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The southeastern portion of the Yangtze River Estuary (or Yangtze Estuary) was considered to be the deposition center and the mudbank of the Yangtze River Delta. As the fluvial sediment supply began to decline in the 1980s and the reduction accelerated after the completion of the Three Gorge Dam in 2003, more fluvial sediment was trapped decreasing the suspended sediment concentration (SSC) environment in the river mouth area. Moreover, the accretion rate of the mudbank has slowed down in recent decades. In fact, the mudbank shrank and has faced a regime shift from sediment sink to source. A better understanding of the tidal-scale dynamics and spatial variability of the system is essential to explore the conversion of the sediment sources and sinks in the Yangtze Estuary affected by natural variations and human activities. Flow velocity, salinity, and suspended-sediment concentration during spring and neap tides were measured at three sites on the mudbank in July 1982 and July 2013. The variation in flow was not significant at all the sites measured in the study area from 1982 to 2013. However, the sediment dynamics changed remarkably over these three decades. The temporal distribution of the SSC increased in the bottom layer. The SSC was much larger during the early flood tide period in 2013. The tidal range increased by nearly 10% and the flood dominance increased in the study area from 1982 to 2013. The salinity dynamics underwent a transition from a stratified system in 1982 to a well-mixed system in 2013. The landward sediment budget increased remarkably from 1982 to 2013. The decreased fluvial sediment supply, increased flood dominance, well-mixed salinity, and increased tidal range were directly responsible for the larger landward sediment budget and more severe erosion in the mudbank in 2013. The current results reveal the flow and sediment dynamics during the conversion of the sediment sink to source. Furthermore, it was determined that the sediment-starved process in the estuarine environment, which occurred due to the reduction in the fluvial sediment, leads to an increased landward transport of sediment. The current study provides a clear understanding of the mechanisms governing the delta system transition in the mudbank of the Yangtze Estuary, which is useful for delta protection in the future. • Sediment in the mudbank of the Yangtze Estuary were transported to offset reduced fluvial sediment into the river mouth. • The mudbank experienced increased tidal asymmetry, weaker stratification, and decreased fluvial sediment in recent decades. • Fluvial sediment reduction and estuarine engineering projects have contributed to the conversion of source and sink. [ABSTRACT FROM AUTHOR]

A combination of two indirect methods to measure sediment flux is presented in this study to evaluate suspended sediment transport in a hydropower reservoir. The acoustic backscatter signal (ABS) from an Acoustic Doppler Current Profiler (ADCP) is therefore applied in pre-defined transects within the reservoir in combination with a Laser In-Situ Scattering Transmissometry – stream lined device (LISST-SL). The stationary LISST-SL derived suspended sediment concentration (SSC) measurements are used to calibrate the ABS. From the LISST-SL measurements a time series of SSC is obtained. This enables, in addition, a comprehensive data analysis to evaluate the influence of natural fluctuations of the SSC on the calculated sediment flux, which should be taken into account when assessing sediment transport. Furthermore SSC measurements are done with the LISST-SL close to the reservoir bed. In areas close to the bed no information regarding the ABS is available from the ADCP measurements due to the side-lobe interference. In various studies the information from the last three valid cells is used for extrapolation. However, as result of a comparison of the LISST-SL measurements with extrapolated SSC values from the ADCP measurements it can be seen that, especially in deep reservoirs, this method has to be adapted to the in-situ conditions. [ABSTRACT FROM AUTHOR]

Aeolian dust is one of the main aerosols in the troposphere, and plays an important role in the Earth’s climate system. In this study, detailed meteorological conditions and dust particle diameters were measured at three sites with different landscape characteristics in the Minqin oasis area of northwest China, on 29 February 2008. We show that as dust storms progressed through the desert into the oasis, variation in the character of the underlying land surface not only influenced the wind profile by modifying the frictional velocity of air (U ∗ ), aerodynamic roughness length (Z 0 ), horizontal sediment flux, and dust concentration of the near surface sublayer (1–49 m), but it also changed the vertical structure of the aeolian sediment transport pattern. The particle size frequency distributions at three distinct sites were all unimodal, comprising a large number of aeolian dust particles with sizes less than 63 μm (more than 65%). During transport, dust particle populations shifted to smaller sizes. Clearly, the influence of landform, windbreaks, and vegetation cover on horizontal sand-dust flux decreased with height as well as increasing particle size, with smaller aeolian particles being more easily captured by windbreaks, and vegetation. [ABSTRACT FROM AUTHOR]

