Main Sediment Source Research Articles

Landslides and Gullies Interact as Sources of Lake Sediments in a Rifting Context: Insights from a Highly Degraded Mountain Environment

Like many other lakes in the world, the interconnected Abaya and Chamo lakes in the Southern Main Ethiopian Rift are affected by rapid sediment accumulation. Although land degradation is a well-known issue in this part of the African continent, the main sediment sources, their spatial distribution and interaction in the Abaya–Chamo lakes’ basin have not yet been documented. Here, we present a systematic inventory, characterization, and spatial analysis of landslides and gullies as concentrated sediment sources, for four representative river catchments impacted by landscape rejuvenation. Using Google Earth imagery and field surveys, we mapped with high accuracy a total of 7336 gullies and 430 landslides. Recent landslides observed during the last decade were few, small and shallow, and appear to have played a minor role in the current sediment dynamics. Large landslides are old and inactive. Although they do not contribute to the current sediment budget, they contribute indirectly to landscape dynamics by favoring the occurrence of gullies. Overall, large percentages of severe to extremely degraded areas of gully erosion are located in rejuvenated landscapes, especially at the level of the old landslides. Many active gullies are connected to the river network, as such acting as the source of sediment. Our analysis is a step towards understanding the nature and control of anthropic activities on sediment production in the region. We also highlight the importance of considering the interactions between sediment sources and the connectivity of the geomorphological system.

Reconstruction of the early-middle Jurassic source-to-sink system in the western Qaidam Basin (North Tibet): Constraints from zircon U-Pb ages of Jurassic sediments and granites

• Detrital zircon ages of Jurassic sediments in the western Qaidam Basin show peaks at ∼450 Ma, ∼380 Ma, ∼260 Ma. • The South Qilian Range to the north and South Altyn Tagh Range to the west provided the sources of sediments during the Jurassic. • The Jurassic basin was developed along the southwestern margin of the Paleo-South Qilian Range. • The Jurassic proto-basin in Western Qaidam is reconstructed by provenance analyses. The Qaidam Basin is the largest intermountain basin within the northeastern Tibetan Plateau, which is a key area to understand the tectonic evolution of the Tibetan Plateau. The evolution history and provenances of the western Qaidam Basin were influenced by the surrounding ranges and recorded the history of the topographic changes. To ascertain the relationship between the sediments in the western Qaidam Basin and surrounding source regions is important to understand the tectonic evolution of the Qaidam Basin and the northern Tibetan Plateau. In this study, the 745 detrital zircon LA-ICP-MS U-Pb ages of 14 samples collected from the Heishuigou and Mangya sections were used to trace the provenances of the Jurassic sediments in the western Qaidam Basin and to further constrain the tectonic evolution of the Qaidam Basin in the Meso-Cenozoic. The detrital zircon ages show three age peaks at ∼450 Ma, ∼380 Ma, and ∼260 Ma. Two dated granitoids from the Mangya area have weighted mean ages of 451 ± 3 Ma and 384 ± 3 Ma, respectively. Compared with published zircon U-Pb ages from the relevant basement and magmatic and metamorphic rocks, our results indicate that the South Altyn Tagh Range and the South Qilian Range were main sources of the early-middle Jurassic sediments in the western Qaidam Basin. Together with published stratigraphic, paleocurrent, and seismic profile data, the Jurassic proto-basin was reconstructed. The original Jurassic basin was developed along the southwestern margin of the Paleo-South Qilian Range and displaced sinistrally by the Altyn Tagh Fault during the Cenozoic.

