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River deltas are often considered as hotspots of atmospheric carbon regulation, but few studies have paid attention to the differences between topsoil and subsoil for carbon sequestration. Here physical and chemical stabilization mechanisms and sources of soil organic carbon (OC) accumulation in different soil layers of a major river delta (Yellow River delta) were studied by fractionation and isotopic analysis. We found that in topsoil, conversion from tidal flat to wetland substantially increases OC by 84%, whereas cotton cultivation decreases OC by 66%. Wetland with a high soil OC content is characterized by substantial accumulation of plant-derived OC and OC in mineral fractions. In subsoil, the OC variation is controlled by the yellow silt layer (YSL)-red clay layer (RCL) sequence. Although the weathering intensity of the RCL is much higher than that of the YSL, the OC age is younger in the RCL, indicating that the highly reactive, secondary minerals and iron oxides are capable of stabilizing younger organic carbon in transportation, deposition and post-pedogenic alteration. C-14 activity demonstrates that modern autochthonous OC is the main component of OC in wetland topsoil. In contrast, millennia-old allochthonous OC is the main component of OC in the subsoil layers, contributing 4-24% of total bulk soil OC. The higher delta C-13 values of carbon fractions (-24.3 to -21.4% for the intra-aggregate particulate organic matter fraction, intramicroaggregate silt and clay fraction, and free silt and clay faction) and bulk samples (similar to -22%) are likely to imply the contribution of aged OC in the Yellow River delta. This study offers direct confirmation that soil OC fractions and sources are influenced by different land-use types and pedological properties in characteristic soil layers. These findings suggest that biogeochemical alteration of the soil matrix controls OC stabilization mechanisms in the river sedimenttidal flat-wetland-farmland continuum. Highlights Land-use types and pedological features control OC storage in topsoil and subsoil, respectively. Reclamation strongly decreases content of all OC fractions and the proportion of fSC and rOC. Soil layers with distinct texture and mineral compositions lead to OC stratification in subsoil. The red clay layer in subsoil is capable of stabilizing both fresh and aged OC.

Intensified field management in orcahrds has resulted in significant and widespread acidification in the soils. However, effectively mapping the spatial patterns of soil pH aiming to support ecological management is impeded by its large variotions across soil types and planting durations. Kriging methods were used to integrate soil type and planting duration information for effective mapping of orchard soil pH in a case study in orchards of the Northeast Jiaodong Peninsula, East China. A total of 1 472 surface soil samples were collected, and the planting duration of each sampled orchard was acquired to generate a planting duration map via Voronoi tessellations. The performance of five kriging methods was compared, namely, ordinary kriging (OK), OK combined with soil type (OK_ST), OK combined with planting duration (OK_PD), cokriging combined with soil type and planting duration (OCK_STPD), and OK combined with soil type and planting duration (OK_STPD). Results showed that soil pH declined significantly with increasing planting duration and exhibited moderate spatial variability over the study area. Soil type and planting duration both had significant influence on the spatial distribution of soil pH. The OCK_STPD and OK_STPD methods showed better prediction efficiency than OK, OK_ST, or OK_PD. With regard to the predicted maps of soil pH, the OCK_STPD and OK_STPD methods highly reflected local variations associated with soil type and planting duration, but the OK method was poorly representative. Categorical soil type and planting duration information may be used as ancillary information to improve the mapping quality of orchard soil pH. The OCK_STPD and OK_STPD methods were practical and efficient methods for interpolating orchard soil pH in the study area. The resultant high-quality soil pH maps can contribute to improved site-specific management in the orchards.

