Plastic pollution in aquatic environments is one of the most fatal environmental issues in the world. Although the distribution of plastic debris in the sea and at coasts has been addressed, the ...transportation of plastics through a river system is unclear but important. The distribution of plastic debris in the Selenga River system is responsible for the environmental pollution of Lake Baikal. Twelve sampling sites along the river shore of the Selenga River system have been surveyed considering the industrial activity and population density. The number of plastics significantly correlates with the population density. The higher the number of plastics is, the smaller is the average size. The size fractions of foam and film plastics show a significant relationship, suggesting that the plastic debris fragmented on-site on the river shores. The most abundant plastic debris is polystyrene foam (PSF), which is usually used for construction and packaging. Plastic debris occurs due to insufficient plastic waste management. Its distribution is affected by seasonal changes of the water level and flow rate of tributaries. Furthermore, the fragmentation of plastic debris is related to temperature changes associated with freeze and thaw cycles, solar radiation, and mechanical abrasion. Smaller microplastics with microscopic sizes were detected in PSF debris. Based on micro-Fourier transform infrared spectroscopy, these microplastics are polystyrene and polyethylene. This study proves that invisible and visible microplastics are transported together.
Foamed plastic debris in aquatic systems has become one of the emerging global contaminants. In this study, the behavior of polystyrene foam (PSF) and microplastics (MPs) adhered on the PSFs were ...investigated on the Tuul River shore in Ulaanbaatar, the capital city of Mongolia. The micro-sized (<5 mm) PSF, which was the dominant PSF over 600 pieces in 100 m2, have accumulated along the shoreline of Tuul River. Carbonyl index (CI) was calculated to evaluate the surface oxidation of macro-sized (20–100 mm), meso-sized (5–20 mm), and micro-sized PSFs and confirm the relative aging depending on photodegradation. CI ranged from 0.00 to 1.09 in the sampled PSFs, whereby the degraded PSFs with high CI were distributed on the shore of downstream of sewer drainage. Micro-sized PSFs showed a wide range of CI and a relatively high average value of CI as compared to those of meso- and macro-sized PSFs. Most of PSFs aggregated with MPs and the adhered MPs have been ubiquitously detected from the surface of PSFs. Adhered micro-sized plastics explored from the surface of PSFs with various sizes, except for mega-sized (>100 mm) PSF, ranged from 5 to 141 items per piece of PSF fragment. The aggregates of PSFs and MPs were common status of PSFs during their transportation. The present findings, which indicated a high concentration of adhered MPs, raise an environmental concern about the widespread aquatic plastic pollution.
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•Polystyrene foams (PSFs) are dominant plastic debris in the studied river shore.•Wide range of surface oxidation of PSFs can be related to their surface status.•Abundance of adhered microplastics on PSFs was different between size fractions.•PSFs have a great potential to transport various types of microplastics.
Environmental plastics which have various adverse effects to the ecosystem services have potentials to interact microplastics from the environment and to form plastic aggregates affecting to aquatic ecosystems by their behaviors.
After reclamation of the Isahaya Bay polder, a conserved area is covered with naturally developed vegetation under high groundwater level conditions. This study investigated how alluvial deposits ...transform into soil without utilizing artificial water drainage systems for agricultural land uses. Soils were surveyed under four vegetation compositions, including those dominated by goldenrods (GR), occupied by high-grown reeds (HRD), covered with low-grown reeds (LRD), or a mixture of goldenrods and reeds (MIX). The microtopography of the polder differentiated the research site with a higher elevation at the GR location, followed by a MIX, HRD, and a lower elevation at the LRD location. The soils were characterized by their physicochemical properties and ionic composition of the soil water. Electrical conductivity (EC), which can be an indicator of residual seawater, was lowest in the GR, followed by the MIX, HRD, and LRD. The soil moisture regimes affected by microtopography led to different frequencies of wet-dry cycles in the soil, resulting in a developing sequence of soil structure from LRD to GR with decreasing EC. The ionic composition of soil water varied with elevation and soil depth. The residual seawater still influenced the ionic composition of deeper soil horizons at lower elevations, while specifically high rates of Ca
2+
and SO
4
2−
were observed in GR. The oxidation of pyrite is stimulated by soil aeration with lowering water level, resulting in soil acidification and the simultaneous dissolution of calcium carbonate from seashells. The sequential changes in soil properties with elevation indicated the effects of microtopography on soil moisture dynamics, which led to variations in soil formation and vegetation in the conserved area.
