite-like clay minerals in surface horizons. Ochreous brown earths studied belong to a developmental sequence of forest soils, from acid brown earths to ferric podzols, developed on sandy or loamy-sandy acid parent materials. In such a soil sequence, both selective chemical and mineralogical data show clearly that podzolization is already active in ochreous brown earths, whereas such an incipient podzolization is quite undetectable by direct morphological observations. The distribution patterns of amorphous Fe and Al hydrous oxides and organic associations, clearly show the intergrade character of ochreous brown earths, when compared with the vertical distribution of Fe and Al forms in acid brown earths and podzolized soils. The Fe/Al ratio of both an NH₄-oxalate extract and an NaOH/Na-tetraborate extract buffered at pH 9.7, measured in the A₁B diagnostic horizon of ochreous brown earths, is a particularly appropriate and useful genetic criterion for the detection of incipient podzolization. Moreover, the presence of expansible clay minerals (degradation smectites) in the clay-sized fraction of the surface horizons of ochreous brown earths (A₁ and A₁B) can be considered as supplementary evidence of incipient podzolization.     

南极半岛海洋气候区的土壤Ⅶ. 矿物学特性

南极海洋气候区岩石风化和土壤形成过程中有明显的原生矿物蚀变作用和自生矿物成矿作用。本文以粗骨寒冻灰化土和石灰性扰动冻土两种有代表性的土壤类型为例,阐述了本区土壤矿物学特征。指出铝氧化物、绿泥石、碳酸盐是本区玄武岩类风化物质上发育土壤中的主要自生矿物类型,蒙脱石、特别是绿泥-蒙脱石混层矿物是南极海洋气候区土壤粘粒部分的特征矿物。不同土壤由于成土环境、成土过程、成土历史的差异,其土壤物质的矿物学组成、含量、形态、分布具有明显不同。土壤发生性铁氧化物与成土作用和土壤过程密切相关,其矿物类型、含量、形态特征、分布模式在不同的土壤中明显不同,是表征土壤发育程度与剖面形态表达的有效指标。     

Clay minerals and potassium status in some soils of Jordan

The physical, chemical and mineralogical characteristics of some soils in the Jordan Valley (Rift Valley) and the Highland (Irbid-region) were investigated. The soils of the Highland (Chromoxererts) contained more clay and smectite than those of the Jordan Valley (Camborthids and Torriorthents). Higher contents of carbonates, salts and mica were found in the latter. In addition to smectite and micam interstratified clay minerals (mica/smectite and smectite/chlorite) and kaolinite were present in the clay fractions of the soils in the two regions. Soils of the Highland, especially those under higher rainfall with larger amounts of highly charged smectite, had lower contents of available and total potassium and higher degrees of potassium fixation than those of the Jordan Valley. Soil properties such as carbonate, salt and potassium contents and clay mineral composition were related to the amounts of annual rainfall in soils of the Highland, whereas differences among the Jordan Valley soils were related to the parent materials, especially the underlying Lisan Marl.     

豫北第四纪沉积物的矿物特征

豫北平原属于黄淮海平原的一部分,位于太行山洪积-冲积扇以东的黄河、漳河之间,是河南新乡和安阳两地区的主要粮棉产地。豫北平原除部分地区是黄土缓丘和山前洪积冲积物外,大部分由黄河、漳河、沁河等现代河流沉积物所组成,其中沁河沉积物、黄土、次生黄土分布在豫北平原西部,漳河沉积物分布在豫北平原北部,而中部和东部则为大面积的黄河河流沉积物。为配合黄淮海平原中豫北平原的治理及南水北调工程中线的选线间题,我们曾对豫北地区各种沉积物上所发育的土壤进行分析,有关华北平原的土壤已有详细专著(熊毅等1965),本文仅就豫北平原地区土壤的矿物性质作简要讨论。     

Influence of the nature of clay minerals on the fixation of radiocaesium traces in an acid brown earth–podzol weathering sequence

The magnitude of radiocaesium fixation by micaceous clay minerals is affected by their transformation, which depends on weathering in soil. The net retention of radiocaesium traces was quantified by sorption–desorption experiments in the various horizons of four sandy soils forming an acid brown earth–podzol weathering sequence derived from sandy sediments and characterized by marked changes in mineral composition. The features of the 2:1 minerals of the four soils, resulting from an aluminization process in depth and a desaluminization process towards the surface, had a strong influence on Cs⁺ fixation. Beneath the desaluminization front, which deepens from the acid brown earth to the podzol, hydroxy interlayered vermiculite was dominant and the ¹³⁷Cs⁺ fixation was the weakest. At the desaluminization front depth, vermiculite was responsible for the strongest ¹³⁷Cs⁺ fixation. In the upper layers, smectite appeared in the podzolized soils and the ¹³⁷Cs⁺ fixation decreased. The magnitude in Cs⁺ fixation therefore appeared as a tracer of the transformation process affecting the 2:1 clay minerals in the acid brown earth–podzol weathering sequence. This magnitude was positively correlated with the vermiculite content of the studied soil materials estimated by the rubidium saturation method.     

Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. I. Effect of iron oxides on ammonium fixation

Experiments were conducted with two typical paddy soils from China and a vermiculite to study the influence of iron oxides on the fixation and release of ammonium. Removing iron oxides, especially amorphous iron oxides, from the soils favoured the release of non-exchangeable NH₄-N and stimulated the fixation of NH₄-N in the presence of added (NH₄)₂SO₄. Addition of artificial goethite and hematite to the original soils or to the soils free of iron oxides reduced the fixation of NH₄⁺-ions. This effect was also observed with vermiculite. We conclude that the coating of clay minerals with iron oxides has an impact on the diffusion of NH₄⁺-ions into and out of the interlayers of the clay minerals. The reduction and dissolution of iron oxides induced by low redox potential (E_h) after flooding of paddy soils is assumed to be an important mechanism controlling NH₄⁺-fixation in paddy fields.     

Zur Genese von Schwarzerden auf der Sontheimer Hochterrasse in der Donauniederung bei Ulm

Pedogenesis of chernozems in the upper river terrace of the Danubian river near Ulm (South West Germany) The “chernozem-like” soils in the upper river terrace of the Danubian river near Ulm (FRG) were examinated. Field analyses as well as soil physical and chemical, clay mineralogical and pollen analyses were carried out. The parent material of the soils was identified as loess, on the basis of its texture, clay mineral composition, structure, carbonate content, the presence of loess molluscs, and the location on an upper river terrace with loess findings in the surrounding. Characteristic pedogenetic processes, such as deliming, silicate weathering, formation of oxides and hydroxides, neoformation of clay minerals and clay translocation prove a non-groundwater-influenced development of the soils within at least the last 8000 years. Therefore an accumulation of organic matter under anaerobic conditions during the peat formation in the lower river terrace nearby was not possible. According to this finding, it can be deducted that the humus accumulation may be due to influences of continental climate and forest steppe during the preboreal period, whereby the humus horizons were formed at deeper horizons through bioturbation. After the groundwater level was raised in boreal age, the steppe stage of the soils had ended and the fluctuating levels of groundwater, rich in carbonates, stabilized humic substances. Thus strong degradation of the soils to date was prevented. Therefore the soils under study could be classified as gleyic Chernozems or luvic Phaeozems.     

Effect of Long-Term Effluent Recharge on Phosphate Sorption by Soils in a Wastewater Reclamation Plant

The Soreq recharge basins, used for wastewater reclamation employing the Soil-Aquifer Treatment (SAT) system, have been recharged, on average, by about 1,800 m depth of secondary effluent during their operation period of ～25 years. An estimated amount of ～6 kg P m^?2 was added to the soil/sediment column during this period. The objective of this study was to compare phosphorous sorption characteristics of representative pristine soils in the Soreq recharge site to those of the basin soils sampled after a long period of effluent recharge. Batch isotherm experiments were conducted: samples of one g of soil were equilibrated with 25 mL of 0.02 M NaCl solution containing 0–3.2 mM of phosphate for 7 days at 25± 1^°C and P sorption was measured. Long-term effluent recharge significantly decreased the maximum P sorption capacity of the top sandy soil (0.15–0.3 m) and only very slightly decreased maximum P isotherm capacity of the deep clayey-sand soil (10–10.5 m). The retention of P in the basin sandy soil primarily involved sorption and surface precipitation reactions on soil carbonates. In the basin clayey-sand soil, P was retained by its sorption on surfaces of Fe, Al, Mn oxide/hydroxides and clay minerals. Long-term effluent recharge increased EPC₀, (the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), of the basin soils compared to the pristine soils. Due to loading of the top horizons with P by prolonged recharge and reduced P concentration in the effluent, EPC₀ of the basin sandy soil is now equal to the average P concentration of the recharged effluents. If effluent P concentration will decrease further, the top sandy soil will become a source of P to the reclaimed water, rather than a sink. The clayey-sand layers and lenses in the vadose zone of the SAT system of the Soreq site offer a large capacity for P adsorption. With gradual leaching of carbonate minerals and synthesis of secondary clay minerals, driven by long-term effluent recharge, P retention mechanisms in the basin soil may be changed, but this process would be extremely slow.     

