Main Sediment Source Research Articles

Origin and geochemistry of surface sediments in the mud deposit area offshore the Shandong Peninsula, China

The waters offshore the Shandong Peninsula separate the North Yellow Sea from the South Yellow Sea, and receive a large amount of terrestrial material from Chinese and Korean rivers, making it an ideal area for studying land-sea interactions. However, little attention has been given to measuring sediment transportation in most previous studies. Based on an analysis in composition of major and trace elements and particle size characteristics from 62 surface sediment samples from the northeastern region off Shandong Peninsula, the type, element composition, and controlling factors of the surface sediments were investigated. In addition, the transportation of sediments from source to sink was described from measured thermohaline data. The results show two types of surface sediments: sandy silt and silt. The sediments were mainly terrestrial; and marine carbonate had little effect on sediment composition. Shown on a binary diagram of Rb/Sc to Co/Sc, the Huanghe (Yellow) and Changjiang (Yangtze) rivers are the main sources of surface sediments in the study area. The component mixing model showed that the relative contribution of sediment from the Huanghe River was up to 92%, followed by the Changjiang River (8%). The Yellow Sea Warm Current and the North Shandong Peninsula Coastal Current met at ~37.7°N in the study area, and were the main forces carrying sediment from the two main river sources. However, there was a deficit of transported material into the study area in summer. The secondary distribution of sediment from the two river sources was controlled by tidal currents and waves.

Agricultural land is the main source of stream sediments after conversion of an African montane forest

In many parts of Africa, soil erosion is an important problem, which is evident from high sediment yields in tropical montane streams. Previous studies in Kenya pointed to a large contribution from catchments cultivated by smallholder farmers. This led to the hypothesis that unpaved tracks and gullies are the main sediment sources in smallholder agriculture catchments of the highlands of Kenya. The aim of this study was to investigate the sediment sources with sediment fingerprinting to generate the knowledge base to improve land management and to reduce sediment yields. Four main sediment sources (agricultural land, unpaved tracks, gullies and channel banks) and suspended sediments were analysed for biogeochemical elements as potential tracers. To apportion the catchments target sediment to different sources, we applied the MixSIAR un-mixing modelling under a Bayesian framework. Surprisingly, the fingerprinting analysis showed that agricultural land accounted for 75% (95% confidence interval 63–86%) of the total sediment. Channel banks contributed 21% (8–32%), while the smallest contributions to sediment were generated by the unpaved tracks and gullies with 3% (0–12%) and 1% (0–4%), respectively. Erosion management strategies should target agricultural lands with an emphasis on disconnecting unpaved tracks form hillslope source areas to reduce sediment yields to Lake Victoria.

Distribución espacio-temporal de los deslizamientos y erosión hídrica en una cuenca Andina tropical

Las cadenas montañosas en las regiones tropicales se caracterizan por las altas tasas de erosión debido a los eventos de lluvia intensa, terrenos escarpados y al alto grado de meteorización del material parental. Los deslizamientos son fenómenos recurrentes, y son considerados como los procesos más importantes de erosión en las zonas montañosas y las principales fuentes de sedimentos en el sistema fluvial. Con el objetivo de cuantificar la contribución de sedimentos provenientes de los deslizamientos al sistema fluvial, se realizó un estudio de caso en la Cuenca del Río Pangór, Ecuador. En este estudio, se cuantificó las tasas de erosión a escala de cuenca por medio de información derivada de estaciones de aforo de caudales e inventarios de isótopos cosmogénicos en sedimentos fluviales. Después, se evaluó la fiabilidad y validez de la información obtenida con el objetivo de cuantificar la carga de sedimento transportado por el río en regiones montañosas. Finalmente, se analizó la fracción de la carga total de sedimento proveniente de deslizamientos en las laderas. La cuenca del Río Pangór fue seleccionada por su extensa serie de tiempo de datos hidrometeorológicos (1974-2009). La carga de sedimento en el Río Pangór fue estimada por medio de un análisis de magnitudfrecuencia de la información recolectada en una estación hidrométrica y datos de concentración de sedimentos en suspensión. Los resultados muestran un valor de un orden de magnitud menor que la tasa de erosión calculada en función de los inventarios de isótopos cosmogénicos. Esta diferencia se explica por (i) la dificultad de extrapolar la información sobre la frecuencia temporal de los caudales y la carga de sedimento en regímenes hidrológicos no estacionarios, y (ii) el submuestreo de eventos extremos. Bajo estas condiciones, la cuantificación de las tasas de erosión derivadas de los isótopos cosmogénicos proporcionan una metodología alternativa para la cuantificación de la carga total de sedimentos en el sistema fluvial. Un inventario multitemporal (1963-2010) de deslizamientos fue desarrollado a partir de imágenes de satélite y fotografías aéreas. Mediante trabajo de campo se generó información sobre la geometría de los deslizamientos para la cuantificación de volúmenes de sedimento producido por los deslizamientos. En la cuenca del Río Pangór las altas tasas de erosión producida por los deslizamientos varían entre 1688+901−326 y 630+300−108 t.km2.y-1, valores que son similares a las tasas de erosión derivadas de isotopos cosmogénicos. Los resultados indican que los deslizamientos son las principales fuentes de sedimento en esta cuenca montañosa.

