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• Hillslope erosion dynamic model integrating vegetation effect was established. • Unified baseline parameters were obtained across different land uses. • Effect of vegetation on soil detachment and sediment transport was revealed. • Contribution rates of vegetation to sediment reduction along slopes were quantified. Developing a process-based soil erosion model that comprehensively considers the effects of vegetation is complex but crucial for evaluating sediment reduction during vegetation restoration. Current understanding of the effect of vegetation on sediment reduction along hillslopes across different land uses is limited. In this paper, we developed a dynamic model of hillslope erosion that integrates the effects of vegetation on soil detachability and hydrodynamics (VED) based on the feedback mechanism between soil detachment and sediment transport. The VED was calibrated and validated with runoff plot data for woodland, grassland, and farmland in the Wuding, Yan, Jing and Wei Rivers of the Loess Plateau in China. Unified baseline parameters and decay coefficients of vegetation were obtained. The model validation results indicated that the coefficient of determination, Nash–Sutcliffe simulation efficiency and relative error ranged from 0.59 to 0.99, 0.56 to 0.90, and −45.99 % to 46.36 %, respectively. The decay coefficients for soil detachment capacity (Φ), sediment transport capacity (T c), and the sediment reduction effect of vegetation exhibited the following order: woodland > grassland > farmland. Compared with VED, existing process-based soil erosion models failed to effectively characterize the influence of vegetation on Φ and T c on the Loess Plateau, with differences of several orders of magnitude. The individual contributions of runoff, soil detachability, and hydrodynamics with vegetation impact on sediment yield were quantified by VED. The contribution rates of vegetation to sediment reduction decreased gradually with increasing slope length because the soil detachment capacity of bare slopes exceeded that of vegetated slopes, resulting in a faster increase in sediment yield. The contribution rates of vegetation to sediment reduction for woodland, grassland, and farmland with 20 %–60 % vegetation covers were 66.75 %–99.95 %, 57.43 %–99.63 %, and 27.91 %–88.63 % in the boundary conditions of this study, respectively. The results reveal the potential for integrating VED into other distributed watershed hydrological and sediment models to assess the effects of vegetation restoration on sediment reduction at a watershed scale. [ABSTRACT FROM AUTHOR]

• Amount & composition of stored sediment in rain-impacted flows affect erosion. • Amount & composition of stored sediment varies until the steady state occurs. • Compositions of stored and discharge sediment differ from each other. • Compositions of soil and sediment discharge is the same at the steady state. Many experiments on erosion by rainfall involve applying artificial rainfall on inclined planar soil surfaces. When sediment is discharged by rain-impacted flows, the transport of silt and sand-sized particles is dominated by raindrop-driven transport processes such as raindrop-induced saltation and rolling. Raindrop-induced saltation is a process which stores detached material on the soil surface as it transports detached material downstream. The amount stored increases with time until it reaches a steady state. If all particles transported downstream travel at the same rate, then the composition of the stored material is the same as that of the original soil. However, particles transported by raindrop-induced saltation travel at rates that vary with their size a density. This results in the composition of the sediment discharged to vary with time until the steady state is reached. In this paper, a qualitative mathematical model is used to demonstrate how the composition of the stored material varies with slope length, rainfall intensity, flow depth and the particle sizes being transported. The results produced by the model demonstrate that fine material is enriched at the expense of coarse material in the sediment discharge while being depleted in the stored material until the steady state is reached. The buildup of detained material on the soil surface also influences the amount of soil material discharge as time progresses during an erosion event. Consequently, the erosion rate will vary with time until the steady state is reached. Many experiments involve applying rain for a fixed time and consider the average erosion rate as the independent variable is regression analyses to determine the effect of factors such rainfall intensity, slope length, slope gradient and soil type on erosion. The inclusion of erosion when the steady state does not exist means that the results of these experiments have limited values beyond the experimental conditions used in the experiment. [ABSTRACT FROM AUTHOR]

In this paper, we examine the effect of vegetation on soil erosion, runoff generation and sediment transport on saline rangeland hillslopes. Rainfall simulations were conducted at a fixed 114 mm/h intensity on 6 m × 2 m erosion plots with varying degrees of vegetation. Plots were grouped into three categories (L, M and H) based on their canopy cover (L: <5%, M: 5–19%, H: >19%) and selected to limit variations in slope across canopy cover groups. Runoff and sediment samples were combined with three dimensional (3D) reconstruction data used to monitor soil surface microtopographic changes. Runoff initiation was significantly delayed on the L plots but cumulative runoff after 20 min of rainfall simulation indicated a positive effect of vegetation on infiltration processes. Cumulative sediment after 20 min of rainfall was similar across vegetation cover categories. The 3D data suggest that vegetation reduced net sediment delivery from the plots by primarily increasing opportunities for deposition while marginally affecting gross soil erosion. Plots with H vegetation cover experienced lower 3D-estimated erosion volumes but average erosion depth on L plots was lower than that on plots with M and H vegetation covers. Lower runoff volumes on M and H plots may have been compensated by greater runoff erosivity on these plots as runoff was concentrated in a narrower inter-patch space compared to L plots. This study highlights the need for an increased integration between traditional runoff measurement techniques and 3D reconstruction methods. [ABSTRACT FROM AUTHOR]

Explaining scale effects for runoff and erosion improves our understanding and simulation ability of hydrological and erosion processes. In this paper, plot scale effects on event runoff per unit area ( Q e ), sediment concentration ( C e ) and soil loss per unit area ( SL e ) were checked at El Teularet-Sierra de Enguera experimental site in Eastern Spain. The measurements were carried out for 31 events occurring in the years 2005 and 2007 in bare ploughed plots ranging from 1 to 48 m 2 . The analysis established the scaling relationship by dimensional analysis and self-similarity theory, and tested this relationship at different temporal scales ranging from event to annual scale. The dimensional analysis and the incomplete self-similarity condition allowed us to establish a power scaling relationship which was found to also be usable for the moments of k (1, 2, 3, 4) order. The power scaling relationship was theoretically deduced applying a boundary condition which is based on the hypothesis that sediment delivery processes do not occur at the selected plot scale. The simple scaling invariance condition was always verified (i.e. for each temporal horizon) for runoff and soil loss while the same hypothesis was not perfectly acceptable for sediment concentration. The analysis of the scaling relationships at event temporal scale showed that the spatial scale effects were less frequent for the composite variable (soil loss = sediment concentration × runoff) than the constituting variables. For 48% of the events, a statistically significant scale effect was detected for all tested variables. With reference to the statistically significant relationships, both runoff and soil loss always decreased and sediment concentration always increased in the passage from the reference area (1 m 2 ) to the largest one (48 m 2 ). The analysis at aggregated temporal scales suggested that annual scale effects for soil loss per unit area should be temporally more stable than those for both runoff and sediment concentration. Finally, at mean event scale the three investigated variables have a similar behaviour in terms of simple scaling invariance. [ABSTRACT FROM AUTHOR]

Sampling strategies and methods used for estimating load can lead to large uncertainties in suspended sediment transport quantification, especially in rivers with a high variability in streamflow. The aim of this paper is to evaluate suspended sediment load, using a number of direct estimation techniques, in order to find a suitable method for temporary river systems, and to assess the uncertainty associated with load estimation, due to the specific method applied. One year of continuous measurement of flow, and discrete sampling ( n  = 216) of suspended sediment concentrations, taken from 2010 to 2011 in the Celone River (SE, Italy), were used to estimate annual load. Averaging, ratio, and regression estimator methods were applied to the entire dataset, and to subsets of data, to calculate load. The results show a wide range of values, from 220 to 1123 t km −2  yr −1 , with respect to the applied suspended sediment load estimation techniques. Averaging methods resulted biased. Sediment rating curves underestimated load, while, if the back-transformation bias correction was used, load was overestimated. The ratio methods generally overestimate load. Increased precision and accuracy was achieved through applying data stratification, based on flow regime and seasonality. After applying three different flow regime stratifications, the annual load ranged from 240 to 606 t km −2  yr −1 and, using seasonal stratification, from 258 to 974 t km −2  yr −1 . It seems that ratio estimator methods, and the regression equations applied to the stratification on a flow regime basis, are more suitable for estimating load in temporary, flashy streams. [ABSTRACT FROM AUTHOR]

Environmental fluctuations during the Holocene caused important landscape changes in the Central Ebro Basin, which is a very sensitive region due to its semiarid climate, lithology, and continuous human presence. Severe erosion processes hinder palaeoenvironmental and archaeological record preservation. Infills of ephemeral stream valleys in semiarid environments are some of the best contexts for geoarchaeological studies. In this paper, we analyse the geomorphological processes, pedological features, and charcoal and pollen content and composition of the sedimentary sequence of La Poza Valley catchment area, with the support of additional information from La Bajada Valley. 14 C dates for 13 charcoal fragments provide the necessary chronological control. We describe 5 sedimentary units and a polycyclic sequence of six soils that covers most of the Holocene, beginning ca. 9.5 ky cal BP. Buried soils help to identify stability periods in the sedimentary sequence, while incision stages are detected through erosive contacts and terraced organisation of the sedimentary units. Charcoal and pollen content and composition, as well as the soil development, reveal an open forest of junipers and pines for the Early Holocene in the lower part of the sequence (mainly in Unit 1), very different from the current deforested landscape, also represented in the sequence (Unit 4). Thus, La Poza record shows the environment was favourable for hunter-gatherers from the Late Mesolithic and for the first Neolithic farmers. From then on, progressive degradation due to a combination of climate changes and increasing human pressure led to the current deforested landscape. [ABSTRACT FROM AUTHOR]

