Downvalley fining of hillslope sediment in an alpine catchment: implications for downstream fining of sediment flux in mountain rivers     

Leonard S. Sklar  Clifford S. Riebe  Jennifer Genetti  Shirin Leclere  Claire E. Lukens 《地球表面变化过程与地形》2020,45(8):1828-1845

The size distributions of sediment delivered from hillslopes to rivers profoundly influence river morphodynamics, including river incision into bedrock and the quality of aquatic habitat. Yet little is known about the factors that influence size distributions of sediment produced by weathering on hillslopes. We present results of a field study of hillslope sediment size distributions at Inyo Creek, a steep catchment in granitic bedrock of the Sierra Nevada, USA. Particles sampled near the base of hillslopes, adjacent to the trunk stream, show a pronounced decrease in sediment size with decreasing sample elevation across all but the coarsest size classes. Measured size distributions become increasingly bimodal with decreasing elevation, exhibiting a coarse, bouldery mode that does not change with elevation and a more abundant finer mode that shifts from cobbles at the highest elevations to gravel at mid elevations and finally to sand at low elevations. We interpret these altitudinal variations in hillslope sediment size to reflect changes in physical, chemical, and biological weathering that can be explained by the catchment's strong altitudinal gradients in topography, climate, and vegetation cover. Because elevation and travel distance to the outlet are closely coupled, the altitudinal trends in sediment size produce a systematic decrease in sediment size along hillslopes parallel to the trunk stream. We refer to this phenomenon as ‘downvalley fining.’ Forward modeling shows that downvalley fining of hillslope sediment is necessary for downstream fining of the long-term average flux of coarse sediment in mountain landscapes where hillslopes and channels are coupled and long-term net sediment deposition is negligible. The model also shows that abrasion plays a secondary role in downstream fining of coarse sediment flux but plays a dominant role in partitioning between the bedload and suspended load. Patterns observed at Inyo Creek may be widespread in mountain ranges around the world. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

A one‐dimensional process‐based approach to study reservoir sediment dynamics during management operations          下载免费PDF全文

Lucie Guertault  Benoit Camenen  André Paquier  Christophe Peteuil 《地球表面变化过程与地形》2018,43(2):373-386

A comprehensive understanding of the dynamics of erosion and sedimentation in reservoirs under different management conditions is required to anticipate sedimentation issues and implement effective sediment management strategies. This paper describes a unique approach combining fluvial geomorphology tools and morphodynamic modeling for analyzing the sediment dynamics of an elongated hydropower reservoir subjected to management operations: the Génissiat Reservoir on the Rhône River. Functional sub‐reaches representative of the reservoir morphodynamics were delineated by adapting natural river segmentation methods to elongated reservoirs. The segmentation revealed the link between the spatial and temporal reservoir changes and the variability of longitudinal flow conditions during reservoir management operations. An innovative modeling strategy, incorporating the reservoir segmentation into two sediment transport codes, was implemented to simulate the dynamics of erosion and sedimentation at the reach scale during historic events. One code used a bedload approach, based on the Exner equation with a transport capacity formula, and the other used a suspended load approach based on the advection–dispersion equation. This strategy provided a fair quantification of the dynamics of erosion and sedimentation at the reach scale during different management operations. This study showed that the reservoir morphodynamics is controlled by bedload transport in upper reaches, graded suspended load transport of sand in middle reaches and suspended load transport of fine sediments in lower reaches. Eventually, it allowed a better understanding of the impact of dam management on sediment dynamics. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Connectivity assessment in Mediterranean vineyards using improved stock unearthing method,LiDAR and soil erosion field surveys   总被引：1，自引：0，他引：1       下载免费PDF全文

Jesús Rodrigo Comino  Saskia D. Keesstra  Artemi Cerdà 《地球表面变化过程与地形》2018,43(10):2193-2206

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Sediment and nutrient storage in a beaver engineered wetland          下载免费PDF全文

Alan Puttock  Hugh A. Graham  Donna Carless  Richard E. Brazier 《地球表面变化过程与地形》2018,43(11):2358-2370

