海岸带土壤有机碳和重金属的积累、动态变化及其影响因素

海岸带土壤是有机碳与重金属的汇，在应对全球气候和环境变化中具有重要的作用。目前对气候变化和高强度人类活动冲击下海岸带土壤有机碳和重金属的积累特征、动态变化和影响因素还缺乏基本和系统认识。本论文基于中国海岸带农用地（农田、果园等）、海防林、红树林、盐沼、海草床、砂砾质光滩和淤泥质光滩的951件表层（0-20 cm）样品和6根红树林、盐沼、海草床的柱状样品，分析了土壤的有机碳和重金属含量与形态、放射性铅同位素、稳定性碳同位素及基本理化性质，从国家尺度阐明了土壤有机碳和重金属的积累特征，揭示了土壤有机碳和重金属积累的百年尺度变化，探讨了海岸带土壤有机碳对重金属积累的影响；并从区域尺度，以受农业活动影响强烈的海岸果园为例，剖析了土壤有机碳和重金属的积累、动态变化与形态分配。这些研究成果可为全球气候变化和高强度人类经济活动下海岸带土壤有机碳和重金属的生物地球化学循环的深入认识以及海岸带可持续发展提供基础数据和科学指导。 本研究的主要结果包括以下几个方面： （1）中国海岸带表层土壤有机碳库储量（0-20 cm）为233.04&plusmn;20.98 Tg，以农用地的&ldquo;绿碳&rdquo;为主，红树林、盐沼、海草床等&ldquo;蓝碳&rdquo;仅占1.4 %。虽然海防林、淤泥质光滩和砂砾质光滩土壤有机碳密度较低，但仍是海岸带土壤有机碳库的重要补充。中国海岸带土壤具有较大的固碳潜力，以农用地最为突出，红树林、盐沼、海草床和海防林等地因面积较小，其固碳潜力不显著。海岸带土壤有机碳储量的分布受气候和地貌影响，其中红树林、盐沼和海草床土壤碳库对气候较为敏感。陆源有机碳和细颗粒物质输入，促进了淤泥质光滩、盐沼和海草床土壤有机碳的累积和保存，但稀释了红树林土壤有机碳密度。海岸带土壤溶解态有机碳、易氧化有机碳和颗粒态有机碳主要来源于植物凋落物和分泌物在土壤的分解过程。海岸带土壤有机碳的积累，16~53 %是以易氧化有机碳形态积累，17~97 %是以颗粒态有机碳形态积累，碳库稳定性不断降低。 （2）由于丰富的陆源泥沙输入，中国典型红树林（广东深圳、广西北海）、盐沼（江苏盐城、浙江宁波）和海草床（山东东营、山东威海）土壤的沉积速率分别高达1.36~2.14、0.81~1.63和0.88~4.00 cm yr-1。红树林土壤有机碳密度（202~210 Mg C ha-1）和埋藏速率（284.9&plusmn;92.3~433.1&plusmn;179.7 g m-2 yr-1）均较高，盐沼土壤有机碳密度（58~67 Mg C ha-1）和埋藏速率（47.3&plusmn;44.3~91.5&plusmn;21.1 g m-2 yr-1）均较低，海草床土壤有机碳密度（45~288 Mg C ha-1）和埋藏速率（39.3&plusmn;17.6~1152.4&plusmn;487.1 g m-2 yr-1）则具有较大的变异性，体现了不同程度的固碳能力。胶东海岸果园土壤有机碳密度（2.81&plusmn;0.82 kg m-2）高于海岸带农用地土壤有机碳密度，体现出了较高的有机碳积累能力，其有机碳含量和密度表现出中等强度的空间变异性。在长期集约化管理过程中，果园土壤有机碳含量呈先上升再下降趋势，同时伴随土壤酸化等问题，导致了果园土壤有机碳库的缩减。 （3）中国海岸带土壤出现了不同程度的重金属积累现象，盐沼土壤Cu、Zn、Pb、Cr和Ni元素、红树林土壤Cu、Zn、Pb和Cr元素、淤泥质光滩土壤Cu、Zn、Pb、Cr和Ni、以及农用地土壤Pb和Cr元素的平均含量都超过了中国土壤元素背景值。而海防林、海草床和砂砾质光滩土壤重金属元素平均含量均显著低于背景值。采样点的海岸带土壤整体处于未污染状态，但存在小范围的中轻度污染现象。经济发达、人类活动密集区域（如深圳红树林柱状样）的海岸带土壤重金属积累趋势显著。海岸带土壤重金属处于轻度污染或未污染状态，但重金属的积累趋势预示着海岸带土壤环境的退化。海岸果园含铜杀菌剂使用较多，导致了土壤铜的积累。总铜含量的积累量为3.30 mg yr-1，其中36.2%是以有效态铜的形式积累，潜在可迁移态铜（弱酸可溶态、铁锰结合态和有机结合态）的比例也呈现不断积累的趋势。Box-Cox、Johnson、Rank order和Normal score正态变换方法均可以降低土壤有效铜和相应残差数据分布的偏斜，使其满足正态分布。结合种植年限信息的插值方法提高了土壤有效铜的空间插值精度，尤以结合Normal score正态转换最有效。 （4）海岸带土壤有机碳含量与大多数的重金属含量具有显著的正相关性，对于少数主要来源于母质（如YC柱状样的Cd元素）或在沉积过程中存在突变的（如DY柱状样中的As元素）重金属元素相关性较弱。海岸带土壤有机碳的积累，提高了对外源性重金属的固持能力。海岸带果园土壤有机碳与总铜、有效铜以及连续提取态中的有机质结合态及弱酸溶解态具有显著正相关性，有利于铜向土壤有效态和有机结合态的分配，可增大铜污染的潜在风险。</p

