Distribution and dynamics of niche and interspecific association of dominant phytoplankton species in the Feiyun River basin,Zhejiang,China

To investigate the dominant species and interspecific association in the phytoplankton community of the Feiyun River basin in Zhejiang Province,East China,the main stream and the Shanxi Zhaoshandu Reservoir in the downstream were chosen as the study area,for which 22 sampling sites were designated.Sampling was conducted in September 2021,January,May,and July 2022.Phytoplankton species were identified from both quantitative samples and in-vivo observations.Phytoplankton was quantified by direct counting.Results show that there were 98 species belonging to 6 phyla and 78 genera.In addition,to clarify the niches of the dominant phytoplankton species and their interspecific association,the dominance index was calculated,and a comprehensive analysis was conducted including niche width,niche overlap value,ecological response rate,overall association,chi-square test,and the stability.The phytoplankton community exhibited characteristics of a Cyanobacteria-Chlorophyta-Diatom type community,showing higher diversity in spring and lower diversity in summer.Among 11 dominants phytoplankton species from 3 phyla,both frequency and dominance degree varied seasonally,of which Microcystis sp.was the dominant species in Spring,Autumn,and Winter.The niche widths of the dominant species ranged from 0.234 to 0.933,and were categorized into three groups.The niche overlap values of the 11 dominant species ranged from 0.359 to 0.959,exhibiting significant seasonal differences-highest in winter followed by autumn,spring,and summer in turn.The overall correlation among dominant species in all four seasons revealed a non-significant negative association,resulting in an unstable community structure.A significant portion(84.2%)of species pairs displayed positive associations,suggesting a successional pattern where Diatoms dominated while other dominant species shared resources and space.Despite this pattern,stability measurements indicated that the dominant species community remained unstable.Therefore,careful monitoring is recommended for potential water environment issues arising from abnormal proliferation of dominant species in the watershed during winter.This research built a theoretical foundation with a data support to the early warning of eutrophication and provided a reference for water resources management in similar watersheds along the eastern coast of China.

Variability and trends of near-surface wind speed over the Tibetan Plateau:The role played by the westerly and Asian monsoon

Near-surface wind speed exerts profound impacts on many environmental issues,while the long-term(≥60 years)trend and multidecadal variability in the wind speed and its underlying causes in global high-elevation and mountainous areas(e.g.,Tibetan Plateau)remain largely unknown.Here,by examining homogenized wind speed data from 104 meteorological stations over the Tibetan Plateau for 1961-2020 and ERA5 reanalysis datasets,we investigated the variability and long-term trend in the near-surface wind speed and revealed the role played by the westerly and Asian monsoon.The results show that the homogenized annual wind speed displays a decreasing trend(-0.091 m s^(−1)per decade,p<0.05),with the strongest in spring(-0.131 m s^(−1)per decade,p<0.05),and the weakest in autumn(-0.071 m s^(−1)per decade,p<0.05).There is a distinct multidecadal variability of wind speed,which manifested in an prominent increase in 1961-1970,a sustained decrease in 1970-2002,and a consistent increase in 2002-2020.The observed decadal variations are likely linked to large-scale atmospheric circulation,and the correlation analysis unveiled a more important role of westerly and East Asian winter monsoon in modulating near-surface wind changes over the Tibetan Plateau.The potential physical processes associated with westerly and Asian monsoon changes are in concordance with wind speed change,in terms of overall weakened horizontal air flow(i.e.,geostrophic wind speed),declined vertical thermal and dynamic momentum transfer(i.e.,atmospheric stratification thermal instability and vertical wind shear),and varied Tibetan Plateau vortices.This indicates that to varying degrees these processes may have contributed to the changes in near-surface wind speed over the Tibetan Plateau.This study has implications for wind power production and soil wind erosion prevention in the Tibetan Plateau.

Response to comment by Daley et al.,on"Assessing gully erosion and rehabilitation using multi temporal LiDAR DEMs:Case study from the Great Barrier Reef catchments,Australia"

Daley et al.(2023a)argue that at least 10-15 years apart Digital Elevation Model(DEM)derived DEMs of Difference(DoD)surveys are needed to detect reliable geomorphic change within the gullied landscapes of the Great Barrier Reef,Australia.We acknowledge that the reliability of observed geomorphic change increases as more subtle geomorphic processes are detected with longer monitoring periods.As further good quality long-term legacy datasets become available,we encourage utilising these to improve confidence in targeting erosion rehabilitation.However,our approach to consistently apply 2-3 year DoDs to contrasting gully morphologies enabled capture of more intense geomorphic processes acting over shorter timeframes and provided valuable and timely information on(i)contrasting erosional mechanisms and erosion rates between variable gully morphologies,and(ii)rehabilitation efforts un-dertaken.In this paper,we take the opportunity to concisely address all the concerns raised by Daley et al.(2023a).

