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Submarine groundwater discharge (SGD) has received increasing attention by studies on coastal areas; however, its effects on biogeochemical zonation have not been investigated to date. The Yellow River Estuary (YRE) is a world class river estuary with high turbidity, and heavy human regulation. This study investigated how SGD is related to the benthic biogeochemistry of the YRE. Based on the distribution of several parameters (e.g., salinity, temperature, dissolved oxygen (DO) levels, pH, radium isotopes, and nutrients), the YRE was subdivided into six different zones, and the SGD fluxes within each zone were quantified and compared. The highest SGD flux was found in the northwest nearshore zone, where it was more than one order of magnitude higher than in the offshore zone. High SGD resulted in low DO and pH, but high nutrient levels in the benthic boundary layer. The southeast nearshore zone was also characterized by high SGD flux, but benthic waters were more oxic because of the dominating inputs by the Yellow River. These data suggest that such a zonation would help to understand benthic biogeochemical processes. High SGD may not only contribute to the estuarine nutrient budget, but may also contribute to the formation of hypoxia and acidification.

Radon is an excellent natural tracer for studying various geophysical processes. In the past centuries, radon isotopes measurement approaches for marine research have been fully developed but still suffer limitations. Here we present the setup and validation of an improved continuous online measurement system (PIC-ORn) to measure dissolved radon in the surface ocean and other water bodies. We demonstrated that the PIC measurement efficiency is ~2 times higher than a RAD7 and is less affected by relative humidity and produces reliable results. Laboratorial measurements indicated that the new PIC-ORn system responded timely to the change of radon activities in water. The new system was successfully deployed during a cruise to the northwest Pacific Ocean in June 2021. Despite low radon-in-water activities, the results obtained by the new PIC-ORn system matched the traditional measurement systems within the estimated uncertainties. The PIC-ORn detector takes advantage of higher efficiency, lower cost, and power consumption, and is less affected by air moisture. The new system does not rely on drying units, further reducing on-site supervision, which would benefit the researches in submarine groundwater advection and diffusion and ocean-atmosphere gas exchange.

The three large marine ecosystems (LMEs) bordering China (Yellow Sea/Bohai Sea, East China Sea, and South China Sea) have received excess nitrogen (N) and phosphorus (P) in the past decades with de...

How an interfacial superconductivity emerges during the nucleation and epitaxy is of great importance not only for unveiling the physical insights but also for finding a feasible way to tune the superconductivity via interfacial engineering. In this work, we report the nanoscale creation of a robust and relatively homogeneous interfacial superconductivity (TC ≈ 13 K) on the epitaxial FeTe surface, by van der Waals epitaxy of single-quintuple-layer topological insulator Bi2Te3. Our study suggests that the superconductivity in the Bi2Te3/FeTe heterostructure is generated at the interface and that the superconductivity at the interface does not enhance or weaken with the increase of the Bi2Te3 thickness beyond 1 quintuple layer (QL). The observation of the topological surface states crossing Fermi energy in the Bi2Te3/FeTe heterostructure with the average Bi2Te3 thickness of about 20 QL provides further evidence that this heterostructure may potentially host Majorana zero modes.

The sediment-water interface in the coastal ocean is a highly dynamic zone controlling biogeochemical fluxes of greenhouse gases, nutrients, and metals. Processes in the sediment mixed layer (SML) control the transfer and reactivity of both particulate and dissolved matter in coastal interfaces. Here we map the global distribution of the coastal SML based on excess 210Pb (210Pbex) profiles and then use a neural network model to upscale these observations. We show that highly dynamic regions such as large estuaries have thicker SMLs than most oceanic sediments. Organic carbon preservation and SMLs are inversely related as mixing stimulates oxidation in sediments which enhances organic matter decomposition. Sites with SML thickness >60 cm usually have lower organic carbon accumulation rates (−2 yr−1) and total organic carbon/specific surface area ratios (−2). Our global scale observations reveal that reworking can accelerate organic matter degradation and reduce carbon storage in coastal sediments.

Superconductivity and ferroelectricity are typically thought of as incompatible because the former needs free carriers, but the latter is usually suppressed by free carriers. This is unless the car ...