海岸带蓝碳研究及其展望

海岸带蓝碳是海洋碳汇的重要组成部分,在应对全球气候变化中具有十分重要的作用.通过系统调研,综述了海岸带蓝碳的组成、碳通量及其影响因素.针对海岸带蓝碳组成,重点阐述了红树林、盐沼和海草床这三种海岸带地区最具固碳效率生态系统的有机碳捕获与埋藏特征.在此基础上,从海岸带地区的水-气、土-气、地下水(孔隙水)向上交换的垂直界面,以及河口-(潮滩)湿地-近海的陆海水平界面两个维度分析了海岸带系统中不同形态碳的交换、输送过程及其通量,探讨了海岸带碳库收支对全球碳循环的影响.同时,结合海岸带人类活动特点以及对气候变化的响应规律,提出当前中国海岸带地区的蓝碳和碳汇功能正在经受着新一轮沿海土地开发、流域筑坝建库..

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

Spatial Distribution and Dynamics of Soil Organic Carbon and Total Nitrogen in Apple Orchards in Coastal Regions

【Objective】Soil organic carbon (SOC) and soil total nitrogen (STN) are two key indicators of soil fertility and quality, and closely related to soil productivities of farmlands and orchards. As the largest apple producer in the world, China has orchards distributed in all the corners of the country across different climate zones,in a huge variety of soils and under different management practices. Therefore, the orchards vary sharply in spatio-temporal distribution of soil C and N between different regions. However, as for spatial distribution and dynamics of SOC and STN in the apple orchards of the coastal regions, little system study has been made and little is known about differences and commons between the orchards in inland and coastal regions.In order to optimize management of the orchards, spatial distribution and dynamics of contents and densities of SOC and STN in large-scale apple orchards typical of the coastal region were studied.【Method】A total of 488 soil samples were collected from the surface soil layers of apple orchards differentin age in Jiaodong, Shandong Province, East China for analysis of SOC, STN, SOCD (soil organic carbon density), STND (soil total N density), spatial distribution of C/N ratios, and their dynamics and affecting factors.【Result】Results show that the average SOC and STN content in the orchards of that region was 10.80 and 1.42 g kg~(-1),respectively, the average SOCD and STND was 2.81 and 0.37 kg m~(-2), respectively, and the average soil C/N ratio was 7.70. Compared with the inland apple orchards located inWest Liaoning, suburbs of Beijing, Weibei of Shaanxi and Ili of Xinjiang,the apple orchardsin Jiaodong were generally higher in SOC and STN, but lower in C/N ratio. The apple orchards in Jiaodong are often located in temperate humid hilly areas, quite loose in soil texture, and enjoy rich hydrothermal resources, endowed by the maritime climate of the Yellow Sea. All the natural conditions, generally speaking, are favorable to accumulation of soil carbon and nitrogen. The Nugget/Sill ratio of SOC, STN, SOCD, STND and C/N was 0.432, 0.340, 0.420, 0.387 and 0.301, respectively, indicating that the spatial heterogeneityis moderate in level, as affected jointly by structural and stochastic factors in the area. The conclusion is quite consistent with that of the researches on SOC and STN in inland orchards. With the orchards established, SOC and STN appeared to be on a rising trend, but after 30 years of cultivation, SOC began to decline, while STNkept on rising, though at a slower pace. SOC and STN did not synchronize in accumulation, with C/N ratio declining first, then rising and declining again. SOC and STN in the apple orchards of Jiaodong were also affected by soil type, which is determined by its parent material and inherits certain properties of its parent materials. Moreover, the distribution of soils has its zonality, which also makes the orchards in Jiaodong different from the inland ones in SOC and STN. Terrain is only a minor factor affecting SOC and STN in the orchards of Jiaodong, which is mainly because the orchards there sit mainly on low hills and mounds, low in undulation and soil water loss. But the strong soil acidification in the orchards of Jiaodong may affect the activity of soil microbes, and in turn, the cycling of soil C and N. However, in inland orchards the soils are mostly alkaline ones, which have strong acid buffering capacity, so the impact of soil acidification is insignificant therein.【Conclusion】The apple orchardsin Jiaodong are generally high in carbon and nitrogen content and hence soil fertility and they have their own especific characteristics of spatio-temporal variation, and much higher soil C and N turnover rates and more dramatic dynamic variation, compared with inland orchards

