The water-sediment regulation scheme (WSRS), beginning in 2002, is an unprecedented engineering effort to manage the Yellow River with the aims to mitigate the siltation both in the lower river ...channel and within the Xiaolangdi Reservoir utilizing the dam-regulated flood water. Ten years after its initial implementation, multi-disciplinary indicators allow us to offer a comprehensive review of this human intervention on a river-coastal system. The WSRS generally achieved its objective, including bed erosion in the lower reaches with increasing capacity for flood discharge and the mitigation of reservoir siltation. However, the WSRS presented unexpected disturbances on the delta and coastal system. Increasing grain size of suspended sediment and decreasing suspended sediment concentration at the river mouth resulted in a regime shift of sediment transport patterns that enhanced the disequilibrium of the delta. The WSRS induced an impulse delivery of nutrients and pollutants within a short period (~20days), which together with the altered hydrological cycle, impacted the estuarine and coastal ecosystem. We expect that the sediment yield from the loess region in the future will decrease due to soil-conservation practices, and the lower channel erosion will also decrease as the riverbed armors with coarser sediment. These, in combination with uncertain water discharge concomitant with climate change, increasing water demands and delta subsidence, will put the delta and coastal ocean at high environmental risks. In the context of global change, this work depicts a scenario of human impacts in the river basin that were transferred along the hydrological pathway to the coastal system and remotely transformed the different components of coastal environment. The synthesis review of the WSRS indicates that an integrated management of the river-coast continuum is crucially important for the sustainability of the entire river-delta system. The lessons learned from the WSRS in the Yellow River provide insights to the integrated management of large rivers worldwide.
•Datasets over 2002–2013 provides a comprehensive review on how dam regulation impacts the lower Yellow River and its delta.•WSRS changed the natural seasonal hydrological rhythm through the artificial flood and the associated sediment delivery.•Both sediment source and grain-size composition differs greatly between the two phases of WSRS.•WSRS alters the nutrients delivery to the sea, and significantly impacts the coastal biogeochemical process and ecosystem.
In this study, we used a 224Ra mass balance model to evaluate the importance of submarine groundwater discharge (SGD) for the budgets of biogenic elements in two major Chinese estuaries: the Pearl ...River Estuary (PRE) and the Changjiang River Estuary (CRE). The apparent water age in the PRE was estimated to be 4.8 ± 1.1 days in the dry season and 1.8 ± 0.6 days in the wet season using a physical model based on the tidal prism. In the dry season, the water age in the CRE was estimated to be 11.7 ± 3.0 days using the 224Ra/223Ra activities ratios apparent age model. By applying the 224Ra mass balance model, we obtained calculations of the SGD flow in the PRE of (4.5–10) × 108 m3 d−1 (0.23–0.50 m3 m−2 d−1) and (1.2–2.7) × 108 m3 d−1 (0.06–0.14 m3 m−2 d−1) in the dry season and wet season, respectively, and the estimated SGD flux was (4.6–11) × 109 m3 d−1 (0.18–0.45 m3 m−2 d−1) in the dry season of the CRE. In comparison with the nutrient fluxes from the rivers, the SGD-derived nutrient fluxes may play a vital role in controlling the nutrient budgets and stoichiometry in the study areas. The large amount of dissolved inorganic nitrogen and phosphorus fluxes together with high N: P ratios into the PRE and CRE would potentially contribute to eutrophication and the occurrence of red tides along the adjacent waters.
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•Physical model and 224Ra/223Ra were used to estimate water ages in the Pearl River Estuary and Changjiang River Estuary.•Submarine groundwater discharge (SGD) was evaluated using a 224Ra mass balance model.•SGD is important for hydrology and nutrient budgets in the Pearl River Estuary and Changjiang River Estuary.
