Y. Jun Xu

Louisiana State University | LSU · School of Renewable Natural Resources

Alluvial rivers are shaped by interactions of flow and sediment transport. Their lower reaches to the world's oceans are highly dynamic, often presenting engineering and management challenges. Here we analyzed over 6,000 single‐beam cross‐sectional measurements surveyed in 1992, 2004, and 2013 in the last 500‐km reach of the highly engineered Missi...

Evasion of carbon dioxide (CO2) from lakes is a significant component in the continental carbon balance, but most current CO2 evasion estimates ignore daily CO2 fluctuations. To test the hypothesis that partial pressure of CO2 (pCO2) and CO2 evasion vary throughout a day due to biological processes driven by solar radiation, we conducted in-situ pC...

Air temperatures, precipitation, and river discharge have been steadily increasing in many river basins over the last century. This is especially the case with North America’s largest river basin, the 3.2-million-km2 Mississippi River Basin, which comprises over 41% of the total land surface area in the contiguous USA. Yet we lack an understanding...

Bed material transport at river bifurcations is crucial for channel stability and downstream geomorphic dynamics. However, measurements of bed material transport at bifurcations of large alluvial rivers are difficult to make, and standard estimates based on the assumption of proportional partitioning of flow and bedload transport at bifurcations ma...

Previous studies have established that under natural conditions, alluvial river confluence zones experience channel scour followed by mid-channel bar development. Less attention is given to bed evolution downstream of large alluvial river confluences under engineered conditions, such as discharge regulation and levee confinement. Here we present fo...

Riverine water and sediment discharge drive global material circulation and energy transfer, and they are crucial to the biogeochemical cycle. We investigated the changes in water-sediment fluxes in six major rivers from north to south in China from the mid-1950s to 2020 under the influence of climate change and human activities, and quantified the...

Understanding the spatiotemporal nitrate retention in streambed is essential for developing management practices in reducing nitrate enrichment. However，the process of nitrate change in the profile of streambed at an elevated nitrate across a watershed scale is still not sufficiently investigated. In this study, we used a combination of hydraulic a...

We analyzed the impacts of land use/land cover types on carbon dioxide (CO2) and methane (CH4) concentration and diffusion in 1st to 4th Strahler order tributaries of the Longchuan River to the upper Yangtze River in China by using headspace equilibration method and CO2SYS program. Field sampling and measurements were conducted during the dry and w...

A mixed land use/land cover (LULC) catchment increases the complexity of sources and transformations of nitrate in rivers. Spatial paucity of sampling particularly low-resolution sampling in tributaries can result in a bias for identifying nitrate sources and transformations. In this study, high spatial resolution sampling campaigns covering mainst...

Deltaic channels are significant landforms at the interface of sediment transfer from land to oceanic realms. Understanding the dynamics of these channels is urgent because delta processes are sensitive to climate change and adjustments in human activity. To obtain a better understanding of the morphological processes of large deltaic channels, thi...

The global demand for sand and gravel is at 50 billion tons per year, far exceeding global resource capacities. It reached 7.6 billion tons in 2021 in the Yangtze River Basin (YRB), China. However, production is severely limited in the YRB. Therefore, the incongruity between the supply and demand of river sand is prominent. Wise management of decre...

Wetlands have been singled out as a potential nature-based solution for improving the resilience and reducing the risks of hydrometeorological extremes. However, whether and to what extent wetlands can affect hydrological droughts is not well understood. To fill this gap, we proposed a general framework to discern the effect of wetlands on: (i) the...

Wetlands and reservoirs are important water flow and storage regulators in a river basin; therefore, they can play a crucial role in mitigating flood and hydrological drought risks. Despite the advancement of river basin theory and modeling, our knowledge is still limited about the extent that these two regulators could have in performing such a ro...

Under the influences of global climate change and intense human activities, the hydrological and biogeochemical processes have been undergoing profound changes in most of the world's watersheds. However, the long-term changes in streamflow, sediment load, and nutrient fluxes, and quantitative attribution of these changes from a basin-wide perspecti...

In 2019, the Mississippi River experienced the longest and largest flood that surpassed by far the 1927, 1973, and 2011 mega floods. This unprecedented event provided a unique opportunity to test the hypotheses that summer floods increase not only lateral dissolved carbon transport but also carbon dioxide (CO2) degassing, and that the increase in C...