In this paper, we report the findings from an experimental study on a parabolic cross-sectional sand bed channel with uniform fine sand under no seepage and downward seepage conditions. Through experiments, we observed that an alluvial channel, which remained at threshold condition of sediment movement during the no seepage experiment, started transporting sediments with the application of seepage in the downward direction. Shields stress of the threshold channel increased significantly from its critical value after the application of downward seepage, which led to the deformation of the cross-sectional shape and consequent development of the bedforms. The role of turbulence in the development of bedforms has also been analyzed. Measures of turbulent statistics show that the time-mean velocities and Reynolds stresses were increased significantly with the application of downward seepage. Under the action of seepage conditions, increase in the flux of streamwise turbulent kinetic energy in the streamwise direction was observed in the region close to the channel boundary. Also, quadrant analysis exhibited an increase in the contributions from all the bursting events and the thickness of the sweep-dominated zone in near-bed region after the application of downward seepage. A bedform tracking tool has been used to evaluate the variability in the geometry of bedforms. We have classified these developing bedforms as current ripples and linguoid ripples according to their evolution with time under the downward seepage condition. It has been further observed that the variation in Shields stress and corresponding bedform geometry reached an equilibrium state in the presence of downward seepage when the experiments were run over a longer period of time (24–31 h). [ABSTRACT FROM AUTHOR]

• Sparse representation is employed to improve the sediment fingerprinting technique. • The SRSF method is advantageous in feature extraction and selection. • Virtual sample mixtures and empirical results tested the reliability of the SRSF. • SRSF is used to quantify contributions of sediment provenances in the Yangtze Delta. Quantitative research on the sediment source to sink process is critical to revealing the evolution of the Earth's surface. The fingerprinting technique is useful for sediment source detection, and machine learning methods are being used with this technique. However, paleo-provenance research with limited measured data from sediment cores is not adequate for big data analysis which demands a large amount of data. Hence, determining how to assess authentic source contributions by using fingerprinting techniques based on very limited measurement data is a key scientific task. Sparse representation (SR), a machine learning method with advantages in feature extraction that treats the source as a linear combination of multiple tracers, has the potential to provide satisfactory answers. In this paper, a sparse representation-based sediment fingerprinting (SRSF) method is introduced. Based on size-specific magnetic and geochemical characterizations, we applied this method to quantize the provenance of three sediment cores from the Yangtze River Delta (YRD), where Yellow River sediment has contributed to delta formation over the past 400–600 years. Our results showed that the sediments of the Yellow River contributed 19.3 ± 5.8 % of the clay and fine silt (<16 μm) and 23.5 ± 9.2 % of the medium silt (16–32 μm) in the delta, which was consistent with previously published results. This study improves the current fingerprinting technique in the feature extraction and selection stage by leveraging SR and provides reference data for the development of the modern YZD delta. The SRSF method has many potential applications, especially in paleo-provenance detection with highly limited measurement data, which could help expand our understanding of paleo-Earth surface evolution. [ABSTRACT FROM AUTHOR]

[Display omitted] • New image processing algorithm to analyse fine sediment deposits on gravel bars. • Method based on a high-pass filter and K-means clustering. • Calibration using close-range pictures proceesed with Basegrain algorithm. • Validation using Wolman pebble count method. • Method more robust to varying image quality than existing method. In this paper, we present a new image processing algorithm to analyse fine sediment deposits on gravel bars. The method is based on pictures taken from the river bank with an average resolution of a few centimetres per pixel. The proposed image processing algorithm consists of two steps. In the first step, the raw image is orthorectified with a 5 cm pixel size. In second step, we used an original combination of two well-known image techniques to classify pixel. First, a high-pass filter is applied in the Fourier domain to correct grey-value potential bias, i.e. to merge wet and dry deposits. Then, an unsupervised classification process based on K -means clustering is conducted to partition image pixels into K classes. The area of fine sediment deposits is calculated by summing the area of each class multiplied by weighting parameters (surface area percentage of fine deposits for each class). The value of K and the weighting parameters are calibrated using local close range photos of the bar surface representing the spatial variation of surface fine sediment distribution. The algorithm is then validated with field measurement using the finest class (d < 4 mm) of Wolman pebble count method. The impact of image resolution is investigated: the algorithm was found suitable for pixel size between 1 and 10 cm. The robustness of the present algorithm to images taken at different times and with different illuminations is studied by comparing it to two methods from the literature. The new method yields the most robust results with an average standard deviation lower than 5%. It yields larger surface of fine sediment since it includes all possible patches around coarse particles. Such results imply that the algorithm can be applied on a long image series to help us understand the temporal dynamics of fine sediment deposits on the bar surface. [ABSTRACT FROM AUTHOR]

• Sediment connectivity concepts, approaches, indices, and methods have been addressed. • The advantages and limitations of the approaches and methods have been depicted. • Structural and functional connectivities have a hard and soft nature, respectively. • Static characteristics are considered rather than dynamic aspects of connectivity. • Simultaneous assessment of connectivities will be a vital consideration for future. In recent years the concept of connectivity has emerged in sediment management to describe transfer of sediment from different sections of landscapes at various spatial and temporal scales. The sediment connectivity concept has two distinct components: structural and functional. Structural and functional sediment connectivities have a hard and soft nature, respectively, in which the former relates to physical characteristics and the latter to soil erosion and sediment transport processes. Although there has been an increase in sediment connectivity studies over the last decade, disagreement and confusion seems to remain about conceptual and especially methodological approaches, related indices, methods of quantifying sediment connectivity at a range of spatial and temporal scales, and the current situation in sediment connectivity research. A review of the relevant literature is needed to address these issues and provide a holistic overview of different aspects of sediment connectivity which would enlighten the directions of future research. In this review, 117 papers have been classified into five different categories, namely (i) developing conceptual frameworks; (ii) depicting spatial and temporal distribution of sediment source and sink areas; (iii) developing sediment connectivity indices; (iv) using and developing models; or (v) investigating sediment delivery likelihood through a network analysis approach. The reviewed contributions within each category were 8%, 23%, 55%, 10% and 4% papers respectively. The results indicated that more studies at both global and local scales are necessary to achieve a comprehensive conceptualization of sediment yield and related processes using sediment connectivity. Most studies have concentrated on static characteristics rather than dynamic aspects of connectivity, leading to mainly structural-based methods and indices, resulting in less attention being paid to functional connectivity. Process-based sediment connectivity studies, by focusing on spatio-temporal variations of sediment transport throughout a watershed, will therefore be a crucial aspect in future studies. [ABSTRACT FROM AUTHOR]

The emergence and diffusion of metallurgical technology had tremendous environmental consequence, however, the spatial-temporal consequences of the metallurgy during Bronze Age are not clear in China. In this paper, X-ray fluorescence (XRF) measurement and principal component analysis (PCA) were conducted on heavy metal element (Cu, Ni, Pb, Zn, Cr and As) concentrations (HMEC) of natural and anthropogenic sediment samples systematically collected from 22 late Neolithic-Bronze Age sites in Hexi corridor to explore the potential for subcontinental-wide changes in soil geochemistry. We place this data within the context of the Cu concentrations in lacustrine sediments located near smelting and mining centers in Bronze Age China. Our results show that variation of HMEC in anthropogenic sediment in Hexi corridor is contemporaneous with the increases of the Cu concentrations in lacustrine sediment around 4000 BP. Comparative data suggests the metallurgical production diffused from the Hexi corridor to central and southwestern China around 3600 BP. We argue that sediment pollution is not an isolated phenomenon during the Bronze Age China, but rather occurred on regional scales and is closely related to the intensity of smelting activities. [ABSTRACT FROM AUTHOR]

Objectives Under the background of global climate change, variations in streamflow and sediment discharge in the Yellow River would continue with intensified human activities and changes in the ecological environment. To harness the Yellow River, analyzing the degrees of change and the reasons for the streamflow and sediment discharge, as well as predicting the future trends, are urgently needed. Methods In this paper, the non-parametric Mann–Kendall test, Sen's estimator of slope, Pettitt's test and wavelet transform were applied to detect the trends, the magnitude of the trends and the abrupt changes and periodic variation in streamflow and suspended sediment discharge at eight hydrological stations from 1950 to 2013 along the mainstream of the Yellow River. Results Over the past 64 years (1950–2013), the spatial distribution of the annual average streamflow was of the “M” type, and the annual average suspended sediment discharge had a parabolic curve shape along the mainstream of the Yellow River. The temporal variation showed a distinct decreasing trend in streamflow since the 1990s and in suspended sediment discharge since the 1980s. Many cycles of oscillations occurred in the streamflow and suspended sediment discharge variation, leading to an alternate change in the wet/dry periods and the high/low sediment discharge periods. Conclusions In various regions of the Yellow River Basin since the 1970s, climate changes contributed reductions of 17.0–45.0% and 12.2–50.3% for streamflow and suspended sediment discharge, respectively, whereas human activities contributed reductions of 55.0–83.0% and 49.7–87.8%. Therefore, human activities were the major causes of the significant decline in the streamflow and the suspended sediment discharge of the Yellow River over the past six decades. Reasonable and possible measures should be taken to achieve water resources optimization and configuration and to promote watershed management and sustainability in the regions of the Yellow River Basin. [ABSTRACT FROM AUTHOR]

