The fate of riverine sedimentary organic carbon and nitrogen, whether buried in the coast or exported to the deep sea, is of considerable interest because the relocated pool of carbon and nitrogen has a bearing on the phytoplankton evolution and climate change. To investigate sediment export fluxes to the East China Sea (ECS), six cruises were conducted between 2011 and 2013. 162 surface sediments were collected and analyzed for Be-7, Cs-137, and excess Pb-210 ((210)Pbex) to investigate the cross-shelf transport of sedimentary particles in a river-dominated margin, the ECS. Distribution of these radionuclides exhibited a clear seasonal variation corresponding to seasonal sediment transport. From the distributions of Be-7/(210)Pbex and Cs-137/(210)Pbex activity ratios, four pathways (I, II, III, and IV from north to south) can be identified, which existed in different seasons: section I for spring and summer, II for spring, III for all seasons, and IV for spring and summer. Using Pb-210 mass balance, the estimated cross-shelf transport particle fluxes (x10(6) ton yr(-1)) are: 1.5, 5.0, 28, and 0.32 for sections I, II, III, and IV, respectively, which in total account for 18% of the annual sediment discharge of Changjiang to the ECS in 2011. The cross-shelf (inner to outer) transport of particulate nitrogen and particulate organic carbon is estimated to be 2.8 x 10(11) g yr(-1) and 2.5x 10(12) g yr(-1), respectively, which is comparable to the Changjiang annual input POC. Quantification of the cross-shelf transport provides insights into particle dynamics in the coastal ocean, as well as insights into nutrients and pollutants as sinks in the marginal sea.

In order to deeply understand the relationship between the diversion and confluence between the Changjiang River and the Dongting Lake under extreme hydrological conditions in 2022, this paper analyzes the historical trend of the diversion of the three outlets of the Jingjiang River and the confluence of the Dongting Lake based on the measured hydrological data of the diversion of the three outlets of the Jingjiang River and the confluence control station of the Dongting Lake from 1956 to 2022. According to the data in 2022, the three outlets of Jingjiang River continue to show a decreasing trend. Under the influence of extreme water conditions, the diversion flow of the three outlets is only 27.62 billion m3, and the diversion ratio is only 7.5 %. Among them, the diversion ratio in August and September decreased most significantly. The confluence of Dongting Lake is 228.9 billion m3, and the confluence ratio is 40.68 %. The confluence ratio in October and November decreased most significantly. The impact of the diversion of the three outlets of the Jingjiang River is particularly significant. Compared with the average value from 2003 to 2021, the diversion flow in 2022 decreased by 22.29 billion m3, which further reduced the inflow from the Changjiang River in Dongting Lake and aggravated the water supply tension in the Dongting Lake area.

Nutrient changes derived from high-resolution sediment records along a typical open coast of the East China Sea were analyzed to assess environmental variations associated with aquaculture practices over recent decades. Biogenic components and stable isotopes significantly fluctuated in the sediment profiles, suggesting substantial environmental changes since the 1930s. Slight increases in total nutrient contents and carbon stable isotopes (S13Corg) were observed from the 1930s to the 1970s, likely due to increasing terrestrial nutrient inputs resulting from population growth within river watersheds. From the 1970s to the 1980s, S15N values slightly decreased, suggesting an influx of anthropogenic nutrients primarily originating from chemical fertilizers. A minor decline was observed in total nitrogen and organic phosphorus, as well as total organic carbon contents during this period, coinciding with the expansion of kelp (Saccharina japonica) cultivation. Since the 1990s, nitrogen and phosphorus have substantially increased by over 31% and 22%, respectively, along with a notable shift toward heavier S15N values attributed to feed inputs. Additionally, fluctuations in S13Corg indicate that feed-based aquaculture has profoundly altered both nutrient structure and composition along the Lianjiang coast. The annual nitrogen and phosphorus loadings absorbed by aquaculture were calculated to be approximately 14,592 f 3812 and 1848 f 762 tin 2020, respectively. Meanwhile, annual nitrogen and phosphorus discharges from feed-based farming amounted to approximately 17,038 f 4465 t and 3343 f 612 t, respectively. Nevertheless, the net N loadings from aquaculture in Lianjiang were one order of magnitude lower than those for discharge or absorption. Kelp accounted for over 86% of nutrient removal in Lianjiang, despite its cultivation period lasting only 4-6 months each year. This suggests that significant net absorption occurs during the kelp cultivation season, which mitigates nutrient loads from adjacent coastal regions. Conversely, during non-cultivation seasons, prominent net discharge of nutrients was expected to affect adjacent coastal areas. Thus, seasonal variations in kelp cultivation practices appear to modify nutrient cycles in the adjacent marine environments.