Sources and quality of dissolved organic matter (DOM) in streams may be largely controlled by the landscape and season. In this study, we attempted to answer three critical questions: 1) Do land use/land cover (LULC) types affect DOM characteristics? 2) Is there seasonal fluctuation in DOM components? 3) How do DOM quality and LULC types influence...

The Mississippi River (MR) discharges on average 474 km3 of water annually into the Northern Gulf of Mexico (NGOM) with a large quantity of carbon, playing a vital role in the ecosystem’s food chain and water quality. In this study, we analyzed exports of dissolved inorganic (DIC) and or-ganic carbon (DOC) from January 2021 to December 2021, during...

Dunes of the lowermost Mississippi River (LmMR) in USA and the lowermost Yangtze River (LmYR) in China have been recently investigated in some reaches. Yet, our understanding of dune formation in large lowland alluvial rivers is still limited. This study compared characteristics of dunes in an 8-km long reach in the LmMR and a 35-km long reach of t...

It is common to conceptualize wetlands as a nature-based flood defense for improving basin resilience to climate change. Yet, such a solution is often ignored when projecting or assessing river flood risk under future climate change. To fill this gap, we apply a hydrological modeling platform integrating wetland modules to a 297,000-km2 large river...

Headwater streams make the majority of commutative stream length in a river basin, carbon dioxide (CO2) emission from headwater (low order) streams is thus an essential component. Anthropogenic activities in headwater areas such as land use change and land use practices can strongly modify terrestrial carbon and nutrient input, which could affect t...

Rapid urbanization has considerably altered carbon biogeochemical cycle and river hydrology. However, the influences of urban land use and urban-induced nutrient increase on dissolved organic matter (DOM) characteristics are poorly understood. Here we hypothesize that the alterations significantly change sources and levels of DOM in river systems t...

Nitrogen pollution has been shown to have strong potential threaten to the human drinking water and agriculture. However, identifying the nitrogen and spatial-temporal variation and nitrogen pollution sources among surface water, sediments and groundwater at the watershed scale still insufficient understanding. In this study, multi-methods (dual is...

The magnitude of the carbon (C) sink due to terrestrial primary production may be overestimated if the C losses through fluvial networks are not properly accounted for. In this study, we hypothesize that terrestrial‐aquatic C transfers represent a major loss of the terrestrial C sink in semiarid catchments. To test the hypothesis, we assessed the n...

Artificial river bifurcations have been widely created for different purposes. Yet, long-term dynamics in the bifurcated channels and natural channels downstream of the artificial bifurcations are not well investigated. Herein, we employed an approach combining 3-decades (1977-2006) bathymetric survey records, GIS application, and bed material tran...

Dissolved organic matter (DOM) is a diverse and highly complex mixture of organic macromolecules, and thus plays a central role in aquatic ecosystems. However, responses of components and sources of DOM to hydrological processes and trophic levels (nutrient stoichiometric ratios) are poorly understood, particularly in monsoonal headwater streams of...

The Yangtze River Tidal Reach (YRTR) is one of the most important land-sea transition zones in China. The YRTR is 640 km long and the adjacent land area of 220,000 km² has a population of ca. 150 million. Even though the effect of Three Gorges Dam (TGD) on its downstream has been extensively studied, a comprehensive understanding of natural and dam...

The Yangtze River Delta (YRD) and Mississippi River Delta (MRD) are two of the largest deltas in the world. Despite similar forcing conditions of fluvial sediment reduction and relative sea-level rise, there are significant differences in delta morphological change caused by hydrodynamics and local human activities. In this review, we compare the m...

Many rivers in the world, especially in their lower researches, are engineered to meet societal needs for purposes including navigation, flood control, and water supply. The engineering efforts often oppose natural tendencies of sediment transport and channel development in lowland alluvial rivers. Being managed as a floodway, the 220-km long Atcha...

During the 2021 winter season, near-record low water and air temperatures occurred in much of the Mississippi River Basin due to disturbances in the polar vortex. Little is known about the impact of extreme winter weather on carbon dioxide (CO2) evasion and dissolved carbon export in large rivers. As extreme weather events become more frequent due...

River damming and reservoir operation alter hydrological process, raising concerns over far-reaching influence on fluvial water, biogeochemistry and sediment fluxes due to the common occurrence of fragmented river landscapes around the world. Here, we investigated carbon, nutrients, and geochemical conditions in the world's largest reservoir, the T...

