Search

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in millions of deaths and seriously threatened public health and safety. Despite COVID-19 vaccines being readily popularized worldwide, targeted therapeutic agents for the treatment of this disease remain very limited. Here, we studied the inhibitory activity of the scutellarein and its methylated derivatives against SARS-CoV-2 main protease (M

Marine aquaculture in semi-enclosed bays can significantly influence nutrient cycling in coastal ecosystems. However, the impact of marine aquaculture on the dynamics of dissimilatory nitrate reduction processes (DNRPs) and the fate of reactive nitrogen remain poorly understood. In this study, the rates of DNRPs and the abundances of related functional genes were investigated in aquaculture and non-aquaculture areas. The results showed that marine aquaculture significantly increased the denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) rates and decreased the rate of anaerobic ammonium oxidation (ANA), as compared with non-aquaculture sites. DNF was the dominant pathway contributing to the total nitrate reduction, and its contribution to the total nitrate reduction significantly increased from 66.72% at non-aquaculture sites to 78.50% at aquaculture sites. Marine aquaculture can significantly affect the physicochemical characteristics of sediment and the abundances of related functional genes, leading to variations in the nitrate reduction rates. Although nitrate removal rates increased in the marine aquaculture area, ammonification rates and the nitrogen retention index in the aquaculture areas were 2.19 and 1.24 times, respectively, higher than those at non-aquaculture sites. Net reactive nitrogen retention exceeded nitrogen removal in the aquaculture area, and the retained reactive nitrogen could diffuse with the tidal current to the entire bay, thereby aggravating N pollution in the entire study area. These results show that marine aquaculture is the dominant source of nitrogen pollution in semi-enclosed bays. This study can provide insights into nitrogen pollution control in semi-enclosed bays with well-developed marine aquaculture.

Estuarine systems are important sites of eliminating reactive nitrogen (N) delivered from land to sea. Numerous studies have focused on N cycling in estuarine sediment. However, the N elimination role of suspended sediments in estuarine turbid water column, which might provide anaerobic microenvironment for N loss, is rarely considered. This study examined the community dynamics and activities of denitrifying and anaerobic ammonium oxidation (anammox) bacteria in the water column of the turbidity maximum zone (TMZ) of the Yangtze Estuary, using molecular and 15N isotope-tracing techniques. Results showed that the anammox bacterial community was dominated by Candidatus Kuenenia and Candidatus Brocadia in the TMZ water column, while the main nirS-harboring denitrifiers were affiliated with Rhodobacterales. The denitrifying nirS gene was two orders of magnitude more abundant than anammox bacterial 16S rRNA gene, ranging from 1.77 × 105 to 1.42 × 108 copies l−1 and from 7.68 × 104 to 4.27 × 106 copies l−1, respectively. Compared with anammox, denitrification, with rates of 0.88 to 20.83 μmol N l−1 d−1, overwhelmingly dominated the N removal in the TMZ water column and was significantly correlated to suspended sediment concentrations (SSC). Based on the measured N removal rates, it was estimated that about 2.5 × 105 ton N was annually removed from the TMZ water column, accounting for approximately 18.5% of the total inorganic N (TIN) discharged from the Yangtze River. Overall, this study implies the importance of estuarine turbid water column in controlling N budget, and also improves the understanding of N loss mechanisms in estuarine TMZ systems.

The Holocene environmental evolution in coastal area, including deltas and estuaries, is vital to the Neolithic colonization in the eastern China. A 29-m long sediment core XL was obtained from the region between the Taihu Lake and Qiantang Estuary, and multiple analyses on the core sediments have been done to investigate the evolution history of the inner coastal zone of Hangzhou Bay during the Holocene. Six sedimentary facies are identified since the late Pleistocene, including the paleosol at the bottom, overlain by tidal-flat-channel complex (TFC), tidal-distributary-channel (TDC), inner estuarine basin (IEB), subtidal-to-intertidal-flat, and fluvial-plain facies. The TFC and TDC facies are dated to be formed before 8500 cal yr BP, featured by relatively coarse sediments, high magnetic properties and less abundant foraminifera, denoting the tide-influenced setting with large terrestrial inputs. The IEB facies characterized by the most abundant foraminifera fossils and the lowest sediment magnetic properties, is inferred to be deposited during the maximum flooding period between 8500 and 7900 cal yr BP. The branch estuary was then infilled by local sediments with a shallowing-upward subtidal-to-intertidal sequence during 7900–4300 cal yr BP. At last the fluvial plain system developed since no later than 4300 cal yr BP, favouring the rapid development of Neolithic cultures in the region.

How flow mixing process influences the wetlands of the Yangtze Estuary is still poorly understood. Hydrological fieldwork was conducted on five vessel-anchored sites (S1-S2; M1-M2-M3) near the major wetlands of the Yangtze Estuary offshore (121°57′-122°30′E, 30°50′-31°23′N) on May 8-11 2004, to examine the dynamics of neap tides in the non-flood season of the Yangtze (∼24, 700 m3s-1 at Datong) and their impacts on adjacent wetlands. Based on the measurement of the acoustic Doppler current profiler (aDcp), direct-reading current meter and optical backscattering sensor (OBS-3A), two flow patterns were revealed: 1) well mixing flow pattern caused by the turbulent tidal currents, and 2) weak mixing flow pattern resulted by the estuarine circulation in the North Port of the estuary. The characteristics of such different flow patterns were analyzed and resultant sediment dispersals were discussed in relation to the adjacent wetlands. It is suggested that the estuarine circulation might be the important process to nourish the eastern wetland of the Yangtze Estuary which has been neglected before.