Pb and Nd Isotopic Data on Granitoids from the Lake Zone, Mongolian and Gobi Altai with Implications for the Crustal Growth of the Central Asian Orogenic Belt

Pb and Nd isotopic composition of granitoids from the Lake Zone, Mongolian and Gobi Altai was analyzed to decipher the continental crustal growth of heterogeneous terranes of the Central Asian orogenic belt. The granitoids were generated in the Late Neoproterozoic–Early Paleozoic juvenile crust of the Lake Zone during island-arc, accretion, and post-accretionary stages at 535–440 Ma. Their Pb and Nd isotopic characteristics are similar and illustrate the dominance of juvenile material in the source of granitoids of all three stages. An insignificant terrigenous contribution in their source provides dispersion of the Pb isotopic composition at a weak effect on the Nd isotopic composition. The Pb and Nd isotopic study of Middle Paleozoic (∼380–355 Ma) synkinematic and Late Paleozoic (∼350–270 Ma) post-kinematic granitoids in the Mongolian and Gobi Altai revealed a significant heterogeneity of their source, which is mainly inherited from terrigenous rocks of the Altai accretionary wedge variably metamorphosed under greenschist to granulite facies conditions. The main source of Altai terrigenous sediments was volcanic rocks from the Lake Zone juvenile crust with subordinate contribution of more mature rocks from the Tuva-Mongolian and Dzabkhan microcontinents, which supplied sediments with highly radiogenic Pb and Nd isotopic composition. The Pb isotopic compositions of the granitoids from the Lake Zone, Mongolian and Gobi Altai, and also the Trans-Altai Gobi (Savatenkov et al., 2016) show that their mantle source has an elevated Th/U ratio compared to the depleted mantle (Kramers and Tolstikhin, 1997). This is a hallmark of the depleted mantle source of the Paleo-Asian province. Juvenile continental crust terrains of the Central Asian orogenic belt (Lake Zone and Trans-Altai Gobi terranes) were formed in various tectonics settings. The island-arc complexes of the Lake Zone developed near the Precambrian Tuva-Mongolian and Dzabkhan microcontinents, which supplied terrigenous material with highly radiogenic Pb to granitoid sources. The Trans-Altai Gobi was a system of ensimatic island arcs separated from the Siberian paleocontinent by a continent-dipping subduction zone, which prevented the influx of ancient terrigenous material from the continent.

HyLands 1.0: a hybrid landscape evolution model to simulate the impact of landslides and landslide-derived sediment on landscape evolution

Abstract. Landslides are the main source of sediment in most mountain ranges. Rivers then act as conveyor belts, evacuating landslide-derived sediment. Sediment dynamics are known to influence landscape evolution through interactions among landslide sediment delivery, fluvial transport and river incision into bedrock. Sediment delivery and its interaction with river incision therefore control the pace of landscape evolution and mediate relationships among tectonics, climate and erosion. Numerical landscape evolution models (LEMs) are well suited to study the interactions among these surface processes. They enable evaluation of a range of hypotheses at varying temporal and spatial scales. While many models have been used to study the dynamic interplay between tectonics, erosion and climate, the role of interactions between landslide-derived sediment and river incision has received much less attention. Here, we present HyLands, a hybrid landscape evolution model integrated within the TopoToolbox Landscape Evolution Model (TTLEM) framework. The hybrid nature of the model lies in its capacity to simulate both erosion and deposition at any place in the landscape due to fluvial bedrock incision, sediment transport, and rapid, stochastic mass wasting through landsliding. Fluvial sediment transport and bedrock incision are calculated using the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model. Therefore, rivers can dynamically transition from detachment-limited to transport-limited and from bedrock to bedrock–alluvial to fully alluviated states. Erosion and sediment production by landsliding are calculated using a Mohr–Coulomb stability analysis, while landslide-derived sediment is routed and deposited using a multiple-flow-direction, nonlinear deposition method. We describe and evaluate the HyLands 1.0 model using analytical solutions and observations. We first illustrate the functionality of HyLands to capture river dynamics ranging from detachment-limited to transport-limited conditions. Second, we apply the model to a portion of the Namche Barwa massif in eastern Tibet and compare simulated and observed landslide magnitude–frequency and area–volume scaling relationships. Finally, we illustrate the relevance of explicitly simulating landsliding and sediment dynamics over longer timescales for landscape evolution in general and river dynamics in particular. With HyLands we provide a new tool to understand both the long- and short-term coupling between stochastic hillslope processes, river incision and source-to-sink sediment dynamics.