Based on high-resolution sub-bottom seismic profiles collected on the coast of the Zhoushan Archipelago in the East China Sea, the distribution and characteristics of shallow gas have been analyzed. The strata in the area were divided into three geological units: Holocene fine-grained neritic facies muddy strata, Late-Pleistocene coarse-grained fluvial or lacustrine facies sandy strata, and bedrock. The presence of shallow gas was evidenced by various acoustic indicators, including acoustic blanking, enhanced reflections, gas chimneys, bright spots, and small mounds. Shallow gas accumulations are observed through the Lower and Upper Holocene strata, presumably related to the degradation of organic matter buried in the Holocene deposits and sealed by soft muddy deposits. The presence of ultra-shallow gas-charged sediment sealed by fine-grained muddy sediment in coastal areas with frequent human disturbance suggests a high potential for sediment instability. Moreover, frequent upward gas migration signatures were found in the study area. These gas migration features mainly occur in nearshore areas where tidal disturbance and human activities are both active. We therefore deduced that the deduction of sediment above probably decreased the pressure, thereby resulting in increased upward migration. The presence of active shallow gas within thin, soft muddy strata, along with the strong tidal turbulence and human activities, indicates that the seafloor of the study area is vulnerable to sediment erosion, and shallow gas is easily released, posing a potential danger to the stability of marine engineering foundations. Since the Changjiang sediment supply has been decreasing over the past decades, it will inevitably lead to corresponding morphological adjustments in the study area, such as seafloor erosion. To what extent coastal erosion will release the buried shallow gas and lead to unpredictable consequences is worthy of our sustained attention.

Arctic fjords are hotspots of marine carbon burial, with diatoms playing an essential role in the biological carbon pump. Under the background of global warming, the proportion of diatoms in total phytoplankton communities has been declining in many high-latitude fjords due to increased turbidity and oligotrophication resulting from glacier melting. However, due to the habitat heterogeneity among Svalbard fjords, diatom responses to glacier melting are also expected to be complex, which will further lead to changes in the biological carbon pumping and carbon sequestration. To address the complexity, three short sediment cores were collected from three contrasting fjords in Svalbard (Krossfjorden, Kongsfjorden, Gronfjorden), recording the history of fjord changes in recent decades during significant glacier melting. The amino acid molecular indicators in cores K4 and KF1 suggested similar organic matter degradation states between these two sites. In contrast to the turbid Kongsfjorden and Gronfjorden, preserved fucoxanthin in Krossfjorden indicated a continuous increase in diatoms since the mid-1980s, corresponding to a 59 % increase in biological carbon pumping, as quantified by the δ13C of sedimentary organic carbon. The increasing biological carbon pumping in Krossfjorden is further attributed to its hard rock types in the glacier basin, compared to Kongsfjorden and Gronfjorden, which are instead covered by soft rocks, as confirmed by a one-dimensional model. Given the distribution of rock types among basins in Svalbard, we extrapolate our findings and propose that approximately one-fifth of Svalbard's fjords, especially those with hard rock basins and persistent marine-terminated glaciers, still have the potential for an increase in diatom fractions and efficient biological carbon pumping. Our findings reveal the complexity of fjord phytoplankton responses and biological carbon pumping to increasing glacier melting, and underscore the necessity of modifying Arctic marine carbon feedback to climate change based on results from fjords underlain by hard rocks.