Since the outbreak of COVID‐19 in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS CoV‐2) has spread worldwide. This study summarized the transmission mechanisms of COVID‐19 ...and their main influencing factors, such as airflow patterns, air temperature, relative humidity, and social distancing. The transmission characteristics in existing cases are providing more and more evidence that SARS CoV‐2 can be transmitted through the air. This investigation reviewed probabilistic and deterministic research methods, such as the Wells–Riley equation, the dose‐response model, the Monte‐Carlo model, computational fluid dynamics (CFD) with the Eulerian method, CFD with the Lagrangian method, and the experimental approach, that have been used for studying the airborne transmission mechanism. The Wells–Riley equation and dose‐response model are typically used for the assessment of the average infection risk. Only in combination with the Eulerian method or the Lagrangian method can these two methods obtain the spatial distribution of airborne particles' concentration and infection risk. In contrast with the Eulerian and Lagrangian methods, the Monte‐Carlo model is suitable for studying the infection risk when the behavior of individuals is highly random. Although researchers tend to use numerical methods to study the airborne transmission mechanism of COVID‐19, an experimental approach could often provide stronger evidence to prove the possibility of airborne transmission than a simple numerical model. All in all, the reviewed methods are helpful in the study of the airborne transmission mechanism of COVID‐19 and epidemic prevention and control.
Endogenous neural stem cells (NSCs) exist in the central canal of mammalian spinal cords. Under normal conditions, these NSCs remain quiescent and express FoxJ1. After spinal cord injury (SCI), the ...endogenous NSCs of a heterogeneous nature are activated and proliferate and migrate towards the lesion site and mainly differentiate into astrocytes to repair the injured tissue. In vitro, spinal cord NSCs are multipotent and can differentiate into neurons, astrocytes, and oligodendrocytes. The altered microenvironments after SCI play key roles on the fate determination of activated NSCs, especially on the neuronal specification potential. Studies show that the activated spinal cord NSCs can generate interneurons when transplanted into the adult hippocampus. In addition, the spinal cord NSCs exhibit low immunogenicity in a transplantation context, thus implicating a promising therapeutic potential on SCI recovery. Here, we summarize the characteristics of spinal cord NSCs, especially their properties after injury. With a better understanding of endogenous NSCs under normal and SCI conditions, we may be able to employ endogenous NSCs for SCI repair in the future.
Sediment oxygen consumption (SOC) rates on the shelves of the East China Sea (ECS) and the Yellow Sea (YS) were measured during five field studies in the period April 2010 to May 2011, using the ...batch intact core incubation technique. The measured SOC rates ranged from 1.73 to 17.56mmol O2m−2d−1, which are comparable to values reported for other typical continental shelves worldwide. For the shelves of both the ECS and the YS there was a remarkable spatial and temporal variation in SOC rates. SOC was used as a proxy to assess the benthic organic carbon mineralization in the ECS and the YS, and to prepare simple organic carbon budget. For the YS it was found that on average approximately 90% of the organic carbon derived from primary productivity was decomposed in the water column and 8% was decomposed in the sediment, resulting in <4% being permanently buried in the YS sediment. In contrast, approximately 70% of the organic carbon derived from primary productivity was decomposed in the water column in the ECS and 17% was decomposed in the sediment, suggesting that the permanently buried percentage (14%, relative to the primary productivity) was higher in the ECS. The contrasting contributions of benthic mineralization to the organic carbon cycle in the ECS and the YS indicated that there is tight coupling between pelagic and benthic biogeochemical processes in the ECS, but in the YS, the regenerated production and external non-marine nutrients regulated pelagic primary production.
Building a safe space for stem cells
The meristem, the collection of stem cells that builds plants, is resistant to viral infection. Wu
et al.
now show that WUSCHEL, a transcription factor that helps ...to sustain stem cell production in the shoot apical meristem of
Arabidopsis
, also protects that stem cell domain from viruses. WUSCHEL inhibited viral protein synthesis by repressing methyltransferases that regulate ribosomal RNA processing and ribosome stability.
Science
, this issue p.