粘土矿物与细菌间相互作用的试验性研究进展

Interactions between microbes and minerals have the potential to contribute significantly to global cycles of various processes and serve as a link between the geosphere and life. Clays and clay minerals occur commonly in agriculturally utilized soils, are naturally grown underground (soil and rock) and are used in construction material. Clay minerals serve as natural, geological and technical barriers in geotechnics and environmental geotechnics. Bacteria in turn are ubiquitous in natural soils, subsoils and rocks and are in permanent contact with clay minerals. There are numerous ways in which bacteria can interact with clay minerals and alter them: dissolution, refinement and transformation, reduction of trace elements incorporated in the clay minerals and uptake of trace elements from these minerals, e.g., by the production of siderophores and chelators and enhancement or reduction of adsorbance of trace elements on clay minerals. In addition, bacteria can influence layer charge, cation exchange capacity (CEC), exchangeable cations, Brunauer-Emmett-Teller surface, swelling and the rheological properties of clay minerals. The field of clay mineral-microorganism interaction is still wide open because of the large potential that the interactions of bacteria with clay minerals in soils and sediments may result in changes in clay mineral properties and behaviors. Further detailed studies on all these tentative changes and underlying mechanisms as well as broad surveys of quantifications of extents and rates of clay mineral-microorganism interactions, especially in mimicking natural systems, are highly required. This review summarizes the influences of various bacteria on the properties of different clay minerals as determined experimentally using viable bacteria.     

A geochemical analytical approach for the evaluation of heavy metal distribution in lagoon sediments

Background, Aim, and Scope  Italian lagoon environments are of great importance due either to their frequency and distribution along the coasts or to their management. Agriculture, urban and industrial activities in lagoon catchments can be sources of heavy metal (HM) pollution by direct waste dumping, atmospheric deposition of fumes or, simply, as a consequence of a lack of natural water recharge. HM concentration in lagoon sediments is a tool of HM monitoring in the surrounding environment. Application of sequential extraction procedures (SEP) to sediments makes it possible to study the HM distribution among the main geochemical phases and to assess their potential mobilization as a consequence of environmental condition variations. In the present study, the three-step SEP (0.11 m HOAc; 0.1 m NH₂OH·HCl; 8.8 m H₂O₂ and then 1 m NH₄OAc), developed by the Measurement and Testing Programme of the European Commission (BCR), was combined with information on the chemical and mineralogical properties of the sediments in order to assess the level and risk of mobility of HM (Cu, Cr, Cd, Pb, Ni, Zn) in sediments from the Fusaro volcanic coastal lagoon of southern Italy. The effect of sediment air drying and physico-chemical properties on the metal distribution in various geochemical forms and fractions was considered. Materials and Methods  Surface (5 cm depth) sediment samples were collected from twenty-one sites on the Fusaro lagoon. Moisture, pH, organic carbon, carbonates, particle-size distribution and HM total content were determined on the dried sediment samples. The mineralogy of the clay fraction was determined at room temperature on random and oriented samples. The different forms of Al, Si and Fe in the bulk sediment (< 2 mm) were analyzed after oxalate, dithionite-citrate and pyrophosphate extractions. The BCR-SEP was used to fractionate trace element chemical forms in nine selected sediment samples. Effects of sediment air-drying on HM fractionation were analyzed. Results  Middle (Cu, Cr) and low (Cd, Pb, Zn) concentrations of heavy metals in sediment samples from the deeper central part of the lagoon were observed. Cadmium resulted in mainly being associated with carbonate forms (∼60%), whereas Cr and Ni occurred primarily as residual mineral phases (>50%). Zn appeared uniformly distributed among the main geochemical forms. Considerable presence of Cr, Cu and Pb was found in the oxidizable fraction (∼50%), indicating organic matter and/or sulphides major sinks for these metals. Differences of heavy metal distribution among sediment samples were observed, depending on the total metal content and on sediment properties. Modifications in metal speciation induced by sediment air drying mainly consist of a transfer of the actual and potentially mobile fractions towards immobile fractions (mineral residue) by oxidation and formation of Fe and Mn oxides. Discussion  Both total content and sequential extraction results did not show an environmental critical situation: the only possible risk, associated with heavy element mobility, could occur in consequence of a drastic pH and redox equilibria variation at the water-sediment interface. Conclusions  Despite all limitations, the BCR-SEP combined with information on the chemical and mineralogical properties of the sediment solid matrix provides a valuable approach to describe the risks related to the potentially toxic HM occurring in sediments (in this paper the case of the Fusaro lagoon is examined). HM distribution among the sequentially extracted geochemical forms is affected by sediment properties, such as pH (Zn), clay (Cd), Fe easily reducible oxides (Pb) and organic matter (Cu) content. Recommendations  Political managers, usually facing limitations of time and resources, have to optimize the cognitive phases, selecting the most useful information to make ‘effective and correct decisions’ in the environmental field. Therefore, although conscious of the limits of the adopted quality assessment, we believe it represents a good compromise between time and resource availability (i.e. type and quality of information). Outlook  The complementary use of the simple and rapid European fractionation scheme with information on the chemical and mineralogical properties of the sediments provides more awareness about the nature of the sediment components involved and offers a more reliable way for studying HM speciation in sediments.     