This study aims to elucidate the environmental changes signified by biogenic components, assess fluctuations in upwelling over the past century, and evaluate the potential risks associated with variations in coastal upwelling intensity on the degradation of fisheries within the Zhoushan Fishing Ground. High-resolution sediment records were established to reveal long-term variations in Zhoushan coastal upwelling. Results showed a significant reduction in nutrient components between 1900s and 1950s, suggesting a decline in upwelling strength. Since the 1960s, lightened delta 15N and the incline of nutrients suggests an increase in anthropogenic nutrients influx, and increased OP and CUISST (SST-based coastal upwelling index) indicates strengthening of upwelling during the 1950s to 1980s. A positive correlation between organic phosphorus (OP) and delta 13C has been observed since the 1960s, implying that P is a limiting nutrient due to increasing anthropogenic N influx, and the change in CUISST coincides well with our OP records. OP is a potential indicator of upwelling strength because upwelling contributes to over 90 % of the P on the East China Sea shelf. A prominent decline in the nutrient composition occurred from the 1980s to 2010s, despite substantially increased anthropogenic nutrients influx and eutrophication in adjoining Changjiang delta regions in the past decades. Weakening upwelling and the consequent decreasing nutrients influx has presumably hindered recovery and thus contributed to the degradation of fishery resources in recent decades.

ABSTRACT To understand the Holocene sedimentary evolution of the Pearl River associated delta–estuary–shelf system, high‐resolution seismic data were acquired from Lingdingyang Bay to the inner shelf. A Pearl‐derived Holocene subaqueous clinoform developed over the pre‐Holocene incised channel/valley network. Overlying the Holocene ravinement surface, progradational highstand and acoustically semi‐transparent or transparent transgressive system tracts are separated by a maximum flooding surface. Restricted and thick in‐channel/in‐valley retrogressive deposits represent an earlier transgressive deposit. Displaying a westward‐oriented along‐shore extent, the highstand sediment accumulated asymmetrically within 30 m water depths, corresponding to a modern hydrodynamic environment. The wedge‐shaped highstand unit thickened landward with a depocentre (>15 m) located in western Lingdingyang Bay, possibly because of higher sediment trap efficiency inside the salinity front. Preliminary analyses suggest that the Pearl River has been trapping sediment to fill its extensive estuarine system for most of the Holocene and its sediment trap efficiency is greater since the sea‐level highstand. Since ca 7.5 ka bp , the total volume of highstand sediment accumulated in the entire delta‐estuary‐shelf dispersal system was approximately 128.36 × 10 9 m 3 . The calculated highstand riverine sediment flux was 16.01 to 16.50 Mt/yr. This value is equivalent to approximately one‐fifth of the flux that occurred prior to widespread dam construction and likely related to late‐Holocene intensified anthropogenic influence in South China. Since ca 7.5 ka bp , only ca 35% of the Pearl‐derived sediment has been dispersed to offshore shelf areas from the delta‐estuary system. With the dramatic decrease in river sediment discharge in recent decades, a larger fraction of Pearl‐derived sediment transported to the shelf might have been interrupted and changed.

对取自北极克罗斯峡湾的沉积物岩芯进行了沉积组分分析和放射性年代测定,探讨了20世纪30年代以来粒度的垂直分布特征和沉积类型变化,以揭示过去几十年高纬度冰川前沿峡湾地区发生的环境变化.结果表明,该区域自20世纪90年代以来沉积速率(0.35 cm/a)显著增加,约为20世纪90年代以前的2倍(0.16 cm/a).20世纪90年代以后平均粒径和中值粒径增大,出现了显著的沉积物粗化现象.同时,分选性下降,偏度向正偏变化,峰态波动增大,粒度组成发生了显著变化.沉积环境的改变反映出近三十年来克罗斯峡湾地区发生了环境变化,气候变化引起冰川的快速融化,进而增加了高纬度冰川前沿峡湾地区的陆源物质输入.