Geochemical insights into spatial and temporal evolution of sediment at catchment scale (Egoutier stream, France)

The transfer and storage of chemical elements in particulate matter are controlled by physical, chemical and biological processes. Their dynamics are well understood, especially in environments that show strong tectonic and/or geomorphic pressures, and are frequently reconstructed over centuries or decades to evaluate climate change effects for example. However, observations carried out at high spatial and temporal resolutions are less common, particularly in lowland areas. The present study aimed to better understand the links between earth surface processes, such as soil weathering and erosion, by combining pedology, geochemistry and hydrology at a small catchment scale. It focuses on the transfer of selected chemical elements (Ca, K, Ti, Fe, Mn, Rb and Sr) associated with particulate erosion and transport. The first (topsoil) and last (subsoil) soil horizons from different soil profiles and stream bed-load sediments of the Egoutier catchment (8 km2, Loiret, France) were studied. The objective was to investigate the relationship between the weathering and erosion processes. The soils are developed on ancient alluvium as evidenced by their physical and chemical properties, which clearly displayed a weathering profile from bedrock to topsoil layers. Ca, Fe and Rb showed migration dynamics from the topsoils to the subsoils, whereas Mn appeared immobilized within topsoils. Enrichments of all investigated elements increased in bed-load sediments. Topsoil erosion is the main source of sediment. However, Fe and Rb enrichments also highlight the remobilization of subsoils during periods of enhanced precipitation. Furthermore, Fe and Rb enrichments show a selective erosion of clay minerals. K and Sr contents evidence mineral break-up processes favoring mechanical erosion of all mineral phases. Moreover, their enrichments can be interpreted as the result of higher erosion rates and deposition during high rainfall events. The same conclusion can be drawn for Mn and Ca although their spatial variabilities depend on contributions from runoff in urban areas, as rainwaters from anthropized areas supply Ca mineral phases and diluted Mn depleted bearing phases from topsoil layers.

Determination of sediment sources in a mixed watershed within the Appalachian-St. Lawrence Lowland Regions of southern Quebec using sediment fingerprinting.

This paper identifies the main sediment sources to the Beaudet Reservoir in Quebec (Canada) using sediment fingerprinting. The reservoir, which is built on the Bulstrode River and provides drinking water to Victoriaville, has decreased in capacity by 35% in the past 35 years. This study provides new data on fingerprinting in large and complex watersheds, a first in the province of Quebec. Nine sampling sites on the Bulstrode River and its three main tributaries were selected and five sampling campaigns were conducted. Samples from river bank profiles and adjacent fields, along with suspended sediments, were collected. All samples were sieved to 2 mm and analyzed for 137Caesium, 15 geochemical elements and sieved to 63 μm for color analysis. Source classification, based on an ANOVA test to verify the independence hypothesis and iterative linear discriminant analysis to optimize the ratio of inter-group/within-group variability, resulted in four sample classes: agricultural soils, forested soils, stream bank bottom and stream bank top. A Kruskal-Wallis H test then identified 21 out of the 32 tracers with p value < 0.05. The linear discriminant analysis led to a set of 14 tracers, namely 137Cs and 13 color coefficients with a discriminating result of 94%. That combination of 137Cs and color coefficients proved to be a cost-effective fingerprint. Based on MixSIAR modeling results, this sediment fingerprinting study has demonstrated that the main sediment sources varied within the watershed but, generally, forested soil particles dominated (33 to 49%), then agricultural soils (43 to 50%) reflecting the land use changes, followed by stream bank bottoms (82%) at the Beaudet Reservoir.