Horizontal (saltation) mass flux is a key driver of aeolian dust emission. Estimates of the horizontal mass flux underpin assessments of the global dust budget and influence our understanding of the dust cycle and its interactions. Current equations for predicting horizontal mass flux are based on limited field data and are constrained to representing transport-limited equilibrium saltation, driven by the wind momentum flux in excess of an entrainment threshold. This can result in large overestimation of the sediment mass flux. Here we compare measurements of the soil entrainment threshold, horizontal mass flux, and their temporal variability for five undisturbed dryland soils to explore the role of threshold in controlling the magnitude of mass flux. Average and median entrainment threshold showed relatively small variability among sites and relatively small variability between seasons, despite significant differences in soil surface conditions. Physical and biological soil crusts had little effect on the threshold value, and threshold appeared to play a minor role in determining the magnitude of sediment transport. Our results suggest that horizontal mass flux was controlled more by the supply limitation and abrasion efficiency of saltators present as loose erodible material or originating from neighboring soil sources. The omission of sediment supply and explicit representation of saltation bombardment from horizontal flux equations is inconsistent with the process representation in dust emission schemes and contributes to uncertainty in model predictions. This uncertainty can be reduced by developing greater process fidelity in models to predict horizontal mass flux under both supply- and transport-limited conditions. [ABSTRACT FROM AUTHOR]

Sediment transport in fluvial systems is a key driver of basin-wide global soil loss, river sedimentation, and the movement and transformation of organic, inorganic, and nutrient materials, all of which can contribute to severe eco-environmental degradation. Since the late 1800s, much research effort has focused on the physics of sediment entrainment, transport, and deposition by river flows. This paper reviews ongoing research aimed at considering the simultaneous physical, chemical and biological processes that characterize riverine sediment flux. Four related issues are considered: riverine sediment flux; soil erosion and chemical transport; fluxes of dissolved organic carbon; and sediment-induced CO2 emission/sequestration. Modelling of sediment flux has moved beyond empirical and statistical approaches to that of a generalized form of the universal integral solution of the basic flux equation, which is now anticipated to lead to a wide range of applications. Whereas soil erosion and riverine chemical transport are now known to cause soil degradation and reduced water quality, limited progress has been made to date on the quantification of erosion rates. As soils erode, CO2 is emitted at erosion and transport sites and sequestered at deposition sites, the net effect being carbon sequestration. However, the rates of CO2 emission/sequestration vary widely, owing to the large spatial variations in soil type, land-slope, rainfall intensity, etc. It is now well established that dissolved organic carbon (DOC) concentrations and fluxes have been increasing over the past two decades, due to reduced atmospheric sulphur concentration, climate warming, and changes in precipitation patterns. The research discussed herein provides insight into the interaction between sediment and multiple material substances, leading to a better understanding of fluvial river ecosystems, which is essential for maintaining river health. [ABSTRACT FROM AUTHOR]

The article describes present-day processes related to sediment flux and deposition in the Puck Lagoon, southern Baltic Sea). In situ sediment traps were used for detennining the sediment properties in the lagoon and its tributaries. Both sediment sources and the volume of incoming sediment were taken into account and a distinct zone of sediment deposition was discovered in the central part of the Puck Lagoon. The rate of sediment deposition in the Rzucewo Deep exceeded 8.0 mm y-1, whereas in other parts of the Puck Lagoon it ranged from 1.9- 3.9 mm y-1 . These findings provide the basis for predicting future sedimentation conditions in the Puck Lagoon. [ABSTRACT FROM AUTHOR]

Abstract: Data on sediment flux at three hydrologic stations from the 1950s to 2006 are utilized to study the decadal, annual, and monthly variations in suspended sediment load delivered from the Pearl River to the ocean. Results show that variations in sediment flux from three main tributaries, including the West River, the North River and the East River, are spatially non-uniform. Since nearly 90% of the suspended sediment load comes from the West River, its variation has dominated the overall tendency of sediment flux in the entire Pearl River. Although a significant decreasing trend exists in the annual variation of the total sediment flux, the decadal change can be divided into an increasing phase and a decreasing phase, with the turning point between the two phases in the late 1980s. From the 1950s to the 1980s, the average annual river sediment flux increased by 30.43%. However, sediment flux has decreased significantly since the 1990s, with the average sediment flux being 38.60% less in the 2000s than that in the 1950s. The current sediment flux is also 52.93% less than its peak in the 1980s. The monthly variation pattern of the suspended sediment load transport to the sea is more interesting. For the West River, all months show a decreasing trend, and for most months the reduction values are significant. However, for the East River the sediment load shows a decrease trend in the dry season and an increase trend in the wet season. The method of regression analysis was used to study the influence of precipitation in the variation on the sediment flux. It was found that the climate change is not the main driving force behind the variation in suspended sediment load. Before the 1990s, intensive land use destroyed the vulnerable ecosystem of the upper Pearl River, and speeded up the process of rocky desertification. Consequently, aggravated soil erosion caused an increase in suspended sediment load. However, sediment retention within reservoirs had begun to play a dominant role after the massive construction of large dams after 1990, and resulted in a decrease in the suspended sediment load delivered to the ocean. [Copyright &y& Elsevier]

