渤海微塑料分布及其影响因素研究

海洋环境中的微塑料污染日益严峻。微塑料在潮汐、波浪、河流输送等作用下可以远距离迁移，并在各层海水、海底沉积物中分布。目前对海洋环境中微塑料的调查大多关注表层水体；国内对海洋水柱中微塑料分布研究尚未有报道，国际上的研究也相当有限。因此，本研究主要关注微塑料在海洋环境中的垂直分布状况及影响因素，主要包括以下内容：（1）开展了渤海各层海水和海底沉积物中微塑料分布的航次调查；（2）选择不同类型的微塑料进行了近海试验，观察、分析微塑料的密度和表面形貌随时间的变化；（3）开展了光照、生物、海水等因素影响下的实验室模拟研究，探讨了人类活动和自然条件交互作用对微塑料的含量和垂直分布的影响。 通过对渤海各层海水和海底沉积物中微塑料分布调查，渤海水体中微塑料的丰度在0.2-23 N/L，平均丰度为4.4±5.0 N/L；在渤海表层沉积物中，微塑料丰度为31.1-256.3 N/kg（沉积物干重），平均值为102.0 (±73.4) N/kg。渤海表层水体微塑料污染主要受到海上行船排污和沿岸居民生产生活的直接影响；有一半的渤海航次站点的中层和底层海水微塑料因受到不同深度海流流速、流向的差异而在5-10 m水体聚集，其他站点微塑料在海洋各水层的分布与其垂直迁移速度和排放入海的速度相关；沉积物中的微塑料的丰度与上层水体浊度以及叶绿素a含量密切相关，较高水体浊度和浮游植物生物量有利于微塑料在沉积物中积累。 渤海环境中的微塑料类型总体以纤维类为主。在表层海水、近海水柱和海底沉积物中发现的最大密度纤维类微塑料均为聚酯类，而最大密度碎片类微塑料依次是聚苯乙烯、聚对苯二甲酸乙二醇酯和聚氯乙烯，最大密度随深度递增；微塑料的密度大小影响着碎片类微塑料在不同水层中的分布情况。微塑料的颗粒大小也随着深度的增加呈规律性分布。近海水层中，粒径小于300 μm和纤维类的微塑料比例有递增的趋势，这表明较小的微塑料和纤维类微塑料更容易迁移至下层水体。同时也说明对于目前在海洋微塑料调查中普遍使用的330 μm浮游生物网采样可能会低估中下层水体中微塑料的丰度。 通过实验室模拟研究表明，光照老化会使微塑料表面变粗糙，出现裂痕和裂纹，并且使聚乙烯微塑料的密度出现小幅升高，但尼龙颗粒和聚苯乙烯颗粒的密度未出现变化；而海水中培养的微塑料表面可以观察到细菌。通过对硅藻共培养的微塑料表面检测发现，微塑料表面出现了胞外聚合物的红外特征峰，电镜照片也显示胞外聚合物在微塑料表面粘结成小片或形成块；纤维类微塑料与硅藻共培养后密度的增加幅度要明显高于颗粒类微塑料，这与渤海调查中纤维类微塑料比例随深度增加而递增的结果相一致。 通过对放置于实际海水环境中的微塑料进行分析，发现微塑料的密度变化总体要大于其在实验室模拟环境中的变化，密度均有不同程度的增加，其中微塑料类型和海洋环境条件是影响微塑料密度改变的主要因素。微塑料的密度变化在不同海水深度上变化有明显差异。放置于表层和中层海水中的微塑料主要受到海流的影响，密度变化较为相近；而放置于底层海水中的微塑料除受到海流影响外，还受到底层沉积物的再悬浮影响，微塑料变化特征与表层、中层海水不同。总体上，稳定的海况有利于微塑料与悬浮颗粒物、藻类等形成相对稳定的复合物，从而改变微塑料的密度。通过扫描电镜和傅里叶变换红外光谱分析表明，微塑料表面粘附的物质包括藻类残体和悬浮颗粒物，这与渤海水体与沉积物调查中发现的微塑料样品表面存在藻类与颗粒物附着的情况一致，进一步证明水体中颗粒物和生物质可能对微塑料在水体中的垂直分布具有一定的贡献