River-lake systems, crucial to both the ecological environment and societal development, have been affected by increasing anthropogenic activities in addition to climate and environmental changes. Here, annual water discharge and sediment load data (1956–2017) and rainfall data (1960–2016) from Dongting Lake in the middle catchment of the Yangtze River were analysed at four major inlets and one outlet, and their connections with lake level variations were evaluated using multiple analytical methods. The results show that minor fluctuations were found in rainfall and discharge during the study period, but the sediment load entering Dongting Lake decreased significantly from 231 mt/year (before 1969) to 123 mt/year (1970–2002) and then 17 mt/year (after 2003, post TGD). The variation in the sediment was mainly induced by increasing anthropogenic activities in the lake system. During period 1 (before 1969), human impact was weak compared to the dominant natural forces. However, anthropogenic force showed an increasing contribution to the loss of sediment load since then, as it increased from 43.0% (1970–1987, post cut-off engineering) to 64.8% (1988–2002, post Gezhou Dam) and extended to 90.2% during 2003–2017 (post TGD). Nevertheless, continuous sediment accumulation over the past decades in the lake has caused a rising water level. During period 1, high sediment input contributed to an average annual increase of 13.96 cm in the lake level, but it decreased significantly to 1.94 cm year−1 during 1970–2002 due to intensive anthropogenic regulations. Since 2003, the completion of the TGD intercepted abundant sediment, eventually leading to a shift from net deposition to net loss of the sediment budget in Dongting Lake, and consequently, the lake level fell. In the future, if the net sediment supply was kept below ~18 mt/year, the lake level would continue to fall, causing severe problems to the lake ecosystem, especially during drought years.

Well-known for its intensive land-sea interactions and the brilliant Neolithic Cultures, the South Hangzhou Bay (SHB) of eastern China has been the focus of early agricultural rise in adaptation to coastal environmental change. In this study, geological records from sediment cores were integrated with archaeological findings in SHB to establish the linkage between coastal geomorphological processes and Neolithic occupation since the Holocene. It showed that the Holocene geomorphological evolution of SHB was inherited from the south wing of the Late Pleistocene Qiantang incised valley. During ca.10,000–7600 cal yr BP, the paleo-incised valley was inundated and infilled by marine transgressive deposits, forming an estuary. Then coastal progradation started and gradually formed the periphery of SHB. Noticeably, freshwater wetlands firstly occurred at the apex of SHB, enabling foragers to settle down and fostering the Kuahuqiao Culture and rice exploitation (7800–7400 cal yr BP). In the semi-closed Yaojiang Valley (YJV), east of SHB, alluvial plain developed after 7800–7600 cal yr BP with coastal progradation, providing a habitat to favor the early arrivals and later became the centre of the Hemudu Culture (7000–5000 cal yr BP). Meanwhile, the Neolithic sites sporadically occurred off the YJV due to the existing inundation. The coastal progradation slowed down ca.5000–2500 cal yr BP, in association with decreased sedimentation rates. In the last 2500 years, the Shaoxing Plain and the Cixi Plain of SHB showed rapid progradation resulting from increasing sediment input and intensive reclamation. The diverse geomorphological processes of SHB were modulated by the combination of Holocene sea-level changes, sediment input and the inherited local topography. The Neolithic migrations were in phase with landscape transformations and gradual formation of coastal plain since the Mid-Holocene, facilitating the Neolithic subsistence transition from hunting-gathering to rice farming and fostering the brilliant Neolithic cultural sequence in SHB.

The environmental impact of the Three Gorges Dam has been a subject of vigorous academic, political and social debate since its inception. This includes the key issue of post-dam river channel erosion, which was predicted by the feasibility study to extend to the river mouth. In this paper we examine the geomorphic response of the channel of the middle Yangtze for 660 km downstream of the dam. Using data on channel characteristics, bed material and sediment transport, we show that in the decade following the dam closure, pre-dam seasonal erosion has been replaced by year-round erosion, a pattern most marked at the upstream end of the study area. The sediment carrying capacity of the river channel has been largely reduced below the dam. The locus of bed scour has moved progressively downstream, ceasing as the bed material became too coarse to be transported (e.g. D50: 0.29 mm pre-dam coarsened to 20 mm below the dam by 2008). About 400 km below the dam there is a reduction in channel slope that changes the sediment carrying capacity from 0.25 kg m−3 to only about 0.05 kg m−3, which is insufficient to move bed sediment. The new long-term hydro-morphological equilibrium that will be established in this section of the middle Yangtze will prevent the further incision downstream initiated by the Three Gorges Dam. The results suggest that the full extent of adverse environmental impact predicted by the pre-dam studies will not eventuate.

The well-14C–dated sediment core HM retrieved from the Yangtze River mouth was used to reconstruct the Holocene sedimentary–ecological complex of its incised valley. The complete Holocene sedimentary facies that were exclusively formed in the valley and evidenced by bio-geochemical measurement, showed the Latest Pleistocene fluvial facies to the Early-Holocene marine facies, and the Middle-Late Holocene deltaic facies. The established Holocene stratigraphic framework consists of 3 (I-III) infilling phases, of which phase I demonstrated the most rapidly infilling with coastal sediments into the valley (1.0 cm/yr), driven by the Early Holocene marine transgression. The remarkably low sedimentation rate of 0.1 cm/yr of phase II to the relatively low rate of 0.7 cm/yr of phase III occurred during the Middle-Late Holocene, reflecting sediments transported from river basin to directly fill in the valley along with deltaic depocenter shifted seawards as retrogressive processes. In addition, our microfossil (foraminifera and diatom) spectra displayed 3 distinctive biological stages with related sedimentary–ecological implications. During the Early Holocene, there were remarkably high numbers of diatom communities but few foraminifera, then followed a zone of less abundant microfossils between ca. 9.0–5.0 ka. After this time, richer foraminiferal communities appeared but diatoms were less abundant. The massive sediment infilling in the Early Holocene in the deeper (>60 m) incised valley would suppress benthic foraminiferal development, most likely due to anaerobic conditions in the lower water column. However, the flourishing diatom communities persisted in the brackish marine water associated with sea-level rise. The zone with fewer microfossils corresponded generally with the Middle Holocene sandy ridge formation at the core site, leading to poorer bio–preservation. After ca. 5.0 ka, foraminiferal communities gradually became adapted to the reduced salinity of the estuarine water associated with the deltaic progradation, though this appears not to have supported the diatom communities.