Provenance of northwestern Patagonian river sediments (44–48°S): A critical evaluation of mineralogical, geochemical and isotopic tracers

The ability to trace and quantify sediment provenance in northwestern Patagonia is increasingly needed to properly understand modern sediment erosion and transport processes in this rapidly changing environment, and to accurately interpret sediment records from adjacent basins in terms of climate and environmental change. Nonetheless, no study so far has systematically evaluated the effectiveness of different tracers to reconstruct sediment provenance in this region. To fill this gap, we assess the effectiveness of commonly-used provenance indicators, including bulk mineralogy, major and rare earth element (REE) geochemistry, and Sr and Nd isotopes, to reconstruct sediment provenance in northwestern Patagonia. First, the ability of these tracers to discriminate between the main sources of sediment in the region is investigated, mostly using data compiled from the literature. Then, the potential of these tracers for provenance reconstruction is assessed by comparing the composition of sediments from six major Chilean rivers between 44 and 48°S to lithological proportions in their respective watersheds. The results suggest that mineralogy, major element geochemistry, and REE geochemistry can be used as qualitative tracers of sediment provenance. However, the compositional overlap between the sources and the relatively large variability within them prevent quantitative reconstructions. By comparison, 87Sr/86Sr and εNd allow to clearly differentiate between the sources, most likely due to significant age differences between the main lithologies, and to estimate the relative contribution of each source. End-member mixing results based on Sr and Nd isotopes show that the relative source contributions are in general agreement with the lithological proportions in the river watersheds. Differences between estimated contributions and lithological proportions in the watersheds are interpreted as the result of the high regional precipitation gradient and unequal glacier distribution, which lead to variable erosion rates across the study area. Our results demonstrate the suitability of 87Sr/86Sr and εNd for quantitative provenance reconstruction in northwestern Patagonia. They constitute a strong basis for the interpretation of sediment archives from the Patagonian fjords and from the eastern South Pacific, and they should be particularly useful to quantitatively investigate modern and past earth-surface processes.

Mineral composition and particle size distribution of river sediment and loess in the middle and lower Yellow River

Hyperconcentrated flows often occur in the middle and lower Yellow River (MLYR) and its tributaries, within which the main sediment source originates from the Loess Plateau of China due to serious water erosion. Little is known about the properties of river sediment that is transported by hyperconcentrated flows, particularly with respect to the mineral composition and size distribution. Samples of sediment and loess were collected in the northern, middle, and southern Loess Plateau and the mainstream and tributaries of the MLYR. A total of 18 loess samples and 24 river sediment samples were analyzed to determine their sediment size distribution and mineral composition. The bottom loess samples reflected the original sedimentary features of the Loess Plateau, and the median particle size reduced, and the clay content increased from the north to the south of the study region. The surface loess has been weathered under the action of wind and rainfall, and the clay particle content in the surface loess samples was higher than that in the undisturbed bottom loess. Erosion of the surface soil due to rainfall and surface runoff means that fine particles (mostly clay) have been washed away. The median diameter of surface loess particles was a little larger than that of the bottom loess particles where water erosion dominates. The particle size became coarser with increasing distance from the estuary in the MLYR, which reflects depositional sorting in the river channel. Significant logarithmic relations were found between the median diameter of the sediment particles and the i) non-clay mineral content and ii) clay mineral content. Thus, clay and non-clay mineral compositions can be conveniently estimated from the particle size distribution.

Combining spectroscopy and magnetism with geochemical tracers to improve the discrimination of sediment sources in a homogeneous subtropical catchment