Tonmineral- und K-Ca-Austauscheigenschaften von Oberböden des Nährstoffpotentialversuches Hallertau

Clay mineralogy and K-Ca-exchange properties of surface soils from the nutrient potential trial Hallertau (Bavaria) In soils of four locations of the Hallertau nutrient potential trial, with a soil texture consisting of sand, silty sand, silty loam and sandy clayey loam, clay mineral properties were measured with the standardized glycerol expansion method and with n-alkylammonium (Rn_c-NH₃⁺-clay). The expandable minerals of the sandy soils consist exclusively of smectites s.s., (s.s. = sensu stricto) with 0.42 to 0.28 charge equivalents per formula unit (p.f.u.). The expandable minerals of the loams are an assemblage of smectites s.s. and vermiculites. The total layer charge of the smectites s.s. extend from 0.54 to 0.28 charge eq. p.f.u. The fine clay fractions (< 0.1 μm) do not contain vermiculites. The layer charge density of vermiculites with homogeneous charge in the coarse fractions varies between 0.60 and 0.95 charge eq. p.f.u. The immediate K-Ca-exchange was extended with the values of the continued K exchange versus Ca at low K intensity. The Q/I isotherms of sandy soils have a more pronounced curvature than the isotherms of the loams; in all cases, however, the exchange curves have a continuous form. This phenomen is discussed in terms of the clay mineralogy of the soils. After 8 years without K fertilizing, samples gave values between 168 and 497 kg smectite-K/ha for the surface soils. The constant rates of K-desorption vary between 12.8 and 28.7 kg K/ha (surface soil). The rates are better differentiated between unfertilized and fertilized soils for the loams than for the sandy soils. The constant rates of K release were found to be controlled at an AR-level between 1.6 · 10^?4 M^1/2 (unfertilized sandy soil) and 5.2 · 10^?4 M^1/2 (fertilized sandy clayey loam soil).     

Geochemistry of stream sediments within the reclaimed coastal floodplain as indicator of anthropogenic impact (River Neretva,Croatia)

Purpose

This study used multi-element signatures of stream sediments to assess both natural and human-induced impact on fluvial system in the River Neretva delta receiving environment over time. The river basin actually comprises several sub-catchments, and the geochemical features of major elements, trace metals radiometric and mineralogical characterisation of river bed sediments were used to assist the interpretation of the environment of deposition and its subsequent modifications caused by various anthropogenic pressures within the river basin.

Materials and methods

Five sites were chosen for sediment sampling at key locations within the study area with assumed undisturbed, continuous sedimentation process. At each of the sites, three representative cores were taken by scuba divers. Sample sites were selected in order to reflect the influence of different sub-catchments they belong to and the land-use pattern of the surrounding area. Samples were analysed for pH, redox-potential, granulometry, mineralogy, thermogravimetry, major and trace element concentrations and radionuclide activities. The univariate and multivariate statistics were applied. The geochemical normalisation of data was done using Al, the procedure based on calculation of the regression line of the metal on the normaliser followed by testing the ratios metal/normaliser on all data-points.

Results and discussion

All studied sediments are classified as silt, ranging from clayey silt to silt and sandy silt. Mineralogically, the sediments were dominated by carbonates and quartz. The chemical contaminant data are generally of good quality, mostly below guideline levels. Sedimentation rates were estimated using vertical distribution of ¹³⁷Cs activities. Normalisation of TMs done by using Al shows strong R ² _adj values for the regressions of Al and V, Al and Cr, and Al and Ni. However, Al cannot fairly explain the fluctuation of the concentrations of Cd, Cu, Pb and Zn in sediment cores from all of the sampling sites. Generally, inorganic scavengers such as clay minerals followed by Fe and Mn oxides and S (pyrite and gypsum) seem to be dominant factors controlling TMs in studied sediments.

Conclusions

Although the River Neretva delta occupies a rather small area, the geochemical features of major and trace elements and ¹³⁷Cs activities show complex sediment provenances. Each of the sampling sites reflect exactly different effects of anthropogenic intervention that particularly refer to the changes in river morphology and ecology, along with the altered flow regimes within the catchment on sediment loads and quality.

     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.