In this paper, we describe the mineral and grain size compositions of sand from the major dune areas adjacent to the now dry Owens Lake, California and compare them with sand from potential sources including washes draining the Inyo and Coso ranges to the east and south of the basin, as well as to the Owens River and washes draining the Sierra Nevada, which lies to the west of the Owens Valley and Owens Lake. The semi-quantitative mineral compositional data indicate that the dune sands are all very similar and are composed of approximately 47% quartz, 33% plagioclase and 13% potassium feldspar, with minor amounts of calcite and other minerals. The relative proportions of quartz, plagioclase, and K-feldspar indicate that the sands are derived from granodioritic source rocks. It is therefore considered that the primary source of sand for dune fields in the Owens Lake basin is sediment derived from the Sierra Nevada via the Owens River from the north as well as from granitic rocks in the Coso Range to the south. Sediment from fluvial and alluvial sources reached the dune fields in the northeastern sector of the basin by wind transport across the exposed bed of Owens Lake during periods of low lake levels. The pathway by which sand reached the Olancha Dunes located to the south of the lake is less clear, but probably involved transport from the South Sand Sheet, via the Dirty Socks Dunes. The source of sand for the South Sand Sheet area is hypothesized to be the adjacent Vermillion Canyon wash system draining the Coso Range. [ABSTRACT FROM AUTHOR]

• Lulao catchment (LLC) is a small, homogeneous watershed on Guizhou Plateau, SW China. • Farmland soil (FS) has higher IRM 300mT /SIRM due to stronger pedogenesis in LLC. • Grassland soil (GS) has low IRM 300mT /SIRM & higher HIRM in LLC where a reservoir lies. • Contribution of FS vs GS to reservoir sediment is inferred with sediment's magnetism. • Changes in erosion is inferred as FS is distant from the reservoir than GS. This paper demonstrates that land use could enhance spatial discrimination of soil magnetism in a homogeneous watershed, and such differences help infer alterations in sediment sources and erosion. One sediment core was sampled from a reservoir built in 1958 and fifteen soil profiles from its catchment on the southern Guizhou Plateau, SW China. The whole watershed was covered by yellow earth developed on limestone. Magnetic measurements and granulometric analysis were performed on the soils and sediments while TOC and TN analysis on two soil profiles and 137Cs analysis on the sediment core. Information of seven years' land-use was derived from remote sensing images. The farmland and grassland soils had different magnetic characteristics while the downwards distributions of TOC and C/N were similar in the two profiles. The grassland soils had higher HIRM, lower χ fd % and IRM 300mT /SIRM. The higher χ fd % and IRM 300mT /SIRM of the farmland soils suggested stronger pedogenesis under cultivation. The average HIRM, χ fd % and IRM 300mT /SIRM were 38 and 334 10-6 A m2 kg−1, 5.7 and 3.6%, and 0.91 and 0.66 for the farmland and grassland soils. The farmland soils were finer probably due to tillage. The reservoir has been closely surrounded mainly by the grassland whereas the farmland, embedded with patches of the grassland, has occurred in the terrains relatively distant from the reservoir. The sediments of 1958–1985 had lower HIRM (156 10-6 A m2 kg−1) and higher IRM 300mT /SIRM (0.79), indicating greater contributions of the remote farmland soils mixed with grassland soils and stronger erosion. HIRM increased (229 10-6 A m2 kg−1) and IRM 300mT /SIRM decreased (0.67) in the sediments of 1985–2019, implying decreased distant-soil contributions and relatively increased input of the grassland soil closely around the reservoir. Erosion thus weakened, as proven by the finer sediments. The declining erosion was mainly due to farmland shrinkage and grassland expansion. [ABSTRACT FROM AUTHOR]

[Display omitted] • MUSLE is able to predict sedimentary response and mitigation measures in burnt areas. • High-severity fire increase soil erosion and sediment load at the basin scale. • Emergency stabilization and soil erosion barriers are effective to reduce soil erosion. • SWAT model may be a post-fire management decision tool. The present paper contributes to bridging the gaps in modelling post-fire impact and mitigation measures on soil erosion. The specific aims were to predict the effects of forest fires and post-fire mitigation measures on runoff and specific sediment yield (SSY) in a river basin (Celone, S-E Italy). The Soil and Water Assessment Tool model, calibrated with field observations, was used to evaluate runoff and SSY for the current land use (baseline) and six post-fire scenarios. From 1990 to 2011, at the basin scale, the average annual SSY was 5.60 t ha- 1yr−1 (SD = 3.47 t ha-1yr−1). 20% of the total drainage area showed a critical value of SSY (>10 t ha−1 yr−1). The effects of different fire-severity levels were predicted for one year after the fire, acting on a limited area (2.3% of the total basin area). At the basin scale, the post-fire effect on surface runoff was negligible for all scenarios (<0.4%), and the impact on SSY increased from 5.86 t ha−1 yr−1 up to 12.05 t ha−1 yr−1. At the subbasin scale, the post-fire logging scenario showed the highest increase of soil loss (SSY increased from 9.48 t ha−1 yr−1 to 57.40 t ha−1 yr−1). Post-fire mitigation treatments like straw mulching and erosion barriers effectively reduced soil erosion in high- and moderate-severity fires (19.12 t ha-1yr−1 and 20.93 t ha−1 yr−1, respectively). At the hydrological response unit level, the SSY estimated for the forest in the baseline ranged from 1.18 t ha- 1yr−1 to 2.04 t ha−1 yr−1. SSY increased more than one order of magnitude for the high-severity fire scenarios and ranged from 4.33 to 6.74 t ha−1 yr−1 in the very low-severity fire scenario, underlining the scale effect from the HRU to the basin scale. [ABSTRACT FROM AUTHOR]

Abstract: Field studies documenting fine-sediment (<2mm) transport in gravel-bed rivers are rare. For the first time in a fluvial environment, a technique that enhances the magnetic susceptibility of sand is used to trace its longitudinal dispersion and storage. This paper describes the methodology behind the artificial magnetic enhancement of iron-stained sand, and presents the results from sand tracing exercises conducted on two gravel-bed channels with pool-riffle morphology; one unregulated and sinuous in nature (site A), the other regulated and straight (site B), both situated on the River Rede Northumberland, UK. Two tonnes of magnetically enhanced tracer sand was introduced to site A and four tonnes to site B, to provide information on fine-sediment storage dynamics, interaction of fines with the stream bed, and rates of movement, expressed as virtual velocity (Vi ). Sand transport pathways appeared to differ between the reaches; for site A, sand storage was found on bars and riffle margins with no storage or signs of transport through pools, and in contrast pool storage of tracer was a key feature shown at site B. Topographic forcing may cause differences in sediment sorting at site A; topographic highs tend to have low sand transport rates with sand grains becoming congested in these areas, whereas topographic lows show higher transport rates resulting in greater dispersion. Supply limitation of sand on the falling limb of the hydrograph may also become an issue in the topographic lows at this site. Hydrograph differences between the regulated and unregulated reaches could also play a role; however this could not be quantified in this study. There was no evidence of sand infiltration into the bed at site A; however marginal evidence for infiltration into the near-surface (0–15cm) substrate voids was found at site B. The general lack of evidence for significant infiltration may reflect limited availability of void space in substrate framework gravels. Tracer sand was transported over the bed surface, with little vertical interaction with the substrate, despite periods of gravel mobilisation at site A. Vi over the study duration for site A was 2.28mday−1, and 0.28mday−1 for site B. These values are greater than those calculated using existing predictive equations developed from gravel tracer data, possibly reflecting differences in the mode of transport between bedload and saltation load. [Copyright &y& Elsevier]

Abstract: In this paper, temporal variations in the hydrological process of the Pearl River delta (PRD) are examined based on monthly datasets for water discharge, sediment load and suspended sediment concentration (SSC) since the 1950s using the methods of power spectrum analysis and Fourier transform. In addition, the underlying causes of the variations are examined to address the influence of diverse human activities on hydrological process. The results indicate that (1) for the monthly low pass filtering series with a timescale of more than 8a, the water discharge from the Pearl River increased insignificantly with an average rate of 1.66m3/s per year, whereas the sediment load and SSC decreased significantly with an average rate of 18.54kg/s and 0.002kg/m3 per year, respectively, between 1957 and 2009; (2) decadal change in the water discharge of the Pearl River can be identified with low periods in 1950s–1972, 1984–1992 and 2003–2009 and high periods in 1973–1983 and 1993–2002, which is in good agreement with precipitation changes. Decadal change in the sediment load generally differed among three tributaries. For the West River and the North River, before the 1970s, no significant change in the sediment load can be observed because of the balanced influences of dam construction and deforestation. In the 1980s, a significant increase occurred because deforestation exceeded dam construction. Since the 1990s, large reservoirs were constructed in the West River and North River basins. And total deposition rate of all the reservoirs in two river basins was estimated to be 168.8×106 m3/a in the 1990s and reached to 881.1×106 m3/a in the 2000s, respectively. The influences of dam construction and soil conservation have outweighed the impact of deforestation, which has resulted in a significant decrease in the sediment load. For the East River, since the dam construction in 1960, the influence of deforestation on the sediment load did not outweigh the influence of the dam construction, which gradually decreased the sediment load; (3) for the PRD, temporal change in the water discharge and sediment load in the West River and North River deltas correspond well with the change in the water discharge and sediment load upstream of the West River and the North River before the 1990s. Due to the uneven down-cutting of the riverbed in the upper PRD since the mid-1980s, which is primarily caused by intensified sand excavation from the river channel, the divided flow ratio and divided sediment ratio at Sanshui station in the North River delta increased by 7.8% and 7.7%, respectively, in the 1990s–2000s compared with the 1960s–1980s. Therefore, the water discharge and sediment load in the North River delta increased by 57.0% and 12.2%, respectively. These changes have resulted in morphological changes in the PRD and caused many environmental problems across the PRD, which should be paid special attention. [Copyright &y& Elsevier]