We have examined the possible use of Mn/Ca ratios in benthic foraminifera as a proxy for hypoxia, which has increasingly become a serious environmental issue in many coastal zones. We collected samples from the Yangtze River Estuary, one of the largest and most intense seasonally hypoxic zones in the world. In order to obtain high quality Mn/Ca data, unaffected by contamination, we examined two different cleaning protocols and instrument-based analysis methods. Our results showed that a relatively simple physical cleaning approach coupled to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) provided excellent results on single specimens. Our observations were comparable to ICP analyses of solutions made up from dozens or even hundreds of specimens and involving complicated sample pretreatments. Using the LA methodology, we analyzed Mn/Ca ratios from living Florilus decorus (F. decorus) specimens from stations in the Yangtze River Estuary with varying bottom water dissolved oxygen (DO) concentrations. Our results showed that Mn/Ca ratios in penultimate chambers of living benthic foraminifera are sensitive to bottom water DO concentrations. We also observed significant variations of both Mn/Ca and Mg/Ca ratios from different chambers within foraminiferal shell specimens. These fluctuations were likely a response to changing ambient water DO and temperature during the specimen’s growth history. Combined use of foraminiferal Mn/Ca ratios together with other proxies could provide a powerful tool for historical reconstruction of low oxygen conditions in seasonal hypoxia areas.

Agave angustifolia is an important crassulacean acid metabolism plant species, with wide applications in beverage and sisal fiber production. In this study, we carried out a transcriptome analysis of A. angustifolia leaves, generating a total of 58,482,436 clean reads through Illumina paired-end sequencing. De novo transcriptome assembly generated 67,314 unigenes, with about half of them having homologs in four public databases. In the Nr database, Asparagus officinalis was shown to be most closely related to agave, and the early angiosperm Amborella trichopoda was selected as an outgroup species. We further identified five, two, seven, seven, seven, six and six CAD genes in asparagus, amborella, A. deserti, A. tequilana, A. americana, A. hybrid H11648 and A. angustifolia, respectively. The maximum likelihood phylogenetic tree revealed the species-specific expansion of CAD genes in arabidopsis, rice and agave. The expression analysis indicated the conservatively expressed CAD1/2/4/6, providing candidate targets for manipulation to improve lignin traits. The species-specific expression of CAD3/5/7 indicates the existence of different regulatory mechanisms controlling the expression of these genes in agave species. This study presents the first transcriptome dataset of A. angustifolia, facilitating future studies on lignin biosynthesis in agave.

In recent years, the spectacular massive green tide of Ulva prolifera has become a recurrent phenomenon appearing every summer in the coastal waters off Qingdao (Yellow Sea, China), attracting the attention of scientists and local government. Based on multidisciplinary data collected during summer and winter, this study focuses on the hydrological characteristics and regional biogeochemical processes in coastal waters off Qingdao. The results show that the boundary of the Yellow Sea Cold Water Mass (YSCWM) can reach the Qingdao coastal region in summer and is locally raised to the upper layers to form coastal upwelling beyond tidal mixing and favorable wind. The regional summer upwelling off the Qingdao coast effectively enriches the nutrient concentrations in the upper water column and thus promotes growth of phytoplankton but reduces the dissolved oxygen (DO) concentration and pH value in the bottom. The regional summer upwelling off Qingdao coast may facilitate the growth and regional blooming of the U. prolifera that migrate to this region with the southerly wind. Additionally, the effects of the front on the aggregation of U. prolifera may be significant. In winter, the Yellow Sea Warm Current (YSWC) extends and spreads along the offshore region off the Subei Shoal towards the Qingdao coastal sea. This tongue-shaped warm water meets the cold coastal water off Qingdao, which leads to the formation of a physical front. As a consequence, remarkable fronts of nutrient and chlorophyll a (Chl a) also form between the shoreward warm water and the cold coastal water. This study increases the understanding of the interactions between the regional physical, chemical, and biological processes off the Qingdao coast.

The hydro-biogeochemical processes in the world's largest area of green tide occurrence, off the Jiangsu coast in the Yellow Sea, are investigated in the summer, and their implications for Ulva prolifera blooms are discussed. The results show that the offshore transport of coastal water and the inshore upwelling of offshore bottom water both occur off the Jiangsu coast, and the upwelling position is consistent with the 20- to 30-m isobath off the Subei Shoal. The upwelling results in nutrient supplementation off the shoal, where a rapid decrease in the suspended particulate matter content contributes to good light conditions. As a result, a high-value area of phytoplankton is formed within the 20- to 30-m isobath. Eutrophication in the shoal has provided nutrients for the frequent occurrence of Ulva prolifera in recent years, whereas the upwelling area off the shoal has served as a "service station" or "courier station" for floating Ulva prolifera and promoted the species' propagation. The propagation of Ulva prolifera in the upwelling area and its blooms within the Subei Shoal can have a spatially synergistic effect, leading to its large-scale development. Our findings reveal the mechanisms that trigger the world's largest green tides from the perspective of physical-biogeochemical interactions.