Rivers and streams play a central role in global carbon budget, but our knowledge is limited on the magnitude and extent of urbanization influence on riverine methane (CH4) dynamics. In this study, we investigated dissolved CH4 (dCH4) concentration and CH4 diffusive fluxes in 27 river segments of two 4th-order and three 3rd-order tributary rivers t...

The importance of natural water towers to water resource demand of the ecological environment and human activities is self-evident. They are also vulnerable and extremely sensitive to the effects of anthropogenic activities and climate change. However, water bodies change in water towers have not received sufficient attention. Therefore, Changbai M...

Irrigation discharge is a relevant water resource for lake ecosystems in arid and semi-arid regions. However, high concentrations of nitrogen and phosphorus in the irrigation discharge raise concerns over potential lake eutrophication in these regions. A Delft3D hydrodynamic-water quality model was used to explore the effects of multiple water sour...

The Mississippi River (MR) and its largest distributary, the Atchafalaya River (AR), discharge a combined volume of approximately 670 km 3 (474+199 km 3) each year into the Gulf of Mexico. While the MR deltaic plain has been losing land at an average rate of 30 km 2 annually since the 1930s, the AR has been building deltaic land at a much lower rat...

In 2019, the Lower Mississippi River (LMR) experienced the largest flood that surpassed by far the 1927, 1973, and 2011 mega floods. River water at Baton Rouge, located 357 kilometers upstream of the river's mouth at the Gulf of Mexico, stayed above flood stage consecutively 212 days from the 6 th of January through the 5 th of August. The extremel...

Dunes are critical for understanding riverine sediment transport, deposition, flow resistance and channel flow processes. Although previous studies have examined the riverbed micromorphology of the Lower Mississippi River in the USA, our knowledge of detailed quantification of dune morphology in this and other large alluvial rivers is still limited...

Rapid urbanization has been reported to affect carbon biogeochemical cycle of waterways, contributing to even higher carbon dioxide (CO2) outgassing from rivers to the atmosphere. However, knowledge on the magnitude and extent of the urbanization influence on riverine CO2 dynamics is still limited. In this study, we investigated partial pressure of...

The global scale wetland loss or degeneration triggers the assessment on how their function provisions are likely to change under different management scenarios. However, how and to what extent river damming can modify the hydrological function of wetlands remain largely unknown. In this study, we apply a distributed hydrological modeling platform...

The study focused on the question of how the natural and human forcing has affected the morphodynamic evolution of bars in the middle Yangtze River. A large channel bar was investigated using satellite remote sensing data during 1986-2017. A novel algorithm was proposed to select images acquired at the similar river stage. The bar was delineated fr...

During January 2021, much of the continental United States was affected by a polar vortex, which led to record cold temperatures for many areas within the Mississippi River Basin. Little is known about how such an extreme weather event could affect water temperature and outgassing of carbon dioxide (CO2) from rivers downstream near their mouths. Th...

Determining the dynamics of surface hydrological connectivity in a landscape of multiple lakes with different sizes and depths is challenging. This is especially the case for ungagged, large areas of multi-lake systems. Integrated use of remote sensing and geostatistical analysis can be a useful approach for developing metrics that can be used to i...

Many world’s large rivers have experienced significant sediment reduction in the past century. However, channel aggradation near the mouth of these rivers may be still occurring or even accelerating, as evidenced by a recent study on the Lowermost Mississippi River. This study aims to investigate whether such a trend exists near the mouth of anothe...

Floodplain wetlands of low-gradient rivers are especially sensitive to alteration of hydrologic conditions. Although many studies have investigated changes in downstream hydrologic regimes caused by river dam construction, no study has specifically quantified the long-term effect of altered flood pulse on floodplain wetlands. Such knowledge is need...

Ecological water replenishment (EWR) has been increasingly applied to the restoration and maintenance of wetland hydrological conditions across China since the beginning of the 21st century. However, little is known about whether EWR projects help protect and/or restore wetland ecohydrology. As one of the earliest and longest-running EWR projects i...

Ecological water replenishment (EWR) has been increasingly applied to the restorationand maintenance of wetland hydrological conditions across China since the beginning of the 21stcentury. However, little is known about whether EWR projects help protect and/or restore wetlandecohydrology. As one of the earliest and longest-running EWR projects in C...

Connectivity metrics for surface water are important for predicting floods and droughts, and improving water management for human use and ecological integrity at the landscape scale. The integrated use of synthetic aperture radar (SAR) observations and geostatistics approach can be useful for developing and quantifying these metrics and their chang...