Phytoplankton communities have been changed recently in the giant and dynamical China's Yangtze Estuary primarily due to intensifying human activities and climate warming. A large amount of riverine material fluxes into the estuary has been significantly altered in their balances, leading to a change of phytoplankton from siliceous- to non-siliceous-dominated communities. We established inter-linkages of changing phytoplankton communities to various controlling factors and revealed that this bio-transformation occurred around 2000. Before this time, there were fewer dominant diatom taxa, but since then more have emerged as the variation, along with many dinoflagellates driven by the altered riverine nutrient ratios of N:P:Si delivered to the estuary, averagely from 75:1:946 (1960s–1970s) to 86:1:272 (1980s–1990s) and to 102:1:75 (2000s–2010s). Excessive nitrogen and lowering dissolved silicate (DSi) has exerted the key environmental stress on such a bio-transformation. Skeletonema spp. the most popular in diatoms has lost its dominance by ca 50% since the early 2000s. We further convinced the long-increasing dissolved inorganic nitrogen (DIN) (presently, 150 μmol L−1, maxi., ca 3.5 folds more than that of 1960s–1980s) to meet the long-decreasing DSi (ca 60% off since 1960s) at 110 μmol L−1, around 2004 (Redfield ratio balance 1:1) as a threshold. Since then, this balance has broken, serving as an engine for driving the bio-transformation. Phytoplankton development did not fully follow the Redfield ratio, especially during the algal blooming season, as revealed by the scattered distribution of dinoflagelate:diatom vs. DIN:DSi when DIN:DSi >1. This implies a much more eutrophic setting attributable to over-loaded nitrogen concentration in the Yangtze Estuary. Besides, the lowering sediment flux in the estuary (lowest after 2003 when the Three Gorges Dam closed) and the rising sea surface temperature (SST) in recent decades has enhanced the bio-transformation. Consequently, the estuarine water tends to be more acidic than before, manifested by continuously lowering of pH and dissolved oxygen (DO) in the study area.

Many of the world’s major cities are expected to face significant water shortages in coming decades, largely due to increased demand arising from economic and population growth. In this paper, we estimate the effects of economic and population growth on future public water needs in Shanghai, one of the world’s megacities. Despite significant investment in a new reservoir and associated supply systems, and its location at the estuary of one the world’s major rivers (the Yangtze), it is widely believed that Shanghai is vulnerable to water shortages, though the causes of this have hitherto not been systematically examined. Our method of estimating future water needs involves extrapolation from past trends and principal component analysis regression, and from the experience of comparable cities around the world, to construct three scenarios of future GDP and population growth and associated water needs. Our analysis shows that under various scenarios, by 2050 the difference between demand and present supply capacity will range between 1.6 and 6 million m3/day and that the critical constraint to meeting future demand is treatment capacity, which will need to increase by between 35 and 83% beyond present levels. We discuss four options for managing the estimated deficit between future water demand and supply in Shanghai.

Environmental degradation in the Changjiang Estuary has recently become a global topic, given its proximity to Shanghai with a population >23 million. Intensification of human activities affecting the river basin is responsible for this degradation. Dam construction has cut off ca. 2/3 of the sediment flux to the sea, ca. 60% of the dissolved silicate load (DSi) has been retained in the reservoirs, while total phosphorous (TP) and total nitrogen (TN) transport to the sea are many times more than they were a few decades ago. Under such circumstances, details of the estuarine degradation remain poorly understood. This study uses sedimentary biological silicate (BSi) and total organic carbon (TOC) as environmental proxies to reveal the process-response of such degradation since the 1950s. Our results demonstrate the spatial differences of such degradation. The inner zone of the estuary used to be highly turbid, but presently has increasing diatom (BSi) and primary production (TOC), due to lower suspended sediment concentration (SSC) in relation to dam construction. In contrast, increasing riverine dissolved inorganic nitrate (DIN) and dissolved inorganic phosphorous (DIP) input (up to 2–5 times) and decreasing DSi provide a unique setting, with an excess in N and P, which catalyzes non-diatom algae in the less-turbid middle zone of the estuary. These are reflected by decreasing BSi and BSi/TOC since the 1950s, together with an increase of TOC of 20–40%. In the outer zone of the estuary, increasing DIN, DIP, and sea surface temperatures (SSTs), have resulted in the increase of diatom biomass by 15–20% and the growth of primary production by 30–60% since the 1950s. But the drastic decrease in DSi, Si/N, and Si/P depresses the ability of diatoms to develop, resulting in a reduction of 5–10% diatom proportion (BSi/TOC) since the 1930s. This study improves the understanding of the changing estuarine ecosystem in response to global change.

Summary Much has been written on the hydrology of the Yangtze River in China, especially since the construction of the Three Gorges Dam. Given the range of views in the literature on the impacts of dams and other natural and anthropogenic activities in the catchment on monthly flows, we here set out to analyse the behavior of monthly flows over the period of record 1955–2014. In the literature, the Three Gorges dam has been singled out for particular comment, mostly adverse. In this paper we analyse trend in temperature, precipitation and discharge of the Yangtze River at the monthly time scale over a period that includes the 11 years since the Three Gorges Dam came into operation. The results show that for the upper basin, there has been a marked increase in discharge in the low flow months of January to March that began abruptly in 2003 and an abrupt decrease in flow in October at the same time. Similar changes are found for discharge from the lower basin but in that case the changes have occurred gradually over the period of record. These changes are the outcome of the operation of hydroelectric and flood control dams that have been built continuously in the lower basin since 1955 while in the upper basin the building of the Three Gorges Dam began a phase of rapid dam building not seen in the lower basin. The decreased flows in the late summer and autumn are not of sufficient magnitude to cause any problems for navigation or water supply. The enhanced flows in the winter low flow period are beneficial in that they reduce the likelihood of salt water intrusions in the estuary adversely affecting the supply of freshwater to Shanghai.