River deltas have long been considered as important carbon sinks. However, the presence of shallow gas (mainly composed of methane) and the processes of delta erosion caused by diminished sediment supply bring complexities to the present situation. This study investigates the response of the gas charged deposits in the Yangtze subaqueous delta to erosion process based on historical bathymetric data and the dataset obtained from a seismic survey. Both seismic and bathymetric data reveal a prominent erosion belt at water depth ranging from 5-20 m, extending from the southwest to the northeast in the nearshore area of the Yangtze subaqueous delta. Erosion is severe in the south while slight in the north area due to the differences in hydrodynamic condition, sediment erodibility and sensitivity to sediment reduction. Seabed erosion reduces the thickness of cap bed, as well as overburden pressure at gas front, making it easier for gas to seep through the sediment column and bypass the process of anerobic oxidation of methane within the SMT (an important methane filter). The spatial coincidence between the shallower gas front and pockmarks also indicates that sea bed erosion accelerates gas seeping activities. It expected more greenhouse gas would be expelled into atmosphere under the impact of bed erosion induced by ongoing decline of riverine sediment supply.

High-resolution seismic and side-scan surveys were conducted to investigate shallow gas accumulation and seepage in the Holocene sediment of the Pearl River Estuary. Extensive shallow gas accumulation and active seepage were detected in the Holocene sediments of the estuary and adjacent shelf regions. Laterally continuous and extremely shallow gas fronts were observed in areas with relatively higher sedimentation rates, whereas shallow gas was absent or discontinuous in regions with the sediment with lower sedimentation rates. Gas accumulation was present at extremely shallow depths in the West Shoal, which is the recent depocentre location. The co-occurrence of shallow gas distributions and variations in the sedimentation rate was related to the role of sediment accumulation in organic carbon burial and preservation, both of which are required for gas generation and accumulation in sediment. In addition, the consistency between the distribution of high water column methane concentrations in the West Shoal, the super shallow gas accumulation pattern in the sediment profile, and active seepage indicate that shallow gas in the Holocene sediment is a methane source in the Pearl River Estuary. Further, considerable evidence of recent or relic seepage is present in areas that have experienced active anthropogenic disturbances, including sand mining, dredging, and bridge building. The disrupted and discontinuous gas fronts at these sites suggest that active shallow gas releases were influenced by anthropogenic activity.

High sediment flux in large rivers provide sufficient dilution to the heavy metals' concentration. However, sediment starvation caused by hydrological engineering in recent decades has been reported worldwide. Thus, a study is necessary on the influences of recent declining sediment flux on heavy metal pollution change in the suspended sediments. In this study, heavy metal concentrations and speciation (Cd, Pb, Zn, Cu, Co, Ni, and Cr) in suspended sediments were investigated downstream the Three Gorges Dam (TGD) during dry and flood seasons. Substantial changes of Pb, Zn, Cd, and Cu along the river channel were found which were constrained by the dilution efficiency of suspended sediment during the dry season. High proportion of labile fraction revealed anthropogenic sources of heavy metal. Moreover, the historical trend of metal content illustrated TGD construction together with anthropogenic influx both contribute to the increasing environmental risk in the Yangtze River basin.

Under eutrophication background, the increasing dinoflagellates blooms relative to diatoms blooms off the Changjiang Estuary has caused much concern. We have provided sediment evidence for the first time that the time window of diatoms-to-dinoflagellates shift off the Changjiang Estuary in the East China Sea is early 1990s. Investigations to the water column revealed different surface-bottom concentration matchup patterns between peridinin (dinoflagellates) and fucoxanthin (diatoms), which suggests that the diatoms-dinoflagellates shift recorded in the sediment may have come from more dinoflagellate blooms since 1990s. Physical-biogeochemical 3D numerical simulations for the past decades suggest that the effect of increasing spring sea surface temperature and increasing N/P ratio on the diatoms-dinoflagellates shift is dominant and recessive, respectively.