Abstract: The palaeoecological study, presented in this paper, investigates the biomorphic (phytoliths and other biological microfossils), loss-on-ignition and pollen records in the sedimentary sequence of the Blatna Brezovica Eneolithic settlement (Ljubljansko barje, Slovenia, ca.3100cal B.C.). At the beginning of the 4th millennium cal B.C., the study site was covered by a freshwater lake, surrounded by a broadleaved Quercus–Fagus forest. In subsequent centuries, people settled at the Blatna Brezovica location, albeit the hydrological conditions remained wet and the archaeological settlement was likely located in the vicinity of a river. People living at Blatna Brezovica constructed wooden houses, whereas Phragmites plants were likely used for roofs and/or bedding. Eventually, the landscape became more open due to agriculture (Hordeum cultivation) and grazing. After the abandonment of the settlement at the end of the 4th millennium cal B.C., hydrological conditions became drier, marsh formed at the study site, and predominantly Abies forest grew around the basin. [Copyright &y& Elsevier]

[Display omitted] • Stabilizing sand dunes with tar mulch can result in environmental pollution. • An alternative is to fingerprint key sources of aeolian sediment. • Geochemical data were combined with weathering indices to trace sand dune sources. • Alluvial fan material was the key source of the target sand dunes. • The weathering indices offer low-cost options for aeolian fingerprinting. Confirmation of cost-effective and reliable tracers for aeolian sediment (sand dune) source fingerprinting warrants further research. Accordingly, the main objective of the work reported in this paper was to investigate the efficiency of weathering indices in aeolian sediment fingerprinting using a case study of a fragile arid region in Qom Province, Iran. Eight geochemical elements (Al, Ca, Fe, K, Na, Mg, Si, Ti) and 17 associated weathering indices were measured in 34 aeolian source samples and 10 sand dune target sediment samples in three absolute particulate size fractions. For each fraction, three final composite fingerprints (i.e., geochemical elements only, weathering indices only and a combination of the two) for discerning and ascribing the aeolian sediment sources were selected. The Modified MixSIR Bayesian un-mixing model was used to apportion aeolian source contributions using the final composite fingerprints. Regardless of the composite fingerprint used, all results across the different size fractions suggested that the south-eastern alluvial fan is the dominant (average contribution 50.6%, SD 19.0%) source of the sand dune samples, with the western alluvial fan being the second most important (average contribution 38.4%, SD 20.4%) source. Comparisons of the posterior distributions for the predicted source proportions generated using the nine composite fingerprints (three kinds of composite fingerprints*three particle size fractions) showed that the composite fingerprints combining the geochemical elements and weathering indices generated the most powerful source material discrimination. Our results demonstrate the use of weathering indices alongside more conventional elemental geochemistry tracers for investigations into sand dune sediment provenance. [ABSTRACT FROM AUTHOR]

• We reconstructed environment changes with the use of multi-proxy approach. • Permafrost degradation led to a radical transformation in the flow of groundwater. • The paludification of the basins was determined by local conditions. • The process of subsidence determined the characteristics of the sedimentation basins. The paper presents records of lithofacial succession in the sediments of the Bagno Staw alkaline fen (Western Polesie Lowland, Eastern Poland), documenting the phase of rapid morphogenetic transformations during LG/H in the Lublin chalkland. Environmental conditions responsible for the morphogenesis and evolution of the site (from a shallow periglacial lake to an alkaline fen) were reconstructed. A detailed geological survey in combination with the analysis of Cladocera assemblages revealed the presence of numerous palaeodepressions under the plain covered today by the alkaline fen, which were initially small shallow lakes with a well-developed phytolittoral zone. Geochemical data and the analysis of stable O and C isotopes indicated that these lakes were supplied by ascending waters. Karstic phenomena under periglacial conditions, including subsidence at the bottom of biogenic accumulation basins, played an important role in the transformation of this site. These changes were largely determined by the chronology and dynamics of permafrost degradation. [ABSTRACT FROM AUTHOR]

• We reconstructed environment changes with the use of multi-proxy approach. • Permafrost degradation led to a radical transformation in the flow of groundwater. • The paludification of the basins was determined by local conditions. • The process of subsidence determined the characteristics of the sedimentation basins. The paper presents records of lithofacial succession in the sediments of the Bagno Staw alkaline fen (Western Polesie Lowland, Eastern Poland), documenting the phase of rapid morphogenetic transformations during LG/H in the Lublin chalkland. Environmental conditions responsible for the morphogenesis and evolution of the site (from a shallow periglacial lake to an alkaline fen) were reconstructed. A detailed geological survey in combination with the analysis of Cladocera assemblages revealed the presence of numerous palaeodepressions under the plain covered today by the alkaline fen, which were initially small shallow lakes with a well-developed phytolittoral zone. Geochemical data and the analysis of stable O and C isotopes indicated that these lakes were supplied by ascending waters. Karstic phenomena under periglacial conditions, including subsidence at the bottom of biogenic accumulation basins, played an important role in the transformation of this site. These changes were largely determined by the chronology and dynamics of permafrost degradation. [ABSTRACT FROM AUTHOR]

Abstract: Badlands have long been considered as model landscapes due to their perceived close relationship between form and process. The often intense features of erosion have also attracted many geomorphologists because the associated high rates of erosion appeared to offer the opportunity for studying surface processes and the resulting forms. Recently, the perceived simplicity of badlands has been questioned because the expected relationships between driving forces for erosion and the resulting sediment yield could not be observed. Further, a high variability in erosion and sediment yield has been observed across scales. Finally, denudation based on currently observed erosion rates would have lead to the destruction of most badlands a long time ago. While the perceived simplicity of badlands has sparked a disproportional (compared to the land surface they cover) amount of research, our increasing amount of information has not necessarily increased our understanding of badlands in equal terms. Overall, badlands appear to be more complex than initially assumed. In this paper, we review 40years of research in the Zin Valley Badlands in Israel to reconcile some of the conflicting results observed there and develop a perspective on the function of badlands as model landscapes. While the data collected in the Zin Valley clearly confirm that spatial and temporal patterns of geomorphic processes and their interaction with topography and surface properties have to be understood, we still conclude that the process of realizing complexity in the “simple” badlands has a model function both for our understanding as well as perspective on all landscape systems. [Copyright &y& Elsevier]

Abstract: The spatial scale dependency of runoff generation and sediment yield and accuracy to extending the results of experimental plots to surrounding watersheds is rarely taken into account. The present paper aimed to evaluate the accuracy of soil erosion plots with different lengths in estimation of runoff and soil loss from a small watershed in Iran. Towards this attempt, two similar sets of experimental plots with lengths of 2, 5, 10, 15, 20 and 25 and fixed width of 2m were installed on two north and south facing slopes (i.e. 6 plots on each slope and totally 12 plots) in Sanganeh watershed, Razavi Khorasan Province with an area of ca. 1ha. Runoff and sediment was collected at the outlet of each plot as well as main outlet of the watershed associated with 12 storm events occurred during November 2006 to June 2007. The results verified that the accuracy of plot estimates on sediment and runoff improved while the plot length increased. The optimal lengths for estimation of sediment and runoff parameters were found 15 and preferably 20m for plots located on southern slope. No significant difference was also proved among estimates obtained from plots established on north facing slope and those measured at the main outlet of the watershed. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an integrated study that considered the relationship between erosion and stream sediment yield in an agroforestry catchment (16km2) in NW Spain. The study combined measurements of soil erosion by concentrated flow at field scale with sediment yield measured at the catchment outlet during winter 2007/08. The results indicate that concentrated flow erosion, i.e., rills and ephemeral gullies, occurred on unprotected crop fields. Erosion by concentrated flow was highly discontinuous within the catchment, both spatially and temporally. Soil loss differed significantly from event to event. About 68% of soil loss took place in a single event with a sediment yield of 8.5Mg, i.e., about 30% of the winter sediment load. Soil losses measured at the Corbeira catchment outlet (28.53Mg) were indeed more than 5 times lower than those measured on the fields (140.5Mg of rills and ephemeral gullies and 15.6Mg for estimated interrill erosion) due to sediment deposition along the route from field to catchment outlet. The sediment delivery ratio was 22%. This value is relatively low due to the presence of abundant vegetation-induced sediment deposition. Sediment delivery to the catchment outlet was determined to a great extent by the spatial distribution of land use, as well as by the poor connectivity between erosion areas and the stream. This catchment is characterized by mosaic vegetation with the grasslands located at the bottom of cropped fields, making sediment delivery to the stream difficult. The results of this study suggest that in the Corbeira catchment soil loss cannot be estimated from the sum of individual field soil losses. Our observations reveal that soil erosion rates measured at one scale are not representative of sediment yield at another scale level. [Copyright &y& Elsevier]