How the Yangtze delta responds to riverine sediment decline has become a hot research topic and an urgent issue to be addressed, especially after the impoundment of the Three Gorges Dam in 2003. This study investigated sedimentary features through the sediment granularity of surficial samples and short cores over the entire Yangtze subaqueous delta, aiming to better understand the spatial response of the subaqueous delta to sediment supply decline and local hydrodynamic adjustment of the estuary. The results show that four sedimentary zones of estuarine sand bar (Zone I), prodelta (Zone II), delta-shelf transition zone (Zone III) and residual sand (Zone IV) are distributed from the estuary to the shelf, characterised by first fining from zone I to zone II, and then coarsening from zone II to zone IV on grain size of surficial sediments. In the past few hundred years, the subaqueous delta has been generally prograded seaward following this sedimentary system spatially, manifested by generally fining upwards in the cores of the main subaqueous delta. However, sediment coarsening occurs on the top of the cores in the delta-shelf transition zone (Zone III), implying a recent retrogradation process. Based on the results of 210Pb and 137Cs, the sedimentary transition from progradation to retrogradation occurred since 1950s and was intensified after 1980s in the north part of Zone III, mainly caused by channel shrinking of the North Branch and riverine sediment decline. Comparatively, such a sedimentary transition is not significant in the south part of Zone III. But it is worth noting that surficial coarsening in the core (of the south part of Zone III) is probably related to drastic sediment decline since 2003 when the Three-Gorges Dam closed, which means that the Yangtze subaqueous delta has probably been in a full sedimentary transition. The sedimentary transition of the north subaqueous delta can provide an insightful reference for the sedimentary response of the Yangtze delta to further decline of sediment supply in the future.

South Hangzhou Bay (SHB) in eastern China is one of the regions where agriculture began in the early Holocene. To better understand how farming-based societies developed in this region, we examined pollen, charcoal, foraminifera and grain size information of a well-dated sediment core (YJ1503) in the Yaojiang Valley (YJV). Pollen assemblages show that before 8600 cal yr BP, Pinus, Quercus, Juglans and Pterocarya woodlands were dominant. During ca.8600–8400 cal yr BP, abundant foraminifera suggest a transient marine incursion. Although the former woodland species re-established during 8400–7600 cal yr BP, freshwater algae and dinoflagellates indicate a transition to brackish environments. Two peaks of charcoal at around 8200 and 7800 cal yr BP, are possible early signs of human occupation that pre-dated the Hemudu Culture. After 7600 cal yr BP, an increase of salt-tolerant herbs including Chenopodiaceae, Cyperaceae and Poaceae (

This study, on the basis of ca. 50-year hydrological data (discharge, salinity, and tides level), assesses the spatiotemporal distribution of freshwater sources for Shanghai, with a population of 23 million in the Changjiang River estuary. These are threatened by saltwater intrusion, a natural process that is however exacerbated by water transfer projects, the Three Gorges dam in the upper basin, and the sea level rise in the estuary. The historical relationships among discharge, salinity, and the duration of saltwater intrusion were established quantitatively and demonstrate that (1) the lower is the river discharge, the higher is the salinity and the longer is the residence time of saltwater in the estuary, and (2) the threshold value of the river discharge for salinity intrusion impacting the freshwater supply is 15,000 m3 s− 1 discharge. Based on this, we estimate that freshwater will be unavailable from the Qingcaosha reservoir every 10 years from about 2040, that is, in the near future, during the extremely low flow season for periods of up to 80–126 days, which would dwarf against the remediation plans for the freshwater supply in the reservoir. Remedial measures are necessary to prevent this possible event.

This paper assesses the impacts of the Three Gorges Dam, the South–North Water Transfer Project and other water abstractions on the probability of long-duration salt intrusions into the Yangtze River estuary. Studies of intrusions of saltwater into estuaries are typically constrained by both the short duration of discharge records and the paucity of observations of discharge and salinity. Thus, studies of intrusions of saltwater into estuaries typically seek to identify the conditions under which these intrusions occur, using detailed observations for periods of 20–60 days. The paper therefore first demonstrates a method by which to identify the conditions under which intense intrusions of long-duration occur and then applies that method to analyse the effect of the three projects. The paper constructs a model of the relationship between salinity and discharge and then employs Monte Carlo simulation methods to reconstruct the probability of observing intrusions of differing intensities and durations in relation to discharge. The model predicts that the duration of intrusions with chlorinity ≥ 250 mg L−1 (or ≥ 400 or 500 mg L−1) increases as the number of consecutive days with discharge ≤ 12 000 m3 s−1 (or ≤ 8000 m3 s−1 increases. The model predicts that in 1950–2014, the number of consecutive days with chlorinity ≥ 250 mg L−1 averaged 21.34 yr−1; if the three projects operate according to their normal rules, that average would rise to 41.20 yr−1. For a randomly selected year of discharge history from the period 1950–2014, under normal operating rules for these projects the probability of an intrusion rises from 0.25 (for 30-day intrusions) or 0.05 (for 60-day intrusions) to 0.57 or 0.28, respectively.