The widespread distribution of plastic debris in riverine environment is one of the major concerns of environmental pollution because of its potential impact on the aquatic ecosystem. In this study, ...we investigated the accumulation of metal(loid)s on polystyrene foam (PSF) plastics collected from the floodplain of the Tuul River of Mongolia. The metal(loid)s sorbed on plastics were extracted from the collected PSF via sonication after peroxide oxidation. The size-dependent association of metal(loid)s with plastics indicates that PSFs act as vectors for pollutants in the urban river environment. The mean concentrations of metal(loid)s (i.e., B, Cr, Cu, Na, and Pb) indicate a higher accumulation of the metal(loid)s on meso-sized PSFs compared with macro- and micro-sized PSFs. In addition, the images from scanning electron microscopy (SEM) indicated not only the degraded surface of plastics showing fractures, holes, and pits but also the adhered mineral particles and microorganisms on the PSFs. The interaction of metal(loid)s with plastics was probably facilitated by the physical and chemical properties of altered surface of plastics through photodegradation, followed by an increase in surface area by size reduction and/or biofilm development in the aquatic environment. The enrichment ratio (ER) of metals on PSF samples suggested the continuous accumulation of heavy metals on plastics. Our results demonstrate that the widespread plastic debris could be a carrier of hazardous chemicals in the environment. Considering that the negative impacts of plastic debris on environmental health are major concerns to be addressed, the fate and behavior of the plastics especially their interaction with pollutants in aquatic environments should be further studied.
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•Relatively high concentrations of metal(loid)s were detected in meso-sized PSFs.•Adhered mineral particles and microorganisms were detected on PSFs.•Metals were quantified for extracts through digestion of field-collected PSFs.•Interaction between PSF and metal(loid)s could be dominated by surface complexation.
Purpose
In modern times, farmlands in Japan have been reconstructed at a large-scale through the cutting and filling of soils. In principle, such reconstruction should be carried out with a minimum ...amount of soil transportation to decrease environmental impacts and cost, and the soil distribution and properties should be determined by the subsequent reclamation process. To assess this issue, we attempted to evaluate the impacts of farmland reclamation on soil distributions in Japan.
Materials and methods
Farmland soil in the reconstructed area was surveyed from a pedological perspective using geographic information system (GIS) data. To enable a simple comparison of topsoil thickness and soil distribution before and after farmland reclamation, we selected survey soils classified as “High-humic Cumulic Allophanic Andosols” under the Japanese soil classification system, which are more than 50 cm in thickness in the Melanic horizon. Changes in the thickness of the topsoil were evaluated by direct measurement at 30 field survey positions. The extent of farmland affected by large-scale reclamation was calculated from a GIS-based comparison of topography before and after reclamation based on a digital elevation model (DEM).
Results and discussion
The reclamation process decreased the thickness of topsoils from more than 50 cm to an average of 26.9 cm over the 30 surveyed positions. The minimum topsoil thickness of 15 cm observed in this study corresponds to the recommended topsoil conservation level under Japanese guidelines for the reclamation of paddies. There was no significant difference in the topsoil thicknesses obtained through soil filling and cutting reclamation processes. These results indicate that the original soil distributions potentially lost the “High-humic Cumulic” feature. Although the topsoils were conserved during farmland reclamation processes carried out in accordance with the Japanese guidelines, the results of this study revealed the influence of the reclamation process on soil properties and, as a result, their classification, through a decrease in topsoil thickness and mixing with subsurface horizons.
Conclusions
We confirm the importance of taking topsoil conservation into account in determining the influence of agricultural reclamation on soil distribution in Japan. In reclaimed upland fields, most managed topsoils have sufficient thickness to fill the diagnostic surface horizon. An exception is managed topsoil in reclaimed paddies, which can have insufficient to thickness to meet the corresponding diagnostic surface horizon. We suggest that some soils in modern reclaimed farmlands do not currently fulfill the criterion of diagnostic surface horizon regardless of their reclamation magnitude.