Abstract: This paper tackles two main questions by linking observations, determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models. First, do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values? Secondly, deterministic soil erosion models make the assumption that there is a relationship (often further assumed to be linear) between shear stress and soil detachment; is this suitable for representing real erosion process combinations in natural rills? Following most process based deterministic soil erosion models, derived hydraulic and erosion parameters should be similar. However, the results from the different experiments showed clear differences in sediment concentration, transport rates and other measured as well as calculated values. In contrast to our experimental results, a model simulation would produce erosion parameters with low variations, represented by the relative measurement error and the empirical variation coefficient. This reveals the general problems of using process based deterministic models for erosion in shallow rills. While soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface, other processes like side wall failure, headcut retreat and plunge pool dynamics are not taken into account. Our results suggested that these other processes may contribute substantially to rill erosion processes. The results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes. Measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution. This combination cannot be described by a single equation. [Copyright &y& Elsevier]

Abstract: The Tinto River shows very high concentrations of toxic elements and acidity from its source in the mining area to its mouth. In this paper, we studied the evolution of the levels of toxic elements during part of the Quaternary from the analysis of fluvial deposits that, forming terraces, were originated by the dynamics of the Tinto River. Using a detailed geomorphological cartography, up to nine terrace levels were differentiated in the lower sector of the basin, whose ages range from the Pleistocene to the Holocene. Sampling and geochemical analyses (major elements and trace) were carried out in six of these levels, in addition to sediments of the current flood plain. The results of these analyses do not show any bias from the mid Pleistocene (T8 — Terrace 8) to the early Holocene (T1). Moreover, these geochemical contents are similar to the average values obtained by other authors for the entire South-Portuguese Zone of the Iberian Massif. However, the current sediments of the Tinto River (T0) show a sharp increase in the levels of As, Cu, Pb and Zn compared to the rest, which indicates a serious increment of contamination by toxic elements. Although there are evidences on the existence of a natural process of oxidation of sulfides since the Miocene, the amounts of toxic elements released should be very small compared to those generated since the beginning of the mining activities in the Iberian Pyrite Belt. [Copyright &y& Elsevier]

Abstract: The study area is the Bajo Segura Basin, located in the easternmost sector of the Betic Ranges. The existence of a wide coastal lagoon occupying the depressed spaces (at least since the Middle Pleistocene) has been inferred, in previous works, from the stratigraphic, micropaleontological and sedimentological analyses. Particularly during the Upper Holocene the environmental morphology was modified. This paper aims to correlate the geomorphological, sedimentological and micropaleontological data with archeological and geoarcheological information of the Upper Holocene. This will allow to hypothesize the recent environmental evolution and its relation to human settlement. The geomorphological approach consists in the analysis of six mechanical cores and geoarcheological studies in several sites. Archeological data is based on sites dating to the 2nd millennium B.C. (Bronze Age), 725–550 B.C., 8th–6th centuries B.C. (Early Iron Age), 550–206 B.C. (Iberian Age), 6th–3rd centuries B.C., 206–500 B.C. (Roman Age), 3rd century B.C.–5th century A.D. and 500–900 A.D., 5th–8th centuries A.D. (Early Middle Ages). During the Bronze Age, the Bajo Segura Basin was occupied by a coastal lagoon with marine communication. The fossil assemblage indicates a greater marine influence near the coast and fresher conditions further away from it. At least since the subsequent period, and especially since the Iron Age, an activation of the alluvial processes is recorded establishing paleogeographical changes in the lagoons. During the roman period the southern landscape (Segura River) is dominated by the flood plain with associated lagoons and freshwater marshes, at least in the inner part. To the north, the Vinalopó alluvial fan progrades and reduces the dimensions of the lagoonal areas. The swampy conditions remained until the Modern Age. Agricultural expansion reached its maximum development in the 18th century A.D. and gave rise to the present landscape. [Copyright &y& Elsevier]

Abstract: This paper describes the results of geomorphological, sedimentological and 14C analyses of Late Holocene fluvial sequences in the Moldova River Valley of Romania. This river originates from the Carpathians mountains and is known for the extent of its large floodplain and sediment thickness. Between the Molid and Timişeşti localities (river length: 86km), numerous large fossil trunks of oak, poplar and beech trees are exposed in the riverbanks. Six wood samples were selected for radiocarbon absolute dating (conventional method), and their ages ranged from 410 to 3200calyrs. BP. The thickness of the alluvial sediments above the sampled fossil trunks varied between 2 and 3m, and these sediments predominantly consisted of coarse gravel materials that had similar granulometry to sediments that were present in the modern riverbed. Additionally, in the same investigated areas, successive floodplain cross-sections were constructed based on more than 20 hydrogeological boreholes. For each cross section, all data were used to calculate the local values of bed loads, and these values were compared to the absolute ages of the fossil trunks and were in the range of 300m3/m and 5500m3/m. Based on the calculated values, during the last 780years, the floodplain sedimentation rates were estimated to be in the range of 0.4m3/year at the Molid Section, which was located in the mountainous area of the valley and 44km downstream from the river headwater, and during the last 410years, the sedimentation rate at the Praxia Section, which was located 125km downstream from the river headwater, was 13.3m3/year. In the past 100years, the fluvial processes along the Moldova River were dominated by a narrowing (by an average of 76%) and an incision (up to 2.5m), and a channel metamorphosis from braided to wandering was reported. These results are discussed in the context of Late Holocene regional and local palaeoclimatic reconstructions as well as that of human interventions. [Copyright &y& Elsevier]

Abstract: Heavy metal contamination of bottom sediments of the Changjiang River is widely reported, however, the potential source and methods of transportation of these heavy metals in the contaminated sediments is poorly defined. This paper examines the correlation between heavy metals and geochemical indices, including Fe2O3, Al2O3, total organic carbon (TOC) and black carbon (BC), as well as magnetic susceptibility (MS). Using these indices we investigate the contamination characteristics of heavy metals in the sediments by with Principal Component Analysis (PCA). Results from 83 sediment samples collected in the lower reach of Changjiang River (from Nanjing to Shanghai) show that the first principal component accounts for 52.23% of the total variance, corresponding to the heavy metals, Co, Cr, Cu, Ni and Zn, and conservative components of Fe2O3, Al2O3 and TOC. This result indicates that heavy metal distributions are controlled by the transportation and sedimentation of fine particles which is also confirmed by particle size analysis. The second principal component explains 24.81% of the variance and is dominated by Cd, Pb and MS, which, collectively, result chiefly from industrial and transportation activities and, for MS, fly ash production. The third principal component accounts for 7.91% of the variance and corresponds solely to Hg. Principal component analysis/multiple linear regression (PCA/MLR) was used to estimate the contribution of the three principal components to each heavy metal. PCA/MLR results suggest that more than 50% of Co, Cr, Cu, Ni and Zn were influenced by the particle size effect. Particle size effect and fly ash account for 37.1% and 27.7% of As. Cd and Pb were mainly explained by fly ash. 98.9% of Hg was related to PC3, which represented black carbon (BC). Our study indicates that the combination of geochemical and multivariable statistical methods clearly characterizes the geochemistry of heavy metals in sediment of the lower reaches of the Changjiang River and suggests that power plants are the main source of heavy metal pollution. [Copyright &y& Elsevier]

Abstract: Long-term changes to the Yellow River delta in China have received considerable attention not only because of the growing economic importance of the delta region but also because they provide a clear example of the dominant role played by anthropogenic effects upon a large dynamic river delta. This paper presents a detailed study on the morphological consequences of reduction in river sediment load and influence of human activities based on sediment load data at three gauging stations in the upper, middle and lower reaches of the Yellow River basin from 1950 to 2007. The results indicate that sediment loads at all three gauging stations display a gradually decreasing trend over the past 58years. The primary reason for this decrease is shown to be due to various human activities, including the construction of Longyangxia and Liujiaxia reservoirs in the upper reaches, water–soil conservation practices and the commissioning of Sanmenxia and Xiaolangdi reservoirs in the middle reaches. It is estimated that water–soil conservation practices which are a major factor to the decrease of sediment load at Huayuankou gauging station account for 40% of the total amount of reduction, sediment trapping by Sanmenxia and Xiaolangdi reservoirs account for 30% of the total amount of reduction and the 10% decrease is caused by human activities in the upper reaches. The remaining 20% decrease is attributed to precipitation decrease. The reduction of sediment load has directly impacted on the lower Yellow River and the delta region, causing alternate changes between siltation and scouring in the lower river channel along with an increased rate of erosion over the whole Yellow River delta. [Copyright &y& Elsevier]