PURPOSE: Coastal orchards, with greater humidity and precipitation, are favorable for fruit production, as well as mildew fungi development, thus becoming hot spots of Cu concentrations in soils due to the use of copper-based fungicides. However, little is known on the variation tendencies of Cu availability and mobility from these soils. This study aims to investigate the accumulation, spatial-temporal distribution, and chemical fractions of soil Cu in one of the largest coastal apple-producing area with over 40-year intensive cultivation in China. MATERIALS AND METHODS: A total of 104 orchard and 31 farmland topsoil samples were collected from Jiaodong Peninsula, Shandong Province. The total Cu concentration (T-Cu) and major element components (MnO, TiO(2), SiO(2), Fe(2)O(3), and Al(2)O(3)) in the soil were determined by X-ray fluorescence spectroscopy. Available Cu concentration (A-Cu) was extracted with HCl or DTPA. Chemical fractionations of Cu were determined via sequential extraction method. The variation tendencies of T-Cu, A-Cu, Cu available ratio (AR), and chemical fractions with planting duration in the orchards were explored while a cokriging method was selected to predict their spatial distributions. Moreover, Pearson’s correlation and multiple linear stepwise regressions were constructed to distinguish the vital factors in controlling Cu availability and mobility from these soils. RESULTS AND DISCUSSION: The results showed that long-term application of Cu-containing fungicides had increased Cu concentrations in orchard soils (85.77 mg kg(−1)) 3.5 times higher than the background value (24.0 mg kg(−1)) of local agricultural soils, in which 23.8% existed in the available form. Cu in the weak acid-soluble fraction (F1, 5.0 ± 3.5 %), reducible fraction (F2, 24.7 ± 6.6%), and oxidizable fraction (F3, 18.5 ± 7.8%) in orchard soils increased significantly with increasing planting durations whereas the residual fraction (F4, 51.7 ± 15.4%) exhibited a reverse trend. Total content, available content, and chemical fractions of Cu showed strong spatial heterogeneity. The availability and mobility of Cu in orchard soils were mainly controlled by total Cu content, pH, and soil organic carbon. CONCLUSIONS: Coastal orchards under warm and humid climate condition in China exhibited higher Cu input, along with acidification and rapid organic carbon turnover in the soils, eventually leading to large accumulation and high mobility of Cu in the soils.

Vegetated coastal habitats (VCHs) rank among the most intense carbon sinks in natural ecosystems, playing an important role in the global carbon cycle. A significant part of the organic carbon (OC) they store may be allochthonous OC that has been sequestered elsewhere. Yet, the compositions of allochthonous OC are largely unknown. Here, we present concentrations and carbon isotopic (13C and 14C) compositions and accumulation rates of carbon in the VCHs from major temperate-subtropical deltas of China: Yellow, Yangtze, and Pearl river deltas. We find that black carbon (BC) amounts to 9-25% of OC across sites. Temperate VCHs exhibit lower BC contents but higher BC contributions than subtropical VCHs. This seemingly counterintuitive result can be explained by increased accumulation of long-term, stable, allochthonous OC in temperate VCHs. BC in temperate VCHs contains 1.5-2 times more fossil BC than that in subtropical VCHs in the 1 m depth soil, which is likely influenced by atmospheric input and the aging effect. We estimate an accumulation rate of BC in China's VCHs of 33.1 ± 14.5 g m-2 year-1, acting as a hotspot for BC burial. These results point to a substantial and hitherto unquantified contribution of BC components to blue carbon storage, as well as the VCHs to global BC storage. Preservation of this old-aged, stable OC implies an important ecosystem service of the VCHs for climate change mitigation.

Microplastics may lose buoyancy and occur in deeper waters and ultimately sink to the sediment and this may threaten plankton inhabiting in various water layers and benthic organisms. Here, we conduct the first survey on microplastics in the water column and corresponding sediment in addition to the surface water in the Bohai Sea. A total of 20 stations covering whole Bohai Sea were selected, which included 6 stations specified for water column studying. Seawater was sampled every 5 m, with maximal depth of 30 m in the water column using Niskin bottles coupled with a ship-based conductivity, temperature and depth sensor (CTD) system and surface sediment samples were collected using box corer. The results indicated that higher microplastic levels accumulated at a depth range of 5-15 m in the water column in some stations, suggesting the surface water survey was not sufficient to reflect microplastics loading in a water body. Fibers predominated microplastic types in both seawater and sediment of the Bohai Sea, which accounted for 75%-96.4% of the total microplastics. However the relatively proportion of the fibers in the deeper water layers and sediment was lower than that in the surface water. Microplastic shapes are more diverse in the sediment than in the seawater in general. The microplastic sizes changed with depth in the water column and the proportion of the size-fraction300 μm increased with depth, probably as a result of rapid biofouling on the small microplastics due to their higher specific surface area. Such depth distribution also implied that sampling with manta net (330 μm) that commonly used in the oceanographic survey might underestimate microplastics abundance in the water column. Further studies are recommended to focus on the sinking behavior of microplastics and their effects on marine organisms.