In this work, we demonstrate that the nonsuperconducting single-layer FeTe can become superconducting when its structure is properly tuned by epitaxially growing it on Bi2Te3 thin films. The properties of the single-layer FeTe deviate strongly from its bulk counterpart, as evidenced by the emergence of a large superconductivity gap (3.3 meV) and an apparent 8 × 2 superlattice (SL). Our first-principles calculations indicate that the 8 × 2 SL and the emergence of the novel superconducting phase are essentially the result of the structural change in FeTe due to the presence of the underlying Bi2Te3 layer. The structural change in FeTe likely suppresses the antiferromagnetic order in the FeTe and leads to superconductivity. Our work clearly demonstrates that moire pattern engineering in a heterostructure is a reachable dimension for investigating novel materials and material properties.

Dynamics and textures of magnetic domain walls (DWs) may largely alter the electronic behaviors in a Weyl semimetal system via emergent gauge fields. However, very little is known about even the basic properties of these domain walls in Weyl materials. In this work, we imaged the spontaneous magnetization and magnetic susceptibility of a ferromagnetic (FM) Weyl semimetal CeAlSi using scanning SQUID microscopy. We observed the ferromagnetic DWs lined-up with the [100] direction (or other degenerate directions). We also discovered the coexistence of stable and metastable domain phases, which arise likely due to magnetoelastic and magnetostriction effects and are expected to be highly tunable with small strains. We applied an in-plane external field as the CeAlSi sample was cooled down to below the magnetic phase transition of 8.3K, showing that the pattern of FM domains is strongly correlated with both the amplitude and the orientation of the external field even for weak fields of a few Gausses. The area of stable domains increases with field and reaches maximum when the field is parallel to the main crystallographic axes of the CeAlSi crystal. Our results suggest that the manipulation of these heterogeneous phases can provide a practical way to study the interplay between magnetism and electronic properties in Weyl systems, and that these systems can even serve as a new platform for magnetic sensors.

How an interfacial superconductivity emerges during the nucleation and epitaxy is of great importance not only for unveiling the physical insights but also for finding a feasible way to tune the superconductivity via interfacial engineering. In this work, we report the nanoscale creation of a robust and relatively homogeneous interfacial superconductivity (

The Changjiang (Yangtze) River Estuary (CJE) is one of the largest and most intense seasonal hypoxic zones in the world. Here we examine the possibility that submarine groundwater discharge (SGD) may contribute to the summer hypoxia. Spatial distributions of bottom water 222Rn suggest a hotspot discharge area in the northern section of the CJE. SGD fluxes were estimated based on a 222Rn mass balance model and were found to range from 0.002 ± 0.004 to 0.022 ± 0.011 m3/m2/day. Higher SGD fluxes were observed during summer hypoxia period. The well-developed overlap of the distribution patterns for SGD flux and dissolved oxygen (DO) implies that SGD could be an important contributor to summer hypoxia in the region off the CJE. We suggest that SGD contributes to the seasonal hypoxia either: (1) directly via discharge of anoxic groundwaters together with reducing substances; and/or (2) indirectly by delivering excess nutrients that stimulate primary productivity with consequent consumption of DO during organic matter decomposition.

We introduce an improved on-site rapid analysis system for measuring 224Ra in natural waters. Radium isotopes are pre-concentrated on “Mn-fibers” before measurement of 220Rn. A Nafion drying system is used to lower the humidity in the detectors while maintaining a relatively constant moisture level in the Mn fiber in order to maintain a high and reproducible radon emanation. River water samples measured by this method agreed well with an analysis via RaDeCC, a very sensitive technique for measuring 224Ra. This method is recommended for fieldwork in remote areas when electricity and helium gas, required by traditional techniques, are not available.