227
Manipulation of protein synthesis restricts viral invasion in stem cells of the
Arabidopsis
shoot apical meristem.
Stem cells in plants constantly supply daughter cells to form new organs and are expected to safeguard the integrity of the cells from biological invasion. Here, we show how stem cells of the
Arabidopsis
shoot apical meristem and their nascent daughter cells suppress infection by cucumber mosaic virus (CMV). The stem cell regulator WUSCHEL responds to CMV infection and represses virus accumulation in the meristem central and peripheral zones. WUSCHEL inhibits viral protein synthesis by repressing the expression of plant
S
-adenosyl-
l
-methionine–dependent methyltransferases, which are involved in ribosomal RNA processing and ribosome stability. Our results reveal a conserved strategy in plants to protect stem cells against viral intrusion and provide a molecular basis for WUSCHEL-mediated broad-spectrum innate antiviral immunity in plants.
The South China Sea (SCS) is one of the largest marginal seas in the world, but the processes that control the silicon cycle are not well understood. Here, we analyse the factors that affect the ...distribution of biogenic silica (bSi) in SCS sediments and discuss the silicon cycle based on a box model. Our results show that the bSi content (~ 1.2%) in the shelf-slope (< 2000 m) sediments is lower overall than that (~ 2%) in the basin (> 2000 m) sediments. The dilution by terrestrial input, degradation rate of biogenic materials and lateral transport by current patterns are the main factors influencing the bSi content in SCS sediments. The bSi burial flux in the shelf-slope region (161 ± 156 Gmol-Si yr
−1
) is six times greater than that in the basin region (27 ± 18 Gmol-Si yr
−1
) due to higher burial rates, larger sea area, and coarser sediments. The estimated bSi burial efficiency (ratio of the bSi burial rate divided by the sum of the benthic silicic acid (dSi) diffusion rate and the burial rate) in SCS sediments is 27%, comparable to those of other marginal seas. Therefore, at the sediment–water interface, 73% of Si is recycled back to the water column. From compiled datasets of water fluxes and dSi concentrations over the past decades, we calculate a total output silicon flux of dSi of 2259 ± 397 Gmol-Si yr
−1
for the SCS, which is not significantly different from the total input flux (2196 ± 458 Gmol-Si yr
−1
), suggesting that the Si cycle of this marginal sea is in a steady state. Interestingly, the submarine groundwater discharge (SGD) flux (477 ± 140 Gmol-Si yr
−1
) in the SCS is 2.5 times higher than the riverine dSi and dissolvable amorphous silica input (194 ± 40 Gmol-Si yr
−1
).
Axonal regeneration has been the research focus in the field of clinical treatment for spinal cord injury (SCI). The growth and extension of neuronal axons is a dynamic biological process mediated by ...the cytoskeleton, and microtubule plays an important role in axonal growth. Moderate stabilization of microtubule promotes axonal growth and eliminates various intra- and extracellular mechanisms that impede axonal regeneration. After SCI, the damaged axons rapidly form a growth cone, wherein the stability of tubulin decreases, impairing axonal regeneration. Taxol with proven clinical safety is commonly used as a broad-spectrum antitumor drug. Importantly, Taxol can promote axonal extension by enhancing and stabilizing the microtubule assembly. In our study, we systematically investigated the differentiation of neural stem cells (NSCs) in vitro and functional recovery in injured rats in vivo following Taxol treatment. Low-dose Taxol promoted differentiation of NSCs to neurons and significantly extended the axons in vitro. In vivo, Taxol promoted the expression of βIII-tubulin in the injured areas and motor function recovery after SCI. Low-dose Taxol is a promising clinical agent to promote axonal regeneration after SCI.