Microplastics ( 3000 km of coastline in Shandong province, east China, adjacent to both the Bohai Sea and the Yellow Sea coastlines under different land use management. Microplastics were separated from the soil samples using a continuous flow and floating separation apparatus. The shape type, size, abundance, spatial distribution, polymer composition and surface morphology of the microplastics were identified by a range of advanced microscopic and micro-analytical methods. The analytical results show that seven shape types, namely foams, pellets, fragments, flakes, fibers, films and sponges, were present in the beach soils. The polymer composition of the microplastics included polyethylene, polypropylene, polystyrene, polyether urethane and a polymer blend of both polyethylene and polypropylene. Approximately 60% of the observed microplastics had a size range

Microplastics are a type of emerging environmental pollutant that has been the subject of increasing concern worldwide. The surface morphology, composition and changes in the distribution of microplastics in the environment are poorly understood. The corresponding research methodology is also at the exploratory stage. Here, we examine typical estuarine sediments from Shandong Province, east China, that are influenced by intensive human activity. The microplastics are separated from the sediments using an apparatus of continuous flow and floating separation. The microplastics samples are processed to determine the types, morphology and changing composition of microplastics present using a range of advanced microscopic and micro- analytical methods. The aim is to understand the weathering and subsequent surface changes in the microplastics under the environmental conditions of estuarine sediments. Optical microscope and scanning electron microscope-energy spectrum (SEM-EDS) analysis shows that foams and pellets, together with fragments, fibers and films, are present in the estuarine sediments. The five shape types of microplastics had different weathering surface morphologies compared to the corresponding large plastic debris from the same sampling sites and to the corresponding commercial plastic products. The surfaces of the commercial products are smooth. The surfaces of plastic debris appear to be slightly broken and aged while the surface of microplastics from the same sites show many more microholes, cracks or protuberances. This indicates that the surfaces of microplastics on the estuarine beaches have been strongly weathered. Scratches, creases, microholes, cracks, either concave or convex and of various shapes and sizes were found on the surfaces of microplastics from the coastal environment, possibly due to mechanical friction, chemical oxidation and/or biological attack. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR) was used to find oxygen-containing functional groups such as carboxylic acids, aldehydes and esters or ketones on the microplastic surfaces from the tidal flats on the basis of polymer component analysis. The two selected shape types, namely foams and fragments from soft plastic woven bags, had different infrared spectra than their corresponding large plastic debris from the same sampling sites and to the original commercial plastic products. The surfaces of these two microplastics had more complicated infrared spectra near the fingerprint area. This implies that the aging process of large plastic debris may be an important source of microplastics in the environment. A polymer blend of both polyethylene and polypropylene was identified in the fibers using pyrolysis gas chromatography-mass spectrometry (pyr-GC-MS). The pyr-GC-MS analysis also indicates that the pyrolysis products were much common on the aged surfaces of foams from the beach than on the inner part of foams after removal of the aged surfaces, including mainly compounds containing oxygen or nitrogen such as oleanitrile, trans-13-docosenamide, α-n-normethadol; 1,1-diphenyl-spiro [2,3] hexane-5-carboxylic acid, methyl ester, hexadecanoic acid, octadecyl ester and hexadecanoic acid, hexadecyl ester. The surficial morphology, composition and possible properties of microplastics from the estuarine beaches were clearly different from those of the original commercial plastic products. We suggest that surface weathering can cause changes in the surface components of microplastics under the actual conditions prevailing on coastal beaches. By observation of the weathering of microplastic surfaces it is difficult, using a single identification method, to distinguish between finer polymer components, particularly in samples of blends or copolymers. This study shows that pyr-GC-MS can be used directly to obtain and verify the specific weathering products of microplastics and the ATR-FT-IR may be used as an ancillary tool for recognition of microplastics in the environment. Much effort needs to be devoted in the future to understanding the changes in surface processes, ecological and environmental effects, and methods of identification of microplastic particles in coastal and oceanic environments.