An important step in the sediment source fingerprinting approach is the selection of the appropriate tracing parameters to maximize source discrimination. The use of multiple tracing properties may reduce uncertainties and increase discrimination between sources. Accordingly, this study investigates the discrimination and quantifies the contribution of sediment sources delivering sediment to a river draining a homogeneous subtropical agricultural catchment based on the combination of ultraviolet–visible spectra derived parameters (UV), magnetic (M), and geochemical tracers (GEO). The investigated catchment (Conceição River − 804 km2), located in Southern Brazil, has predominantly deep and strongly weathered Ferralsols. The main land-uses found in the area are cropland (89%), pasture (5%) and forest (5%). A total of 187 samples were collected to characterise the five main sediment sources, including cropland, pastures, unpaved roads, gullies and stream banks. A total of 53 tracers, including 21 geochemical tracers, two magnetic properties and 30 parameters derived from UV spectra, were analysed. Tracers were selected following a three step procedure, including: (i) an interquartile range test, (ii) a Kruskal–Wallis H test, and (iii) a linear discriminant function analysis (LDA). The LDA was performed using six different sets of variables: (i) GEO only; (ii) UV only; (iii) M + UV (MUV); (iv) GEO + UV (GUV); (v) GEO + M (GM) and (vi) GEO + M + UV (GMUV). The selected tracers were introduced into a mass balance mixing model to estimate the source contributions to in-stream sediment by minimizing the sum of square residuals. Most geochemical tracers were considered not conservative by using the interquartile range test in this catchment with highly weathered soils. The GM approach resulted in the highest percentage of samples correctly classified (SCC), with 74%, followed by the approaches with GMUV and GUV, with 73%. Alternative tracers, UV individually or combined with M tracers, correctly classified only 59 and 60% of the samples, respectively. Moreover, they did not provide significant additional discrimination power even when combined with the GEO tracers. The apportionment model resulted in similar source contribution results for all approaches, with the absence of significant difference when comparing the mean source contributions obtained for the entire set of sediment samples (Cropland: 17–23%; Pastures: 24–34%; Unpaved Roads: 3–12%; Stream Banks: 26–31%; Gullies: 14–19%). Due to the strong homogeneity of soil types found in the Conceição catchment, these differences in source contributions remained very low and the results of the mixing model were impacted by the high number of potential sources and the relatively limited quality of the sediment source discrimination. According to the model results, the low discrimination between the potential sediment sources illustrates the difficulties for discriminating land-used based sediment sources, with more than three potential sources, in homogeneous catchments with highly weathered soils (e.g. Ferralsols, Nitisols) under tropical conditions.

Distribution of rare earth elements in surface sediments of the western Sunda Shelf: Constraints from sedimentology and mineralogy

To understand the modern sedimentation and land-sea interaction processes in the Sunda Shelf, we evaluated the rare earth element (REE) compositions, the total organic carbon (TOC) contents, grain sizes, and detrital minerals of 39 surface sediments, collected from the western Sunda Shelf. All of the sampled sediments are characterised by a higher content of light REEs (LREEs) relative to the content of heavy REEs (HREEs) with negative Eu anomalies. The total content of REE (ΣREE) in the sediments ranges from 7 μg/g to 193 μg/g, with an average of 119 μg/g. Due to the uneven spatial distribution of REEs in the study area, a Q-cluster analysis is applied to the mean grain size (Mz), ∑REE, δEu, δCe, (La/Yb)N, and (Gd/Yb)N data. On this basis, the study area can be classified into three geochemical provinces. The north to central zone in the study area is designated as province I, which has the highest REE content among the three provinces. This is a result of the finer grain size, dominance of siderite, and higher TOC contents of the sediments in province I. The REE content of province II in the southwest coastal zone is lower than that of province I due primarily to a coarser grain size and high quartz, biodetritus, and plagioclase contents. Covering the central coastal zone, province III has the lowest REE content among the three provinces because of the extremely coarse grain size and very high quartz and biodetritus contents. The upper continental crust (UCC)-normalised REE patterns differ markedly among the three provinces, thereby indicating different provenances and transport mechanisms. Based on the provenance discrimination plot and the UCC-normalised REE patterns of these three provinces and adjacent rivers, we infer that province I is largely fed by the Mekong and Kelantan rivers. The fine-grained sediments from these rivers are transported to north and central zone by the northeast monsoon current. The Pahang River is identified as the main sediment source of province II. The coarse-grained sediments from this river mostly accumulate near the estuary via hydrodynamic sorting, while finer-grained sediments are transported to the south by the southward coastal currents. The sediments in province III are inferred as being primarily the result of coastal erosion due to the strong wave energy in this area, as well as offshore and longshore sediment transport acting, in parallel to the coast line. Our study can serve as a reference for studying the diffusion and transport processes of mountainous river sediment and the evolution of the paleoclimate and paleoenvironment in tropical low-latitude regions.

Sea-level changes controlled detrital sediment inputs to the Bicol Shelf in the western Philippine Sea since 150 ka

