水电梯级开发真的破坏下游河段营养盐情势吗?

River damming is believed to largely intercept nutrients,particularly retain more phosphorus(P)than nitrogen(N),and thus harm primary productivity,fishery catches,and food security downstream,which seriously constrain global hydropower development and poverty relief in undeveloped regions and can drive geo-political disputes between nations along trans-boundary rivers.In this study,we investigated whether reservoirs can instead improve nutrient regimes downstream.We measured different species of N and P as well as microbial functions in water and sediment of cascade reservoirs in the upper Mekong River over 5 years and modelled the influx and outflux of N and P species in each reservoir.Despite partially retaining total N and total P,reservoirs increased the downstream flux of ammonium and soluble reactive phosphorus(SRP).The increase in ammonium and SRP between outflux and influx showed positive linear relationships with the hydraulic residence time of the cascade reservoirs;and the ratio of SRP to dissolved inorganic nitrogen increased along the reservoir cascade.The lentic environment of reservoirs stimulated algae-mediated conversion of nitrate into ammonium in surface water;the hypoxic condition and the priming effect of algae-induced organic matter enhanced release of ammonium from sediment;the synergy of microbial phosphorylation,reductive condition and sediment geochemical properties increased release of SRP.This study is the first to provide solid evidence that hydropower reservoirs improve downstream nutrient bioavailability and N-P balance through a process of retention-transformation-transport,which may benefit primary productivity.These findings could advance our understanding of the eco-environmental impacts of river damming.

Distinct community assembly processes underlie significant spatiotemporal dynamics of abundant and rare bacterioplankton in the Yangtze River

The rare microbial biosphere provides broad ecological services and resilience to various ecosystems.Nevertheless,the biogeographical patterns and assembly processes of rare bacterioplankton communities in large rivers remain uncertain.In this study,we investigated the biogeography and community assembly processes of abundant and rare bacterioplankton taxa in the Yangtze River(China)covering a distance of 4300 km.The results revealed similar spatiotemporal patterns of abundant taxa(AT)and rare taxa(RT)at both taxonomic and phylogenetic levels,and analysis of similarities revealed that RT was significantly influenced by season and landform than AT.Furthermore,RT correlated with more environmental factors than AT,whereas environmental and spatial factors explained a lower proportion of community shifts in RT than in AT.The steeper distance–decay slopes in AT indicated higher spatial turnover rates of abundant subcommunities than rare subcommunities.The null model revealed that both AT and RT were mainly governed by stochastic processes.However,dispersal limitation primarily governed the AT,whereas the undominated process accounted for a higher fraction of stochastic processes in RT.River flow and suspended solids mediated the balance between the stochastic and deterministic processes in RT.The spatiotemporal dynamics and assembly processes of total taxa were more similar as AT than RT.This study provides new insights into both significant spatiotemporal dynamics and inconsistent assembly processes of AT and RT in large rivers.

Global trends in water and sediment fluxes of the world’s large rivers

Water and sediment transport from rivers to oceans is of primary importance in global geochemical cycle.Against the background of global change,this study examines the changes in water and sediment fluxes and their drivers for 4307 large rivers worldwide(basin area!1000 km2)based on the longest available records.Here we find that 24%of the world’s large rivers experienced significant changes in water flux and 40%in sediment flux,most notably declining trends in water and sediment fluxes in Asia’s large rivers and an increasing trend in suspended sediment concentrations in the Amazon River.In particular,nine binary patterns of changes in water-sediment fluxes are interpreted in terms of climate change and human impacts.The change of precipitation is found significantly correlated to the change of water flux in 71%of the world’s large rivers,while dam operation and irrigation rather control the change of sediment flux in intensively managed catchments.Globally,the annual water flux from rivers to sea of the recent years remained stable compared with the long-time average annual value,while the sediment flux has decreased by 20.8%.