Abstract: The Souar lithologic formation in semi-arid Tunisia is undergoing severe gully erosion which is threatening soil and water resources. Soil conservation strategies have focused more on terracing than on gully control techniques, since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown. The paper reports investigations into the sediment yield provided by head-cut as well as sidewall–floor erosion of first order gullies on gentle and steep slope catchments underlined by the Souar lithologic formation. We measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments, respectively. Two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established. The treatment with a Geographic Information System (Arc View) of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls–floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights. Total gully erosion was on average 1.66 m3 ha−1 year−1 for the gentle slopes and 5.603 m3 ha−1 year−1 for the steep slopes. Sidewalls–floor contribution in total erosion was on average 81.5% for the gentle slopes and 77.8% for the steep slopes. We found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds. Two equations between these two variables were established both for gentle and steep slope catchments. [Copyright &y& Elsevier]

Abstract: Pinpointing erosional ‘hot spots’ or sediment source areas within a watershed can be difficult because of the highly non-linear and episodic nature of effective runoff and sediment transport. Continuous monitoring of stream networks can provide insight into sediment source areas not possible from routine sampling by capturing episodic events and integrating entire storm events. This paper presents the results of a three-year study of spring snowmelt runoff in watersheds of Lake Tahoe, California, USA, using a network of nine nephelometric turbidometers. We estimate that montane badlands, comprising 1.2% of the Ward Creek watershed (25 km2), contributed 10–39% of snowmelt-derived suspended sediment load. The badlands are comprised of poorly-vegetated and deeply-incised gullies formed in parent material of Miocene volcanic mudflow breccia. The larger (29.5 km2) Blackwood Creek watershed also showed high relative erosion rates from volcanic terrain. Tributaries draining forested granitic and metasedimentary headwater regions had minimal sediment loads. Monitoring networks indicated that temporary main channel storage regulated release of fine sediment eroded from steep headwater slopes. This lag between erosion and delivery may lead to underestimation of gully erosion contribution to sediment budgets. [Copyright &y& Elsevier]

• The near-dam region contributed 10.8% of the total sediment into the reservoir. • Sedimentation mainly occurred in bending, branching and near-dam reaches. • The key factor influencing sedimentation was the incoming sediment load. • New formulas were proposed to calculate sediment trapping efficiency. Sedimentation in the Three Gorges Reservoir (TGR) affects flood control, navigation, power generation and the ecological environment. We present a comprehensive analysis of the characteristics of sedimentation in the TGR from 2003 to 2018. The data set includes field measurements (runoff and sediment) at hydrological stations and estimation for areas where measured data are not available. Based on the data set, the amount of sedimentation in the TGR was calculated with the Sediment Budget Model (SBM) and Section Topography Method (STM). Finally, the variation in sediment Trapping Efficiency (TE) in the TGR was assessed. The results indicate that sediment from smaller tributaries in the TGR region, which has been ignored in most previous studies, constituted approximately 10.8% of the total incoming sediment. The total sedimentation in the TGR was 205478 × 104 t in 2003–2018, and the contribution rates of sediment load flowing into the TGR, the water depth in front of the dam, and runoff discharge flowing into the TGR were 94.4%, 24.5% and −18.9% respectively. The average annual TE was 78.5% in 2003–2018, and it was closely related to the ratio of reservoir storage capacity to flow discharge in the flood season and to sediment concentration in the non-flood season. The results in this paper not only play an important role in the optimal operation of the TGR but also have important reference value for other large reservoirs worldwide. [ABSTRACT FROM AUTHOR]

• Fire-induced hydrological impacts were assessed using the OpenLISEM model. • Rainfall dominated the catchment hydro-sedimentary responses before and after fire. • Fire led to a mean increase of 57% in peak discharge and up to 31% in sediment yield. • Sediment sources partly changed from croplands to burnt areas. Wildfires can have strong negative effects on soil and water resources, especially in headwater areas. The spatially explicit OpenLISEM model was applied to a burned catchment in southern Portugal to quantify the individual and combined impacts of wildfire and rainfall on hydrological and erosion processes. The companion paper has calibrated and assessed model performance in this area before and after a fire. In this study, the model was applied with design storms of six different return periods (0.2, 0.5, 1, 2, 5, and 10 years) to simulate and evaluate pre- and post-wildfire hydrological and erosion responses at the catchment scale. Our results show that rainfall amount and intensity played a more important role than fire occurrence in the catchment discharge and sediment yields. Fire occurrence was found to be an important factor for peak discharge, indicating that high post-fire hydro-sedimentary responses are frequently related to extreme rainfall events. The results also suggest a partial shift from runoff to splash erosion after fire, especially for higher return periods. This can be explained by increased splash erosion in burned upstream areas saturating the sediment transport capacity of surface runoff, limiting runoff erosion in downstream areas. Therefore, the pre-fire erosion risk in the croplands of this catchment was partly shifted to a post-fire erosion risk in upper slope forest and natural areas, especially for storms with lower return periods, although erosion risks in croplands were important both before and after fires. These findings have significant implications to identify areas for post-wildfire stabilization and rehabilitation, which is particularly important given the predicted increase in the occurrence of fires and extreme rainfall events with climate change. [ABSTRACT FROM AUTHOR]

Abstract: Draining toward the South China Sea, the Pearl River is the third largest river in China. Based on datasets begun in the 1950s of water and sediment flux at the main gauging stations and measured deposition rates in some reservoirs, this paper examines the impact of dam construction on the sediment flux of the Pearl River. The results and conclusions are as follows: (1) The total storage capacity of reservoirs in the Pearl River basin had reached 65 km3 by 2005, which is 23% of the annual water discharge of the Pearl River. (2) The total deposition rate in the reservoirs has now probably reached 600 Mt/yr, one order of magnitude higher than the annual sediment flux into the sea (40 Mt/yr in 2000–2005). (3) The sediment flux of the Pearl River has shown a drastically decreasing trend since the mid-1980s, which is attributed mainly to deposition in the reservoirs. (4) A further decrease in sediment flux into the sea is expected to occur in the Pearl River in future decades because of the construction of new dams. This drastic decrease in sediment flux may be very import for the environments of the river channel, the estuary and the coastal areas, which need to paid considerable attention in scientific research and management. [Copyright &y& Elsevier]

• System-based targets are required to address the failings of current approaches. • Colmation of the gravel bed results in the most detrimental ecological impacts. • Ecosystem engineers play a significant role in gravel bed sediment budget. • Targets must consider the four mechanisms that control the sediment budget. • Critical fine sediment accumulation thresholds for key species must be determined. Fine sediment has a critical role in river ecosystems and is essential for habitat heterogeneity, ecosystem structure and function. Expansion and intensification of specific land uses, including agriculture, have increased fine sediment inputs into river networks. The detrimental impacts of excessive fine sediment on river ecosystems have been well documented and numerous sediment targets have been proposed or adopted to assess the gap between target and current levels of fine sediment. Where sediment targets exist, these are often over-simplified and applied across a wide range of river environments irrespective of the processes of fine sediment deposition and the tolerance or sensitivity of river biota to fine sediment. Thus, targets often fail to provide a reliable basis for identifying the need for management interventions to restore ecosystem health. This review adopts a system-based approach to the impacts of fine sediment after reviewing the suitability of existing targets for guiding management in chalk stream catchments specifically. Chalk streams are groundwater-dominated systems characterised by stable hydrological, ecological and thermal regimes and thus respond differently to excessive fine sediment compared with other fluvial systems. Chalk streams are often subject to high levels of sedimentation and siltation despite their low suspended sediment loads. In this paper, we review the characteristic processes and dynamics of chalk streams and how these influence fine sediment accumulation. The impacts of excessive fine sediment on chalk stream habitats and biota and the role ecosystem engineers play in the processes of fine sediment dynamics are discussed. Finally, we discuss the application of fine sediment targets for chalk streams in relation to the implementation of both source and process-based techniques for meeting the requirement for improved ecosystem management. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents two new definitions of sediment and water flux connectivity (from source through slopes to channels/sinks) with examples of applications to sediment fluxes. The two indices of connectivity are operatively defined, one (IC) that can be calculated in a GIS environment and represents a connectivity assessment based on landscape''s information, and another that can be evaluated in the field (FIC) through direct assessment. While IC represent a potential connectivity characteristic of the local landscape, since nothing is used to represent the characteristics of causative events, FIC depend on the intensities of the events that have occurred locally and that have left visible signs in the fields, slopes, etc. IC and FIC are based on recognized major components of hydrological connectivity, such as land use and topographic characteristics. The definitions are based on the fact that the material present at a certain location A reaches another location B with a probability that depends on two components: the amount of material present in A and the route from A to B. The distance to B is weighted by the local gradient and the type of land use that the flow encounters on its route to B, while the amount of material present in A depends on the catchment surface, slope gradient and type of land use of said catchment. Although IC and FIC are independent from each other, and are calculated using different equations and different inputs, they complement each other. In fact, their combined use improves IC''s accuracy. Hence, connectivity classes can afterward be rated using IC alone. This procedure has been applied in a medium-size watershed in Tuscany (Italy) with the aim of evaluating connectivity, identifying connected sediment sources and verifying the effects of mitigation measures. The proposed indices can be used for monitoring changes in connectivity in areas with high geomorphological or human induced evolution rates. [Copyright &y& Elsevier]