Increased erosion of high-elevation land during late Cenozoic: evidence from detrital thermochronology off-shore Greenland

Mountain regions at high altitudes show deeply incised glacial valleys that coexist with a high-standing low-relief landscape, whose origin is largely debated. Whether the plateaus contributed to sediment production during the late Cenozoic is a currently debated issue in glacial geomorphology and paleoclimatology. In this study, we used detrital apatite fission-track dating of marine sediments to trace provenance and spatial variation in focused erosion over the last 7 million years. The decomposition of age distributions into populations reveals that, moving upwards through the sections, two young populations get younger, while two older populations get progressively older. We interpreted these trends as the effect of glacial erosion on the valley floors and an increased sediment contribution from the high elevations. To test this hypothesis, we compared the measured ages with synthetic age distributions, which represented a change in the elevation of focused erosion. We conclude that the central-eastern Greenland region is the main source of sediments, and in addition to enhanced valley incision, sediments have also been sourced from progressively higher elevations since 7 Ma. The ageing trend provides an unusual case in detrital thermochronology and a strong evidence that intensified Quaternary glaciations amplify the erosional process both in valley bottoms and at high elevations.

The Maldives, a key location of carbonate drifts

Wind-driven surface currents and deeper water-mass circulation shape carbonate sediment drifts in shallow- to deep-water depositional settings of the Maldives. Drift sediments are located in the platform interior, on top of drowned banks, and around the atolls. They are composed of an admixture of pelagic and shallow-water components. Drift bodies vary in dimension, architecture, and genesis. Small patch drifts and sheeted drifts are present in the platform interior and on top of drowned atolls; large patch drifts preferably form in the current-shadow of large atolls and banks. Small inter-atoll channels and large gateways are dominated by channel-related drifts. The Inner Sea, a large perched basin surrounded by atolls comprises a complex contourite depositional system of giant elongated mounded and sheeted drifts, mixed drifts, as well as delta drifts. This succession of different drift types is organized in sequences, delimited by unconformities caused by changes in the current regime. These may be triggered by a re-configuration of the inter-atoll gateways or by allo-cyclic processes such as climate variability. Effects based on to changes in the global water-mass circulation could not be proven. With exception of the delta drift, carbonate drift types in the Maldives are analogous to their siliciclastic counterparts. By contrast, however, these carbonate drifts are emplaced at a short distance to the shallow-water carbonate factory, which acts as main sediment source. Variability and abundance of drifts in the Maldives emphasize the significant role of current-controlled sediment transport and redistribution in carbonate platform development.

A Field Investigation on Gully Erosion and Implications for Changes in Sediment Delivery Processes in Some Tributaries of the Upper Yellow River in China

Erosion and sediment delivery have been undergoing considerable variations in many catchments worldwide owing to climate change and human interference. Monitoring on-site erosion and sediment deposition is crucial for understanding the processes and mechanisms of changes in sediment yield from the catchments. The Ten Kongduis (kongdui is the transliteration of ephemeral creeks in Mongolian) are 10 tributaries of the upper Yellow River. Severe erosion in the upstream hills and gullies and huge aeolian sand input in the middle reaches had made the 10 tributaries one of the main sediment sources of the Yellow River, but the gauged sediment discharge of the tributaries has decreased obviously in recent years. In order to find out the mechanisms of changes in the sediment load of the tributaries, topographic surveys of four typical gullies in 3 of the 10 tributaries were made repeatedly in the field with the terrestrial laser scanning (TLS) technique. The results show that all the monitored gullies were silted with a mean net rate of 587–800 g/m2 from November 2014 to June 2015 and eroded by a mean net rate of 185–24,800 g/m2 from June to November 2015. The monitoring data suggest that the mechanism of interseasonal and interannual sediment storage and release existed in the processes of sediment delivery in the kongduis. The contrast of the low gauged sediment load of the kongduis in recent years against the high surveyed gully erosion indicates the reduction in their sediment delivery efficiency, which can be attributed to the diminution in hyperconcentrated flows caused mainly by the increase in vegetation coverage on slopes and partly by construction of sediment-trapping dams in gullies.