Abstract: The relative erosion rates of wind and water erosion have rarely been studied simultaneously and are poorly quantified. In this study, wind and water erosion rates were simultaneously measured and compared over 2yrs for a small rangeland watershed in the Santa Rita Experimental Range in southern Arizona. Average horizontal, wind-driven sediment flux was 7.0gm−1 d−1 during the study period. The combined soil erosion rate by water and wind was 7.60tha−1 yr−1, with only 0.08tha−1 yr−1 attributed to wind during the 2yrs. The results of this study showed that rates of soil erosion by water greatly exceeded rates of erosion by wind during the study period in this small watershed. Comparison between these results and other recent studies in the same area suggest that measurements of horizontal sediment fluxes by wind and water are not necessarily indicative of relative net soil erosion rates on a unit area basis because the measurements of the wind flux sediment cannot be considered as mass of soil loss per unit area per unit time. [Copyright &y& Elsevier]

A sediment model has been developed to simulate the Sediment Oxygen Demand (SOD) and sediment nutrient fluxes after a sudden input of Particulate Organic Matter (POM). Compared with previous sediment models, the main advances are the use of a continuous function to represent the kinetics of POM diagenesis and inclusion of the biomass content in POM diagenesis. Laboratory experiments were also carried out to investigate the SOD dynamics and sediment nutrient fluxes after an input of fish food pellets into the sediment. The simulation results of SOD and nutrient fluxes compared fairly well with the experimental measurements. [ABSTRACT FROM AUTHOR]

The formation and dynamics of turbidity maxima (TM) in the Pearl River estuary (PRE) are not well understood but the existence of TM in the estuary have great potential engineering and environmental impacts. Based on the measurements of two large-scale field surveys conducted in the wet season of 1978 (July of 1978) and the dry season of 1979 (March of 1979), the existence and seasonal variations of TM in the PRE focusing on the two major natural navigation channels have been studied. The sediment transport fluxes over two consecutive tidal cycles have been analyzed in detail. The analysis results reveal that the formation mechanisms of TM in the estuary are rather complex. In general, gravitational circulation, tidal trapping, and sediment resuspension and deposition processes are the primary TM formation mechanisms in the PRE. The clockwise back flow pattern around Lingding Island also leads to the formation of TM in the West channel of the PRE. The occurrence of TM far upstream of the salt water wedge is the result of the complex hydrodynamic and sediment transport processes generated by the runoff of the major rivers. [Copyright &y& Elsevier]

Response of nitrous oxide N2O sediment/air flux to nitrogen addition was assessed in mangrove (Rhizophora mangle) sediments. Fluxes were enhanced with both ammonium and nitrate loading. Greatest fluxes (52 μmol m−2 h−1) were obtained with ammonium addition and saturation was achieved with additions of 0.9 mol m−2. Maximum flux following ammonium addition was 2785 times greater than control plots and 4.5 times greater during low tide than with equivalent ammonium addition at high tide. Nitrate enrichment resulted in exponential growth, with maximal mean flux of 36.7 μmol m−2 h−1 at 1.9 mol m−2; saturation was not achieved. Differential response to ammonium and nitrate, and to tide and elevation, indicate that microbial nitrification is responsible for most of the observed gas flux. Mangrove sediments constitute an important source of global atmospheric N2O and increases in nitrogen loading will lead to significant increases in the flux of this atmospherically active gas. [Copyright &y& Elsevier]

An overview of the field work research projects under the LOIS Biological Influences On interTidal Areas (BIOTA) program is presented. The main objective of BIOTA is to characterize and quantify fluxes of sediments and the influence of biological components within the intertidal saltmarsh and mudflat zones of the main LOIS study area. Three studies concerned with sediment dynamics and the biota at a variety ofsites and salt marsh types on the east coast are described, and a saltmarsh flux study at a single site in Norfolk is briefly outlined (Fig. 1). Some examples of the preliminary research findings are shown with reference to selected sites in the Humber estuary. Regular monitoring of sediment levels out on the sand and mudflats showed remarkable stability, with the amplitude of variation rarely exceeding 5 cm over the four years of measurement. Some sites (generally the more cohesive sediments) displayed a seasonal pattern of elevation change. Oscillations of surface level changes decreased towards the marsh and damping continued with increasing vegetation cover. As expected net accretion generally decreases landward under reduced submergence times,particularly on the open coast marshes; however different sedimentation profiles were observed. In the Humber estuary, net accretion was generally greatest in the middle to lower marsh, with periods of erosion at the seaward edge. The role of vegetation in accretion is complex and may be site specific, affected by a variety of physical factors. The cord grass, Spartina anglica appears to have little effect on sediment deposition, but is more important as a sediment stabilizer during periods of erosion. The types of models that can be derived from the BIOTA study are briefly outlined. [ABSTRACT FROM AUTHOR]