Shanghai is located on the world’s third largest river (by volume).Yet it faces therisk of shortages of drinking water. Many decisions and environmental charac-teristics have contributed to this threat. First, Shanghai has become dependent onwater brought into the municipality by rivers. Second, it has become increasinglyreliant on water from the Changjiang (Yangzi River), principally in order tocontrol the levels of pollution in the water that enters its treatment plants. Third,for reasons associated with inter-provincial administrative arrangements, thecity’s water intakes are located within the municipality, within the estuary zoneand subject to tidal intrusions of salt water. Fourth, at high tide and when theChangjiang’s discharge is low, salt intrudes far into the estuary, beyond thecurrent water intakes. If sea levels rise, these intrusions will become more pro-nounced. Fifth, large-scale central government infrastructure projects (such asdams and the South-North Transfer) are altering the hydrological characteristicsof the river. Such projects raise the probability of salt water intrusions into thewater intake zone. The Shanghai and central governments have thus made a seriesof decisions that, taken together, have led the municipality to rely on a source ofdrinking water that is increasingly unreliable and subject to the risk of shortagesdue to salt water intrusions. Why these decisions have been made – independently– is an important problem for those who would understand the provision of waterfor cities and the practical efficacy of Chinese governance systems.KEY WORDS

The densely-populated mega-city of Shanghai relies increasingly on freshwater from the Changjiang estuary (70% now). However, this strategy is facing potential threats due to extensive water diversion in the lower Changjiang basin and future sea-level rise. Given this, the present study evaluates the ability of Shanghai to source its water from the estuary, especially in the dry season. Flow 0.45 for 20–65, 75–90 and 120–128 days (in 2020, 2030, and 2040, respectively), for extreme low-flow conditions. These periods exceed the present 68-day maximum freshwater storage in Qingcaosha reservoir, which is meant to secure freshwater for Shanghai in the future. Urgently countermeasures are needed to secure the Shanghai's water in the future.

Summary The catchment of the Yangtze River in China has a long history of human occupation and the intensity of human impacts has increased markedly since economic reforms began in the late 1970s. In order to try to assess the impact of these changes on the hydrology of the river, we analyse both the annual flows of the Yangtze River and annual temperature and precipitation for the Yangtze catchment for the period 1955–2011 and for the three sections of the catchment, Upper, Middle and Lower as defined by the location of the gauging stations at Yichang, Hankou and Datong respectively. Mean annual temperature increases downstream from 12.7 °C in the Upper to 16.0 °C in the Lower section. A significant increasing trend in mean annual temperature is detected over the period 1955–2011 in the whole catchment and all subsections. Mean annual precipitation for the whole catchment is 1045 mm ranging from 859 mm in the elevated Upper section to 1528 mm in the Lower section. Precipitation variability is low by world standards with an annual Cv of 0.066. Using the Mann–Kendal and Rank Sums tests we do not find any trend in precipitation in the catchment. Mean annual runoff for the whole catchment is 515 mm ranging from 421 mm in the Upper Catchment to 838 mm in the Lower Catchment. Runoff variability is also low by world standards with an annual runoff Cv of 0.129. For the Middle Catchment we find a small but statistically significant increase in runoff and the runoff ratio over the period 1955–2011, possibly caused by change in the nature of the surface due to accelerated urbanization post 1980 and increased area of water storage. Overall, annual runoff in the Yangtze River shows little response to the major changes occurring in the basin. In a multiple correlation analysis of discharge, precipitation, dam volume, population and GDP, only precipitation is significantly correlated with discharge, explaining 80% of the variance. Widespread reporting of the impact of development on the annual water yield of the Yangtze, especially the impact of dams and notably the Three Gorges Dam, are not supported by this analysis.

Shanghai is experiencing drinking water supply problems that are caused by heavy pollution of its raw water supply, deficiencies in its treatment processes, and water quality deterioration in the distribution system. However, little attention has been paid these problems of water quality in raw water, water treatment, and household drinking water. Based on water quality data from 1979 to 2016, we show that microbes (TBC), eutrophication (TP, TN, and NH3−N), heavy metals (Fe, Mn, and Hg), and organic contamination (chemical oxygen demand (COD), detergent (Linear Alklybenzene Sulfonate, LAS), and volatile phenols (VP)) pollute the raw water sources of the Huangpu River and the Changjiang (Yangtze River) estuary. The average concentrations of these contaminants in the Huangpu River are almost double that of the Changjiang estuary, forcing a rapid shift to the Changjiang estuary for raw water. In spite of filtering and treatment, TN, NH3−N, Fe, COD, and chlorine maxima of the treated water and drinking water still exceed the Chinese National Standard. We determine that the relevant threats from the water source to household water in Shanghai are: (1) eutrophication arising from highly concentrated TN, TP, COD, and algal density in the raw water; (2) increasing salinity in the river estuary, especially at the Qingcaosha Reservoir (currently the major freshwater source for Shanghai); (3) more than 50% of organic constituents and by-products remain in treated water; and, (4) bacteria and turbidity increase in the course of water delivery to users. The analysis presents a holistic assessment of the water quality threats to metropolitan Shanghai in relation to the city’s rapid development.

Although archaeological findings show the synchronous collapses of major well-documented Chinese Neolithic cultures around 4000 cal. yr BP, the driving mechanism for the phenomenon is still unclear and debatable. Spatial climatic features in China spanning this time period suggest a generally cold-dry setting. This is evidenced by 130 well-dated geological records at 97 sites located in climatically and topographically diverse regions, with occurrences of some extreme hydrological events like severe floods in the Chinese Loess Plateau, and in basins of the lower Yellow River and the middle-to-lower Yangtze River. The weakening of the Asian Summer Monsoon (ASM) since the mid-Holocene would have made Neolithic subsistence living unfavourable by decreasing the warmth and wetness in arid and semi-arid regions. However, it might not have been the sole factor that destroyed the Neolithic cultures in the vast territories of China ca. 4000 cal. yr BP. Environmental alterations in the major cultural territories of China reacted in response to precipitation anomalies caused by high variability of the ASM and the westerlies, which were modulated by centennial- to inter-annual- scale driving factors such as solar insolation, the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO) and El Nino-Southern Oscillations (ENSO). This most likely accounted for the nearly synchronous Chinese Neolithic cultural collapses.