Sediment Particle Size Composition in the Riparian Zone of the Three Gorges Reservoir

The riparian zone is a transitional zone of terrestrial ecosystems and aquatic ecosystems, which is one of the main sources of reservoir sediment and pollutants. The sediment loss has an increasing trend in the riparian zone of the Three Gorges Reservoir (TGR), which was closely related to sediment particle size composition change in the riparian zone, but its distribution and factors are still unclear. Hydrological conditions, sediment particle size composition and vegetation properties in the riparian zone were investigated in 3 mainstream and 8 tributary sections along the Yangtze River within the TGR across 450 km. On the one hand, both sediment sand content and median particle size (D50) showed a horizontal raising trend from the upstream to the dam region of the TGR at the mainstream and tributary sites. On the other hand, compared to the upper-middle mainstream and the tributaries of Longxi, Wu, Longxi, Pengxi, Daning, Tongzi rivers, the D50 was much higher in the lower altitudes of the riparian zone in the tributaries of Wubu, Ruxi, and Xiangxi and the mainstream in the lower reaches of the Yangtze River. With the raising of the riparian zone slope, D50 decreased in the mainstream riparian zone sites, while increased in the tributary riparian zone sites (p < 0.05). Besides, D50 was 2.3 times higher in the south aspect relative to the north aspect of the riparian zone in the TGR. No significant relationship was found between root biomass of a local dominate species-Cynodon Dactylon (Linn.) and D50. Hydrological and geographical variables could predict 64%–67% of the D50 variance, and thus could be regarded as the main predictor of D50 in the riparian zone of the TGR.

Sedimentary Provenance From the Evolving Forearc‐to‐Foreland Central Sakarya Basin, Western Anatolia Reveals Multi‐Phase Intercontinental Collision

AbstractCollision between the Pontides and Anatolide‐Tauride Block along the İzmir‐Ankara‐Erzincan suture in Anatolia has been variously estimated from the Late Cretaceous to Eocene. It remains unclear whether this age range results from a protracted, multi‐phase collision or differences between proxies of collision age and/or along strike diachroneity. Here, we leverage the Cretaceous‐Eocene evolution of the forearc‐to‐foreland Central Sakarya Basin system in western Anatolia to determine when and how collision progressed. New detrital zircon (DZ) and sandstone petrography results indicate that the volcanic arc was the main source of sediment to the forearc basin in the Late Cretaceous. The first appearance of Pontide basement‐aged DZs, in concert with exhumation of the accretionary prism and a decrease in regional convergence rates, indicates intercontinental collision initiated no later than 76 Ma. However, this first contractional phase does not produce advanced thick‐skinned deformation and basin partitioning until ca. 54 Ma. We propose three non‐exclusive and widely applicable mechanisms to reconcile the observed ∼20 Myr delay between initial intercontinental collision and thick‐skinned upper plate deformation: slab breakoff, relict basin closure north and south of the İAES, and underthrusting of progressively thicker passive margin lithosphere. These mechanisms highlight the links between upper plate deformation and plate coupling during continental collision.

Coupling Effects of Precipitation and Vegetation on Sediment Yield from the Perspective of Spatiotemporal Heterogeneity across the Qingshui River Basin of the Upper Yellow River, China

Interactions between precipitation, vegetation, and erosion are crucial and not fully solved issues in the area of earth surface processes. The Qingshui River Basin (QRB), as the main sediment source tributary of the upper reaches of the Yellow River, is characterized by spatial heterogeneity of rainfall, vegetation, and soil erosion. In this study, we investigated the spatiotemporal variations of sediment yields within the QRB and further identified the coupling effects of precipitation and vegetation on soil erosion. We collected annual (1955 to 2016) and daily (2006 to 2016) hydrological and sediment series from six hydrological stations, which subdivided the whole basin into six different sub-basins with heterogeneity in climate and landscape. Variations in parameter a of the sediment rating curves among the six sub-basins continuously declined, showing the continuously increasing effect of vegetation coverage on reducing soil erosion. The unique combination of relationships between precipitation characteristics and vegetation patterns in six sub-basins and these coupling effects resulted in different precipitation–vegetation–erosion patterns in six sub-basins. Sediment yield followed bell-shaped relationships with vegetation and precipitation, with a clear critical threshold at normalized difference vegetation index (NDVI) = 0.36/precipitation = 100 mm at a monthly scale. Based on these thresholds, the non-linear relationships between precipitation, vegetation, and erosion were also explained. We also found that reducing the time lags in which vegetation follows precipitation may be effective in suppressing sediment yield. These findings could provide a quantitative approach to estimating the potential changes in sediment yield associated with proposed ecological rehabilitation schemes in this region.

