International Journal of Sediment Research最新文献

The release of internal phosphorus (P) is a key and complex process relative to a lake’s nutrient levels. The P response to nitrogen input should be clarified to obtain better detail, especially with respect to the mediation role of iron (Fe) connecting nitrogen and P. A simulation study was done in batch vials containing sediment and overlying water collected from Lake Moshui—a shallow lake. Because of nitrate (${\text{NO}}_3^{-}$) input, the abundances of Firmicutes and Proteobacteria at the phylum level increased, as did the abundances of Crenothrix, Sideroxydans, and Flavobacterium at the genus level. Moreover, nitrate input enhanced the proliferation of nitrate-reducing Fe(II) oxidization bacteria and the activity of denitrifying enzyme in sediment, but decreased the concentrations of total phosphorus (TP), soluble reactive P, and enzymatically hydrolyzable P in the water phase. The suppressive effect of nitrate on P release was mainly attributed to the increase in Fe(III) (hydr)oxides generated by Fe(II) oxidation. With sequential extraction, two types of dominant iron fractions—easily reducible oxides and reducible oxides (Fe_ox1 and Fe_ox2, respectively)—seemed to contribute to the fixation of P largely in the sediment. In addition, more P is converted to Fe_ox2, which is induced by the transformation of Fe_ox1 to Fe_ox2. Driven by nitrate, a higher content of P bound to Fe_ox1 and Fe_ox2 was observed after a 7-day incubation, indicating the potential function of the Fe(II) oxidation process. The current study revealed that the P transformation is influenced by nitrate input from the angle of iron as the connecting bridge to better understand the geochemical cycle of P in the anoxic environment of lakes.

A model of the channel and catchment components of sediment runoff has been developed. The model makes it possible to estimate the intensity of redistribution of river and bottom sediment in the riverbed, the size distribution of deposited or migrating particles, the mass of particles in the riverbed and catchment components of sediment load, as well as the contribution of the catchment component. The model is based on the assessment of the transport potential of the watercourse and the dynamics of the curves of the granulometric composition of bottom sediment, and products of soil and channel erosion. This approach is focused on the steady flow movement without additional sources of tributary sediment, intensive abrasion of river banks, and products of anthropogenic load. Calculations based on the model applied to the Narva River showed that the contribution of the catchment component to the sediment flow of this watercourse after intense rain is approximately 98%. The obtained results are well confirmed by the weak dynamics of channel deformations in the studied part of the watercourse.

The current study deals with experiments on hydro-suction removal of cohesionless bed material from reservoirs. The primary focus lies in scrutinizing the scour profile and the volume of bed material removed through hydro-suction. A comprehensive record of 252 datasets was collected from experiments done on various combinations of governing parameters. The resultant equilibrium scour profile exhibited a symmetrical configuration resembling a semi-ellipsoidal shape. Notably, for the densimetric Forude number equal to or less than 5.8, a small central hump within the scour hole was seen. The investigation found that the optimal sediment removal efficiency was obtained when the C/D ratio was zero (where C is the suction inlet height and D is the suction pipe diameter) and with the highest densimetric Froude number. The sediment to water volume removal was highest in the initial few seconds, and reduced swiftly, followed by a subsequent smaller peak and gradually decreased to zero at equilibrium. Empirical equations for computing maximum scour depth, scour radius, and scour profile at equilibrium also were developed, which predict values within a commendable ±10% error range.

Identifying organic carbon (OC) sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management. However, the complexity of sources as well as environments in the land–river–lake continuum makes it challenging to accurately identify OC sources. Accordingly, the current study utilized a systematic approach to identify and validate OC sources in a typical land–river–lake continuum. Two tracer groups (group 1: δ¹³C and δ¹⁵N; group 2: fluorescence index and biotic index, respectively (where C is carbon and N is nitrogen)) and one model (MixSIAR) were eventually selected from five tracer groups and two models to identify the OC sources in a land–river–lake continuum according to a consistency evaluation and virtual mixing test. The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous. Closer to the lake center (from sampling site S1 to S3), the autochthonous contributions increased while the allochthonous contributions decreased. Downstream of the inlet river (site S1) was dominated by allochthonous contributions (78.6%), especially cropland (28.7% ± 0.5%, where ± indicates a standard deviation range) and urban land (30.5% ± 2.5%). From site S1 to S2, the allochthonous contribution decreased 11.4%. Autochthonous OC gradually became the major source closer to the lake center (site S3: phragmites: 48% ± 4.5%). This distribution of OC sources in the land–river–lake system was attributed to the mixing effect of the autochthonous sources, selective transport of sediment, and human activities. The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management.