Foraminiferal taphocoenose characteristics, notably allochthonous tests in surface sediment samples from the Yangtze River Estuary and adjacent areas in the East China Sea, were examined during (July, 2016) and after typhoon Nepartak (February, 2017) crossed this region. A comparison of transport indices from five sample stations reveals that this typhoon significantly strengthened sediment transport, although the transport in predominate direction (TWCnorth branch) occurs all year. Moreover, findings from a comprehensive impact of currents, topography, test size and shape, as well as other abiotic factors, show that transport occurs in the order (from stronger to weaker): south-north path ≫ southeast-northwest path > nearshore-northeast path. Along the south-north path, the TWCnorth branch transports larger tests of taxa Ammonia compressiuscula and Cavarotalia annectens as bed load along the gentle seabed in a rolling or saltating process. Results from the southeast-northwest path show smaller and bulging tests of the dominant species Epistominella naraensis and Bolivina robusta may be transported as suspension load along the steep submarine valley by the TWCnorthwest branch. On the nearshore-northeast path, only part of allochthonous tests Ammonia beccarii vars. was transported, probably due to distance travelled and weakening of the typhoon. Furthermore, we also infer the northeastern area as a sink zone that accumulates grains of allochthonous tests predominantly from the southern source zone, and a selection of tests from littoral species originating from the nearshore source zone. It is important to identify and independently count allochthonous test samples if a large number of these tests are recorded. Findings from this study provide a reference to identify and investigate typhoon modern effects in areas with complex currents and frequent strong physical dynamic events, as well as their geological records.

In order to examine the mixing behavior of dissolved uranium (U) in estuaries under different suspended particulate matter (SPM) regimes, three laboratory-based experiments were conducted by mixing seawater with river water containing different concentrations of SPM. Comparing this study with other field and laboratory-based experiments, dissolved U behaved differently depending upon the concentration of SPM. When SPM concentrations are > 0.8 g/L in the Yellow River, desorption/dissolution of U from SPM becomes predominant and dissolved U is enriched relative to the theoretical mixing line. However, when SPM concentrations are

Biogenic Silica (BSi) plays an essential role in availability of dissolved silicate (DSi) in aquatic ecosystems , but its role in silica cycling is still poorly characterized in the river and estuary systems. This study addressed the riverine BSi composition and reactive silica (RSi) export in the Yellow River, and estimated the contribution of terrestrial BSi dissolution to the estuary silica pool. Our results indicated that phytoliths comprised 1.3%–87% of the riverine BSi, while diatoms accounted for 13%–99% of the riverine BSi. The Yellow River transported 24 Gg yr −1 of BSi and 26 Gg yr−1 of DSi loadings, respectively; 63% of the riverine BSi and 54% of the riverine DSi fluxes were transported during the period from April to July. In total 46% of annual BSi loading was contributed by phytolith BSi in the Yellow River. The terrestrial BSi dissolution in the estuary would represent 15%–63% of riverine DSi loading on the basis of dissolution test, and low salinity could play an important role in enhancement of terrestrial BSi solubility, especially in the first few days during the estuarine mixing process. Although the terrestrial BSi represents a significant DSi contribution to the silica biogeochemical cycle in coastal waters, it tends to be refractory with the increasing of salinity.

The existence of false components with the Hilbert vibration decomposition (HVD) method has seriously restricted its application in practical rotor fault diagnosis. To solve this problem, an improved HVD method was proposed by adopting Kullback–Leibler (K–L) divergence values as a distinguishing index of true and false components, which is named the KL-HVD method. First, it calculated the K–L divergence values between the HVD components and the original signal, and then, these values are compared with the set threshold. Finally, it eliminated the false components whose K–L divergence values were larger than the threshold. The experimental results of rotor fault signal analysis demonstrated that the KL-HVD method could more accurately extract the time–frequency characteristics of the faults and the K–L divergence value was more suitable as the distinguishing index of true and false components than the mutual information and correlation coefficient values.

The study was carried out to address a method for separation of terrestrial and marine biogenic silica (BSi) in estuaries based on BSi compositions and δ 13 C values in BSi associated organic matter (δ 13 C BSi ). We used two world-class major rivers - the Changjiang (Yangtze) and Huanghe (Yellow) Rivers as examples to illustrate our approach. Our results for these rivers indicate that riverine BSi is comprised mainly of phytoliths and diatoms. River BSi concentrations vary with terrestrial inputs and in-stream primary production. Although the fluvial BSi sources are complex, the terrestrial δ 13 C BSi signals are quite unique (− 24.7 ± 0.8), significantly lower than the marine δ 13 C BSi values (− 21.3 ± 0.07, central Yellow Sea) ( p 13 C within BSi organic matter can provide terrestrial source information on the biogeochemistry of silicon in estuaries and the adjacent shelf. The δ 13 C BSi combination could potentially act as an efficient tool to study environmental change in coastal areas on decadal time-scales since this index may respond to variable terrestrial fluxes from land, as well as to changed phytoplankton assemblages in the coastal ocean.