Enhanced hydrological cycle during Oceanic Anoxic Event 2 at southern high latitudes: New insights from IODP Site U1516

The Oceanic Anoxic Event 2 (OAE 2) represents one of the most profound global environmental disturbances of the Mesozoic Era, which was associated with a positive carbon isotope excursion due to widespread organic carbon burial. However, the character, evolutionary history, and exact driving mechanisms of OAE 2 are still much debated, exacerbated by the lack of records from climate-sensitive southern high latitudes. Here we present a multi-proxy record of a stratigraphically continuous succession spanning the late Cenomanian to early Turonian at the International Ocean Discovery Program Site U1516 in the Mentelle Basin off southwest Australia, which was located at southern high latitudes (~ 60–62°S) during the Late Cretaceous. Sedimentary records at Site U1516 allow the first detailed insights into source-to-sink processes in the Mentelle Basin and associated paleoenvironmental reconstruction in the southern Indian Ocean during OAE 2. Rare earth element abundances and clay-bound neodymium isotopes of the siliciclastic sediment fractions indicate that southwest Australia was the main detrital source of sediment at Site U1516 during OAE 2, with volcanogenic sediments representing only a minor component. A major provenance shift is observed across OAE 2, indicating an increased sediment contribution from distant sources (i.e., Yilgarn Craton and Albany-Fraser Orogen) relative to proximal sources (i.e., Perth Basin and Leeuwin Block) in southwest Australia, interpreted as reflecting a major reorganization of the drainage system due to enhanced fluvial runoff. Based on these findings, we infer that the OAE 2 interval showing the most prominent δ13C excursion was associated with an intensification of the hydrological cycle in the high-latitude southern hemisphere, with potential impacts on regional ocean chemistry and marine productivity. In particular, we suggest that enhanced terrigenous input and riverine nutrient export likely played a key role in controlling siliceous productivity at nearby ocean margins. As a consequence, the intense burial of organic matter (i.e., black shale) at Site U1516, which occurred episodically throughout OAE 2, possibly resulted from the combination of enhanced riverine-driven marine productivity and increased burial efficiency associated with the development of anoxic/euxinic bottom water conditions.

Headcut erosion characteristics revealed through simulated rainfall and scouring experiments in the gully region of the Loess Plateau

Headcut erosion is the main sediment source that may cause severe damage to the ecological environment and agricultural production. The study of headcut erosion characteristics, such as gully headcut morphological evolution and sediment particle transport processes, is essential for understanding the mechanism of gully erosion. A series of simulated rainfall combined scouring experiments with constant rainfall intensity (0.8 mm min^–1) and variable flow discharge (3.6, 4.8, 6.0, and 7.2 m³ h^–1) were conducted to illustrate the headcut erosion process in the gully region of the Loess Plateau. The results showed that gully width and gully depth increased as time and flow discharge increased. The headcut retreat length increased exponentially with experiment time. The gully head heights decreased by 10, 13, 21, and 26 cm at different flow discharges after 180 min. The contents of clay and silt in eroded sediment particles decreased by 7.97% to 16.59% and 7.98% to 15.34%, respectively, whereas the sand volume fraction increased by 9.33% to 20.04% compared to that of the original soil. The enrichment rates of clay and silt sediment were 0.83 to 0.92 and 0.85 to 0.92, while the enrichment rate of sand sediment was 1.09 under different flow discharges. The critical particle size was 0.0326 mm. The fractal dimension of the eroded sediment particles was 2.61 to 2.67 and showed good agreement with the clay volume fraction, with a coefficient of determination (<i>R</i>²) of 0.93. These results provide a basis for headcut erosion model establishment, ecological management, and soil and water conservation in the gully region of the Loess Plateau.