Assessing gully erosion and rehabilitation using multi temporal LiDAR DEMs:Case study from the Great Barrier Reef catchments,Australia

Millions of dollars are being spent on gully rehabilitation to help reduce excess fine sediment delivery to the Great Barrier Reef(GBR).There is an urgent need for(i)prioritisation of active gullies for rehabilitation and(ii)the development of methodologies to inform the effectiveness of remediation.In this study we analyse DEMs of Difference derived from 0.5 m resolution 2-3 year interval multi-temporal LiDAR data collected pre and post rehabilitation at three variable gully morphologies in the Burdekin catchment.Our analysis indicates that the highest annual average fine sediment erosion rates for the untreated control gullies occur at the linear gully(53.38 t ha^(-1)y^(-1))followed by linear-alluvial gully(34.24 t ha^(-1)y^(-1))and least at the alluvial gully(14.41 t ha^(-1)y^(-1)).The proportional loss or export of fine sediment from the gullies in their un-treated condition ranges from∼68 to 90%of what is eroded,and when the gullies are treated the proportion of fine sediment that is retained in the gully proportional to what is eroded increases to∼60%at all sites.Without pre-treatment baseline erosion rates,and additional post treatment LiDAR captures,it is difficult to quantify the treatment effectiveness.Our results offer insights in the erosion mechanisms within different geomorphic gully morphologies and rehabilitation effects in these erosional landforms.This study provides crucial knowledge of gully dynamics that can be coupled with other lines of evidence for better prioritisation of rehabilitation in the GBR catchments.

A novel mathematical template for developing fDOM probe fluorescence signal correction models for freshwaters

The reliable application of field deployable fluorescent dissolved organic matter(fDOM)probes is hindered by several influencing factors which need to be compensated.This manuscript describes the corrections of temperature,pH,turbidity and inner filter effect on fluorescence signal of a commercial fDOM probe(fDOMs).For this,Australian waters with wide ranging qualities were selected,e.g.dissolved organic carbon(DOC)ranging from∼1 to∼30 mg/L,specific UV absorbance at 254 nm from∼1 to∼6 L/m/mg and turbidity from∼1 to∼350 FNU.Laboratory-based model calibration experiments(MCEs)were performed.A model template was developed and used for the development of the correction models.For each factor,data generated through MCEs were used to determine model coefficient(α)values by fitting the generated model to the experimental data.Four discrete factor models were generated by determination of a factor-specificαvalue.Theαvalues derived for each water of the MCEs subset were consistent for each factor model.This indicated generic nature of the fourαvalues across wide-ranging water qualities.High correlation between fDOMs and DOC were achieved after applying the four-factor compensation models to new data(r,0.96,p<0.05).Also,average biases(and%)between DOC predicted through fDOMs and actual DOC were decreased by applying the four-factor compensationmodel(from3.54(60.9%)to 1.28(16.7%)mg/L DOC).These correction models were incorporated into a Mi-crosoft EXCEL-based software termed EXOf-Correct for ready-to-use applications.

未来厄尔尼诺-南方涛动变率影响南大洋及南极陆架水增暖

南大洋包含复杂的海洋和大气过程,是全球最重要的热量存储地,可吸收约70%的由温室气体引发的额外热量[1,2].中高纬南大洋强劲的西风引发了广泛的海洋上升流,海表面以下2~3公里的海水可沿着陡峭的等密面涌升至海表面,之后分为两支路径[3,4].一支在大约60°S以北,海洋次表层温度较低,海水涌升后在西风驱动的北向Ekman流作用下向北输运,途中从大气吸收大量的热量、淡水和碳,转化为亚南极模态水和南极中层水并在45°S附近海域下沉;尽管部分上升流会被海洋中尺度涡旋向南的质量和热量输运效应(减小等密面垂向梯度)减弱,该上层经向环流是南大洋从大气中吸收并储存热量的主要途径.

人类活动影响20世纪厄尔尼诺-南方涛动变化

厄尔尼诺-南方涛动(ENSO)是地球气候系统在年际时间尺度(2~8年)上最强的海-气耦合变异现象,对全球极端天气、渔业生态环境及人类经济社会产生广泛而深远的影响[1].全球变暖背景下ENSO究竟如何发展变化,决定着ENSO对天气、气候、生态和农业等生产生活要素的影响范围、程度及方式.

Tropical cyclogenesis:Controlling factors and physical mechanisms

In this review,advances in the understanding of the controlling factors and physical mechanisms of tropical cyclogenesis(TCG)are summarized from recent(2018–2022)research on TCG,as presented in the Tenth International Workshop on Tropical Cyclones(IWTC-10).Observational,theoretical,and numerical modeling studies published in recent years have advanced our knowledge on the influence of large-scale environmental factors on TCG.Furthermore,studies have shown clearly that appropriate convective coupling with tropical equatorial waves enhances the development chances of TCG.More recently,illuminating research has been carried out on analyzing the mechanisms by which oscillations and teleconnections(El Ni˜no Southern Oscillation(ENSO)in particular)modulate TCG globally,in association with changes in the sea surface temperature(SST).In addition to this,recent research has diligently addressed different aspects of TCG.Multiple studies have reported the applicability of unified theories and physical mechanisms of TCG in different ocean basins.Recently,research has been carried out on TCG under different flow pattern regimes,dry air intrusion,importance of marsupial pouch,genesis of Medicanes,wind shear,convection and vertical structure.Furthermore,studies have discussed the possibility of near equatorial TCG provided that there is enough supply of background vertical vorticity and relatively low vertical wind shear.Progress has been made to understand the role of climate change on global and regional TCG.However,there are still significant gaps which need to be addressed in order to better understand TCG prediction.