Detrital sediments derived from the Philippine Islands are one of the main sources of deep-sea sediments in the western Philippine Sea. However, systematic research on their characteristics and transport mechanisms are lacking. We used parametric end-member analysis to quantitatively partition the grain size of detrital sediments in core MD06-3052 from the Bicol Shelf in the western Philippine Sea; three end-members EM1, EM2, and EM3, whose respective modes were at 2, 10, and 45 µm, were separated. We also measured the Sr and Nd isotopic compositions of different size fractions ( 20 µm) of the detrital sediments and the results showed that the detrital sediments mainly originate from the Philippine Islands. Components EM1 and EM2 are transported to the Bicol Shelf mainly by surface and bottom currents from the islands, and component EM3 is delivered by gravity flow from the exposed shelf during low sea-level stands. The content of the total detrital fraction and the three end-members, as well as the mass accumulation rates (MARs) of the coarse detritus (EM2 and EM3), were considerably higher during glacial periods (40–14 ka and 150–130 ka) than during other intervals; the glacials corresponded to a low sea level, while the MAR of the fine detritus (EM1) did not increase remarkably during 40–14 ka. We therefore concluded that the input of coarse detritus to the Bicol Shelf from the islands was mainly controlled by sea-level change. Variations of the input of fine-grained detritus (EM1) was influenced not only by sea level but also by ocean currents and regional precipitation. Overall, our results help understand “source-to-sink” processes in the western Pacific marginal seas and their response to global change.

Fingerprinting sediment sources in a typical karst catchment of southwest China

Due to the complex hydrogeological conditions in karst regions, it is difficult to measure sediment source contributions at a catchment scale directly. The objective of this study was to quantify the relative contributions of sediment sources and their temporal variability in a karst catchment in southwest China. Karst depressions can trap eroded sediment similar to a dam or reservoir and, thus, are representative and typical test beds for identifying sediment sources in karst regions. Three sediment cores were taken from a karst depression, 58 soil samples from three potential sediment sources were collected, and 18 soil properties were analyzed. The relative contributions of cropland, forestland, and fissure or crack soils were calculated using a multivariate mixing model. The fingerprinting results demonstrated that the cropland was the main sediment source in karst catchment. Specifically, according to the mean sediment contributions of the three deposited sediment cores, the sediment contribution from cropland topsoil was 69.3%, varying from 46.9% to 92.3%, and forestland soil and crack soil accounted for 8.6% and 22.1% of the sediment yield, and varying from 2.8% to 16.5% and 4.8%–36.6%, respectively. This result indicated that great attention should be paid when using only a single core to quantify sediment provenance. Due to the deposited sediment was generally disturbed as cropland in the karst depression, the area that has not been disturbed in recent decades in depression was more appropriate to trace sediment sources in karst catchment. To the best of our knowledge, this study was the first to quantify the contributions of sediment sources in the karst catchment of southwest China. This study provides valuable information and a preliminary reference for applying a composite fingerprinting technique to quantify sediment sources in karst catchments.

Effects of "Grain for Green" program and coal mining on sediment production in a typical small watershed of Yushenfu Mining Region, Northwest China

Soil erosion in the ecologically fragile zone is severely affected by the intensified coal mining activities in the Yushenfu Mining Region of the Loess Plateau. Soil erosion controlling projects such as the "Grain for Green" program are continuously implemented by the government, which has effectively mitigated or even controlled soil erosion. Coal mining results in new environmental problems, which has changed the erosion characteristics and sediment transport in watersheds. In this study, we identified the sediment source trapped behind the check dam using a composite fingerprinting approach and clarified the impact of "Grain for Green" program and coal mining on variation of the amount and sources of sediment during two decades, in a representative check-dam which controlled the watershed of Laoyeman. The two decades were divided into two stages, i.e. an earlier decade (1990-1999) and a later decade (2000-2010) with respect to the implement of the "Grain for Green" program in the flood couplets sequence established during the running of the dam. The annual average thickness of flood couplets during 2000-2010 decreased from (42.7±29.9) cm to (16.6±13.7) cm during 1990-1999, and the annual sediment deposition per unit area (square meter) at the sampling site reduced from 579.9 kg·m-2 to 245.8 kg·m-2. The main source of sediment was gully wall (averaged 79.2%±10.1%) during the study period. However, compared with sediment sources during 1990-1999, the contribution of sediment from slope during 2000-2010, which was greatly affected by the "Grain for Green" program, showed an increasing trend (average annual contribution increased by 7.4%). According to the coaling mining and the variation of rainfall erosivity, our results indicated that under the combined effects of the "Grain for Green" program and decreases of rainfall erosivity, the intensity of sediment production in the watershed was substantially decreased. Coal mining had important impacts on sediment contribution from the slope, and obviously affected soil erosion controlling effects of the "Grain for Green" program. It is obvious that coal mining has increased the risk of erosion and sediment production on the slope, and that soil erosion control on the slope should focus on areas affected by coal mining.