At present, the oilfield development has entered the late stage of high water cut, and the exploitation objects have been changed to the second and third types of oil layers. The distribution of remaining oil is highly fragmented and complex, and the exploitation difficulty is gradually increasing. In view of a series of geological characteristics of Development Zone A, such as “numerous layers, complex reservoirs, severe phase transition and high viscosity”, the potential tapping technologies of Class II and Class III reservoirs, such as combination of two and three and ASP flooding, have been carried out one after another. In order to further enhance oil recovery and increase recoverable reserves, a large number of fracturing measures have been implemented to increase oil production. In view of the fact that it is more and more difficult to select wells and layers by this measure, we combine the results of fine reservoir description with dynamic data, take Block B as the investigation object, establish the potential pool of sedimentary unit-level measures, recognize the potential distribution of 82 different sedimentary units, clarify the target units of potential tapping measures, and finally explore relatively perfect ways and means to optimize fracturing well layers, and strive to achieve targeted adjustment and accurately tap potential. At present, in the early stage of fracturing in this area, the average daily oil increase of a single well is 7.9 tons, and the above practices also provide empirical reference and guidance for other similar blocks.

One of the largest “green tide” (Ulva prolifera) outbreaks in the world has occurred every year from 2007 to present in the Southern Yellow Sea, China. Currently, the coastal area around Jiangsu Province (Subei Shoal region) is thought to be the origination point of these giant green tide blooms. The combination of high nutrient demand but low river discharge and other inputs suggests that there is a significant flux of submarine groundwater discharge (SGD) in this area. By using a radium mass balance model, we estimated the SGD flux in the area to be (0.7–1.4) × 109 m3 d−1 (6.1–12 cm d−1), at the high end of SGD fluxes worldwide. Geographically, Subei Shoal is less than 5% of the entire Southern Yellow Sea area, while our calculated SGD flux just for the shoal area is ~3 times larger than previously documented for the whole Southern Yellow Sea. Therefore, Subei Shoal may be considered a SGD hotspot that plays an important role in SGD associated material fluxes. Compared to inputs from local rivers, atmospheric deposition, and anthropogenic activities, SGD-derived nutrients are the main source term that can support the growth of macroalgae. We specifically highlight that this type of areas that are shallow, intensively mixed, anthropogenically polluted, sandy or muddy with heavy bio-irrigation, may have a higher risk of suffering harmful ecological problems, even with limited terrestrial runoff.

Materials with strong magnetoresistive responses are the backbone of spintronic technology, magnetic sensors, and hard drives. Among them, manganese oxides with a mixed valence and a cubic perovskite structure stand out due to their colossal magnetoresistance (CMR). A double exchange interaction underlies the CMR in manganates, whereby charge transport is enhanced when the spins on neighboring Mn3+ and Mn4+ ions are parallel. Prior efforts to find different materials or mechanisms for CMR resulted in a much smaller effect. Here we show an enormous CMR at low temperatures in EuCd2P2 without manganese, oxygen, mixed valence, or cubic perovskite structure. EuCd2P2 has a layered trigonal lattice and exhibits antiferromagnetic ordering at 11 K. The magnitude of CMR (104 percent) in as-grown crystals of EuCd2P2 rivals the magnitude in optimized thin films of manganates. Our magnetization, transport, and synchrotron X-ray data suggest that strong magnetic fluctuations are responsible for this phenomenon. The realization of CMR at low temperatures without heterovalency leads to a new regime for materials and technologies related to antiferromagnetic spintronics.

Radium (Ra) isotopes are useful for tracing water mass transport and examining estuarine hydrological dynamics. In this study, several hydrological parameters, nutrients, chlorophyll-a (chl-a), suspended particulate matter (SPM) and Ra isotopes (223Ra, 224Ra and 226Ra) of surface waters of the Zhujiang (Pearl) River estuary (ZRE) were measured. This was done for both winter (December) and summer (July) seasons, to quantitatively understand the seasonal characteristics of river plume flow rate and trajectories, as well as the ecological response. The results show that Ra concentrations in summer were higher than in winter, especially 224Ra (about 2–5 times higher). The spatial distribution of three Ra isotopes and relative Ra water ages indicated that river water mainly flushed out of ZRE through the western side in winter, where the water transport was about 5 days faster than in the eastern zone. In summer, diluted river water expended to the east side, resulting in fairly similar water ages for both sides of the river mouth. Although nutrients were higher during the summer season, lower chl-a concentrations indicated that reduced primary production might be caused by high SPM (low light penetration). The results obtained from this study will provide knowledge needed for effectively developing and managing the ZRE.