A river's planform pattern changes due to erosion of banks and the bed near the outer bend. The primary cause of these planform changes is the formation of helical flow patterns in response to centrifugal forces. Uncontrolled bed scouring can have a negative impact on the river's geometry, aquatic habitat, and floodplains. To alleviate this scouring, various structures, such as spur dikes, can be placed at any accessible location along the bend. The current research was accomplished by installing two meandering models with different sinuosities of 1.3 and 1.5, in a flume. For both sinuosities, the maximum bed scour was observed at an approximate angle of 45° relative to the bend apex. Thus, the main objective was to control this maximum scour by installing spur dikes with varying porosities, ranging from 0% to 75%, at five locations along the outer bend. The spur dikes were found to divert the helical flow regime away from the outer bend and protect the riverbed from severe scouring. However, the results show that the effectiveness of spur dikes decreases as sinuosity increases. Furthermore, for both meandering models, a 50% permeable spur dike installed at the +30° location yielded the best performance. Finally, a regression-based predictive equation is proposed to determine the proportion of scouring around a spur dike in a meandering channel.

Spur dikes are structures built along riverbanks that serve two purposes: stabilizing the banks and minimizing erosion risk by controlling water flow in the river channel. The current study used L-shaped spur dikes in an alluvial channel to analyze the bed morphology and flow pattern in the spur dikes zone with the influence of no-seepage and two distinct seepage velocities, V_S1 = 0.075 mm/s and V_S2 = 0.15 mm/s near the channel bed z/h < 0.2. The experimental study was also done to examine and compare the transformation in the local scour depth for the seepage condition. According to the study results, downward seepage movement causes significant modification in the channel's bed elevation and the development of scour depth. Observations indicate that the maximum local scour occurs at the first spur dike's leading edge. Seepage velocity V_S1 results in a 16.1% increase in the maximum scour depth compared to the no-seepage scenario. In comparison, seepage velocity V_S2 causes an increase of 25.2% in the maximum scour depth. Due to downward seepage, the flow distribution is shifted down near the channel's boundary. With an increase in the seepage rate, the magnitude of velocity, Reynold shear stress, turbulent kinetic energy, and bed shear stress also rise close to the channel's boundary. The current study also examined bursting events near the channel's bed under seepage and no-seepage conditions. These events included outward interaction, inward interaction, ejection, and sweep. Quadrant analysis of velocimeter data revealed that ejection and sweep were the dominant events contributing to the production of Reynolds shear stress in seepage and no-seepage flows. Meanwhile, outward interactions and inward interactions made minor contributions compared to ejection and sweep events to the Reynolds shear stress.

In some areas of southern Italy, the change in land use over the last 4–5 decades has increased pressure on land and water resources and caused different forms of soil degradation. In order to mitigate the magnitude of soil erosion, different strategies that include construction of flood control structures and reforestation programs have been done in several areas. However, quantifying the effectiveness of these strategies is difficult in absence of direct measurements of soil erosion. To cover this information gap, the use of distributed numerical models coupled with measurements of the radionuclide cesium-137 (¹³⁷Cs) offers a good alternative to the classic experimental sites (plot, catchments) that, on the contrary, require long term datasets to produce reliable estimates of soil loss. In this paper, measurements of ¹³⁷Cs in a floodplain area are firstly described for a representative Calabrian catchment as an example to reconstruct the trend of soil deposition rates during the last six decades. These measurements have been integrated with estimates of soil loss obtained with the Revised Universal Soil Loss Equation (RUSLE) model for which land use maps of different periods are available. The final comparison between estimates of soil erosion provided by the RUSLE at catchment scale and sedimentation rates derived from ¹³⁷Cs measurements on depositional areas allowed interesting information on the trend of soil erosion and deposition rates in these areas to be obtained.

Hydromorphodynamic interactions with vegetation are a part of fluvial biomorphodynamics in actively meandering rivers. Using palynofacies and grain size from sub-urban to urban reaches across the river valley, the spatial patterns of organic matter behavior are examined in a 38 km reach of the Gomati River in Lucknow District, Uttar Pradesh, India. This is done to understand how they respond to the alteration, preservation, and degradation after getting transported and deposited in sediment. Thirteen surface sediment samples of the Gomati River floodplain were analyzed for palynofacies and grain size to ascertain its fate in this reach, which comprises the big picture for past human settlement. The shifts in the proportions of palynofacies associations, i.e., phytoclasts, palynomorphs, and amorphous organic matter (AOM) along with grain size, are considered to visualize the depositional process. The CONISS cluster analysis revealed four zones reflecting high degradation and alteration of palynofacies in the urban regime compared to the sub-urban reaches where the low interference with natural settings illustrates the low deterioration of palynofacies. The relation between grain size and palynofacies was obtained using Principal Component Analysis (PCA) to emphasize the correlation with palynofacies in the meandering fluvial system of the Gomati River. In the floodplain deposits, the behavior of palynofacies, allows for the distinction of the regional aspects of fluvial sediment disposition. The current study compares urban and sub-urban settlement premises of today's communities and contributes to the understanding of the growth, dispersal, and decline of earlier human settlements.