Cenozoic sequence stratigraphy and sedimentary evolution of forearc basin in Ryukyu Island Arc region

琉球弧前盆地位于菲律宾海板块北部与欧亚板块汇聚部位，发育于琉球海沟北部增生楔与琉球岛弧之间，是典型“沟-弧-盆”体系的组成单元。现利用多道地震资料，首次建立琉球弧前盆地的层序地层格架，分析其新生代层序地层特征，阐明弧前盆地沉积充填演化过程，并探讨各盆地主要物源。通过地震剖面解释分析，表明:①始新世为岛弧变质基底沉积期，晚渐新世晚期-早中新世阶段发育残余伸展盆地基底沉积，属于浅海环境，主要受岩浆活动影响，发育火山碎屑岩相；②中中新世-第四纪时期是弧前盆地的主体沉积期，盆地从半深海沉积环境向深海环境过渡，发育典型深海沉积相，局部为火山碎屑岩相；中中新世时北部的南琉球群岛是弧前盆地主要物源区；晚中新世至第四纪时期，台湾岛东北部陆区成为对该弧前盆地贡献最大的物源区，而南琉球群岛的物源供给量降为次要地位。该研究结果是对琉球岛弧及周缘构造控盆作用研究的拓展，并对台湾岛陆地与东部海域“源-汇”系统研究有重要的指导意义。;The Ryukyu forearc basin is located at the convergence of the northern Philippine Sea plate and the Eurasian plate. It is developed between the accretionary wedge in the northern Ryukyu trench and the Ryukyu Island Arc. It is a component unit of a typical 'trench-arc-basin' system. Now, based on the multi-channel seismic data, the sequence stratigraphic framework established for the first time in the study area is used to analyze the Cenozoic sequence stratigraphy and sedimentary evolution characteristics, and discuss the main source of sediment. According to the characteristics of seismic reflection and the contact relationship of reflection layer group, it is revealed that the Cenozoic in the study area experienced the process of shallow marine facies, semi-deep marine facies and deep-sea facies. It is considered that island arc metamorphic basement sedimentation developed in Eocene, and the basement sedimentation period of residual extensional basin from Late Eocene to Early Miocene belongs to the basement sedimentation period of fore arc basin, which is a shallow sea environment and mainly develops pyroclastic lithofacies; The Middle Miocene to Quaternary is the main sedimentary period of the forearc basin. It transited from the bathyal to the deep-sea sedimentary environment. The local volcanic clastic facies developed many typical sedimentary systems, such as gravity flow, turbidite fan, underwater delta and turbidite channel. It is inferred that the South Ryukyu Islands in the northern part of the Middle Miocene was the main provenance in the forearc basin period. Since the Late Miocene, the land area in the northeast of Taiwan Island has become the largest provenance, and the South Ryukyu Islands is in the second place. The results are an extension of the study on the basin control of the Ryukyu Island Arc and its surrounding structures, and have important guiding significance for the study of the 'source-sink' system of the land and eastern sea area of Taiwan Island.

Using Geochemical Fingerprints for Assessing Sediment Source Apportionment in an Agricultural Catchment in Central Argentina

In the hilly semi-arid region of central Argentina, where the agricultural frontier expands at the expense of natural ecosystems, soil erosion is one of the most alarming environmental problems. Thus, obtaining knowledge about the dynamics of erosive processes and identifying erosion hotspots constitutes a primary scientific objective. This investigation is focused on estimating the apportionments of main sources of sediments, at the mouth of a small catchment called Durazno del Medio, located in the province of San Luis, Argentina. Elemental Analysis, measured by Energy Dispersive X-ray Fluorescence (EDXRF), was used to select potential geochemical fingerprints of sediment. The unmixing model MixSIAR was applied to approximate the contribution of each identified source in the sediment accumulation areas at the mouth of the catchment. Potential sediment sources were selected using two criteria: (i) a hierarchical approach to identify the main geomorphological units (GUs) and (ii) the main land uses (LU), recognized by examining satellite images and field recognitions. The selected geochemical tracers were able to distinguish sources located in the Crystalline basement hills with loess-patched (CBH) as the main sediment contributors.

