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The quantity and grain size of river‐borne sediment are critical to geomorphological evolution and ecosystem health of river deltas. Compared to quantitative aspects of fluvial systems, however, studies describing the physical properties of river sediment are still quite limited. This work examines how an unprecedented engineering effort (the Water‐Sediment Regulation Scheme, WSRS) within the lower Yellow River system has caused important changes in the volume and grain size patterns of transported sediment. After the implementation of the WSRS, artificial floods dominated the delivery of water and sediment to the delta region—the natural (seasonal) rhythm of the hydrological cycle has been replaced by impulsive delivery. Compared to natural floods, the duration of the artificial flood due to WSRS is substantially shortened, and timing has changed to early summer (June to July), which is two to three months ahead of the usual flood season. Now, as a result of WSRS, there are high sediment loads over a shorter than usual time frame. The Yellow River's sediment load rebounded and coarsened, because artificial floods have strongly scoured the river channel. These changes turned the Yellow River delta from a recession phase to one of progradation, and caused impulsive delivery and rapidly buried of terrestrial organic carbon and pollutants. For other rivers worldwide, the lower Yellow River system provides an illustrative example of how transporting coarse‐grained sediment, otherwise deposited on river bed, may be used to mitigate coastal land loss on intra‐decadal time scales, however with the potential for adverse ecological impacts. Key Points: The seasonal rhythm of the hydrological cycle has been replaced by impulsive delivery of Yellow River water and sedimentArtificial floods increased both the volume and grain size of sediment to the sea by scouring the lower Yellow River channel bedDam‐released floods could be utilized to mitigate deltaic land loss, but with potential adverse ecological impacts [ABSTRACT FROM AUTHOR]

Today's deltas are impacted negatively by (1) accelerated subsidence (e.g., from ground fluid extraction), (2) global eustatic sea level rise, and (3) decreased sediment supply, which increasingly starves these landforms of sediment necessary to sustain their footprint. This growing vulnerability threatens many megacities that have developed due to the rich resources offered by deltas and therefore urgently calls for efforts to maintain sustainability. The Yellow River of China is classic example of such a landform under threat and which requires human intervention to maintain its resilience. Since 2002, the Yellow River Conservancy Commission has enacted an annual water and sediment regulation scheme (WSRS) by coordinated operation of three large reservoirs in the mainstream. Here we evaluate the efficiency and sustainability of this man‐made experiment on delta evolution. The impulsive delivery of muds and sands, within ~20 day intervals (averaged duration of the WSRS), did indeed move the present Yellow River delta from a destructive phase to an accretion phase. With continuous scouring, however, the downstream riverbed erosion efficiency has decreased, due to coarsening of surface bed material sediment. Concomitantly, sediment delivery has decreased, resulting in the present delta once again entering an erosive (destructive) phase, since 2014. From a perspective of delta restoration, the WSRS on the Yellow River is effective but potentially unsustainable. Restoring delta resilience necessitates an enhanced, coordinated effort, relying upon new sciences advances, rather than simply assuming channel scour will address the sediment deficit of the delta. Plain Language Summary: Deltas are highly dynamic systems which lie on the interface between rivers and oceans. Due to accelerated sea level rise and terrestrial sediment decrease, over half of global deltas are presently under a growing risk of being submerged. How best to protect these important terrestrial surface has become an urgent problem to be resolved. With our manuscript, we describe the successes and unintended consequences learned from one of the largest man‐made experiments in the world. Since 2002, the Yellow River Conservancy Committee started to release flushing water from the Xiaolangdi Reservoir annually to remove accumulated sediment from the reservoir and to erode the lower riverbed of the Yellow River. This man‐made experiment did increase the quantity and particle size of sediment reaching the sea, and thereby nourishing the Yellow River delta successfully. With gradually eroding, however, the enhanced particle size has armored the lower riverbed, making it progressively difficult to be eroded by reservoir‐released flushing water. Consequently, the sediment delivery from the Yellow River to the sea declined, resulting in that the Yellow River delta, has once again retreated landward since 2014. Key Points: The impact of reservoir regulation along the Yellow River on delta evolution was systematically evaluatedThe man‐made experiment through reservoir regulation along the Yellow River did mitigate delta erosion by scouring the lower river bedWith sediment coarsening of lower riverbed, bed scouring through reservoir regulation is not a sustainable way to nourish delta lobe [ABSTRACT FROM AUTHOR]

The grain-size distribution of surface sediments in the Bohai Sea (BS) and the northern Yellow Sea (NYS), and its relationship with sediment supply and hydrodynamic environment were investigated based on grain-size compositions of surface sediments and modern sedimentation rates. The results showed that the surface sediments in the BS and the NYS were primarily composed of silty sand and clayey silt with a dominant size of silt. In addition, the Yellow River delivered high amount of water and sediments to the BS, and they are dominated in surface sediments (mainly silt) in the Bohai Bay, the Yellow River mouth, the center of the BS, and the north coast of Shandong Peninsula. The coarse-grained sediments were mainly deposited at the river mouth due to the estuarine filtration and physical sorting. Meanwhile, there was a significant relationship among the modern sedimentation rate, the surface sediment grain size distribution and sediment transport pattern. The areas with coarser surface sediments generally corresponded low sedimentation rates because of strong erosion; whereas the sedimentation rate was relatively high at the place that the surface sediments were fine-grained. Furthermore, the grain-size trend analysis showed that the areas with fine-grained surface sediments such as the mud area in the central BS and the upper Liaodong Bay were the convergent centers of surface sediments, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident. [ABSTRACT FROM AUTHOR]