Biogenic silica in the surface sediment of the Bohai Sea

The 103-surface sediment samples collected from the Bohai Sea were extracted by 0.1 mol/LHCl and 1%Na_2CO_3 sequentially for the analysis of biogenic silica. The results showed that biogenic silica contents were in the range of 7.3~54.7 g/kg, with an average of 31.5 g/kg. The measured contents of the biogenic silica were higher than other reported values in the same study area. This might be the result of different extraction methods that were employed in the studies, the extraction by 0.1 mol/L HCl may dissolve the oxides plaque coated on the biogenic silica in the sediment and therefore increase the release of the biogenic silica. Spatial distributions of the biogenic silica were characterized using geographic information system(GIS)and the spatial heterogeneity of the biogenic silica was observed in the surface sediments of the Bohai Sea. The highest content located along the coastal marine of Hebei province, in contrast to the lowest content located in the Laizhou Bay. This suggested long-term terrestrial input of nutrient substances and frequent disturbance by the input of the Yellow River sediments may govern the abundance and distribution of biogenic silica in this area. Principal component analysis indicated the contents of biogenic silica had a significantly(P < 0.01)positive correlation with the contents of clay, fine sand, total organic nitrogen, and organic carbon in the sediment of the Bohai Sea, which further confirmed the effects of grain size and nutrient substance on the accumulation of biogenic silica in the sediment

Variation of Organic Matter in Soil Aggregates with the Succession of Tidal Flatland from Barren Land-Saltmarsh-Upland in the Yellow River Delta

Organic matter in soil aggregates (POM, particulate organic matter) is a biologically and chemically active fraction of soil organic matter that plays an important role in terrestrial carbon cycling. The objectives of this study were to characterize the fraction of organic matter and to analyze stability and sources of the soil organic carbon pool in this study area. 【Method】 Soil samples were collected from three tracts of land typical of the studied region in land use, that is, barren land, saltmarsh and upland, for analysis of POM and stable organic carbon isotopes. 【Result】Results show that the content of soil organic carbon presented a curve of first rising from barren land to saltmarsh and then declining from saltmarsh to upland, and was found in a significant positive relationship with the content of soil macroaggregates. The organic matter in soil aggregates could be fractionated into free particulate organic matter (fPOM) on the surface of macro- (micro-) aggregates, intra-macro- (micro-) aggregate particulate organic matter (iPOM, 250~2 000 μm) and mineral-associated soil organic matter. Contents of fPOM, iPOM and mSOM (Mineral-associated Soil Organic Matter) were quite low in the barren land, but soil organic carbon content increased significantly in the three types of SOM in the saltmarsh where some halophytes began to grow, reaching as high as 410.0 g•kg-1, 98.8 g•kg-1 and 18.8 g•kg-1 respectively. When saltmarsh was reclaimed into upland, the rising trend of the three types of POMs leveled off. The POM (including fPOM and iPOM) accounted for only 20% or below of the organic carbon in the barren land, for 41.8%~75.2% in the saltmarsh that had some halophytes growing, and for 54% in the upland. In terms of δ13C, the three types of POM exhibited an order of fPOM < iPOM < mSOM, and the three tracts of lands did an order of saltmarsh < upland < barren land. 【Conclusion】 All the findings in this study demonstrate that although the content of total soil organic carbon is relatively lower in the barren land in the Yellow River Delta, it has a relatively stable carbon pool consisting mainly of mineral-associated organic matter, which is highly affected by marine originated organic carbon. The growth of halophytes in the saltmarsh (wetland) increases the content of total organic matter in the soil and its relative proportion in the active carbon pool, too. Soil organic carbon pool is very sensitive to changes in environment. Cultivation of corn and wheat lowers the relative proportion of active carbon pool, but enhances stability of the so carbon pool

Surface weathering and changes in components of microplastics from estuarine beaches

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 microanalytical 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