High-resolution seismic surveys were conducted off the eastern coast of Hainan Island to study the distribution and mass budget of Holocene subaqueous clinoform sediments. The Holocene subaqueous clinoform extends 45 km seaward across the shelf and more than 80 km northeastward along the shore. It covers an area of over 3,000 km2, which is almost equivalent to the expansion of large river systems. Overlying the transgressive surface, the deltaic sequence can be divided into a transgressive unit and a highstand unit separated by a downlap maximum flooding surface. The volume of sediments within the Holocene subaqueous clinoform is estimated to be 33.12×109 m3, equivalent to an annual accumulation of 3.61–3.31 Mt/yr, which is substantially higher than the global average. The high sediment yield presumably resulted from strong tropical weathering and active tectonics. The sediment flux during the transgression and sea-level highstand were 3.85–3.08 and 3.47 Mt/yr, respectively, suggesting no substantial changes in sedimentation. Compared to river systems originating from high mountain glaciers, the sedimentation variation of small tropical rivers throughout the Holocene is relatively minor. However, the sediment discharge of the Wanquan River has drastically decreased in recent decades because of increased human activity.

为深入认识不同工况下泥石流灾害的堆积特征及潜在危害,采用FLO-2D模型对白龙江流域泥湾沟在有无治理情景不同降雨频率条件下泥石流堆积特征及危险区进行模型分析.结果显示在有工程治理情景下,泥湾沟危险区面积相对无工程时减少29.71％ ～52.06％;无工程治理情景下1％ 、2％ 、5％ 等3种降雨重现期工况的冲出固体物质量是有工程治理同等条件下的1.55～2.99倍.结合构建的泥石流一次最大冲出量模型对模拟结果进行误差分析,结果显示在有无工程治理情景下泥石流最大堆积厚度及冲出固体物质总量相对误差分别在0.74％ ～28.48％ 、2.03％ ～14.97％ 范围内,模拟效果较好,可为今后白龙江流域降雨型泥石流工程防治提供技术参考.

High-resolution seismic surveys were carried out in the inner shelf of the East China Sea to investigate the distribution of shallow gas in Holocene sediments. Shallow gas is distributed extensively in the Holocene strata of the shelf which is dominated by the Yangtze River. Organic-rich, fine-grain sediments deposited throughout the Holocene are essential for gas generation and accumulation. The thickness of the Holocene sediment is the main controlling factor determining the distribution of shallow gas. Gas seepages were found mostly at a water depth up to 20 m, where sediment erosion mainly occurs. Coincidence between shallow gas seepage and high methane concentration in the water column suggests that gas emission from these sediments is a potentially significant source of greenhouse gas. The interaction between shallow gas migration and coastal erosion would therefore potentially lead to increased greenhouse gas emission and accelerated sediment erosion. Such results can be applied to other costal locations around the world.

The Lake Tian E Zhou (TEZ, an oxbow lake) was formed during the rerouting of the Changjiang River in 1972, with strong influences from the main river channel and flood events. Herein, a sediment core was collected from the Lake TEZ for the measurements of carbon isotopes and biomarkers, including stable carbon isotopes (δ13C), radiocarbon composition (Δ14C), and lignin phenols, as well as lead-210 to reconstruct recent heavy flood events over the past 70 years. At the 24–26 cm interval, the sediment contained the highest OC%, TN%, and lignin phenols content, as well as significantly depleted 13C but enriched 14C, corresponding to the extreme flood event in 1998. In addition, statistics from t-test showed that lignin phenols normalized to OC (Λ8), the concentration of 3, 5-dihydroxy benzoic acid (3, 5-BD), and the ratio of p-hydroxy benzophenone to total hydroxyl phenols (PHB/HP) were all significantly different between the layers containing flood deposits and the layers deposited under normal non-flood conditions (p<0.05). These results indicate that the later three parameters are highly related to flood events and can be used as compelling proxies, along with sediment chronology, for hydrological changes and storm/flood events in the river basin and coastal marine environments.

白龙江地区泥石流沟谷内大量松散固体物质在强降雨的激发下易形成规模较大的降雨型泥石流,泥石流一次冲出量比同等条件下要放大数倍,应用以往泥石流活动规模预测模型进行计算的结果与实际值误差较大,因此,需构建适用于白龙江流域暴雨型泥石流一次最大冲出量定量预测方法.以区内降雨频率为10 a一遇的24条沟谷型泥石流历史活动规模为典型实例,结合野外调查,利用MATALB多元非线性统计方法建立泥石流一次最大冲出量预测模型,结合舟曲三眼峪沟"8·8"特大泥石流等5条暴雨型泥石流灾害特征对预测模型优化完善,构建了不同规模降雨频率下的泥石流活动规模定量表达式.结果表明:影响泥石流一次最大冲出量的有泥石流灾害爆发区面积、流域内松散固体物质总量及诱发泥石流的降雨条件等3个因素,所建立的模型适用于白龙江流域降雨沟谷型泥石流活动规模的预测.该方法可为经济建设安全地段选址和未来城镇泥石流快速风险管理提供重要依据.