Mangroves are a unique and important type of coastal wetlands in the tropical and subtropical zones worldwide. The abundance and spatial distribution of microplastics in the mangrove sediments however are still poorly understood. The present study aimed to illustrate the characteristics, abundance and spatial distribution of microplastics in different mangrove sediments along the south-eastern coastal zones of China. Microplastic samples (roughly 10–20 kg fresh sediments at each site) taken from 21 sampling sites showed various shapes, colors, composition, sizes, surface morphology, abundance and strong spatial heterogeneity. Five different shapes of microplastics with a variety of colors were detected in the mangrove sediments, among which foams (74.6%) and fibers (14.0%) were the dominant types. The polymer composition of the microplastics identified based on the FT-IR and μ-FTIR covered polystyrene (75.2%), polypropylene (11.7%), rayon (4.6%), polyester (3.4%), polyethylene (2.8%) and acrylic (2.4%). The observed microplastics with a size range of less than 2 mm made up 58.6% of the total microplastic particles. The microplastics had various surface morphologies, exhibiting complicated weathered surfaces. The abundance of microplastics showed a substantial variation among the sampling sites, ranging from 8.3 to 5738.3 items kg−1 (dry sediment). Altogether, our study provides a better understanding of microplastic pollution status and prevention policy-making of mangrove habitats in China.

The transport of organic matter in coastal areas plays an important role in global biogeochemical cycles. The present study used stable isotopes including carbon (δ13C) and nitrogen (δ15N) and C/N ratio to assess the sources and fate of organic carbon and nitrogen in soils and sediments of a coastal plain-river plume-bay system. Changes of the δ13C and δ15N values from natural to agricultural soils in the Yellow River coastal plain reflected the contribution of C4 carbon, decomposition of organic matter and application of nitrogen fertilizer. The organic carbon in the marine sediments adjacent to the coastal plain mainly originated from C3-dominated terrestrial systems. The spatial heterogeneity of both δ13C and δ15N values indicated that Yellow River sediment transport and anthropogenic wastewater discharge were two driving forces for the sedimentary organic carbon and nitrogen dynamics in large river plume and inner bay areas. Meanwhile, the marine primary production and denitrification process as affected by excessive nutrient input also contributed to the cycling of organic matter. Wetland soils, cropland soils, vegetable soils, coastal and deep-sea sediments were the five systems controlling the cycle of organic carbon and nitrogen in the study area. A significant positive correlation between δ13C and δ15N in the Yellow River coastal plain-plume-bay region was observed, which implied the flux of organic matter from a labile pool in source regions into a more recalcitrant pool in sink regions. These findings would provide a better understanding of carbon sequestration in the coastal soil and sediment.

Veterinary antibiotics are emerging contaminants of concern. A total of 139 samples comprising 104 marine sediments and 35 estuarine sediments were collected from the Bohai Sea area and analyzed for seventeen antibiotics. The results reveal that the presence and concentration of antibiotics were generally higher in the estuaries than in the sea. The highest antibiotic concentration, 4695μgkg(-1) of oxytetracycline, occurred in the estuarine sediment from Ziya New River. Bohai Bay and Laizhou Bay and the surrounding estuaries had higher concentrations of antibiotics. However, low levels of antibiotics detected were detected in Liaodong Bay in contrast to the high concentrations present in the surrounding estuaries. Spatial heterogeneity and principal component analysis suggest a large impact of terrestrial sources of the antibiotics contaminating the Bohai Sea. Risk quotients indicate that current levels of norfloxacin and oxytetracycline might be potentially hazardous to sensitive biota both in the Bohai Sea and in its surrounding estuaries.

Microplastics ( - 3) followed by visual selection. All the microplastics were photographed and image analysis was performed using the program Nano Measurer 1.2 for counting and size measurement. The microscopic features of the microplastic surfaces were characterized using a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS).