Sediment Sources and Dispersion on the Western Sunda Shelf, Malay Peninsula, Southern South China Sea

Thirty-nine surface sediment samples collected from the western Sunda Shelf off the Malay Peninsula (WSSMP) in the southern South China Sea (SCS) were analysed for grain size, major and trace elemental compositions, and light/heavy mineral contents to trace the sediment sources and their transport mechanisms in the study area. In the WSSMP, the surface sediments are relatively poorly sorted but transportable. A principal component analysis of 37 elements and grain size fractions indicates that the surface sediments can be grouped into four major assemblages in the study area. Integrating with the light/heavy minerals data in the 63–125 μm fractions of the surface sediment samples, to better trace the sediment sources of the coarse-grained components in the marine environment, the study area can be further divided into four sediment provinces. Province I is located in the northwestern part of the study area. The concentrations of TiO2, Na2O, garnet, siderite, and glauconite in Province I were higher than in the other provinces. The main sediment source for this province originated from the Kelantan River and the Gulf of Thailand transported by the northeastern monsoon current. Province II is located offshore of the Pahang and Endau Rivers. The percentages of TiO2, rare earth elements, Al2O3, quartz, plagioclase, hypersthene, and magnetite in the surface sediments were typically higher in this province than in the other provinces. The Pahang and Endau rivers provide most of the sediments to this province, which are transported by southward coastal currents. Province III is located in the northeastern and eastern parts of the study area, where the coarse-grained sediment fraction had relatively high hornblende and biotite contents. Sediments in this province are mostly transported from the Mekong River during the northeastern monsoon. The other parts of the study area belong to Province IV, where the surface sediment elemental and mineral concentrations were mostly between those of the other three provinces. Therefore, we suggest that Province IV has a mixed source due to inputs from the surrounding rivers.

Soil C, N and P contents and their stoichiometry as affected by typical plant communities on steep gully slopes of the Loess Plateau, China

The contents and stoichiometric characteristics of soil carbon, nitrogen and phosphorus greatly influence the structures and functions of the ecological system. The steep gully slope is the main source of erosion sediment in the small watershed on the Loess Plateau, China. It is vital to fully quantify the potential effects of vegetation restoration on soil nutrients and their stoichiometry under such harsh standing environments. To investigate the effects of plant communities on soil C, N, P contents and their stoichiometry on steep gully slopes. Two shrubs (Hippophae rhamnoides Linn., Caragana korshinskii Kom.), four typical grasses (Carex lanceolata Boott., Artemisia giraldii Pamp., Bothriochloa ischcemum (Linn.) Keng. and Artemisia sacrorum Ledeb.), and one slope farmland planted with Zea mays (as control) were chosen as the testing sites. Soil samples were collected from seven layers (0–10, 10–20, 20–30, 30–40, 40–60, 60–80, and 80–120 cm). The results showed that grassland had higher soil total carbon, soil total nitrogen, soil total phosphorus, and stoichiometries than shrubland on steep gully slopes. The C/N ratio had the minimum variation between different communities, while N/P and C/P ratios gradually decreased with soil depth. Both N and P were scarce on steep gully slopes. Soil C, N, P contents and their stoichiometry were closely related to bulk density, plant litter density and root mass density. The results are helpful to understand the spatial variation of soil nutrients and their stoichiometry and vegetation management on steep gully slopes in arid and semi-arid regions.

Systematics of detrital zircon U–Pb ages from Cambrian–Lower Devonian rocks of northern Morocco with implications for the northern Gondwanan passive margin

The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession.