Summary Anthropogenic controls on water and sediment may play important roles in river system transformations and morphological evolution, which could further affect coastal hydrodynamics and nutrient behavior. We used geochemical tracers to evaluate the influence of an intentional large release of water and sediment during the so-called “Water Sediment Regulation Scheme” (WSRS) on estuarine morphology, hydrodynamics and nutrients in the Yellow River estuary, China. We discovered that there was a newly formed small delta in the river mouth after the 2013 WSRS. This new morphologic feature altered terrestrial material distribution patterns from a single plume to a two-plume pattern within the estuary. Our results show that the WSRS significantly influenced the study area in the following ways: (1) Radium and nutrient concentrations were significantly elevated (two to four times), especially along the two river outlets. (2) Estuarine mixing was about two times stronger during WSRS than before. Average aerial mixing rates before and during WSRS were 50 ± 26 km2 d−1 and 89 ± 51 km2 d−1, respectively. (3) Our data is consistent with P limitation and suggest that stoichiometrically based P limitation was even more severe during WSRS. (4) All river-derived nutrients were thoroughly consumed within one to two weeks after entry to near-shore waters. (5) The extent of the area influenced by terrestrial nutrients was two to three times greater during WSRS. Human influence, such as triggered by WSRS regulations, should thus be considered when studying biogeochemical processes and nutrient budgets in situations like the Yellow River estuary.

Reworked muds, including mobile muds, resuspended sediments, and bio-mixed muds are ephemeral layers in the benthic boundary of large-river delta-front estuaries (LDEs). In this study, multiple radiotracers (210Pb, 137Cs, 234Th, 7Be, 235U, 228Th, 228Ra, 226Ra and 40K) were combined to evaluate the sedimentary dynamics of the mud belt on the inner shelf of the East China Sea (ECS) adjacent to the Changjiang River Estuary. We first categorized eight types of typical 210Pb profiles in marine sediments, and specified which ones could be used as possible evidence of reworked muds. The types of 210Pb profiles observed in previous studies and this study were then used to examine the depth distribution of reworked mud layers of the benthic boundary of ECS. We found that reworked mud depth in the along-shore mud belt of the inner shelf of ECS was deeper than those in the outer shelf and slope area, reaching up to 150 cm deep in the Changjiang River LDE, and up to 50 cm deep in the Zhejiang–Fujian coast mud area. Sediment core tracer profiles also showed that the reworked mud layer could be further divided into several sub-layers with distinct redox conditions and microbe (sulfate-reducing bacterial) abundance. SRB abundance intensively fluctuated with changing redox environment, and larger abundance values were usually observed in anoxic conditions. Based on 7Be and 234Th, the top layer (ca. 2–4 cm thick) was the most modern and active zone, showing evidence of reworking on seasonal timescales. The deeper sections of the reworked mud layer were generally modified over longer timescale (years) which were examined using the more long-lived tracers, e.g., 137Cs, 228Thex, and 228Ra/226Ra ratio. We found for the first time in this region that age of the reworked layers was usually much younger than underlying accumulating (burial) layers. We posit that this multi-radionuclide approach is critical for evaluating the complex biogeochemical sediment record on delta-front estuaries of large rivers subject to changing climate conditions and human impacts over the last several centuries.

Radium isotopes are known to be excellent geochemical tracers for study of oceanographic processes. We show here that radium isotopes can also be used to assess adsorption/desorption and transport processes in rivers. The Yellow River (Huanghe), one of the longest, most turbid and heavily regulated rivers in the world, is used as an example. We first investigated the temporal and spatial behavior of radium isotopes (224Ra and 226Ra) in the lower reaches of the river, and found that this zone displayed some of the highest known riverine radium concentrations and fluxes in the world. Suspended particulate matter (SPM) is shown to be the dominant factor controlling radium activities. Laboratory simulation experiments showed that radium desorption from SPM obeys an exponential relationship in fresh water (S = 0). When salinities are >10, the increase in radium concentration follows a linear increase with respect to the amounts of SPM added. Significantly higher radium concentrations (3–5 times), especially for short-lived 224Ra, were observed during the “Water-Sediment Regulation Scheme” (WSRS), an annual management event when ∼15%–55% of the annual water discharge and ∼30%–75% of the annual sediment load are released from a reservoir to control sedimentation in the Yellow River. The radium fluxes during WSRS periods (∼2 weeks long) accounted for more than half of the entire annual load during the periods studied. Sediment erosion and pore water release are also thought to be important processes supplying radium to the river. After a WSRS, Ra desorption from SPM increases and becomes the prevailing process.