The Sansha Yongle Blue Hole is the deepest blue hole in the world and exhibits unique environmental characteristics. In this paper, Illumina sequencing and qPCR analysis were conducted to obtain the microbial information in this special ecosystem. The results showed that the richness and diversity of bacterial communities in the hole was greater than those of archaeal communities, and bacterial and archaeal communities were dominated by Proteobacteria and Euryarchaeota , respectively. Temperature and nitrate concentration significantly contributed to the heterogeneous distribution of major bacterial clades; salinity explained most variations of the archaeal communities, but not significant. A sudden increase of bacterial 16S rRNA, archaeal 16S rRNA, ANAMMOX 16S rRNA, nirS and dsrB gene was noticed from 90 to 100 m in the hole probably due to more phytoplankton at this depth. Sulfur oxidation and nitrate reduction were the most abundant predicted ecological functions in the hole, while lots of archaea were predicted to be involved in aerobic ammonia oxidation and methanogenesis. The co-occurrence network analysis illustrated that a synergistic effect between sulfate reduction and sulfur oxidation, and between nitrogen fixation and denitrification, a certain degree of coupling between sulfur and nitrogen cycle was also observed in the hole. The comparisons of bacterial and archaeal communities between the hole and other caves in the world (or other areas of the South China Sea) suggest that similar conditions are hypothesized to give rise to similar microbial communities, and environmental conditions may contribute significantly to the bacterial and archaeal communities. [ABSTRACT FROM AUTHOR]

Straits are both a choke point and passage through which material and energy are exchanged between two adjoining water bodies. Understanding the mechanisms that drive these exchanges therefore is vital to quantifying the water and sediment budgets in regional and global oceans. Here we present a study in which a novel, phase‐averaging method was employed to better estimate the net‐suspended sediment fluxes through the entire Bohai Strait, the only passage for the massive Yellow River‐delivered sediment to leave the enclosed Bohai Sea for the open Yellow Sea. In winter, the transport through the strait was nearly barotropic in waters well mixed by the energetic winter monsoons. The transport became primarily baroclinic (opposite directions between upper and lower layers) in spring due to stratification, especially in the southern part of the strait. Intermittent but frequent southerly winds in northerly dominated winters were responsible for a net westward sediment transport into the Bohai Sea, a finding contrary to a status quo view. Hence, previous studies in which these intermittent southerly wind busts were not included are believed to have overestimated the sediments export from the Bohai Sea. Plain Language Summary: Water and sediment transport through a strait (a natural and narrow waterway that connects two larger water bodies) is important for global oceanographic circulation and biogeochemical processes. The residual current is a continuous movement of seawater that plays an important role in sediment transport. Profiles of residual currents across the entire strait are indispensable for estimating these transports but extremely difficult to obtain especially in tidal coastal ocean. Here we present data from two cruises of repeated surveys that produced these residual current profiles across the Bohai Strait, with the help of a novel detiding scheme. The sediment flux through the Bohai Strait is in opposite directions between upper and lower layers in late spring but unidirectional throughout the entire water column in winter. Even intermittent southerly winds in northerly dominated winters can cause a net sediment import into the semienclosed Bohai Sea through most of the strait, which is different from the long‐held view of winter transport through the Bohai Strait. Key Points: Profiles of residual current across the entire Bohai Strait were surveyed for the first time using the phase‐averaging method (PAM)Intermittent southerly winds in northerly dominated winters caused a net sediment transport into the Bohai Sea through the straitThe sediment fluxes through the Bohai Strait were primarily baroclinic in late spring but barotropic in winter [ABSTRACT FROM AUTHOR]

Surface sediment samples from 15 stations around the present Huanghe (Yellow River) river mouth were collected before, during and after the Water-Sediment Regulation Scheme (WSRS) in 2010 for grain size analysis. Hydrographic surveys conducted simultaneously at stations along three transects off the river mouth during the WSRS in 2013 were used to investigate the dispersal and accumulation of the Huanghe sediment off the present Huanghe subaqueous delta. During the WSRS period, the diluted water from the river covered all over the study area within the surface layer, whereas high-concentrated sediment was found in the bottom layers and to be limited in nearshore area shallower than 12 m, indicating that the buoyant river plume was the main sediment dispersal pattern during the WSRS. At the early stage of the WSRS when large amount of clear water was released from the Xiaolangdi Reservoir, sediment eroded from the downstream riverbed in the lower reaches increased the median grain size of surface sediment at the river mouth. During the second stage when water discharge was reduced but sediment discharge was dramatically increased, the fine-grained sediment derived from the Xiaolangdi Reservoir mixed with the previously deposited coarser surface sediment, leading to the decreasing median grain size of surface sediment that approached to be poorly sorted. After the physical sorting from winter storms, the surface sediment was redistributed and varied regularly with water depth. As the median grain size of suspended sediment discharge to the sea has been significantly increased due to the WSRS, the river-delivered sediment mostly accumulated in the nearshore area, which effectively extended the subaerial delta and steepened the subaqueous slope off the present river mouth. [ABSTRACT FROM AUTHOR]