Neural stem cells (NSCs) transplantation is regarded as a promising therapeutic strategy to treat severe spinal cord injury (SCI) by compensating the neuronal loss. However, significant challenges ...including long‐term survival, directed neuronal differentiation, and functional integration of the transplanted NSCs and their progenies within the host spinal cord are yet to be solved. In this study, NSCs are trained on differently modified collagen scaffolds to increase their neuronal differentiation rate when cultured under the simulated SCI microenvironment. Then, a functional scaffold is screened out, on which the cultured NSCs show high neuronal differentiation rate and generate both sensory and motor mature neurons. Subsequently, that NSC seeded functional scaffold is transplanted into a rat severe SCI model. The results show that higher endogenous neurogenesis efficiency as well as in vivo survival and neuronal differentiation rate of the grafted NSCs are observed. Moreover, both sensory and motor neurons are found to be differentiated from the grafted NSCs in the lesion site and those newly generated neurons can functionally interact with each other and the host neurons. Taken together, the in vitro training systems for modulating the differentiation profiles of NSCs are instructive and exhibit strong potentials for SCI treatments.
Neural stem cells (NSCs) trained on the functional collagen scaffolds achieve comparatively high neuronal differentiation rate and generate both sensory and motor mature neurons. After transplanting the NSCs seeded functional scaffold into a rat severe spinal cord injury model, higher survival and neuronal differentiation rate of the grafted NSCs are observed. Moreover, the grafted NSCs can generate sensory and motor neurons throughout the lesion site.
Glacial meltwater has been suggested as a significant source of potentially bioavailable iron to the oceans. However, the supply of dissolved iron (dFe) in glacial meltwaters is poorly constrained as ...few sites have been studied, and because the chemical processing of Fe during transport from glaciers to the adjacent coastal ocean is not well understood. In order to better constrain glacial fluxes of dFe to the ocean, iron concentrations, iron stable isotopes (δ56Fe), and other supporting chemical and physical measurements were made along a ∼4 km long glacial meltwater river on Svalbard and in estuarine waters that it flows into. Dissolved iron concentrations in the Bayelva River decreased from a maximum of 734 nM near the glacier to an average value of 116 nM near the mouth of the river. Measurements in the Kongsfjorden estuary suggest that 3 to 10 nM of dFe from the Bayelva River is stabilized in glacial waters by the time it mixes into the ocean. Incubation of Bayelva River waters over two weeks in both the light and dark show similar results, with the majority of dFe being quickly precipitated and 4 to 7 nM Fe stabilized in the dissolved phase. Evidence suggests that Fe is most likely lost from the dissolved phase by aggregation and adsorption of nanoparticulate and colloidal Fe to particles. Dissolved δ56Fe was between −0.11‰ and +0.09‰ for all river samples and did not vary systematically with dFe concentrations. We infer that the Fe is lost from the dissolved phase by a process that fractionates Fe isotopes by less than 0.05‰, indicating that the Fe bonding environment does not change during precipitation. This is consistent with DOC loss that is much faster than predicted photo-oxidation rates, suggesting that DOC is also lost through adsorption and precipitation. Dissolved Fe concentrations in the Bayelva River (15–734 nM), and Fe concentrations which are stabilized in the dissolved phase (4–7 nM) are much lower than some previous estimates of Fe in glacial meltwaters, with roughly 80% of dFe lost during transit in the Bayelva River and roughly 90% of the remaining dFe lost in the estuary. This may mean that glaciers are a less significant source of dissolved Fe to the global oceans than has been previously hypothesized, that cold base glaciers of the type studied here do not contribute significantly to the dissolved Fe flux, or that the flux of reactive particulate Fe to the oceans is more important than the dissolved flux. In Arctic regions with similar proglacial environments, bedrock composition, weathering intensity, and as precipitation of colloidal and nanoparticulate Fe may all play an important role in regulating the glacial meltwater iron flux to the ocean.
•Much dissolved Fe in glacial meltwaters is lost in the proglacial environment.•Fe loss may be due to precipitation of colloidal/nanoparticulate Fe or organically-complexed Fe.•Glacial δ56Fe in the Bayelva river is generally −0.1‰ to +0.1‰.
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