River confluences are important nodes for downstream sediment transport and geomorphological development. Previous studies have established the knowledge that under natural conditions, river confluence zones experience channel scour followed with middle channel bar development. Less care is however given to the intensity of a confluence scour zone...

The salinization of freshwater lakes by agricultural activities poses a threat to many lake ecosystems around the world. Quantitative, medium-to long-term studies are needed to understand how some common agricultural practices, such as the discharge of crop irrigation in the vicinities of large lakes, may affect lake salinization. In this study, hy...

Hydrological drought for marshy rivers is poorly characterized and understood. Our inability to quantify hydrological drought in marshy river environments stems from the lack of understanding how wetland loss in a river basin could potentially change watershed structure, attenuation, storage, and flow characteristics. In this study, hydrological dr...

Delta deposits show large spatial heterogeneity in terms of depositional rate and age, which is critical to the study of delta erosion in response to the declining fluvial sediment load observed at many river mouths in the world. In this study, we show that the magnetic susceptibility (χ) can be an indicator to reveal age variations and stratigraph...

Past research on fluvial dynamics at the confluence of two alluvial rivers has mainly focused on downstream flow structure and bed scoring, often using laboratory experiments and numerical modeling. Little is investigated about yearly and episodic dynamics of confluence mouth bars that can affect downstream morphology using field measurements. In t...

Background Interferometric Synthetic Aperture Radar (InSAR) has become a promising technique for monitoring wetland water levels. However, its capability in monitoring wetland water level changes with Sentine-1 data has not yet been thoroughly investigated. Methods In this study, we produced a multitemporal Sentinel-1 C-band VV-polarized SAR backs...

Although the hydrological services of individual wetlands have been much acknowledged, their cumulative effect at the watershed scale has not been assessed as extensively. In this study, a distributed hydrological modeling platform, the PHYSITEL/HYDROTEL, was used to (i) investigate watershed hydrological processes with and without abundant wetland...

A major inland alkalinity lake in Northeast China, the Chagan Lake, was studied for the changes of its water qualities over the past three decades. Water quality data, including total nitrogen (TN), total phosphorus (TP), pH, dissolved oxygen (DO), and fluoride (F⁻), were analyzed to derive key indices for guiding water quality management. Our stud...

Spatiotemporal changes in the surface area of inland water bodies have important implications in regional water resources, flood control, and drought hazard prediction. Although inland water bodies have been investigated intensively, few studies have looked at the effect of human activities and climate variability on surface area of inland waters a...

Carbon dioxide (CO2) emission via water-air interface from fluvial networks plays a central role in the global carbon budget. Large uncertainties, however, exist because field measurements are often spatially and temporally biased, while aqueous carbon (C) processing can be strongly affected by anthropogenic activities in rapidly urbanizing areas....

Coastal restoration efforts have been under way for coastal Louisiana since the 1980s. In the past three decades, numerous projects and large amounts of funding have been invested into restoring wetlands on the Mississippi River Delta (MRD). Unfortunately, coastal land on the MRD continues subsiding, while the sea level continues rising. The 2017 M...

Global water resources are affected by climate change as never before. However, it is still unclear how water resources in high latitudes respond to climate change. In this study, the water resource data for 2021–2050 in the Naoli River Basin, a high-latitude basin in China, are calculated by using the SWAT-Modflow Model and future climate scenario...

Many studies have found that damming a river can change downstream hydrology, sediment transport, channel morphology, and fish habitat. However, little is known about river dam effects on downstream riparian wetland dynamics and their quantitative relationship with hydrological alterations. In this study, hydrological time series and wetland distri...

Antibiotics are increasingly used in livestock production in rural China, raising concerns over pollution and health risk in countryside waterways. The Yinma River Basin in China’s far northeast is an agriculture-dominated area mixed with a densely populated province capitol city, providing a suitable area for investigating the influence of a typic...

Sediment transport and channel dynamics of large alluvial rivers in their lower reaches can strongly influence physical, chemical and biological conditions in their deltaic regions. In this paper, we report the latest assessment on sediment transport and riverbed dynamics of the last 500-km reach of the Mississippi River before entering the Gulf of...

Sediment transport and channel dynamics of large alluvial rivers in their lower reaches can strongly influence physical, chemical and biological conditions in their deltaic regions. In this paper, we report the latest assessment on sediment transport and riverbed dynamics of the last 500-km reach of the Mississippi River before entering the Gulf of...