The Digital Elevation Model (DEM) based on the historical sea-charts and on-site hydrological records were used to examine the morphological change of the Elbe River estuary. The results show that siltation predominated in the tidal flat in the northern estuary, with a net siltation rate of 1.8 cm·a−1 during 1927–2006. In contrast, a continuous erosion prevailed in the main river channel, south of the estuary, with a net erosion rate of 2.5 cm·a−1 in the same time. In addition, a seaward shift of the estuarine island has happened with the old island coalescing to the northern tidal flat and new one emerging through siltation process. The tidal asymmetry via ebbing flow (maximum at 140 cm·s−1, and average at 76 cm·s−1) prevailed in the tidal flat, meaning continuous aggradation northwestward, while flooding flow (maximum at 100 cm ·s−1, and average at 67 cm·s−1) dominated in the main river channel with deepening thaweg at south, showing a landward sedimentation via the tidal pumping processes. This dextral extension of the estuarine morphology is due to the Coriolis force, leading to the inconsistent directions of in-out flows, which enables to facilitate the estuarine siltation. Human dredging prevailing in the estuary has dramatically altered the nature of the silted river channel to erosional since the last century. This is characterized by a net erosion rate of 3.2 cm·a−1 derived from the DEMs mapping, but only partially accounting for the dredging amount of 1994–2006, when the total dredging volume was 67 × 106 m3, equal to 5.9 cm·a−1.

This study gives a thorough assessment of the occurrences of dissolved inorganic nitrogen (DIN) in the Yangtze River in the past half century. The results have shown that nitrogen fertilizer, a major DIN source, has been replaced by domestic sewage in the last decade, which has dramatically driven up DIN loads in the Yangtze. DIN concentrations showed a rapid increase from − 1 in the 1960s to nearly 1.5 mg L − 1 at the end of the 1990s. Since then DIN has remained steady at ca. 1.6–1.8 mg L − 1 . A significant relationship between the historical DIN record at the downstream gauging station (Datong) and nitrogen (N) sources in the Yangtze River basin is established using principal components analysis. This allows us to apportion DIN loads for the year 2007 (the most recent year of measured DIN data available) to various N sources, listed here in order of weight: sewage (0.391 million tons); atmosphere (0.358 million tons); manure (0.318 million tons), N-fertilizer (0.271 million tons). Therefore, we estimated that a DIN load of 1.339 × 10 6 t was delivered to the lower Yangtze and its estuarine water in that year. We established scenarios to predict DIN concentrations in the lower Yangtze at 10 year intervals to 2050. For a dry year (20,000 m 3 s − 1 ) DIN concentrations would range from 2.2–3.0 mg L − 1 for 2020–2050. This far exceeds the 2.0 mg L − 1 defined on the Chinese National Scale as the worst class for potable source water. The scenario results suggest that upgrading the sewage treatment systems throughout the basin will be an effective way to help reduce DIN concentrations to less than 2.0 mg L − 1 in the lower Yangtze. This would save the Shanghai megacity from the increasing threat of heavily polluted water sources, where > 23 million people are at present dependent on the Yangtze estuary for 70% of their freshwater intake.

Big cities are often said to have big water problems, and Shanghai is no exception. In this paper, we examine and compare the influence of the major factors that give rise to the risk of water insecurity in Shanghai. There is an extensive and diverseliterature onthese issues, dealtwith in isolation, and here, we provide a synthesis of the litera- ture, together with our own assessments and calculations, to assess what are the risks to Shanghai's water supply and what is our degree of confidence in this assessment. We describe the systems that supply water to the city, and past and future changes in the systems, including changes in the glaciers that supply some water to the river, changes in cli- mate, changes in land use, the construction of dams, and water diversions. We show how, at the same time as Shanghai is increasing its dependence on the Yangtze river, waterdiversionsandsealevelriseareincreasingtheriskthat this water will be too saline to consume at certain times of the year. This analysis suggests that most of the major drivers of the risk to water security in Shanghai are within the power of environmental managers to control.

article A survey was conducted to examine river bedforms using side-scan sonar, sub-bottom profiler and an Acous- tic Doppler Profiler in the middle-lower (mid-lower) Changjiang (Yangtze) River (downstream of Wuhan), China, during August 14-20, 2003 when the discharge was 27,000-36,000 m 3 s −1 . The results show bedforms of a range of sizes occur in the channel and their heights and lengths follow an exponential correlation below Flemming's maximum line. Not all bedforms were formed under the flow conditions experienced during the survey, as shown by comparison to three existing models in the literature. Small-scale bedforms with a length b60 m, defined as flat bed, mega-ripple and small dune in the present study, are mostly in equilibrium and are probably formed under the existing flowconditions.The large dunes witha lengthofN60 m are not in equilibrium and are believed to be the relicts of previous largedischargesnow undergoing adjustment. Different bedform types occur in the five riverreaches inthis section of the Changjiang (Wuhan-Tianjiazhen, Tianjiazhen-Anqing, Anqing- Maanshan, Maanshan-Jiangyin and Jiangyin-estuary downstream). In the narrow and single channel reaches above Anqing, large/small dunes are limited to the channel with higher water surface slope where stream power is strong enough for riverbed sediments to be moved frequently. In the downstream reaches be- tween Anqing and Jiangyin, characterized by anabranching channels, small-scale bedforms superimposed on large dunes occur widely due to intensive riverbed sediment transport from frequent diverging/converging flow during both floods and low-flow periods. Mega-ripples and flat beds prevail in the lowermost channel