Sediment transport characteristics above a gobi surface in northwestern China, and implications for aeolian environments

Gobis (gravel deserts) cover large areas in northwestern China and other parts of the world, but sediment transport above gobi surfaces has not been widely investigated; thus, there is insufficient empirical data to support dust source identification. In the present study, we used the LDDSEG vertically segmented sediment sampler to collect sediment transport data above a gobi surface. The results demonstrated that the sediment transport rate above the gobi surface was larger than that above a sandy surface, with rates as high as 9.7 kg m-1h−1. The transport flux can be expressed as a Gaussian peak function, with the maximum sediment transport at 0.05 to 0.09 m above the surface. Principal-components analysis (PCA) indicated that the mean grain size of the transported sediment was controlled mainly by the content of silt and clay (<63 μm) and fine sand (125 to 250 μm); this explains the inflection height for sediment transport. PCA also indicated that dry lacustrine deposits were the main sediment source in the study region. About 90% of the cumulative sediment transport occurs at a height below 0.65 m. Our results indicate that sediment transported over a gobi surface has higher trajectories and longer distances than above a sandy surface. The larger silt and clay component (about 30%) of the sediment transported over the gobi surface means that gobi surfaces are important dust sources in northern China, although the dust likely originated from dry lacustrine sites upwind of the study site.

The Effect of Soil Conservation Measures on Runoff, Soil Erosion, TN, and TP Losses Based on Experimental Runoff Plots in Northern China

Total nitrogen (TN) and total phosphorous (TP) are the main pollutants affecting the water quality of the Miyun Reservoir, Beijing. However, few studies have been conducted on their responses to implemented soil conservation measures at a slope scale in northern China. To explore the impact of soil conservation measures on TN and TP losses, field monitored data from 18 runoff plots under natural rainfalls were used to analyze the changing characteristics of runoff, soil loss, and nutrient losses during 2014–2019. The results indicated that runoff, soil erosion, as well a TN and TP losses from the plots varied significantly, depending on land use and soil conservation measures. Bare plots suffered the highest soil, TN, and TP losses, followed by cultivated plots without soil conservation measures, cultivated plots with contour tillage, and other plots. Event-averaged runoff and soil loss rates ranged from 0 to 7.9 mm and from 0 to 444.4 t km−2 yr−1, and event-averaged TN and TP losses from cultivated plots were the highest, with values of 39.8 and 3.0 kg km−2, respectively. Bare and cultivated plots were the main sediment and nutrient sources. Among the cultivated plots, the terraced plot had the lowest soil and nutrient losses. The vegetated plots had insignificantly lower soil and nutrient losses. Most TN and TP were lost in particulate status from the plots, especially from the plots with soil conservation measures. Soil conservation measures can effectively prevent TN and TP losses. To guarantee water resource use, contour tillage is preferred for the bare and cultivated lands in the study region.

Reconstructing the Changes in Sedimentation and Source Provenance in East African Hydropower Reservoirs: A Case Study of Nyumba ya Mungu in Tanzania

This study aimed to reconstruct the sedimentation rates over time and identify the changing sources of sediment in a major hydropower reservoir in Tanzania, the Nyumba ya Mungu (NYM). Fallout 210Pb measurements were used to estimate age of sediment deposits and broad changes in sedimentation rates were reconstructed. Sedimentation peaks were cross referenced to geochemical profiles of allogenic and autogenic elemental constituents of the sediment column to confirm a causal link. Finally, geochemical fingerprinting of the sediment cores and potential sources were compared using a Bayesian mixing model (MixSIAR) to attribute the dominant riverine and land use sources to the reservoir together with changes through recent decades. Reservoir sedimentation generally increased from 0.1 g cm−2 yr−1 in the lower sediment column to 1.7 g cm−2 yr−1 in the most recent deposits. These results correlated to changes in allogenic and autogenic tracers. The model output pointed to one of two major tributaries, the Kikuletwa River with 60.3%, as the dominant source of sediment to the entire reservoir, while the other tributary, Ruvu River, contributed approximately 39.7%. However, downcore unmixing results indicated that the latest increases in sedimentation seem to be mainly driven by an increased contribution from the Ruvu River. Cultivated land (CU) was shown to be the main land use source of riverine sediment, accounting for 38.4% and 44.6% in Kikuletwa and Ruvu rivers respectively. This study explicitly demonstrated that the integration of sediment tracing and dating tools can be used for quantifying the dominant source of sediment infilling in East African hydropower reservoirs. The results underscore the necessity for catchment-wide management plans that target the reduction of both hillslope erosion reduction and the sediment connectivity from hillslope source areas to rivers and reservoirs, which will help to maintain and enhance food, water and energy security in Eastern Africa.