Weathering Characteristics of Microplastics of Low Density Polyethylene Film in the Coastal Environment of the Yellow River Estuary

【Objective】Microplastic pollution has become a global environmental issue that has caused widespread concern. Coastal zone is a region of land-ocean interaction under the dual impacts of global climate change and human activities. It is also an important sink for microplastics in the environment. However, by far little attention has been paid to long-term weathering characteristics of microplastics in coastal environments. In this study, microplastics of low density polyethylene(LDPE)film, which were commonly found in the coastal environments of the Yellow Sea and the Bohai Sea, were selected as the object for test in exploring long-term weathering characteristics of the microplastics in different coastal environments, including supratidal, intertidal and subtidal zones at the Yellow River Estuary. The aim of this study is to lay down a scientific basis for clarifying fates and effects of microplastics in the coastal environments. 【Method】Microplastics of LDPE film were left in the tidal zones for exposure to the coastal environment for 12 and 18 months. At the end of the each exposure period, they were retrieved for analysis of surface morphology, chemical functional groups(carbonyl index)and density with scanning electron microscopy, Fourier transform infrared spectrometry, and pycnometry. Weathering degree of the microplastics was characterized. 【Result】 Results show that after 18 months of exposure in the field, colonies of microorganisms were observed on the surface of the microplastics in all the zones and so were significant weathering characteristics. The microplastics in the supratidal zone exhibited the highest degree of cracking. Carbonyl groups were also observed on the surface of the microplastics regardless of where they were in, and in terms of carbonyl index of the microplastics, the three zones displayed an order of supratidal zone (0.28-0.81) > intertidal zone (0.18-0.22) > subtidal zone (0.16-0.20). The microplastics did not show much spatio-temporal variation in density. However, having been subjected to ultrasonic cleaning for removal of surface attachments, the microplastics exposed aboveground at the supratidal zone for 18 months were by (0.850.02 g·cm~(-3)) significantly lower than the untreated ones (0.930.03 g·cm~(-3)) in density.【Conclusion】The dynamic changes in morphological characteristics, chemical functional groups (carbonyl index) and density of the microplastics of LDPE film indicate that weathering degree of the microplastics varying with the tidal zone shows a declining order of supratidal zone > intertidal zone > subtidal zone, and the microplastics in the supratidal zone varied sharply with time in weathering characteristics. The microplastics in the coastal environment are subjected to physical, chemical and biological weathering, such as light, friction, chemical oxidation, and biodegradation. Among them, light-triggered photochemical oxidation may contribute the most to the weathering of microplastics. In the future, more attention should be paid to the research on potential environmental effects and fate of microplastics as affected by the complex environmental factors in the coastal environment