Development of the Yangtze delta during the late Holocene, and its relationship to human activities in the drainage basin, was analyzed using data from 16 cores collected from distributaries to the prodelta. We used AMS14C dating and digital elevation model (DEM) data from marine charts from 1864 through 2005 to determine ages and estimate sediment accumulation rates. The results demonstrate that the latest major subaqueous delta front formed within the past c. 0.8 cal. ka and features remarkably high accumulation rates (1—4 cm/yr) in comparison with those of previous delta fronts. We also examined the temporal distribution of grain size and magnetic susceptibility in all 16 cores. Results show soil-derived superparamagnetic (SP) minerals generally occur, and even dominate, in the recent ( c. 1.7 cal. ka) Yangtze delta fine-grained sediment, as shown by high values of frequency-dependent magnetic susceptibility (both χFDand χFD%). Rock-derived magnetite dominates generally in the river channel and delta front sand bodies as a result of hydrodynamic sorting, but is also enriched in both fine and coarse-grained sediment formed more recently ( c. 0.8 cal. ka), as evidenced by rising values of mass specific magnetic susceptibility (χLF). SP grains were deposited as early as the late Neolithic, possibly indicating local deforestation associated with the use of fire at that time. We suggest major deforestation in the drainage basin started c. 1.7 cal. ka BP, and intensified after c. 0.8 cal. ka BP when both χLFand χFDshow the highest values. We therefore conclude that upland deforestation and cultivation as a result of the migration of human populations from northern China since c. 1.7 cal. ka BP resulted in increased sediment discharge of the Yangtze and played an important role in recent delta construction.

This paper examines the morphological development of the Yangtze River mouth, which has been diverting southeasterly (dextrally), according to historical (150 years) chart-based digital evolution model and on-site measured tidal flow data. We reveal a significantly narrowing of the northern river mouth branch from formerly >30 km wide to presently 10 km wide due to rapid siltation. Net siltation there, however, decreases gradually, which largely contrasts with the fact that the siltation has shifted to the southern river mouth area, as shown by many newly-emerged estuarine islands, sandy shoals and bifurcated branches. Our data have further demonstrated that the ebb flow that dominates in the study area changes its direction gradually from east to southeast from the inner to outer river mouth area, and its duration is much longer than the flood flow in the inner river mouth area, but nearly equal at the river mouth area. Accordingly, the sediment transport pathway has been diverted from east to southeast. We examine whether the Coriolis Force could explain the dextral diversion of the ebb flow and the altered morphodynamical processes. Although too weak to strengthen the tidal flows, the Coriolis Force can drag the ebb flow southeasterly, and so influence sediment transport paths at the estuarine scale. The Coriolis Force is limited in the inner river mouth, but substantial at and in the outer river mouth area when gradually free of estuarine topographic constraints. The Coriolis Force causes an offset in propagation of in-out flow directions at the river mouth area to form a slack water setting prone to estuarine siltation. Using the present approach also enables explanation of the morphological development of the Holocene Yangtze delta-coast that extends to the southeast. Copyright © 2010 John Wiley & Sons, Ltd.

In 2000 and 2003 before the closure of 3-Gorges Dam, numerous sediment samples were taken from the middle-lower Yangtze River channel to examine sediment transport processes and associated hydromorphological nature of the river. Analytical results show that the riverbeds consist mostly of medium to coarse sands and gravelly sands, and fine sand occurs locally, especially near the river coast. The results further indicate a downstream fining trend in riverbed sediment from Yichang to the river mouth, totaling about 1900 km long with 12 sediment zones (I-XII). These were identified as alternate coarse- and fine-grained sediment on the riverbed, although the zonation of I–III below Three-Gorges Dam site is weaker. The mode of sediment transport in the river is dominated by saltation (20–80%), followed by bed-load transport with 3–15%; transport by suspension is quite low. Grain-sizes associated with hydrological parameters have greater values in the Jingjiang Reaches (from Yichang to Chenglingji; unit stream power: 5–18 N m − 1 s − 1 , boundary shear stress: 14 Nm − 2 and mean flow velocity: 2–3.2 ms − 1 ), whereas the values obtained from Chenglingji downstream are considerably low ( − 1 s − 1 , 1–4 Nm − 2 and − 1 ). These values, when compared with on-site measured velocity of the ADP flow column, revealed the erosive riverbed sediment transport in the Jingjiang Reaches, and the accumulative riverbed transport downstream, from Wuhan to the river coast. Hydrological parameters together with distribution of grain-sizes indicate a coarsening riverbed in the Jingjiang river, largely because damming peaked since the last half-century. This corroborates the weakening sediment zonation in the Jingjiang Reaches, which is expected to extend further downstream towards the river coast in response to the potential impact of 3-Gorges Dam in the coming decades.

Six bathymetric transect profiles were drawn from the nautical charts of 1942, 1962 and 1992 to show that the nearshore seabed remained unstable during the recent 50 years in the middle channel of the eastern entrance to the Qiongzhou Strait, South China Sea. Our results demonstrate that the multi-year averaged seabed aggradational rate was 25 cm/a and erosion rate was 12.5 cm/a. Lateral migration rate of the sea bedform identified from the historical contours was about 100 m/a in the SE direction. Bedform measurements were made using GPY Shallow Seismic Profiler in 1994 in the study area. The records revealed four types of distinctive bedforms that were composed of fine and medium sands. The average spacing of large and small-scale sand dunes is 416 m and 144 m and the average height remains 8.8 mand 4.9 m. The spatial and temporal equilibrium-range spectra of numerical bedform records were applied to estimate short term celerity of bedform movement. Results indicate that large and small dunes migrated at an average celerity of 0.02 cm/hr eastward and 0.09 cm/hr westward in the calm sea weather, while their celerity can reach 53 cm/hr eastward during typhoon season and is only 0.008 cm/hr westward when NNE winds prevail. The results also show that the larger the temporal and spatial scale is, the smaller the bedform movement celerity appears. On the other hand, the smaller-scale bedform celerity of the present study is much greater than that of flume, empirical and theoretical data, but close to the wind tunnel and field-measured data of similar grain size.