Application of USLE and MUSLE Models for the Assessment of Soil Loss and Sediment Yield in Kuala Kari, Kelantan

Soil loss is one of the most essential issues in the world. It is considered as the main source of sediment that introduces into the ambient environment and cause extensive impact to the. The objective of the current study is to estimate the soil loss and sediment yield by applying the Universal Soil Loss Equation (USLE) and Modified Universal Soil Loss Equation (MUSLE). Data from a real site which is located in Kuala Kari, Kelantan, Northern Malaysia was obtained and utilized in which the site is subdivided into five catchments. Results show that the sediment yield produced from all the catchments was very high which has a significant impact to the adjacent water bodies. It is recommended that erosion, sediment and drainage control measures need to highlighted in an Erosion and Sediment Control Plan (ESCP) to be installed in the site so as to minimize soil loss and sediments generated from the site.

Provenance of heavy and clay minerals in bottom sediments of Green Lake, an Amazonian fluvial lake in Brazil

ABSTRACT Studies on provenance of minerals in Amazonian rivers focus mostly on suspended sediments, while processes that control bottom-sediment production and distribution are still little known. We determined the provenance of the bottom sediments of Green Lake, a micro-basin draining into the Tapajós River, in the eastern Brazilian Amazon. We used X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and, cathodoluminescence techniques to analyze clay, light and heavy minerals of 22 samples. The lake is L-shaped, with 5.5 m maximum depth, and predominance of mud over sand in the center. Quartz and feldspar were dominant in the light fraction, while zircon, tourmaline, kyanite, rutile, and staurolite were dominant in the heavy fraction. The clay fraction was dominated by kaolinite, with morphology and degree of crystallinity indicative of a detrital origin related to weathering. The Alter do Chão Formation (ACF) is suggested as the main source of sand sediments and heavy minerals, due to their mineralogical and percentage similarity. The provenance of kaolinite was mainly the ACF, with a minor contribution of the Amazon and Tapajós rivers. The primary origin of the heavy minerals in the ACF indicates the basement of the Amazonas Basin as source rock and this formation as a source of sediments for Green Lake through weathering and erosion processes under current tropical conditions. The presence of Aulacoseira granulata and Aulacoseira ambigua indicates the importance of current erosive processes on sediment production.

Arquitectura estratigráfica, paleogeografía y proveniencia sedimentaria de las rocas cenozoicas del sur de Perú (Tacna, 18° S)

The Cenozoic rocks lying in the Province of Tacna (18° S), southern Perú, represent approximately 600 m of stratigraphic thickness. This stacking groups the Sotillo (Paleocene), Moquegua Inferior (Eocene), Moquegua Superior (Oligocene), Huaylillas (Miocene) and Millo formations (Pliocene), and these are the sedimentary fill of the Moquegua Basin. The sediments of the three latter formations are organized into nine sedimentary facies and five architectural elements. Their facies associations suggest the existence of an ancient highly channelized multi-lateral fluvial braided system, with upward increase of pyroclastic and conglomeratic depositions. The heavy mineral spectra make each lithostratigraphic unit unique and distinguishable, being the sediments of the Moquegua Superior Formation rich in garnets, titanites and zircons; while the sediments of the Huaylillas and Millo formations in clinopyroxenes. This mineral arrangement becomes an excellent tool for stratigraphic correlations between outcrops and subsurface stratigraphy (by means of well cores studies) and allow to sketch out a new stratigraphic framework and a complex of rocky blocks bounded by normal faults, often tilted. The sediment mineralogy also suggests that the rocks conforming the Western Cordillera were the main source of sediments for the Moquegua Basin in Tacna. In this context, the detritus of the Moquegua Superior Formation derives mainly from the erosion of the rocks forming the Coastal Basal Complex (Proterozoic), the Ambo Group (Carboniferous) and the Junerata/Chocolate Formation (Early Jurassic). The Huaylillas Formation is a pyroclastic and sedimentary unit which components derived mainly from the Huaylillas volcanism (Miocene) and partly from the denudation of the Toquepala Group (Late Cretaceous). The Huaylillas Formation widely contrasts to the underlying Moquegua Superior Formation due its mineralogy and facies. Finally, the detritus of the Millo Formation derived mostly from the rocks forming the Barroso Formation (Pliocene), and their facies represent a higher contrast in relation to the underlying units due its notorious conglomerate facies.