Recent sedimentary processes in the Atrato River Delta – Colombia based on physicochemical characterization of surface sediments

The Atrato River Delta (ARD) is a unique landform of the Colombian Caribbean shaped by the hydrologic and geological framework of the Colombian Pacific. This study analyses modern sedimentation in the ARD through grain size, mineral abundances, chemical weathering and concentrations of major and trace elements in 60 surface sediment samples surveyed over fluvial, lacustrine, estuarine and marine depositional settings within six geographic sectors. Sediment size patterns decrease towards the bays into the Gulf of Urabá, varying from very fine silt to fine sand and from moderately well to very poorly sorted, implying moderate energy flows in the delta. Transport regimes vary from traction inland to suspension in the north sector, with the predominance of saltation in central and east sectors. Mineralogy shows a dominant mineral phase of quartz, followed by feldspars and plagioclase, clay minerals, pyroxenes, micas and Fe-Mg and Ti oxides, indicative of heterogeneous bedrock sources. The distribution of these minerals responds to the effects derived from sorting, degree of weathering and mineral density. The tectonic setting and provenance designate the Oceanic Island Arc as the main source of sediments. Compared to Upper Continental Crust values and regional geochemistry, samples show a depletion of SiO2, Na2O, CaO and K2O, representing high dilution processes along the delta. High abundances of other oxides (Al2O3, Fe2O3, MgO, TiO2, P2O5 and MnO), by contrast, imply oxidation processes with moderate to high weathering. High concentrations of Organic Carbon, Cl, Na, P and S, mainly at bays, indicate a saline wedge as a signature of organic matter degradation, oxidation processes, marine productivity and sediment reworking towards the Gulf of Urabá. Zn, Ni, Cu, Co and Cr remain high along the delta and indicate both natural and anthropogenic contributions. The study contributes to recent efforts to understand the sedimentary dynamics of this active tropical delta.

Vertical and lateral facies variability in organic-rich mudstones at the reservoir scale: A case study from the Devonian Duvernay formation of Alberta, Canada

Organic-rich mudstone successions are known to have significant vertical and lateral heterogeneity. This has been well documented in literature at the core scale and the basin scale in many unconventional reservoirs around the world. Investigating geological heterogeneity at the km-to sub-km scale is not always possible because of the dense well coverage necessary for such assessment. Therefore, facies heterogeneity assessment of organic-rich mudstones at the km-scale of investigation is poorly accounted for in literature. Using a case study from the Devonian Duvernay Formation of Western Canada, this study takes advantage of the large amount of well data available in the public domain to perform a heterogeneity assessment of organic-rich mudstone successions at the km-resolution. The five key petrofacies identified through core-to-well log tie – a) organic rich black siliceous mudstones, b) carbonate-rich mudstones, wackestones, and packstones, c) organic-poor clay-rich mudstones, d) organic-rich clay-rich mudstones, and e) interbedded silica-rich and carbonate-rich – were displayed in cross-sections and mapped across the study area for assessment of vertical and lateral heterogeneity. Analysis reveals that the Duvernay Formation has a significant degree of vertical and lateral heterogeneity, which varies depending on the location with respect to the main sediment sources active at the time of Duvernay deposition. These include debris flow channels originating from carbonate reefs, carbonate platforms in the NE that prograded westward towards the study area, and ocean currents that transported detrital clays into the area. In the upper Duvernay Member, parasequences of shallowing upward petrofacies can be correlated across the study area. However, these are locally interrupted by carbonate- or clay-rich petrofacies that comprise a significant part of the succession decreasing the thickness of the organic-rich petrofacies. Our analysis confirms that the Duvernay Formation shows significant lateral changes in occurrence and thickness of petrofacies at the sub-km scale, making it an extremely heterogeneous reservoir. This understanding may be applied to other shale plays worldwide which lack the well control necessary to perform a similar assessment.