Beavers, primarily through the building of dams, can deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes. Research is required to understand the implications and possible benefits of widespread beaver reintroduction across Europe. This study surveyed sediment depth, extent and carbon/nitrogen content in a sequence of beaver pond and dam structures in South West England, where a pair of Eurasian beavers (Castor fiber) were introduced to a controlled 1.8 ha site in 2011. Results showed that the 13 beaver ponds subsequently created hold a total of 101.53 ± 16.24 t of sediment, equating to a normalised average of 71.40 ± 39.65 kg m². The ponds also hold 15.90 ± 2.50 t of carbon and 0.91 ± 0.15 t of nitrogen within the accumulated pond sediment. The size of beaver pond appeared to be the main control over sediment storage, with larger ponds holding a greater mass of sediment per unit area. Furthermore, position within the site appeared to play a role with the upper‐middle ponds, nearest to the intensively‐farmed headwaters of the catchment, holding a greater amount of sediment. Carbon and nitrogen concentrations in ponds showed no clear trends, but were significantly higher than in stream bed sediment upstream of the site. We estimate that >70% of sediment in the ponds is sourced from the intensively managed grassland catchment upstream, with the remainder from in situ redistribution by beaver activity. While further research is required into the long‐term storage and nutrient cycling within beaver ponds, results indicate that beaver ponds may help to mitigate the negative off‐site impacts of accelerated soil erosion and diffuse pollution from agriculturally dominated landscapes such as the intensively managed grassland in this study. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Factors influencing biodeposit production by the New Zealand freshwater mussel Echyridella menziesii     

Kevin J. Collier  Susan J. Clearwater  Paula H. M. W. Neijenhuis  Susanna A. Wood 《新西兰海洋与淡水研究杂志》2018,52(1):1-15

Laboratory experiments on the New Zealand freshwater mussel Echyridella menziesii were used to investigate the short-term effects (7–8 days) of food type on rates of biodeposition and benthic substrate respiration. Post-feeding biodeposition rates ranged from 0.34 to 1.52?mg?g^?1?h^?1 (mean?=?0.50?mg g^?1?h^?1) and were unaffected by the addition of toxin-producing Microcystis. Addition of suspended sediment (30?mg?L^?1) visibly altered substrate composition, and increased total and inorganic biodeposit production rates by 24–33% compared to mussels fed commercial phytoplankton stock. Biodeposition rates of mussels in lake bed substrates were 38% higher than those in silica sand for identical feeding regimes, suggesting that a significant proportion of material produced in this experiment could have been derived from feeding on organic matter in the lake bed sediments. Respiration rates were higher in treatments with Microcystis but were unaffected by the presence of mussels. This laboratory study suggests that biodeposition by E. menziesii is resilient to short-term exposure to Microcystis, and highlights the ability of mussels to alter benthic substrate composition by incorporating suspended sediment into substrates.  相似文献   

Depth of closure: New calculation method based on sediment data     

Luis Aragonés  Jose Ignacio Pagán  Isabel López  José C.Serra 《国际泥沙研究》2018,33(2):198-207

Obtaining depth of closure (DoC) in an accurate manner is a fundamental issue for coastal engineering, since good results for coastal structures and beach nourishment depend mainly on DoC. Currently, there are two methods for obtaining the DoC, mathematical formulations and profile surveys. However, these methods can incur important errors if one does not take into account the characteristics and morphology of the area, or if one does not have a sufficiently long time series. In this work the DoC is obtained from the break in the trend of the sediment with the depth, that is, in general with the increase of the depth a decrease in the size of the sediment takes place. However, at one point this tendency changes and the size increases, and then decreases again. When comparing the point where the minimum sediment size occurs before the increase, it is observed that the error incurred is small compared to other methods. If the Standard Deviation of Depth Change (SDDC) method is considered as the most accurate method, the error incurred by the proposed method is less than 7%. In addition, it can be seen that the dispersion of the sediment method always occurs outside the zone of bar movement. Whereas in the methods of profiles survey (using 2 cm precision profiles), sometimes the DoC is obtained within the active zone of bar movement. In addition, where the relative minimum of the median sediment size is found, and the sizes of 0.063 and 0.125 mm predominate in the composition of the sample. Therefore, this new method allows the precise location of the DoC to be obtained in a fast and simple way. Furthermore, this method has the advantage that it is not affected by the modifications that may be experienced by both the study area and the cross-shore beach profile.  相似文献   

Time-averaged sub-layer concentration profiles in oscillatory sheet flows     

Yuhai Wang  Wenhong Cao  Wen Lu  Huifeng Liu  Gauhu Sun  Chonghao Wang  Fei Liu 《国际泥沙研究》2018,33(4):433-440