Photocatalytic degradation of amoxicillin by carbon quantum dots modified K2Ti6O13 nanotubes:Effect of light wavelength

A novel carbon quantum dots modified potassium titanate nanotubes(CQDs/K2 Ti6 O13)composite photocatalyst was synthesized by hydrothermal treatment combined with calcination.X-ray diffraction(XRD)pattern and transmission electron microscopy(TEM)indicated formation of potassium titanate nanotubes and successful deposition of CQDs onto K2 Ti6 O13.The photocatalytic performance of CQDs/K2 Ti6 O13 composite was evaluated by degradation of amoxicillin(AMX)under the irradiation of visible light and lights with the wavelengths of 365,385,420,450,485,520,595 and 630 nm.The results showed that the photocatalytic activity of CQDs/K2 Ti6 O13 hybrid material was greatly enhanced compared with the neat K2 Ti6 O13 calcined at 300 ℃.The narrowed band gap energy(Eg)and transfer of photo-excited electron by CQDs inhibited the immediate combination of electron-hole pairs,thus promoting photocatalytic activity.Moreover,CQ,Ds/K2 Ti6 O13 exhibited a broad spectrum of photocatalytic ability and it was interesting that the photocatalytic activity decreased with the increase of the irradiation wavelength.Reactive oxygen species(ROS)quenching tests suggested the hole(h^+)and hydroxyl radical(^·OH)played the primary roles in photocatalytic degradation of AMX.Moreover,CQ.Ds/K2 Ti6 O13 showed good reusability for AMX photocatalytic degradation after five successive runs.This study proposed an available method for titanate nanomaterials modification,and the developed novel CQDs/K2 Ti6 O13hyb rid material is p ro mising fo r potential application on antibiotics removal fro m water and wastewater.

Antibiotics in global rivers

Antibiotics have received extensive attention due to their sophisticated effects on human health and ecosystems.However,there is an extreme scarcity of information on composition,content,geographic distribution,and risk of riverine antibiotics at a large spatial scale.Based on a systematic review of over 600 pieces of literature(1999-2021),we established a global dataset containing more than 90,000 records covering 169 antibiotics and their metabolites in surface water and sediment across 76 countries.The occurrence of prioritized antibiotics largely depended on socioeconomic developmental levels,and the current“hotspots”of polluted rivers were found mostly in less developed countries or emerging economies(e.g.,some in Africa,South America,and Asia).By developing the screening protocol for risk-based prioritization of antibiotics,we advanced a rank list of antibiotics for guiding formulation of region-specific strategies,which highlighted the importance of whole life cycle management of antibiotics in health maintenance of the world’s rivers.

Emerging pollution and emerging pollutants

Emerging pollutants/contaminants are usually regarded as naturally or artificially occurring chemicals that are potentially harmful to ecological and/or human health but have not yet been commonly monitored or regulated.Despite the presence of emerging contaminants at a trace level in the environment,they have received extensive attention in recent years owing to their bioaccumulation,persistence,and toxicity.Nowadays,emerging contaminants are continually detected not only in wastewater treatment plants and municipal solid waste treatment/disposal sites but also in the air,soil,and aquatic systems.

6PPD-quinone affects the photosynthetic carbon fixation in cyanobacteria by extracting photosynthetic electrons

Photosynthetic carbon fixation by cyanobacteria plays a pivotal role in the global carbon cycle but is threatened by environmental pollutants.To date,the impact of quinones,with electron shuttling properties,on cyanobacterial photosynthesis is unknown.Here,we present the first study investigating the effects of an emerging quinone pollutant,i.e.,6PPD-Q(N-(1,3-dimethylbutyl)-N0-phenyl-p-phenylenediamine-quinone),on the cyanobacterium Synechocystis sp.over a 400-generation exposure period.Synechocystis sp.exhibited distinct sequential phases,including hormesis,toxicity,and eventual recovery,throughout this exposure.Extensive evidence,including results of thylakoid membrane morphological and photosynthetic responses,carbon fixation rate,and key gene/protein analyses,strongly indicates that 6PPD-Q is a potent disruptor of photosynthesis.6PPD-Q accepts photosynthetic electrons at the plastoquinone QB site in photosystem II(PSII)and the phylloquinone A1 site in PSI,leading to a sustained decrease in the carbon fixation of cyanobacteria after an ephemeral increase.This work revealed the specific mechanism by which 6PPD-Q interferes with photosynthetic carbon fixation in cyanobacteria,which is highly important for the global carbon cycle.