Erosion processes and features for a coarse-textured soil with different horizons: a laboratory simulation

Severe water erosion of coarse-textured soils, thereby exposing subsurface horizons at the surface, is a serious problem in southern China. Currently, there are few systematic studies on erosion processes and features as the various coarse-textured subsurface horizons are exposed. The main objective in this study was to investigate the effects of rainfall intensity and inflow rate on the runoff, soil loss, and erosion features of three horizons of a typical soil developed from granite (topsoil horizon, illuvial horizon, and parent material horizon) in the steeply sloped region. A series of laboratory simulation tests were conducted in a 0.8-m by 3-m flume using two combined rainfall and upslope inflow condition (90 mm h−1 plus 2 L min−1 and 120 mm h−1 plus 2.66 L min−1, respectively). Runoff coefficient and soil loss increased with the evolution of erosion phase from sheet erosion to rill advancement to rill maturity phase. Runoff generation increased as soil horizons with higher bulk density were exposed on the surface and as the rainfall-inflow rate increased. Additionally, rainfall-inflow rate and soil horizon had significant effects on soil loss rate, headward erosion rate, and rill density (p < 0.01). The hillslope roughness was dependent on the interaction of soil properties (clay content) and rainfall characteristics (rainfall intensity and duration). Despite the different hillslope roughness levels exhibited as result under the different rainfall-inflow treatments, the topsoil horizon always exhibited low soil loss. Moreover, as rainfall duration increased, coarse grains (quartz) were gradually enriched on the hillslope surface, which worked as “armoring” to protect the soil surface of interrill areas from further erosion, especially for the topsoil horizon. Due to the surface armoring, rill erosion was considered the main sediment source during the rill maturity phase. These results suggested that coarse grains could be an effective on-site soil conservation practice controlling soil erosion, which should be considered in future erosion prediction and bare land restoration in coarse-textured soils.

Monitoring of Morphological Changes in an Estuary based on Time-Series Analysis of Sediment Discharge Using a Hydrophone

Jun, K.W.; Kin, S.D.; Lee, H.J., and Choi, J.H., 2020. Monitoring of morphological changes in an estuary based on time-series analysis of sediment discharge using a hydrophone. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 516–521. Coconut Creek (Florida), ISSN 0749-0208.The purpose of this study is to predict the littoral transport rate and morphological changes of estuaries by measuring the discharge of sediments from rivers into the sea in a time series using a hydrophone. To identify the problem of longshore sediments, an understanding of waves and currents is necessary. However, the runoff characteristics of sediments in river estuary that serve as the main source of sediments should be grasped first. It is important to predict the discharge of sediments from rivers into the sea and understand the coastal processes involved in the formation of sandbars in the estuary and the transport of sediments to coastal waters. The selected study area was the Gagok River located in the East Coast of Korea, where periodic estuary occlusion occurs due to the behavior of rivers and waves. This study investigated the morphological changes in the estuary according to the changes in sediment discharge. The sediment discharge was measured using a hydrophone capable of measuring the continuous sediment transport from the acoustic information based on the movement of the sediments. Based on this method, the hydrophone was applied to the field, and measurements of major rainfall events were taken to investigate the influence of changes in sediment discharge on the morphological changes in the estuary. In addition, to verify the results, the morphological changes in the estuary were linked to the ground LiDAR data measured over several years. The results of the survey confirmed that the occlusion phenomenon of the Gagok River estuary occurred according to the seasonal changes. Except for the flood season, there was a small amount of runoff through the river. As a result, a sand barrier developed in the estuary due to the influence of the sediments transported by the waves from the open sea.

Erosion after an extreme storm event in an arid fluvial system of the southern Atacama Desert: an assessment of the magnitude, return time, and conditioning factors of erosion and debris flow generation

Abstract. The contribution of an individual extreme storm event to long-term erosion rates has been estimated for the first time in the Atacama Desert. A mean erosion of 1.3 mm has been calculated for the March 2015 event that impacted the southernmost part of the Atacama Desert. The estimated erosion is consistent with millennial erosion rates and the previously reported return times of high-sediment-discharge events in the study area. This is significant because erosion rates, related to events of high sediment discharge in arid fluvial systems, are difficult to measure with sediment loading due to destruction of gauges by devastating flash floods and therefore have not been directly measured yet. During the March 2015 storm, debris flows were reported as the main sediment transport process, while gullies and channels erosion were the main source of sediments that generated debris flows reaching the tributary junctions and the trunk valleys. Sediment yield at tributary outlets is highly dependent on the ability of catchments to store sediments in stream networks between storms. The largest tributary catchments, the high hydrological hierarchy, the low topographic gradient and the gentle slopes are the most determining factors in generating debris flows capable of reaching alluvial fans in any storm event from large sediment volumes stored in the stream networks. Our findings better assess the susceptibility to debris flow of arid catchments, which is significant for the southernmost valleys of the Atacama Desert because human settlements and industries are mostly established in alluvial fans.