210Po and 210Pb are well-known tracer pairs for some biomass and chemical processes in the marine system. In this study, 210Po and 210Pb were analyzed in surface seawater collected from the East China Sea (ECS), in atmospheric deposition, and in riverine input water collected along the ECS coast. The atmospheric fallouts of 210Po and 210Pb were higher in the dry season, due to the arrival of storm dust from the northwestern region of China. In the riverine input water, the particulate 210Po and 210Pb dominated (corresponding to 33–94% and 50–92% of the total, respectively), especially during the flood season. In the surface seawaters, the percentage of particulate 210Po (17–85%) was generally greater than that of 210Pb (10–76%). Additionally, in the Changjiang Estuary, log Kd(Po) and log Kd(Pb) were negatively correlated with log suspended particulate matter (SPM) (R = 0.71, P = 0.013 for Po, R = 0.67, P = 0.019 for Pb). 210Pb showed a stronger “particle effect” than 210Po when SPM <1.00 mg L−1, and vice versa when SPM >1.00 mg L−1. The deficit of 210Po relative to 210Pb gradually decreased from the Changjiang Diluted Water, to the Shelf Merged Water and the Taiwan Warm Current Water. The mass balance of 210Po and 210Pb in the water column of the estuary indicated that the Changjiang River was the dominating input source (providing 91% and 88% of the 210Po and 210Pb, respectively); meanwhile, the shelf export was the dominating output source (accounting for 68% and 78% of the 210Po and 210Pb, respectively).

以白龙江流域石门乡至羊汤河段为例,采用松散物质面密度、地层岩性、构造断裂密度、地震密度、坡向、土壤可蚀性、土地利用类型、坡长坡度、沟床比降、流域沟壑密度及年均降雨量等11项评价因子的归一化值,在GIS平台下运用层次分析法建立泥石流易发性评价模型,将研究区泥石流易发性评价栅格图划分为4个等级.研究表明:泥石流中高易发区域占整个研究区面积的51.04％,区内发育的泥石流流域面积占中高易发区面积的68.71％,其分布特点具有沿大型活动性断裂呈带状分布,在次级断裂和小型褶皱密集区集中发育;沿易崩易滑地层呈片状展布,在沟壑密集带分区块集中发育;在坡面侵蚀强的区域多为泥石流高易发区,呈串珠状连片分布.利用研究区泥石流数据库对评价结果进行检验,检验曲线表明分区效果良好,检验曲线下面积即AUC值为62.13％,说明易发性评价结果较为可靠.

High resolution sediment records in the Yangtze Delta front were constructed to reveal recent environmental changes in response to river basin human activities. Increases in nutrient and organic C influxes that began in the 1950s, together with elevated primary productivity and increased chemical fertilizer application, suggested a shift toward anthropogenic-predominated environmental changes during this period. The depletion of total organic C (TOC), total N (TN), and biogenic Si (BSi), along with the decline in sedimentation rate and coarsening of sediment coincided with the development of hydrological engineering in the river basin from the 1980s. Reservoir Si retention substantially altered river mouth primary productivity community composition from diatoms to non-diatoms, thereby changing the BSi/TOC molar ratio in the sediment profile. Estimation of biogenic component burial fluxes was conducted to assess the variation and potential impacts. A recent dramatic decline in biogenic component burial in the delta area suggested a low nutrient removal efficiency in this region, due to the decrease in sediment discharge. Consequently, more nutrients have been further transported to the inner shelf and open waters instead of being buried in the delta sediment, thereby increasing the environmental pressure in the Yangtze Delta and adjoining coastal area.