Sulfate- and sulfite-reducing prokaryotes (SSRP) communities play a vital role in both sulfur and carbon cycles. Community composition and abundance of SSRP were investigated using dissimilatory sulfite reductase β subunit ( dsrB ) gene sequencing in sediments from the Changjiang estuary and its adjacent area in the East China Sea (ECS). Clone libraries were constructed and real-time fluorescence quantitative polymerase chain reaction (qPCR) was applied to understand the community information of SSRP. In addition to sequences affiliated to sulfate-reducing prokaryotes (SRP), those affiliated with sulfite-reducing prokaryotes (SiRP) were also observed. Four phylotypes of SRP in this study showed genetic similarity to Desulfobulbaceae, Syntrophobacteraceae, Desulfobacteraceae and Peptococcaceae, and an unknown group that could not be clearly affiliated with known lineages was found. Salinity, temperature and contents of total organic carbon (TOC) were most closely correlated with the SSRP communities by canonical correspondence analysis (CCA). 210 Pb activities demonstrated the sedimentary environment at S33 was more stable than that at S31. Intense resuspension and reconstruction of sediments made the vertical abundance profile of SSRP fluctuate violently. For surface sediments, the dsrB gene copy numbers near the Changjiang estuary were higher than those in the mouth of Hangzhou Bay and the mud deposits along the Zhejiang coast, and contents of TOC were positively related to the copy numbers of dsrB gene. Our data provided valuable information to achieve a better understanding of the potential role of SSRP in sediments from the Changjiang estuary and adjacent East China Sea.

The Water–Sediment Regulation Scheme (WSRS) is an important water conservancy project in the Yellow River basin, which is usually operated annually from June to July to control water and sediment release from the Xiaolangdi Reservoir in the middle reaches. As a greatly concentrated period of delivering terrigenous materials from the Yellow River to the sea, the WSRS can serve as a natural laboratory to examine the geochemical behavior of elements during their transport along the river. Uranium isotopes (234U and 238U) were measured in Yellow River waters at stations Xiaolangdi (located in the middle reaches of the Yellow River) and Lijin (the last hydrologic station near the Yellow River estuary) during the WSRS 2012. Compared with station Xiaolangdi, dissolved uranium concentration at station Lijin was markedly higher, showing a significant impact from the WSRS. Budget calculation for dissolved uranium during the WSRS indicated that two major sources of new added dissolved uranium in the section of the Yellow River between Xiaolangdi and Lijin: suspended particles (46%) and porewater of bottom sediment (45%). The flux of dissolved uranium from the Yellow River to the sea was estimated to be 2.40 × 107 g during the WSRS 2012.

A gravity core collected from the East China Sea (ECS) inner shelf was analyzed for elemental and stable isotopic composition, lignin-phenols, and sedimentary pigments to investigate changes of organic carbon (OC) inputs during the past two centuries. In particular, we examined the linkages between terrestrial and marine OC inputs with climate variability and anthropogenic activities. The decrease of terrestrial OC contribution (from 41% to 28%) and increasing diagenetic indices of lignin-phenols (P/(S + V): from 0.12 to 0.22; 3,5-Bd/V: from 0.03 to 0.09) after the 1970s were possibly attributed to intensified deforestation, dam construction, and channel erosion. Lignin content (Λ8) ranged from 0.35 mg/100 mg OC to 6.92 mg/100 mg OC, with lower values corresponding to the worst flooding events in the Changjiang watershed and weaker East Asian Winter Monsoon (EAWM), while higher Λ8 was more correlated to the strengthening of EAWM. This indicates that terrestrial inputs to Zhe-Min Coast are different from those in Changjiang Estuary during flooding events and strongly linked with regional climate variability. The total contents of sedimentary chloropigments (i.e. pheophorbide-a, pheophytin-a, pyropheophytin-a, sterol chlorin esters, and carotenol chlorin esters) ranged from 663.4 to 74.9 nmol g−1 OC, and decreased exponentially downwards. Sedimentary chloropigments that were used to document historical change of phytoplankton biomass were decoupled with historical changes of Changjiang riverine nutrient inputs but corresponded well to the fluctuation of regional climate variability. Higher phytoplankton biomasses usually were observed during positive phases of Pacific Decadal Oscillation (PDO) and/or warm El Niño-Southern Oscillation (ENSO) events, and lower algal biomass usually corresponded to the negative phase of PDO and/or cold ENSO events.