Although thin on the order of several to tens of millimeters, sheet flows normally comprise a lower pick-up sub-layer and an upper contact-load sub-layer, separated at the bed level (z = 0). The time-averaged concentration profile in the pick-up sub-layer shows a ‘convex upward’ curvature, but ‘concave upward’ shape characterizes the time-averaged concentration profile in the contact-load sub-layer. The time-dependent concentration in the contact-load sub-layer is approximately in-phase with the free stream flow velocity, whereas it is nearly in anti-phase with the free stream flow velocity in the pick-up sub-layer. Two distinct analytical expressions of the time-averaged concentration profiles for the respective sub-layers are proposed. The expressions are validated with detailed observation datasets collected in the Groβer Wellenkanal (GWK) prototype wave flume in Hannover, Germany. The agreement between the predicted and the measured values is excellent. Interparticle collisions in the pick-up sub-layer and convective lifting processes associated with vortex shedding in the contact-load sub-layer are considered responsible for the opposite curvatures and in-phase/anti-phase concentration variations. Both transitional boundary and reference concentration are also elaborated.  相似文献   

断层氢气观测技术实验     

谢恒义  李源  夏修军  孙召华 《地震地磁观测与研究》2018,39(4):176-182

采用ATG-6118H痕量氢在线自动分析仪，在朱夏-商丹断裂带南阳地区布设独山、马山口2个氢气观测台，研究设备取气深度、抽气时间设置长短对观测断层氢气浓度的影响，从而为利用痕量氢设备进行断层氢气观测提供参考依据。实验结果表明：①取气深度越浅，观测到的氢气浓度越高，日变化幅度越大；②集气管内氢气浓度偏低时，抽气时间设置略高于导气管路排空时间，氢气浓度明显变化，否则变化不明显。  相似文献   

太湖五里湖水体悬浮物中水溶性有机质(WSOM)的荧光光谱组分鉴别及其与氮形态的关系   总被引：2，自引：2，他引：0  

张博  王书航  姜霞  黄晓峰  王雯雯 《湖泊科学》2018,30(1):102-111

采用三维荧光光谱-平行因子法(EEMs-PARAFAC)分析太湖五里湖水体悬浮物中水溶性有机质(WSOM)的荧光光谱特征,研究其组分类型、分布规律以及来源,进一步探讨悬浮物中水溶性有机氮和无机氮含量与WSOM荧光组分之间的关系.结果表明,悬浮物中WSOM荧光组分主要由2个类腐殖质(C1、C2)和1个类色氨酸类蛋白质(C3)组成.总荧光强度在57.56~200.01 R.U./g之间,平均为115.42 R.U./g,其中C1、C2、C3的相对比例分别为35.55%、34.05%和30.40%;空间上由西向东逐渐增强,东五里湖高于西五里湖,沿岸区高于湖心区.荧光指数和生物源指数变化范围分别在1.48~2.34和0.65~0.87之间,反映了悬浮物中WSOM主要来源于微生物、藻类的自生生物源.多元回归统计分析结果表明,悬浮物WSOM与氮元素的迁移转化密切相关,且有机氮与WSOM荧光组分的相关系数大于无机氮.  相似文献   

东洞庭湖沉积物覆水后磷形态变化及其释放量   总被引：4，自引：1，他引：3  

王婷  王坤  姜霞 《湖泊科学》2018,30(4):937-947

研究干燥覆水后低流速条件下东洞庭湖沉积物中磷的形态变化及释放量,可以为轻度富营养化湖泊中磷的生物地球化学循环提供基础数据,为季节性湖泊內源营养盐的迁移转化规律研究、內源营养盐的释放风险评价提供理论依据.本文采集处于干湿交替状态的东洞庭湖表层沉积物,利用室内模拟装置,研究风干沉积物低流速条件下覆水后沉积物及上覆水中磷的形态变化.结果表明,低流速覆水后东洞庭湖沉积物中的磷向上覆水及大气中迁移释放,上覆水中磷的释放量随覆水时长增大,释放速率随覆水时长减小,上覆水流速和磷释放量相关性显著.上覆水循环过程中释放到上覆水中的溶解态有机磷比溶解态活性磷更容易吸附于颗粒物而转化为颗粒态磷.覆水后沉积物中各形态有机磷、无机磷及磷的生物有效性均发生转变,覆水初期沉积物中无机磷向有机磷转化,磷的生物可利用性增大;上覆水循环过程中有机磷向无机磷转化,磷的生物可利用性减小;覆水后沉积物的无机磷的主要组分由铝磷转变为铁磷,有机磷的主要组分有从中活性有机磷向活性有机磷转变的趋势.  相似文献