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

Surface properties and changes in morphology of microplastics exposed in-situ to Chinese coastal wetlands

Coastal wetlands are key areas of accumulation of microplastics. However, until now only a few studies have focused on the surface properties and morphological changes in microplastics in the real coastal wetland environment. Here, two typical biogeographic coastal soils, the Yellow River Estuary salt marsh wetland in the temperate zone and the Beibu Bay mangrove wetland in the subtropical zone, were selected for study. Polystyrene foams and polyethylene films were used and exposed within two coastal wetlands sites through in situ soil burial (underground exposure) and surface placement (above-ground exposure). The samples were sampled after 6, 12, 18 and 24 months of exposure to reveal the characteristics of the surface properties and morphological changes in microplastics in typical wetlands from the southern and northern biogeographic coastal zones. The surface morphology, microstructures and attached materials were observed using scanning electron microscopy using an energy dispersive spectrometer. Surface properties of the microplastics, i.e. the surface roughness, specific surface area, pore size distribution, functional groups and hydrophobicity, were analyzed by using atomic force microscopy, a surface area analyzer, a mercury porosimeter, Fourier transform infrared spectrometry and a contact angle meter. The surface morphology of the polystyrene foams in the Beibu Bay mangrove wetland exhibited more pits and holes than those in the Yellow River Estuary salt marsh wetland. The polystyrene foams exposed aboveground in the Beibu Bay mangrove wetland showed embrittlement and exfoliation after 18 months, while those exposed underground did not show such features. The specific surface areas of the polystyrene foams and the polyethylene films in the Yellow River Estuary salt marsh wetland were higher than those in the Beibu Bay mangrove wetland. The pore distributions on the surfaces of the two microplastic types mainly comprised macropores and mesopores. However, the porosity of the polyethylene film in the Yellow River Estuary salt marsh wetland was slightly higher than in the Beibu Bay mangrove wetland. The porosities in both regions were higher than in the original control samples. In terms of carbonyl index, rates of change in the Yellow River Estuary salt marsh wetland were higher than those in the Beibu Bay mangrove wetland. The surface hydrophobicity of the polyethylene film in the two regions declined with increasing exposure time. The changes in surface morphology of the polystyrene foams were more rapid than those in the polyethylene films, but the degree of change in specific surface area of the polyethylene films was greater than in the case of the polystyrene foams. It can be concluded that the surface properties and changes in morphology of microplastics in the coastal soil environment are related to multiple factors including the types and conditions of the wetlands, types of microplastics, exposure mode and exposure time. However, the specific mechanisms of these surface changes require further study. In summary, this study provides a scientific basis for research on the chemical processes of the micro-interfaces on the microplastic surfaces and environmental behavior and risk assessment of microplastics in the Chinese coastal zone