In this study, sediment grain size (MGS), specific surface area (SSA), total organic carbon (TOC) contents, C/N molar ratios, stable carbon isotope, and P species in a sediment core, collected from the East China Sea (ECS) inner-shelf were measured to explore the applicability of detrital phosphorus (De-P) as a potential indicator of past flooding events in the Changjiang River Basin (CRB). In particular, we examined the linkages between the evolution of floods with regional climate changes and anthropogenic activities in the CRB. Peaks of De-P concentrations in sediments corresponded well with the worst flooding events of the CRB over the past two centuries (e.g., 1850s, 1860s, 1900s, 1920s, 1950s, 1980s, and 2000s). Moreover, De-P also corresponded well with the extreme hypoxic events in 1981 and 1998 in the Changjiang Estuary as indicated by Mo/Al ratios, indicating potential linkages between De-P as a flooding proxy to flood-induced hypoxia events in this region. In addition, a robust relationship was found among De-P, the floods in 1950s, 1980s, and 2000s of the CRB, the intensive El Niño-Southern Oscillation (ENSO), the abnormally weak East Asian Summer Monsoon (EASM) and the warm phase of Pacific Decadal Oscillation (PDO), suggesting that De-P also provided insights to linkages between regional climate change and flooding events in this region.

The BWater-Sediment Regulation Scheme^ (WSRS) is critically important to the hydrologic evaluation of the Yellow River estuary since a huge pulse of water and sediment are delivered into the sea during a short period. We used the natural geochemical tracers radium ( 223 Ra, 224 Ra, 226 Ra) and radon ( 222 Rn) isotopes as well as other hydrolog- ical parameters to investigate the mixing variations and sub- marine groundwater discharge (SGD) in the Yellow River estuary under the influence of the 2013 WSRS. Dramatically elevated radium and radon isotopic activities were observed duringthisWSRS comparedwithactivitiesmeasuredduringa non-WSRS period. Radium Bwater ages^ indicated that the offshore transport rate nearly tripled when the river discharge increased from 400 to 3400 m 3 /s. We calculated the SGD flux in the Yellow River estuary based on a radium mass balance model as well as radium and radon time-series models. The SGD flux was estimated at 0.02~0.20 m/day during a non- WSRS period and 0.67~1.22 m/day during the 2013 WSRS period. The results also indicate that large river discharge tends to lead more intense SGD along the river channel direc- tion with a large amount of fresh SGD.

Submarine groundwater discharge (SGD) in estuaries brings important influences to coastal ecosystems. In this study, we observed significant SGD in the Yellow River estuary, including a fresh component, during the Water–Sediment Regulation Scheme (WSRS) period. We used the 222Rn and 220Rn isotope pair to locate sites of significant SGD within the study area. Three apparent SGD locations were found during a non-WSRS period, one of which became much more pronounced, according to the remarkably elevated radon levels, during the WSRS. Increased river discharge (from 245 m3 s−1 to 3560 m3 s−1) and the elevated river water level (from 11 m to 13 m) during the WSRS led to a higher hydraulic head, enhancing groundwater discharge in the estuary. Our results suggest that high river discharge (>3000 m3 s−1) might be necessary for elevated fresh submarine groundwater discharging (FSGD). Vertical profiles of salinity, DO and turbidity anomalies along the benthic boundary layer also indicated significant FSGD in the estuary during the WSRS. Nutrient concentrations had positive correlations with 222Rn during a 24-h observation, which indicates that SGD is a dominant nutrient pathway in this area.

Lonsdalea quercina N-5-1 is a bacterial pathogen that causes poplar bark cankers. It has been isolated from the branch of Populus × euramericana cv. "74/76" in Henan, China. Previous studies have revealed that the Type III secretion system (T3SS) acts as an essential pathogenic factor in L. quercina N-5-1. HrpW is a putative effector of T3SS in strain N-5-1, which has a typical harpin domain at the amino terminal and a pectate lyase (Pel) domain at its carboxyl terminal. Genetic evidence had shown that, compared to the wild-type and the complementary strain, the hrpW mutation causes a small but significant reduction in virulence when inoculated on the poplar branches. The amino terminal domain of HrpW was found to trigger tobacco hypersensitive response, but the carboxyl terminal domain of HrpW was not. Unlike most HrpW homologs in other bacteria, the carboxyl terminal domain of HrpW of strain N-5-1 exhibited detectable pectate lyase activity. Site-direction mutations (W104A, W171M) further demonstrated that two tryptophan residues were essential to its pectate lyase activity. The results of the present work suggest that HrpW in L. quercina N-5-1 possesses pectate lyase activity and acts as a nonessential but important pathogenic factor in poplar bark canker disease.