Abstract: During the past 40 years colluvial and alluvial deposits have been used in Brazil as good indicators of regional landscape sensitivity to Quaternary environmental changes. In spite of the low resolution of most of the continental sedimentary record, geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data. This paper presents results obtained from pedostratigraphic sequences, in near-valley head sites of southern Brazilian highlands, based on geomorphologic, sedimentologic, micromorphologic, isotopic and palynologic data. Results point to environmental changes, with ages that coincide with Marine Isotopic Stages (MIS) 5b; 3; 2 and 1. During the late Pleistocene, although under temperatures and precipitation lower than today, the local record points to relatively wet local environments, where shallow soil-water saturated zones contributed to erosion and sedimentation during periods of climatic change, as during the transition between MIS 2 and MIS 1. Late Pleistocene events with ages that coincide with the Northern Hemisphere Younger Dryas are also depicted. During the mid Holocene, slope-wash deposits suggest a climate drier than today, probably under the influence of seasonally contrasted precipitation regimes. The predominance of overland flow-related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology. This environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area. Due to relative sensitiveness, resilience and short source-to-sink sedimentary pathways, near-valley head sites deserve further attention in Quaternary studies in the humid tropics. [Copyright &y& Elsevier]

Abstract: Catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency. This paper introduces the concept of landform impediments, termed buffers, barriers and blankets, that impede sediment conveyance by limiting the connectivity between landscape compartments. Buffers restrict sediment delivery to channels, barriers inhibit sediment movement along channels, and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment. These features operate as a series of switches which turn on/off processes of sediment delivery, determining the effective catchment area at any given time. Using previously documented examples, the role of these features in affecting the operation of sediment cascades in a low relief, passive landscape setting such as the Australian landmass is contrasted to examples from high relief, uplifting settings in New Zealand. The Australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since European settlement have impacted upon landscape sensitivity and prospects for river recovery. This approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting. [Copyright &y& Elsevier]

Abstract: This study investigates how dust deposition samplers affect the grain size characteristics of the sediment they catch. Sediment samplers act as obstacles in the flow and their collection efficiency varies with the grain size and other factors. Some particle fractions are collected more efficiently than others, resulting in a modification of the original grain size distribution of the sediment. This paper presents wind tunnel results for five dust deposition samplers and five wind velocities ranging from 1 to 5 m s−1. The catcher''s effect on the grain size was apparent in all experiments. Dust accumulated in a catcher is finer than undisturbed dust. For the dust used in the tests the difference (in median grain diameter) was of the order of 10–20%, but differences up to 40% and more were observed. In general, the error is higher when the catcher is less aerodynamically shaped. The study concludes that grain size data on sediment collected by a catcher should be interpreted with care, as they do not necessarily reflect the characteristics of the original sediment. [Copyright &y& Elsevier]

Abstract: The RheinLUCIF project investigates the effects of land use and climatic impacts on sediment fluxes in the river Rhine catchment. Among the world''s large rivers the Rhine system has been particularly affected by land use changes for 7500 years, resulting in its transformation to an entirely man-controlled environment. Geomorphologically this transformation is performed by largely man-induced sediment fluxes since the mid-Holocene. As the large scale of the Rhine catchment inhibits a renewed recording of stratigraphic records, the main goal is to synthesize quantitative data on sediment flux, climatic and human impacts from already available data from various fields of Earth surface and social sciences (particularly history and archaeology). This paper presents the first steps and results of methodological groundwork exploring how to derive sediment budgets from available spatially distributed data (soil maps, geological maps, DEMs). Furthermore, a new basically statistical approach utilising archaeological data is outlined. This approach provides time series of quantified human impact, i.e. information on population densities and open land/woodland ratios. The first results derived from four different sediment budget approaches are helpful in order to assess the quality of available data for budget calculation purposes. Although some estimates on erosion and alluvial deposition seem to broadly agree, a considerable disparity of Holocene erosion and colluviation values occurs when these values are compared to the outcome of an independently recorded soil mapping campaign in a pilot area. However, in general the results suggest that all applied approaches chiefly require an improved estimation of sediment storage. On the one hand, this accounts for the need of more precise information on Holocene floodplain deposits. On the other hand, as the larger portion of man-induced sediments still resides in the sloping parts of catchments, realistic estimates on man-induced colluvial deposition on slopes are essential. Apart from budgeting issues all data on Holocene erosion and sedimentation in the Rhine catchment lacked a sufficient dating control. Therefore further investigations on fluxes between budget components necessitate additional datings. Quantified data on human impact is indispensable to the modelling of sediment fluxes because human impact is deemed to be the major driving force of sediment production and re-distribution. Although the archaeological approach was developed and tested by utilising well documented data about the Neolithic era, the promising statistical evaluation suggests that this method can be applied to even less well documented proto-, prehistoric and historic periods. [Copyright &y& Elsevier]

Abstract: Gully erosion attracts increasing attention from scientists as reflected by two recent international meetings [Poesen and Valentin (Eds.), Catena 50 (2–4), 87–564; Li et al., 2004. Gully Erosion Under Global Change. Sichuan Science Technology Press, Chengu, China, 354 pp.]. This growing interest is associated with the increasing concern over off-site impacts caused by soil erosion at larger spatial scales than the cultivated plots. The objective of this paper is to review recent studies on impacts, factors and control of gully erosion and update the review on ‘gully erosion and environmental change: importance and research needs’ [Poesen et al., 2003. Catena 50 (2–4), 91–134.]. For the farmers, the development of gullies leads to a loss of crop yields and available land as well as an increase of workload (i.e. labour necessary to cultivate the land). Gullies can also change the mosaic patterns between fallow and cultivated fields, enhancing hillslope erosion in a feedback loop. In addition, gullies tend to enhance drainage and accelerate aridification processes in the semi-arid zones. Fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion. In this respect, tracers such as carbon, nitrogen, the nuclear bomb-derived radionuclide 137 Cs, magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment. Recent studies conducted in Australia, China, Ethiopia and USA showed that the major part of the sediment in reservoirs might have come from gully erosion. Gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess (European belt, Chinese Loess Plateau, North America) and sandy soils (Sahelian zone, north-east Thailand) or in soils prone to piping and tunnelling such as dispersive soils. Most of the time, the gullying processes are triggered by inappropriate cultivation and irrigation systems, overgrazing, log haulage tracks, road building and urbanization. As exemplified by recent examples from all over the world, land use change is expected to have a greater impact on gully erosion than climate change. Yet, reconstructions of historical causes of gully erosion, using high-resolution stratigraphy, archaeological dating of pottery and 14C dating of wood and charcoal, show that the main gully erosion periods identified in Europe correspond to a combination not only of deforestation and overuse of the land but also to periods with high frequency of extreme rainfall events. Many techniques have proved to be effective for gully prevention and control, including vegetation cover, zero or reduced tillage, stone bunds, exclosures, terracing and check dams. However, these techniques are rarely adopted by farmers in the long run and at a larger spatial scale because their introduction is rarely associated with a rapid benefit for the farmers in terms of an increase in land or labour productivity and is often contingent upon incentives. [Copyright &y& Elsevier]

Abstract: The paper presents a sedimentological, palynological, and phytolith record from a 13 m deep Holocene sedimentary sequence, located in the Tsoaing River valley, southwestern Lesotho. Six conventional radiocarbon and two AMS dates provide a relatively high resolution Holocene record for the sedimentary sequence, ranging from ca. 12000 to 4000 years BP. Pollen is absent in the upper section but present in the lower 2 m, confirming terminal Pleistocene/Holocene conditions reported in previous published pollen and charcoal records from the region. The absence of pollen in the upper layers of ca. 9000 years BP and younger suggests that conditions over southwestern Lesotho throughout much of the Holocene was typified by a seasonal climate that prevented long-term preservation of plant remains, although other plant material like robust spores, microscopic charcoal, and phytoliths withstood oxidation. Sedimentological and phytolith results suggest that the period from ca. 8600 to 8450 years BP experienced rapid environmental change towards drier conditions. Phases of chemical disintegration with organic input (including local swamp phytoliths) are suggested at ca. 7000 years BP and again after 4500 years BP. [Copyright &y& Elsevier]

Ash from plants occurs in archaeological soils all over the world. It is particularly significant in cave deposits but is also found on open air sites where dissolution has been discouraged by aridity, deep burial or calcareous surrounding sediments. This paper describes the main microscopic characteristics of ash, as well as providing details and illustrations of their origin from plant mineral and organomineral compounds. Chemical summaries are presented which reflect the major trends in phytomineralogy and highlight some additional groupings running through plant physiology. Emphasis is placed on the importance of understanding the complete range of transformations acting on ash as a result of heating and cooling, followed by weathering and dissolution. Finally, some future directions for ash research are suggested, both from within the central topic of plant ashes and extending to other types of ash. [Copyright &y& Elsevier]