The Selenga River contributes to 50% of the total inflow to Lake Baikal. Large tracts of the Selenga River Basin have been developed for industry, urbanization, mining, and agriculture, resulting in ...the release of suspended solids (SS) that affect downstream water quality and primary productivity. This study addressed SS as the main factor controlling pollutant transport and the primary indicator of land degradation in the Selenga River system. Tributaries with larger areas dedicated to agricultural use had higher SS concentrations, reaching 862 mg L
−1
, especially during the high runoff and intensive cultivation season. Although the large SS flux was detected in the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to widespread development in the watershed. Watersheds with high potential of SS release are sensitive to intensive land uses. SS in the river system had a constant elemental composition consisting mainly of Fe and Al oxides, indicating that surface soils were major constituents of the tributary SS. Three minor heavy metals (Zn, Cu, and Cr) appeared in high concentrations downstream of urban and mining areas (two- to sixfold increases), indicating that these contaminants are carried by SS. At two tributary junctions, the concentration of contaminants on the SS decreased due to a large influx of SS with low heavy metal contents. Changes in electric conductivity and pH at downstream of tributary junctions enhanced the sedimentation of SS and the removal of contaminants from the water phase after aggregation of the SS. Land use changes in the tributary watersheds are major controlling factors for the fate of contaminants in the river system.
This study aimed to clarify the distribution trend of sapric peat soils in Japanese agricultural fields from the view point of drainage and landform conditions using the Geographic Information System ...(GIS). To this end, the environmental conditions in the distribution area of organic soils were divided by combining existing GIS databases of environmental factors that consist of groundwater level, drainage condition, landform classification, and grain size of sediment. In order to evaluate the contribution of these environmental factors to the distribution trend of sapric peat soils, we applied quantification method type II to construct the discrimination model that enables the differentiation of the distribution area of sapric and non-sapric peat soils. In the case of organic soils without mineral surface cover, our discrimination model clearly suggests that sapric peat soils tend to be distributed under good drainage condition on floodplains, and with coarse sediments. This indicates that the effect of drainage conditions on peat decomposition is determined by landform condition. On the other hand, in the case of the land covered with mineral soils on the surface, sapric peat soil distribution was not well estimated. Determining the relationships between the distribution trend of sapric peat soils and the environmental factors by analyzing the existing GIS database is a new application. This was achieved by the combination of GIS and quantification method type II, which contributes to the description of the peat decomposition process from the viewpoint of geographical conditions.
Because of low net production in arctic and subarctic surface water, dissolved organic matter (DOM) discharged from terrestrial settings plays an important role for carbon and nitrogen dynamics in ...arctic aquatic systems. Sorption, typically controlling the export of DOM from soil, may be influenced by the permafrost regime. To confirm the potential sorptive control on the release of DOM from permafrost soils in central northern Siberia, we examined the sorption of DOM by mineral soils of Gelisols and Inceptisols with varying depth of the active layer. Water-soluble organic matter in the O horizons of the Gelisols was less (338 and 407 mg C kg⁻¹) and comprised more dissolved organic carbon (DOC) in the hydrophobic fraction (HoDOC) (63% and 70%) than in the O horizons of the Inceptisols (686 and 706 mg C kg⁻¹, 45% and 48% HoDOC). All A and B horizons from Gelisols sorbed DOC strongly, with a preference for HoDOC. Almost all horizons of the Inceptisols showed a weaker sorption of DOC than those of the Gelisols. The C horizons of the Inceptisols, having a weak overall DOC sorption, sorbed C in the hydrophilic fraction (HiDOC) stronger than HoDOC. The reason for the poor overall sorption and also the preferential sorption of HiDOC is likely the high pH (pH>7.0) of the C horizons and the smaller concentrations of iron oxides. For all soils, the sorption of HoDOC related positively to oxalate- and dithionite-citrate-extractable iron. The A horizons released large amounts of DOC with 46-80% of HiDOC. The released DOC was significantly (r=0.78, P<0.05) correlated with the contents of soil organic carbon. From these results, we assume that large concentrations of DOM comprising large shares of HiDOC can pass mineral soils where the active layer is thin (i.e. in Gelisols), and enter streams. Soils with deep active layer (i.e. Inceptisols), may release little DOM because of more frequent infiltration of DOM into their thick mineral horizons despite their smaller contents of reactive, poorly crystalline minerals. The results obtained for the Inceptisols are in agreement with the situation observed for streams connecting to Yenisei at lower latitudes than 65°50' with continuous to discontinuous permafrost. The smaller sorption of DOM by the Gelisols is in agreement with the larger DOM concentrations in more northern catchments. However, the Gelisols preferentially retained the HoDOC which dominates the DOC in streams towards north. This discrepancy can be explained by additional seepage water from the organic horizons that is discharged into streams without intensive contact with the mineral soil.
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