Understanding C formation and budgets in soils of large river deltas is necessary in studying the global C cycle because deltas are important interfaces between continents and oceans for material fluxes. Soil organic carbon (SOC) and soil inorganic carbon (SIC) were assessed at different soil depths in wetlands and farmland of the Yellow River Delta. SOC content decreased by 54% in the topsoil after converting wetland to farmland and there was little soil inorganic carbon (SIC enrichment). However, the contents and stocks of SOC and SIC in the subsoil were significantly enhanced in the red clay layer (RCL) in both land use types. The RCL also showed high accumulation rates of SIC (197 ± 95 g C m−2 yr−1), highlighting its importance in carbon sequestration in this large estuary. A negative correlation between SIC and δ13CSIC throughout the dataset and more negative values in the RCL indicate a larger contribution of secondary carbonate under C3 vegetation in the RCL. A positive correlation between SIC and SOC suggests that an enhancement of SOC may lead to an increase in SIC, especially in the subsoil YSL–RCL sequence with its relatively low SOC content. The RCL formed in the fluvial-deltaic sedimentary system with both higher carbonate content and stronger weathering intensity indicates that adsorption and precipitation of atmospheric derived carbonate on fine–grained suspended particulates may be important factors in carbonate accumulation.

Chemical pollution in the microplastics has been concerned worldwide as pollutants might potentially transfer from the environment to living organisms via plastics. Here, we investigate organophosphorus esters (OPEs) and phthalic acid esters (PAEs) in the beached microplastics collected from 28 coastal beaches of the Bohai and Yellow Sea in north China. The analyzed microplastics included polyethylene (PE) pellets and fragments, polypropylene (PP) flakes and fragments and polystyrene (PS) foams. The tris-(2-chloroethyl)-phosphate (TCEP), tris (1-chloro-2-propyl) phosphate (TCPP) and di-(2-ethylhexyl) phthalate (DEHP) were the three predominant compounds found overall. The maximum Σ4 OPEs concentration was 84,595.9ngg-1, almost three orders of magnitude higher than the maximum Σ9 PAEs concentration. The PP flakes and PS foams contained the highest concentrations of the additives in contrast to the PE pellets which contained the lowest. The high concentration level of carcinogenic chlorinated OPEs and DEHP with endocrine disrupting effects implied the suggested potential hazards to coastal organisms. Spatial differences and compositional variation of the additives among the different microplastics suggests different origins and residence times in the coastal environment. This indicates that the characteristics of chemical additives might be a useful approach when tracing sources of microplastics in the environment.

Mapping the spatial distribution of available copper (A-Cu) in orchard soils is important in agriculture and environmental management. However, data on the distribution of A-Cu in orchard soils is usually highly variable and severely skewed due to the continuous input of fungicides. In this study, ordinary kriging combined with planting duration (OK_PD) is proposed as a method for improving the interpolation of soil A-Cu. Four normal distribution transformation methods, namely, the Box–Cox, Johnson, rank order, and normal score methods, were utilized prior to interpolation. A total of 317 soil samples were collected in the orchards of the Northeast Jiaodong Peninsula. Moreover, 1472 orchards were investigated to obtain a map of planting duration using Voronoi tessellations. The soil A-Cu content ranged from 0.09 to 106.05 with a mean of 18.10 mg kg−1, reflecting the high availability of Cu in the soils. Soil A-Cu concentrations exhibited a moderate spatial dependency and increased significantly with increasing planting duration. All the normal transformation methods successfully decreased the skewness and kurtosis of the soil A-Cu and the associated residuals, and also computed more robust variograms. OK_PD could generate better spatial prediction accuracy than ordinary kriging (OK) for all transformation methods tested, and it also provided a more detailed map of soil A-Cu. Normal score transformation produced satisfactory accuracy and showed an advantage in ameliorating smoothing effect derived from the interpolation methods. Thus, normal score transformation prior to kriging combined with planting duration (NSOK_PD) is recommended for the interpolation of soil A-Cu in this area.