In soil erosion by overland flow, sediment discharge is driven by discharge and gradient against the resistance of the soil and vegetation. The form of the relationship, which is taken as a sum of power law terms, may then be inferred from several data sources: (1) ephemeral gully head location, (2) permanent channel head location, (3) slope profile form, (4) consistency with evolutionary models and (5) erosion plot data. The paper focuses on (1) to (4), in order to understand how far these data constrain the form of the dependence on discharge and gradient. Field data from mapping a set of ephemeral gully heads after storms show a weak inverse relationship between channel head gradient and catchment area, which flattens towards an upper threshold gradient of about 25%. These relationships are compared with those theoretically obtained for a range of sediment transport laws which have been previously used, and which are analysed to forecast both overall slope profile form and the location of stream heads. The theory predicts that the location of ephemeral gully heads produced in a single storm will differ from the long-term average stream head location. There is a fairly good relationship between theoretical and observed locations, associated with the form of the sediment transport law. For a single event, the location depends on storm magnitude which cannot be well defined from the data sets, creating a spread of data with an envelope curve defined for the largest events. The empirically acceptable sediment transport equations have also been used to analyse families of slope profiles in a small area, and used within a landscape evolution model to generate landscapes which are compatible with those observed in the field, and provide confirmation of the long-term viability of the expressions obtained to forecast the direction, style and rates of landscape evolution in response to land use or climate drivers. [Copyright &y& Elsevier]

Some upland gravel-bed streams often undergo frequent channel change in response to floods and changes in sediment supply. However, in others, where local conditions permit, long-term channel planform stability can be observed. This paper uses evidence from Swinhope Burn in upper Weardale, Northern England, to demonstrate relative channel stability over a 180-year period.Channel planform change is identified using seven historical maps and air photographs dating from 1815 to 1991. The 1.4-km study reach has retained a stable meandering pattern over a period of 180 years, with a temporary but dramatic change to a straight, low sinuosity, partly divided channel, at some point between 1815 and 1856 (identifiable on the 1844 Tithe Map). Channel planform stability, observed over the historic period, is related in part to the low channel gradient upstream of a cross-valley moraine situated at the lower end of the study reach. This moraine has led to partial closure of the valley system and the development of a small upstream floodplain or ‘sedimentation zone’ (average width of 150 m). The resulting low channel gradient (0.012) inhibits coarse bedload transport and encourages overbank sedimentation. Cohesive banks promote lateral channel stability and the wide floodplain reduces potential coupling between the channel and valley-side slope sediment sources.The probable cause of the observed channel planform change is the combination of a succession of four major floods in the River Wear catchment during the 1820s, and episodic inputs of sediment generated by upstream metal mining between 1823 and 1846. Large floods in the past 40 years have produced very little evidence of lasting channel change. However, locally a channel avulsion has been documented following a flood in February 1997. This represents a useful modern analogue for previous mechanisms of channel change. [Copyright &y& Elsevier]

[Display omitted] • Future impacts of LULC and climate on the streamflow and erosion by new approaches. • SWAT model was applied to estimate future runoff-erosion. • Future climate data generated using GCM coupled to regional circulation model. • The methodology contextualizes potentially significant hydrological changes. • The changes may impact the sustainability of water resources management. Water management in the Caatinga/Atlantic forest ecotone in Brazil is critically dependent on better understanding of potential future changes in streamflow and sediment dynamics. This paper evaluates both the future impacts of land use and land cover (LULC) changes and the impacts of climate change on the streamflow and sediment yield in the Tapacurá River basin in northeastern Brazil, using a novel combination of approaches. Projected climate data derived using global circulation model HadGEM2-ES were coupled to regional circulation model ETA-CPTEC/HadCM3 for two representative concentration pathways (RCP 4.5 and 8.5), with bias correction. Two future LULC scenarios were generated: (a) optimistic (current LULC), and (b) pessimistic (land use change trends continue), using the multilayer perceptron algorithm (MP). The Soil and Water Assessment Tool (SWAT) model was used to estimate future streamflow and erosion for different periods (2011–2040, 2041–2070 and 2071–2099). The SWAT model was calibrated for period of 1995–2003 and validated for 2004–2013. The results showed good accuracy in relation to R2, NSE and PBIAS for the calibration and validation of the runoff, as well as for the verification of the sediment yield. Simulations indicated significant increases in erosion for the pessimistic scenario under RCP 8.5, followed by the pessimistic scenario and RCP 4.5. Lower sediment yields occurred for the optimistic and RCP 8.5, with lower still for the optimistic and RCP 4.5. However, the latter estimates are still considerably higher than baseline conditions. Although higher flows are found for some scenarios, the increases in sediment yield have serious implications for reservoir siltation and storage reduction. Despite modeling uncertainty, the results demonstrate that the proposed methodology has promising scope to contextualize potentially significant regional hydrological changes which have implications for land and biodiversity management and the sustainability of water resources in the Caatinga/Atlantic forest ecotone. [ABSTRACT FROM AUTHOR]

• Elements' concentration in near surface sediments of a coastal area were analysed. • Geochemical mapping allows to visualize element distribution in the area. • Factor/cluster analysis have permitted to distinguish different sediment origin. • Higher Cu, Pb and Zn cencentrations were detected in urban near surface sediments. • Sampling depth should be likely increased in urban areas' investigations. The study reports the results of a geochemical survey in a coastal area of northern Italy with focus on the distribution of chemical elements in near surface sediments as result of both sediment origin and anthropogenic activities. In addition to emphasizing the source-to-sink element dynamics in the area, the main purpose of this paper is to ascertain if anthropic presence could have altered the composition of near surface sediments in urban and industrial areas. We considered 173 sampling sites, and collected soil material from a depth of 90–110 cm. Major and trace elements assessment on milled 2 mm fraction was conducted using WDXRF for Al, As, Ba, Ca, Ce, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Nb, Ni, P, Pb, Rb, Si, Sr, Th, Ti, V, Y, Zn and Zr. In addition, Loss On Ignition (LOI) was determined. Principal component analysis (PCA) and cluster analysis (CA) were performed for data interpretation. The distribution of element concentration is heavily related to sediment origin. The major presence of Al, Fe, K, LOI, Mg, Nb, Rb and V characterizes alluvial plain sediments. These materials of Apenninic origin have a finer texture and a major presence of carbonates in respect to the other sediments of the area. Coastal sediments display a general wider range of variation in element concentrations (i.e. Al, Ca, Cr, K, Mg, Mn, P, Si, Ti and Zr) due to a dual origin. In particular, the greater Cr, Mn and Zr content is related to sediments enriched by heavy minerals (e.g. garnet, chromite, zircon) of Alpine origin, while the lesser concentrations trace back to Apenninic origin. Near surface sediments of urban and industrial areas always contain higher Cu, Pb and Zn concentrations with respect to the same sediments not impacted by urban and industrial settlements. This is likely a consequence of the movement of materials made by men over the last 2000 years. These results suggest that the adopted depth of sampling for the calculation of background values might need to be increased in urban and industrial areas to reach unaltered near surface sediments. [ABSTRACT FROM AUTHOR]

• Ephemeral Gully (EG) Erosion is a major erosion concern and needs to be addressed. • Very few models simulate EG erosion. • A thorough review of processes behind EG simulation in existing models is discussed. • Future needs and directions to improve EG simulation processes in models are enumerated. Modeling of ephemeral gully (EG) erosion has lagged that of other soil erosion processes despite its major contribution to watershed sediment losses. Several process and semi-empirical based simulation models have been used to assess the occurrence and location of EGs, magnitude of soil losses from EGs, and degradation, aggradation, and transport of sediment through EGs, but no comprehensive EG model exists. This paper reviews these models and presents a thorough discussion of their background, general formulations, key equations, field assessments, assumptions and limitations. Most current EG models evolved from the original formulations used in CREAMS, with incremental improvements by EGEM, WEPP, AnnAGNPS-REGEM, RUSLER-EphGEE models. These models provide process-based estimation of EG processes and field-scale soil-erosion contributions, but all models, except EphGEE, require users to have a priori knowledge of EG locations and all have significant shortcomings. Several topographic index models are discussed that provide simplistic approaches to locate EGs on the landscape using only topographic features. Process-based threshold index models may provide a more robust simulation of EG location and length, though testing has been limited. EG modeling appears to still be in its infancy, with great opportunities for future research, as discussed herein, to improve the understanding and simulation of EG erosion and transport processes. [ABSTRACT FROM AUTHOR]

• The ratio of the CH 4 production paths in freshwater sediments changes with depth. • The quality of organic matter is main controlling factor of the CH 4 production pathways. • The incompletely degraded organic matter favours hydrogenotrophic methanogenesis. • Higher contents of labile organic matter favours acetoclastic methanogenesis. The paper presents the research results on methane production (CH 4) pathways in freshwater sediments of the Nielisz Reservoir located in south-eastern Poland. The research was performed in spring, summer and autumn 2018 at four research stations located along the reservoir and in three sediments layers: 0–5 cm, 5–10 cm and 10–15 cm. The values of δ13C-CH 4 in pore water, the fractionation coefficient α CH4-CO2 , and the δ13C isotope mass balance of pore water CH 4 and CO 2 were used to determine the temporal and spatial changes of CH 4 production pathways. The obtained values of δ13C-CH 4 in the pore water of the Nielisz Reservoir ranged from −68.40‰ to −50.87‰, the α CH4-CO2 values varied from 1.04 to 1.07, and the calculated contributions of hydrogenotrophic methanogenesis in the total production of CH 4 (f CH4,h) ranged from 7% to 85%. These values varied depending on the research station and the sediment layer studied. During the entire study period, both acetate and hydrogenotrophic methanogenesis participated in CH 4 and the contribution of hydrogenotrophic methanogenesis increases in the deeper layers of sediment and in the autumn season. The main controlling factor of CH 4 production pathways in sediments is the qualitative composition of organic matter (content of labile organic matter and humic substances). [ABSTRACT FROM AUTHOR]