Variations of dissolved silicate (DSi) flux in the Yangtze River have caused great concern among scientists. Analysis of spatial and temporal variations of DSi indicates that the distribution of DSi concentration (DSiC) is closely related to the occurrence of bedrocks in the river cathchment. On average, the upper Yangtze River and Dongting and Poyang Lake of the middle Yangtze basin serve as the major DSi sinks, retaining 3.39 × 104 t y−1, 5.59 × 104 and 2.51 × 104 t y−1. The middle and low Yangtze River remains DSi sources, emitting 2.85 × 104 and 2.48 × 104 t y−1, respectively. Geochemical data at Datong hydrological station recorded the flux of nutrients entering into the sea during the flood season, i.e. 74% for DSi, 73% for DIN (Dissolved Inorganic Nitrate) and 68% DIP (Dissolved Inorganic Phosphate). The yearly DSiC and flux show a sharp decrease since 1950s. The mean DSiC was 109.47, 91.09, and 77.56 μmol l−1 in the 1960s, 1970s and 1980s, respectively. The mean DSi fluxes for the same time period were 2.72, 2.23, and 2.13 × 106 t. A PP (primary productivity) model estimates 3.14 × 105 t of DSi (13.08% of the annual mean flux entering into the sea) was fixated within the 162 reservoirs in 2002. On the other hand, DIN and DIP concentration and flux have increased greatly since the 1950s. Fertilizer application peaked after the 1980s can interpret these high DIN and DIP. A sharply decreasing DSi flux and quickly increasing DIN and DIP fluxes into the sea have enhanced eutrophication and caused frequent harmful algal blooms in coastal waters. On average, red-tide frequency was from 0.04 during 1933–1979 to 7.0 during 2000–2002. The Skeletonema costatum (siliceous alga), the red-tide-predominant species that is in positive proportion to DSi flux, decreased from 33% during the 1980s to 24% during 2000–2002. The present data evidence the increase of Prorocentrum dentatum (non-siliceous alga) from 12.5% in the 1980s to 36% in 2000–2002, which tends to be dominant species of the red tides off the Yangtze estuary. The number of big dams in the Yangtze River basin will double in the next 30–50 years. This will significantly influence the variations of nutrient fluxes in the river basin and estuary, in relation to health management of river-coast ecosystem.

In the original publication of the article, when changes were made to make the exponents uniform throughout the paper, the decimal points were not adjusted accordingly. Following are the correct numbers: • On page 4 the first line in the first paragraph should read as follows: of 4.10 × 109 m3 a-1. These are located in remote and rural. • On page 4 the second line in the second paragraph should read as follows: supplied 3.12 × 109 m3 a-1 in 2013, and which are mostly. • On page 4 the numbers on the y axes of both Fig. 1a, b should be reduced by a factor of 10. • On page 4 lines 11 to 16 in the third paragraph should read as follows: period 1978–2013 increased from 0.97 × 109 m3 a-1 to 3.10 × 109 m3 a-1; of this, the water for residential and public open space increased from 0.36 × 109 m3 a-1 to 1.97 × 109 m3 a-1, a fivefold increase and therefore a rate obviously greater than that of industrial water (0.62–1.15 × 109 m3 a-1 over the same period) (Fig. 1a). • On page 4 lines 20 and 21 in the third paragraph should read as follows: water pumping grew from 1.17 × 109 m3 a-1 in 1978 to 4.10 × 109 m3 a-1 in 2013 (Fig. 1b). • On page 6 the numbers on the y axis of Fig. 5 should be reduced by a factor of 10. (Figure presented.) • On page 6 lines 3 and 4 in the first paragraph of the section entitled “Estimating Shanghai's aggregate municipal water demands” should read as follows: Shanghai in 2050 is estimated to be between 4.2 billion m3 (scenario 1) and 5.7 billion m3 (scenario 3), representing • On page 6 line 9 in the first paragraph of the section entitled “Estimating Shanghai's aggregate municipal water demands” should read as follows: between 4.9 and 6.8 × 109 m3. Particularly when • On page 6 line 3 in the second paragraph of the section entitled “Estimating Shanghai's aggregate municipal water demands” should read as follows: (4.10 × 109 m3 a-1) will be adequate to meet Shanghai's The authors wish to apologise for these errors.

In late May and early June, 2002, a field investigation was conducted along the Three-Gorges valley of the upper Yangtze catchment by ADP (Acoustic Doppler Profile SONTEK-500). Data obtained when surveying were accompanied with discharge of 1000 m) and shallower water depth ( 50 m) and U-shaped river-channel morphology. Mapping the river cross-section area at those sites can determine that smaller cross-section area accelerates the flow velocity. From Wanxian to Fengjie, the average flow velocity ranging from 3.0 to 4.5 m/s is in-phase with the water depth. The high-flow velocity is associated with narrower river-channel, where V-shaped gorges valley occurs with small cross-section area. Further downstream from Fengjie to Zigui, the low flow velocity is linked to deep river channel characterized by W-shaped valley morphology of large cross-section area, in general. The average flow velocity is 2.5–3.5 m/s, and maximum can reach 6.0 m/s near Wu-Gorge. Our survey had also detected a slow-flow velocity (mostly 100 m; maximum) in the gorges valley (30–40 m below the present mean sea level). This contrasts to the relative shallow water river-channel above Fengjie, i.e. 20–30 m in general and 50–60 m, maximum at gorges site. The present ADP investigation displays the hydromorphological feature in the Three-Gorges valley, and most importantly, it accumulates invaluable dataset for the post-dam study in the near future.